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September 22

What are/ may be floating conditions to float any thing over water surface

Sir/ Madam I wish to know what are the floating conditions to make any thing float over water surface(Normal potable water not salty).

Wish for an early reply

Thanx a lot — Preceding unsigned comment added by 182.156.153.151 (talk) 04:20, 22 September 2011 (UTC)

Is this a homework question? 67.169.177.176 (talk) 04:45, 22 September 2011 (UTC)

For specifically FLOATING, you're probably after buoyancy. Vespine (talk) 04:47, 22 September 2011 (UTC)

(EC) For a large object in a stable configuration, the object will float if the mass of the object is no more than the mass of a volume of water equivalent to the portion of the volume of the object that’s below the surface of the water, i.e., the mass of the object is no more than the mass of the displaced water. See Displacement (ship) and Displacement (fluid). For very small objects, surface tension can cause an object to float even if it has a greater mass than the displaced water. Red Act (talk) 04:49, 22 September 2011 (UTC)

In other words, for all but the smallest objects, if the object's density is less than that of water, it will float. Very small objects (sewing needles, etc.) can sometimes float despite being more dense than water, because they are supported by surface tension. 67.169.177.176 (talk) 05:11, 22 September 2011 (UTC)

And, of course, an object can still float despite being made of materials far denser than water, like steel, so long as they contain a far lighter material, like air, beneath the waterline, so that the average density of everything is less than water. StuRat (talk) 06:25, 22 September 2011 (UTC)

And, with a more liberal interpretation of the word "float", we could include a hydroplane, hydrofoil, hovercraft, or ground effects airplane (only the first two actually require water). StuRat (talk) 06:36, 22 September 2011 (UTC)

Conditions:

1. Being Jesus.
2. Being an ice skater when it's cold
3. Any theologically admissible combination of the above. Cuddlyable3 (talk) 11:22, 22 September 2011 (UTC)

A solid sphere can float if the radius is less than

$R={\sqrt {\frac {3\gamma }{2\rho g}}}$

where $\gamma$ is the surface tension of water and $\rho$ is the density of the sphere. Count Iblis (talk) 16:02, 22 September 2011 (UTC)

Wouldn't $\rho$ rather be the density of the sphere minus the density of water? Dauto (talk) 21:06, 22 September 2011 (UTC)

If a vessel such as a nuclear submarine violated the "floating criteria" given by Red Act, as by having some compartments flooded, but had 200 megawatt nuclear reactors powering propellers driving it forward, and diving planes set to drive it upwards, couldn't it remain with a portion above the surface (of "potable water" such as Lake Michigan)? Would such a vessel be "floating?" This would be analogous to an airplane (as opposed to a "lighter than air craft" flying. Edison (talk) 04:15, 23 September 2011 (UTC)

To call that situation "floating" would be literary license at best, and abuse of terminology at worst. The submarine you just described is not "floating," it is "propelling itself upwards above the water." It's not buoyant. On the other hand, people do sometimes describe a heavier-than-air airplane as "floating," even in technical contexts like the FAA's Airplane Flying Handbook (Chapter 8, "Floating During Roundout," an undesired condition); but even then, the conditions are not due to buoyancy - it's used as an analogy to describe a dynamic effect. Nimur (talk) 04:55, 23 September 2011 (UTC)

OK, now I'm confused myself. What about a sub that's neutrally buoyant and cruising underwater at constant depth (say 60 feet)? Would that be considered "floating"? 67.169.177.176 (talk) 06:11, 23 September 2011 (UTC)

I think floating implies "less than" not "less than or equal to" if you see what I mean..Imgaril (talk) 10:40, 23 September 2011 (UTC)

So a neutrally-buoyant sub would not count as floating. 67.169.177.176 (talk) 19:59, 23 September 2011 (UTC)

Surface tension (mentioned above) is an impressive "floating agent." I tried the experiment of putting tapwater (density about 1 gm/cm² in a dish, and then placed placed a very large steel sewing needle (density about 8 gm/cm² on the surface, where it floated nicely. Edison (talk) 19:03, 26 September 2011 (UTC)

low boiling dopamine receptor agonists

Can someone help me brainstorm of new agonists I could use for fruit fly experiments? We've been working with cocaine for ... years and months, but I also want to try something else. For one, the success rate of aerosolising cocaine with a consistency amenable to experiment is rather unpredictable.

Feeding it into a test chamber by say, distillation often means the cocaine crashes out and crystallises on random surfaces, unable to be taken up by flies. For the love of the flying spaghetti monster, are there any agents better than cocaine that might be easier to administer through the air? (We cannot administer through their food, for various complex reasons.) elle _{vécut heureuse} ^{à jamais} (be free) 04:53, 22 September 2011 (UTC)

THC ? Nicotine ? Ethanol (might be a bit of an irritant, though) ? Or how about the chemical in some dry erase markers that just about makes me pass out ? StuRat (talk) 06:27, 22 September 2011 (UTC)

Those aren't dopamine agonists. While Methamphetamine and apomorphine have relatively low molecular weights, that's a lousy huristic for organic compounds, so what you really need is to go through Category:Dopamine agonists in CAS for an hour or two until you find something sufficiently soluble and volatile. 69.171.160.5 (talk) 06:52, 22 September 2011 (UTC)

Looking at the category on wikipedia - nearly all of those are essentially involatile - exceptions are amphetamine, and Propylhexedrine. These would need to be in the free base form - amphetamine is volatile enough to have a strong distinctive amine smell, and cause excitation if you leave the top of the bottle and smell it.. So it might create a great enough concentration in air naturally to affect your flies.

It's possible that there is dopamine agonist so potent that is it more effective than amphetamine despite lower volatility - but I don't know it - not my subject.Imgaril (talk) 13:17, 22 September 2011 (UTC)

Generally the way to introduce a non-volatile compound would be to convert to Aerosol form, generally using a Atomizer nozzle.Imgaril (talk) 13:36, 22 September 2011 (UTC)

The experiments are very sensitive to the size of the aerosol particles -- too big and the flies will simply not be affected by it! elle _{vécut heureuse} ^{à jamais} (be free) 21:41, 22 September 2011 (UTC)

Amphetamine free base looks like your best bet by far, and if you're already licensed for cocaine, it should be easy to come by. Are there any reasons it won't do what you want? 75.71.64.74 (talk) 21:48, 22 September 2011 (UTC)

Why are you trying to get flies high on hard drugs? 208.54.40.213 (talk) 04:56, 23 September 2011 (UTC)

I think she's trying to study the mechanisms of drug addiction. 67.169.177.176 (talk) 06:14, 23 September 2011 (UTC)

Does the pH of the environment affect crystallization rate? I'm wondering if you had a touch of ammonia in the atmosphere, would it stay in a free base form and be slower to precipitate out? (No idea if that works) Wnt (talk) 17:37, 23 September 2011 (UTC)

Cocaine boils at 187C (368F) - anything below that and it condenses out of vapour. If you start with the free base form it stays in the free base form, if you start with a cocaine salt and try to vapourise it I think it decomposes usually.Imgaril (talk) 21:19, 23 September 2011 (UTC)

My main concern was that if individual molecules pick up protons from some environmental source, would they make better nuclei for precipitation? After all, you say you see inconsistency and unpredictability, and it's not the boiling point that is changing. Wnt (talk) 03:36, 24 September 2011 (UTC)

Why does collagen cross-link in scar tissue?

After reading the scar tissue article, http://en.wikipedia.org/wiki/Scar, I came across this tidbit: "Sherratt et al, explain that scar tissue is the same protein (collagen) as the tissue that it replaces,[1] but the fiber composition of the protein is different; he explains that instead of a random basketweave formation of the collagen fibers found in normal tissue,[1] in fibrosis the collagen cross-links and forms a pronounced alignment in a single direction.[1] This collagen scar tissue alignment is usually of inferior functional quality to the normal collagen randomised alignment. For example, scars in the skin are less resistant to ultraviolet radiation, and sweat glands and hair follicles do not grow back within scar tissue. A myocardial infarction, commonly known as a heart attack, causes scar formation in the heart muscle, which leads to loss of muscular power and possibly heart failure. However, there are some tissues (e.g. bone) that can heal without any structural or functional deterioration."

I was wondering what exactly cause the collagen fibers to cross link and possible why the scar tissue replicates itself instead of normal skin since its constantly being replaced. Is there a specific gene for this? — Preceding unsigned comment added by 139.62.167.82 (talk) 20:42, 22 September 2011 (UTC)

I'm not sure that scar tissue does replicate itself. I think the same scar tissue may just remain with you for the rest of your life, similar to adult teeth (if they don't fall off). StuRat (talk) 04:31, 23 September 2011 (UTC)

September 23

Neutrinos

(I've taken the liberty of merging this section to #FTL neutrinos below) Wnt (talk) 17:54, 23 September 2011 (UTC)

Photon Mass?

So, I heard that, even though photons do have zero rest mass, they have relativistic mass due to their motion. Could anyone care to explain this in wide detail? Thanks.186.29.118.196 (talk) 01:45, 23 September 2011 (UTC)

Sure. Energy is mass. As long as a photon has energy, it has mass. QED. See mass-energy equivalence and relativistic mass and rest mass for more details. --Jayron32 02:24, 23 September 2011 (UTC)

Any given photon has EVERY mass value from the tiniest amount above zero to as high as you want to count. The observed mass is purely in the eye of the beholder. (Pun intended.) The electron is different. Each electron can be found at any mass level from the base "rest mass" to as high as you want to count. It all depends on who catches it. Hcobb (talk) 02:34, 23 September 2011 (UTC)

If, indeed there is more than one electron. Maybe, there isn't. --Jayron32 03:15, 23 September 2011 (UTC)

That's it. I'm going to start engraving my initials on all of my electrons to make sure I don't lose any. (Shock!) What size font should I use? Hcobb (talk) 16:17, 23 September 2011 (UTC)

Bode phase plot guidelines

(I'm not sure if this might belong in Maths). I've got a set of Bode plots for a bunch of different circuits. On each one, I am supposed to (by analysing the transfer function) "sketch the Bode amplitude plot asymptotes and phase guidelines". However, I have no idea what "phase guidelines" are, and Google is unhelpful. Does anybody here know? --130.216.55.172 (talk) 03:24, 23 September 2011 (UTC)

Yes! Have a look at how to draw a Bode plot by hand. You need to decompose the transfer function into poles and zeros, usually by factoring the denominator of your transfer function. There are many related techniques to accomplish this - partial fraction analysis is the most common - have you covered any of these methods before?

This section explains the rules of thumb for a phase plot. All these "rules" are derived from more rigorous mathematical analysis (frequency-domain analysis, formally by taking the partial derivative of phase and amplitude of the transfer function with respect to frequency. By writing the function in canonical form, you can just churn out the various asymptotes and estimate the value of the phase for any frequency, without ever having to crunch it computationally. Nimur (talk) 04:32, 23 September 2011 (UTC)

Electra 10-E

Does anyone here happen to know where to find a maintenance manual for the Lockheed L-10 Electra? I'd like to know how to (non-fatally) sabotage and then repair one (for a writing project, of course), and for that I'd like to know how the mixture control linkages are arranged on that aircraft. (Don't worry, I'm not trying to sabotage an actual aircraft, just trying to arrange a malfunction and consequent forced landing as a plot device...) 67.169.177.176 (talk) 06:42, 23 September 2011 (UTC)

Does this relate to your shabbat navigation? What are you trying to do, find some way to kill a kharedi? :p Sir William Matthew Flinders Petrie | ^{Say Shalom!} 24 Elul 5771 06:45, 23 September 2011 (UTC)

No, no, no. The only thing these two questions have in common is that they're for the same writing project. And BTW, didn't I specify that the malfunction and force-landing would be non-fatal? Just for the record, I don't want to kill my characters in this case, but I want to have them force-land in a hostile area after running out of fuel (this condition caused by the mixtures sticking in full-rich position) and barely escape with their lives. Any deaths (if such there be) can wait until later. ;-) 67.169.177.176 (talk) 06:56, 23 September 2011 (UTC)

You could go for the simpler approach: have your saboteur drain some of the fuel pre-flight. According to the forums of people asking the same thing as you, there was one website that had the information, but I can't get it to load. It's [1] in case the problem's on my end. You're probably best off tracking down an enthusiast and asking them. Teshmanesh (talk) 08:10, 23 September 2011 (UTC)

I can't get it to load either, and the reason is that it's members-only. 67.169.177.176 (talk) 20:13, 23 September 2011 (UTC)

I would hope that the pilots would notice the fuel level was lower then expected before it was enough of an issue to cause a forced landing. Googlemeister (talk) 13:23, 23 September 2011 (UTC)

Hmmm, would it work to dump a bunch of golf balls down the fuel intake? (I assume they'd fit?) Wnt (talk) 16:48, 23 September 2011 (UTC)

Nah, draining fuel would be too obvious. Second of all, I want the crew to have to get spare parts upon arrival -- that's supposed to be part of the action too. Finally, when I said "sabotage", that was a figure of speech: I meant that I, as the author, want to create this malfunction, but not necessarily by having an actual (well, fictional) saboteur do it. In fact, the plane doesn't get truly sabotaged until reaching Pakistan, and the malfunction of the mixture controls is planned to happen naturally because of worn-out/defective parts. So obviously there's no way to drain fuel "naturally" (barring a leak in the fuel tanks). As for the golf ball idea, it would simply plug the lines and cause engine failure. And as for the pilots noticing the low fuel level, here's the situation: they're flying nonstop from Addis Abeba to Calcutta, so even after noticing the high fuel consumption, they still hope to make it to Ahmadabad, but run out of fuel over the coast and have to dead-stick into Karachi instead. 67.169.177.176 (talk) 20:12, 23 September 2011 (UTC)

Just remembered from one of those Discovery Channel programs: water in the aviation fuel. See [2] [3] etc. Wnt (talk) 15:09, 25 September 2011 (UTC)

Wouldn't this cause engine failure shortly after takeoff, as opposed to many hours later? 67.169.177.176 (talk) 04:00, 27 September 2011 (UTC)

I should admit, I have no idea. I vaguely recollect reading in some planes there are various different fuel tanks - maybe the pilot switches from one to the other and gets a surprise? Or maybe the water can pool somewhere and only come through later? Waving my hands here. Wnt (talk) 12:44, 27 September 2011 (UTC)

I remember being told during flight training that water contamination usually causes engine failure during takeoff/climb to altitude, not during cruise flight. As for the Electra, it has four wing tanks and ten fuselage tanks with a total capacity of roughly 1100 gallons, and the normal procedure is to draw fuel from the fuselage tanks first (because they mess up the trim) and then switch to wing tanks. Anyway, water in the fuel is a "no spares required" emergency (provided that the pilot can safely make a dead-stick landing -- and in my case she indeed can with her level of expertise), and I want the crew to have to get spare parts. 67.169.177.176 (talk) 23:38, 27 September 2011 (UTC)

Do you disagree?

The law which prevents doing anything in the past is the law which states a distance above zero can not be traveled in zero or less time rather than the distance light travels in unit time can not be exceeded. In other words light might get somewhere faster than sound and warn of an explosion faster but that does not mean light (compared to sound) can send information into the past and to do that requires time reversal not speed faster than light. --DeeperQA (talk) 07:35, 23 September 2011 (UTC)

If I understand what you're getting at, see tachyonic antitelephone.

Summary: Sending information faster than the speed of light in your frame of reference doesn't send it backwards in time, in your frame of reference. But it does send it backwards in time in some other frame of reference.

If the mechanism by which you can send the information faster than light is frame-invariant and isotropic, that is if it works the same in everyone's frame of reference and in all directions, then you can combine forces with someone moving quickly with respect to you, to send information backwards in time even in your own frame of reference.

It takes two steps: You send the information to the other party. This takes positive time in your frame, but negative time in his. He repeats the trick, sending it backwards in time in your frame. --Trovatore (talk) 07:53, 23 September 2011 (UTC)

This can be demonstrated using sound in the place of light as the fastest possible means of communication and light as the newly discovered faster than fastest method. What I want to confirm is that the true basis for not being able to go back in time is that no distance can be traveled in zero or less time which time travel or travel to an earlier time would require. --DeeperQA (talk) 10:49, 23 September 2011 (UTC)

No, the speed of sound and the speed of light are fundamentally different. The laws of physics have the same form in all inertial frames of reference. The speed of light is the same constant value in all inertial frames of reference. The speed of sound is not the same constant value in all inertial frames of reference. The speed of light is special.

It isn't necessary to have instantaneous travel, or "faster than instantaneous" travel, in order to travel backwards in time. If something looked like it's travelling faster than the speed of light in some inertial frame of reference, then there exist other inertial frames of reference in which it would look like it's travelling backward in time. All inertial frames of reference have an equally valid perspective, so travelling faster than the speed of light is equivalent (in a different, but equally valid inertial frame of reference) to travelling backward in time. Red Act (talk) 11:49, 23 September 2011 (UTC)

I think it's important to emphasize the two-step nature of the process. In one step, you get information travelling backwards in time in someone's coordinate system. Who cares? That's just a number (the time coordinate) going down.

It's not actually interesting unless the information can be sent back to an earlier time at the same point in space; that is, unless you can get a causal loop. For that you need more than a coordinate system. That's where the two-step process comes in. --Trovatore (talk) 19:08, 23 September 2011 (UTC)

Unfortunately going back in time at the same place in space implies that events which happened there like burning a candle can be reversed since the same point in space can be occupied by only one object at any given time. --DeeperQA (talk) 16:45, 24 September 2011 (UTC)

exceding speed of light

(Merged to #FTL neutrinos Wnt (talk) 17:57, 23 September 2011 (UTC) )

To whom who knows about genomic databases

a. Where can I find genomic databases, to the level of the (DNA) bases ? In particular, I need the human one and that of SV40 virus.

b. Where do I find, there or elsewhere, details regarding the integration sites of SV40 in the human genome ? Thanks, BentzyCo (talk) 08:33, 23 September 2011 (UTC)

Looks like you will need to learn how to navigate either the NIH's genome database or the corresponding UK/EBI genome database. You can get the complete SV40 genome sequence here. The human genome is considerably larger, but you can also download it by following links from either of the sites I gave. Another great resource for visualizing the genome is the UCSC Genome Browser, which provides a user-friendly interface. With regard to question (b) you can do a Google Scholar search on "SV40 human genome integration sites" which yields a few promising looking hits about mapping SV40 sites in the human genome. --- Medical geneticist (talk) 10:18, 23 September 2011 (UTC)

Remote controlled lighting etc.

