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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.[1] In other news, see this lovely video from Alberta.[2] ;) 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, [3], 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 ([4]) or Myosotis scorpioides ([5]), 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) 

It is highly unlikely that it looks this much like time exists if it doesn't. That said, it most likely doesn't exist as an explicit dimension. The nearby universe (see many-worlds interpretation) that you'd call the immediate future is generally in a different direction than the immediate futures of other universes are from them. This is known as Timeless Physics. It's not well-known enough to have a page on Wikipedia, but it's much simpler and more elegant then any other interpretation, and therefore much more likely to be correct, by Occam's razor. It's hard to say how likely it is compared to ideas that we haven't considered, but there's no reason to suggest that they would have time as an explicit dimension. — DanielLC 23:47, 27 September 2011 (UTC)

Taking other universes for granted but implying that the existence of time is an open question is the fallacy of the stolen concept. μηδείς (talk) 23:23, 28 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 [6]. 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 [7], and then re-added upon checking the source along with the quotes [8]. 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 [9] 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)

I agree with this, although it makes me wonder then why they are christian at all then. ScienceApe (talk) 17:44, 27 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)

No, that's absurd. When people say "god doesn't exist" they mean it in the colloquial sense. In the same way as me saying Vishnu doesn't exist, or Thor doesn't exist, or Bigfoot doesn't exist. Do I mean that literally that it has been proven that they don't exist? No of course, not, it's impossible to prove a negative. But no one will knock you for saying Bigfoot doesn't exist, but when it comes to god, people get pedantic and start arguing about how you can't disprove god, thinking that's a good argument when they are actually committing a logical fallacy called argument from ignorance. In dealing with these pedantic idiots, you have to be more literal and say "I don't believe in god, I reject your claims unless you have evidence supporting them." ScienceApe (talk) 17:44, 27 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.^[10] 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)

As for freezing to make the solution denser, it works with artificial tear eye drops: DO NOT apply eye drops you have just taken out from the freezer, wait till it melts instead. – b_jonas 20:54, 28 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)

There's also a Discovery channel documentary called If We Had No Moon that's very informative. It may be available online. --George100 (talk) 14:43, 29 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)

Yes, as per the ice worms article. ←Baseball Bugs ^{What's up, Doc?} carrots→ 01:58, 27 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)

I'm thinking more on the order of tardigrades mentioned above. --DeeperQA (talk) 00:51, 27 September 2011 (UTC)

A grylloblattid

• Snow fleas live on snow packs eating bacteria and algae and there is the glacier midge Diamesa sp.
• Grylloblattidae is a family of extremophile and wingless insects that live in the cold on top of mountains.

μηδείς (talk) 01:27, 29 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)

I'm still baffled by what kind of answer you are seeking. It seems the specifications of this weapon are that if fires 600 metric ton or possibly .6 gram (big difference there between mg and Mg) projectiles at 30 km/sec, operates in a zero-g vacuum, and is around 1 km long. The caveat about existing technology makes this simple, however. Such a device probably cannot be built at all with existing technology. For one thing, we don't have the technology to lift a single projectile into orbit (the closest source of zero gravity and vacuum), much less the firing hardware. We can't even begin to imagine the other engineering problems and technological solutions. We are talking about a device 1 billion times more powerful than any yet constructed. Your 1 kilometer storage space would have to contain a large scale nuclear powerplant just to charge whatever you used to store energy to fire the device.

If you have any followups, I can try to help more, but you should specify if you are talking about a railgun or a coilgun (and why do you care which?) and if you meant metric tons (Mg) or milligrams (mg). And I'm still struggling with what kind of information would constitute an answer.gnfnrf (talk) 17:43, 27 September 2011 (UTC)

Coilgun specifically, as the rails in a railgun firing at these energies, would turn to plasma on the 1^st firing. Eitherway, I've decided on a coilgun. And, megagrams nor miligrams. Assume the weapon is already in orbit, and it is powered by a nuclear fussion plant supplying all the energy it could need. Is it best to have multiple short coils, or few long coils? Would there be any advantage in using ferromagnetic liquids to better control the magnetic field evolution. How should the weapon be held together. This is the kind of information I need. Plasmic Physics (talk) 23:35, 27 September 2011 (UTC)

A gun that fires a 600-ton shell at a speed of 30 km/s in zero gravity will have a recoil that will certainly disturb the orbit of even the biggest battleship, very likely causing it to tumble out of control after the very first shot. I recommend you seriously consider reducing the caliber of your big cannon. 67.169.177.176 (talk) 23:47, 27 September 2011 (UTC)

