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October 12

Rattlesnake Anti Venom avalibility

I did not get bitten but it sure was close today when I almost stepped on a very large Timber Rattler.

We both startled each other and I sure did jump quick. The snake is still alive and out behind the house somewhere as I don't kill wild animals that have as much right as I do to live.

My question goes more to "What if" I had been bitten and needed the Anti Venom quick.

Do hospitals keep this stuff on hand?

How long might it take for the hospital to locate it and get it in an emergency?

I live in the NY Catskill Mountains, Sullivan County. These snakes are here but not very common, I have seen only 3 in almost 60 years. —Preceding unsigned comment added by Gamalot52 (talk • contribs) 00:33, 12 October 2009 (UTC)

It is my understanding that US hospitals keep antivenoms for all native snakes. As for how long can the hospital locate it? I'm sure they could have it to you quicker than it would take them to identify the snake. In any case, be careful. By all accounts, rattlesnakes hurt a lot, and can make you pretty sick. Call your local hospital and ask. They'll know if they have it on hand. Falconus^{p t c} 01:48, 12 October 2009 (UTC)

In my experience as a medical student in Kentucky, your antivenom would have been CroFab. It's expensive. If a small hospital were to stock it, have no patients, and let it expire, it would cost the hospital thousands of dollars per vial [1] and several vials are necessary to treat even one adult. This scenario is very likely given the sporadic nature of snake bites. Thus by pure economics, most small rural hospitals will not have it on hand, and you would be transferred to a tertiary care center if you really needed it. - Draeco (talk) 05:56, 12 October 2009 (UTC)

Why is sneezing convulsive?

As we now know, many animals sneeze. That's understandable, but why does it have to be convulsive - why does the individual have (almost) no control over it? Why can't it be just like other processes that clean the body (defecation and urination), that give the individual some discretion about the timing? It's not hard to think of circumstances in which it could be disastrous for an animal to sneeze at the wrong time - such as a when it means being detected by a predator or prey. I doubt that it's always of such life threatening importance that it has to be done immediately. Waiting a bit, while just breathing through the mouth for the time being, seems like a much better adapted alternative. Why can't we do that? — Sebastian 00:45, 12 October 2009 (UTC)

Coughing is a similar deal though - we can't help doing that either. SteveBaker (talk) 02:54, 12 October 2009 (UTC)

You're right. But coughing is convulsive for a reason: If something's stuck in our windpipe, we need to get it out quickly before we suffocate - there's no way to bypass the windpipe by breathing some other way. — Sebastian 03:02, 12 October 2009 (UTC)

Actually I remember reading somewhere that if a human isn't systematically toilet trained from a young age then they will most likely fail to develop an ability to control when they go to the toilet, to a greater extent. I think the fact that you have mucous membrane in your nose and throat probably plays a large part, it's probably more sensitive to infection and such, so there is probably a biological advantage to not let dirt or whatever sit on your membranes for longer then possible. Vespine (talk) 04:57, 12 October 2009 (UTC)

So i just had a quick read of the mucous membrane article and it actually says that the mucous acts against infection by trapping it, i'm sure it's still more prone then epidermis and your body still probably rather avoid (relatively) large bits of dirt sticking to it. Vespine (talk) 05:01, 12 October 2009 (UTC)

Its thought that the ancestral mammalian condition was obligate nose breathing (that is, our evolutionary predecessors used to only be able to breathe through their nose, and not their mouth). For many (but not all) non-human mammals that is still the case. Thus having a semi-autonomous mechanism in place to clear the airway of obstruction/infection would be quite advantageous, as Sebastian notes about coughing. Note also that human neonates are pretty much obligate nose breathers for the first few months, so they don't really have the option of waiting a bit, while just breathing through the mouth for the time being. I expect uncontrollable sneezing is a physiological artifact from before oronasal breathing was an option. Rockpocket 06:53, 12 October 2009 (UTC)

Thanks, that sounds plausible! — Sebastian 15:58, 12 October 2009 (UTC)

I frequently can control coughing and sneezing. Also, just because you can't consciously control something doesn't mean you can't unconsciously control it. The sneeze and cough responses may well be suppressed during times when they would cause trouble, such as when sleeping or hiding. StuRat (talk) 15:23, 13 October 2009 (UTC)

Interesting! From Vespine's post, I conclude that you must have been hanky trained as a child! And you're right, unconscious control would address the predator/pray situations I mentioned. This non-RS says "Experts say that you cannot or one is incapable of sneezing while at sleep." (With a quick google search, I couldn't find research on that, but I did find this related discussion.) But if it's true that we can't sneeze in our sleep, doesn't that negate the assumption that sneezing is vital to prevent us from suffocating? — Sebastian 16:44, 13 October 2009 (UTC)

"Can't sneeze" is a bit strong. The response is somewhat suppressed at times, but you would still sneeze if you really needed to, such as if someone blew pepper up your nose. StuRat (talk) 21:45, 18 October 2009 (UTC)

Windmill? Wind turbine? Wind Widget?

The article windmill makes it clear that that term refers to a wind powered grinding mill. Wind turbine refers to a wind powered electrical generator. These two devices have something in common, a big spinny bit. What is the spinny bit called? I'm looking for a name that includes both windmills and wind turbines, but excludes other similarly appearing spinny bits, such as propellers.

Alternately, I'm asking this question. What is the name for a device which captures wind energy, regardless of what purpose that energy is channeled into?

gnfnrf (talk) 01:25, 12 October 2009 (UTC)

Does this diagram help? Intelligentsium^review 02:07, 12 October 2009 (UTC)

They are called sails - see Windmill_sail. Exxolon (talk) 02:09, 12 October 2009 (UTC)

They seem to be called "sails" on a windmill and "blades" on a wind turbine. I guess it depends on their shape and purpose; blades are designed to move a lot faster.--Shantavira|^{feed me} 07:57, 12 October 2009 (UTC)

As far as I can tell, it looks to me like the difference between a sail and a blade may be a matter of the construction. A sail is generally made of a flexible material attached to a rigid frame, whereas a blade is one solid rigid piece. So modern wind turbines uniformly have blades, old-style windmills have sails, and typical (relatively) modern windmills as were commonly found in the American West have metal blades. I'm not certain that's the defining distinction between a sail and a blade; I'm just making an observation based on how the terms are used in the windmill and wind turbine articles. Red Act (talk) 12:23, 12 October 2009 (UTC)

The third sentence of the windmill article implies, without making it quite clear, that in popular parlance they all tend to be called windmills. If you read the whole article carefully, you'll see that the word is in fact used therein to refer to devices other than grist mills. I know that I've never heard the water-raising devices used on the American plains (as described in the section Windmill#In Canada and the United States) referred to as anything other than windmills; and the existence of articles such as Boardman's Windmill and List of drainage windmills in Norfolk suggest that usage isn't confined to grist mills in England, either. Deor (talk) 12:31, 12 October 2009 (UTC)

In fact, the more I look at the lede of the windmill article, the more it seems to me dead wrong. If you look at the dictionary definition linked in note 2 of the article, you'll see that windmill is in fact the correct word for any "device which captures wind energy, regardless of what purpose that energy is channeled into." Deor (talk) 15:23, 12 October 2009 (UTC)

Mytoses question

In my Biology class, we are doing a experiment about cells and mytoses (or howrevr you spell it. There's a question I can't figure out, and the page here is to complicated for me. The question is "What two differences are apparent at the poles of plant and animals cells?" (during mitoses). I thought the difference was that there is only a cell wall in a plant cell, but not in a animal. But there have to be 2! I've already tried, could someone explain it to me? Im not aksing for you to gimme the answer, just to explain. Help would be appreciated! Warmly, --Amber. —Preceding unsigned comment added by 69.210.134.227 (talk) 02:04, 12 October 2009 (UTC)

Mitosis -- you're sort of asking for the second difference. If you'd tell use what you don't understand about the second thing, we can explain it to you in easier-to-understand words. DRosenbach ^{(Talk | Contribs)} 02:30, 12 October 2009 (UTC)

It's spelled mitosis; please check out that article, it mentions at least two differences. — Sebastian 02:31, 12 October 2009 (UTC)

I checked the article -- and it doesn't specifically speak of two differences at the poles. Perhaps there are unmentioned differences, such as regarding the asters, the microtubal arrangements, the centromeres/-somes, etc. I'd hardly say that cleavage vs. cell wall formation occurs "at the poles." DRosenbach ^{(Talk | Contribs)} 02:33, 12 October 2009 (UTC)

You're right - I just didn't read the question thoroughly. Your reply was better than mine anyway; mine was only there due to an edit conflict, so I am striking it. I do take exception to your editing my reply though; it was meant as a reply to the question, not to your reply, and I'm undoing that herewith. — Sebastian 03:38, 12 October 2009 (UTC)

Higher plants have neither centrioles nor their product centrosomes. Perhaps that's your answer - Draeco (talk) 04:47, 12 October 2009 (UTC)

Silver in a plastic cutting board - antimicrobial/antibacterial or just BS?

I see in the Silver Nitrate article that there are legitimate disinfection uses for it, but I'm having a hard time seeing how scattering a few silver (cat?)ions across a plastic cutting board can cut down on the nasties living thereon... despite what the bodacious labeling wants to scream at me.

Can someone clear this up? 218.25.32.210 (talk) 02:08, 12 October 2009 (UTC)

Probably BS. I think any antiseptic properties would be short-lived at best. Either (A) the silver is covalently bound to the plastic which is permanent but doesn't allow it to interact with bacteria or (B) it's free to dissolve in water (which is the key to most medical uses of silver) making it possibly effective during the first use but subject to having all the ions washed away for subsequent uses. Having said this, I don't know of any real scientific evidence on cutting boards in particular, and I doubt it exists. Asking the manufacturer might be your best bet. - Draeco (talk) 05:04, 12 October 2009 (UTC)

I don't know about this specific product or what material is used, and I wouldn't be surprised if a manufacturer replied with the same marketing BS (if indeed that's what it is). However, there is literature about the effectiveness of silver in this type of use. See [2] for example. DMacks (talk) 05:10, 12 October 2009 (UTC)

Abrasive toothpastes

If toothpaste (and probably dentist cleaners too) contain abrasives which are at least as hard as teeth, then what is to prevent it from wearing them down to nothing? (well, at least polishing all the way through the enamel) If I guess a molecule of enamel is at least 600pm, and you brush twice a day for 25,000 days that's 0.03 mm. The dentist probably does at least that much again with his tools and his goops. Add to that that many people have really fast toothbrushes instead of manual ones, and it's remarkable that they could put sand in it and still have it remove so little each time. Sagittarian Milky Way (talk) 02:53, 12 October 2009 (UTC)

I'm no expert on dental care products, but you began with an "if" that might be important! How do you know those abrasives are "at least as hard as teeth"? Wouldn't it be smart to make them a little harder than plaque, but softer than tooth enamel? -- Scray (talk) 03:28, 12 October 2009 (UTC)

I know for a fact that silica is harder than teeth and calcium phosphates are just as hard (Mohs scale 7 and 5 respectively). Carbonates, sufates, organics, some elements, and halides tend to be soft. It only has to equal the hardness of something to scratch it. Sagittarian Milky Way (talk) 03:53, 12 October 2009 (UTC)

I would think that toothbrush bristles do not press the abrasives against the enamel with enough force to do damage. - Draeco (talk) 04:39, 12 October 2009 (UTC)

Actually, worn down enamel at the neck of the tooth is a very common problem caused by wrong brushing technique (too much force, to vigorous back-and-forth). To avoid it, follow best practices (little pressure, circular motion) and avoid brushing when the enamel has been weakened by recent acid contact (e.g. shortly after eating fruit). --Stephan Schulz (talk) 12:41, 12 October 2009 (UTC)

This recent article[3] mentions that tooth enamel and dentin can repair themselves. Usually the body is constantly repairing small amounts of damage.Cuddlyable3 (talk) 14:25, 12 October 2009 (UTC)

Dentist here -- enamel and dentin will not repair themselves after having been worn away by overzealous toothbrushing. DRosenbach ^{(Talk | Contribs)} 23:01, 12 October 2009 (UTC)

Somehow, I'd be too lazy to push either zealously or fast even if dentistry said it was better. I'd brush more often if that were the case. Sagittarian Milky Way (talk) 03:38, 13 October 2009 (UTC)

I once asked my dental hygienist a question of this nature and she told me that teeth are organic and do regenerate themselves spontaneously. Assuming adequate health. Vranak (talk) 17:03, 12 October 2009 (UTC)

Amazing, after all you hear about cavities you would've thought it was inert as a rock. Sagittarian Milky Way (talk) 20:00, 12 October 2009 (UTC)

Suffice to say that there are many many people out there driving around very nice cars because of the widespread belief that only a dentist can keep your teeth from rotting away to stumps. Perhaps there is some truth to that notion but it's far from being the whole story. Vranak (talk) 22:45, 12 October 2009 (UTC)

Tooth enamel "remineralizes" (so said the article on the main page for October 12th). I guess this is not the same thing as growing new enamel. I haven't been to a dentist for 20 years, still have all my teeth and they still seem good. Perhaps a dentist could give them a deep clean and make them better and likely to last longer, but as you say, very nice cars. —Preceding unsigned comment added by 81.131.7.241 (talk) 20:04, 13 October 2009 (UTC)

I'm sure excessive use is harmful, as toothpaste manufacturers and the American Dental Association all give upper limits for the recommended amount of brushing. 66.65.140.116 (talk) 20:28, 12 October 2009 (UTC)

The main component contributing to tooth abrasion is overzealous brushing, hence the name "toothbrush abrasion." Without enough force, the abrasive content of toothpastes will not wear away tooth structure, and with excessive force, toothbrush bristles will cause abrasion even without any paste at all. Thus controlling for both false negatives and false positives, it is the force of the brushing and not the abrasive that does it -- the abrasives may add to the effect, but the majority of brushing time finds the toothpaste already dissipated in large part. As for manual vs. electric toothbrushes, little force used to push the bristles of the latter against tooth structure doesn't add any forces that are not present with manual brushing. DRosenbach ^{(Talk | Contribs)} 23:01, 12 October 2009 (UTC)

Let's back up a bit to discuss why toothpaste contains abrasives. During the day (or night) deposits build up on the teeth. Everyone gets a buildup of plaque, and some also get tartar. The abrasives are to wear those off. Beyond this, they may indeed wear off a bit of the enamel, but, as previously stated, it can regrow if it's worn down at a slow enough rate. And, even if your teeth are worn down too fast for this, as long as it's slow enough that you die before the enamel has a hole in it, then you will keep your teeth your entire lifetime, which is the goal, after all. I suspect that those who manage to wear their teeth down by brushing are suffering from an obsessive-compulsive disorder which causes more frequent and vigorous brushing than is recommended. StuRat (talk) 14:53, 13 October 2009 (UTC)

when is dQ different from dH?

I'm having a hard time separating these two concepts.

In addition the enthalpy article states dH = TdS which can be greater or equal than dQ?! John Riemann Soong (talk) 04:28, 12 October 2009 (UTC)

Also, I really don't get the equation H = U + PV -- how is enthalpy more than the internal energy, and why does an object having a finite volume against environmental pressure contribute to its enthalpy? John Riemann Soong (talk) 04:31, 12 October 2009 (UTC)

Enthalpy is a defined value. It means absolutely nothing. The reason it was defined that way is to simplify expressions in constant-pressure processes, which is often what happens in research. Tim Song (talk) 05:18, 12 October 2009 (UTC)

More specifically, pressure exerted on the walls of a container is itself a form of potential energy (it becomes kinetic when the walls blow out...) so even under constant pressure conditions there is potential energy which must be taken into account. The PV part of your enthalpy definition is that little bit of potential energy, which is added on to the potential energy internal to the molecules. It should be noted that internal energy is a finite and real, but immesurable quantity, a property that is passed on to enthalpy as well. Thus, we tend to deal in ΔH rather than H, since enthalpy changes should equal the total energy changes to a system as a result of a chemical change, so long as pressure does not change. In cases where the reaction vessel is open to the atmosphere, any minute pressure changes are "washed out" as the "system" becomes the entire atmosphere, and since lots of chemistry is done in open air, enthalpy is a convenient way to measure energy changes. In situations where you have a sealed reaction vessel, then enthalpy must also taken into account the changes in potential energy due merely to changes in pressure, complicating the calculations significantly. --Jayron32 06:06, 12 October 2009 (UTC)

Which is why plain internal energy is used in those cases - constant volume => no pV work => dU = dQ if there is no other work. Tim Song (talk) 06:38, 12 October 2009 (UTC)

Okay, so enthalpy is any internal energy plus that little bit of potential energy due to "previous" work done against atmospheric pressure? I'm also having a little problem with the derivation of dH.

So H = U + PV; dH = dU + PdV + VdP

since U = H - PV, then dU = dH - PdV - VdP; does dH - VdP = dQ?

I still don't know how to make sense of the difference between dH and dQ. How can the increase in enthalpy be greater than the increase in heat added? John Riemann Soong (talk) 06:45, 12 October 2009 (UTC)

If the heat added also does work; for example, thermal expansion is a form of work. The confusing thing for a chemist is that chemists don't like to think about work as a form of energy. All chemists care about is the "q" factor; heat energy changes as measurable by temperature change. However, in situations where real work is done, then that ALSO has to be taken into account. PdV and VdP are the "work" factors in your equations. All of these factors are interrelated, so its a complete mess if you are trying to work out all of the details. For example, a decrease in internal energy could cause both changes in the surroundings temperature (a change in q) OR it could do work on the surroundings. You could also envision situations where a process is exothermic, but endergonic, that is work is done ON the system, but heat is release BY the system. For us simple chemists, if we ignore work, all of this mess goes away. --Jayron32 06:51, 12 October 2009 (UTC)

Okay, yeah, I can do that with my specific situation equations ... (isobaric, isochoric, etc.) but I just want to know facts that hold universally. So, let's say I transfer 1 J of heat to a system from the environment ... the enthalpy can increase by 1 J and on top of that, work can also be done? How does that not violate some form of conservation energy principle? John Riemann Soong (talk) 07:20, 12 October 2009 (UTC)

No, if you transfer 1 joule of energy from the system to the environment (dH = - 1), that energy can do both work and heat; in other words dW + dQ = - 1 Joule. For most common processes, dW is so close to zero it might as well be zero; however you aren't doing work ON TOP OF the heating of the environment. Its just that in some situations, releasing 1 joule of energy from a chemical reaction will not result in 1 joule of heating; it may result in MORE than 1 joule of heating (if the surroundings do work on the system WHILE the system is also heating the environment) OR it may result in LESS than 1 joule of heating (if the system does work on the surroundings WHILE the system is heating the environment). Remember that dQ and dW can be opposite signs. Ignore what Dauto says below about enthalpy not obeying the laws of conservation. Enthalpy does obey the laws of conservation; unless you ignore work. If you ignore work when you shouldn't, then you are introducing an error which makes it appear to not obey the laws of conservation. --Jayron32 18:32, 12 October 2009 (UTC)

It doesn't violate energy conservation because enthalpy isn't energy (even though it is also measured in Joules). U is the internal energy that must be subjected to the internal energy conservation. From the equation H=U+PV you get dH = dU + d(PV) = (dQ - PdV) + (PdV + VdP) = dQ + VdP. And that's that. Dauto (talk) 15:00, 12 October 2009 (UTC)

So wait -- as heat is withdrawn from a system enthalpy decreases faster than U does? I'm also trying to think of this in terms of heat capacity at constant pressure versus heat capacity at constant volume. Heat capacity at constant volume is less than heat capacity at constant pressure because of the heat transfer during a constant pressure process is diverted to work i? So at constant pressure, is the q that becomes part of U less than the q that the environment gave to the system?

Also, how do I distinguish between pressure of the system and pressure of the environment? John Riemann Soong (talk) 16:45, 12 October 2009 (UTC)

If the system is isolated from the environment, in a sealed container, than the two may have a different pressure. If the system is open to the environment, then you have the definition of a constant pressure situation, which is what is required for dQ to equal dH. If you did not have a constant pressure situation, then you would have two energies to keep track of; dQ and dW (heat and work). It really doesn't matter whether we say that dQ = dH - dW or dQ + dW = dH; that is conceptually it doesn't matter whether the work factor causes us to misestimate the enthalpy or the heat if we assume that dQ = dH. However, if the reaction is open to the surroundings, then no meaningful work is done (strictly speaking, work is almost always done, but when the denominator on the fraction is the moles of gas in the entire atmosphere, then for all intents and purposes that number is so small as to be meaningless). So, to answer your question again, the two pressures are the same unless you have a closed system, and in that case, you need to account the work factor in calculating the enthalpy (the PdV + VdP). --Jayron32 18:24, 12 October 2009 (UTC)

Jayron, dH = dQ + VdP which is not the same as dQ + dW because dW = PdV

OK, yes, you are right about that bit. Technically, VdP does not represent actual work, since nothing moves; however VdP is the potential energy change generated by the change in pressure; functionally it behaves like work in this case. Its much easier to think conceptually that there are two factors here; heat energy and mechanical energy. Mechanical energy has two forms; kinetic (work) energy (PdV) and potential energy (VdP). Any deviations between Q values and H values are due to mechanical energy changes, either kinetic or potential. The crux of the OP's problem is ignoring these mechanical energy issues. Since mechanical and heat energy could be the same sign OR opposite signs, the deviation between dQ and dH could be either positive or negative. --Jayron32 19:13, 12 October 2009 (UTC)

I agree with everything you said except with the carachterization of PdV and VdP as being kinetic and potential energies. I don't see how that fits. Dauto (talk) 19:40, 12 October 2009 (UTC)

Kinetic energy means something is moving. If the volume of a container is changing (a non-zero dV) then something must be physically moving, so it is kinetic energy. If there is no movement, but there is a change in pressure, then there is a change in the force on the walls of the container, and that change in force is a potential energy. To see that, imagine what would happen if the pressure, say, ripped a hole in the wall of the container. That would represent the conversion of that potential energy into kinetic energy. Increasing pressure increases the forthcoming kinetic energy involved in such a rupture, which is the definition of potential energy. So changes in volume are kinetic changes, while changes in pressure are potential changes. --Jayron32 20:31, 12 October 2009 (UTC)

"So at constant pressure, is the q that becomes part of U less than the q that the environment gave to the system?"