Typically, I see remote controlled lighting and music systems (as simple as a remote control or merely button somewhere else) sold as part of high end systems. But how difficult would it be to find something to attach to a light and control it from the other end of the room; how costly? Grandiose (me, talk, contribs) 09:35, 23 September 2011 (UTC)

Not that expensive on cost of parts eg http://www.maplin.co.uk/remote-control-lamp-holder-with-dimmer-339239?c=froogle&u=339239&t=module - that's a dimmer. I've seen remove control plugs (4 sockets) selling for about £15. Switching relays can be very cheap eg http://www.maplin.co.uk/ultra-miniature-high-power-mains-relay-218688?c=froogle&u=218688&t=module (this is overspecced for light) - as for the remote control system - I don't know prices - but electronics as well established and simple as this is going to tbe dirt cheap.Imgaril (talk) 10:38, 23 September 2011 (UTC)

I have a remote control outlet that came with my garage door opener. I believe the idea is you use it to turn on a light (plugged into the controlled outlet) when you arrive home at night. StuRat (talk) 15:41, 23 September 2011 (UTC)

I bought a power bar that came with a remote control a year or so ago. The remote allows the outlets on the power bar to be turned on and off. It was marketed as a "green" thing, so that you could unpower your entertainment system when you are going out (preventing consumption of energy in standby mode). Caveat: the remote didn't work well for me. After a month or so, I could no longer reliably turn the power on and off from any significant distance. --Srleffler (talk) 16:28, 26 September 2011 (UTC)

Wifi and cell-phones on board of a plane

Cell-phones are (or were) banned on flight, however, I don't remember any wifi prohibition. Although I don't believe that either could interfere with flight instruments, why was the former banned and the latter not?Quest09 (talk) 11:17, 23 September 2011 (UTC)

Because cellphones are older and is responsible for the persistant myth. Average people aren't smart enough to know that it uses the same technology, so the myth hasn't carried through. Plasmic Physics (talk) 11:45, 23 September 2011 (UTC)

The onboard wi-fi system is fully tested for safety issues, and presumably the aircrew have some control over it, which is not the case with cell phone signals. See this fact sheet from the FAA.--Shantavira|^{feed me} 11:59, 23 September 2011 (UTC)

I didn't mean that "WiFi in the Sky" system, just a plain laptop with WiFi on (even if there were no hotspot to connect to). Airlines never complained, never banned it, never went on the completely secure side. Quest09 (talk) 12:42, 23 September 2011 (UTC)

The last time I was on a flight, which was admittedly about two years ago at least, the stewardess asked for all electronic devices to be turned off. Dismas|^(talk) 12:51, 23 September 2011 (UTC)

Does that include pacemakers? Plasmic Physics (talk) 14:31, 23 September 2011 (UTC)

Don't WiFi adapters transmit at a lower effect and use other wavelenghts than cell phones? Sjö (talk) 13:14, 23 September 2011 (UTC)

The norm I believe is to turn off all electronic devices before take off. Certain devices can be switched on again when the aircraft reaches cruising altitude. They should be switched off again whenever an instruction is given, which includes before landing. IIRC we've discussed this before. I believe the reason is because of the greater risk of things going wrong, not just of any minute risk of interference but also because the devices themselves are a hazard as they can go flying. It also reduces the number of distractions so they are more likely to have your attention if something goes wrong (the onboard entertainment systems are under their control although you could be reading or sleeping with ear muffs). As Sjö mentions wifi which uses the public frequencies generally transmits at a far lower power (as they are limited by the regulations surrounding unlicensed devices) than mobile phones which use licenced frequencies (see dBm and remember mobile phones on planes will at least briefly likely to operate at max power as they attempt to find a network).

Wifi devices also don't tend to have the risk of causing problems for stuff on the ground because of the low range (it's commonly suggested one of the reasons to limit mobile phones on planes is because of the effect on base stations of the rapidly moving transceivers).

And to state the obvious, one of the biggest differences is before smart phones and in the absence of microcells on planes, there was little use to mobile phones on planes other then the silly games and checking or composing existing messages (except if you did happen to get a signal from the base stations but as mentioned that would usually not be something the mobile operators liked). In this smart phones era, most have a flight mode. There were of course some early smart phones as well as semi-smart phones which support J2ME apps and have cameras and music or other media without a flight mode but I don't know how often this was really an issue. Laptops on planes have plenty of uses without wifi including for the higher end clientele and most people would have little idea how to turn off their wifi. So telling people to turn off their mobile phones was often an acceptable tradeoff far less so than telling people to turn off their laptops, and telling them to they can use their laptops but should turn off their wifi is a recipe for confusion.

Nil Einne (talk) 14:41, 23 September 2011 (UTC)

In case I didn't say it before, the ban is a result of a myth. There is no justifiable reason for issueing such a ban. Plasmic Physics (talk) 14:31, 23 September 2011 (UTC)

There are two justifiable reasons. First, there has been recorded coincidences between aircraft control anomalies and use of electronic devices. Second, many people strongly support the ban simply to keep people from using cell phones on an airplane. -- kainaw™ 14:33, 23 September 2011 (UTC)

I would be interested in seeing some of the references on the recorded coincidences you mention Kainaw. Googlemeister (talk) 16:12, 23 September 2011 (UTC)

This is Wikipedia. See mobile phones on aircraft. Make sure you don't incorrectly translate "coincidences" as "causes". -- kainaw™ 16:19, 23 September 2011 (UTC)

Not sure about your experience, but back in the days before in-flight wifi, I clearly remember flights where they instructed us that devices with active wifi connections could never be used on planes. In general, it is still usually the case that all electronic devices must be turned off during take-off and landing. Dragons flight (talk) 16:36, 23 September 2011 (UTC)

I can understand why they would want you to turn off anything that transmits communications, especially during takeoff and landing. What I don't see is why they also make you turn off non-transmitting devices. I have a rather irksome fear of flying that usually only bothers me during takeoffs and when the flying is in what I would call "a hazardous situation" (like the one time a plane I was on had to fly right in between two thunderstorms). One of the things I have found to be an immense comfort during such situations is watching the plane's altitude, speed, and location on my GPS receiver (I'm not sure, but I think it comforts me because I would be able to see abnormal changes in them). I've always wondered why I'm not allowed to use a GPS receiver given that it doesn't transmit any signals and thus couldn't interfere with the aircraft. Ks0stm ^{(T•C•G•E)} 16:51, 23 September 2011 (UTC)

[4] mentions a case where the navigational system of a Boeing 737 stopped working but started again after a passenger was asked to turn off his hand held receiver. [5] (from 1997) notes possible interference from AM/FM radios and CD players Nil Einne (talk) 17:33, 23 September 2011 (UTC)

I suppose the problem is that many receivers also accidentally transmit on another frequency and this accidental transmission could, just possibly, with unfortunate positioning and inadequate shielding, just possibly interfere with some over-sensitive equipment on the plane. I can't imagine how a GPS receiver alone (without other functions) could possibly transmit anything measurable beyond a few centimetres, but the aircraft staff don't have the expertise or equipment to check that the receiver is not combined with some other transmitting equipment. Dbfirs 09:14, 24 September 2011 (UTC)

All, or at least nearly all, radio-frequency receivers also emit radio-frequency signals to some extent. This is because they use superheterodyne technology, generating a signal that they allow the incoming wave to interfere with, and measuring the beat of the combined signal. The power, I expect, is rather low (well, it would have to be; my GPS receiver will run for 24-48 hours continuously on two AA batteries) but I can't guarantee a priori that it's impossible for it to interfere with airline equipment. I'm pretty skeptical though.

My cynical theory about why some airlines don't want you to use the GPS is that they don't want you to have a record of the plane's track, in case that could somehow be useful to you in a lawsuit. A lawsuit about exactly what, I'm not really sure. --Trovatore (talk) 09:23, 24 September 2011 (UTC)

About missing an important business meeting because the flight was diverted? 67.169.177.176 (talk) 19:19, 24 September 2011 (UTC)

Definitely NOT that. Airlines do not guarantee their service, in the fine print it says that they can't beheld liable (above the cost of the ticket) for any delays or cancellations, even if it is their own fault. If you could sue airlines for being late, they would have all been out of business a long time ago. Skeptoid did an episode on cell phones in airplanes. I'm a fan of skeptoid but I have to say, Brian's Libertarian outlook colors this episode more then most, I think the commentary is more just as interesting as the episode. Vespine (talk) 22:41, 25 September 2011 (UTC)

Airlines, definitely, can be held liable for being late, even if it's not their fault (!). They might not be liable of any damage caused by their poor service, but they have to compensate you up some number of hours of delay. (at least in the EU). Wikiweek (talk) 19:12, 26 September 2011 (UTC)

Yes, sorry I should have been more specific, yes they can be liable for things like transfers and hotel accomodation and incidentals arising from delays; what I specifically meant is that you can't sue them for damages (as you state), like "if you miss a very important meeting" and it costs your company millions of dollars, as the post above mine seems to suggest. Vespine (talk) 22:34, 26 September 2011 (UTC)

It's worth remembering the Ks0stm was talking about the ban on all electronic devices, including GPS receivers, during take off and landing which is different even if related to what Trovatore is talking about. As I mentioned above, I believe on of the possible reasons for the ban is because many electronic devices make good missiles so it's preferred if they are stowed during such criticial times. (Of course there's also concern about possible interference.) From [6] it seems the majority of airlines allow GPS receivers during the flight (excluding when it's disallowed by the pilot). Also some phones allow GPS in flight mode [7] [8] [9], I wonder whether they actually mention the ban on GPS during the flight and if not, whether someone using such a phone is likely to appreciate the ban. Speaking on both the ban during criticial times and a general ban, the possibility of intereference may be tiny but I don't think it's that surprising some some airlines would be concerned since the risks to them from problems can be rather severe. In other words, IMO they're far more likely to be concerned about lawsuits if one of their planes crashes (although yes I'm aware there are various laws limiting their liability). As I also mentioned, they are far more likely to be willing to take the risk when they can see an advantage to them, this is there for laptops (although again not enough for them to allow them during takeoff and landing) but with GPS receivers it's far less obvious since it's only the geeks and those like the Ks0stm who are likely to care much. Oh and as for people like Ks0stm, there is the option of the inflight entertainment system which often shows info from the planes internal navigation system, even for more budget airlines some may have it as an optional extra (and if it does cost which one do you think they'd rather you use?). As someone mentioned, it's also difficult for the flight attendant to know if the device is an active transmitter (as opposed to something which has some minor incidental transmissions), modern GPS receivers often have bluetooth and some even have a mobile data connection. There are of course those reports of apparent interference (or problems that were resolved when the devices were switched off) which don't help. I couldn't find any more specifics on the GPS case (I did look before my first post) so the details aren't clear but of course such stories are likely to raise concern (and some of the people making the decisions probably don't know all the details either). BTW, it's worth remembering as for the hypothetical advantage to the passenger having their own GPS track, it would only seem to be an advantage if the passenger either wouldn't know to (because they're not aware of the issue), or wouldn't bother to (because of cost or whatever), or wouldn't manage to (i.e. a court wouldn't allow it) to subpoena the airline's own track of the flight which is the obvious recourse if you want a track. Well unless you come up with conspiracy theories involving either an inaccurate or a modified track from the airline which seem a little far fetched. Nil Einne (talk) 11:46, 27 September 2011 (UTC)

Heavy metal concentration

How can I measure the concentration of heavy metals in a water sample? --70.134.53.27 (talk) 14:54, 23 September 2011 (UTC)

Mass spectrometry, I think is the usual way. Looie496 (talk) 15:05, 23 September 2011 (UTC)

X-ray fluorescence is also usual, as can be X-ray absorption spectroscopy. There are quite a few ways in fact. You really need to search and narrow the field "heavy metal water determination" is a good start, as will be "heavy metal water quantitative analysis". It may also depend on the expected concentrations what methods are best.Imgaril (talk) 16:11, 23 September 2011 (UTC)

Here I was hoping this was a question about doing homework while listening to Opeth. Vespine (talk) 22:42, 25 September 2011 (UTC)

Seriously?

I just saw something that almost made me vomit: a woman with facial hair. I'm not trying to sound mean, but it was disgusting and odd. Earlier today, I saw a young woman with hair on her chin. How is it possible that a female can have facial hair? Is something wrong with her hormones? That's not normal. B-Machine (talk) 15:11, 23 September 2011 (UTC)

Yes, there's something 'wrong' with her hormones: she has too many of the masculine kind. Wikiweek (talk) 15:14, 23 September 2011 (UTC)

All women have hair on their faces. See Facial_hair#In_women. I'm sure at least some of them also find your appearance "disgusting and odd" (I'm not trying to sound mean). Perhaps this person is a female with a hormone imbalance. Perhaps she is intentionally pursuing hormone therapy as a part of gender reassignment. Perhaps she was born with male sex organs, but lives and presents the female gender. Get used to the fact that human bodies come in magnificent variety, and we don't all share your particular set of social norms and gender norms. SemanticMantis (talk) 15:28, 23 September 2011 (UTC)

Also see hirsutism, which explains this rather better.--Shantavira|^{feed me} 15:29, 23 September 2011 (UTC)

Many women have some visible facial hair, or would, if they didn't remove it or bleach it. So, the unusual thing about women who retain visible facial hair isn't that it grows, but that they choose not to do something about it. StuRat (talk) 15:35, 23 September 2011 (UTC)

What is it about American society (and others?) and phobia about hair on women? I mean, even hair on the legs and under the armpits, where it's supposed to be in the sense that most women have it, some kind of fashion junta treats as if unfeminine. Is this unattractive? How did such a phobia ever get started? Wnt (talk) 15:37, 23 September 2011 (UTC)

It started in the 1920s if I recall. Googlemeister (talk) 16:10, 23 September 2011 (UTC)

In general, regardless of society, women are competitive when it comes to beauty. One woman claims to be more beautiful because she shaves her legs. Another says she is more because she shaves her armpits. Another claims she is more beautiful because she shaves her pubic hair. It doesn't need to be hair. It could be skirts in the 60s... Mine's shorter. No, mine's shorter. No, mine's shorter. It could be lace in the 80s... I got lace braided in my hair. I got it on my wrists. I got lace gloves. I got lace legwarmers. In none of these cases are men asked what is beautiful, but all men are blamed for all the "work" required to become beautiful. -- kainaw™ 16:45, 23 September 2011 (UTC)

I've heard it suggested by a psychologist friend that the fashion trend towards no body hair on both males and females is a trend towards paedophilia, i.e. a preference for an impossible look that only exists before puberty. Please discuss. HiLo48 (talk) 20:50, 23 September 2011 (UTC)

...with references. —Akrabbim^talk 21:07, 23 September 2011 (UTC)

That notion is rubbish. Also, wikipedia is not a discussion board. SemanticMantis (talk) 21:08, 23 September 2011 (UTC)

I could turn it into a question... It's a more rational position than vomiting upon seeing hair on woman's face. Whatever would P T Barnum have done without bearded ladies? HiLo48 (talk) 08:36, 24 September 2011 (UTC)

See also: Bearded lady. Mitch Ames (talk) 06:11, 24 September 2011 (UTC)

'Almost made you vomit'? *rolls eyes* I bet seeing a vagina with hair would make you faint. -- Obsidi♠n Soul 07:40, 24 September 2011 (UTC)

Before you people start accusing me of something I'm not, let me clarify what I did here: I was joking. I didn't really see a woman with facial hair. I was bored, so I made this up to see what kind of reaction I would get. Very funny. And as for the accusations, no, I'm not a pedophile (are you sick?), no, I'm not gay, and yes, I like a hairy vagina. I prefer women to have hairy vaginas over shaved vaginas. B-Machine (talk) 22:57, 24 September 2011 (UTC)

If you feel it's funny to make up a question, feel free to also enjoy the attributes we make up to apply to you. HiLo48 (talk) 23:01, 24 September 2011 (UTC)

Calm down, man. I was joking. Can't you take a joke? B-Machine (talk) 23:25, 24 September 2011 (UTC)

Strictly speaking, vaginas typically don't have hair, vulvas do. Mitch Ames (talk) 12:16, 26 September 2011 (UTC)

Whatever the troll's intentions, I am surprised no one mentioned drag kings. I personally know a rather militant lesbian who glues clippings of pubic hair to her chin as a form of transgressivism. I find it kind of sexy in her case. μηδείς (talk) 01:54, 26 September 2011 (UTC)

FTL neutrinos

Is it true? What are the implications for physics? --70.134.53.27 (talk) 15:27, 23 September 2011 (UTC)

Presumably you're interested in recent announcements by CERN, as reported in this BBC article - Speed-of-light experiments give baffling result at Cern? Here's the official press release, OPERA experiment reports anomaly in flight time of neutrinos from CERN to Gran Sasso. If you're interested in the implications, consider reading the papers linked from that, or watching the broadcast seminar, featuring a QA session.

Here's the pre-print, Measurement of the neutrino velocity with the OPERA detector in the CNGS beam. The claim is that tau neutrinos arrived 60.7 ns earlier than they should have, after a flight of 730 km. Unfortunately, as always, high energy physics is much more complicated than that: the tau neutrinos did not fly the entire distance; they are produced somewhere en-route out of muon neutrinos. If you want to understand the details, ... the research is outlined in the paper and websites.

In my opinion, the best way to assess the "implications" of the experiment is first to establish an understanding of the sources of error, and the methods used to control those errors. As a skeptical scientist, I believe it is more probable that a large team of physicists measured time and distance incorrectly, as a result of invalid statistical data processing; but it's also possible that the behavior of 15,000 neutrinos did actually violate all other known physical observations. After you review the data and experimental presentation, and if you believe all experimental errors are accounted for, the next step would be to undertake an explanation for the speed. Finally, you could proceed to derive physical consequences that follow from this apparent violation of the "speed limit." Nimur (talk) 16:47, 23 September 2011 (UTC)

I have to correct you on the tau neutrinos - as far as I know only a single tau neutrino has so far been seen at the OPERA detector (I remember reading that they expect a total of only 11 tau neutrinos over the several years of the research project). Many more muon neutrinos have been detected, and the recent preprint on arXiv states that there were "about 16000" neutrino events detected by OPERA. And since we know about neutrino oscillation, we actually shouldn't talk about tau neutrinos, muon neutrinos and electron neutrinos but about ν₁, ν₂ and ν₃; then e.g. beta decay creates a certain superposition of the 3 neutrinos characteristic for the electron, and there is another superposition for the muon and another one for the tauon. Icek (talk) 18:48, 23 September 2011 (UTC)

(Merged from "Exceeding the speed of light" above - Wnt (talk) 17:59, 23 September 2011 (UTC))

[10] Now i am not a science guy but nothing could exceed the speed of light right?but than whats this? — Preceding unsigned comment added by 175.110.242.217 (talk) 08:10, 23 September 2011

(Merged from #Neutrinos above - Wnt (talk) 17:55, 23 September 2011 (UTC))

Sorry to be the first cranky neutrino question after the CERN release of data, and this is probably a very stupid question. Is there a good reason to think that neutrinos must have a positive mass? I'm sure there must be, but I can't see it in our article neutrino. Our article says that neutrinos must have a non-zero mass, and that our main source of information on the masses depends on the squares of the masses (if I'm reading that right)? Please disappoint me with a reasonable explanation, or I'll be too excited to sleep :P 86.164.78.26 (talk) 21:59, 22 September 2011 (UTC)

Okay, we need to distinguish three different things here:

1. Negative mass. This has nothing directly to do with tachyons. Tachyons don't have negative mass.
2. Negative mass-squared (also called imaginary mass) in classical relativistic particle theory. Classical particles with negative m² go faster than light.
3. Negative mass-squared in relativistic field theory. This is mathematically related to the classical particle case, but the practical upshot is very different. In a field theory, the mass-squared behaves like a spring constant—if you think of the field as a rubber sheet then the higher the mass, the more resistant the sheet is to stretching. If the mass-squared is negative, then not only does the sheet not resist stretching but it actually pushes in the same direction you pull it, leading to an exponential feedback loop if the field is even slightly disturbed. The only way for this to make any sense is if there's a counterbalancing effect that comes into play at larger amounts of stretching, so the sheet only stretches to the point that these opposing effects balance each other. This actually happens in the Standard Model with the Higgs field, and is called tachyon condensation. The result is a field that behaves for practical purposes like it has a positive mass-squared.