Just to show what I mean: Suppose your battleship has a displacement of 45,000 tons (which is a pretty reasonable size), and you fire a 600-ton shell from one of the ship's main guns at a speed of 30 km/s. By Newton's third law, action = reaction, which (since your battleship is in orbit) translates to m₁v₁ = m₂v₂, or in this case m[shell]v[shell] = m[ship]v[ship]. So, when you fire that 600-ton shell with a speed of 30,000 m/s, your battleship will start going the other way at 600*30,000/45,000 = 400 m/s! And what's worse, this delta-v of 400 m/s will occur in a tiny fraction of a second, which will subject the ship (and its entire crew) to a sudden acceleration on the order of several hundred g's! Definitely a very bad idea. (Besides, there's no conceivable purpose for firing conventional munitions of this size -- any target requiring such massive firepower is better dealt with by using nuclear weapons.) 67.169.177.176 (talk) 05:56, 28 September 2011 (UTC)

Cruiser not battle ship. The cruiser is approximately 1.17 km long and has mass of over a 100 Gg. Is it possible for the cruiser to redirect the recoil? Have the gun recoil into a hydrolic chamber, combine this with explosive retrothrusters (a thruster that produces an instantaneous directed explosive force). Plasmic Physics (talk) 07:20, 28 September 2011 (UTC)

I need a weapon can compensate for very large target distance. Nuclear weapons in this case, is only lethal on direct contact, so is too expensive compared. Plasmic Physics (talk) 07:48, 28 September 2011 (UTC)

Each "bullet" is 0.6% of the mass of the ship. Seems like you might have trouble if you get into a sustained firefight. Googlemeister (talk) 13:42, 28 September 2011 (UTC)

It is not really the kind of weapon to get into a firefight with, it is a rock to kill an ant, a final resolution. It is targeted by an A.I., requiring confirmation by the person on command. You tend to use it only if you're certain that it will find the target. Plasmic Physics (talk) 21:45, 28 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)

Only if you consider that in both cases something complex is broken down into small, manageable units, but this is true of many tasks. StuRat (talk) 20:35, 27 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)

The question looks like an LC item. In any case, he's alluding to what Jor-El did in the first Superman film. Kryptonian technology was rather more advanced than ours (although their common sense apparently wasn't). Another approach could be the way Spock copied the essence of his being to Bones in Star Trek II. ←Baseball Bugs ^{What's up, Doc?} carrots→ 01:56, 27 September 2011 (UTC)

I wouldn't say 'years absent'. They've been coming back to the RD with accounts and IPs every so often usually getting blocked when they went too far. The most recent account should be obvious from their promotion of their fairly obscure (i.e. if you see someone promoting it you have to wonder who that person is) work both above and on their talk page (which I noticed a few weeks ago) as well as the similarity of intererests and views expressed on the RD. Nil Einne (talk) 02:55, 27 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)

Hang on, read the Consciousness article on this very site. Capturing a human conscience is not simply a matter of recording their memory - you would have to capture and replicate all of the operational aspects of their brain AND the input and output routes that helped to form and will be needed in order to continue to form the structure and experience of the concsiousness i.e. connecting the replicated consciousness to the outside world via an accurate simulation of a human with a body, eyes, ears etc.. otherwise the 'person' wouldn't respond or react to the world or experience it in a manner equal to the way they did in their original body - crucial to get right if you want an accurate simulation of a person and all their characteristics. I guess you could modify the programme to take account of the lack of a real body, but you'd be massively limiting the realism of the simulation. In short to accurately reproduce a human mind, I suspect that you would need to accurately reproduce an entire human being. — Preceding unsigned comment added by 213.120.209.210 (talk) 15:34, 27 September 2011 (UTC)

Cryonics could be used to preserve the information in your brain until it could be uploaded or repaired. — DanielLC 23:38, 27 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)

There is, of course, no guarantee that any particular combination of search criteria will result in precisely one hit. There's also the practical matter of what kind of search engine to use, and the question of applying judgment to individual cases. Can search engines screen for everything that we expect HR professionals to understand? Why not replace them all with robots, then? -GTBacchus^(talk) 00:59, 27 September 2011 (UTC)

Some writers start by trying to memorize every word in the dictionary and to that end playing crossword puzzles and scrabble. The psychologist's goal as a scientist is to form words and phrases that describe the most esoteric of conditions. All that is required to automate the process of identification by search engine is to use these words as keywords and to use them in the personnel database(s) to be searched. The key is to use all of them by either stating that they define or do not define the entry. The creating of new words, phrases and phrase combinations may one day be the privy of computers but for now it is still pretty much limited to the privy of human beings. See Optimal Classification--DeeperQA (talk) 03:34, 28 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)

— Preceding unsigned comment added by 75.6.243.251 (talk • contribs)

I believe that last time, you were refered to the Bristol Stool Scale and informed that feces is far too variable a substance to come up with a single numerical answer for the density of stool. It will vary wildly from person to person, and from sample to sample for even the same person. --Jayron32 00:23, 27 September 2011 (UTC)

Jayron is correct (as usual). If all faeces stools were the same density we would not have developed the "sinker" and "floater" terms! These two words validate what Jayron is saying. Richard Avery (talk) 06:19, 27 September 2011 (UTC)

Crowbar in a blender...