Yes, that's right. If you heat the gas at constant pressure, it will expand and do useful mechanical work on the environment, which means some of the energy you put in as heat is now gone from the system (for example off powering a generator), and not included in U. Change in enthalpy includes that work portion, which is why it's larger in this case than the actual energy that ends up in the gas. Rckrone (talk) 04:37, 14 October 2009 (UTC)

map distances and multiple crossovers

So let's say I have a cis genotype AB/ab (linked on the same chromosome) test-crossed with ab/ab and I'm supposed to find the amount of progeny that will end up AB/ab. If A and B are 10 m.u. apart, is this proportion 45% or 47.5% (or something a little larger than that?). Basically, if two genes are 1 m.u. apart, is the chance of no crossing over equal to 99%, or is that the chance of having parental type gametes? I'm trying to sort this out from the idea that the longer distances lead to underestimated recombination frequency. John Riemann Soong (talk) 06:39, 12 October 2009 (UTC)

1 map unit = 1% observed recombination. Therefore, given 100 meioses containing two loci 1 m.u. apart, one would expect to see 1 with a cross over event between the loci and the other 99 will not cross over. You should be able to apply this up to your experiment, which has two loci 10 m.u. apart. Bear in mind you would start off with half (50% is the value you would get with no crossing over at all) then subtract the percentage of those alleles that will have recombined between the two loci. Rockpocket 07:10, 12 October 2009 (UTC)

blood platelets

[Removed paraphrase of existing medical question.] APL (talk) 12:48, 12 October 2009 (UTC)

Time-matter conversion

I once read about some scientist's theory that said, among other things, that time and matter are just different forms of the same thing, much like heat and work are just different forms of energy. In this theory:

• Tachyons are the elementary particle that mediates time, just like the graviton would mediate gravity.
• When tachyons decelerate below the speed of light (I don't remember the exact process for this described in the paper), they "decay" into quarks, leptons and bosons, and when matter accelerates above the speed of light, it "decays" into tachyons. Therefore, c is not an absolute barrier, just a door between the realms of time and space.
• General relativity seems to preclude the transmission of information or matter above the speed of light; this is because it fails to consider the transformation from matter into time. Therefore, the only reason that matter cannot travel above the speed of light is because when it does it automatically becomes time.

I find it difficult to accept this theory, but because I have little knowledge of fundamental particle physics, I would appreciate it very much if someone could please tell me what is the observational evidence against the above theory. Thank you. --Leptictidium (mt) 13:08, 12 October 2009 (UTC)

I don't think you need observational evidence against it - it just doesn't make sense. Time is the progression from cause to effect, it makes no sense to talk about it being mediated by a particle. --Tango (talk) 13:45, 12 October 2009 (UTC)

I think the point here is to re-think what the definition of "time" is, so replying that "time" isn't what he says it is seems a little tautological. Again, I don't know the theory, but dismissing it just because "it doesn't make sense" in a very basic explanation seems silly to me, and unscientific. As one writer put it, the theory that the Earth sits on an endless series of turtles isn't wrong because it is ridiculous, it's wrong because we don't find any turtles at the South Pole... --Mr.98 (talk) 14:41, 12 October 2009 (UTC)

Time is time. If you want to define a new concept you need to give it a new name. There is a difference between ridiculous and nonsense - the theory as described doesn't make sense, the Earth sitting on turtles makes perfect sense, it just happens to be wrong. --Tango (talk) 15:11, 12 October 2009 (UTC)

A theory is scientific only if it has Falsifiability. This one doesn't. Cuddlyable3 (talk) 14:07, 12 October 2009 (UTC)

That seems, uh, to be a little premature of a judgment, no? I mean, I don't know the first thing about this reported theory, but I do know that a lot of new theories and high-end physics sounds pretty silly and out-there for a non-practitioner, especially when it is new. --Mr.98 (talk) 14:39, 12 October 2009 (UTC)

No. To clarify, my post did not conclude that the reported theory is wrong, just that it is not scientific i.e. ameanable to the scientific method. Cuddlyable3 (talk) 16:06, 13 October 2009 (UTC)

How could the speed of light be a "door"? It's a speed, not a door. In a diagram of space or time intervals, the speed of light is the locus of points that is identical in all frames of reference and separates definitely-space-like from definitely-time-like intervals; but this is not a "door". If you're looking for an analogy, consider it more of a wall. You might want to read the article spacetime for an overview. As has been pointed out, there's not observational evidence against these postulates because they don't make claims about observable phenomena. Nimur (talk) 14:14, 12 October 2009 (UTC)

Where did you read this theory? And which scientists believe it?

I don't ask to be contrary, I ask because the way you described it, it seems very confused. Perhaps if we could see the source... APL (talk) 14:33, 12 October 2009 (UTC)

Yes, I think we'd need to know the details a little bit better to even start to get a sense of it. If it is a "real" theory and not just on-the-internet speculation, then there is likely a lot more to it. --Mr.98 (talk) 14:39, 12 October 2009 (UTC)

I wouldn't take very seriously any theory that depends on the actual physical existence of tachyons in order to make sense. It smells like crackpot to me. Dauto (talk) 16:35, 12 October 2009 (UTC)

Er, why not? I mean, yeah, nobody has any evidence yet for tachyons, and they seem a little fishy, but there's no reason that one can't say, "if they exist..." and so on. Scientists have been doing that for a long time. (Remember that there was very little hard evidence for atomism at all until the early 20th century, yet it proved a pretty useful concept before then.) Again, I don't know about this purported theory at all... but I think dismissing things just because they sound weird is a little silly, given how weird the reality of things is (I think complementarity is pretty weird, but that doesn't mean it's wrong). --Mr.98 (talk) 18:20, 12 October 2009 (UTC)

Tachyons don't sound a little weird to me. They sound plain wrong. That theory described here doesn't pass the smell test. Atomism is not a good analogy. Dauto (talk) 18:38, 12 October 2009 (UTC)

The observational evidence against any theory that says time and matter are interchangeable is that no-one has observed time changing into matter or vice versa. You would think the effects would be quite noticeable - "hey, I just lost 5 seconds and lost of tracks have appeared in my cloud chamber". Equivalence of work and heat is easily demonstrated; equivalence of matter and energy is demonstrated in every nuclear reactor; but there is no demonstration of the equivalence of matter and time. Gandalf61 (talk) 17:00, 12 October 2009 (UTC)

...though it's of note that the matter-energy equivalence was not observed until the twentieth century, even though it was technically happening all the time. --Mr.98 (talk) 18:20, 12 October 2009 (UTC)

In the early 20th century, many well regarded scientists said relativity was a crackpot theory. Edison (talk) 19:11, 12 October 2009 (UTC)

True and irrelevant. Dauto (talk) 19:14, 12 October 2009 (UTC)

I'm sorry that I can remember no more details: I read about the theory in a magazine in an English library and only remembered about it the other day when watching a documentary about M-theory, but I don't remember the author or the name of the theory. Leptictidium (mt) 21:05, 12 October 2009 (UTC)

Weather

I need some good weather websites. Anyone have some? Surface maps, radars, cool graphics, stuff like that. I would like that. Thanks! <(^_^)> Pokegeek42 (talk) 14:03, 12 October 2009 (UTC)

Google is your friend. Entering "Weather forecast" gave[4] me 37 million "hits". Cuddlyable3 (talk) 14:10, 12 October 2009 (UTC)

If you're interested in weather in the United States, you should check out the National Weather Service, http://nws.noaa.gov. Their website provides the most authoritative forecasts in the country (in fact, it is the source for most redistributed commercial forecasts); and you can also access much of the raw data, including maps, radars, satellite imagery, and atmospheric conditions data. Being both a government website, and a website run by scientists, the imagery has a little less gloss and veneer than you might be used to if you mainly pull from commercial weather websites... but that rustic rawness is scientific accuracy. Nimur (talk) 14:20, 12 October 2009 (UTC)

Depending on what you need... Unisys or NRL TC might be useful. -Atmoz (talk) 16:21, 12 October 2009 (UTC)

And don't forget Wunderground (a.k.a. "Weather Underground") at http://www.wunderground.com/ and the amazing Masters's blog [5]. Bielle (talk) 16:55, 12 October 2009 (UTC)

Age hardening of Mild steel under water

Could anyone please advise on this topic.

I am designing a Remote underwater drilling rig. I will drill Mild Steel (Grade 43 A) at 600 RPM, with a Diamond Tipped Rotary Drill. The current force I have calculated to drill throught the 6mm thk plate is 1.7kN. Do I need to concider the effects of Age Harding during this underwater drilling process or not. If so presumably the effects of Age-Hardening could increase the surface hardness of the Mild Steel to four times, is this correct?

Please confirm

Regards,

Lyndon —Preceding unsigned comment added by Longone02031966 (talk • contribs) 14:25, 12 October 2009 (UTC)

I have some follow-up Q's for you:

1) How long has the mild steel been underwater ?

2) How deep ?

3) Is this ocean water ?

4) What is the temperature of this water ?

5) Is there any corrosion (rust) on the mild steel ? StuRat (talk) 14:39, 13 October 2009 (UTC)

North Texas weather

Why is it rainier than usual?Accdude92 (talk) (sign) 15:06, 12 October 2009 (UTC)

The extra 6 inches of rain (beyond the average) since September 1 appear to be due to a series of four heavy-rain days (as opposed to steady drizzle over the entire month). My guess is that these were all part of this front (visible in this satellite IR image). Take a look at climate and weather - explaining deviations from average values is not always possible. This is a pretty significant statistical variation, though. One really big weather system can knock off the statistics pretty strongly. Nimur (talk) 15:21, 12 October 2009 (UTC)

It's all the more weird because it follows a record-breaking series of 100 degF days through the summer. SteveBaker (talk) 01:05, 13 October 2009 (UTC)

You seem to be getting our rain! We had over fifteen inches of rain in July alone here in northern UK, and August was mainly wet, too, but the autumn is unusually dry here. We would gladly exchange climates! Dbfirs 08:55, 13 October 2009 (UTC)

Texas weather has no "why". When I moved from Denton to Toronto, long about November sometime, it was a little bit chilly, maybe around freezing. So I went on the web and looked up Denton. It was eight degrees. Fahrenheit!!!. --Trovatore (talk) 09:47, 13 October 2009 (UTC)

Urinary Tract Infections

It has commonly been stated that human females, generally, are more susceptible to urinary tract infections. One reason would logically be the shorter length of the urethra tract of females, and it being closer to the anus compared to males, but my question is do you know of any components in urine that might differ from male to female resulting in males not being as susceptible as females. I know that in old age there seems to be an equal frequency of infection between men and women as stated on the wiki UTI page. It also states that women lack bacteriostatic properties secreted from the prostate in males. This is not referenced, and if that is right would that "property" be prostatic acid phosphotase (PAP)? Pjohnso8 (talk) 21:38, 13 October 2009 (UTC)pjohnso8 —Preceding unsigned comment added by Pjohnso8 (talk • contribs) 19:13, 12 October 2009 (UTC)

Time speed shift

In some days I have a quite strong feeling that the time, particularly, the minutes, run faster. Ultimately, the way which usually takes me say 30 minutes to walk, eats 35 min or so. Is there any explanation? 85.132.109.227 (talk) 19:39, 12 October 2009 (UTC)

Our sense of time article is in sorry shape, but some of the reference links might be interesting, as might googling for time perception. --Sean 19:53, 12 October 2009 (UTC)

Perception is a purely psychological phenomenon; that is such differences between expected time differences and actual time differences are entirely products of your own mind. The world itself is unchanged. It is a very common human trait to ascribe psychological effects to the world itself rather than to recognize them as purely internal processes. There is a real phenomenon where time for two people will pass at different rates, called time dilation, but that is a very different thing than what you are describing. --Jayron32 20:27, 12 October 2009 (UTC)

Jayron32's phrases "products of your own mind" and "internal processes" should be interpreted liberally; some drugs alter the perception of time. Comet Tuttle (talk) 20:54, 12 October 2009 (UTC)

As noted in this recent news story. --Sean 00:20, 13 October 2009 (UTC)

The story is ok but the newsreaders' sniggering is juvenile. Cuddlyable3 (talk) 15:44, 13 October 2009 (UTC)

Yes, but the drugs don't actually change the way time works. They change the way your mind works. That's the whole point. Doing drugs of this type doesn't expand your capacity for knowledge or wisdom, as was often claimed, it merely increased your own perception of your own knowledge or wisdom. You don't expand your consciousness, you just think you do. Nothing changes in the way the world works, just in how you perceive how it works. --Jayron32 02:39, 13 October 2009 (UTC)

KC135 boom

How long can the refueling boom on the KC135 be extended? Googlemeister (talk) 21:23, 12 October 2009 (UTC)

This photograph of the boom operator's instrument panel has a dial labeled "Telescoping" which appears to range from 0 to 20 feet. It is not clear to me whether this is the full extended length or merely the extra length added by telescoping; also, the units ("feet") are obscured by the dial needle so I may be reading it incorrectly. Nimur (talk) 21:57, 12 October 2009 (UTC)

I don't recall the actual length of the telescoping boom - 20 feet seems way too short. If you look at photos of the boom, it looks to be about as long as the vertical stabiliser fin is tall. The fin is 40 feet tall - so I'd guess the boom was at least that. I do know that the alternative 'hose and drogue' system used by some aircraft types (eg when refuelling two planes at once) extends to about 75 feet...so again, 20 feet for the boom system seems way too short. It's possible the dial is indicating how far one section of the telescoping boom is extended - rather than the total length. SteveBaker (talk) 00:56, 13 October 2009 (UTC)

I think the US military uses metric units Metrication_in_the_United_States#Military. 20 metres would be about right, 65 feet or so. Our article on aerial refueling says the receiver pilot flies "directly below and 50 feet behind" the tanker, which matches up well. Franamax (talk) 15:44, 13 October 2009 (UTC)

It's possible that it's in meters - but I rather doubt it. I have a kinda half-suspicion that the dial is telling the operator something much more important. I think that the center section of the boom is designed to telescope in and out in order to take up the slack between the tanker and the plane that's being refuelled. After all, neither of them can fly perfectly straight and level - and it would be expected that they would drift around and that center section would need to be able to telescope in and out. However, if the pilots ever got so close together (or so far apart) that they ran out of telescopability (is that even a word?) - then the boom might run into some kind of end-stop limiter - and it might get really nasty. So perhaps the guy on the boom station is required to watch that gauge and either yell out warnings on the radio - or perhaps manually disengage the boom - if the two planes get too far away from their optimum positioning. Now THAT distance could easily be as little as 20 feet. So out of a 60 foot boom (or whatever it is), it is easily possible that only 20 feet of it might be telescopic. SteveBaker (talk) 21:42, 13 October 2009 (UTC)

I just took another look at the photo - and now I'm 100% convinced that my explanation above is right. The center section of the dial is marked with a green arc - with red markers at either end. That surely has to mean that so long as the telescoping of the boom falls between those two red marks, everything is OK - and that if it ever compresses so much that it's in danger of sticking and ramming itself through the pilot's windshield - or stretches so much that it's going to be yanked off of the plane - then you're outside of the green band. Even more convincing is that the danger zone on the full-extension side of the dial is smaller than the one on the left. That too would make sense since if the boom is stretched too far, it'll simply disconnect - but if it's squashed up more than it can handle - then there would be a hard collision with the refuelling plane - which could easily get someone killed. Hence, the dial is in feet - but that tells us nothing about the overall length of the boom. Oh - except that it must be at least 40 feet at fullest extension in order to allow 20 feet of telescoping with a single rigid sliding section. SteveBaker (talk) 21:50, 13 October 2009 (UTC)

Lump on penis

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Time over distance...

... I have heard that clocks on the top of really tall buildings go through an hour a few minutes either fast or slower than a regular clock. But due to them being so high up, the time difference equals out so they match a regular clock on the ground. Is there any truth to this, if so, where can I find more information?

Thanks in advance!

74.218.50.226 (talk) 22:25, 12 October 2009 (UTC)

No building on Earth is tall enough to experience any measurable time dilation from either the gravitational difference nor the net difference in rotational motion - certainly not minutes on the hour. Nimur (talk) 22:32, 12 October 2009 (UTC)

How about the buildings on other planets? Just kidding... I didn't think there was that big of a differance. Thanks!74.218.50.226 (talk) 22:38, 12 October 2009 (UTC)

Not on other planets - but perhaps a tall building built on a neutron star might show some serious weirdness - but making a building more than a millimeter or two tall would be an impressive engineering feat! SteveBaker (talk) 00:47, 13 October 2009 (UTC)

Clocks at tops of buildings run very slightly faster than clocks at bottoms of buildings, due to gravitational time dilation. The difference is big enough to measure, but only if extremely precise equipment is used. The Pound–Rebka experiment, which was the first experiment to show this effect, took place in a building that wasn't even all that tall. The height difference between the bottom and top was only 22.5 meters (73.8 feet). Red Act (talk) 23:12, 12 October 2009 (UTC)

Sorry, but it just sounds bogus. It is very surprising and counter-intuitive that there should be an easily measurable effect in such a small distance in such a gravitational field. Edison (talk) 03:40, 13 October 2009 (UTC)

The original Pound-Rebka paper (1959) states that there should be a factor of 1.09x10^-18 frequency multiplier for each centimeter above the earth's surface. The derivation seems dubious; the approximation seems more dubious; and the prospect of measuring an effect on the order of 10^-18 even today, let alone in 1959, seems very dubious. Finally, the paper states a method for observing this effect - by observing hyperfine structure on nuclear gamma ray emission spectra (which can be measured very accurately) - but does not actually state that the gravitational redshift experiment has been performed. Thus the theoretical derivation of the frequency redshifting was not validated with experimental data. Nimur (talk) 04:01, 13 October 2009 (UTC)

The 1960 followup paper, Apparent Weight of Photons, does explicitly claim to have completed experimental measurement. Again, I have to call "dubious" all over this paper - the introduction outlines their "systematic measurement errors" that they attempt to mitigate by what I would consider data cherry-picking (using only certain combinations of experimental results and measuring a delta); they compensate for the temperature shift by what appears to be an arbitrary multiplication; etc. I'm not a relativistic physicist; I know little about hyperfine structure of gamma ray spectra - but I am an experimental physicist - and I don't like claims that are buried so far below the noise floor that you have to subtract elaborate models of the noise to "find" your result. I think it speaks volumes that this work, published in the early 1960s, has not been brought up since then as a bastion of scientific method and empirical proof of relativity - it's been cited once or twice in five decades. The discerning wikipedian will probably want to read the paper series themselves and decide whether my harsh judgement of "dubious" is warranted; after all, these papers were peer-reviewed and published - but needless to say, the effect is miniscule if it is measurable at all. Nimur (talk) 04:14, 13 October 2009 (UTC)

For context, Gamma ray spectrometer shows several plots from modern equipment (with about 12 bits of frequency resolution, or ~ 1000 "channels"). This is the top-of-the-line gear in 2009. To measure a frequency deviation of 10^-18, one would need to pull about 64 bits (equivalent) of resolution - fifty years ago - out of a custom-built analog experimental apparatus. Nimur (talk) 04:29, 13 October 2009 (UTC)

Pound-Rebka isn't some forgotten experiment that's been ignored by mainstream physicists. The experiment is widely referenced as being an important confirmation of general relativity in general relativity textbooks. For example, MTW, which is generally considered to be the "Bible" of general relativity, devotes more than two pages to the experiment (see pages 1056-1058). Other GR textbooks I happen to have that reference Pound-Rebka are "Gravity" by James Hartle, which devotes half of p. 118 to it, and "A first course in general relativity" by Bernard F. Schutz (see p. 120).

The experiment didn't need to measure anything accurate to one part in 10¹⁸. The 10^-18 is the relative amount of change per centimeter of height. But the apparatus had a height difference of 22.5 meters, so it was only necessary to measure a relative change of about 2.5x10^-15.