I know nothing about this new announcement from OPERA except that they claim to have found actual superluminal propagation. This sounds like the second case above, but modern particle physics is built on quantum field theory, where the second case is irrelevant; "tachyons" don't propagate superluminally in quantum field theory. So, if this is real, it would pretty much require rebuilding modern particle physics from the ground up. It could be a quantum gravity effect, and this might give a hint as to the right theory of quantum gravity. But more likely it's experimental error. -- BenRG (talk) 23:05, 22 September 2011 (UTC)

Might you be referring to the Reuters article that they are travelling faster than light? I just got it linked to me. Excitement should be withheld as it's almost certainly an error, but honestly, given the fact that the scientists aren't crackpots, my heart did rush a little when I got to the end of the article without indication that they're crackpots. SamuelRiv (talk) 23:21, 22 September 2011 (UTC)

[11]. Nil Einne (talk) 00:54, 23 September 2011 (UTC)

Here's the preprint. The official announcement doesn't happen until 4PM Friday in Geneva (13 hours from now). As that blog post says, it's way too early to get excited about this. -- BenRG (talk) 01:01, 23 September 2011 (UTC)

Note from some reports [12] [13] it appears that while the team think there is a possibility their results are correct and would be confirmed by independent replication and that would obviously be their preference, they think the more likely explanation is there's an error they didn't notice. Some further comment on the Sn1987A neutrinos [14] Nil Einne (talk) 01:08, 23 September 2011 (UTC)

The news reports on the report said the neutrinos travelled through the Earth faster than the speed of light in vacuum. What would be the speed of light through dirt and rocks, ignoring the fact that dirt and rocks would absorb the light? Edison (talk) 14:13, 23 September 2011 (UTC)

Can one talk about the speed of light through totally opaque media? Whatever the answer is, it's not faster than it would be a vacuum, so how would that get you anything? --Mr.98 (talk) 19:29, 23 September 2011 (UTC)

opacity is not an absolute characteristic, it is relative. Even dirt and rocks allow EM to propagate through it, albeit not very well, but there is still a "speed of light". —Akrabbim^talk 19:44, 23 September 2011 (UTC)

Well, that's true. I was thinking only about visual frequencies, which are not very penetrative, but of course there are lots of forms of EM. But either way, it's going to be slower than in a vacuum. --Mr.98 (talk) 22:57, 23 September 2011 (UTC)

http://xkcd.com/955/. Deor (talk) 14:36, 23 September 2011 (UTC)

Perhaps they pass through the 8th dimension. Wnt (talk) 17:32, 23 September 2011 (UTC)

Just as likely as The 5th Dimension. Edison (talk) 17:45, 23 September 2011 (UTC)

Ah, but the neutrino oscillation overthruster allows it to tap into the dimension of space inside solid matter.^[15] ;) Wnt (talk) 18:07, 23 September 2011 (UTC)

Perhaps even the Sixth dimension? Hot damn! SamuelRiv (talk) 18:19, 23 September 2011 (UTC)

All kidding aside, I almost wonder if there could be something to this idea. The passage with solid matter is what distinguishes these neutrinos from the ones from distant supernovae. Now a standard force like electromagnetism, so far as I understand from a previous discussion here, can be modeled as an extra dimension, a bending of space just like gravity. But neutrinos ignore this force, so they shouldn't be slowed by the Earth's optical refractive index. Is it conceivable that some obscure force acting on the neutrino could have a different kind of refractive effect, where passing through solid matter actually makes them go faster than passing through empty space? As if there were some other dimension in which space could be bent, but one which is bent in the vacuum, but which can be straightened out by matter? (Almost surely this is bogus - yes, I know that calculation is quite indirect and errors or unspectacular physics oddities could slip in in many places, but if we want to imagine a way to explain the result if it were real...) Wnt (talk) 02:35, 24 September 2011 (UTC)

Err, don't most neutrinos detected go through a lot of solid matter? My understanding is that most neutrino detectors are deep underground to avoid cosmic ray contamination. I don't think passing through matter (which is an imprecise way of saying "didn't interact with any matter", right?) is really the distinguishing factor here. The distinguishing factor is that these guys claim to know when they created the neutrino, precisely, which is exactly what we don't know with regards to supernovae or stars. Right? --Mr.98 (talk) 04:45, 24 September 2011 (UTC)

While the neutrinos measured from SN 1987A did travel a relatively long path through the Earth (if you look at the 3 neutrino detectors mentioned in the article, they are all so far north that the supernova couldn't have been visible from their position at any time of day; and for neutrino detectors with direction sensitivity the neutrinos from above are usually discarded as far as I know, because there is more background of muons being created when cosmic rays hit the atmosphere), that wouldn't have much effect on the average speed from the Large Magellanic Cloud to the Solar System.

Maybe it is some kind of near-field effect like it also occurs in electromagnetic dipole radiation, but that's just something that came to my mind now without any calculations to back it up. In any case, if information really travels faster than light, then causality is broken or special relativity is wrong. Icek (talk) 13:26, 24 September 2011 (UTC)

The world's observatories did a great job on some of these supernovae, but 60 ms precision is surely beyond them! However accurately the neutrinos speed was measured relative to their travel time to Earth, any small variation within the Earth would have gone unnoticed, I would say.

It doesn't break causality or special relativity to go faster than the speed of light, if that speed is measured in water, glass, etc. Only the speed of light in vacuum counts, because it is the fastest and most fundamental speed. But what if it isn't? What if there's some slightly faster speed of light that applies in this case? Wnt (talk) 14:27, 24 September 2011 (UTC)

Of course I mean the speed of light in vacuum. Assuming that the Lorentz transformation is correct, then you could indeed send a message into your own past (you only need a neutrino emitter in the vicinity of the neutrino detector which receives the information from the neutrino detector; the neutrino emitter has to be moving at a very high speed away from the original neutrino source and emit neutrinos towards a detector close to the original source; from the rest frame it will look as if the neutrinos from the fast moving emitter are moving backwards in time).

If you think there is some slightly faster "speed of light" applying in this case (because there is actually no way that light moves in a straight line from CERN to Gran Sasso?), then what would happen if you build a long straight tube from CERN to Gran Sasso? You could repeat the Michaelson-Morley experiment with light sent through the tube and with the interferometer traveling at various speeds (obviously there are many practical problems with these experiments, but in principle they can be done). Would the neutrinos travel slower because the tube exists, or what else would happen (things could be arranged so that the measured neutrinos would move through the soil close to the tube, but not through the vacuum inside the tube)? Icek (talk) 14:58, 24 September 2011 (UTC)

To disclose fully, I don't know (but ought to) whether the Lorentz transformation or electrical formulas involving c would be noticeably inaccurate if they should be using the hypothetical super-fast c accessible to neutrinos passing through solid matter, but instead are using a somewhat slower measure of light passing through a vacuum. On the other hand, since I'm just handwaving anyway, for all I know the neutrino path might be one of these straighter-than-straight non-Euclidean geometry things in 11 dimensions. Alas, my imagination has gotten beyond what I know. But I'm skeptical that the Michaelson-Morley experiment applies, because you can't use it to come up with anything important when a medium slows the speed of light, so why would you be able to use it if it speeds it up? Wnt (talk) 03:41, 25 September 2011 (UTC)

Nature News has printed the extra dimension idea (citing a professor emeritus......)^[16] but without the assistance of Buckeroo Banzai they still have failed to make the connection with the space inside solid matter. ;) Wnt (talk) 17:00, 25 September 2011 (UTC)

—Wow, only on weekends!  :) All kidding aside, I think that this discovery may actually be slightly less revolutionary than it first appears.

It was always my understanding (please feel free to correct me, if I err) that Albert Einstein theorized that the speed of light in a vacuum was a universal speed limit, by claiming that as something approached light speed, the flow of time—relative to it—would proportionately slow down, or "dilate." By extension, as said object hit light speed, time would stop, rendering any further acceleration (speed / time) impossible. There are two "gaps" in this hypothesis, however.

1.) Einstein himself never said that something couldn't travel faster than light speed if it were ALREADY moving that fast when it was created.

2.) Niels Bohr (to whom we owe the current atomic model, along with Ernest Rutherford) in one of his arguments with Einstein, even went so far as to propose that a particle travelling at, say, 9/10 of light speed, may even be able to "quantum jump" to 1-1/10 of light speed.

Long story short, I don't believe AT ALL that Einstein was mistaken in his theories; rather, CERN may have just confirmed the existence of the very first Tachyon! Pine (talk) 21:00, 24 September 2011 (UTC)

As I said above, tachyons are violating causality. For a tachyon at speed v you only need a tachyon emitter traveling faster than ${\frac {2v}{1+{\frac {v^{2}}{c^{2}}}}}$ (a speed which is below c). Send a tachyon from a stationary tachyon emitter to a tachyon detector traveling along the moving tachyon emitter. When the moving tachyon detector detects a tachyon, the moving tachyon emitter shall emit a tachyon back at the stationary tachyon emitter, and it will arrive there before the original tachyon was emitted, as can be calculated using Lorentz transformations. Icek (talk) 22:13, 24 September 2011 (UTC)

This is a really problematic argument because it makes an assumption about emitter vs receiver that isn't even logically coherent. It assumes that you can always choose to emit a tachyon going "forward in time", where "time" is for some reason the coordinate time of your rest frame. I see no reason why the world should work that way in any case, but a more serious problem is that the tachyon's worldline can go forward in time with respect to the rest frames of both endpoint labs, i.e., it can be "emitted" on both ends by this definition. Obviously this makes no sense from a causality perspective. The most obvious solution is to impose some kind of global Lorentz-violating causality relation, perhaps coincident with the rest frame of the cosmic microwave background. But if you do that then of course your procedure for sending a signal into the past no longer works. -- BenRG (talk) 22:54, 24 September 2011 (UTC)

Special relativity, as it existed in 1905, could accommodate faster-than-light travel in a certain limited sense, if you didn't worry too much about causality. But a lot has happened since then. As I said earlier in this thread, quantum field theory, which is the foundation of modern physics, can't deal with faster-than-light particles. It does have a concept of "tachyons," but they don't go faster than light, despite the name. If this phenomenon is real then it undermines the foundations of quantum field theory and everything is potentially up in the air, even basic concepts like "mass" and "speed". -- BenRG (talk) 22:54, 24 September 2011 (UTC)

I'll just note a disagreement with the idea that FTL must equal time travel - this assumes that relativity always applies, but FTL is clearly beyond relativity anyway. I am rather fond of the idea that an absolute rest frame can be defined at any point in space; most of the matter we see stays within 0.1c or so of this rest frame. Provided that under hypothetical new laws of physics an FTL particle is never permitted to move backward in time relative to the locally defined rest frame, it could never possibly move in a complete closed circle in spacetime. Of course there is no shred of evidence for this, but we cannot dismiss FTL a priori based on time travel paradoxes. (And it is also very much possible that time travel is possible, and the single past and the single future simply reconcile their fates as best they may) Wnt (talk) 03:48, 25 September 2011 (UTC)

Here's a good readable summary of the experiment, by Chad Orzel. -- BenRG (talk) 23:17, 24 September 2011 (UTC)

Nature News has a lot of people coming out of the woodwork, you might say.^[17] I am curious about one poster there who has spun a Dutch blog about it^[18] citing an obscure quantum theory of gravity by Vasily Yanchilin. I don't understand the argument but it sounds juicier than its hundred rivals. Wnt (talk) 03:25, 27 September 2011 (UTC)

Relative risk of tuna

There's a warning that canned tuna may contain mercury. However; beef, pork, and chicken definitely contain unhealthy substances like animal fat and cholesterol, in greater quantities. So, my question is, what's the total relative health risk of all of those ? That is, are you likely to live longer by choosing canned tuna over those other options, and ignoring the mercury risk ? (Obviously there are even healthier alternatives, but I don't want to discuss those here.) StuRat (talk) 15:27, 23 September 2011 (UTC)

(comment - I don't think I properly answered your question below - the issue is that - mercury tends to send you mad, not necessarily put you in an early grave)

I read up about this a few months ago when I was feeling quite peckish towards tuna salads, tuna sandwiches etc..

Firstly different tunas have different quantities of mercury. Secondly other seafish and creatures are just as bad, some are worse -halibut, shark etc can be problematic to name just two. Also some crustacae have issues like this, whilst others are relatively metal free.

Also note that mercury is not the only 'toxin' - cadmium is another problematic element- and there are several others.

I'm concerned that what I will say next will be construed as medical advice but here goes - 1 tin of tuna a week should not be a problem (according to the accepted limits for mercury intake) eg - 1 tin a day in the long term will (or is likely) to start to affect you .. that could be as minor effect as friends noticing that you are "acting a bit strange" - people really do start to go a bit loopy if they get too much.

A shame because I find it absolutely delicious.

Also see Mercury in fish, this table is usefull too http://www.fda.gov/food/foodsafety/product-specificinformation/seafood/foodbornepathogenscontaminants/methylmercury/ucm115644.htm Imgaril (talk) 16:20, 23 September 2011 (UTC)

A lot of it comes down to who you are, too. Young children eating tuna is a big deal, someone in their 50's isn't going to be affected by trace amounts of methyl mercury. Cholesterol is actually healthy in proper amounts, some people get paradoxical cholesterol problems by not taking in enough (the body isn't always sensible with synthesis), and fat is necessary at a basic level due to fat-soluble vitamins. The fat in fish is actually deficient in certain diets and may actually be healthy. Certain foods can be very bad for certain people (e.g. phenylketonuria because I'm staring at a can with a warning label, food allergens are another very situational problem). Is eating tuna or pork "better" is an impossible question, whether it's better for you is an answerable one, but it's basically medical advice. If you're seven years old, tuna should be beaten away with a very large trout. If you're seventy, it might be the ideal thing for your diet. SDY (talk) 21:38, 23 September 2011 (UTC)

In 22 documented cases, pregnant women who consumed mercury contaminated fish showed mild or no symptoms but gave birth to infants with severe developmental disabilities. Cuddlyable3 (talk) 23:00, 23 September 2011 (UTC)

Out of curiosity, does anyone know the mechanism of how the Hg causes damage? Does it block a specific reaction? The mechanism section of our articles on Mercury poisoning and Minamata disease give no information? SDY (talk) 00:32, 24 September 2011 (UTC)

This video [19] shows a mechanism by which mercury causes neural degeneration. --173.49.15.225 (talk) 17:38, 24 September 2011 (UTC)

Thanks for the answers so far. I haven't seen any comparison of the relative risk of eating canned tuna versus chicken, beef, and pork, though. StuRat (talk) 02:54, 25 September 2011 (UTC)

The answer, overall, is that there is no answer. Comparing tuna to beef/pork/chicken, the relative risk of contributing to heart disease is lower, relative lisk of developmental abnormalities is astronomically higher, though beef could nominally contribute vCJD, which is only "developmental" in a literal sense. SDY (talk) 06:41, 25 September 2011 (UTC)

Since genetic factors influence your likelihood of heart disease, cancer, and many other ailments, it's impossible to say which is healthier for you to eat. --Colapeninsula (talk) 16:31, 26 September 2011 (UTC)

I didn't ask about me. Just use the typical non-pregnant adult as your model. StuRat (talk) 20:41, 27 September 2011 (UTC)

Human Organ Importance Essay

This is a question about a website resource that I cannot locate.

Several years ago I saw a long, text essay by a physician (I believe internal medicine resident) that listed human organs in importance and he explained why each one was--in his opinion--at that level of importance. It was just fascinating, edifying read and gave a great description of each organ and why it's important. Brain, heart, lungs, so forth.

Have any of you come across such a website or know of a better way to possibly locate this resource (other than Google)? I thought it was possibly a Google Answers response but from what I can remember it might be on a science message board archive site, usenet archive, or something like that. It was a great read.

Thanks for any help on this. — Preceding unsigned comment added by 198.146.5.4 (talk) 16:01, 23 September 2011 (UTC)

I suggest you try to recall some unique phrase from the essay and google it as a strict search. There is nothing in your question which suggests wikipedia can provide an answer for you. μηδείς (talk) 21:28, 23 September 2011 (UTC)

Neurobiology

while study about the "Giant squeed axon" experiment, i learned that when the Axon was in Resting potential., it's ECF was at the electric measure of 0 mv. but the ICF was at -70 mv.

did i understand that correctly?., and another question please; does the Extra-cellular fluid always like that? (0 mv), even in living organisms?.., or it's unique to the experiment..?.

much thanks guys. 79.180.14.78 (talk) 16:44, 23 September 2011 (UTC)

That's the squid giant axon. It is correct that the membrane potential (the voltage difference between intracellular and extracellular points) was about -70 mV. And yes, that is a typical value for the resting potential of neurons in living organisms.

Membrane potential is often a difficult concept for beginners to understand. It might help to look at our membrane potential article. One of the most important facts is that a voltage is always a difference between two points. It does not mean anything to say that the extracellular voltage is 0 mV, unless you specify the reference point used for making measurements. It does mean something to say that the voltage difference between the intracellular and extracellular areas is 70 mV. Looie496 (talk) 17:18, 23 September 2011 (UTC)

is it right that the membrane potential is always 70mv less than the ecf's voltage?. 79.180.14.78 (talk) 17:36, 23 September 2011 (UTC)

No. You are not using the words correctly. This is a difficult concept, and I am afraid your English is not good enough to understand an explanation. If you think you can, please read Membrane potential#Voltage. Looie496 (talk) 18:02, 23 September 2011 (UTC)

I don't think he's wrong. If you define the ECF potential at 0, then the ICF potential is at -70 mV ... provided the axon is at a resting potential. Once depolarization occurs as part of an action potential things can change. See the graphs in action potential for how the ICF reading can vary over time. Wnt (talk) 02:46, 24 September 2011 (UTC)

(ec, and the other editor may have done a better job ;) You're speaking of the giant axon from a species of Loligo, most likely. Note it's a giant "squid axon", not a giant squid axon. ;) Squids, unlike vertebrates, don't use myelination, so if they want to send a nerve signal a long way really fast, they have to resort to making a really huge axon. (the bigger the axon, the faster the transmission speed) These huge axons happen to be convenient for teaching young experimenters in neurophysiology. Now when dealing with electrical potential, the zero point is really quite arbitrary - generally we define it as ground (electricity). As I understand it the potential of "ground" can change greatly as, say, a thunderstorm passes overhead, but all the other potentials change with it. (Why? Because as weak as the current from a neuron or a battery may seem, when that current flows one way without opposition, it adds up quickly to a huge potential difference) So the ECF electrode is set, somewhat arbitrarily, to 0 because it's the electrode which is physically sitting in a conductive saline solution in which the neuron is immersed, where any ground electrode you might have would sit. The ICF electrode will be the one poking through a cell membrane into an electrically insulated environment whose potential can change. Wnt (talk) 17:26, 23 September 2011 (UTC)

How giant is a giant squid giant axon which a giant squid acts on? But seriously, how big is it in a giant squid? SamuelRiv (talk) 19:05, 24 September 2011 (UTC)

As our article says, the squid giant axon reaches 1 mm in diameter -- about the thickness of a pencil lead. Very convenient for experimental work in the 1940s. Looie496 (talk) 19:50, 24 September 2011 (UTC)

Thought experiment regarding an closed and expanding universe.