Is there any blender currently on the market that can successfully blend a crowbar without breaking? This is related to the Will It Blend? YouTube vids. People keep requesting that he do a crowbar, but he keeps finding ways to avoid doing a crowbar.

Also, would it actually be possible to blend diamonds? I know that he blended cubic zirconia in one vid when people were requesting diamonds (due to the cost), but those are less hard. --Kurt Shaped Box (talk) 01:05, 27 September 2011 (UTC)

How many blenders do you know of whose blades are stronger than steel? ←Baseball Bugs ^{What's up, Doc?} carrots→ 01:49, 27 September 2011 (UTC)

None - but that doesn't really mean much. I'm not up on the current cutting-edge blender tech. --Kurt Shaped Box (talk) 01:52, 27 September 2011 (UTC)

The blades of a blender cannot slice or cut a diamond, but if it strong enough, it can smash the diamonds into dust. While diamonds are hard to scratch or cut, they are quite fragile, they can be smashed using a hammer. Plasmic Physics (talk) 03:16, 27 September 2011 (UTC)

And as for the crowbar, it's best to just fuhggedaboutit altogether... 67.169.177.176 (talk) 03:50, 27 September 2011 (UTC)

A crowbar will jam the blades and burn out the motor. Plasmic Physics (talk) 06:05, 27 September 2011 (UTC)

Maybe unless it's a really big blender. ←Baseball Bugs ^{What's up, Doc?} carrots→ 20:13, 27 September 2011 (UTC)

"Will it Blend" is an advertisement, I think it's safe to say that if that brand of blender were capable of it, he would do it.

But seriously, a crowbar would be tough to get through quickly with anything short of a plasma torch. (And if a blender's blades can't make it through the thing in one go, it'll just jam.) APL (talk) 07:14, 27 September 2011 (UTC)

It should work if the crowbar was made from elemental rubidium instead of carbon steal. Plasmic Physics (talk) 08:20, 27 September 2011 (UTC)

I thought that there might actually be a video on YouTube of someone trying to blend a crowbar using a BlendTec blender (and failing), just to diss Tom. Not so. Yet. --Kurt Shaped Box (talk) 11:59, 27 September 2011 (UTC)

This man sized blender could do it I bet. Googlemeister (talk) 13:51, 27 September 2011 (UTC)

Another tunnel-boring machine: "delivers 2.99 million pounds of thrust, the equivalent of 12 Boeing 747s." Bus stop (talk) 02:59, 28 September 2011 (UTC)

There certainly are machines that can tear a crowbar apart, but I doubt if anyone would call any of them a "blender". StuRat (talk) 20:26, 27 September 2011 (UTC)

Hypothetically-speaking, how would one go about designing a blender capable of slicing up a crowbar? I'm just picturing the infomercial now - the pitchman being all like "Look! It will even blend a crowbar and still make guacamole!". Billy Mays would have approved. --Kurt Shaped Box (talk) 23:32, 27 September 2011 (UTC)

Well, it would need to be huge, with blades far bigger than a crowbar (imagine a battleship's prop), and the blades would need to be coated with something hard enough to cut through the steel in the crowbar (corundum would be fine, no need for diamond), and the blades would need to spin at a hellacious speed, which would require a huge amount of energy. StuRat (talk) 00:37, 28 September 2011 (UTC)

I bet it would make a wicked daiquiri tho... --Jayron32 02:47, 28 September 2011 (UTC)

Blades of corundum may crack and or shatter on impact. Plasmic Physics (talk) 06:39, 28 September 2011 (UTC)

Machines which grind off pavement have steel teeth with carbide cutting tips welded on. The same trick is used on carbide circular saw blades. It is a very old trick. Archeologists found an axe from (if I recall correctly) the dark ages which had a hard but brittle steel welded (by heating and hammering) onto a softer iron base, so that it could maintain a sharp cutting edge but would not shatter as easily as the harder and more brittle edge material. Industrial metal shredders are close to what is desired, shredding thick metal castings, but no indication they would handle a crowbar: [11]. I have seen shredders at scrap metal recycling companies which could handle an automobile, including the frame and axles, and I expect a crowbar wouldn't even be noticed. The cutting part shown at 2:20 has a rotating cylinder with long teeth sticking out which basically shears the metal into little pieces. That video is a toy sized operation compared to some. Others have a pair if meshing cutter arrays:[12]. Here they shred steel rebar ans structural steel such as angle. Seems like such a company could build a "blender" with a vertical hopper and a spinning vertical shaft with teeth projecting from it. From captions on some of the videos, it would likely need couple hundred kw motor. Edison (talk) 15:26, 28 September 2011 (UTC)