A relative change of 2.5x10^-15 is enormous compared to what is measured by modern gravitation experiments. For example, LIGO measures relative changes down to 10^-21, i.e., more than a million times smaller than what needed to be measured by Pound-Rebka. Red Act (talk) 05:45, 13 October 2009 (UTC)

Here is a document by Dr. John Mester, a physics prof at your school, which refers to the Pound-Rebka experiment. So you could stop by his office and ask him about Pound-Rebka, if you're still dubious about it. Red Act (talk) 07:59, 13 October 2009 (UTC)

I'll follow up on that lead. As I disclaimed earlier, I'm not an expert in this field - and the experiment did get published in a reputable peer-reviewed journal - so as much as I flail around shouting "dubious", my opinion is only worth so much. The Gravity Probe B mission, and the LIGO, also seeking to measure relativistic gravitational effects, also both suffer from tiny signal amongst huge noise. I think the ultimate answer here is that the OP's suggestion of "minutes per hour" is very far from reality; the predicted changes should be femtoseconds - which cannot be measured by even the most accurate atomic clocks. To measure these, it seems necessary to build a complex custom "device" and extrapolate a time dilation via a frequency shift. Nimur (talk) 11:47, 13 October 2009 (UTC)

I'd be really cautious about suggesting that the Pound-Rebka device needs 64 bits of precision to make a successful measurement. Remember, the experimenters don't need to measure the frequency from scratch. They just need an apparatus sensitive to minor differences in frequency — which the universe handily provides in the form of crystalline iron-57. It's the difference between measuring elapsed milliseconds between two events on the bench (trivial) and attempting to measure elapsed milliseconds since the start of the universe, twice, and taking a difference (ludicrous). TenOfAllTrades(talk) 12:38, 13 October 2009 (UTC)

It took me an hour to write one lousy sentence, but I put that little factoid into our Isotopes of iron article. People with some actual understanding of the topic may wish to review my wording.[6] Franamax (talk) 16:51, 13 October 2009 (UTC)

Y'all think you're so smart talking about gravitational redshift that you endded up missing the trivial answer to that question that a grandfather clock's period will change as you go up a building because the formula for the period of oscilation of a pendulum pendulum#Period of oscillation depends on the local acceleration of gravity that changes as you move higher up a building. Dauto (talk) 15:00, 13 October 2009 (UTC)

Like the original poster, I vaguely remember hearing that the effect of gravitational time dilation is exactly canceled by the effect of the changing gravity on a pendulum clock. Unfortunately, unless I miscalculated, they only half-cancel—the change in the swing rate is half the change from time dilation. That only applies for small height differences (where both effects are negligible anyway) and only for pendulum clocks, of course. -- BenRG (talk) 19:47, 13 October 2009 (UTC)

Viscous damping by air slows a pendulum clock slightly. This is why pendulums often have sharp edges to minimise air friction. At the top of a building the air pressure is lower which contribures to a clock going faster. (But something is wrong with the clock if the time difference is as much as minutes in an hour.) Cuddlyable3 (talk) 15:38, 13 October 2009 (UTC)

Air pressure changes over time just due to different weather - that variation is more significant than the change in air pressure for all but the tallest buildings. --Tango (talk) 16:56, 13 October 2009 (UTC)

So how many experiments published in peer-reviewed journals in the 50 years since the original publication have managed to replicate the Pound-Rebka experiment? Science is not about citing some teacher or book writer who "believes" the result. For a miniscule effect buried down in the noise and rescued by post-hoc correction factors, actual replication is appropriate. Edison (talk) 17:49, 13 October 2009 (UTC)

Edison, your excepticism is very healthy but in that specific case it is unfounded. Indeed, the Mossbauer effect effect, (which is the effect used in this experiment), can measure extremely small frequency shifts. This experiment is not bogus. Dauto (talk) 19:12, 13 October 2009 (UTC)

The Mössbauer effect is sensitive to very tiny frequency shifts; the Pound-Rebka experiment is famous and cited by every relativity textbook; the theoretical prediction of time dilation follows directly from the equivalence principle; and it's been empirically detected in other ways (like the GPS). But looking at P&R's actual published data (top of page 340) I see why Nimur and Edison are complaining. It looks too noisy to justify even the claimed 10% accuracy of the result. -- BenRG (talk) 20:13, 13 October 2009 (UTC)

That was just the initial experiment. By 1964, Pound and Snider had improved on the precision of the Pound-Rebka experiment by a factor of 10. See Pound and Snider's 1964 paper.[7] Red Act (talk) 21:13, 13 October 2009 (UTC)

Actually, Pound and Snider's 1965 paper might be better. That's the one MTW cites. See [8]. Red Act (talk) 22:02, 13 October 2009 (UTC)

October 13

The irregular dark spots on sidewalks

What are they and how are they formed? Thanks. Imagine Reason (talk) 00:55, 13 October 2009 (UTC)

Very very old gum, actually. This is what you're talking about, right? Someguy1221 (talk) 01:15, 13 October 2009 (UTC)

I thought it might be an urban legend. That's gotta be a lot of gum, though, coz most sidewalk blocks have quite a few of them each! 66.65.140.116 (talk) 19:59, 13 October 2009 (UTC)

They could also be the imprints of fallen leaves: I've noticed that sometimes (perhaps when the cement of the sidewalk was recently poured) a fallen leaf will stain the sidewalk brown. Sometimes the outline of the leaf is unmistakably clear. (I think there's a sidewalk near me that displays this; perhaps I can take a picture tomorrow.) —Steve Summit (talk) 01:45, 13 October 2009 (UTC)

Such leaf stains would be caused by tannins - effectively permanently dyeing the concrete. Even after the leaf blows or erodes away, the tannins can remain, staining the sidewalk. Nimur (talk) 04:19, 13 October 2009 (UTC)

An interesting opposite effect I've seen is bleaching of the sidewalk by acids in pine needles. --Sean 13:42, 13 October 2009 (UTC)

Does this staining and bleaching occur on cement that's dried, too? 66.65.140.116 (talk) 20:00, 13 October 2009 (UTC)

To tell whether your sidewalk spots ("pavement" spots for Brits) are from gum or leaves, here are some suggestions: Are they under a tree (then probably leaves) or where people gather, like bus stops, benches, corners, entrances to buildings, etc. (then probably gum). Gum spots tend to be black and relatively smooth at the edges, while leaf stains can be brown or other colors and have rough edges. StuRat (talk) 14:32, 13 October 2009 (UTC)

volume change in an isothermal process versus an adiabatic process

I'm trying to figure out which is more in magnitude ... and not being very successful at it? I'm using the ideal gas equation. Help! I get as far as -Int[nRT/V dV] = change in U and stuff, but just need some direction here. John Riemann Soong (talk) 06:15, 13 October 2009 (UTC)

It's going to depend on what you consider to be "equivalent" adiabatic and isothermal processes. Comparing the volume change for an equivalent change in U doesn't make sense since U doesn't change in an isothermal process. We can compare them for an equivalent amount of mechanical work W done. At a given state, dW/dV = nRT/V regardless of what kind of process it is, so the infinitesimal change is the same. If we regard two processes where the low volume states are set equal, the adiabatic one will have to undergo a larger volume change, since it'll be cooler than the isothermal gas, and dW/dV will be lower. If the high volume states are set equal then the opposite is true.

The work formula you have there $W=\int nRT/VdV$ is good for the isothermal case since T is constant. For adiabatic, the constant is PV^γ = c, so $W=\int cV^{-\gamma }dV$. Rckrone (talk) 21:36, 13 October 2009 (UTC)

If you're comparing the change in volume for an equivalent change in pressure, then the isothermal case requires the bigger change. As the volume increases, the adiabatic gas looses internal energy doing work so the pressure drops by more than for the isothermal case. Rckrone (talk) 22:10, 13 October 2009 (UTC)

symbols of restraint in women's fashion

Hi - I'm interested in the idea that some clothes and accessories worn by women symbolise helplessness and/or restraint. Some examples might be tight skirts, stilettos, chokers - and at the more extreme end of the scale, footbinding and neck rings. I'm also interested in the idea, once ascribed to Catherine MacKinnon, that all sex is rape -- of course this isn't literally true, and is it turns out, it was never made as a serious quote, but I do wonder about the fact that the females of so many mammals, with some exceptions, are statistically smaller and weaker than the males. Are the two things related? Were we more likely to breed if a male was able to run down and restrain a female? Did this result in weaker females being selected for? Is this why we have 'restraint-fashion'?

Have these ideas ever been seriously discussed? If so, I'd appreciate it if someone could let me know who and where.

sorry - I realise these ideas are sort of ugly, but it'd be great if we could discuss them without rancor.

Thanks all,

Adambrowne666 (talk) 06:28, 13 October 2009 (UTC)

The rules of the RD say that this is not a forum for discussion and if the subject of the question is dry then this rule is usually adhered to; but when sex is the subject of the question the rules go out the door - just watch. Caesar's Daddy (talk) 07:03, 13 October 2009 (UTC)

Fashions like leggings or mini-skirts are far less restricting than men's trousers for example, and therefore contradict your hypothesis. Currently womens fashion seems to be similar to the fashion that male Cavalier's wore centuries ago (high boots, big belts for example). 92.24.99.195 (talk) 12:10, 13 October 2009 (UTC)

I find ties to be very restrictive. Heck, they are even named "ties", what could be worse, maybe "chains" ? StuRat (talk) 13:30, 13 October 2009 (UTC)

In any case, this probably belongs on the Humanities desk since it asks about cultural norms and sociological ideas. Nimur (talk) 13:34, 13 October 2009 (UTC)

Not the part about natural selection, that belongs right here. StuRat (talk) 13:41, 13 October 2009 (UTC)

As for the hypothesis that most male animals rape the females, I don't think this matches observations, where most females exhibit considerable choice. Even if the males overpowered the females, the females still sometimes exert their own control by not ovulating or else rejecting (perhaps even eating) the offspring. StuRat (talk) 13:41, 13 October 2009 (UTC)

A young woman wearing a tight skirt was at the front of the queue when the bus arrived. She struggled to step up but her skirt was too tight. So she reached behind and loosed the zip, and tried again. Still she couldn't reach the step. So she loosened the zip some more to try again. But the impatient man behind her just picked her up bodily and put her in the bus. The woman turn furiously on him with How dare you touch my body when I don't even know you? The man answered I thought we were getting aquainted after you twice unzipped my trousers. Cuddlyable3 (talk) 15:21, 13 October 2009 (UTC)

I believe the idea was that all sex is rape in a society where woman are marginalized. I don't think Xena would be all that upset by... well... things of this nature.

Also, in The Second Sex, Ms. Beauvoir touches on the idea that all clothing is in fact bondage, a mutilating bridle that chafes the skin and burdens the senses. Vranak (talk) 15:33, 13 October 2009 (UTC)

I recall reading someplace that the costume designers for the original StarTrek show went to a LOT of trouble to discover what kind of womens' clothing most attracted men. (I suspect I read it in one of Gene Roddenberry's biographies...but I'm not 100% sure.) It turned out that it didn't matter AT ALL how tight/restraining the clothing was - nor (to their surprise) how revealing it was. What attracted men most was how much it appeared that the clothing was likely to fall off at any moment. When you look at the costumes they produced with this in mind - you can see where they were going with that. SteveBaker (talk) 21:33, 13 October 2009 (UTC)

I don't really believe that, even generally. To me it sounds like something either a feminist or a misogynist would make up, trying to deny or excuse responsibility for human actions. Females choosing who to mate with is commonly observed in many mammal species. A great example I saw recently was lionesses who sneak away from the pride to mate with solitary nomad males, even at risk of physical retribution. This has the obvious biological advantage of mixing the gene pool in groups where the alpha male does the majority of the breeding. Also helps mitigate the impact on the group if the Alpha male just happens to be sterile or have some other genetic abnormality, which could otherwise just about wipe out a whole generation if the alpha is otherwise fit and strong. Vespine (talk) 23:46, 13 October 2009 (UTC)

Sorry i've kind of missed the point.. To answer the actual question, I think it is the opposite that is true. It isn't "females are weaker because males will mate with them easier" I think it is "males are stronger because females select the strong males to breed with". Vespine (talk) 23:51, 13 October 2009 (UTC)

And before someone argues with me, I do mean "select" in the broad "natural selection" meaning, not the "females making individual personal choice" meaning. "Strong" males will tend to be fitter, healthier, better able to provide and protect, therefore make a better choice for mate. Females on the other hand are not chosen for strength but for fertility and other maternal qualities. Vespine (talk) 23:56, 13 October 2009 (UTC)

Yes, very good point, Vespine - I didn't think of that. Adambrowne666 (talk) 22:14, 14 October 2009 (UTC)

I don't believe it either. Think Muslim garb vs. bikini. Imagine Reason (talk) 04:57, 15 October 2009 (UTC)

Of course, I'm not saying symbolic restraint is the only factor, ImagineReason - attractiveness is multifactorial - it was just the one I wanted to talk about here, and I certainly would say it figures in a lot of fashion Adambrowne666 (talk) 10:06, 16 October 2009 (UTC)

The Victorian Crinoline put a steel cage around the lower half of a woman that hampered most activities except dancing. Males can find the sight of such an encumbered woman performerpleasurable. Cuddlyable3 (talk) 13:41, 18 October 2009 (UTC)

I'm not one of those males, as it happens, but thanks, Cuddlyable, good example. Adambrowne666 (talk) 22:25, 18 October 2009 (UTC)

Physics

is C= 2F in [lens]? its no, but why? use n/v-1/u= n-1/r if n= 1.5 i.e. glass —Preceding unsigned comment added by Fantasticphysics (talk • contribs) 09:53, 13 October 2009 (UTC)

The second formula is the thin lens formula. See Lens (optics). Depending what is meant by C, the first formula might be to find C = diameter of a spherical mirror. Cuddlyable3 (talk) 13:38, 13 October 2009 (UTC)

The sexual desire of post-op transexuals

Because they have lost their testes and do not have ovaries, does this mean they have no or a greatly reduced sexual desire? I recall hearing that they cannot orgasm. Perhaps taking female hormones results in desire, but I've heard that it may be normal for them to stop taking it after a while. 92.24.99.195 (talk) 11:40, 13 October 2009 (UTC)

I believe they need to take hormones for the rest of their life if they expect to look like their chosen gender. If they stop, they will regress to "something in-between", and it's not a pretty sight. StuRat (talk) 13:26, 13 October 2009 (UTC)

The OP must mean a male-to-female transexual. The article Eunuch cites Wille, Reinhard & Klaus M. Beier (1989), Castration in Germany. Annals of Sex Research, vol. 2, pp. 103–33 Convicted sex offenders who have been castrated are rare; a lack of testosterone and the consequent ability to better control their own libido does result in negligible recidivism. Cuddlyable3 (talk) 13:30, 13 October 2009 (UTC)

Does transexuals getting female hormones make a difference in this respect? 92.26.174.34 (talk) 19:38, 13 October 2009 (UTC)

In the best study I can find, transsexual male-to-females had a 34% incidence of decreased libido, which was more prevalent than in true females (23%) but not statistically significant. Libido is (controversially) thought to correlate with serum testosterone levels, even in women. The transsexuals' testosterone levels were lower than true females on average, but their testosterone levels did not appear to correlate with their libido (as it did in true females). This is according to Elaut E; De Cuypere G; De Sutter P; Gijs L; Van Trotsenburg M; Heylens G; Kaufman JM; Rubens R; T'sjoen G. Hypoactive sexual desire in transsexual women: prevalence and association with testosterone levels. European Journal Of Endocrinology 2008 Mar; Vol. 158 (3), pp. 393-9. - Draeco (talk) 17:03, 14 October 2009 (UTC)

What is TRAIL PCR?

What is TRAIL PCR? My Google-fu is weak today :/ ----Seans Potato Business 12:52, 13 October 2009 (UTC)

Without some context, there isn't much we can do... Are TRAIL and PCR useful? --Tango (talk) 13:03, 13 October 2009 (UTC)

Yes, I think Tango is correct, it is likey a reference to Polymerase Chain Reaction (PCR) of Tumor necrosis factor-Related Apoptosis-Inducing Ligand (TRAIL) encoding DNA. Rockpocket 16:43, 13 October 2009 (UTC)

And going by this, I think the relevant article is RT-PCR. Franamax (talk) 16:45, 13 October 2009 (UTC)

Medicare catheters

In the US there are TV ads for catheters that say Medicare formerly only provided 4 a month and now provides 200. Why the huge change ? Can't they be sterilized and reinserted ? This seems to run counter to recent attempts to contain exploding medical costs. Not a request for medical advice as I don't know anyone who uses these. StuRat (talk) 15:45, 13 October 2009 (UTC)

U.S. Medicare policy change in catheter guidelines Improves patient care in home and hospice setting. Apparently it's a convenience, not a necessity, to have a fresh catheter each time. Nimur (talk) 16:06, 13 October 2009 (UTC)

Cost reduction based on reduced UTIs. The cost of a UTI involves a doctor visit, lab culture, prescription and follow-up lab culture. hydnjo (talk) 18:23, 13 October 2009 (UTC)

But why would there be more UTIs ? Aren't people willing and able to sterilize a used cath ? StuRat (talk) 13:22, 18 October 2009 (UTC)

TV ad?

Sorry to sidetrack, but was it a political ad, or do they seriously advertise catheters on TV in the USA? ("Buy now and get 200 for the price of 150!") AlmostReadytoFly (talk) 17:49, 13 October 2009 (UTC)

Serious ad, yes sir. But it's not a discount price. There are lots of home-medical-care ads, and one of their selling points exactly is that it's a reimbursable or covered cost. Some companies even advertise that they will help with the medicare/insurance paperwork. "Why not buy up to the covered limit? It's not really costing you and you'll appreciate having them" is the message. DMacks (talk) 18:33, 13 October 2009 (UTC)

And then what? Sell them on eBay? Stockpile medical supplies just in case you ever need them and the local hospital is BYOC? AlmostReadytoFly (talk) 18:42, 13 October 2009 (UTC)

Why would you expect health insurance to cover a cost that is not related to a diagnosed actual need? Again, it's not a special sale targetted to the general public buying with their own money. DMacks (talk) 18:49, 13 October 2009 (UTC)

The ads I have seen were catering to people who already needed urinary catheters for at home medical reasons. The point was that Medicare at that time required these patients to sterilize and reuse catheters many times per month, while the advertised company would gladly sell you a month's supply of use-once and discard sterile catheters. Hence it catered to reducing people's fear of infection and increasing their convenience. A niche market certainly, but not at all crazy. Dragons flight (talk) 19:06, 13 October 2009 (UTC)

Ah, now I understand. Thanks. AlmostReadytoFly (talk) 19:10, 13 October 2009 (UTC)

Sorry if I came across too snarky. DMacks (talk) 19:39, 13 October 2009 (UTC)

Not in the slightest. I was too baffled by the basic concept of advertising "all-you-can-claim" medical equipment on TV to work out what to expect. AlmostReadytoFly (talk) 20:43, 13 October 2009 (UTC)

Very large object

Some years ago, out of idle curiosity, I did a google search for "largest object in the universe", or a similar phrase. What this turned up was a long page about astronomy that covered many topics. Somewhere in the dense text it told me about the object in question, which was referred to by a codename consisting of letters and numbers. I think "object" here refers to things like stars, rather than things like galaxies. Wading through the technical information, I established that this object was:

• Very, very far away
• Problematically large
• Inexplicably toroidal

Rather than doing any more searches, I just left it at that and went away with the pleasing impression that God is a giant doughnut. Today I want to know more about this object. Do we have a page on it? 81.131.7.241 (talk) 18:34, 13 October 2009 (UTC)

A quick Google search suggests that a giant blob is a good candidate for "largest thing". It fails your "things like stars rather than galaxies" criterion, but I'll note that "star" is wholly incompatible with what modern astronomy considers "very far away". For example, VY Canis Majoris is the largest known star but it's practically on our doorstep, less than 5000 light years distant. If you prefer an intermediate biggest object, the black hole at the center of quasar OJ287 is 18 billion solar masses -- a galaxy, give or take. — Lomn 19:06, 13 October 2009 (UTC)

OJ287 is an impressive thing and may have been what I read about. Perhaps at the time it seemed inexplicably doughnut shaped, before it was explained and found not to be. 81.131.7.241 (talk) 19:54, 13 October 2009 (UTC)

See Dunkin' Donuts. Bus stop (talk) 18:42, 13 October 2009 (UTC)

If you ignore the "star-like and not galaxy-like" definition, and instead focus on an object being any gravitationally-bound collection of matter, then the Sloan Great Wall, a massive collection of galaxies known as a galactic filament, is the largest known "structure" in the universe. If you want the largest identified star in our galaxy, then VY Canis Majoris is the largest, it is about 2000x as massive as our sun. We don't have the ability to resolve the size in other galaxies, though individual stars have been located and identified in other galaxies, such Cepheid variable stars; however I am not sure if these have been accurately sized. The so-called "blob" referred to above is a type of Lyman-alpha blob, a class of galaxy-sized, unorganized diffuse hydrogen clouds, though these are also probably more "galaxy-like" objects than "star-like". --Jayron32 19:23, 13 October 2009 (UTC)

I only put the "star not galaxy" bit in because, thinking about it, I couldn't see why it would be surprising for a galaxy to be toroidal, or why even an unusually large galaxy should raise questions about how it came to exist. Maybe it wasn't anything like a star. Oh, I remember that it was known to be toroidal by watching how it obscured other things passing behind it. (Or gravitational lensing, maybe?) So I guess it was a dark object, whatever it was. 81.131.7.241 (talk) 19:38, 13 October 2009 (UTC)