Presuppose that the universe is a closed manifold universe, so if you travel in a straight line long enough, you'll end up back at your starting location. What if one were to build a solid rod, perfectly straight, so that it "looped" around the universe and connected with itself (never mind how you'd do it). What would happen as the universe expanded? Would the rod necessarily break apart (let's also assume it's made of ultra-strong unobtainium)? Would it heat up? Would the universe expand like a balloon being pinched by a ring? --Goodbye Galaxy (talk) 17:00, 23 September 2011 (UTC)

A strain would build up in the material, which could lead it to break. Compare to how minigrail works. Free test particles would move due to a passing gravitational wave, but a solid material will resist this, leading to strains building up in the material, which give rise to an accoustic signal. Count Iblis (talk) 17:11, 23 September 2011 (UTC)

If you actually had a rod solid enough to apply tension to the universe, it would act as some kind of cosmological constant and affect the size of the universe (at least in that direction?). See dark energy, etc. But the details get me confused every time. Wnt (talk) 17:28, 23 September 2011 (UTC)

Iblis is right, assuming there were some force requiring it to stretch along a great circle path in higher dimensions. In such a circumstance it would break once the increase caused sufficient strain on the atomic bonds holding the rod together. Or, more likely, it would simply "fall off" the universal great circle to one "side" and simply become a great loop. μηδείς (talk) 21:25, 23 September 2011 (UTC)

With a sphere, it could "fall off". If the universe were a torus (or any other non-simply connected space) then you could build the rod in such a way that it couldn't. I agree that, in that case, the rod would eventually break. Does anyone know what would happen if is were a cosmic string that was wrapped around the universe? Can they break? --Tango (talk) 16:14, 24 September 2011 (UTC)

Actual doing of experiments seeing if more oxygen causes larger insects

The fossil record shows that there were larger insects during the carboniferous period when oxygen levels were believed to be around 35%, which is higher than it is now. I'm not aware of a plausible sequence of events that would cause insects to grow larger in a richer oxygen environment, but it seems like an easy enough experiment to do, that is, creating a large terrarium of sorts, maintain an internal atmosphere with a high oxygen content, like 35%, and supply plants, water, sunlight, etc. and maintain many generations of a relatively short-lived species of insect like fruit flies for a couple of years and track the average mass of the flies at death to see if any measurable increase is occurring.

Pick apart the idea if you must, but I don't care so much about anyone's thought experiments determining whether they'd grow or not. I only want to know if it has been done/tried. 20.137.18.50 (talk) 18:45, 23 September 2011 (UTC)

I used Google Scholar to search for drosophila+enriched+oxygen and found thousands of research papers. There are many results indicating physiological changes and adaptations, including mass changes. Nimur (talk) 18:50, 23 September 2011 (UTC)

Those species had evolved over aeons in conditions of higher oxygen and their genotypes were adapted to the conditions. It wasn't the presence of oxygen which made what would have been smaller insects grow large, but the presence of oxygen which allowed species to evolve to larger sizes. Contemporary insects would not all of a sudden become giants if given higher levels of oxygen during development. Their genes don't code for such a response. But were there a sufficient number of generations raised in such high-oxygen conditions, and some sort of significant evolutionary pressure encouraging an increase in size, then you might see a trend toward increase in size over time among such experimental specimens. μηδείς (talk) 21:20, 23 September 2011 (UTC)

" and some sort of significant evolutionary pressure encouraging an increase in size " Maybe "breeders" only letting the largest of each generation survive to reproduction age? Those breeders would then unabashedly stop being scientists and start being just guys who want to see a bigger bug testing to see the effects, if any, of increasing oxygen level alone. Peter Michner (talk) 21:41, 23 September 2011 (UTC)

One can be both. Cuddlyable3 (talk) 22:21, 23 September 2011 (UTC)

I've been trying to re-create Arthropleura from millipedes for some time now, but so far no success :( . Count Iblis (talk) 23:06, 23 September 2011 (UTC)

I think this is less a matter of looking for oxygen to create a selective pressure toward large size than looking for lack of oxygen to create a pressure toward small size. In theory, if our biggest bugs are limited by the amount of oxygen in our air, putting them into an environment with somewhat lower oxygen should force a decrease in size relative to controls with a normal atmosphere. Wnt (talk) 03:33, 24 September 2011 (UTC)

Charge of a magnetic field to repel a positron?

Okay, so just checking, since I'm years out of basic Physics: if you want to repel an electron, you can repel it using a negatively-charged magnetic field. If you want to repel a positron - which is positively charged - you use a positively-charged magnetic field. Have I got that straight? --Brasswatchman (talk) 18:50, 23 September 2011 (UTC)

Not correct at all. Magnetic fields do not have charge. Magnetic fields do not repel electrons; they exert a force on the charged particle proportional and perpendicular to electron velocity. A stationary electron remains stationary in a static magnetic field. A positron experiences an opposite force compared to an electron in the same magnetic field, because it is oppositely charged. Nimur (talk) 18:52, 23 September 2011 (UTC)

All right. So how do magnetic mirrors work, then? Is this merely a result of a magnetic field being strong enough / arranged in such a way that it appears to reflect a high-velocity particle? --Brasswatchman (talk) 19:12, 23 September 2011 (UTC)

Read the article you linked... the positron will merely gyrate the opposite way in the magnetic field, but it will be repelled as well (because its charge is also of opposite sign, so the Lorentz force from the radial component of the converging field lines still acts in the same direction). Icek (talk) 19:47, 23 September 2011 (UTC)

Reading the article is one thing. Understanding it is another. So, basically - magnetic fields in general repel charged particles? Regardless of what charge they (the particles) have? --Brasswatchman (talk) 20:37, 23 September 2011 (UTC)

(ec) No, that's still incorrect. In general, magnetic fields exert a force only on charged particles that are moving. This works for any charged particle (positive or negatively charged; electron, proton, positron, muon, ... anything with electric charge). And, just to reiterate - the force is only present when the charged particle is moving relative to the magnetic field.

The details of the geometry of relative motion between a field and a particle are actually somewhat complicated, and require a little advanced mathematics to explain totally. Those mathematical descriptions are summarized as Maxwell's equations. Particles that move very fast still obey these equations, but you would need to use relativity to get the geometry correct.

But to answer your original question, in plain, simple terms: magnetic fields do not repel charged particles. Magnetic fields affect the motion of charged particles. Nimur (talk) 21:15, 23 September 2011 (UTC)

(edit conflict) No. magnetic fields generally cause moving charged particles to curve. try this needs java

Or try these videos [20] Imgaril (talk) 21:14, 23 September 2011 (UTC)

Okay. So it sounds to me like the whole "magnetic bottle" metaphor mentioned in the article I linked to above is a lot more accurate than "magnetic mirror." Since what it sounds like you're really doing is using a set of magnetic fields to keep high-energy/high-velocity particles curving around and around within the "bottle," thus containing them. Do I have that right, or at least right enough? --Brasswatchman (talk) 22:38, 23 September 2011 (UTC)

okay, think I get that. Did some more reading, and felt like I started to remember something -- so magnetic fields don't have charge. Do *electromagnetic* fields? --Brasswatchman (talk) 21:59, 23 September 2011 (UTC)

Check the article on Electric field which may be what you are thinking of. Cuddlyable3 (talk) 22:18, 23 September 2011 (UTC)

No. Neither electric nor magnetic fields have charge. An electric charge may be thought of as the end point of a field line. In other words, a point-like electric charge (like an electron) creates a field directed towards the charge or away from the charge (depending on the sign of the charge), with the strength of the field being proportional to the inverse of the square of the distance from the charge.

Magnetic field lines on the other hand are always closed loops, thus there are no magnetic charges and no endpoints of magnetic field lines (as a sidenote, there also are electric field lines which are closed loops, in addition to those ending at charges). Icek (talk) 22:21, 23 September 2011 (UTC)

Hmm. Okay. So would the electric field generated by a sufficiently large mass of protons repel a positron? --Brasswatchman (talk) 22:41, 23 September 2011 (UTC)

Yes — and even one proton is sufficiently large. --Tardis (talk) 01:15, 24 September 2011 (UTC)

just wanted to thank everybody who put up with my very basic questions tonight. You've been a big help. --Brasswatchman (talk) 02:13, 24 September 2011 (UTC)

eka-radon at 0 °R

in theory; properties at 0 °R and can eka-radon Perpetual Motion spontaneous fission A half-life fussion of one to another eka-radon — Preceding unsigned comment added by 207.6.211.175 (talk) 23:13, 23 September 2011 (UTC)

You might want to look at our article on Ununoctium. SpinningSpark 00:43, 24 September 2011 (UTC)

Nothing in the theory of fusion or fission allows for perpetual motion (unless you have a perpetual supply of nuclear fuel, that is). Wnt (talk) 03:16, 24 September 2011 (UTC)

I think the question is whether, at absolute zero, could you have an element that would fission and then re-fuse again, and then fission and re-fuse again, and so on. The problem is that you're losing energy with every fission and fusion. So it can't possibly go on indefinitely, especially since both fission and fusion require a little energy in the first place. I suspect that after the first fission you'll just have two fragments that won't fuse without introducing (a lot) more energy into the system. --Mr.98 (talk) 14:44, 24 September 2011 (UTC)

September 24

Energy

i just saw this question on a discussion page, if energy cannot be created nor destroyed, where did it came from?

It has always been. At least as far back as the Big Bang. Modern science can't really even begin to speculate on what, if anything, existed before that. APL (talk) 03:20, 24 September 2011 (UTC)

To expand on that slightly, matter and energy can be exchanged in certain cases, but the total matter and energy in the universe is the same as it ever was. APL (talk) 03:21, 24 September 2011 (UTC)

You can read Big Bang and Timeline of the Big Bang and Planck epoch and so forth ... which kind of dance around the main point: we don't know. There always has been energy and always will be. Wnt (talk) 03:30, 24 September 2011 (UTC)

In general relativity, energy is not really conserved in general, and according to inflationary cosmology the energy of the early particle soup essentially did appear out of nowhere, with the help of general relativity. More broadly, physical principles (like energy conservation) aren't given to us engraved on stone tablets. We deduce them from experiments we do in the here-and-now, but we don't know if they're valid in absolutely every circumstance. -- BenRG (talk) 04:49, 24 September 2011 (UTC)

superfluidity react to Neutrino hypothesis

very long and totally unreadable list of incomprehensible questions
The following discussion has been closed. Please do not modify it.
How hydrogen Absolute zero superfluidity react to Neutrino? neutrino travel near speed of light if accelerated infinitly increase in mass? could massive neutrino webs be used to gather their particals for energy? fold space superfluidity of anti matter (?dark matter)? graviton of gravity yet has force to pull photons without mass itself emitted powerful gamma ray jets? do gamma ray column ever are parallel with another jet and collide? would this travel faster then light? the universe is curved were is its centre and does it have a gamma ray jet? are there super symetrical forces surrounding the universe one universe being symetrical to the next and particale infintly symetrical in mass interger or fractal, both ? or nothing beyond its perameter and finite? do all objects in the universe travel at one constent relative to the big bang as other mass moves or are all things static, relative to other moving objects? is time a mesurement of one thought to the next and it is humans inability to use sensury perseption to notice? Is there 5 or 11 dimention then would it be possible for any number of dimentions to exist. If all things are made of two dimentional particals they can make up anything could a single string be a unverce, a person, a star and if a human brain are made up of the universe is that why we have imagination, then all we think, imagine exists as some string, would this be a fact if energy can not be destroied or created changed or redirected does that apply to all particals? Before a chemical reaction between two particals occurs it is not a molacule itself or the other what is it does it exist as anything? If there is zero its angle would be nothing; does nothing exist? Regardless of any mathematical equation; explanation, metaphysical, religeus ,quantum. the expressions are diffrent yet it seems that their solution to the system is an assignment of values to all the unknowns so that all of the equations are real, conclutions the same; is their a formula for all that we concieve becomes reality? Even if it contradics physics with diffrent formulas of the orgin of reality; is there abstract formula were our law of physics do not function the same values and particals do not have the same properties? Is reality just a matter of perception? If physiologicly we are made of strings and have imagination would that mean that our thoughts, dream could become what is considered sensery perception reality,(like miricals)? Do we exist on some level of a reverberating string like dimention where anything probable or not all happen simutaniosly ? It just our sences absolute threshold to notice what is around us and do we ignore this human potential and just mirror quantitivly, qualitivly? without the ability to imagine would we ever evolve, one nerve net react to stimuli of simple life? Similar to boson gauge? Is it nerves ,brain imagined the next step reacted evolved by ingesting a amino acid and replicated itself adapting one gene at a time why we evolve? To understand that this is all placed in thought; the entire universe, trilions or infinate (for every string in the brain) and each mind of every person as though we all share one? Would naturaly we evolve with our imagination to create miricale? no longer phenominon being made entirerly of strings a part of many facts that build reality? If knowlege is built on knowledge, based on more resent finding of quantum physics these formulas ancient; human know this as a fact? Being so why hide reality from the world considering there are more pros then cons? — Preceding unsigned comment added by 207.6.211.175 (talk) 01:04, 24 September 2011 (UTC)

Defense against positrons

Okay, maybe it's best if I just came out and asked about what I'm specifically looking for. I'm writing a story where I've got a stream of near-light-speed positrons being used as a weapon. I'm trying to come up with some kind of defense against said weapon. Thus far, thanks to the previous question I asked, I've got the following possibilities:

1. A strong and properly angled magnetic field, which uses the Lorentz force to deflect/curve the positrons away from their target;
2. A positively-charged electric field - possibly just from a big mass of protons - which will repel the likewise positively-charged positrons;
3. A stream of electrons, aimed precisely at the thing generating the positrons, with the intention of meeting the positrons in flight and annihilating them ahead of the target. (Keeping in mind, though, that as we're talking about very tiny particles traveling very fast, I don't know how effective that would be.)

Does anything I just mentioned have any bearing whatsoever on reality? Am I at least close to something scientifically plausible? If not, could you guide me in a better direction?

Thank you very much for your time. --Brasswatchman (talk) 03:30, 24 September 2011 (UTC)

None of those things will work if the positrons are moving too fast -- whatever you do needs to overcome their kinetic energy. Even intercepting them and annihilating them will result in a beam of high-energy gamma rays shooting straight toward you. Looie496 (talk) 03:37, 24 September 2011 (UTC)

Wait a second, though. Doesn't the Lorentz force actually increase in proportion to the velocity of the incoming particle? Or am I reading that wrong again? --Brasswatchman (talk) 03:42, 24 September 2011 (UTC)

How high energy and how many positrons? Until you get to really high energies positrons really have very little penetrating power. You could stop them with a several feet of air or a few inches of water / brick. They'll annihilate into gamma rays which could be a worse risk than the positrons themselves depending on how many of them there are. Dragons flight (talk) 04:41, 24 September 2011 (UTC)

It is useful to know the radius of the circle on which a positron will move in a (homogeneous) magnetic field. The formula is

$r={\frac {p}{e\cdot B}}$

where p is the momentum of the positron, e is the charge of the positron and B is the magnetic flux density. In the low-speed limit the momentum is just the product of mass and velocity, but for speeds close to the speed of light (denoted by c) you need the relativistic formula:

$p={\frac {m\cdot v}{\sqrt {1-{\frac {v^{2}}{c^{2}}}}}}$

Expressing the momentum in another way, in terms of kinetic energy (E) instead of speed:

$p={\sqrt {{\frac {E^{2}}{c^{2}}}+2\cdot E\cdot m}}$

For the highest values of B that are currently technically possible, see Electromagnet#High field electromagnets

Icek (talk) 14:21, 24 September 2011 (UTC)

So, basically, if I've run through the math correctly here - for a 1000 Telsa magnetic field, the distance moved by the positron by the Lorentz force is on the order of microns. Yeesh. Do I have that right? --Brasswatchman (talk) 19:16, 24 September 2011 (UTC)

Um, I haven't checked your arithmetic, but I think you're misinterpreting the answer. If you got the right number, then it does not mean that the positrons would be deflected by only microns. It means they would travel in a circle whose radius is only microns. That is, the small answer means they would be deflected very strongly, not very weakly as you seem to have interpreted it. --Trovatore (talk) 22:03, 24 September 2011 (UTC)

That... makes quite a bit of difference then, doesn't it? :) That works, then. Thank you! --Brasswatchman (talk) 23:35, 24 September 2011 (UTC)

You seem to simply use p = m*c. If you look at the relativistic formula, you can work out that this would be the real momentum if the speed would be c/sqrt(2). That seems like pretty low-energy positrons. Their energy would only be 212 keV. The highest energy man-made positron beam was at the Large Electron–Positron Collider at 104.5 GeV, that would translate to a radius of about 35 cm at 1000 Tesla (but that was a very large machine). High-energy positrons will also create a lot of synchrotron radiation in a magnetic field, and you would have to shield against that. Wnt's suggestion of just using something massive makes sense, as you have to use it anyway due to the synchrotron radiation (the synchrotron radiation is emitted in all directions in the plane of gyration, and if you let the positrons impact on matter there will be bremsstrahlung which will at least be preferentially emitted toward the direction the positrons were coming from). Icek (talk) 21:48, 24 September 2011 (UTC)

You're correct. Sorry, was just simplifying the math for myself so I could try and get a basic if inaccurate idea of what the effect would be. Either mass or a very strong magnetic field would work as a solution, then. Radiation is less of an issue for me, since I was thinking about this weapon in the context of an unmanned weapons platform. (Yes, I know that radiation does affect computers and machines; but at least it's a bit more plausible that they could be engineered to resist those kinds of stresses than a manned spaceship or station.) Thank you very much for your time, and for all the effort you've put into instructing me. I very much appreciate it. --Brasswatchman (talk) 23:35, 24 September 2011 (UTC)

You could use an electric or magnetic field to gently nudge them around and back at the source, but only if you can, say, set up something on the order of a particle accelerator out in space (around the size of the one accelerating them in the first place, that is). Doing this in a hurry would seem to require quite a set-up.

If you have any access to mass, I'd say that's your answer. Throw a brick out at the beam and (assuming it's strong) it'll blow to smithereens, and the vapor/dust thus created will screen a large area, at least momentarily, so after that your enemy can't just fan the beam around your settlement at will. Throw a large number of bricks and he'll be left heating a dust cloud in space with no real prospect to get through to you, I think. Wnt (talk) 14:37, 24 September 2011 (UTC)

An electromagnetic field would be your best bet. But like what someone else said, if their energy is too high, they will come through. Just posit an immensely powerful electromagnetic field. ScienceApe (talk) 18:23, 24 September 2011 (UTC)

Okay. What about the second possibility I mentioned? Putting a positive electrostatic charge on a surface in the path of the beam, for instance? Would that have much influence at all, or is the kinetic energy in this case simply too great for it to have much influence? --Brasswatchman (talk) 19:16, 24 September 2011 (UTC)

So far I don't see enough scientific context in the question to be able to answer it. How near light speed are you talking about? The difference between 0.99c and 0.999c is greater than the difference between 0 and 0.9c. It makes all the difference in the world how much energy the particles actually have. Secondly, unless you are using this "weapon" in a near vacuum, then the whole notion of them being positrons is moot. In the presence of air (or anything else) low-energy positrons annihilate into gamma rays, while high-energy positrons will scatter into showers of secondary particles. Either way, the only place you'd have a pure positron beam is in a vacuum. Hence it matters what environment the beam travels through in order to determine what kind of shielding is actually necessary. At the moment it just sounds like a very contrived plot device. If your weapon is going to be pseudo-scientific, then I'm not sure why you are looking for a scientific defense. Dragons flight (talk) 23:09, 24 September 2011 (UTC)

Let's say I am talking about a vacuum weapon, as in space-based. So the mass shielding suggested before does work for me; I'm just looking for options, that's all. --Brasswatchman (talk) 23:35, 24 September 2011 (UTC)

Just wanted to thank everyone who responded to this thread again. You've been a big help. --Brasswatchman (talk) 23:36, 24 September 2011 (UTC)

UARS: the falling, burning re-entering satellite

The UARS satellite should have reentered, but there is no update, more than one orbit past the re-entry time NASA picked as most probable, plus or minus a few hours.. Does NASA, or the various world powers, have radar to actually track a satellite, or do they wait for reports from amateur astronomers, commercial airline pilots, commercial shipping, Inuits, or African villagers who might have seen or heard something? The US and the other world powers are supposed to have the capability to track things in space in real time, to detect nuclear attacks, for instance. Edison (talk) 04:48, 24 September 2011 (UTC)

The last update had it falling between 3:45 and 4:45 UTC. Yes, they can track it. Dragons flight (talk) 05:04, 24 September 2011 (UTC)

NASA web page, if anyone is interested. Mitch Ames (talk) 06:07, 24 September 2011 (UTC)

... and an update therefrom ... "NASA’s decommissioned Upper Atmosphere Research Satellite fell back to Earth between 11:23 p.m. EDT Friday, Sept. 23 and 1:09 a.m. EDT Sept. 24. The Joint Space Operations Center at Vandenberg Air Force Base in California said the satellite penetrated the atmosphere over the Pacific Ocean. The precise re-entry time and location are not yet known with certainty."