Those videos are awesome. I'm sooo going to be watching those 'Shred of the Month' vids tonight. It's like a document shredder - but on steroids (anyone else here love feeding the document shredder?). Also, car shredder redirect created... --Kurt Shaped Box (talk) 18:24, 28 September 2011 (UTC)

Homopolar generator

If a conductor were buried at ether the North or the South pole at the rotational axis of the Earth and another at the equator and an insulated wire laid so that a meter could measure any voltage or current between them what would the voltage and current be? --DeeperQA (talk) 01:21, 27 September 2011 (UTC)

Why would 2 metal rods 8,000 miles apart conduc electricity between them? ←Baseball Bugs ^{What's up, Doc?} carrots→ 01:51, 27 September 2011 (UTC)

Homopolar generator --DeeperQA (talk) 02:46, 27 September 2011 (UTC)

It's a reasonable question. Astrophysical unipolar inductors have been analyzed. However, I don't know the answer. Red Act (talk) 02:38, 27 September 2011 (UTC)

The question is how much power would be generated if such a scheme did in fact work. Could enough power be generated to solve the energy crisis? --DeeperQA (talk) 03:17, 27 September 2011 (UTC)

For an 8000-mile insulated wire, the internal resistance would be extremely high, which would defeat the whole purpose of the scheme. 67.169.177.176 (talk) 03:53, 27 September 2011 (UTC)

Near absolute zero casing. --DeeperQA (talk) 04:19, 27 September 2011 (UTC)

And how much energy input would that require? 67.169.177.176 (talk) 04:27, 27 September 2011 (UTC)

Making the process efficient and worth doing comes after knowing if it will work at all. --DeeperQA (talk) 06:48, 27 September 2011 (UTC)

It (voltage and current) depends on how much work (watts) you try to extract from it - which in turn is related to the (reaction) force being exerted on the wire due to the motion of the earth - the general equation is given at the top of Lorentz force. You need the magnetic field at the earths surface, and the angle it makes with the surface of the earth (Magnetic dip ?)Imgaril (talk) 11:00, 27 September 2011 (UTC)

To a first order of approximation, the Earth's magnetic field is fixed in magnitude and rotates along with the circuit, so there's no time-varying change in magnetic flux through the circuit, which means no current is induced. However, there can be geomagnetically induced current due to geomagnetic storms. However, GIC isn't steady or reliable, and hence would make a poor energy supply. Red Act (talk) 16:41, 27 September 2011 (UTC)

So you are saying it will not work because the copper disk and the magnet are turning in sync together? --DeeperQA (talk) 17:04, 27 September 2011 (UTC)

Yes. Red Act (talk) 17:22, 27 September 2011 (UTC)

What if you forget about the equator and build some superconducting hexagons over the north magnetic pole? As it moves you sap the energy from one hexagon, dismantle it, and move it around in the direction the pole is going. How much energy would that produce? Is it possible to trap the pole and keep it from moving with enough superconducting hexagons cutting across the field lines - or even deliberately give it freedom to move only in a direction you want? (Note: this is theory only - real superconductors have limits to the current they can carry, which I think in practice would severely limit the amount of power extracted) Wnt (talk) 18:51, 27 September 2011 (UTC)

Some responders have been too quick to dismiss the question. When a solar flare reaches the Earth, utilities sometimes experience hundreds of volts and hundreds of amperes through neutral conductors when the transformer neutral is grounded at each end of the line. This is seen in lines under a hundred kilometers, at various orientations. There are also earth currents of electricity of varying magnitude, due to different points of the Earth';'s surface being at varying potentials. They were studied by Sir Humphrey Davy, Becquerel and others from the beginning of the 19th century. W.H. Barlow in the 1840's found them strongest in a N-S orientation. They vary during the day and during the year, and are influenced by electrical storms, and relate to the auroras, and to sunspots.. They were sometimes large enough to interfere with telegraph operations. They generally prevented telegraphy from August 29-September 4, 1859. It produced 800 volts on a 600 km line in France. It produced an effect near Boston equal to 200 Grove cells, or about 380 volts. Telegraph lines could in fact be worked without batteries, powered only by the earth currents. In Europe that particular storm had its strongest effect in a NE-SW direction, but would have likely had a huge effect from pole to equator. In 1881 a similar storm produced 1.1 volt per km in England. You could take 1.1 volts/km times 10,000 km from the pole to the equator as a representative value when conditions are favorable, and expect 11,000 volts between the ends of the line. If the ionospheric currents which induce the earth currents have more localized circulation (on the scale of 1000 km,) then over such a long line there could be some cancellation. As a result, a somewhat longer or shorter line might have a higher end-to end voltage. A telegraph line in the 19th century had appreciable resistance, which held the current to .28 amperes in one report from the last work cited, in a 200 mile line from New York to Providence, corresponding to 644 volts. The ground resistance at the terminals and the resistance per unit length of the conductor would be the limiting factors holding down the current.Today researchers use the term "Telluric current"in place of the older "earth current," to indicate that current in seawater is included in the topic. The latter source, from the 1980's indicated that a 2650 volt potential had been measured along a transatlantic cable in the 1950's. It also notes (p245) that in 1921 a geomagnetic storm produced 1kv over a 100 to 200 km line, with 2.5 amperes of current available (probably one or the other conditions would apply: high voltage at zero current, or high current in a short circuit condition.) The source discusses telluric problems on long power lines, including 100 amps of telluric current in 1972, sufficient to damage power transformers. Edison (talk) 19:12, 27 September 2011 (UTC)