I would say that the largest known structure in the universe is probabily the CMB cold spot, that is if voids are acceptable... Dauto (talk) 20:06, 13 October 2009 (UTC)

Whoa. Does anyone know if a specific word/phrase has been coined to describe the feeling of awe combined with the sad realization of the utter insignificance of one's own existence that I just felt when reading about the large-scale structure of the cosmos? --Kurt Shaped Box (talk) 20:31, 13 October 2009 (UTC)

I've had it. Does that count? 90.208.3.84 (talk) 20:39, 13 October 2009 (UTC)

I don't know about a name for it, but the Total Perspective Vortex is a device to induce this feeling. Rckrone (talk) 20:42, 13 October 2009 (UTC)

The sadness at realizing our lack of significance in the universe is called existential depression (what, no article ?). See [9]. StuRat (talk) 15:22, 18 October 2009 (UTC)

The real problem at the heart of this question is the definition of the word "thing" and the definition of "largest". Assuming we really mean "biggest in volume" rather than "most massive", that helps a bit - and we only have to worry about what a "thing" is. There are many possibilities - distinguished only linguistically - and not scientifically:

• If a collection of solid objects like (say) a solar system (comprising of a star, some planets, some moons, many asteroids and comets, a bunch of dust and gas and a heck of a lot of vacuum) is a "thing" - then so (presumably) is a galaxy, a galactic cluster, an the entire universe itself. The largest thing in the universe is the universe. You could argue that this doesn't count - but then you're just down to who can invent a noun describing the largest number of somewhat related galaxies that doesn't include the entire universe? It's a meaningless limit...it's just down to what words you want to use.
• But if you don't allow collections of objects to be a 'thing' - then you're down to looking at stars, black holes and such like - but what about dust clouds? Are those 'things'? Or are they collections of little bits of dust? If a dust cloud can be a 'thing' but a galaxy cannot - then they are the biggest things around because they are vastly larger than stars.
• If you disallow dust clouds then we really are looking at things like stars and black holes. But strictly speaking, a black hole can't be the largest thing in the universe because it's really a zero-sized singularity - making them the smallest things in the universe - not the largest! You have to include the event horizon - but is that a 'thing'? It's not solid - and in some cases, you could cross one without ever being aware of having done so.
• So if you rule out black holes - then you're really down to stars. So what is the largest star? VY Canis Majoris appears to be the winner (out of all of the stars we could reasonably measure). There will probably be a mathematical limit on the biggest possible star anyway: If the star is very dense - and large - then it'll collapse into some sort of neutron star or a black hole or something; If the star is very large but not very dense - then it won't be able to sustain fusion, the mutual gravitation will pull it back together - and it won't be very large anymore. So there must be limits - we could calculate that limit and when we find any star that's that big, we can say that we have at least one of the largest 'things' in the universe.
• There are other possibilities: You could argue that nothingness is a "thing". After all, we talk about the Grand Canyon as if it were a thing - when it's really a very, very big lack of rock and dirt! So how about the voids between galaxies? If we were to call the void between galaxies by some cute name "The intergalactic rift" - then the intergalactic rift would easily take the prize.

So - how you define the word "thing" is the entire question here. It's not science - it's linguistics. SteveBaker (talk) 21:13, 13 October 2009 (UTC)

Back to the original question. You say it had a "code name" — almost certainly, the name followed the standard convention of simply giving the coordinates of the object, preceded by some letters specifying the type of object or the catalogue in which it appears. The largest objects that carry such names are clusters of galaxies. I'll try a shot in the dark: How about the dark matter ring in the cluster of galaxies Cl0024+1654? Not really the largest object in the Universe, not problematically large (and quite possibly not even real), but at least it's toroidal. --Wrongfilter (talk) 22:52, 13 October 2009 (UTC)

These sorts of questions lead me to strange (poss. nonsensical) ponderings. If the universe is indeed infinite - does that mean that it may contain an object (somewhere) that is of infinite size and infinite mass? --Kurt Shaped Box (talk) 22:59, 13 October 2009 (UTC)

I don't see any reason why the one would imply the other. The universe is thought to have finite mass as far as I know. If that were not the case, then I guess you could describe the universe itself (or certain subsets) as an object of infinite mass. Rckrone (talk) 03:56, 14 October 2009 (UTC)

It's back down to linguistics again. What is your definition of an "object"? If an object can be all of the stars (but nothing else) - then an infinite universe contains an infinite object (that being all of the stars). But if you're talking about a 'continuous' solid object like a star - then, no, I don't think so because it would have an infinite gravitational field...and that's something we'd probably have noticed by now! SteveBaker (talk) 13:46, 16 October 2009 (UTC)

Lake at the bottem of the Ocean

i was watching the Discovery channel and there was a show going on where thay where exploring deep uncarted areas of the ocean. in the exploration thay came apon what looked like a lake at at the bottem of the ocean, and after thay disidended to try and desend into it it was so dence that the substance just rippled and was to dence for them to go into. i was wandering what this lake was and if there are any articles on it. --Talk Shugoːː 20:42, 13 October 2009 (UTC)

Might it have been a Brine pool? --Kurt Shaped Box (talk) 20:54, 13 October 2009 (UTC)

that sounds like your right, because thay mentioned alot of sea life serounding it. the pool was a black color aswell. thanks that pool had we bumb founded for a long time. --Talk Shugoːː 17:10, 14 October 2009 (UTC)

exothermic reaction with iron powder

Hello, In an exothermic reaction involving iron powder, cellulose, water, activated carbon, vermiculite and salt (like in a disposable hand warmer), which ingredient would you change to increase the average/max temperature of the reaction? How much or how little would you have to change it per degree of temp change? paddleballnut (talk) 21:38, 13 October 2009 (UTC)

Well, question 1 you would have to answer would be to find the balanced chemical equation for this reaction. Without that, you cannot figure out the rest. --Jayron32 02:25, 14 October 2009 (UTC)

October 14

H1N1 vulnerability after infection?

My local television news just aired an interview with a studio staffer who had recently recovered from H1N1. According to the producer, he believed that he was still vulnerable to the virus despite having just fought it off; no explanation was offered for this statement. How could this be possible? Or is the staffer simply mistaken? I couldn't find anything on our article about the virus; I can't imagine how immunity would not be conveyed by having the infection. Nyttend (talk) 03:13, 14 October 2009 (UTC)

According to our article on the influenza vaccine, each particular vaccine cocktail is only good for about a year. Since that's largely due to mutation, I'd guess similar caveats would apply to folks who'd had the actual flu (i.e. yes, you could get it again next year if you'd like). This brings up the basic problem of what is meant by "same" when it comes to something that mutates as quickly as the flu bug does. Compound that by the fact that most infections and diseases are not properly identified in a lab and you're left with the unhelpful non-answer of "If he did get it again, how would he know? Matt Deres (talk) 03:38, 14 October 2009 (UTC)

I don't think it is really mutation like that. This year's seasonal flu isn't a mutated version of last year's, it is a different strain (well, combination of strains) that has reached significant levels. Immunity to the current pandemic strain of H1N1 should offer at least partial immunity to mutated versions of it, unless you get a really rapid mutation (which is possible, but unlikely), but it won't necessarily offer immunity to other strains of flu (including other strains of H1N1 - that code refers to a whole family of influenzas). However, as you say, the current strain is just a strain of flu like any other strain of flu, without detailed lab tests there is no way to tell it apart. Unless he was actually tested there is no way to know he ever actually had the pandemic strain and even if he did he could easily catch a different strain of flu in the future. --Tango (talk) 08:42, 14 October 2009 (UTC)

If I remember rightly, the TV guy said something like "I could still get it again"; it was definitely an imprecise statement such as this. I do know that he was tested and was told that the lab confirmed that it was H1N1. Nyttend (talk) 18:07, 14 October 2009 (UTC)

Well, what it means is he could get the flu again, and he could even get H1N1 Influenza A again. But it is unlikely he will get this one strain of H1N1 flu (the 2009 Swine flu) again. Look at it this way. Influenza describes a grouping of viruses which, on the Linnaean scale, would be something like Class. Influenza A would be something like a Order and H1N1 Influenza A would be something like a Family. See, even something like "H1N1" describes a large grouping of related, but distinct, viruses. Specific strains of H1N1 would be something like at the genus or species level, and vaccines are specific to the specific strain only. In fact, the standard cocktail of vaccines given every year to combat the "seasonal flu" usually contains some vaccines against some strains of H1N1 flu, just not the one specific strain being called the "swine flu". Since that strain was only discovered this past spring, it did not have time to make it into that cocktail of vaccines, so a seperate vaccine has to be initiated to catch it. Had the virus been discovered a few months earlier, it likely would be part of the standard annual seasonal flu shot. --Jayron32 20:03, 14 October 2009 (UTC)

A friend of mine actually has the swine flu and she says that she has gotten sick twice. It's been over two weeks now, and she's still very sick. I saw her after a week and she looked fine, then she got really sick again. Maybe it can relapse and then return, like malaria? It's also common to catch a cold after you catch the flu, due to your weakened state. That happened to me once. So that could be another explanation. Swine flu sounds like a very bad virus. Her husband and her brother are both in the hospital right now because of the pneumonia brought on by swine flu. So, I imagine her immune system must be pretty weak right now. I'm terrified of swine flu!--Drknkn (talk) 07:45, 15 October 2009 (UTC)

It could be a relapse (don't overdo it as soon as you start to feel better!) or it could be really bad luck and she's gotten ill twice in a quick succession. Don't be terrified - it really is just the flu. Unless you have an underlying medical condition the chance of you having any complications is really low. --Tango (talk) 11:07, 15 October 2009 (UTC)

Big Bang

Where did Georges Lemaître first use the phrase "a day without yesterday" ? Was it in the 1927 paper or the 1931 letter to Nature, or somewhere else ? Lord Labak Daas (talk) 07:42, 14 October 2009 (UTC)

I don't have access to the 1927 paper, but in the 1931 letter to Nature, which I do have, he does not use the phrase. The closest he gets is to say that "If this suggestion is correct, the beginning of the world happened a little before the beginning of space and time." --Mr.98 (talk) 14:42, 14 October 2009 (UTC)

This book about him says: He would later refer to this ultimate origin in his 1950 collection of essays The Primeval Atom as "the now without a yesterday", which has been translated as "the day without yesterday", a quote often associated with Lemaître's letter to Nature. --Sean 15:35, 14 October 2009 (UTC)

Why is the original paper on the big bang not easily accessible? Something is wrong. Weepy.Moyer (talk) 19:44, 17 October 2009 (UTC)

Antimatter fuel

Does matter/antimatter collision produce enough energy that it could be a viable power source for applications such as space travel once technology is developed to produce antimatter at a significantly lower cost? --Jean-Luc Pikachu (talk) 16:29, 14 October 2009 (UTC)

It produces enormous amounts of energy. The trick is producing antimatter using less energy than would be created - that is rather difficult. --Tango (talk) 16:37, 14 October 2009 (UTC)

See Antimatter rocket and the website How Stuff Works. —Preceding unsigned comment added by Nigelpackham (talk • contribs) 16:39, 14 October 2009 (UTC)

Antimatter utterly annihilates matter, converting all of the mass into energy. Mass-to-energy is given by $E=mc^{2}$, which yields joules if mass is given in kilograms and the speed of light is given in meters per second. The speed of light is 300,000,000 meters/second, so 500 grams of antimatter "exploded" with 500 grams of matter (1 kg total) would produce 90,000,000,000,000,000 ($9x10^{18}$) joules, approximately equivalent to a nine thousand-megaton nuclear bomb, and enough energy to run a 100-watt light bulb for almost 30 million years. In reality, a good portion of the energy would be lost to neutrinos, but yes, antimatter would make a fantastic energy source, assuming 1) we can find a way to produce it cheaply, and 2) we can find a way keep it from spontaneously destroying itself (and everything else around it for a very long distance). J.delanoy^gabs_adds 16:43, 14 October 2009 (UTC)

Since the previous posts didn't say it, I will: there is no prospect of antimatter being a viable fuel in the foreseeable future. Our antimatter article says: "According to CERN, only one part in ten billion of the energy invested in the production of antimatter particles can be subsequently retrieved." There are some schemes floating around to harvest it from cosmic ray interactions with the solar wind, but they are all extremely speculative. --Sean 16:56, 14 October 2009 (UTC)

Being a viable fuel and being a viable energy source are two different things. Obviously it's not a viable energy source since there's not really antimatter sitting around and creating it necessarily takes at least as much energy as it would release when annihilated. But as a way to efficiently store energy for vehicles where carrying around bulky fuel is an issue, it has the highest usable energy content per mass possible if the problems of creating it and storing it could be addressed. Rckrone (talk) 17:41, 14 October 2009 (UTC)

Basically, unless you can find a big pile of antimatter somewhere - AND figure out how to collect it - AND figure out how to store it without spontaneous annihilation with the walls of the container, then you aren't going to be able to use the stuff. It seems unlikely that antimatter exists anywhere in the universe in a 'natural' form...and if it does exist - it's pretty clear it won't be in our galaxy. So we fail at the first hurdle there - there isn't any of this stuff just lying around! We can make tiny amounts of the stuff - but (as others have pointed out) the amount of energy that takes is spectacular. So antimatter as either a primary fuel - or as a way to store energy is pretty much a non-starter, and is likely to remain that way for a very long time to come. However, IF you had a means to produce it with more like 100% efficiency than 0.0000000001% efficiency (which is about what we have right now) - and a way to store it (presumably in some kind of magnetic containment arrangement) - then it would certainly be the densest possible way to store energy - which (in principle) makes it useful for spaceflight - or aircraft or even cars. But we're just so very far from being able to do that - we have to say it's "impossible" until we know whatever it is that we don't already know! SteveBaker (talk) 17:49, 14 October 2009 (UTC)

An exotic application like powering interstellar flight might be one of the earlier things it could be used for, and that is not near term. Might have weapon applications as well. With respect to practical applications of antimatter, we are at the level of people experimenting with static electricity in the 1700's and speculating about electricity's possible use to run motors, for fast communication, or for lighting. Theoretically possible but not even close to practical. Edison (talk) 19:06, 14 October 2009 (UTC)

That's not entirely true. The 'P' in PET scan stands for positron, a form of anti-matter. Dauto (talk) 19:40, 14 October 2009 (UTC)

In a PET scan, we are not technically creating antimatter. We are letting an element undergo beta decay. J.delanoy^gabs_adds 21:00, 14 October 2009 (UTC)

The element undergoing beta decay is not found in nature. I is a man made element in a particle accelerator. Dauto (talk) 00:53, 15 October 2009 (UTC)

Which bit of Steve's post does that contradict? A few positrons is a tiny bit of antimatter and we use a large amount of energy (in the particle accelerators you mention) to make it (indirectly). --Tango (talk) 12:35, 15 October 2009 (UTC)

If a massive space based solar power station was created to power a space based anti-matter production machine, then once enough anti-matter had been produced (even if it took a thousand years) this matter could be taken back to earth for power production. It might be an alternative to beaming solar power down to earth using microwaves, or space elevators, which might not be practical.Trevor Loughlin (talk) 12:58, 16 October 2009 (UTC)

But you still have to solve the containment issue - that's decidedly non-trivial for any significant quantity of the stuff - remember, you can't allow your antimatter to come into contact with ANY normal matter. But in any case - with our best efforts at turning electricity into Antimatter having an efficiency of 0.0000000001% - you'd be better off leaving your space-based solar power station on the ground and connected to the power grid directly! The amount of energy you'd lose due to atmospheric absorption, poor orientation of the collector to the sun, clouds and nighttime would still be irrelevent compared to the horrific inefficiencies of turning electricity into antimatter. SteveBaker (talk) 13:33, 16 October 2009 (UTC)

ko kaaf

I want to know a little about the "Kohkaaf". given the name of the place/home land of Ghost(jin). Please tell me its answer. Thanks Mohsan saleem —Preceding unsigned comment added by Mohsan saleem143 (talk • contribs) 18:00, 14 October 2009 (UTC)

The name is usually transliterated as Koh-e-Qaf (Persian: کوہ قاف), which refers to the Caucasus mountains. See Paristan. Red Act (talk) 18:18, 14 October 2009 (UTC)

Global warming vs. record lows/snowfall

I am getting tired of my friends telling me that because their town in Saskatchewan just had a record snowfall, ipso facto global warming is made up. Is there a response for this specific kind of reasoning? Gohome00 (talk) 19:39, 14 October 2009 (UTC)

Global warming is a climatic effect, not a weather effect. See climate and weather for some differences. The big deal is that climate is the average atmoshperhic conditions over a long period of time. Weather is what is happening in one specific place at one specific point in time. Weather says "It's raining now". Climate says "It rains here a lot". The deal is, global warming says that, on average, the earth is warming up. On a local level, in specific places, on specific days, you can still have cold weather. Global warming does not mean that it will never be cold ever again anywhere. It does mean that there will be less cold days in any given period of time (measurable probably over a year or a decade); and that those "cold" days are a few degrees warmer than cold days used to be. The deal is, that things like polar ice caps grow and shrink very slowly, on the order of decades or centuries, so they will respond to conditions on the scale of decades or centuries, which is why we care about climate rather than weather. So, just because it snows in Saskatchewan today doesn't mean that global warming isn't happening. What you would need to look at is the average temperatures in Saskatchewan over a long period of time, and see what the general trend is; in the case of climate a moving average is probably the best way to judge this. --Jayron32 19:50, 14 October 2009 (UTC)

You can also direct them to the Climate Normals compiled by the Meteorological Service of Canada. They might be interested in looking at local trends over the span of decades, rather than specific days, years, or weather events. Note the important difference between local and global climate, also. I would also like to point out global climate change as opposed to global warming - which are related but distinct phenomena. Nimur (talk) 19:59, 14 October 2009 (UTC)

Riding on what Nimur said, in my neck of the woods (Central NC), a lot of people are rejecting the Global Warming phenomenon and discussing instead Global Climate Change. Global Warming makes it sound like the entire globe is going to heat up. On average, it will, but while it may get hotter in country X, it may get to be a mini-ice age in country Y. Also, Global Warming doesn't begin to cover the ideas of droughts and floods, which are also cited as being major factors associated with this event. Falconus^{p t c} 22:13, 14 October 2009 (UTC)

Am I alone in reading Opie's question as How do you argue against an arguer taking statistically insignificant facts and using them as evidence?"...He asked about this specific kind of reasonining, not this argument. 90.208.3.84 (talk) 23:14, 14 October 2009 (UTC)

A response to the OP's tiresome friends is to invite them to read the article Statistical significance. Cuddlyable3 (talk) 15:13, 15 October 2009 (UTC)

Ah, good point. I would say that the argument that I would use is that 1) it is an average trend over time, not that tomorrow is automatically going to be warmer today, and that 2) Global warming is somewhat of a misnomer as it will warm some places and cool others. The overall general trend however is to get warmer.

Yes - the response is that changing and unusual weather are precisely what proves that there is something weird going on. As we discussed a few days ago, Texas has gone through one of the most prolonged hot periods on record - and is now getting the highest rainfall on record. The key things here are that:

• The "weather" (what's happening here and now at whatever specific place you are at) is getting crazier - sometimes crazy hot, sometimes crazy cold, sometimes crazy windy, othertimes crazy rainy - or droughty. Records are being broken at a much higher rate than in the past - which is quite contrary to expectations - which is that the longer we keep records, the lower the probability that they will be broken.
• The "climate" (what's happening on average over a few years over the entire globe) is getting hotter.

As the climate warms up - the weather will get crazier. Sure, on the average that weather will be warmer than usual - but it's very possible for climatic warming to cause cool weather locally. An unusually cold spell in Saskatchewan is more than balanced by an even more unreasonably hot summer in Texas.