The re-entry seems to have been chaotic (in the sense of there being too many unpredictable variables to calculate accurately), but at least it seems to have been over the sea. Dbfirs 08:45, 24 September 2011 (UTC)

NASA was able to rule out only one continent, North America, as a place the satellite might land.[21] In other news, see this lovely video from Alberta.[22] ;) After all these nimble flips I'm inclined to give the satellite a 9, provided it stuck the landing. Wnt (talk) 14:47, 24 September 2011 (UTC)

It was under 130 km altitude perigee in the South Pacific shortly after it passed over New Zealand around Midnight Eastern. That would have had to have snagged it, the air is just too dense. 208.54.86.178 (talk) 16:30, 24 September 2011 (UTC)

The latest reports are still inferential. They think it fell in the Pacific, because it's altitude was dropping. and it did not seem to have reached North America. They have not reported any actual radar measurements of when and where it reentered. There appear to be spots on Earth where they can measure the apogee and perigee and location of orbiting objects. but there are also apparently large gaps, somewhat worrisome when ballistic missile subs or surface ships might launch from anywhere. Satellites looking down might be able to detect launches. NASA was relying on "amateur satellite watchers," who failed to see it, so by inference it fell in the Pacific. Recent news reports, [23], say they are hoping for reports from airliners or ships of fireball sightings. If someone like the North Koreans fired an ICBM at the US, would they be similarly unable to track it by radar? Edison (talk) 03:39, 25 September 2011 (UTC)

Yes, they would not. Nobody has missile detection capability good enough to keep strategic defense command locations outside mountains. At Saturday the 24th at 04:05 UT, UARS' orbit was in perigee at 3.3 degrees North by 159.9 degrees West at an altitude of 126.1 km. That was the first time it was under 140 km. There's no way it could have continued from there. 69.171.160.56 (talk) 07:40, 26 September 2011 (UTC)

Why don't plants have white blood cells?

Are there any plants that have recruited bacteria or single cell animals to patrol themselves as a natural part of their existence?

No. Plants do not have an adaptive immune system, though a lot of plants have coopted insects and whatnot as defenses, most notably ants. Plants only have an innate immune system (which can also be found among animals), they use defensive chemical warfare instead. It's the reason why so many plants are good sources of antibacterial and antiviral chemicals.

Plants are also a bit more resistant to injury than animals, and they have a greater regenerative capability. If they detect an infection, they isolate it by killing their own cells surrounding the site before it spreads (hypersensitive response). They then start producing messenger chemicals that in turn stimulate production of defensive chemicals in other uninfected parts of the plant at the same time (systemic acquired resistance). For larger attackers, they can also stimulate another response which not only triggers the production of defensive chemicals in the individual plant, but in surrounding plants as well. This includes production of poisons and whatnot against insects and larger herbivores.

See Innate immune system#Host defense in plants and Plant disease resistance.-- Obsidi♠n Soul 08:54, 24 September 2011 (UTC)

Oh and in terms of symbionts and commensals, they do play a part in plant defense. But it's all rather indirect and certainly not internal. The area of study is known as biological control of plant pathogens and is of great interest in agriculture. This usually involves symbiotic fungi or bacteria in the plant roots (and virtually every plant has a great variety of them, some plants barely survive without like orchids).-- Obsidi♠n Soul 09:21, 24 September 2011 (UTC)

I guess (as a non-biologist) that the key here is that this particular form of symbiosis or whatever it is requires circulation, whereas plants draw their fluids from the ground and move them one way. For something like white blood cells to work, they would need a way of moving within the plant. Moving up would be easy, but for moving down they would probably require a lot of energy. This would also require some way of signalling where to go, and it's not clear to me how that would work in a plant context. Hans Adler 09:40, 24 September 2011 (UTC)

Plants have a sort of adaptive immune system, and manage to circulate their counterpart to antibodies through plasmodesmata - namely RNA interference. The distinction is that this acts at a point later in the viral life cycle: not on the encapsulated virus outside the cell, but on its genetic material as it seeks to take over the cell. As that article explains, humans might have the same thing, but evidence has been elusive. Wnt (talk) 14:21, 24 September 2011 (UTC)

RNA silencing is new to me. :D But yeah I suppose it's adaptive. It's quite different from animal protein-based adaptive immunity though, and by its very nature, purely antiviral.-- Obsidi♠n Soul 20:57, 24 September 2011 (UTC)

Was Einstein wrong?

Was Einstein wrong in claiming that nothing can travel faster than the speed of light? --DinoXYZ (talk) 08:33, 24 September 2011 (UTC)

See the previous thread on this: #FTL neutrinos. Bottom line is it's probably experimental error. -- BenRG (talk) 08:38, 24 September 2011 (UTC)

Law One of the Universe: Einstein is ALWAYS correct. Sir William Matthew Flinders Petrie | ^{Say Shalom!} 27 Elul 5771 18:19, 26 September 2011 (UTC)

Can we make high quality image of exoplanet with current technology?

100x100 image of Earth

Today we can make direct images of exoplanets, but with really poor quality. Its extremely complicated, I understand.

Can we make hight quality image of exoplanet with current technology? Is it possible?

What we need for 100х100 pixel image of the nearest exoplanet? Really big telescope? How big?

sorry for my English --Ewigekrieg (talk) 10:04, 24 September 2011 (UTC)

You can calculate from the diffraction limit - the minimal angle that can be resolved with a telescope of a given diameter is roughly λ/d, where λ is the wavelength of the light and d is the diameter of the telescope. Assuming there is a Jupiter-sized planet at ε Eridani, you want about 1400 km per pixel, you need an angle of 1.4*10^-11. At a wavelength of 500 nm (green light), the diameter of the telescope needs to be about 35.5 km. Maybe you should try to build an interferometer of that size instead. Icek (talk) 13:41, 24 September 2011 (UTC)

There is an active NASA Ames project called "lunar micro rover" which is building a system capable of lunar VLBI out of very inexpensive lunar rovers and orbiter, which could have a baseline (equivalent mirror size) over 2,500 kilometers. This sort of system was proposed by the Japanese in 1994 and has since become well understood using solid state heterodynes, e.g. at the Cambridge Optical Aperture Synthesis Telescope and UC Berkeley Nobel laureate Charles Townes' 10 micron VLBI at Mt. Wilson/Palomar. A lunar VLBI system would be able to detect and characterize Earth's nighttime electric lighting out to 100+ light years, and detect ozone (a likely sign of the kind of life we can eat) on exoplanets much further out.

However, there seems to be vast ignorance and some resistance to lunar VLBI in the professional astronomy community for some different reasons. The military has been withholding formation flight control systems for space VLBI since the 1990s so that synthetic aperture radar battlefield imaging -- which uses the same formation flight control systems -- won't fall into the wrong hands, I suppose. However, the average seismic displacement on the Moon is less than a micron, so closure phase computations in the interesting 9-15 micron band (including ozone in 9-10 microns as well as the first two coldest spectral lines of hydrogen for characterizing the coldest interstellar gas clouds and black hole microlensing) would be easy from digital heterodyne post-processing without any adaptive optics, let alone classified formation flight control systems. Combine that with the fact that such a system will, for less than $1 billion, perform with far more resolution, sensitivity, and important scientific results than any other telescopes yet contemplated, and it's not hard to see why this makes professional astronomers a bit uneasy, is it? 208.54.86.178 (talk) 16:58, 24 September 2011 (UTC)

Only if by "uneasy" you mean eager to get the project started. The system may, not will, perform with important scientific results. Synthetic aperture radar imaging seems well understood and is applied in Reflection seismology, see Reflection seismology#Marine(streamer). Cuddlyable3 (talk) 18:40, 24 September 2011 (UTC)

If you want a chance of working on such a project, study Mandarin, not English.

To clarify, are you talking about placing this array on the Moon ? I'm assuming you mean the far side, to eliminate Earthshine. This would certainly be a worthy scientific project, and we've been looking for some reason to go back to the Moon just to practice for Mars. However, I bet the cost would be a lot more than $1 billion, considering there's the delivery cost, the installation crew, the lunar satellites needed to relay the pictures back to Earth (or maybe a series of towers to transmit the pictures to the near side then down to Earth). And would there be a permanent maintenance staff located there ? StuRat (talk) 03:59, 25 September 2011 (UTC)

Not if the first step is to get a mostly self-sufficient robot economy started on the Moon... Wnt (talk) 15:03, 25 September 2011 (UTC)

It's just ~10 rovers with infrared scopes in craters or next to hills for sunshade, spread out on the lunar far side, and an orbiter (or possibly even the existing Lunar Reconnaissance Orbiter) to collect the digital data to be transmitted to Earth for closure phase combination. You don't need astronauts to set it up at all. You don't even need lunar GPS because each rover will have its own clock signal. The issues are: how do you keep the cryostat fluid from boiling off for as long as possible, and how do you keep dust out of the scopes -- point them down and tap them occasionally? Everything else about the system is relatively low tech, unlike the JWST which looks like it could end up costing over $8 billion and has a zillion single points of failure moving parts (while the lunar rovers are fully redundant with each other) without camera capabilities allowing for more than a pixel per exoplanet. The Google Lunar X Prize people say that they can place lunar landers for about $30 million each -- presumably less if a bunch of them go up on the same rocket. 69.171.160.110 (talk) 16:40, 25 September 2011 (UTC)

Species Identifcation

Species to be identified

To aid a rename request what is this specifcally? Sfan00 IMG (talk) 13:37, 24 September 2011 (UTC)

My guess is Myosotis latifolia ([24]) or Myosotis scorpioides ([25]), based on the broad leaves. --Mr.98 (talk) 14:38, 24 September 2011 (UTC)

Circumstantial evidence suggest the second of those - the photographer lives in Matlock, Derbyshire, which is in Europe and near water. 213.122.0.58 (talk) 17:00, 24 September 2011 (UTC)

existence of time

Is TIME just an idea, or does it really exist? how do you prove its existence? does this question make sense? — Preceding unsigned comment added by 203.112.82.128 (talk) 13:51, 24 September 2011 (UTC)

The question is a good one but is a bit hard to answer here. At its heart, time is just the way we mark sequential events. But it gets much more complicated (and interesting) from there. Start by reading the beginning of the article "time", and from then, if you're feeling adventurous, the article on Philosophy of space and time. --Mr.98 (talk) 14:30, 24 September 2011 (UTC)

Arrow of time also addresses your questions. Red Act (talk) 14:38, 24 September 2011 (UTC)

Time is, at root, simply change. Every time you speak a sentence that uses a verb, you presuppose the existence of change -- so this is really a self-answering question: the act of asking it implicitly answers it. Looie496 (talk) 15:01, 24 September 2011 (UTC)

A road changes from a six-lane metallised highway in the city to a dirt track in the hills. But time is not a necessary prerequisite for that change to occur. SpinningSpark 15:39, 24 September 2011 (UTC)

No, for several reasons:

• If time is exactly the same as change, then this is not an explanation. All you've said is that the word "change" could have been used in the question instead of the word "time".
• If time is not exactly the same as change, the question remains: how are they different?
• What SpinningSpark said.
• The fact that the OP is obliged to ask the question in a language with an embedded concept of time does not mean that the concept is correct or refers to any real thing. The English langauge also has an embedded concept of absolute certainty, for instance, which is at odds with fallibilism.  Card Zero  (talk) 17:11, 24 September 2011 (UTC)

Time... time is a magazine.-- Obsidi♠n Soul 16:50, 24 September 2011 (UTC)

Time as a pointer, singling out the present moment as being real, doesn't exist, see e.g. here. Also, simply from the fact that information is conserved, it follows that the distant past and the future exist on an equal footing as the present moment. Count Iblis (talk) 17:08, 24 September 2011 (UTC)

A little change in time is the difference between now and now. The progress of time is required for change. Plasmic Physics (talk) 23:39, 24 September 2011 (UTC)

The next moment already exists in the present moment, because information is conserved. If we assume the intuitive notion of time and assume that somehow the Unverse ended in 1980, we would still subjectively find ourselves alive in the year 2011 posting here on Wikipedia. This is because the physical state of the universe as it exists now in some reference frame can be defined in terms of the state in 1980 by applying the time evolution operator. Count Iblis (talk) 00:03, 25 September 2011 (UTC)

The OP got it right when he asked "Does this question make sense?" Such fundamental concepts as time are so necessary to thought that they are in effect axiomatic--they cannot be denied without implicitly being used in the very denial. For example, what would it mean to say "Elbert Ainstein has proven that time does not exist" or that the OP is waiting for us to answer his question? Another problem that may be lurking here is materialism, the belief that to exist is to be matter. That is a subtle misconception that lurks in our culture. The notion is, roughly, that everything is made of atoms, and therefore, since things like time or thought are not made of atoms they are not really real, just illusions, or so forth. (The obvious problem here is that it implies that illusions exist, which contradicts the premise that all things are only atoms. If you find it hard to believe that all things are not atoms, ask yourself if shadows are real, and if so, what is their molecular mass.) The correct way to analyze time is to see that while it is not an entity, (like a book or a body, or an atom, or a galaxy) and it is not an attribute, (like soft, or pink, or sticky) it is a relationship. Time in the concrete experiential sense is the relationship of before and after and so forth, just as size is the relationship of bigger or smaller than and direction is comprized of the relations nearness and being between and so forth. Time in the sense of "all of time and space" is simply the grand matrix of all the before and after relationships of all entities and the changes which they undergo. Indeed, time is relative, and without change or the entities which undergo change there would be no time. The Newtonian notion of absolute time is ultimately a confusion.

DEFINE TIME if you wanna get a result from that discussion...--Irrational number (talk) 15:49, 26 September 2011 (UTC)

There is no mystery about time, as such. The spacetime that we inhabit has four (macroscopic) dimensions, one of which is distinguished by having a signature in the metric tensor that has the oppsoite sign to the other dimensions - this dimension is time. The existence of the arrow of time - the fact that we cannot travel in either direction through time as we can in any of the spacelike dimensions - is where the real mystery lies. Gandalf61 (talk) 16:21, 26 September 2011 (UTC)

Thats the problem, i cant even define time.  — Preceding unsigned comment added by 203.112.82.128 (talk) 17:08, 26 September 2011 (UTC) 

Horizontal penis

http://en.wikipedia.org/wiki/Bushmen#Neoteny

"Ashley Montagu noted that Bushmen have the following neotenous traits relative to Caucasoids: "large brain", light skin pigment, less hairy, round-headed, bulging forehead, small cranial sinuses, flat roof of the nose, small face, small mastoid processes, wide eye separation, median eye fold, short stature and horizontal penis"

What exactly is a horizontal penis? ScienceApe (talk) 15:48, 24 September 2011 (UTC)

Maybe it means that the opening to the urethra (or w/e it is called) is horizontal as opposed to vertical? Other than that I can't imagine (unless these dudes have a permanent priapism. :p) Sir William Matthew Flinders Petrie | ^{Say Shalom!} 25 Elul 5771 15:54, 24 September 2011 (UTC)

At a complete guess, it means the penis points horizontally when erect. Erection notes most penises point upwards but some are more or less horizontally straight forward. It gives stats take from "Sparling J (1997). "Penile erections: shape, angle, and length". Journal of Sex & Marital Therapy 23 (3): 195–207" which suggests that study found only about 10% had a penis that was more or less horizontal when erect. In the article on Bushmen it's suggested it's a trait associated with Neoteny which I guess means the the curvature or angling of the erect penis often becomes greater during puberty. Nil Einne (talk) 16:32, 24 September 2011 (UTC)

Googling around suggests that Ashley Montagu is the only source for this. Maybe they were just pleased to see him.--Shantavira|^{feed me} 16:46, 24 September 2011 (UTC)

And why was "large brain" placed in scare quotes, while the rest are not? Werdnezz!-- Obsidi♠n Soul 16:49, 24 September 2011 (UTC)

It isn't in the source [26]. I don't think it's that weird either, anything concerning the brain tends to make some people uncomfortable because of perceived connections to intelligence. Also because of the complexity of the brain, large could be taken in different ways. However IMO the quotes should be removed. Incidentally, the source doesn't seem to have any explaination of the penis thing in the part available thru Google Books (to me) although does note persistence of penile prepuce as a neotenous trait but it seems that isn't related to the horizontal thing. I note the page after the section on neotenous traits which refers to penile prepuce (and that is the last visible entry in the table) isn't available so it's possible I'm not seeing some relevant stuff that is in the source. Edit: It seems the larger brain part was removed by the person who added the AM source as they believed it was not in the source [27], and then re-added upon checking the source along with the quotes [28]. On second thought, perhaps quotes are because of confusion as they didn't understand why a larger brain is a neotenous trait, but of course babies and children have much larger brains compared to their bodies then adults because the brain and head doesn't grow as much. Nil Einne (talk) 16:54, 24 September 2011 (UTC)

Wouldn't a small brain (relative to the size of an adult brain) also be a neotenous trait? Which means that an ordinary-sized brain shows inclination towards two neotenous traits.  Card Zero  (talk) 17:24, 24 September 2011 (UTC)

Nope, It's relative to body size. i.e. Small body, big head. Even tiny embryos have larger heads relative to their bodies than adults.-- Obsidi♠n Soul 21:01, 24 September 2011 (UTC)

Yes, I get it: I was just wondering whether a single part of the body which doesn't grow as much as the rest, such as the left hand of a person with Poland syndrome, would also count as a neotenous trait. Neoteny mentions down syndrome, which is associated with microencephaly, I think*, so in that case small brains - in absolute terms - are neotenous, which seems to mean all sizes of brains are neotenous and undermines the meaning of the term.

* Google thinks  Card Zero  (talk) 21:21, 24 September 2011 (UTC)

It was discussing neoteny. It would have been understood that it was referring to physical size relatively. Placing it in scare quotes only makes it more like it was an attempt to appease the which-race-is-more-intelligent moot-pointers. :/ -- Obsidi♠n Soul 18:18, 24 September 2011 (UTC)

I don't see any reason to think the person who added the original ref and placed the quotes understood or even appreciated this. Note as I said above, I agree the quotes should be removed, however I don't think their placement is that surprising and there are plenty of reasons why they could have been added. Nil Einne (talk) 03:13, 25 September 2011 (UTC)

acu

whats the official army acu glove for cold weather — Preceding unsigned comment added by 64.38.197.221 (talk) 17:33, 24 September 2011 (UTC)

I assume acu is Army Combat Uniform. This is what the British army wear (note the trigger finger). Cuddlyable3 (talk) 19:19, 24 September 2011 (UTC)

Factoid WRT pesticides on unwashed shop-bought fruit...

"You take in more toxic chemicals from drinking one cup of coffee or smoking one cigarette than you do from eating unwashed fruit every day for a year".

True or false? It's a line that I've heard people quoting when it comes to people who are concerned that shop-bought fruit is covered in large amounts of highly-toxic (poss. carcinogenic) pesticide residue - as one of those 'well, smart people know that...' things, though I'm not sure where it comes from... --Kurt Shaped Box (talk) 17:49, 24 September 2011 (UTC)

See http://www.thedailygreen.com/healthy-eating/eat-safe/Dirty-Dozen-Foods#fbIndex1.