Red Act's answer above is incorrect. It's such a common misconception that it has a name--the Faraday paradox--that is also discussed in the homopolar generator article. The first error is saying that the Earth's magnetic field 'rotates with the planet'. Since the field is circularly symmetrical, there is no way of knowing whether it's rotating or not; in fact, 'rotates' has no physical meaning in this case. You can't paint a mark on the field so that you can watch it going round. The error may be caused by people imagining that the field is a bunch of field lines rotating, when in fact field lines are a drawing aid and don't actually exist. The field is really a continuum. The second error is the belief that the generator works by the relative motion of the rotor and the field: it does not. What matters is the relative motion of the rotor and the pickup wire, both of which are within a constant (unipolar) magnetic field. I'll stop here because half of you probably don't believe me, but I leave you to read the relevant articles. --Heron (talk) 19:37, 27 September 2011 (UTC)

Are you saying that the difference in potential between the center of the copper disk and the edges of the copper disk is such that a wire attached to the center of the disk will "drain" that potential at each point on the edge of the disk that it touches and that continuous flow then depends upon the wire touching new points on the edge of the copper disk? --DeeperQA (talk) 19:57, 27 September 2011 (UTC)

Not quite. The potential (I think it could be called electromotive force or EMF) does not exist until the disk rotates. It is created by the rotation of the disk relative to the collector. Imagine that you cut away almost all of the disk leaving just a narrow wedge between the axle and the collector. Now you rotate that wedge through say 1°. From the start to the end of that rotation, the geometry of the electric circuit has changed slightly. Before the rotation, let's say that the axle, wedge, collector and external wiring were all in a single plane. After the rotation, the circuit is no longer in a single plane, because the wedge is now out of the plane, and the current has to return through a tiny arc of the collector and back into the original plane. This is equivalent to tilting the plane of the original circuit slightly. The tilted plane is now not quite parallel to the magnetic field lines, so it has gone from having none of the flux passing through it to having a tiny bit passing through it, and that is how it picks up an EMF by electromagnetic induction. Now, if the collector circuit were rotating with the disk, none of this plane-tilting would happen and there would be no EMF. This is all hand-waving stuff and probably sounds oversimplified to a proper physicist (I'm not one). The real answer is due to the Lorentz force on electrons, but I can't remember how that works so I've gone for the geometrical explanation instead. I believe you need to use special relativity to explain the Lorentz force properly. --Heron (talk) 20:44, 27 September 2011 (UTC)

I follow you up to the point of the plane. In my imagination this plane is horizontal and perpendicular to the axis of the disk which is vertical. To follow what you are saying though it seems I am using the wrong orientation for the plane. The plane you are referring to seems to be in line with and parallel to the vertical axis on which the disk is rotating such as is a knife used to cut a piece or wedge of pie. Is the plane you are referring to in line with the axis of the disk or in line with the disk? --DeeperQA (talk) 01:03, 28 September 2011 (UTC)

The plane is in line with the axis and perpendicular to the disk. If the axis is vertical then so is the plane. Therefore the magnetic field vector is parallel to the plane and does not pass through the circuit. If the plane tilts slightly then a small amount of flux will pass through it. This change in flux through a loop, according to classical electromagnetics, is what induces the current. --Heron (talk) 13:20, 28 September 2011 (UTC)

So you are saying that because the disk is turning for a moment in time the circuit moves with it and becomes slightly tilted to the plane such that opportunity is presented to the magnetic flux to pass through it? --DeeperQA (talk) 19:54, 28 September 2011 (UTC)

Yes. --Heron (talk) 20:23, 28 September 2011 (UTC)

Incorruptible data storage

What's the best way (if any) to store and/or transmit sensitive scientific data in such a manner that said data would be immune to tampering (or nearly so) during storage/transmission? If such a method exists, would it be possible to transmit the data in real time from an aircraft in flight over water? 67.169.177.176 (talk) 03:47, 27 September 2011 (UTC)

Use encryption and error-correcting codes. 208.54.83.223 (talk) 04:09, 27 September 2011 (UTC)