SteveBaker (talk) 00:31, 15 October 2009 (UTC)

good point. not only is the mean temp rising, but the standard deviation is rising as well, meaning an increase in the frequency of record lows as well as an increase in the frequency of record highs (but more of the latter). also more record wind velocities, precipitations, dry spells, etc. what you'd expect if more energy is being entered into the system, but it isn't being entered uniformly over space and time. Gzuckier (talk) 20:27, 18 October 2009 (UTC)

Plate movement rvsals

Removed question from sock of banned User:FreewayGuy. Please take any debate to the discussion page. SteveBaker (talk) 23:41, 14 October 2009 (UTC)

Oops! No wonder I never got complete answer. They even mention it on Pangaea Ultima artilce which I never bother to study it. And North American is attach with Eurasian plate. See the green and the brown boundarys and Pacific Plate is yellow. Theose tools have answer my questions. Those questions is probably sound alot like homework questions to normal peoples.--209.129.85.4 (talk) 19:01, 15 October 2009 (UTC)

average size of a penis

laugh all you want, because i am too right now. but i want to know, whats the average size of a mans penis age 18-25? i know im going to be laughing about this one all day --Talk Shugoːː 20:49, 14 October 2009 (UTC)

The NSFW article Human penis size will tell you all you want to know. And more. Just makes sure the kids have gone to bed and/or your boss is not lurking around your cubical. --Jayron32 20:54, 14 October 2009 (UTC)

Well i am at work so I won't be clicking the link. It is probably discussed there, but I find it a really amusing anecdote how there was an old study, IIRC from the 60s or 70s that asked men to measure them selves and record the result. That results of that study were used for decades as the basis for "average" penis size. What they neglected to factor in is that most men when measuring them selves were, lets say, generous with their result, pretty much systematically adding half to a whole inch to the actual result. This probably accounted for a whole generation of "average" men suffering penis envy because they thought they were really an inch below average. A more recent study in which men were measured by nurses revealed a more accurate, and not surprisingly lower figure. Vespine (talk) 23:42, 14 October 2009 (UTC)

About that last sentence you wrote there... Did they get a figure that was lower than the original figures and this was not surprising, or did they get figures that were not far enough below the original figures to surprise anyone? APL (talk) 02:42, 15 October 2009 (UTC)

Sorry probably needs a comma after "surprisingly", as in it didn't surprise anyone that the figure was lower, especially after they realised the error in the method used for the first study. Vespine (talk) 03:14, 15 October 2009 (UTC)

You need two commas: "and, not surprisingly, lower". --Tango (talk) 08:50, 15 October 2009 (UTC)

I'm surprised it wasn't a bit bigger if it was measured by nurses. Interesting to read how they managed that. :) Dmcq (talk) 11:53, 15 October 2009 (UTC)

These days I believe they administer Viagra (or similar) to ensure consistency in that respect. --Tango (talk) 12:57, 15 October 2009 (UTC)

but what if thay didnt have viagra then lol? kinda would make you wander. and thanks jayron for the link, luckly i dont have kids yet but i am at work. --Talk Shugoːː 17:27, 15 October 2009 (UTC)

I think some poeple might be falling for the stereotype, a Nurse in no way implies they were female. And so what if they didn't have viagra? A sperm bank manages just fine without viagra, and there would already be nurses on hand, wouldn't there? "While you're doing that do you mind if we measure your jhonny?" I don't think that's the way they did it since that would also introduce a bias, under average people might be less likely to agree, but i'm just using it as an example why i think "not having viagra" isn't an issue. Vespine (talk) 23:02, 15 October 2009 (UTC)

To be honest, there were so many music hall assumptions in Dmcq's answer that it's about a century out of date with reality. Simpler just to move along than try to unpick it. 86.140.149.215 (talk) 23:16, 20 October 2009 (UTC)

Which parts of the USA have a climate similar to London?

Particularly in terms of the summer and winter temperatures. Many parts of the US have I think extremely hot summers and extremely cold winters compared with those in London. Thanks. 92.29.126.121 (talk) 21:40, 14 October 2009 (UTC)

No part is quite the same, but the Pacific Northwest is most similar -- the area around Seattle. Looie496 (talk) 21:44, 14 October 2009 (UTC)

Given that England is surrounded on all sides by water, it's climate tends to be a lot more moderated. Most of the islands in the US (Alaskan islands aside, for which I do not know the weather patterns) are rather far south, so their climates tend to be far warmer on average. Since none of the continental US is a small island in the North Atlantic, the weather patterns will tend to be more varied and more extreme. Falconus^{p t c} 22:18, 14 October 2009 (UTC)

"Most of the islands in the US...are rather far south" I wonder which islands you had in mind and am not sure the "most" part is correct. Certainly we have a number of islands here in the Great Lakes rather far north and the Seattle area has several as well. 75.41.110.200 (talk) 15:05, 16 October 2009 (UTC)

I agree with Looie, the Pacific NorthWest is pretty similar. TastyCakes (talk) 22:23, 14 October 2009 (UTC)

I'm in Vancouver here and although the general regime is comparable, the 'type' of precipitation, the type of sunny day, the type of frigid air mass, is rather dissimilar. Vranak (talk) 14:03, 15 October 2009 (UTC)

In what way are these things different from London please? And, another item, I've always been suprised that somewhere as far north as Vancouver (and not maritime) could have a nice climate. 78.151.108.233 (talk) 11:46, 18 October 2009 (UTC)

Vancouver is actually closer to the equator than London. Being near an ocean moderates climate - London, where it never, ever, ever gets really cold, is further north than Winnipeg, where actual real authentic cold occurs. This is in part because London is close to the ocean. --NellieBly (talk) 12:03, 18 October 2009 (UTC)

In London it you usually get some snow on two or three days a year. Does not that count as cold? 78.151.114.229 (talk) 09:58, 19 October 2009 (UTC)

The US is farther south, but London (and most of western Europe) gets heated by ocean currents flowing from the tropics. That's why Ireland is considered to have a temperate climate, while southern Labrador, at a similar latitude, is considered subarctic. --Carnildo (talk) 23:19, 14 October 2009 (UTC)

Agreeing with all of the above, at London, you will find a link taking you to Oceanic climate. The map, will show the NW as in the same range as London, with Portland and Seattle listed alongside London in the Notable Cites of Oceanic Climate. --Preceding unsigned comment 02:39, 15 October 2009 (UTC)

On a pedantic note, England is not surrounded on all sides by water (see above). It has two land borders: Wales to the west, and Scotland to the north. If you're visiting, then it's good to not upset the natives. Bazza (talk) 14:28, 15 October 2009 (UTC)

That's actually quite relevant to the question, as Wales and Scotland, being mountainous areas and bordering a large expanse of water, suffer much higher rainfall and lower temperatures than London does. London is in the East Anglian rain shadow, and has a climate more comparable to Brussels or Paris than to Cardiff or Edinburgh. OR it's a good layer of clothing warmer than Wales or Scotland. --TammyMoet (talk) 15:17, 15 October 2009 (UTC)

October 15

Higgs Boson sabotages Large Hadron Collider.

Is this [10] as silly as it sounds? This is a discussion of a hypothesis that the failures of the super-conducting-super-collider and the large hadron collider to actually function is due to the laws of physics acting backwards through time to retroactively prevent a Higgs boson from being formed! The couple of papers I've read here seems to suggest that the authors are reasonably well-respected and that they are actually quite serious! But isn't there a gigantic loophole in their argument for a test of their theory? They say that if the LHC management were to promise to shut down the machine on a one in a million random chance - then if that unlikely event actually happens, then it's extremely strong evidence that there are influences travelling back in time to shut down the LHC!! But surely the odds are good that if the one-in-a-million chance comes up, then there is a high probability that the governments who paid all of those billions of dollars to build the machine would simply fire the LHC management who make this stoopid agreement - and have their replacements turn on the machine despite the result of the random trial? Hence a negative result of the experiment is proof of nothing - and we have an unfalsifiable proposition. Am I missing something? SteveBaker (talk) 03:31, 15 October 2009 (UTC)

I'm sure this isn't really an answer to your question, but I don't see how what they are proposing implies anything traveling 'backwards through time'. Instead, if what the collider produced would be destructive to the universe, then the anthropic principle / many worlds interpretation would imply we are only here to witness it because the collider malfunctioned. 149.169.106.83 (talk) 03:55, 15 October 2009 (UTC)

Reading the article, that seems to be exactly what their argument is, even though the science reporter phrases it as time travel. Basically that if the LHC leads to a paradox, then that can't be part of a consistent timeline that we're experiencing. It seems pretty doubtful to me that the laws of physics could lead to a paradoxical outcome, although I guess I can't think of any reason why not. Quantum mechanics seems like it could grant enough leeway for the universe to be steered away from certain outcomes and we probably wouldn't be able to notice most of the time. Rckrone (talk) 04:29, 15 October 2009 (UTC)

From a general relativistic point of view, the universe is not evolving form initial conditions, it exists as a solution to a system of equations that appears to its inhabitants as if it were evolving. Solutions where a Higgs boson create a time paradox cannot exist, because they would be self contradictory. Therefore, only the solutions where, for example, the LHC malfunctions, will be observed. Also, if the one-in-a-million chance did come up, I think we would try harder to find the Higgs boson, so it would, according to their theory, actually be less likely. 76.67.73.166 (talk) 05:02, 15 October 2009 (UTC)

At the very least, the hypothesis is falsifiable in that if the LHC gets started up successfully, and successfully detects a Higgs boson, then the hypothesis was incorrect. Red Act (talk) 04:25, 15 October 2009 (UTC)

And if we spend 100 years trying to set up this experiment and something always seems to go wrong, then that's pretty strong evidence to confirm the hypothesis. Rckrone (talk) 04:34, 15 October 2009 (UTC)

Really? That's like saying that you hypothesize a magic purple elephant exists in a particular jungle. Each expedition you set out to explore for the magic purple elephant fails. The conclusion, by analogy, would be that (a) the magic purple elephant exists; and (b) it is directly responsible for staging the interferences with your expeditions. Both (a) and (b) are ridiculous. Nimur (talk) 05:34, 15 October 2009 (UTC)

The analogy would be that you hypothesize that no expedition to find a purple elephant will ever even be carried out. Suppose then that every time someone plans an expedition, something unexpected happens that prevents it from even getting off the ground. If enough expeditions fail to happen and you can somehow calculate the probability of all those expeditions failing to happen given the null hypothesis, and that probability is sufficiently low, then you have a good reason to reject the null hypothesis, and conclude that something weird is going on whatever that may be. If the only plausible explanation of that phenomenon were that purple elephants were somehow sabotaging the expeditions, then you might conclude that was the cause, but there would certainly be room for other explanations if others were plausible. Rckrone (talk) 06:01, 15 October 2009 (UTC)

An infinite series of indents to this thread can be generated by remorselessly applying the spell "Absence of proof is not proof of absence". Nature provides one unavoidable reason that this series, as all non-abstract series, must like life be truncated. Sic transit gloria mundi. Cuddlyable3 (talk) 15:04, 15 October 2009 (UTC)

I think you are misunderstanding what I'm saying. Maybe I'm not saying it clearly. There are two experiments going on, not to be confused with one another. There's an experiment to find or not find the Higgs boson, and there's the meta-experiment to see if all attempts at carrying out the first are doomed. Hypothesis 1 is that the Higgs boson exists. Hypothesis 2 is that experiment 1 can actually be run without something against all odds melting it first.

• If experiment 1 is conducted and produces the Higgs boson, that's confirms hypothesis 1 and 2.
• If experiment 1 is conducted and doesn't produce the Higgs boson, that's evidence against hypothesis 1, but confirms hypothesis 2.
• If experiment 1 against the odds fails to be conducted, that offers no evidence for or against hypothesis 1 because there was no experiment, but it is evidence against hypothesis 2.

If enough attempts at the experiment produce the second result, without any producing the first result, then we probably have to conclude there's no Higgs boson. If enough attempts at the experiment produce the third result, without any producing the first or second result, then we probably have to conclude that something we didn't expect is dooming these experiments. That seems pretty far fetched, so there would need to be very strong statistical evidence to rule out just bad luck. But as you said, at some point absence of proof that the experiment can be conducted has to suffice as demonstration of absence of the possibility. Rckrone (talk) 18:10, 15 October 2009 (UTC)

There is a flaw in your logic. If I devise an experiment for detecting a Higgs Boson that involves nothing more than standing on my head and singing "the star spangled banner" (hypothesis 1 says that this will produce a higgs boson) - then if that experiment fails (which, I suspect it will), then it confirms hypothesis 2? Well, yes, it confirms that my stupid experiment can indeed be conducted - but if my experiment is useless in the first place, it doesn't confirm that the universe cannot unexpectedly cause a GOOD experiment to fail. So if the LHC fires up and doesn't produce a Boson - then nothing of any significance really happened and we still don't know whether the universe would have caused it to blow up if it had been sufficiently well designed that it could have produced a Boson. SteveBaker (talk) 20:36, 15 October 2009 (UTC)

That's not a flaw in the logic, although I think it is an important point. Hypothesis 2 relates to a particular experiment which may or may not be a good experiment for finding the Higgs boson. In fact the Higgs boson really has nothing to do with hypothesis 2 (except in motivating it). It's possible that hypothesis 2 could be confirmed and yet it's still true that the universe is conspiring against us, just in a way we haven't detected. As you say, maybe the universe "lets" the experiment happen because it's crappy, or the universe forces a certain result in a case where it could go either way. That's not something the meta-experiment can test. But if the experiment in question does always fail to happen, then we can say something more definitive. In other words, confirming hypothesis 2 wouldn't prove the universe isn't conspiring, but refuting hypothesis 2 would prove that it is.

If every single time someone stood on their head and began singing the star spangled banner the building collapsed or they had a heart attack and died, that would be quite a result. Rckrone (talk) 21:29, 15 October 2009 (UTC)

On reading through the few relevant publications at arXiv, I feel like the original authors (who may be respected physicists) are pretending to publish physics in order to make a political statement. I think this is disingenuous; they are protesting political and economic pressure in the wake of recent troubles at the LHC; but rather than address these issues straightforwardly, they are suggesting throwing caution to the wind and flipping a coin to decide the project's fate - they would prefer to see the LHC fail by random chance - preferring that "...LHC is stopped by our proposed game than if it just failed for some technical or political reason."[11]. Nimur (talk) 05:52, 15 October 2009 (UTC)

Taken as read, that last line is not completely off the wall. If the God Of The Future has to stop the LHC from generating Higgs particles, It would be preferable to do it in a way that doesn't destroy all the equipment or put all the scientists out of work. APL (talk) 13:36, 15 October 2009 (UTC)

I wish I could remember the name of a short science fiction story I read some time ago that sounds like this. A scientist had discovered a contradiction between two laws of physics, but in fact all physics laws had been generated in response by nature to contradictions been found like for instance between the wave and particle nature of light. He was warned not to do the experiment as other such experiments had bad effects but did so and disappeared in a flash of light. Many details are probably left out or wrong as it has been a while Dmcq (talk) 12:19, 15 October 2009 (UTC)

We need to miniaturize a Higgs Boson generator. My plan is to buy 36 of them. I will let them sit on my work bench for a few weeks. Then, based on the 6-bit binary representation of 6 numbers from 1 to 60 I will turn some of the generators on, and smash the rest with a hammer.

I'm being silly, of course, but the papers in question [12] do seem to be seriously proposing reverse causality. However, scientific humor is often so dry that outsiders don't spot it, so it's difficult to guess whether this is intended seriously or as some sort of satire. APL (talk) 13:36, 15 October 2009 (UTC)

Oh wait, My plan is too complicated. I'll just buy a lotto ticket and turn a single generator on if I don't win. Through this means I can take the universe hostage and make it do my bidding. APL (talk) 13:38, 15 October 2009 (UTC)

That's a good idea, I think I'll do it too ;-) Dmcq (talk) 14:05, 15 October 2009 (UTC)

Be wery wery careful. Larry Niven wrote a story called Rotating Cylinders and the Possibility of Global Causality Violation in which a mathematician tried just such a scheme to twist the universe's self-protection to his personal benefit and that of his species. For his trouble, he wound up getting himself and his race fried in a nova. --Trovatore (talk) 22:14, 15 October 2009 (UTC)

This is why we need to miniaturize our high energy reseach facilities. Sixty years ago, the common knowledge was that "nobody needed computers except the Government, the military, and a few nutcase physicists." Today, every desktop in the developed world (and a surprisingly large number in the un-developed world) is home to a miniature, personal, network-attached computer. We have found ways to make the computer usable and useful to everyday people. Meanwhile, the common knowledge has transitioned to "nobody needs high energy large hadron colliders except the Government, the military, and a few nutcase physicists." Imagine the possibilities when every man, woman, and child has access to a hadron collider! Nimur (talk) 14:10, 15 October 2009 (UTC)

Well, we don't really need to miniaturize the LHC. If the universe would care to make a few trillion dollars materialize in my bank account - I promise to use half the money to buy the actual LHC (I'm sure they'd sell it if I offered enough!) and then I'll smash it with a hammer. Hmmmm...nope...no money yet...any time now, I'm sure. SteveBaker (talk) 20:36, 15 October 2009 (UTC)

A hammer might be ineffective at destroying such a large piece of equipment. If the universe conspires to give me super-powers I will use them to destroy the LHC once and for all. APL (talk) 20:47, 15 October 2009 (UTC)

This whole business reminds me of quantum suicide. --Sean 14:21, 15 October 2009 (UTC)

It also reminds me of the Transactional interpretation of quantum mechanics and the Wheeler–Feynman absorber theory of electrodynamics, which require time travel in the form of electromagnetic radiation moving backwards through time. --Carnildo (talk) 21:53, 15 October 2009 (UTC)

I read the paper (the first one). It's... pretty stupid. They start with what I think is supposed to be the Feynman path integral, $\int _{\gamma }e^{i\,S(\gamma )/\hbar }D\gamma$. Here $\int _{\gamma }\,D\gamma$ is an integral (i.e. a sum) over all "paths" (i.e. histories of the system) and S(γ) is the action associated with the path γ. ħ has the same units as action, so S/ħ is unitless, and e^iS/ħ is a unit complex number pointing at an angle of S/ħ (in radians). The result of the integral is called an amplitude, and the square of the absolute value of the amplitude is basically the probability of the system going from a particular initial state to a particular final state. This is all standard physics. If you've read the book QED by Feynman, this is what those little arrows are—unit complex numbers pointing in different directions—and when he adds them up he's doing the path integral. As he explains, when you're near a critical point of S the arrows point in roughly the same direction and so combine to make a large arrow. Away from the critical points the arrows point every which way and don't add up to much; therefore those histories don't matter much and you may as well imagine that they don't happen. This is where the principle of least action comes from.

So, these authors say, what if S is complex rather than real? Then after multiplying by i you still have a real part, so the arrows are no longer all of unit length; they may be smaller or larger. Paths where they're smaller don't count for much, and they think paths with Higgs bosons in them might yield very short arrows. The first problem with this is that if S isn't real then you lose unitarity, and quantum mechanics pretty much falls apart completely without unitarity. The total collapse of the quantum formalism isn't necessarily fatal, but you'd think they'd have something to say about it. It's not apparent that they even know there's a problem. Secondly, they seem to think this modification of the path integral leads to retrocausality somehow, and I can't figure out why. Their whole reason for this seems to be the idea that the path integral is holistic since it treats the whole history at once and any unlikely event in any part of the history makes the whole thing not count. Okay, but that's true in standard quantum theory too, and it (provably) doesn't lead to retrocausality there. Consider proton decay. Proton decay is exceedingly uncommon if it happens at all. To put it another way, "the universe likes to avoid histories where proton decay happens". So, we build a machine to look for proton decay and we don't find any. The machine isn't plagued by technical problems, it just doesn't see what it's looking for; histories where it sees proton decay don't happen. That's not retrocausality, it's life as usual.

A lot of other crazy stuff in the paper. For example, they suggest that one of the options in their card game be to turn off the LHC after seeing 10 Higgs particles. That makes no sense. You don't turn on a particle accelerator and watch exotic particles fly out one by one. The LHC's solid-state detectors produce on the order of a petabyte of raw data per second. The overwhelming majority of that is thrown away almost immediately on the basis of simple heuristics, and the remainder, around a gigabyte per second, is stored in CERN's datacenter and subjected to subtle statistical tests over a period of months or years to tease out a signal. Even if you find a Higgs signal you don't know how many Higgs events there were or which ones they were, you only know that there were enough events of a certain type that it's statistically unlikely that none of them involved the Higgs. It's bizarre that two professional physicists would think that you could just count Higgs particles in real time at the LHC.