—Wavelength (talk) 17:59, 24 September 2011 (UTC)

Mostly true. A study in Science from 1992 [29] looked at the known rodent carcinogens in foods. Such carcinogens can be naturally present, created by cooking / processing, or added as pesticides. They found that the known rodent carcinogens that one consumes from having three cups of coffee a day is roughly 300 times more potent than the total carcinogens the average person consumes via pesticide residues (based on typical American diets and EPA limits on allowable pesticide residues). Relative potency is estimated by looking at the chronic exposure required to cause cancer in 50% of rats. By this measure one can roughly estimate that consuming three cups of coffee per day regularly over a lifetime raises your cancer risk 0.05%. Pesticide exposure risk is similarly ~300 times lower. Now for some caveats. There are many naturally occurring chemicals that have never actually been measured, so the true risk of various foods / cooking is likely to be unknown. Secondly, rats are not necessarily a good model for humans in all, or even most, cases. Third, the risk does not necessarily scale linearly with dose, so figuring out the effect of trace carcinogens from the amount that causes cancer in rats may be misleading in some cases. Lastly, you can't really know whether the food in front of you complies with legal limits for pesticide. Dragons flight (talk) 18:32, 24 September 2011 (UTC)

PS. It's also possible for chemicals in food to be toxic without being carcinogenic. Carcinogens are generally the easiest form of long-term damage to observe though. Dragons flight (talk) 18:41, 24 September 2011 (UTC)

An excellent answer Dragons flight. Thank you. --Mr.98 (talk) 14:22, 25 September 2011 (UTC)

Indeed. Thank you very much for your answer, DF. Just the sort of thing I was looking for. --Kurt Shaped Box (talk) 22:14, 25 September 2011 (UTC)

God

is there any effort, outside religion, that is fully documented to prove God's existence? — Preceding unsigned comment added by 203.112.82.128 (talk) 18:11, 24 September 2011 (UTC)

No, by definition, god is unscientific because it can't be falsified. See falsifiability.

Although this is a science reference desk the OP did not specify that formal Scientific method must be involved in the effort. The question is ambiguous about whether it seeks "a fully documented effort" or "a fully documented proof"; the former seems more likely. Does an off-duty monk making extracurricular prayers for an epiphany count as "outside religion"? Cuddlyable3 (talk) 19:05, 24 September 2011 (UTC)

yeah, im asking if there is a fully documented effort to prove it. — Preceding unsigned comment added by 203.112.82.129 (talk) 19:29, 24 September 2011 (UTC)

First of all, you would need to define "God". If you define "God" as meaning, say, the god described in the Christian Bible, then you're wasting your time. Most Christians don't even think that god exists. If you want a more general definition, then it gets a little tricky. To prove the existence of a god, you need a miracle. That is, something happening that science says is completely impossible We don't have a complete understanding of science, though, so we can't say for certain if something is impossible or not. That means we don't know if it's a miracle or just a mistake in our understanding of science. --Tango (talk) 20:39, 24 September 2011 (UTC)

Does science really say that certain things are impossible, Tango? Scientists might make such pronouncements. My understanding, as a non-scientist, of the scientific method is that phenomena that actually happen are observed and explained. Science per se has an "open mind" as to whether it's possible for something to happen or exist, or not. Scientists sometimes have rather more closed minds, though. Also, a miracle is not something that anyone who knows what they're talking about says is impossible; it's something that has actually been observed to occur, but for which there is currently no scientific explanation. -- Jack of Oz ^{[your turn]} 21:39, 24 September 2011 (UTC)

"Most Christians don't even think that god exists"? That doesn't sound right to me, Tango. --Mr.98 (talk) 21:58, 24 September 2011 (UTC)

It depends on what the meaning of the word "that" is. I'm fairly sure that in the sentence "Most Christians don't even think that god exists.", Tango was using the word "that" as an adjective modifying the word "God", to indicate the god described in the Christian Bible, as opposed to other conceptions of God. But in your objection to that sentence, I think you're probably interpreting the word "that" as a conjunction introducing the subordinate clause "god exists", which I don't think was Tango's intended meaning. Red Act (talk) 05:51, 25 September 2011 (UTC)

Sorry, that was badly worded. Red Act is correct about my intended meaning. I should have said "Most Christians don't even think that that god exists". It was a reference to Biblical literalism being a minority viewpoint. --Tango (talk) 15:26, 25 September 2011 (UTC)

This IS the Science reference desk, so we have every right to give a scientifically oriented answer. That answer is "No". HiLo48 (talk) 20:37, 24 September 2011 (UTC)

Just to be clear, im not asking if there is a fully documented proof of god, but if there is a documented effort to prove god. — Preceding unsigned comment added by 203.112.82.1 (talk) 21:07, 24 September 2011 (UTC)

That term you are using, "documented effort", seems a little strange, but important to you. Can you put it into other words? Exactly what do you mean by "documented effort"? HiLo48 (talk) 21:24, 24 September 2011 (UTC)

yeah, i think its a weird term as well, english is not my primary language, what i mean by documented effort is a study that is published recognized by credible people. — Preceding unsigned comment added by 203.112.82.2 (talk) 21:37, 24 September 2011 (UTC)

Most scientists who lived before 1850 believed in God. Many of the historic scientific discoveries could have confirmed the existence of God, assuming that God really exists (as most scientists used to believe). The "God hypothesis" was always the de facto null hypothesis, since before Galileo. But in every case where the Bible could have been proven correct, it was falsified. It is only because the believers have adapted their belief to make it consistent with every new scientific finding over the centuries, that they have ended up with something that is immune to falsification. Count Iblis (talk) 21:54, 24 September 2011 (UTC)

There have been, and are today, lots of efforts to try and prove God exists. For an historical approach, see, e.g., William Paley. For modern folks trying to do the same thing, see, e.g., Michael Behe or William Dembski. Lots o' documentation available; Ronald Numbers' The Creationists: The Evolution of Scientific Creationism (Univ. Calif. Press, 1993), is chock full o' documentation of these sorts of folks. These efforts have not been successful, if you mean, have actually proven God to exist, or have convinced mainstream scientists that their "proofs" are both accurate and mean what they claim to mean. --Mr.98 (talk) 21:58, 24 September 2011 (UTC)

Just above, our OP referred to credible people. Are creationists, starting as they do from the position that God does exist, credible people in this matter? HiLo48 (talk) 22:02, 24 September 2011 (UTC)

Some are certainly more credible than others. Behe and Dembski are as credible as any other scientist types. What matters is not the starting position — everyone comes to every question with their own starting positions, some quite sane, some quite looney — but how compelling their arguments are for their position. (Newton's starting position for his physics was that God existed and was holding it all up in an active way. But that's not what made him right or wrong in his work, in the end.) In the end, as I've noted, most scientists don't buy their arguments and aren't convinced. But my point is that they've certainly made an effort. --Mr.98 (talk) 22:28, 24 September 2011 (UTC)

One can investigate the universe by starting with "I'm going to find out how the universe began" or with "I'm going to prove that God created the universe". The former is a scientific approach. The latter is not. HiLo48 (talk) 22:49, 24 September 2011 (UTC)

It doesn't matter how you start, or why. What matters is what you end up finding. There have been lots of wonderful science done in the name of bad suppositions. Michelson started his interferometer experiments to find the luminiferous aether. What is found is that the aether didn't exist. He won a Nobel Prize for this, despite his own desperate desire, until his death, to prove the aether did exist. What made him a good scientist was that his results were solid. There are plenty of other examples to be found in the history of science. Every philosopher of science I have read (including the much vaunted Popper) has insisted that the sources of inspiration and direction are immaterial to the validity of the actual findings. This is not at all to deny the importance of context — just to say that you can't differentiate between science and non-science on the basis of motivation. --Mr.98 (talk) 02:08, 25 September 2011 (UTC)

I'll paraphrase what I said earlier in a related discussion. It is impossible to scientifically prove the existance of God. He's exsistance can only be reasoned for through personal experience. Here's a quote, "Then said Jesus unto him, Except ye see signs and wonders, ye will not believe."John 4:48 — Preceding unsigned comment added by Plasmic Physics (talk • contribs) 23:32, September 24, 2011 (UTC)

That's another classic Biblical quotations that can be interpreted in many ways. The word "signs" is obviously a simplification of or metaphor for something else. We all see signs every day, but the relevant signs mentioned there are obviously very special ones, and the quotation doesn't explain any further, so we are left to speculate and wonder. Which brings me to.... I see many "wonders", almost every day. Seeing them doesn't convince me of the existence of the Christian god. I tend to look for scientific explanations. The mystery to me is why some people think that something as yet unexplained (to them) proves that a god did it. HiLo48 (talk) 00:00, 25 September 2011 (UTC)

People have needs. One of them is a need for a kind of certainty about their place in the universe. For many people, that need is satisfied by positing a god as the only plausible explanation. If they say the existence of such a god is thereby proven, they're not thinking properly. It's still in the realm of belief, and will always be. But as far as they're concerned, they believe it, and they act as if it requires no further proof. That's what belief means. The same applies to those who say there is no evidence for a god, and therefore his non-existence is proven. Wrong again, but they still act as if there is no god and that is consistent with their belief system. -- Jack of Oz ^{[your turn]} 00:25, 25 September 2011 (UTC)

A common reason converts give, is that an atheistic view of their own existance is depressing - that it there is no point in living, you come and you go, you exist and then you don't, just another statistic. It is natural for people to seek self-justification/validation. The context of the quotation is: a man heard rumours of the Messianic wonders performed by a man named Jesus, who passed through his town some time before. He was desperate for a cure for his dying son, his last hope was this Jesus, who is rumoured to heal any affliction with word or touch alone. He does not believe, since he has not witnessed, yet he hopes. In hope, he pleads for one such healing wonder for his son. Through words alone from Jesus, his son is cured in an instant, and brought to perfect health. Thus he believes, and he doesn't doubt any further. He required personal experience to verify what he heard. Plasmic Physics (talk) 01:48, 25 September 2011 (UTC)

Your story can't be verified, it's just a story that was almost certainly made up. Even if it were true, how does that prove an entity created the universe? It just proves this man named jesus had super healing powers. ScienceApe (talk) 02:11, 25 September 2011 (UTC)

I'm sorry, but I don't follow your logic, how is it almost certainly made up? I didn't say that it proves that God created the universe. Plasmic Physics (talk) 02:31, 25 September 2011 (UTC)

I think what ScienceApe is getting at is, even if Jesus did heal the kid, all it would justify is a belief that Jesus can heal sick kids. Why would the father's experience justify a belief in God? HiLo48 (talk) 02:38, 25 September 2011 (UTC)

• This conversation has strayed well outside the purpose of this page, which is of course answering questions related to science. Beeblebrox (talk) 02:50, 25 September 2011 (UTC)

The original question has been answered, I'm just answering consequencial queries about the qute I gave. There is no point in giving a quote if no one understands it.

The Messiah was prophesied centuries before, and Jesus is the only one who fits the description. Basically whoever is the Messiah, is also the Son of God according to the prophesy. This man must have known about the prophecy, meaning that if Jesus is indead the Messiah, then He must also be the Son of God, hence God must exist according to the man who witnessed. Plasmic Physics (talk) 02:59, 25 September 2011 (UTC)

That would only work if the man believed the prophesies of the coming of the Messiah, so he was already a believer. HiLo48 (talk) 03:21, 25 September 2011 (UTC)

He was a sceptic, that is why he needed proof. Plasmic Physics (talk) 03:26, 25 September 2011 (UTC)

Proof of what? HiLo48 (talk) 03:31, 25 September 2011 (UTC)

Proof that the prophesies were true. Plasmic Physics (talk) 03:42, 25 September 2011 (UTC)

No, that's circular. For that to work he would have to believe Jesus was the Messiah. HiLo48 (talk) 03:47, 25 September 2011 (UTC)

It is also statistically meaningless: people make prophecies all the time. By simple chance, some will come true - and even more will be claimed to have come true by people reinterpreting later events as 'the prophecy being confirmed'. See Nostradamus and other hogwash for more evidence of the same... AndyTheGrump (talk) 03:53, 25 September 2011 (UTC)

It is not circular, MBR was predicted by the big bang theory. They found it, and other evidence, thus the big bang theory must be right. They were searching for evidence that is predicted by a theory. The prophecy was made several times over by different people over different times, and is too detailed to apply to just anyone. Plasmic Physics (talk) 04:18, 25 September 2011 (UTC)

You have missed the point. I have made mine. And we ARE way off topic. I'll stop now. HiLo48 (talk) 04:25, 25 September 2011 (UTC)

Clearly, there is an anthropic factor at work here:

So, the fact that we are neither machines nor part of a galactic civilization is consistent with anthropic reasoning. Perhaps anthropic reasoning can also explain why we aren't very rational beings. Most people still hold on to religious believes that are incompatible with (modern) science. Perhaps there is an anthropic factor that at work here. Scientific progress has been hindered by religion over the centuries. Perhaps civilizations consisting of more rational beings evolve faster than us and transform to machines in less generations than we will do. The total number of individuals that will ever have lived in our backward civilization may be much larger than in rational civilizations

Count Iblis (talk) 03:49, 25 September 2011 (UTC)

Oh, come on. We are not about to "transform" into machines. It is possible that humans might invent machine intelligences which will kill off or "outbreed" humans ecologically and send them to extinction. But your mind is a relationship between your body and the world. The end of your body is the end of your mind. A copy of your mind (if such a thing is possible) would not be your mind. It would just be a copy of your mind. This sort of "singularity" speculation is even less grounded metaphysically than is the notion of the prime mover. μηδείς (talk) 03:58, 25 September 2011 (UTC)

To try to understand God you must try to understand Good; you must learn and follow the positive movements of people driven by compassion, hope, and faith. If you can understand the historic patterns of these movements and find places and times of great significance, it is possible to encounter one or two of the Lamed Vav Tzadikim, as the Jews call them. Strange things can happen. Wnt (talk) 04:23, 25 September 2011 (UTC)

Here is an interesting answer for you, which would be a yes to your question. Given that Christians consider Jesus the moshiach, the Son of God and God himself, then the fact that archaeologists do actively search for evidence that Jesus Christ did exist (to my knowledge we still don't have concrete contemporary evidence) would mean that there is a serious and scientific effort to prove the existence of God (in one way). Then again, most of the archaeologists doing this are ike myself anyway, so we don't really believe he's God anyway (or the moshiach except for these guys (who are Christians anyway)). ;) You can find it all published in Hershel Shenks's sensational Biblical Archaeology Review. Sir William Matthew Flinders Petrie | ^{Say Shalom!} 26 Elul 5771 06:14, 25 September 2011 (UTC)

What do you mean contemporary evidence? Use Gengis Kahn as an example, what contemporary archealogical evidence is there for his existance? Plasmic Physics (talk) 11:32, 25 September 2011 (UTC)

None that's written by the looks of that article, and I know we haven't found his tomb. Still, no one disputes the existence of Chinghis as far as I know (could be wrong). People do dispute the existence of Jesus and we would need contemporary writings for him. Poor Jesus; can't a Jew get a break? :p Sir William Matthew Flinders Petrie | ^{Say Shalom!} 26 Elul 5771 16:14, 25 September 2011 (UTC)

There's a difference. No one is making supernatural claims about Genghis Khan. No one said he created an empire by killing his enemies using laser beams fired out of his eyes. All of the claims made about him are, well, believable. It's the same thing about Mohammad, I don't dispute his existence, I just don't believe he was a prophet of god. Jesus may have existed, I don't really care either way, I just don't believe the supernatural claims about him. Also I don't believe the prophecies made about him because they may have been fabricated after the fact, and foretell of events that I, nor anyone else, can verify. ScienceApe (talk) 18:11, 25 September 2011 (UTC)

M'yes, and I don't believe the supernatural stuff about Jesus either, but that is not the issue. For many Christians, proving his existence would be proof of God. What I am talking about with regard to Jesus is not whether he was divine or has special power. I was saying that we do not even know if this specific Nazarene Jew even existed as a human being or just a made up character to be the central figure in a new sect of Judaism. Sir William Matthew Flinders Petrie | ^{Say Shalom!} 26 Elul 5771 18:20, 25 September 2011 (UTC)

I know what you were saying. Personally it doesn't matter one way or the other to me. I can accept the claim that he existed but was a normal man. But once they start talking about prophecy and such, I will tell them I can't confirm their story, so their prophecies are meaningless to me. The prophecies, story about his life, and even his own existence could all be fabricated. That's the difference between jesus and Genghis. Mongolians aren't saying "Well we have prophecies that a man will come from poverty and grow up to become a great general who created an empire! This man is god!". Christians on the other hand are claiming this, so I need more evidence. The prophecy has to be true, and the event it predicted must also be true, but in the case of jesus, I can't confirm either. And even then, it still doesn't prove he is god. It would, at most, prove the prediction to be accurate, but the claim that jesus is god can't be confirmed from that prediction. ScienceApe (talk) 22:59, 25 September 2011 (UTC)

Frank Tipler is an example of a (once?) reputable scientist giving a scientific approach to God. Say what you will about his work (I'm unconvinced, to put it mildly), but it is absolutely "a fully documented effort to prove" God's existence using science. I'm sure he's not the only one, but maybe the most successful and visible contemporary one. Staecker (talk) 12:08, 25 September 2011 (UTC)

Perhaps I do not understand what you mean by a fully documented effort but I assume you mean an effort that is done for others in the first place. I know of one effort that was done mainly for the author's satisfaction of disproving a counter claim the author chose to share with others. --DeeperQA (talk) 03:11, 26 September 2011 (UTC)

air pumps

Hypothetically, if I have a narrow tube or pipe down which I want to force air, at a pressure of 0.5psi, say, but that it is in a rather awkward to get to place, then I think through all the options and somehow come to the conclusion that the best way to proceed is to build my own battery powered pump to move the air through, then, how small could such a thing actually be built? What component parts would it need to be made from, I assume there is some limit to the sizes at which they would be able still to work up to that pressure, anyone give some sort of rough estimate here?

148.197.81.179 (talk) 19:29, 24 September 2011 (UTC)

With enough effort it is possible to build a battery-powered pump so small you almost need a microscope to see it. Is that information useful to you? No? I thought not. How about a clearer description of the actual problem? Looie496 (talk) 19:46, 24 September 2011 (UTC)

So how would this microscopic thing actually work, though, would it need some particularly expensive materials to stop such a small thing breaking under the pressure perhaps? What about getting enough power to the mechanism itself? Would the tools to build it be hard to get hold of?

Or if you insist, how about this then, how small would be possible just using things that someone or some people could easily go out and buy and put together? Could people with enough knowledge, somewhere to work and not a huge amount of money build one that could fit through a hole perhaps say 10mm wide? What about 5? 148.197.81.179 (talk) 19:56, 24 September 2011 (UTC)

As Looie says, it would be much easier to help us if you tell us what you are actually trying to do. --Tango (talk) 20:50, 24 September 2011 (UTC)

It would be very much easier and cheaper to buy a standard air pump, site it some distance away, and just insert the outlet pipe through the narrow gap, but I assume your particular application precludes this simple alternative. Dbfirs 06:41, 25 September 2011 (UTC)

September 25

How do slot machines "decide" when to pay out jackpots and other large winnings?