And also digital signatures? 67.169.177.176 (talk) 04:16, 27 September 2011 (UTC)

One more thing: If the plane's RNAV system is integrated with the scientific instruments and the recording/transmitting computer, should the navigator/scientist enter his private key before or after aligning the RNAV? (I'm guessing before, but I need to be sure.) 67.169.177.176 (talk) 04:52, 27 September 2011 (UTC)

An aircraft's flight-critical or flight-essential systems (such as RNAV) should not be integrated with a mission payload. While they might reside on the same computing system, their operation should be independent such that no misconfiguration of mission equipment impacts the safety of the aircraft. — Lomn 13:08, 27 September 2011 (UTC)

Assuming, though, that we're talking appropriate levels of independence, and that the mission payload is pulling some read-only data from RNAV -- I'd have to say, in the very general case, that you always pull data after initialization. It's not at all clear, though, what RNAV data you'd be pulling (a flight plan?) or what "aligning" RNAV would mean, particularly in the context of cryptography. — Lomn 14:01, 27 September 2011 (UTC)

This is correct -- the RNAV feeds position data (including groundspeed/drift angle) to the mission computer, which then uses it to correlate the scientific data (temperature, humidity, solar radiation, levels of CO2 and trace gases, etc.) to the plane's position. So in case of a computer crash, the scientific data is wiped out, but the RNAV system is still operational. As for "aligning" the RNAV system, this involves spinning up the gyros, torquing the accelerometers, and then feeding the plane's current position into the system; this is done before each flight, and is the navigator's responsibility. 67.169.177.176 (talk) 00:07, 28 September 2011 (UTC)

Inertial nav systems -- gyros, accelerometers, and the like -- are not permissible for primary RNAV inputs, as they cannot maintain appropriate NSE. Note also that you're talking positional data, not navigational data. It appears that you ought to just pull from a GPS box. — Lomn 12:33, 28 September 2011 (UTC)

To detect deliberate tampering (i.e., tell legitimate data from bad) you need either a message authentication code or a digital signature. Digital signatures are more expensive to calculate but have some advantages that may or may not matter in your application. To protect against tampering (i.e., ensure that all legitimate data gets through) is impossible in general because the attacker can always just block the signal completely. Error correcting codes might help in certain situations. I can't answer your followup question because I know zilch about aircraft control systems. -- BenRG (talk) 08:00, 27 September 2011 (UTC)

In this case, I am not concerned about the signal getting completely blocked; my main concern is how to prevent the data from being fraudulently altered during storage or transmission. FYI, the aircraft in question is performing a flight around the equator as part of a mission to study climate change (as well as being a memorial flight for Amelia Earhart) -- so the main concern in this case (as far the the data is concerned) is to prevent either the crew or the scientists from altering the data at will for political purposes, just in case they have a mind to. 67.169.177.176 (talk) 00:07, 28 September 2011 (UTC)

It is possible to prevent tampering, rather than just detect it, by using narrow beam transmission and directional antennae at both ends, say to and from a series of satellites. The only way to block such a transmission would be to physically place the jamming signal generator between the plane and satellites, or send a massive EMP to overwhelm the signal. StuRat (talk) 00:22, 28 September 2011 (UTC)

Thanks for the ideas, everyone. Now, how big is a typical narrow-beam directional antenna? Please understand that it would have to fit into an Electra 10-E, which is not only pretty small to start with, but already crammed full of extra fuel tanks (which take up the forward 1/3 of the cabin), navigational equipment, scientific instruments, etc., etc... 67.169.177.176 (talk) 06:13, 28 September 2011 (UTC)

Question about the Galileo Statement

Galileo theorized that in the absence of air, all things would truly fall with the same acceleration and 300 years later demonstrated this by the crew of Apollo-15 on the Moon (which has gravity but lacks air) by dropping a hammer and a feather.

As moon was seen from both the feather as well as hammer with two different gravitational fields [g] therefore just wondering what was the falling acceleration of moon towards aforementioned feather and hammer from the following possibilities [if i'm not wrong]?

1- Moon had the gravitational acceleration of hammer i.e "g" of hammer

2- Moon had the gravitational acceleration of feather i.e "g" of feather

3- Moon had the net "g" of feather and hammer

So, is Galileo's statement correct [Theoretically] if the senario is considered in the absence of all other gravitational attraction.?68.147.43.159 (talk) 03:52, 27 September 2011 (UTC)Eccentric Khattak#1

I'm really struggling to understand the question. Have you seen Newton's law of universal gravitation? VERY strictly speaking, if you drop a hammer and a feather on the moon, I suppose you have a three body problem, but for ALL practical and feasible purposes you can treat the hammer and feather as completely negligible mass compared to the moon. Vespine (talk) 06:53, 27 September 2011 (UTC)

The force on the moon will be the gravitational attraction from the hammer plus the gravitational attraction from the feather. The moon will accelerate towards the centre of gravity of the (hammer+feather) system, a point which will be much closer to the hammer than the feather: so the moon will move very slightly in the direction of the hammer. (The hammer and feather will also accelerate very slightly towards each other, but this tiny movement won't significantly affect the moon's trajectory.)