In short, they're crackpots or it's an elaborate joke, I'm not sure which. -- BenRG (talk) 21:54, 15 October 2009 (UTC)

Alternatively, it could be their effort to erode the credibility of arXiv, which has become notorious for releasing a variety of un-reviewed literature unto the masses (who seem unable to differentiate between "draft" and "publication" - let alone "peer reviewed"). As I noted above, I feel like the authors are attempting to make a point, but in a very roundabout way. Whether they have a prior history of research prestige is irrelevant - this publication series looks nonsensical. Nimur (talk) 23:43, 15 October 2009 (UTC)

I created some Higgs bosons in my backyard, but Schrodinger's cat ate them all. Matt Deres (talk) 17:11, 16 October 2009 (UTC)

Ethanol / isoproyl alcohol

My mom is doing the experiment of extracting DNA from cheek cells (I'm not sure of the exact details, but whatever the usual way for a highschool biology class do it would be), and she only has isopropyl alcohol, not ethanol. Will this give comparable results? 149.169.106.83 (talk) 03:49, 15 October 2009 (UTC)

I'm terrible at Orgo; but, even if I can't answer your question, I'll state some facts facts from the article we have on it. The relevant subsection on our article Isopropyl alcohol says here that it dissolves a wide range of nonpolar compounds, and says it's safe and relatively non-toxic. If your mother is a teacher, can she just run the experiment one time and check to see if it gives comparable results? I don't know the answer, but I would assume the answer is yes. 윤리윤리윤리 (talk) 06:05, 15 October 2009 (UTC)

Using isopropanol throughout will result in a lower quality final product (more salt), although it may still be usable. For the purpose of washing a pellet of DNA (but not precipitating the DNA from solution into a pellet), 70% ethanol is the norm, which you can find in most drug stores (and if she's performing this experiment through a school, she may be able to acquire the higher quality ethanol from biochem providers). Someguy1221 (talk) 06:08, 15 October 2009 (UTC)

quartz thermometer

what is the calibration,uses,advantages,disadvantages and applications of quartz thermometer —Preceding unsigned comment added by Derrickinlove (talk • contribs) 04:47, 15 October 2009 (UTC)

The resonant frequency of a quartz crystal depends on temperature, thus a quartz crystal oscillator plus a frequency counter can serve as a thermometer. Some advantages of this arrangement are small size, ruggedness, the display can be remote from the sensor, small thermal inertia gives fast response and the calibration is completed when the crystal is cut (cutting angle defines its frequency/temperature coefficient) and ground (for center frequency). An example application is an ingestible thermometer. A disadvantage is the electrical power needed for the oscillator and counter. Cuddlyable3 (talk) 13:42, 15 October 2009 (UTC)

Cosmological Constant

Doesn't a nonzero cosmological constant violate (or at least spontaneously break) time-translational symmetry? 76.67.73.166 (talk) 05:06, 15 October 2009 (UTC)

There are at least one or two sci ref desk regulars who are more knowledgeable about GR than I am, so they may (hopefully) come along and provide a more complete and unequivocal answer to this than I am able to. However, I'm fairly certain that the answer to the question is "yes". This of course implies via Noether's theorem that energy isn't conserved, but total energy isn't conserved in general in GR, except in certain cases like an asymptotically flat spacetime. For more information that may be valuable to you, see ADM energy, vacuum energy and cosmic inflation. Red Act (talk) 06:25, 15 October 2009 (UTC)

The big bang violates time-translational symmetry, so the cosmological constant is neither here nor there. --Tango (talk) 08:57, 15 October 2009 (UTC)

A cosmological constant by itself doesn't break time translation or time reversal symmetry. Roughly speaking a cosmological constant behaves like a repulsive acceleration that's proportional to distance, d²x/dt² = (Λ/3)x. This is time translation invariant since there's no explicit dependence on t, and it's time reversal invariant since acceleration doesn't flip sign when you reverse the direction of time. Of course, there are no nontrivial time-independent solutions to that differential equation. The solutions look like combinations of $e^{\pm t{\sqrt {\Lambda /3}}}$, and that's why the cosmological constant is said to cause "exponential expansion". But that kind of violation exists even without a cosmological constant, because the matter will gravitate together. In fact to avoid time dependence in a universe with matter you need a nonzero cosmological constant to counter the gravitational attraction, which was the idea behind Einstein's static universe. -- BenRG (talk) 12:42, 15 October 2009 (UTC)

Proper acceleration

Can anyone explain the following phrase to me, please?

"This first leg takes about 2 years if the acceleration's magnitude is about 1-gee."

I've read it in the proper acceleration article (Select, show for the Animation: high speed trip up then down), and couldn't understand the meaning of "1-gee".--Email4mobile (talk) 08:19, 15 October 2009 (UTC)

"1-gee" is another way of writing "1 g", which means 1 times g, where g is the acceleration of gravity at the Earth's surface. See g-force. Red Act (talk) 08:32, 15 October 2009 (UTC)

Thank you very much, Red Act! I will have to add it in my dictionary :). —Preceding unsigned comment added by Email4mobile (talk • contribs) 08:44, 15 October 2009 (UTC)

I presume this is in the context of some kind of space travel. If you could devise some kind of rocket that would keep you accelerating at 1 g for two years, you'd be moving pretty fast! 9.8 meters per second of speed increase for every second is 9.8 x 2 x 365 x 24 x 60 x 60 meters per second which would be 620,000,000 meter per second...but that's twice the speed of light - so long before you get to that speed, relativity is gonna get in your way and limit you to some significant fraction of the speed of light. Since relativity is involved, your perception of time and space will be distorted and your two year-long "leg" of this epic journey will take you a very long distance indeed! I'm sure someone with more time than me will be able to calculate just how far - but it's a long way. If you are thinking of hypothetical rocket engine designs, choosing an acceleration of 1 g is convenient because your crew would be able to experience earth-normal gravity for the entire ride. SteveBaker (talk) 20:05, 15 October 2009 (UTC)

Perhaps the OP is describing a theoretical acceleration of a massless particle to the speed of light followed by deceleration back to stationary. Cuddlyable3 (talk) 22:39, 15 October 2009 (UTC)

Massless particles can only travel at the speed of light. At any other speed they would have zero energy, which is pretty much the same, as far as we know, as not existing physically at all. (Abstract objects, like the number 2, can exist without having energy, but they don't exist physically.) --Trovatore (talk) 22:49, 15 October 2009 (UTC)

The whole question is about proper acceleration, not coordinate acceleration. So there's no problem with a rocket or other massive object maintaining a constant proper acceleration for arbitrarily long, without ever reaching the speed of light. Red Act (talk) 23:58, 15 October 2009 (UTC)

Relativistic Energy!

Is there a future probability that scientist might also discover Energy will be also relativistic like mass? I mean if they encounter a similar phenomenon to light someday that will account for the start and end of this universe?--Email4mobile (talk) 09:43, 15 October 2009 (UTC)

I'm not sure what you mean; it's already known that all energy is relativistic. Two different observers that are moving relative to each other will in general disagree about how much energy a given photon has. The frequency of light will red shift or blue shift depending on the velocity of the observer, and the energy of a photon is proportional to its frequency.

As far as predicting what may happen in the future, we don't do that here. See the top of this page. Red Act (talk) 10:17, 15 October 2009 (UTC)

Crystal Field effect

how the crystal field theory help us to understanding coordinating bonding and how it link with Jahn-Tller theorem ?Supriyochowdhury (talk) 10:32, 15 October 2009 (UTC)

The question is outside of my areas of expertise, but do the following articles help you?: Jahn–Teller effect, Crystal field theory, Coordination complex Red Act (talk) 11:02, 15 October 2009 (UTC)

Energy crisis and environment

what is energy crisis?and how energy crisis is related to environment —Preceding unsigned comment added by 203.196.249.171 (talk) 11:31, 15 October 2009 (UTC)

"Energy crisis" usually refers to an anticipated problem where energy demand is greater than supply. This can cause environmental problems because the energy gap may well be filled by using fossil fuels, pumping lots of CO_{2 into the atmosphere. --Tango (talk) 11:41, 15 October 2009 (UTC)}

Wouldn't they just increase the price until the supply and demand are equal? — DanielLC 13:47, 15 October 2009 (UTC)

Yes, but that's not always tenable. If it costs $300 to drive a car to the store, and you have a society based primarily around automobile transportation, it has very real effects. If the cost of food becomes unaffordable, then people starve. Yes, the economy stabilizes out eventually, but that can have horrific consequences, especially since affecting the price of fuel, energy, heat, etc., affects the prices of so many other commodities (increased transportation costs = increases goods costs, etc.). "The economy will correct itself" works to a certain degree, but "correcting itself" can mean "crashing". --Mr.98 (talk) 16:40, 15 October 2009 (UTC)

That's not enough to avoid a crisis. Suppose the supply of oil plummets, and as a result gasoline goes to $20 / gallon. Many economic activities that exist today would be totally untenable under those conditions, leading to drastic changes in the economy. Dragons flight (talk) 16:42, 15 October 2009 (UTC)

I think at $20 / gallon we would just adapt without many changes in activities (the price is not that far off in the UK!), but at $200 / gallon there would be drastic changes. Dbfirs 17:55, 15 October 2009 (UTC)

I don't think petrol in the UK has ever gone over $10/gal (I'm not sure how fuel price variations have corresponded with exchange rate variations, so I can't be sure). At double that, it would make a difference. People would use public transport more, travel less, etc. --Tango (talk) 18:14, 15 October 2009 (UTC)

Not to mention, USA is bigger than UK. Far more goods and services need to be trucked across country, and they need to be trucked longer distances. The cost of gas effects the cost of a lot of other things, not just your price at the pump. Groceries are a big one. APL (talk) 18:40, 15 October 2009 (UTC)

Also, the UK has significantly more infrastructure that does not depend on an individual automobile then in the US. Especially outside of major metropolitan areas. Googlemeister (talk) 20:53, 15 October 2009 (UTC)

And our cars are about a third the size of American cars. --Tango (talk) 21:00, 15 October 2009 (UTC)

Have a look at Energy crisis for an overview and Category:Energy crises for a list of specific crises. Regarding the environment, it could be argued that energy crises force people to use less energy or develop innovative ways of conserving energy which may benefit the environment in the long run. This search might help. Zain Ebrahim (talk) 11:54, 15 October 2009 (UTC)

Hydrogen fusion

The fusion of two hydrogen atoms produces a helium atom. But where do the two required neutrons come from? --Leptictidium (mt) 17:49, 15 October 2009 (UTC)

See the proton–proton chain reaction. In short, ¹H + ¹H ≠ ⁴He — Lomn 17:52, 15 October 2009 (UTC)

And note that saying "two hydrogen atoms" does not necessarily mean ¹H₁... it can mean, for example, ²H₁ or ³H₁. --Mr.98 (talk) 18:16, 15 October 2009 (UTC)

And the helium produced doesn't need to be ⁴He₂, it can be ³He₂. --Tango (talk) 18:23, 15 October 2009 (UTC)

Given the "but where do the two neutrons come from", it seems clear that the original question meant standard hydrogen and helium. If deuterium or tritium were involved, then there are your neutrons. If helium-3 was involved, then you don't need two neutrons. On a tangential note, though, why are you guys (and the pp article) specifying the atomic number of hydrogen and helium? Isn't that utterly redundant? — Lomn 19:11, 15 October 2009 (UTC)

The fusion of two ¹H ₁ atoms does not produce helium (standard or otherwise), though (not directly, anyway). D and T are both "hydrogen"; I think that's worth pointing out for someone confused. (And the proton-proton reaction explains how you get D from regular H). As for the notation—yes, technically it is redundant, but I've found personally that keeping track of protons helps students when thinking about nuclear reactions, especially when we are talking about isotopes. --Mr.98 (talk) 19:35, 15 October 2009 (UTC)

Kid in the balloon thing

If you have heard about the kid in Colorado who allegedly went for an unauthorized balloon ride, What volume of helium would be required to lift him off the ground if we assume that he weighs 50 lbs? I suppose we would need to know the pressure and temperature of the helium as well, but do not have a good estimate other then the altitude was something like 6500 ft above sea level and the temperature in the 60s F. Googlemeister (talk) 20:51, 15 October 2009 (UTC)

Helium has a density of .18 g/L at 1 atm, air a density of 1.2 g/L at 1 atm (and reasonably standard temperatures). The lifting capacity of helium is (roughly modeled) the density of air minus the density of helium, times the volume of helium. At altitude, the density of air drops -- it's ballpark 1 g/L at 6500 feet. Additionally, you have to put enough helium to create more than ambient pressure to inflate the balloon (but the sea level density is probably enough to suffice here). So, you get about .8 g/L of lift in the given conditions. To lift 30 kg (a low estimate of kid plus balloon materials), you'd need nearly 37500 L of helium, or a spherical balloon about 13 feet in diameter. The news photos I see don't show a spherical balloon, but it looks like a reasonably close estimate. Incidentally, the lifting power of helium has been discussed here repeatedly; there should be lots more in the RD archives. — Lomn 21:40, 15 October 2009 (UTC)

Turns out that the kid was hiding above his garage, and never flew, so I guess that while it may have been possible, it didn't happen. 152.7.20.66 (talk) 22:54, 15 October 2009 (UTC)

If I'm not mistaken, the balloon had absolutely no room for any children, unless he could breath helium. Vranak (talk) 01:14, 16 October 2009 (UTC)

Wonder what the density (lifting power) of Trimix is? DMacks (talk) 05:17, 16 October 2009 (UTC)

See also cluster ballooning.--Shantavira|^{feed me} 07:14, 16 October 2009 (UTC)

For Trimix you can work out the average molecular weight using the proportions given. The oxygen and nitrogen will dominate the mass since their molecules are so much more massive than helium. Using lighter gasses than Helium will not make much difference in lift either. eg Helium-3 would be more pricey. Graeme Bartlett (talk) 11:52, 16 October 2009 (UTC)

The New York Times reported that in a Wolf Blitzer interview on CNN, the kid said the reason he did not answer when he heard people calling his name was “You guys said… that, um, we did this for the show.” Mr. Heene denied that this meant it was all a publicity stunt. Local law enforcement has indicated they do not believe it was a hoax. Has there been any indication that the balloon ever had a gondola which could have carried the boy, or that the boy could have been inside the silver mushroom or the little stub below it? How long after the family called a TV station to report the balloon was away did they call 911? Edison (talk) 14:12, 16 October 2009 (UTC)

In a press conference that evening, Mr. Heene said the balloon was an experimental vehicle which was supposed to rise and descend via helium, but that it was supposed to move laterally via million volt pulses of electricity it would emit. Heene said that an egg timer on board was supposed to regulate the million volt emissions while it was tethered, before it escaped. Where was the electricity supposed to come from? Various accounts have mentioned a video of the actual launch, but I can only find coverage of the flight, pursuit and landing. Are there any images of the intact balloon and gondola prelaunch or of the liftoff? Edison (talk) 14:39, 16 October 2009 (UTC)

Found the launch video at CNN.com.[13] No sign of any basket or gondola other than the apparently sealed silver nub below the gasbag. Edison (talk) 14:53, 16 October 2009 (UTC)

I believe that's the wrong link and/or it changed. [14] gives the launch video for me called "'Balloon boy' story unfolds" (it's near the end) Nil Einne (talk) 20:00, 16 October 2009 (UTC)

Tree trunks painted white

Upon visiting certain developing countries, it is immediately noticeable that the bases of many tree trunks have been painted white, or with some form of whitewash. This usually occurs with cultivated trees or those at the edge of a forest area, and in some areas this is a very common practice. Regarding this subject, I have some doubts.

First, what purpose does this practice serve? In what way is this beneficial to the tree or to the ones who planted it? Is it done for biological protection, or merely for aesthetic purposes (despite the fact that I find it a bit of an eye-sore)? If effective in any way, to what degree is it recommendable?

Second, how prevalent is this practice? Upon mere observation, and from the experiences I can immediately recall, I cannot remember having observed this practice in developed countries, namely those with Western civilizations. However, upon visiting developing countries such as Brazil, Colombia, Mexico, and Kazakhstan, I have noticed that this practice is prevalent in varying degrees. Unfortunately, my inquiries into this subject with the natives have turned up fruitless.

Third, has this practice ever been used in developed countries in the past? —Preceding unsigned comment added by 201.21.180.57 (talk) 21:34, 15 October 2009 (UTC)

Not sure about Brazil etc., but when I've seen tree trunks painted white in temperate climates, it's been to prevent Sun scald (see section "Painting"). It's a form of sunscreen for trees. -- 128.104.112.179 (talk) 22:11, 15 October 2009 (UTC)

Trees along a road side sometimes have painted white stripes to guide traffic, e.g. in France. Cuddlyable3 (talk) 22:32, 15 October 2009 (UTC)

In some circumstances, might it be a way of marking trees selected for felling? 87.81.230.195 (talk) 23:31, 15 October 2009 (UTC)

If I remember correctly (I never paid attention to these things while I used to live in Mexico), it is to prevent sun scald, like 128.104.112.179 said. Titoxd^{(?!? - cool stuff)} 23:39, 15 October 2009 (UTC)

Roadside trees in WW2 London were often painted white because of the blackout. Some were still white during my 1960s childhood. Didn't seem to do them any harm.

In the U.S. I have seen foresters use "safety yellow" paint to mark trees to be felled for timber production. Some on the very base of the tree and some higher on the trunk. This way the harvesters know which trees they are to cut. Could the white paint be intended to provide the tree some protection against dog urine, when in parks or next to sidewalks? Edison (talk) 23:47, 15 October 2009 (UTC)

Second, how prevalent is this practice? China does it. 218.25.32.210 (talk) 00:52, 16 October 2009 (UTC)

When I used to live in downtown Manhattan as a kid, tree trunks were painted white -- and included those in the backyard parks with no access by car. Explanation for the white paint was that it was some form of protection against infestation of some sort. DRosenbach ^{(Talk | Contribs)} 02:34, 16 October 2009 (UTC)

In Spain, especially Andalucia, tree trunks in patios and to some extent street tree trunks are whitewashed partly for decoration and partly to discouraged ant and thus aphid infestation. The practice seems to be confined largely to citrus trees. It doesn't prevent infestation. Caesar's Daddy (talk) 06:22, 16 October 2009 (UTC)

My next door neighbor here in rural California paints her young fruit trees' trunks white. See tree paint. --jpgordon^{::==( o )} 18:48, 16 October 2009 (UTC)

Used to be quite common in former USSR for apple trees etc. Apart from sunburn protection already outlined above, another benefit is that it somewhat delays development of flower buds, relieving the risk of frostbite in case of spring air frost. The practice used to apply to ordinary (not fruiting) trees as well but, for example, city of Moscow banned it, except for apple trees, in 1997. NVO (talk) 20:23, 17 October 2009 (UTC)

October 16

Wy does refraction occur?

What is the cause of refraction? I know about change in speed of light, but why does the speed of light change in different media? --shanuu (talk) 05:06, 16 October 2009 (UTC)

To quote our Speed of light article: "Light travels more slowly in a transparent material than it does through a vacuum due to interaction of the light with the electrons in the material." The Refractive index article explains it in terms of other intrinsic properties of the material. DMacks (talk) 05:12, 16 October 2009 (UTC)

In addition to what what DMacks said, the book QED: The Strange Theory of Light and Matter by Richard Feynman is an excellent (advanced) secondary-school-level treatment of the physics of optical phenomenon. I'd highly recommend it to everyone. -- 128.104.112.179 (talk) 14:30, 16 October 2009 (UTC)

Special relativity.

I am currently reading a book on theoretical physics called, "The Elegant Universe, by Brian Greene". I've just finished reading the section on special relativity, and I had a question.

According to special relativity, every observer sees the speed of light at the same speed, regardless of their state of motion. This raised a question in my mind. I've read that light can be slowed down when it's in different media, eg rubidium gas. So, my question is this: If we always see light travelling at the same speed, how do we know that it changes speed in different media?Unique and proud of it (talk) 08:38, 16 October 2009 (UTC)

There is a constant called c, which is the speed of light travelling though a vacuum, as observed by all observers. If instead the light is travelling through a medium, all observers will instead observe the speed of the light to be less than c. Furthermore, if the light is travelling through a medium, the observed speed of the light depends on the velocity of the medium relative to the observer. It's only in a vacuum that the speed of light is the same for all observers. Red Act (talk) 09:09, 16 October 2009 (UTC)

Just as with the question right before this one, the speed of light and refractive index articles will provide a more thorough explanation. Red Act (talk) 09:17, 16 October 2009 (UTC)

I don't think it's correct to say "according to special relativity, every observer sees the speed of light at the same speed". The constancy of c is an empirical result (e.g. from the Michelson-Morley experiment), and Special Relativity examines the consequences. AndrewWTaylor (talk) 13:44, 16 October 2009 (UTC)

Right—Special Relativity comes out of assuming c is constant for observers. It does not prove it or even argue for it (and it's unclear how attentive Einstein was to experimental results like M-M, anyway). Of course, confirmations of SR's predictions further lend themselves towards believing the assumption is correct. An easy way to explain SR is that it is to say that it's the combination of two assumptions—that Galilean relativity is generalizable, and that c is constant. Everything else in SR just falls out of those two assumptions and what they imply about physical reality. --98.217.71.237 (talk) 14:24, 16 October 2009 (UTC)

No, it isn't entirely right. Special relativity gives rules for transforming space and time coordinates for an observer in motion. Those rules were formulated with the aim of making Maxwell's equations valid in moving reference frames. The constancy of the speed of light is a consequence of them. Looie496 (talk) 17:13, 16 October 2009 (UTC)

Yes,the Special theory of Relativity was inspired from Maxwell's equations, how they referred to a specific speed of light, c. Rkr1991 ^{(Wanna chat?)} 05:14, 17 October 2009 (UTC)

The "coordinate" approach to SR was not inherent to Einstein's original work, but is a later development by Minkowski (which Einstein originally was skeptical of, but later embraced totally). Einstein's original papers do not explain the constancy of the speed of light, but take it as a given. I am aware this is not how SR might be taught in a modern physics classroom, but as an assessment of its historical development, it is correct. As our article on the Annus Mirabilis papers puts it: "First, he applies the classic principle of relativity, which states that the laws of physics remain the same for any non-accelerating frame of reference (called an inertial reference frame), to the laws of electrodynamics and optics as well as mechanics. In the second postulate, Einstein proposes that the speed of light has the same value in all inertial frames of reference, independent of the state of motion of the emitting body." This is very clear from reading his 1905 paper on the subject. --Mr.98 (talk) 16:44, 17 October 2009 (UTC)

nuclear reactor model

i want to make a pressurised heavy water reactor for a science exibition to be held on 30th october. i need to complete my model till 26th october. i have find many a thing about its theory. but i'm unable to make the model of nuclear reactor of this type. i've the full explanation.

i'm in trouble in making its inside structure through which i can explain its working and its components. (full working,coolent used,its component) i'll also be including india's advanced heavy water reactor theoratically to enhance this project.