What kinds of variables, factors, formulas, etc. do they use? Thanks. --70.179.163.168 (talk) 01:42, 25 September 2011 (UTC)

Have you read Slot_machine#Technology? --Mr.98 (talk) 01:47, 25 September 2011 (UTC)

I have every once in a blue moon read some intriguing news snippet about people prosecuted for using "an electronic device" to influence the odds of slot payouts. I assume that the organized crime syndicates that set up the casinos must have ways to make it as easy for someone to win big as it is for someone delivering a payment to arrange to lose everything; otherwise it wouldn't be a very effective way to tracelessly launder money. Though apparently lower-tech methods work pretty well.^[30] Wnt (talk) 03:55, 25 September 2011 (UTC)

Looks like someone might have been watching too many James Bond movies... ;-) 67.169.177.176 (talk) 04:21, 25 September 2011 (UTC)

Frozen milk

Why is it that when you defrost a bottle of frozen milk, that the liquid milk is initially richer in lactose, making it digustingly sweet? Only once the milk is completely defrosted, does the lactose concentration return to normal. Plasmic Physics (talk) 06:27, 25 September 2011 (UTC)

Ice formation means that the water is all tied up, so anything in the rest of the milk is more concentrated, basically fractional freezing. SDY (talk) 06:43, 25 September 2011 (UTC)

Oh. That reminds me, can you filter out the additives from denatured ethanol using fractional distallation? Add water to denatured ethanol, and partially freeze it so that it forms a crust of ethanol/water. Collect the crust, and repeat after adding more water. Melt all the crusts back down into a ethanol solution. Keep adding anhydrous magnesium sulfate untill anhydrous ethanol is obtained. Will the crusts be free of additives? Plasmic Physics (talk) 09:13, 25 September 2011 (UTC)

I don't think so - fractional freezing will enrich the liquid portion in the lower freezing part of the mixture -eg alcohol - but it will not remove methanol from the alchohol mixture - this remains in the alcohol part not the frozen water part.Imgaril (talk) 11:03, 25 September 2011 (UTC)

I don't have to worry about methanol - in modern times, methanol is banned in many countries, from being added as a denaturant. According to the article, the frozen component contains ethanol, that is what I am taking advantage of. Plasmic Physics (talk) 11:23, 25 September 2011 (UTC)

Do you have a reference for that? My understanding is that methanol is still the most common additive used to denature ethanol. That's what our article on denatured alcohol seems to say. The whole point of denaturing it is to make it undrinkable, so that methanol is highly toxic is hardly a reason not to use it. --Tango (talk) 15:31, 25 September 2011 (UTC)

Denatured alcohol may or may not contain methanol; what it does usually contain are isopropanol (gives you a tummyache like you wouldn't believe), denatonium and various ketones (taste awful) and also pyridine (makes you throw up). Note that the additives are purposely chosen so that they cannot be easily removed from the alcohol. 67.169.177.176 (talk) 02:25, 26 September 2011 (UTC)

The way fractional freezing/freeze distillation works is that when water (or any other substance) freezes, it wants to form a regular crystalline lattice, as that's the most energetically favorable way of forming a solid (especially for water, which has all those hydrogen bonds to form). Any impurity would disrupt that crystal lattice, so the substance tries to exclude it from the lattice when possible (but if you freeze something long enough or fast enough, the impurities will get trapped in the solid eventually). Therefore anything that's not what's crystallizing gets concentrated in the still-liquid portion. -- 174.24.217.108 (talk) 18:01, 25 September 2011 (UTC)

I had a second look at the references, they seem to contradict each other, so I retract the statement on methanol. What about the remaining additives? Can the alcohol be removed using the above technique? Plasmic Physics (talk) 22:29, 25 September 2011 (UTC)

Why do farms have soil?

So I've been reading the article on hydroponics, and it occurs to me that if it is a method which is cheaper due to various efficiencies savings, and reliable, it is in the main simply better. In particular, better for industrial growing because the disadvantages can be dealt with by using good precautions. But latifundia of farms don't use hydroponics, almost all fruit and veg is still grown in all countries using traditional fields. Why is this, surely a hydroponic farm would be cheaper and therefore 'better' for the farmers? Prokhorovka (talk) 11:29, 25 September 2011 (UTC)

"Using good precautions" certainly costs money. And soil is getting cheaper and cheaper. The same applies to the logistics, which enables you to trade products across the globe, and therefore, from places with even cheaper soil. Quest09 (talk) 12:02, 25 September 2011 (UTC)

Cheaper in the long run and in bulk amounts. It requires a substantial amount of capital and know-how to start up. Something inaccessible to most people.-- Obsidi♠n Soul 12:34, 25 September 2011 (UTC)

So it's soil economics and capital costs in the main? Many thanks. Prokhorovka (talk) 17:01, 25 September 2011 (UTC)

Add to it the risk of epidemics. Hydroponics are also an excellent for the cultivation of bacteria. Quest09 (talk) 19:02, 25 September 2011 (UTC)

Can you imagine the sheer complexity of having millions of hectares of hydroponics? How would you mechanically harvest a field of wheat or maize (let alone potatoes) without destroying the equipment? For veg it is already a reality (so long as 90 hectares is a latifundia) - check out Thanet Earth. SmartSE (talk) 22:20, 25 September 2011 (UTC)

Moon escape away from Earth

If the Moon were able to escape from its current orbit to a far enough point where no more Earth-Moon tides would be significant, would this affect Earth's day and by how amount approximately?--Almuhammedi (talk) 14:21, 25 September 2011 (UTC)

The answer to this type of physics question always depends: how would the moon "escape" from its orbit? If you can specify that, we can follow through with the consequences by solving the equations of motion for the Earth-Moon system.

For example, if you hypothesize that a giant comet large and fast enough to change the moon's orbit were to impact the moon, .... well, we would need to calculate the effect that such a large comet has on the orbits of Earth and everything else in the solar system, too. We could solve that problem by setting up an n-body problem to model the solar system, including Earth, Moon, Sun, and other planets; and we would use perturbation theory to study how sensitively the system reacts when we add in a new comet on a course to impact the moon. The results are difficult to compute, but this can be done in a reasonable amount of time with a reasonable amount of effort.

Our article on tidal locking has some mathematics, including this equation, but it's lacking the context you would need to apply it in our hypothetical case. (The equation depends on some assumptions, e.g., that the moon is smaller than the earth, and so on - and the question is about Earth's day - so we need to reformulate that equation to solve for Earth as the object that will become tidally locked... which is just a little messy mathematical manipulation). Suffice to say: the timescales for tidal locking (i.e., engaging an orbital/rotational resonance) depend very strongly on the distance between the Earth and the Moon. By being farther away, the moon has a much smaller effect on Earth's rate of rotation. This effect (semimajor axis to the sixth power) almost always will overpower any other effect, including a change in the Moon's mass, angular momentum, etc., due to inelastic collision with a comet.

On the other hand, if you just want to make something up, "just imagine" that the moon magically changes its orbit, all bets are off. We can't meaningfully speculate what consequences follow when one law of physics breaks "because of magic." Anything could happen. Everything we know about the way the Moon's orbit couples into the Earth's rotation depends on the rules of physics as we currently understand them. Nimur (talk) 15:16, 25 September 2011 (UTC)

I'm afraid I was trying to just imagine that Moon has dropped suddenly from the 3 body or 2 body problem and I wasn't paying attention to other effects that will definitely take place. I was just interested in Earth's spin because I though it would be if affected the most significant thing we would realize (tides for example won't make things worse as I expect).--Almuhammedi (talk) 15:52, 25 September 2011 (UTC)

Tidal acceleration#Effects of Moon's gravity explains the effect of the Moon on day lengthening. Removing it would stop the change in day length, but the Earth needs no outside power source to keep turning. Simple conservation of momentum keeps it spinning. Wnt (talk) 16:48, 25 September 2011 (UTC)

The tidal interaction between the Earth and Moon is causing the Moon to slowly move further away from the Earth and for the Earth to slow down in its rotation (lengthening the day). Removing the moon would stop that and the length of the day would become pretty much constant. There is a theory that the presence of the Moon has helped keep the orientation of the Earth's axis stable, so that orientation may start moving around more if the Moon disappeared. See What If the Moon Didn't Exist for a description of some work that was done trying to work out what the Earth would be like if the Moon had never existed (that's a little different to the moon disappearing now, but still interesting). --Tango (talk) 17:04, 25 September 2011 (UTC)

Neutrinos speed at OPERA

What was the speed of alleged superluminous neutrinos in OPERA experiment? Our article doesn't specify it.--178.181.211.251 (talk) 18:19, 25 September 2011 (UTC)

From OPERA experiment: (1.0000228 ± 0.0000028_statistical ± 0.0000030_systematic) times the speed of light. Dragons flight (talk) 18:26, 25 September 2011 (UTC)

Which is what in km/h? 178.181.144.239 (talk) 19:15, 25 September 2011 (UTC)

1,079,277,460 km/h Dragons flight (talk) 19:18, 25 September 2011 (UTC)

The implication that communication may travel backwards in time if neutrinos go faster than the speed of light is still nullified by the fact that neutrinos nor light can travel into the past by going more fast from point A to point B than in zero time. Going back in time requires time reversal and not just exceeding the speed of light. Try unburning a candle first. --DeeperQA (talk) 20:42, 25 September 2011 (UTC)

DeeperQA, who are you replying to? No one in this conversation mentioned sending messages back in time. APL (talk) 20:54, 25 September 2011 (UTC)

but since you mention it, I feel compelled to reply because what you said isn't correct. It would be correct if we lived in a Euclidean space. But Physicists know that this is not the case. That's been known for over a century now. This is a relativistic effect. Faster than light travel (FTLT) does indeed allow for messages to be sent backwards in time and that's why FTLT is believed by most physicists to be impossible. Dauto (talk) 23:16, 25 September 2011 (UTC)

Well I mentioned it because its usually the next thing to come. Lets say there is an electromagnetic wave that can travel in empty space but at slower speed due to a hiccup in its electromagnetic interaction. If you send info via that wave it will get there after the same info sent by light. You can send info by light versus by "slower" wave traveling back in time but it is not the same as time reversal except perhaps for using the speed of "slower" wave as your reference. My reference, however, is zero time in which it is not possible to travel at all. A candle will not burn in zero time and you can not unburn it if you started at a later time and tried to get time to go in reverse. --DeeperQA (talk) 01:14, 26 September 2011 (UTC)

See tachyonic antitelephone. If anything can travel faster than light, then it is always possible in principle to construct a system that allows information to be sent back in time. If your tachyon is only slightly faster than light (as per the neutrino claim), then one half of your system must be moving just slower than the speed of light in order for it to work, but such things are always possible in principle. Dragons flight (talk) 01:40, 26 September 2011 (UTC)

But either end could be the moving end, right? Maybe Wikimedia should build a stationary receiving end now, in case the Wikimedia foundation at some point in the future builds the 99.99+% speed-of-light spaceship needed to form the transmitting end. Imagine the advantages of letting editors from the future edit the encyclopedia. APL (talk) 02:00, 26 September 2011 (UTC)

Dauto and Dragons flight, the standard argument that FTL communication is always possible with tachyons makes very little sense, as I said in the #FTL neutrinos thread. It depends on the weird quasi-Newtonian assumption that the causal "future" for an emitted tachyon consists of later coordinate times in the rest frame of the emitter. This is all kinds of crazy. First, I can't imagine why anyone would expect it to be true in the first place, post-1905; it's comparable to emission theories of light. Second, both ends of a tachyon worldline, or neither, can be "the emitter" by this definition, so it isn't even logically coherent. Third, what exactly is "the rest frame of the emitter" in quantum field theory? Fourth, wouldn't "the emitter" here be a muon traveling toward the detector at much more than (1 − .0000228) c wrt the ground? Because if so, and you believe this silly rule, then the emitted tachyon would have to be going at much less than (1 + .0000228) c. -- BenRG (talk) 02:22, 26 September 2011 (UTC)

I like the idea of recording something now and preserving it for the future so that it can be edited later on. It is the sending the edit back in time that I do not think will work. --DeeperQA (talk) 02:27, 26 September 2011 (UTC)

Oddly enough, its true that the theory of relativity is not a Euclidean model of space, and yet still, it has resulted in a century's worth of complex and useful modeling. Nevertheless, that has not stopped me from trying to sort this mess out for my own peace-of-mind, thus I should be blogging my Euclidean toy model in the near future, as it might help us to incorporate a recently discovered quantum mechanics analog, as well the new neutrino data, if necessary... such that we can perhaps ditch a load of metrics. Modocc (talk) 04:35, 26 September 2011 (UTC)

entry and exit door lock logic

Some front door locks have a small chisel edge knob in the center of the door knob that turns to lock or unlock the door. For some doors the chisel knob position controls both exit and entry. On other doors the chisel knob position does not effect exit but only entry. Where can I find a table or diagram for all types of entry and exit door lock logic? --DeeperQA (talk) 18:53, 25 September 2011 (UTC)

I believe that it's called a "Snib" if it helps. Alansplodge (talk) 21:45, 25 September 2011 (UTC)

...humm, that introduces another level of logic where you can block use of a key. The entry logic would then have three states:

1. door unlocked
2. door locked requiring a key to open
3. door locked

--DeeperQA (talk) 01:27, 26 September 2011 (UTC)

Living on Mount Everest

Does anything live on the top of Mount Everest? Whoop whoop pull up ^{Bitching Betty | Averted crashes} 19:16, 25 September 2011 (UTC)

No. Please stop asking all these frivolous questions. We have an article on Mt. Everest you know, perhaps you should try reading it. Beeblebrox (talk) 19:21, 25 September 2011 (UTC)

The article only says what lives on the mountain (all elevations,) not if anything lives on the TOP (summit) of Everest. And I do not believe i have asked many frivolous questions >:-( (two is not a lot.) Whoop whoop pull up ^{Bitching Betty | Averted crashes} 19:26, 25 September 2011 (UTC)

Ok, let's try it another way. The top of the mountain is referred to as the death zone. What do you think might live in the death zone, where it is extremely cold and the air is so thin you have to bring your own oxygen? Beeblebrox (talk) 19:36, 25 September 2011 (UTC)

Well, come on, humans have to bring their own oxygen. Doesn't follow that everything does. I don't know whether there's any life that can survive in that environment (some sort of plant or cyanobacterium with some serious antifreeze in its tissues?) but the question is not absurd on its face. --Trovatore (talk) 19:47, 25 September 2011 (UTC)

i have the same question in my mind, but im glad someone else asked it looking at the response it gets — Preceding unsigned comment added by 203.112.82.128 (talk) 19:48, 25 September 2011 (UTC)

Well, others have asked too. This astronaught chap went all the way to the summit in May 2009 to find out: "Searching for signs of life on Mount Everest could provide a window into the extreme environments that organisms might inhabit elsewhere in the universe. So, former astronaut Scott Parazynski will set up instruments to hunt down elusive evidence of life at the top of the world when he attempts to summit Everest Wednesday." Watch this space while I try to find out what happened. Alansplodge (talk) 20:18, 25 September 2011 (UTC)

More about Scott Parazynski's search here; apparently NASA were hoping to find some Endoliths. Alansplodge (talk) 20:29, 25 September 2011 (UTC)

According to our article, tardigrades have been found at altitudes of over 20,000 ft in the Himalayas, and they have survived exposure to the vacuum of space, so I imagine they could live at the top of Everest. Gandalf61 (talk) 20:44, 25 September 2011 (UTC)

This article states: "Pressure decreases with increasing altitude, such that at 10 kilometers (6.2 miles) above the Earth's surface, the pressure is only about one-fourth that at sea level. Organisms have been discovered growing on the top of Mount Everest, the highest point on the Earth's surface (more than 8.8 kilometers [5.4 miles])." Frustratingly there are no more details, but there is a list of sources at the end. Alansplodge (talk) 20:47, 25 September 2011 (UTC)

There have been periods in Earth's history when the entire Earth was frozen solid, see Snowball Earth and Huronian glaciation. Count Iblis (talk) 21:58, 25 September 2011 (UTC)

According to Alpine_Chough#Distribution_and_habitat, 'It has been observed following mountaineers ascending Mount Everest at an altitude of 8,200 m (26,900 ft)' (ref's from a book, so I can't check it myself). Not inconceivable that it might also make it up to summit or thereabouts for a scrat around sometimes. --Kurt Shaped Box (talk) 22:12, 25 September 2011 (UTC)

If there is something living on Everest it has not been found Yeti. Cuddlyable3 (talk) 22:36, 25 September 2011 (UTC)

The thing about the oxygen is, from what I understand, most of us have lungs far too small for such high altitudes to deal with the scarcity of oxygen. So, with people living at higher altitudes, natural selection would favour larger lungs, ya? Couldn't successive generations gradually moving up say 20 ft each generation maybe be able to adapt to permenant life on top of the mountain (not saying that the larger lung adaptation is given)? Provided they have some sort of food and water source as well as some bit of warmth. Sir William Matthew Flinders Petrie | ^{Say Shalom!} 26 Elul 5771 22:47, 25 September 2011 (UTC)

You've hit upon the real issue, which is sustenance. If a tiny organism could survive the climate at the top of Everest, presumably it still has to eat something, unless it can somehow subsist on ice and snow. ←baseball Bugs ^{What's up, Doc?} carrots→ 23:31, 25 September 2011 (UTC)

Yea, except in a few rare, extraordinary cases, animal life follows plant life. Animals won't migrate to a place without plants. APL (talk) 23:37, 25 September 2011 (UTC)

Maybe, That'd be about a 10,000 year experiment. However, 10,000 years later you may find that your entire experimental tribe had dwindled to nothing and gone extinct.APL (talk) 23:37, 25 September 2011 (UTC)

(after ec) Human corpses? There's quite a few up there now. Too difficult/risky to get them down. Scavengers gonna scavenge. --Kurt Shaped Box (talk) 23:39, 25 September 2011 (UTC)

I'm not seeing it in the George Mallory article, so my memory may be faulty... but it seems to me I had read someplace that there was evidence of birds or other scavengers having fed on Mallory's body to some extent before he solidified. That wasn't at the summit, obviously. ←baseball Bugs ^{What's up, Doc?} carrots→ 00:21, 26 September 2011 (UTC)

Mount Everest#Flora and fauna mentions some birds being seen at fairly high elevations, and a spider that lives at about 22,000 ft, but that is still well below the summit. Up here in AK we have the highly improbable ice worm, which scientists currently have a very poor understanding of, but I've never heard of them living in the Himalayas. Beeblebrox (talk) 00:35, 26 September 2011 (UTC)

You learn something new every day here on wikipedia. Worms that are so well-adapted to the frigid that if it gets above 40 they disintegrate. Amazing. Like a worm form of Dracula. And they feed on algae, and the algae's presence there on glaciers has to be a story in itself. It would be interesting to take some of these worms and algae to the top of Everest and see how they would do. ←baseball Bugs ^{What's up, Doc?} carrots→ 00:43, 26 September 2011 (UTC)

Well plants only need CO₂ and water and minerals they could get from under the ice on the surface of rock and light which they may need only 1/10th as much as full sunlight to grow. They produce oxygen and nutrients so animals could grow.--DeeperQA (talk) 01:38, 26 September 2011 (UTC)

"... if it gets above 40 they disintegrate." -- One presumes you mean 40 degrees Fahrenheit, not 40 Celcius. Mitch Ames (talk) 12:24, 26 September 2011 (UTC)

Lichen might be a candidate for living atop Everest. StuRat (talk) 12:33, 26 September 2011 (UTC)

And what animals might live on Lichen? --DeeperQA (talk) 17:32, 26 September 2011 (UTC)

Caribou enjoy a nice lichen and are better suited for cold then most, but I don't think they could handle the lack of O2. Googlemeister (talk) 18:42, 26 September 2011 (UTC)

Sanitary storage of cups and glasses

I keep coffee mugs, as well as other cups and glasses in a cupboard that has solid shelves. I've noticed that some people like to set receptacles in there upside-down, so they won't collect dust on the inside while waiting for use. Others like to place them right side-up, so the lip of the vessel won't be resting on the potentially dusty surface of the shelf.