Since F = (G m₁ m₂)/r, and a=F/m the total acceleration on the moon will be G (m_feather+m_hammer)/r, or with a 1kg hammer and 10g feather about 4x10^-17 m s^-2 (by my calculations). If you drop them from one metre up, the moon will move something of the order of the diameter of a proton. The moon's surface will be much bumpier than this (plus there will be stray gas and dust molecules on the way down), and its gravitational field is non-uniform (because it's not a perfectly homogenous sphere) so in theory the moon will hit the hammer first, but in practice the difference in gravitational attraction will be unimportant to the outcome. --Colapeninsula (talk) 10:40, 27 September 2011 (UTC)

Hammer and Feather Drop - Apollo 15's hammer and feather experiment was carried out by Commander David Scott during the crew's third EVA. . Cuddlyable3 (talk) 18:00, 27 September 2011 (UTC)

Is it correct to say that even if force experienced by hammer is more due to its more mass, acceleration gained by the hammer is same as that of feather because hammer has more inertia due to its more mass? - 61.16.182.2 (talk) 04:03, 28 September 2011 (UTC)

Gender-specific athletic performance

I just noticed that the ratio for men's and women's world records in the marathon is 1:1.0953 and that of the 100 meter sprint is 1:1.0959. I find it fascinating that they are currently equivalent to the thousandth decimal. Is this a coincidence or is this performance ratio present is other events? The Masked Booby (talk) 03:55, 27 September 2011 (UTC)

List of world records in athletics will hold the information you need. --Colapeninsula (talk) 10:42, 27 September 2011 (UTC)

Just crunching numbers for a couple other events, I got a ratio of 1.1215 for the 800m, 1.1319 for the mile, and a ratio of 1.1893 for the high jump, so it looks like a coincidence. Googlemeister (talk) 13:46, 27 September 2011 (UTC)

hall effect

can the following multilayer hall effect sensor be realized by using alternate set of hall sensor(InAs) and a diode(GaAs) both of composition as said in the paper.please suggest.if a diode would not work what else could be substitute in its position of GaAs material.? http://www.waset.org/journals/waset/v39/v39-80.pdf 203.197.246.3 (talk) —Preceding undated comment added 05:18, 27 September 2011 (UTC).

Hypervalency

Bringing back an old topic. In hyper valent molecules, is it correct to say that the hypervalent atom only contributes to some of the orbitals, meaning that the remaining ligands effectively borrow the otherwise LUMO orbitals to complete their valencies? Take pentachloro-λ⁵-phosphane or pentachloridophosphorus as an example. According to my theory, the phosphorus only has a total bond order of 4, despite having 5 ligands. The three equatorial bonds have a bond order of one each, the orthogonal bonds have a bond order of a half each. To make this arrangement work, the two half order bonds will have to be spin paired. Essentially, phosphorus does not contribute to the HOMO. This would should result in a triagonal bipyramidal molecule with a 1+ charge on two chlorines each, and a 2- charge on the phosphorus. The two positively charged chlorines, will move to opposite locations to minimise electrostatic repulsion. The remaining chlorines will move to equatorial positions. Because half bond order bonds are lower in energy than 1 bond order bonds, they are longer. As a result, the orthogonal bonds should be longer than the equatorial bonds, which is what is observed. This is my own idea, the three-centre-four-electron article doesn't make much sense to me, so I synthesised this one. I call it orbital borrowing, since the ligands borrow an orbital(s) from the host, without the host contributing. Another thing to note, is that this orbital borrowing should only be a stable system for molecules where the gap energy between the HOMO and LUMO orbitals of the host is small. So orbital borrowing shouldn't be happening for 1^st period elements, except under extreme conditions. is orbital borrowing correct, and is it a useful description? Plasmic Physics (talk) 11:56, 27 September 2011 (UTC)

Orbital "borrowing" is a useful heuristic to describe what happens in either hybridization theory or molecular orbital theory. However, it is important to remember that in MO theory, the idea is to describe all orbitals of the molecule as belonging to the molecule as a whole; without giving actual care as to where they "came" from. When a molecular orbital has a character which resembles what would be expected from the mathematical combination of two atomic orbitals, we can say it "formed" from those orbitals; likewise if a molecular orbital is largely identical to the atomic orbital in an unbonded atom, we can say that the orbital "did not participate in the bonding" of the molecule; but these are heuristic approximations. Strict MO theory actually treats all electrons (and thus all orbitals) as belonging to the molecule as a whole and describes the orbital space around the entire molecule, and does not pretend to assign electrons or orbitals as "originating" at any particular atom. MO diagrams, in this way, present a good heuristic for predicting what the MO structure is going to look like; but to be scrupulously correct, actual molecular orbitals are described purely by the wavefunction of the molecule in exactly the same manner as the atomic orbitals are described purely by the wavefunction of the atom. And you've also gotten way past the level of mathematics I have experience with, so I'm not sure I can get more detailed than that. The concept of "hypervalency" is a way to jibe the mathematical results of the wavefunctions with the heuristic predictions of the simpler models, like the "octet rule" and Lewis/Valence bond theory. In actuality, MO theory doesn't treat "hypervalent" molecules as a special case; they just are what they are. --Jayron32 16:55, 27 September 2011 (UTC)