this project cannot be a working one but somehow we can use some goodoies to make it a attracting one.

can you please help me out in making this project i've very less days left with me. so pls help me. —Preceding unsigned comment added by Sunny kuchya (talk • contribs) 12:35, 16 October 2009 (UTC)

What materials are you using to make the model, and how large is it going to be? Our article on the CANDU reactor has a pretty nice schematic of one; this page gives a more clear explanation of the core area. Perhaps others will have concrete ideas as to what could be done to make something similar on a small scale without too much work? --Mr.98 (talk) 12:43, 16 October 2009 (UTC)

black hole

How do we know that a black hole is in fact a singularity and not simply an object where all dimensions are smaller then the event horizon, but not zero (say where all the mass is in a volume the size of a grape)? Googlemeister (talk) 16:24, 16 October 2009 (UTC)

We don't, as we have no way to retrieve information from beyond a black hole's event horizon. However, general relativity predicts the existence of a gravitational singularity, and since GR holds up well where we can observe and test it, it's reasonable to expect the math here to be a good model as well. It may also be worth noting that my understanding of the singularity is that it expresses the unavoidable eventuality that all matter within the event horizon will converge to a point. This statement does not preclude that, at the present time, the matter still has some non-zero volume (such as a grape). — Lomn 16:54, 16 October 2009 (UTC)

I'm afraid "at the present time" doesn't make much sense here. I don't believe there's a natural coordinate system in which you can talk about events inside the event horizon with the same time coordinate as events outside. In the usual coordinate system — I think they're called Schwarzchild coordinates or something like that — the time dilation means that, at the event horizon itself, time completely stops. --Trovatore (talk) 19:00, 16 October 2009 (UTC)

There are coordinate systems that cover the whole space except the singularity itself, but the timelike coordinate doesn't really coincide with what we would call "time" - the whole point of relativity is that there isn't really a global concept of "time". It makes sense to talk about the time things near you happen but if they happen somewhere else (and the other side of an event horizon definitely counts as "somewhere else") then it gets complicated. See Relativity of simultaneity. --Tango (talk) 09:06, 17 October 2009 (UTC)

Apparently the Penrose–Hawking singularity theorems prove it, but I don't understand that article. --Sean 17:01, 16 October 2009 (UTC)

Those are mathematical theorems, they just prove that the basic assumptions of GR imply singularities at the centres of black holes, they don't prove that those basic assumptions hold. I think most (if not all) scientists agree that those assumptions are perfect, since they don't explain quantum effects. --Tango (talk) 09:06, 17 October 2009 (UTC)

It isn't actually presumed that there physically exists a gravitational singularity at the center of a black hole. The singularity predicted by general relativity is commonly perceived as signaling the breakdown of the theory near that point. In particular, in some volume near that point, the extremely high density should result in quantum mechanical particle interactions that are not yet understood. To date it has not been possible to combine quantum and gravitational effects into a single theory. It is generally expected that a theory of quantum gravity will feature black holes without singularities. (Borrowing some from Black hole#Singularity.) Red Act (talk) 07:06, 17 October 2009 (UTC)

Perhaps for all we know the black hole, singularity or whatever else cease to exist inside the event horizon, but the effects still occur on the outside because the information about this non-existance cannot be transmitted to the outside without exceeding the speed of light?Trevor Loughlin (talk) 08:42, 17 October 2009 (UTC)

That sounds a little like the holographic principle. --Tango (talk) 11:30, 17 October 2009 (UTC)

Does "dark gravity" exist?

Scientist talk about "dark matter" and about "dark energy". They say that gravity "pulls the Universe together", while dark energy "pushes the Universe apart". But there are weird results from the formulas. So does "Dark Gravity" exist? Are any scientists investigating dark gravity? Lemonyjuicy (talk) 17:38, 16 October 2009 (UTC)

It's not clear what sort of concept "dark gravity" would be. Have you read our articles on dark energy and gravity? Our dark energy article in particular discusses its relationship with gravity and the rationale behind its proposal. — Lomn 17:55, 16 October 2009 (UTC)

We unfortunately don't yet have an article on dark gravity, not even a stub. Dark gravity just redirects to dark matter, which is incorrect.

It is not yet known whether dark gravity "exists" or not, i.e., whether a dark gravity theory will wind up matching experimental data better than a dark energy theory. Dark energy, in some form or another, is currently the most popular way to explain the acceleration of the universe's expansion. And general relativity is generally taken to be a very solid part of the foundations of modern physics, so any idea like dark gravity that involves tweaking general relativity faces an uphill battle.

Yes, scientists are investigating dark gravity, in that some theoretical physicists are playing around with trying to find an appealing dark gravity theory to fit the available data. Whether some complete, self-consistent dark gravity theory will be developed, which will hold up to theoretical scrutiny to the point where experimental physicists will start to get involved in testing the theory, is at this point a matter of speculation. Red Act (talk) 06:27, 17 October 2009 (UTC)

Really? I've never heard the phrase "dark gravity". There is lots of work going on trying to find new theories of gravity to explain various things, but do any of them use the term "dark gravity"? "Dark matter" and "dark energy" are just names, the word "dark" doesn't have a specific meaning, it just sounds good in applications for research funds. --Tango (talk) 09:08, 17 October 2009 (UTC)

Agreed. Some theories that try to explain the effects we ascribe to dark matter by modifying gravity are called Modified Newtonian Dynamics or MOND. They can explain some of the discrepancies in the rotation rate of galaxies, but not e.g. the Bullet Cluster. --Stephan Schulz (talk) 09:20, 17 October 2009 (UTC)

Yeah, MOND and some other older alternate gravity theories couldn't explain the gravitational lensing in the Bullet Cluster. But there are a couple newer alternate gravity theories, STVG and TeVeS, that supposedly can. Red Act (talk) 09:57, 17 October 2009 (UTC)

Yeah, I'd never actually heard of dark gravity either, before I started researching this question. But Google turns up tons of hits. It's basically modifications of the Einstein field equations in ways that would explain the acceleration of the universe's expansion, in ways that don't fit the form of the cosmological constant or an additional contribution to the stress-energy tensor. It's rather new; I think the oldest date I saw on anything was 2001 or 2003, with most stuff being since 2005 or 2006. I'm sure the "dark gravity" name arose as a contrast to "dark energy", which it's an attempt to avoid hypothesizing. Dark gravity basically differs from earlier alternative gravity theories like MOND in that it's addressing a different problem. Dark gravity addresses the expansion of the universe; MOND was developed to address the much smaller scale problem of galaxy rotation curves. However, very recently there are also alternate gravity theories like STVG and TeVeS, that address both cosmological and galactic gravitational problems. Red Act (talk) 09:51, 17 October 2009 (UTC)

I don't think the recent appearance of the term "dark gravity" in place of "modified gravity" means much; it's just become fashionable to put "dark" in front of everything in cosmology. I don't think the bullet cluster can be explained without dark matter. STVG and TeVeS introduce new vector and scalar fields, and their explanation of the bullet cluster, if it works at all, involves independent motion of those extra fields. Scalar and vector fields are also known as "particles", and particles introduced to explain gravitational anomalies are known as "dark matter". There are lots of other dark matter candidates, so it's hard to get excited about one more. MOND was interesting because it didn't have those extra degrees of freedom. -- BenRG (talk) 00:27, 18 October 2009 (UTC)

Chewing gum or no chewing gum on the pavement

Are these marks on the pavement of every city which look like chewing gum, really chewing gum? I read somewhere they were something else, like dirt getting clumped together with oil rests, but I am having trouble in finding the article. --Quest09 (talk) 17:57, 16 October 2009 (UTC)

If it looks like this picture, then it's chewing gum. If it looks like this on the other hand, it's still chewing gum, but after Ben Wilson has dealt with it. SpinningSpark 19:21, 16 October 2009 (UTC)

Could these be some kind of bird excrement or perhaps treesap blobs? What about insect residue like snail trails or worm matter? 66.102.199.179 (talk) 14:31, 17 October 2009 (UTC)

Water supply in developing countries

Why is it that in many developing countries, it is not safe to drink water from the mains supply but yet it is safe to use it for washing etc? Clover345 (talk) 18:49, 16 October 2009 (UTC)

Because it is far more easy for a pathogen to infect you if you directly consume it. You are far less likely to get infected from using infected water to wash your clothes as most of the nasties will die when the clothing dries, or from soap you use while washing. Of course, it would be better to use uninfected water for washing as well if it is available.

To put it another way, drinking the infected water would be like making out with someone who has the flu, vs washing would be like entering a room that someone with the flu exited 10 minutes ago. Which is more likely to give you the flu? Googlemeister (talk) 19:11, 16 October 2009 (UTC)

Similar to the reason you (well, children anyway) wipe your hands on your clothes before eating - the dirt and grime is a drag to get on your cheeseburger, but it won't do too much harm on your shirt sleeve. ~ Amory (u • t • c) 21:00, 16 October 2009 (UTC)

I understand that in many parts of India, for example, the water supply drawn from wells and acquifers (sp?) is naturaly contaminated with low levels of arsenic - not enough to kill you, buy enough to cause health problems. 78.151.108.233 (talk) 11:42, 18 October 2009 (UTC)

Oxygen production in the dark?

Can photosynthetic organisms produced oxygen in the dark?

Aaadddaaammm (talk) 20:43, 16 October 2009 (UTC)

Yes. Photosynthesis is technically two reactions, and only the first requires light energy. The second requires the products of the light reaction, not light itself, so it is not directly dependent on sunlight. Often plants will perform this second reaction (called the "dark reaction") during the daytime, when the reactants made from the light reaction or readily available, although in climates where water is scarce they will often wait until after dark to prevent water loss. ~ Amory (u • t • c) 20:56, 16 October 2009 (UTC)

Thanks for the reply. But only the first reaction generates oxygen, doesn't it? The light reactions produce proton gradient (then ATP), NADPH and O2, and then the dark reactions use the ATP and reducing power to fix CO2. So in the very basic scheme, oxygen shouldn't be evolved in the dark, but are there certain circumstances or other processes known?? Aaadddaaammm (talk) 21:06, 16 October 2009 (UTC)

In general terms yes, most of the oxygen is likely to be released during the day. Some crassulacean acid metabolism plants uptake most of their CO₂ during the night but oxygen release is still during the day [15]. I'm not aware of any plant that releases significant amounts of oxygen in the dark Nil Einne (talk) 09:32, 17 October 2009 (UTC)

October 17

Spin quantum number

Why do they have the two possible values for the spin quantum number be -1/2 and 1/2 rather than -1 and 1? --76.211.91.59 (talk) 00:43, 17 October 2009 (UTC)

Spin quantum numbers are a measure of a particle's intrinsic angular momentum, in units of ħ, the reduced Planck constant. In other words, the component of an electron's intrinsic angular momentum, as measured along any direction, can be either +1/2 ħ or -1/2 ħ. That begs the question of why the reduced Planck constant was chosen to be defined as it is, instead of defining a unit of angular momentum that's half as big. Why that happened was really a matter of notational convenience in other places in quantum mechanics where ħ shows up. I'm not sure of the original equation(s) for which ħ were historically used first, but as an example, the energy of a photon with angular frequency ω is given by E=ħω. If instead of ħ, a constant was instead defined which had the value of ħ/2, then the equation for the energy of a photon as expressed using that different constant would have to have an extra factor of 2 in it. Red Act (talk) 03:15, 17 October 2009 (UTC)

Masturbation and a teen

Hi, if a 17 year old boy masturbates, could that affect his physical growth? --FromSouthAmerica (talk) 02:04, 17 October 2009 (UTC)

No. Masturbation is a normal, healthy practice, and even has some health and psychological benefits. See Masturbation#Benefits. Red Act (talk) 02:23, 17 October 2009 (UTC)

Yes but the growth is only temporary. Cuddlyable3 (talk) 10:46, 17 October 2009 (UTC)

What Red Act said goes for 17 year old girls too. Unfortunately many so called "civilized" cultures have indoctrinated us with various moral taboos on this subject (and sex in general) resulting in taking a 100% natural part of life and adding in artificial components of guilt, shame, and even horror to the idea of masturbation. Thus we get wive's tales of "If you do that it will stunt your growth". As we enter the 21st century we are just now (as a society) beginning to finally realize that such negative components are psychologically harmful and that masturbation (in moderate use) has physically and mentally beneficial effects. 66.102.199.179 (talk) 14:00, 17 October 2009 (UTC)

The primary factor behind stunted growth, worldwide, is malnutrition. Masturbation doesn't have anything to do with it. --Mr.98 (talk) 15:20, 17 October 2009 (UTC)

Why do some people so eagerly promote a self abuse (that was an accepted term) that is indisputably debilitating, un(repro)ductive, messy and not the sort of thing a competitive athlete does before the Olympics? Cuddlyable3 (talk) 16:32, 17 October 2009 (UTC)

I don't think I'd promote it, but it's a bit like defecation: don't talk about it in polite society, but don't deny that it exists or that it happens or that it's a perfectly normal part of the human experience. SDY (talk) 16:37, 17 October 2009 (UTC)

I'd promote it, sure. I think people coming to terms with their own sexuality, the reality of orgasm, and things of that nature are perfectly healthy. It is not debilitating in the slightest, it is not much messier than blowing one's nose, and does in fact relieve quite a bit of mental stress and allows many a young man to focus on things other than trying to have actual sex. Compared to teenage intercourse, masturbation is downright healthy and a social good. I promote it, sure, why not? I don't see any evidence that moderate masturbation does any harm, whereas self-denial, self-shame, fear-of-sexuality, marrying-at-too-early-an-age, having-children-at-too-early-an-age, and many of the mental and social activities that have gone along with the discouragement of masturbation have done legions of harm across the ages. If you don't want to do it, then don't, but don't make it out like it is not a perfectly natural human activity. --Mr.98 (talk) 23:23, 17 October 2009 (UTC)

I should remind all posters of the Ref Desk prohibition on giving medical advice - some of the above comments are getting dangerously close to it... Tevildo (talk) 20:31, 17 October 2009 (UTC)

Stating factual information isn't media advice. —Preceding unsigned comment added by 82.44.55.2 (talk) 20:43, 17 October 2009 (UTC)

This is common sex education information that anyone who paid attention in health class should know. It's not medical advice in the slightest. --Mr.98 (talk) 23:23, 17 October 2009 (UTC)

I still think there's a difference between "Masturbation doesn't stunt your growth/make you blind/put hair on the palms of your hands" and "Masturbation is good/bad for you" - however, the line has not been crossed, and I withdraw my remark. Tevildo (talk) 00:32, 18 October 2009 (UTC)

Set of 4 questions: Nanotech, astrophysics, and structural engineering related.

This is basically a set of mostly math-based questions but to answer them also requires knowledge of other advanced scientific subjects (see the Subject above).

The core of this question set is based on a hypothetical proposal, to wit:

Build a simplified Niven ring made entirely of carbon nanotubes and set it in an equatorial orbit around the Earth.

Two major types of nanotubes are required:

• Type One are to be engineered for use as a rigid frame for the ring structure, perhaps formed like a belt of interlocked large (2m) triangular or hexagonal cells).
• Type Two are to be engineered for use as a optical screen mesh mounted across the frame in panels.

Dimensionally the "belt" must be wide enough to fully shadow the Thermal equator during peak periods of insolation. That dimension will in turn depend on the belt's diameter which is open for discussion (see below).

So here is my question set...

1. Ideally this belt would be located in the upper atmosphere between 100km and 300km above sea-level. However, at that altitude the belt would be exposed to a large amount of atmospheric turbulence and might not be able to sustain orbit. Nanotubes should be well suited to such stresses but in the event that this is not a practical location what is the next best location (altitude/radius) to accomplish the desired shadow area?

2. Having selected an altitude what is the full set of dimensions for such a belt? Thickness obviously will be negligible unless structural design mandates a frame depth of more than nano dimension.

3. Based on the answer to #2, what is a rough estimate of the total mass of the ring? That is, how much nano carbon material would be needed to build this structure?

4. According to the WP article on optical properties of carbon nanotubes, it states:

"Their unique feature is not the efficiency, which is yet relatively low, but the narrow selectivity in the wavelength of emission and detection of light and the possibility of its fine tuning through the nanotube structure."

So, assuming you couold create the Type Two nanomaterial to filter only certain frequencies, what optical frequencies would need to be filtered to create a shadow effect that reduces the thermal energy of insolation by approximately 2% in the belt's shadow zone, but leaves the visible and botanically important sunlight frequencies unaffected?

66.102.199.179 (talk) 06:02, 17 October 2009 (UTC)

I don't see why you need carbon nanotubes. The Ringworld needs to be really strong because it rotates really fast to create artificial gravity. Your ring could rotate at orbital velocity, so there would be no forces on it at all (beyond the turbulence, etc., that you mention, but that is manageable). The problem with your idea is that the visible and botanically important sunlight frequencies make up the vast majority of the sun's emissions - that is why our eyes and plants have evolved to use those frequencies. You can't block out the thermal energy without blocking those frequencies because the energy is carried by those frequencies. --Tango (talk) 09:18, 17 October 2009 (UTC)

... and don't forget (a) to account for tidal forces due to Moon and (b) you'll need some sort of stabilising mechanism. Gandalf61 (talk) 11:14, 17 October 2009 (UTC)

I'm not sure it would be too unstable - you can consider each molecule separately as being in a stable orbit, the forces within the body will be fairly small (how big they are depends largely on the size of the body) and shouldn't affect the stability. --Tango (talk) 11:34, 17 October 2009 (UTC)

For a discussion of the dynamic instability of Niven rings see Why Niven rings are unstable by Erik Max Francis. Gandalf61 (talk) 14:17, 17 October 2009 (UTC)

Tango: As for "why nanotubes?", simply because I believe that (or some other nano structure) would be the material that would be lightest and least resource consuming yet still able to maintain structural integrity (thus my interest in answering Q#3). The inspiration for its use came from Bradley C. Edwards' idea of using a nanotube ribbon for a space elevator cable. 66.102.199.179 (talk) 13:28, 17 October 2009 (UTC)

On Q#4: If we are only trying to reduce thermal energy, what about reducing of the infrared and/or the ultraviolet? What about selectively filtering out a motled sampling of the spectrum using a wide variety of freqency atuned nano-devices in low quantities? Recognize that we only need to filter about 2% of the energy, not all of it. The end-intent should be to ensure we don't make the days "always grey" and piss off the local tourist industries. :) 66.102.199.179 (talk) 13:28, 17 October 2009 (UTC)

Gandalf61: Agreed, the belt would need a set of basic attitude actuators just as any satelite does for station keeping. This may be a huge belt shaped object but it is still an artificial satelite in the end. The issue of orbital stability does however have great bearing on the answer to Q#1. 66.102.199.179 (talk) 13:28, 17 October 2009 (UTC)

Could Alain Robert have escaped the Twin Towers?