Is one method really more sanitary, or is this just down to personal preference? I apologize if this has been asked and answered before; my search of the archives didn't quickly reveal it. Thanks in advance for reasoned opinions. -GTBacchus^(talk) 23:08, 25 September 2011 (UTC)

For the two options you gave, it is personal preference. The completely sanitary methods I've witnessed there are two more choices. Once is to place a saucer on the shelf and the cup upside down on the saucer. So, the saucer is clean and the cup is upside down on the clean surface. The other is to have cupholders so the cups hang and don't touch anything (except the handle where they hang). -- kainaw™ 23:21, 25 September 2011 (UTC)

... and a further option that I thought Kainaw was going to suggest ... place the mugs right side up, but with a sheet of paper over the top so that dust doesn't fall in. Are we being paranoid about a bit of dust? -- we breathe it in all day! Dbfirs 08:12, 26 September 2011 (UTC)

Paranoid? No. I don't care that I ingest dust. This question was asked out of academic interest. I'm not going to change the way I store cups, which seems to be about 50/50 between the two original methods asked about. -GTBacchus^(talk) 15:34, 26 September 2011 (UTC)

I was once grossed out at my grandparents house, since they stored glasses on a high shelf, with the opening down. Since the shelf was high, and they were short, they couldn't see that he shelf had dead bugs on it. Yuk !

Personally, I always rinse glasses after I remove them from the shelf, to get the dust and germs off them. Note that none of the methods listed so far prevent a spider from dragging it's pus-filled butt along the glass on the outside, where your lower lip goes when you drink. StuRat (talk) 12:25, 26 September 2011 (UTC)

Here's the solution to that Arachnid menace. Cuddlyable3 (talk) 13:24, 26 September 2011 (UTC)

I have taken to using the tops from Pringles tubes, and similar clear plastic tops from other similar food packaging (according to size requirements), to use as coasters on which to place upside-down drinking vessels, or as covers for ones displayed right-way-up (I collect branded beer glasses). {The poster formerly known as 87.91.230.195} 90.197.66.194 (talk) 15:21, 26 September 2011 (UTC)

Another variable: After washing, I have taken to stacking glasses and bowls irregularly such that they will be certain to dry out completely over a few hours. When stacking plastic bowls in the normal fashion, a seal can be formed that traps the moisture currently on the bowls. I have no proof that my method prevents explosive bacteria growth within the trapped water, but that's what I've been doing. Comet Tuttle (talk) 19:28, 26 September 2011 (UTC)

Another option is to have one cup and one bowl. You want to use it. You wash it. You know it is always clean when you use it. -- kainaw™ 19:32, 26 September 2011 (UTC)

Now you're singing my tune! Get enough cups and bowls, and you start to think you need a washing machine! Something about simplicity... -GTBacchus^(talk) 19:52, 26 September 2011 (UTC)

RhD reaction

What are RhD+, weak, and RhD- reactions?Markid1 (talk) 23:28, 25 September 2011 (UTC)

While there may be other reasonable interpretations, my guess is that this refers to the D antigen in the Rh blood group system. That page I linked should explain the reactivities pretty clearly. -- Scray (talk) 02:18, 26 September 2011 (UTC)

September 26

Coilgun

What would be the ideal specifications of a railgun with a 'muzzle velocity' of 30 km s^-1 for an 600 Mg projectile? Coilgun, not a railgun. Plasmic Physics (talk) 02:21, 26 September 2011 (UTC)

Are there two separate questions here? Are you prepared for the Recoil associated by Newton's Law with the time derivative of the projectile momentum you describe? Here are ideal specifications: Railgun: Fits in pocket, uses ordinary AA batteries and is clearly marked "Warning: bullet comes out this end". Coilgun: Available in a range of pastel colours, fits in pocket, uses ordinary AA batteries and is clearly marked "Warning: bullet comes out this end". A page in Wikipedia gives many sources of information on railguns, among them is Count Zero by William Gibson that states: "You can rig a railgun to blow itself to plasma when it discharges." This danger should be addressed by an obligatory warning label. Cuddlyable3 (talk) 13:17, 26 September 2011 (UTC)

I mean, how can it be achieved using existing technology? Assume that recoil is accounted for, that the weapon operates in a vacuum, and that it is no longer than one kilometer in length. Plasmic Physics (talk) 13:34, 26 September 2011 (UTC)

You would need to be very specific on what you mean by ideal. Engineering is all about compromises. If you want it stronger, it will either be more expensive, or weigh more is a common trade off, so without knowing exactly what you want, specifications are quite impossible to provide. Also, I would be surprised if many here are deeply involved in the finer points to coil gun engineering, so even with a great list of specs you need, we probably can't help all that much. Googlemeister (talk) 14:00, 26 September 2011 (UTC)

OK, I'll see how far I can get. It is a naval artillery piece, opperating in a vacuum and zerogravity, it needs to be energy efficient, easy to repair, prefferably not self-destruct on firing. Cost and weight is not not an issue, assume infinite construction supplies, so the design can be as exotic. Plasmic Physics (talk) 14:14, 26 September 2011 (UTC)

conciousness

I need to store my conciousness in the computer so my family can have acess to me after I die. Are there any software programs that can do this? — Preceding unsigned comment added by 78.148.142.217 (talk) 11:13, 26 September 2011 (UTC)

There is work being done in areas that would seem to relate to the question you pose, as reported here and here, but the results do not seem to be ready for prime time. Bus stop (talk) 11:34, 26 September 2011 (UTC)

Those studies are just about recording visual images you are currently thinking about. Next they need to be able to scan visual images stored in your memory, then non-visual images, then they need to read your personality, then they need to put it all together to form a consciousness. Each of those steps is a massive leap. So, there's a long way to go, yet. StuRat (talk) 12:06, 26 September 2011 (UTC)

They aren't even quite that, yet. What they are matching bloodflow patterns in your visual cortex to a library of bloodflow patterns from other visual cortexes. Which is pretty damn cool and just the tip of the iceberg, to be sure. But they aren't really about recording visual images — they're looking at patterns and finding ways to correlate those to other patterns, which through very clever work actually corresponds in a recognizable way to images actually seen. But they aren't really able to show what the visual cortex "sees" in its raw form, and it's not clear that it even works for things you are "currently thinking about," as opposed to "stuff your eyes actually are seeing right then." --Mr.98 (talk) 14:20, 26 September 2011 (UTC)

This might sound dumb, but is that kind of like how sound can be translated into little electromagnetic signals and then the magnets on a speaker can recreate the vibrations? Sir William Matthew Flinders Petrie | ^{Say Shalom!} 27 Elul 5771 15:45, 26 September 2011 (UTC)

When do you need it by? We're not quite at the singularity yet, but give it a few decades and who knows. We'll even throw in a jet pack with it, for you. --Mr.98 (talk) 12:01, 26 September 2011 (UTC)

Actually, we do have jet packs now, it's just that they are rather dangerous and run out of fuel way too quickly to be useful. StuRat (talk) 12:08, 26 September 2011 (UTC)

It was meant to be a wry comment on the value of predictions about future technology. Just because something is technologically feasible does not mean it actually will be adopted. --Mr.98 (talk) 14:17, 26 September 2011 (UTC)

I'll take two please. And a death ray.-- Obsidi♠n Soul 12:09, 26 September 2011 (UTC)

For something less ambitious, how about recording video clips containing your thoughts on a variety of topics, and indexing them on your computer, so your family can access those clips whenever they wish ? StuRat (talk) 12:12, 26 September 2011 (UTC)

A single copy of your software for backup purpose is allowed but you may not distribute copies yourself of yourself. Before you go to immortal dataspace please install Skype so that one can still converse with you posthumously. Will Mr. Magill in Manchester grant an exclusive interview to this uplifting magazine ? Cuddlyable3 (talk) 12:43, 26 September 2011 (UTC)

Sadly, even if the software did exist, (and it doesn't), your desktop PC likely lacks sufficient memory to store your consciousness with full fidelity. Also, I suspect most humans last longer then most desktop PCs, and most hard drives contained therein. Googlemeister (talk) 13:56, 26 September 2011 (UTC)

I thought I read somewhere you would need 20 TB of HDD space to store a human conciousness, though I have no idea how they came up with it. Sir William Matthew Flinders Petrie | ^{Say Shalom!} 27 Elul 5771 15:45, 26 September 2011 (UTC)

The human brain has 10¹¹ neurons in it — which is 1000GB worth if each neuron were just a byte. But what's really important are the connections between neurons — there are about 10¹⁴ to 10¹⁵ of those (or, if every connection was 1 byte, between 100TB and 1PB). (In these byte estimates, I am using true GB, TB, and PB definitions, not GiB, TiB, or PiB). So I don't know where 20TB would come from, as a number. All of this makes a lot of arbitrary and no doubt incorrect assumptions though about how much data this technology would require. Assuming these were just stored as fairly simple numbers, you could probably achieve extremely high levels of compression... but anyway, these numbers are kind of meaningless except as an order of magnitude estimate of how complex the human brain is as an organ. (Numbers from Neuron#Connectivity.)--Mr.98 (talk) 20:49, 26 September 2011 (UTC)

I doubt that the question was serious, but in any case the most appropriate answer is a pointer to our article on mind uploading. Looie496 (talk) 15:04, 26 September 2011 (UTC)

In case it was, has the author thought about how unhappy such an existence would be? It would effectively be like living as a quadraplegic, able to see the world in front of you, but not actually go into it. Of course by the time the tech is available, advances in robotics might make my arguement null. Sir William Matthew Flinders Petrie | ^{Say Shalom!} 27 Elul 5771 15:45, 26 September 2011 (UTC)

Well, the robotics needed is far beyond the current state of the art, but the technology needed for mind uploading is quite a bit farther beyond the current state of the art. Looie496 (talk) 17:37, 26 September 2011 (UTC)

Believe it or not you can be simulated by a variety of methods of which neural networking is the current favorite used by IBM's Watson. Just restrict the input data to all of your past and present thoughts (rules) and Watson or its equivalent will use neural networking to simulate you. My personal favorite in terms of strictly logical thinking. --DeeperQA (talk) 19:04, 26 September 2011 (UTC)

Sigh. None of the previous paragraph is correct. That is a total misrepresentation of the Watson project; and the article you linked to is dumb. Comet Tuttle (talk) 19:24, 26 September 2011 (UTC)

IBM Watson does not use a neural network. IBM Watson uses a large, eventually consistent database and advanced natural language processing, as well as massively parallel computing. A neural network is a programming-paradigm for solving specific types of numerical math problems. It's actually a very poor algorithm, in my opinion, compared to formal numerical optimization. Neural networks have an amazing tendency toward system-instability and are not very resilient at escaping from local minima. The term "neural network" has been coopted by various science-fiction writers who think it "sounds cool;" in science fiction, it is used to describe "any type of smart computer software." In fact, a neural network is just a specific technique for solving estimating solutions for matrix algebra. User:DeeperQA, most of what you wrote above is incorrect. You might want to read the Watson FAQ. Watson was never intended to "simulate" a human. It is intended to "greatly improve information seeking tasks" and "help make computers more effective at communicating in human terms." Nimur (talk) 21:43, 26 September 2011 (UTC)

Where did you get the idea that IBM's Watson used neural networking? Or even that Neural Networks were the "Current favorite"? I thought they mostly passed out of fashion in the late eighties. I think nowadays they're mostly the "Current favorite" for High School level AI projects. (You know, science fair projects titled "Can a Computer be Taught to Recognize Faces?".)

Also, that article you linked is horrible. I wish I knew who wrote it so I could never read anything by him or her again. APL (talk) 21:53, 26 September 2011 (UTC)

Heh, I recognize the author's email addy; it's the handle of a years-absent Ref Desk "memorable eccentric". — Lomn 22:25, 26 September 2011 (UTC)

This only serves to further my theory that there are only about twelve actual people on the internet; four of them are reference-desk trolls. Nimur (talk) 22:32, 26 September 2011 (UTC)

...and I'm really a dog. HiLo48 (talk) 23:00, 26 September 2011 (UTC)

We'll only have access to this technology for a very brief time, if at all, see here why. Count Iblis (talk) 23:35, 26 September 2011 (UTC)

Maximum number of options from which a human can make a rational decision on optimal choice

What does research indicate is the largest number of applicants a single hiring manager could rationally consider and deliberately pick a single optimal final choice from without resorting to something arbitrary yet decisive such as pulling a resume out of the stack of equally acceptable applicants and being done with it, thereby reducing the winner's attribution of success to pure luck? 20.137.18.50 (talk) 14:31, 26 September 2011 (UTC)

One. (Sorry.) Looie496 (talk) 15:03, 26 September 2011 (UTC)

There's the well-known paper, "The Magical Number Seven, Plus or Minus Two", which claims 7±2 as the number of items the average person can usefully consider simultaneously. That said, I see no inherent reason that a hiring manager couldn't break an arbitrarily large applicant pool into some sort of bracket-style process. That might not get the "best" candidate at the end, for certain values of "best", but it's certainly not success by "pure luck". — Lomn 15:04, 26 September 2011 (UTC)

You've got 375 resumes on the table and your superior is demanding that you fill the position by COB this Friday. 20.137.18.50 (talk) 15:14, 26 September 2011 (UTC)

You didn't say anything about time pressure in your original question. —Bkell (talk) 15:20, 26 September 2011 (UTC)

I would suspect that a hiring manager not subject to any Workplace stress in his/her position in the real would would be like unto a Spherical cow. There are many things about life that inhibit ideal behavior. I wanted to know the usual result of how successful the optimization effort is after taking the real world into account (which has such pressures and more pretty consistently). 20.137.18.50 (talk) 15:36, 26 September 2011 (UTC)

(ec) With 375 resumes, I would first separate them into 7 +/- 2 piles, eliminate some of those, subdivide, and repeat. -GTBacchus^(talk) 15:38, 26 September 2011 (UTC)

375 resumes and a week? No problem, at least for your statement. Divide and conquer. Interviews of finalists the last couple of days. I'll repeat: "might not get the 'best' candidate at the end, for certain values of 'best', but it's certainly not success by 'pure luck'". — Lomn 15:40, 26 September 2011 (UTC)

Would your grouping not be simply mechanical "pulling out of the stack," making it a matter of luck whether someone was in the group that got picked all the way to the finals, making the finalists at least lucky that they got there? To elaborate, imagine the question: Why did you initially put applicant #253 in group number two? Did you have a rational reason for doing so? What did he/she have in common with the other 53 people in group number two and not have in common with everyone not put in group number two, and what made you eliminate group two? Was it the aspect that all of them had in common (if indeed there was one)? In other words, what's the difference between your grouping game and just picking seven resumes off the top or bottom or middle? If one of the applicants that was eliminated for being in the wrong 53-person group upon your first elimination was clearly better upon hearing him/her in an actual interview than any of the other finalists, would not that be very lucky for the finalists that he/she wasn't there? This could be the case for any of the 368 humans you didn't see that got eliminated along the way. 20.137.18.50 (talk) 15:48, 26 September 2011 (UTC)

You seem to have confused my proposal with GTBacchus'. His appears to arbitrarily eliminate groupings. I'm saying "grab 5 resumes, set aside the best, discard the others. Proceed thusly through all 358 resumes. Now return to your set-aside stack of 70 and repeat. Interview the appropriately small subset of finalists." This is necessarily a rough grading (thus "for certain values of 'best'"), but it is not random selection nor significantly luck-driven. — Lomn 16:32, 26 September 2011 (UTC)

What kind of terrible HR person would do anything arbitrary? Allow me to specify more detail: I would separate them into groups according to some criterion (e.g., type of experience), and then make eliminations based on my professional judgment. Then I would choose a finer criterion, etc. Sheesh.

The disadvantage of your method is that the first 5 you grab might be the 5 best. The next 5 you grab might be the 5 worst. Why eliminate one of the best and keep one of the worst in the very first step? -GTBacchus^(talk) 17:09, 26 September 2011 (UTC)

The criterion of being a member of the ingroup of the hiring manager or having one of his or her trusted employees as a reference is a very fortunate "qualification." 20.137.18.50 (talk) 19:13, 26 September 2011 (UTC)

Secretary problem is about a different scenario, but may be vaguely relevant. AndrewWTaylor (talk) 16:24, 26 September 2011 (UTC)

There is a huge qualitative difference that is being overlooked here. One issue is the problem of selecting the optimal member from a large number of items in a group. A second issue is the problem of defining "optimal" by combining a large number of variables - some that are weakly defined - and trying to distill this into a single value suitable for strict "better-or-worse" comparison. The former is a problem of scale, and is fairly trivial to deal with. The latter is a problem of dimensionality. Even with a powerful computer, a high-dimensional optimization problem is difficult to solve; a human may sometimes outperform a digital computer on such problems by using heuristics to sparsify the search-space.

Formally, if the set is comparable, and follows a strict total ordering rule, or at least partial ordering, it is trivial for a human to optimize the selection. The most appropriate technique would be the manual application of a sorting algorithm; the best algorithm to choose depends on the size of the set and the expected distribution. There will be a time-vs.-space tradeoff for each algorithm, and a tradeoff between "best-case," "average-case" and "worst-case" performance. The use of a sorting machine or a digital computer will invariably speed up this process, but is not required. A human can run quicksort on a pile of paper resumes, if they know how to do it. (Use selection sort if you have a small desk; use quicksort if you only have ten minutes until your next meeting).

If the set is highly dimensional and is not strictly orderable, the human will be trying to solve a high-dimensional nonlinear optimization problem; human brains and modern computers are poorly equipped to solve these problems in the general case. Resume-sorting is a good example: there's not a "quality number" printed on top of each resume; the human must estimate whether Resume #3,041 is "better" than #3,042 by applying heuristic interpretations of the resume content. The assumption that there is an optimal choice is formally an assumption that some total-ordering metric can distill a one-dimensional objective function out of the problem, and then we can try to find its "best value." Nimur (talk) 17:31, 26 September 2011 (UTC)

The Paradox of Choice is about consumer decisions, but this is what I was thinking of as I asked the question. The hiring manager is trying to "buy" the best employee for his (company's) dollar. 20.137.18.50 (talk) 17:49, 26 September 2011 (UTC)

Hopefully he plans to pay for an employee and isn't planning on forcing free labor! -- kainaw™ 17:59, 26 September 2011 (UTC)

That is pretty much how I do a lot of things. For this, I'd make two piles: Above average and below average. Then, I'd toss the below average in the garbage. I'd repeat again with Just Average, and Better than Average on the previous Above Average stack. I'd toss the lower group in the garbage and repeat. Eventually, my good stack will have a few resumes that I can look at in detail - even though I've already scanned them multiple times and know them pretty well. It probably make me comfortable to sort this way because it is just a binary tree sort, which is something I've worked with for about 30 years. -- kainaw™ 17:45, 26 September 2011 (UTC)

Honestly what is going to happen is that of the 375 applications, probably 200 will be at least qualified, and the top 50 will have only a negligible difference in quality. Thus mix the pile of applications and take the first 50 from you new mixed pile. Toss the rest. This will have the added advantage of separating the lucky from the unlucky applicants, since you don't need unlucky people in your company. Divide that group into qualified vs unqualified. Toss the unqualified. You should be down to around 30 qualified applicants. Now go through in detail in groups of 10 and keep very highly qualified, and toss those who are barely qualified. Interview these remaining applicants and have a nice week. Googlemeister (talk) 18:22, 26 September 2011 (UTC)

..."the top 50 will have only a negligible difference in quality" - this is only applicable to some scenarios. Nimur (talk) 19:15, 26 September 2011 (UTC)

Simply use a search engine to find all of the applicants that included all of the attributes you desire. If the results are greater than one add another quality until you find "The One". --DeeperQA (talk) 19:21, 26 September 2011 (UTC)

September 27

My question wasn't answered?

See Wikipedia Reference Desk Archives: Science: September 19 2011, Section ″Feces″, a previous reference desk question. Quoted:

Could you possibly find me the exact number for density and buoyancy [of feces]?

— An IP Address

Thank you! 00:16, 27 September 2011 (UTC)