The survival prospects of those above the Twin Towers explosion were limited. Would someone with the "French Spiderman" Alain Robert's near superhuman climbing skills have escaped by climbing down the outside of the building, rather than take the lethal alternative of jumping?Trevor Loughlin (talk) 08:32, 17 October 2009 (UTC)

We can only speculate and the ref desk doesn't do speculation. Sorry. --Tango (talk) 09:20, 17 October 2009 (UTC)

Ask him. His website has a contact page. Cuddlyable3 (talk) 10:36, 17 October 2009 (UTC)

If he had been in the building above the burning portion, there would be absolutely no way that he could have climbed down through the fires. If he had been below the burning portion, he could have taken the stairs down like the other survivors. 72.94.164.21 (talk) 10:44, 17 October 2009 (UTC)

I would be hesitant to rule it out as impossible. There may well have been a path around or through the fires, any reply we can give would be guesswork. --Tango (talk) 11:32, 17 October 2009 (UTC)

Philippe Petit might have stood more chance, but...--Shantavira|^{feed me} 12:27, 17 October 2009 (UTC)

On September 11, 2001 this could have happened: 8:46 a.m. plane hits WTC North Tower. Philippe Petit rushes to the roof and throws a line and anchor that he happened to have stored "just in case" to WTC South Tower. By 8:55 a.m. he is balancing on the line between the towers. Just before 9:03 a.m. he arrives on the roof of WTC South Tower and breathes a sigh of relief "Mon dieu, I am - how you say - out of zat frying pan! Cuddlyable3 (talk) 16:25, 17 October 2009 (UTC)

One question would be whether he would have time: the South tower lasted 55 minutes after the impact, the north tower about 100 minutes. Climbers like this seem mainly to go up buildings not down, although Robert has been up and down a few, e.g. the RBS Tower in Sydney, but it's hard to estimate how long it would take to climb down (especially as he normally stops to chat on the way). --82.41.11.134 (talk) 13:58, 17 October 2009 (UTC)

Right, this is what I imagine the question is. How far could he have gone in 55 minutes? The towers are pretty tall—I doubt he could do them from the very top. If one had some idea of what his speed is climbing down, you could calculate around where the cutoff would be for feasibility. --Mr.98 (talk) 15:24, 17 October 2009 (UTC)

I thought about the timing too as well but once finding out the time it took for the buildings to collapse I decided it was impossible to rule it out with that. No one said it had to be the south tower right? According to Alain Robert it took him about 100 minutes to climb the Petronas Twin Towers. This is climbing up not down but I don't see any reason to presume he would definitely take longer to climb down, in fact it's possible it would be faster therefore it seems you can't rule it out Nil Einne (talk) 15:44, 17 October 2009 (UTC)

I would personally suspect down to take longer, but I don't really know. Climbing up a tree is easy. Climbing down is hard—you've got to limit your own momentum, and you are somewhat going against the orientation of your body (you can't use your upper arms as well, and you can't see what your feet are doing as well). But I'm no climber. --Mr.98 (talk) 16:40, 17 October 2009 (UTC)

I don't know much about climbing buildings, but it seems like the facade of the trade towers would be difficult. I don't think there were any horizontal elements to grip. Rckrone (talk) 16:54, 17 October 2009 (UTC)

Cold Fire

Hello I'm looking for info on cold fires i.e. fires that have unusually low temperature they don't burn, just glow. I could not find anything about it in Fire. I've been told that such fires are possible but how? Aurora sword (talk) 12:29, 17 October 2009 (UTC)

will o the wisp or ghost light is a natural kind. Does cold fire have anything? (No) Graeme Bartlett (talk) 12:33, 17 October 2009 (UTC)

Burning methane clathrate is a sort of cold fire. It's like burning ice. It does have a regular flame, though, not just glowing. Red Act (talk) 12:41, 17 October 2009 (UTC)

Interesting, is this the kind of thing commonly used in chemistry demos? Aurora sword (talk) 12:46, 17 October 2009 (UTC)

"Fire" is just a self sustaining reaction between something and oxygen which generally generates heat. It self sustained by the local diffusion of both heat and radicals, but there is no reason why in absolute terms it has to be hotter than room temperature say. The heat generated will tend to heat things up but if the starting material is naturally cool (for example has latent heat associated with a phase transition at a cool temperature) then it is possible for the fire to stay cold. But it needs to be fairly reactive to burn cold. So if you burn something which boils at body temp (Diethyl ether for example) the liquid under the flame will not get to above its boiling point, and you can pour it over your hands and light it without burning yourself (although not recommended, jugglers use it but it needs skill to avoid the flame itself burning you). A solid which sublimes but is reactive enough could surface burn cold but personally I cannot name one. Methane Clathrate seems a plausible candidate. --BozMo talk 12:53, 17 October 2009 (UTC)

In that case, what is actually burning is just methane so it is just like any other methane flame - the source of the methane is cold, but the fire itself is hot. --Tango (talk) 13:02, 17 October 2009 (UTC)

The light from a flame is usually because it is hot, so you're not going to get a bright orange flame like you get with a candle without it being hot. Any light will be from chemical emissions, like the blue flame you get from complete combustion of natural gas (eg. a gas cooker or Bunsen burner). I don't know of any chemical reactions that result in emissions at low temperatures. --Tango (talk) 13:02, 17 October 2009 (UTC)

Well, there's bioluminescence and other chemiluminescence. Red Act (talk) 13:13, 17 October 2009 (UTC)

Have a look at "pyrophoricity". Plutonium is one of the classic examples. Axl ¤ [Talk] 13:25, 17 October 2009 (UTC)

To have a visible flame - you need enough temperature for the blackbody radiation to be in the visible range. When the temperature is below the 'Draper point' (Huh! No article?!?) - which is at about 500 degrees Centigrade - there is no light emitted. So that's pretty much the coldest a visible flame can possibly be. There may be other chemical reactions that produce light as a byproduct that could kinda look like a flame - but those aren't properly 'flames'. There may be cooler oxidation reactions that produce the characteristic plume of a flame - but with no visible light. Methane clathrates look like a lump of ice - if you set light to it, it looks like you're burning an ice-cube - which is surprising and interesting - but the flame is just a normal methane flame - it's plenty hot! SteveBaker (talk) 13:26, 17 October 2009 (UTC)

I thought the OP asked for no visible flame but surface burning? So why are you suddenly all talking about flames? Surface burn cold was the request, my flame bit was intended to be an analogy. --BozMo talk 14:07, 17 October 2009 (UTC)

I think the glow from white phosphorus in damp air pretty much fits the bill of what is being asked for. The reaction is essentially a kind of fire, in that it's ultimately a gas phase oxidation process, but it merely glows instead of burning normally with a flame. And the reaction is cold, because it's a form of chemiluminescence, not a form of incandescence, in which the Draper point of black body radiation would be a consideration. Red Act (talk) 14:16, 17 October 2009 (UTC)

I may be interpreting the OP's question incorrectly, but perhaps they'd be interested in coal seam fires that often simply smoulder for years and years, but don't "flame up" in the usual manner. Smoulder has more information on that kind of topic. Matt Deres (talk) 21:15, 17 October 2009 (UTC)

How do deleaved trees breathe?

How do trees that have lost all their leaves in the fall breathe through the winter? 71.161.59.133 (talk) 15:36, 17 October 2009 (UTC)

Trees don't breathe like you or me. See the article Leaf. During tree growth, leaves absorb carbon dioxide from the air. When the tree is not growing it needs little or no carbon dioxide, and the article implies that if the concentration of carbon dioxide in the atmosphere were higher than it is now, a tree could absorb all its needs through its branches or roots. Cuddlyable3 (talk) 16:06, 17 October 2009 (UTC)

Trees only use CO2 for photosynthesizing. The rest of the cells consume oxygen.

The living tissue of the woody stems (the cambium) breath through organs in the bark called lenticels. --SB_Johnny | ^talk 16:26, 17 October 2009 (UTC)

I'm not entirely sure but perhaps this interesting [16] conference paper I found yesterday about common misconceptions taught in school including on the difference between breathing and respiration will help. While it's directed at educators it may help clear up any misconceptions Nil Einne (talk) 10:17, 18 October 2009 (UTC)

How to make my doorbell ring for longer

I find that people tend to politely press doorbell buttons for just a microsecond, which is difficult to hear. Is there any simple circuitry that could turn a brief closing of the circuit into a ten-second bell ring? My doorbell is I think 6 volts, off a mains transformer. I'd prefer somthing with rugged relays rather than transistors. This explains why bad-taste musical doorbells are popular. Thanks 92.29.130.77 (talk) 17:31, 17 October 2009 (UTC)

You could put together something using a 555 timer IC, a couple of resistors and capacitors, and a relay. See the "Monostable mode" section of the article for the circuit diagram. If your transformer is AC/AC, you'll also need a rectifier pack and voltage regulator. A good introductory electronics project. :) Tevildo (talk) 20:36, 17 October 2009 (UTC)

No need to mess around building electronics. You can buy a timer relay that does the job straight away. You can get different voltages ac/dc and timing ranges so there's bound to be one that suites your doorbell. Here's a data sheet. Tevildo's idea is a more interesting project though, if you are trying to learn electronics. SpinningSpark 21:09, 17 October 2009 (UTC)

That is a nice data sheet but none of the relays shown are rated for control by 6V. It is unsafe to connect mains voltage to a doorbell button. Cuddlyable3 (talk) 21:25, 17 October 2009 (UTC)

Ah, I missed the OP requires 6V. Those ones go down to 12V and I certainly was not suggesting connecting it to the mains (as a paperboy while still at school I once got a shock from someones doorbell) agreed that is highly dangerous. 6V is a lot less common for relays but I will see if I can find something, are you sure you need 6V? SpinningSpark 22:21, 17 October 2009 (UTC)

To press a button for literally a microsecond or 10^-6 second is practically impossible. Cuddlyable3 (talk) 21:15, 17 October 2009 (UTC)

You and your pointy-eared logic, Spock.[[Special:Contributions/Dr. Leonard McCoy|209.244.187.155]] (talk) 00:04, 18 October 2009 (UTC)

Maybe the gross motion of the button mechanical system is slower than a single microsecond event; but the electrical contact may be as short as 1 microsecond, and may actually twitter back and forth on that sort of timescale (usually due to micromechanical behavior of the switch contact plate or spring). Digital samplers often need to correct for this on any mechanical user-interface button. Nimur (talk) 21:44, 17 October 2009 (UTC)

How about a little sign that says "Please press the doorbell for at least 10 seconds". Low-tech, but effective! SteveBaker (talk) 22:16, 17 October 2009 (UTC)

Obvious answer - replace the chime with one that plays for much longer - common ones here in the UK play the opening chimes of Big Ben for instance - around 6 seconds. Exxolon (talk) 04:30, 18 October 2009 (UTC)

I am reminded of the TV show WKRP in Cincinnati, where the character Jennifer had a doorbell that played the opening notes of Fly Me to the Moon. --Anonymous, 07:02 UTC, October 18, 2009.

I've had a closer look at the old "Friedland" transformer and it has a choice of 4v, 8v, or 12v. Currently it is set up for 8v, which I recall is the current required by the bell itself. Thanks 78.151.108.233 (talk) 12:05, 18 October 2009 (UTC)

Modifying a mobile phone / cell phone to use only as a computing device.

I do not like mobile phones. But some mobile phones can be used as a miniture computer. Is it possible to tinker with its insides and stop it being usable as a mobile phone but keeping it working as a computing device? 92.29.130.77 (talk) 17:39, 17 October 2009 (UTC)

Why not just put it in airplane mode? --Cameron Scott (talk) 17:44, 17 October 2009 (UTC)

Not OP, but not all phones have "airplane mode". Indeed, I've never seen a phone that had that, although I've not seen many newer model phones recently. —Preceding unsigned comment added by 82.44.55.2 (talk) 17:47, 17 October 2009 (UTC)

Well, many do. Mine does, and I use the feature frequently. See flight mode --NorwegianBlue ^talk 18:21, 17 October 2009 (UTC)

Actually I suspect most phones probably have airplane mode or something similar. It's not actually new at all, or uncommon. My bet is that your phones have had it but you didn't know how to use it. --Mr.98 (talk) 19:07, 17 October 2009 (UTC)

Pretty sure they don't, then again I'm talking about very old (5 years) phones here.

My 3.5 year old phone (Panasonic VS2) did not have a flight mode although it supported (limited) video playback, most audio formats, had a 1.3 MP camera, infrared, a good (for the time and price) colour 320x240 screen and had 32mb of memory. I would expect most new model phones in that price range to have a flight mode but I'm pretty sure it wasn't unusual for the time and it was in the low mid to mid price range (IMHO). It didn't have bluetooth, 3G, or expandle memory (the later being the biggest limitation). The ~2 year old Nokia 1110 I use occasionally since my Panasonic VS2 broke which is a fairly basic phone with a monochrome screen, no camera etc also lacks a flight mode. It's replacement model, the Nokia 1200 also does not have a flight mode I'm pretty sure. The usefulness of a flight mode for such a basic phone is of course fairly questionable. Of course if you're intending to use your phone as a computer you're unlikely to be using either a basic phone or a 3+ year old model however I would suspect when we think in world wide terms they do represent a substanial percentage of the market so I think it's questionable if 'most phones' have an flight mode Nil Einne (talk) 07:32, 18 October 2009 (UTC)

Probably... but the phone's computer is NOT very powerful. It strikes me that anything you might want to do on a cell phone could be EASILY better done on a machine better suited to that purpose. I mean, I use mine as a calculator. It's not the best calculator and it's a pain to use. It is ONLY convenient as a calculator because it is also a phone, and I am already bringing the phone with me. If I didn't have a phone, and I needed a calculator, I'd just carry a regular calculator around—it'd be a lot easier to use. --Mr.98 (talk) 19:07, 17 October 2009 (UTC)

The phone indicated by NorwegianBlue above has a higher memory and storage spec than a DOS laptop I had a few years ago. If it has an operating system that allows the introduction of other programs, then it should be able to do a lot. Perhaps the drawback would be the difficulty of using the tiny 'keyboard'. 92.29.130.77 (talk) 19:35, 17 October 2009 (UTC)

Perhaps, but for the price of the phone (probably a few hundred dollars) you can just get a netbook and skip all of the hassle and the very tiny monitor, no? --Mr.98 (talk) 20:04, 17 October 2009 (UTC)

It might help if you explained why you don't want it to work as a phone. You can choose not to make any phone calls without disabling the feature. --Tango (talk) 19:52, 17 October 2009 (UTC)

Obviously for situations like being on an airplane or not wanting a phone without a sim card to radiate you with signals when it's not being used for calls. —Preceding unsigned comment added by 82.44.55.2 (talk) 20:05, 17 October 2009 (UTC)

Obviously for situations like being on an airplane which if it is powerful enough to add as a small computer is going to have an aircraft mode for.. --Cameron Scott (talk) 20:10, 17 October 2009 (UTC)

The OP hasn't mentioned aircraft and there can be other motives for disabling the call function on a mobile phone, such as lending it to child for game playing only. Cuddlyable3 (talk) 20:55, 17 October 2009 (UTC)

Rather than modify a phone, why not just get a PDA? Does about the same thing... SDY (talk) 20:17, 17 October 2009 (UTC)

For those who wonder why anyone would want to do this, mobile phones have a very good performance / power consumption ratio so it could be seen as some kind of a green act and a cheap way to waste time to build a cluster of recycled phones. Why you would want to disable calling I do not know. --194.197.235.240 (talk) 20:48, 17 October 2009 (UTC)

If I just threw away the "sim" card, would that be the solution? Do all these phones have sim cards? I'd like to use such a device because its probably easy to get one cheaply or perhaps even for free as people upgrade, and because they are very light. PDAs or netbooks weigh 500g+ (weight of a jar of jam) as far as I recall and would be no fun to carry around in your pocket for any length of time. And because its fun getting something to work like that, particularly for little or no cost. I like to work things to the max. 92.29.130.77 (talk) 21:29, 17 October 2009 (UTC)

I'm not sure what you think of when you think "PDA", but most PDAs are the size of a phone. A PDA is something like a PalmOS device. PDAs are not the same thing as a netbook. APL (talk) 22:52, 17 October 2009 (UTC)

If I just threw away the "sim" card, would that be the solution? Depends, you are in the UK, so yes, you could just remove the SIM card, the only problem is that some smartphones will not operate for long without the presence of a SIM card. As for the weight and size, well as the size decreases, so does the screen size. --Cameron Scott (talk) 21:32, 17 October 2009 (UTC)

Actually some phones won't operate at all without a sim card (well they will just say "no sim card" or "emergency calls only" and won't let you do anything). You can get wiped sim cards from places like Deal Extreme may avert this problem however if the phone is sim locked they probably won't work. Also this won't necessarily stop the phone from transmitting so there may still be battery life and other such issues. So I have to agree a PDA of some sort would be a better bet. Why get something with the phone part if you don't want it? Nil Einne (talk) 07:36, 18 October 2009 (UTC)

I'm surprised the no one has mentioned the iTouch yet. It's essentially an iPhone without the telephone stuff.

I'd also like to mention the Open Pandora which will eventually ship its first unit. That's going to be the size of a NintendoDS which can fit your pocket, depending on the kind of pockets you have. APL (talk) 22:52, 17 October 2009 (UTC)

One of the reasons why I'd like to try using a mobile phone as a computing device is for the same reason that I keep a minature radio all the time in my bag: the radio is extremely light so I do not notice the weight, it is very small so takes up no space, and it is very cheap so I'm not worried about it being lost damaged or stolen. If I find I've got some time to waste while on a journey then the radio is there if I want to play with it. 78.151.108.233 (talk) 12:20, 18 October 2009 (UTC)

stomach pressure in vomiting

What pressure (mm/Hg) is needed for the stomach to eject its contents? Please cite authoritative reference. —Preceding unsigned comment added by 72.75.125.231 (talk) 23:43, 17 October 2009 (UTC)

The stomach must merely apply positive pressure to its contents while the pyloric sphincter is tensed and the esophageal sphincter is relaxed. Stomach contents will then be brought to the oropharynx via esophageal reverse peristalsis. It's not as though the stomach has to pump its contents through a conduit of static/merely elastic vessels like the heart must do to sustain blood pressure. DRosenbach ^{(Talk | Contribs)} 00:29, 18 October 2009 (UTC)

Physiology and pharmacology of vomiting, (1953), discusses the ability to induce vomiting by applying pressures to various sections of the gastrointestinal tract. Vomiting was induced by 300 mm-Hg applied to the biliary ducts; or 30 to 35 mm-Hg applied to the pyloric pouches. These experiments were conducted on dogs. Nimur (talk) 00:45, 18 October 2009 (UTC)

Respiratory mechanics of vomiting in decerebrate cats, (1974), states that "the respiratory muscles provide the motive force in vomiting..." and that "the retching pulses were generally 0.5 s or less in duration, and at their peak amplitude often exceeded minus 75 mmHg in the thorax coincident with 125 mmHg in the abdomen, adding up to transdiaphragmatic pressures greater than 200 mmHg." This paper presents time-versus-pressure plots, as well as EMG plots of the control signal, so you can actually see the vomiting process as a dynamic event (rather than an approximate average pressure). It also might explain why human studies are more or less impossible - decerebrate cats were used in this study. I would like to comment for the record that the procedures described in this paper are not necessarily pleasant. We can hope that the useful scientific data may help (or may have already helped) the medical and biological community; hopefully, assisting our understanding of the neurological issues which motivated the original research and spurning medical progress. Nimur (talk) 00:52, 18 October 2009 (UTC)

October 18

Voltage drop in an extension cord

So, here's a break from relativity and black holes and all that high-powered stuff...

My "good" 14-ga, 100-foot extension cord wasn't really that good, and finally died today. Bought a new one, CostCo had 12-ga cords for less than 14-ga cords at the local home repair store. I swear that my leaf blower is running faster on the new cord than the old -- speed being indirectly perceived by the racket it makes.

(1) Is this actually possible, or am I suffering from too much observer bias? (2) Can I safely measure the voltage at the end of the cord with a simple V-O-A meter, just sticking the prongs into the outlet holes?

Thanks to the electricians in the audience! --DaHorsesMouth (talk) 01:09, 18 October 2009 (UTC)

Certain voltmeters are designed for probing high-voltage, AC sources. However, this is categorically not safe - even if you are a trained electrician, it is still not safe. But, there is an alternative - and a better one, actually.

First of all, you don't care about the "resting" voltage - there will be virtually no voltage drop unless the leaf-blower is on, since no (net) current is flowing through the extension cord. So, you need to measure the voltage when operating the leaf blower. Consider buying one of these plug-in outlet voltage monitors. They are much safer to use, and you can use them while operating the leaf blower - to see whether turning it on causes a voltage drop at the end of the cord. Nimur (talk) 01:15, 18 October 2009 (UTC)

Here's a digital one, for ~ $25. Nimur (talk) 01:22, 18 October 2009 (UTC)

Calculating from the values in American wire gauge, using the 14 AWG cable instead of the 12 AWG should introduce an extra resistance of 0.1874 Ohms. Assuming it's a 20 amp circuit, that means the voltage drop could be at most 3.748 volts, and is actually something less than that. So the voltage to the appliance is being dropped by only about 3% or less, which one wouldn't think would be noticeable. Extra resistance due to corrosion on the contacts of the old extension cord, however, could make a much bigger difference. Red Act (talk) 01:42, 18 October 2009 (UTC)

OK, that'll do nicely. Nimur, I promise not to do something patently stupid -- today.

Resolved

Hychlorite?

I toured George Eastman's house today and in his bathroom was a bottle labeled "Hychlorite". After doing a search, I see that there's a Flickr image of the bottles. I never expected to see an image of the exact same bottle on the net but okay... What was this? The closest I can find here or on Google seems to be Hypochlorite. Are these the same thing? From what I gather, hychlorite was used as an anti-septic. Can anyone confirm this? Dismas|^(talk) 02:59, 18 October 2009 (UTC)

From this, it appears that hychlorite is another name for sodium hypochlorite. Red Act (talk) 03:17, 18 October 2009 (UTC)

Looks like Hyclorite was a brandname for a commercial '''sodium hypochlorite''' preparation. See TALK:Sodium_hypochlorite#Hychlorite_and_Zonite for a link that supports this. 66.102.199.179 (talk) 03:22, 18 October 2009 (UTC)

External Speaker Noise Problem

Very recently my external speakers (5.1) connected through its own amp, has started making really huge buzzing noise. The noise starts if I just turn on the speakers. I have tried disconnecting the audio in cables, but the problem persists. Any help ? —Preceding unsigned comment added by 59.93.204.61 (talk) 04:12, 18 October 2009 (UTC)

I'm no audio engineer but two things spring to mind - the first is inteference - have you plugged in/installed new appliances either nearby or on the same ring main as the speakers/amps? Try disconnecting them/switching off if so. Secondly could be poor connections - check all plugs and sockets, then look for loose wires or poor solder joints. Exxolon (talk) 04:26, 18 October 2009 (UTC)

Regulation of cholesterol in blood

Hi everyone I am a little confused about how cholesterol levels are regulated. The article on Cholesterol says that fat intake, especially that of saturated fats, plays a large role in blood cholesterol. My question is why? Surely our bodies can choose not to convert the fat we eat to cholesterol? I realise that fatty foods contain cholesterol but if my understanding is correct our bodies produce cholesterol from fat as well - why would it do this if the cholesterol levels were already high enough? Can't the process be inhibited in some way? Thanks in advance for any contributions! RichYPE (talk) 10:29, 18 October 2009 (UTC)