Love hurts

Our articles on limerence and being lovestruck mention chest pain as a "symptom". Having experienced this on more than one occasion, I know that it's not made up. My question is, what's the physiological basis/mechanism for this pain? What's making my chest hurt when I'm in love/lovesick? ElMa-sa (talk) 12:53, 27 September 2011 (UTC)

It is commonly called a "broken heart". See Takotsubo cardiomyopathy. -- kainaw™ 13:59, 27 September 2011 (UTC)

This is OR, but my impression is that the ache actually arises from the solar plexus, not the heart. In fact, when people have actual damage to the heart, the pain sensation is frequently referred to other body parts, such as a shoulder. Looie496 (talk) 14:27, 27 September 2011 (UTC)

Takotsubo sounds a bit too serious. If it's the nerves in the solar plexus, what's causing it? Hormones? ElMa-sa (talk) 14:41, 27 September 2011 (UTC)

That article focuses on the worst cases, but in general, stress weakens the heart, allowing for some ballooning to take place, which causes chest pain. There are many kinds of stress and this particular kind tends to follow deeply emotional events - which is why it is referred to as broken heart syndrome. -- kainaw™ 14:45, 27 September 2011 (UTC)

A lot of medical articles on Wikipedia tend to focus on the worst-case scenarios. Thanks for the answers! ElMa-sa (talk) 16:41, 27 September 2011 (UTC)

Hoax about CFL danger?

[13]. Thanks. Imagine Reason (talk) 15:20, 27 September 2011 (UTC)

The linked report collects together various worries about compact fluorescent lights.

• Emission of carcinogens at switch on
• Skin is affected by ultraviolet radiation
• Eye irritation, though new bulbs are widely claimed to have no perceptible flicker
• Migraine: see BBC News
• Pollution to environment by mercury

This gives the UK government's current view "Energy efficient light bulbs are not a danger to the public." This healthcare article is the most up to date I can find and has a comments section that can be worth watching for new developments. Useful Wikipedia articles are Compact fluorescent lamp and Fluorescent lamps and health. Cuddlyable3 (talk) 16:26, 27 September 2011 (UTC)

I scanned over the news-website you linked; noticed strong claims; and so as I am typically inclined to do, I searched for the original paper. The article didn't mention where it was published, so I turned to Google Scholar search. All I turned up is ... nothing. It appears User:Edison also searched for an original publication back in April and independently reached the same conclusion: who is "Peter Braun"? Where does he work? Where did he publish his research? Absent such clarifications, we can't really evaluate the claims. This is a case of serious shortcoming of internet "journalism." The original "newspaper report" does not actually answer any of these questions. I think we should probably call "citation needed" on that Telegraph article. Nimur (talk) 16:55, 27 September 2011 (UTC)

Thank you. Let's just say I found it at an alternative health site. Imagine Reason (talk) 21:41, 27 September 2011 (UTC)

You might need to ask on the "alternative science" reference desk... Oh wait.. ;) Vespine (talk) 22:06, 27 September 2011 (UTC)

It's bad enough that they contain mercury and should be taken to a recycle center. So much for "eco-friendly". ←Baseball Bugs ^{What's up, Doc?} carrots→ 23:16, 27 September 2011 (UTC)

Have you looked at the amount of mercury involved? Yes, it is technically correct to say that a CFL contains mercury, but the amount involved is minuscule. For comparison, the amount of mercury released into the environment by smashing a CFL is far less than that released by burning coal to power an incandescent bulb for the 10000 hours or so that a CFL will last. --Carnildo (talk) 01:11, 28 September 2011 (UTC)

Even so, CFL's are considered toxic waste in some states. Are LED's also considered toxic waste? ←Baseball Bugs ^{What's up, Doc?} carrots→ 05:02, 28 September 2011 (UTC)

Yes, because of the soldering. That mercury and lead and tin and zinc are all considered hazardous materials these days is just a ploy to make you get rid of those for free so they can recycle them. The official reasoning is usually just some chemical compounds containing those metals that are actually harmful on your health, but you can find harmful compounds of any element; or allergic reactions, but you can find allergy and skin irritation for any material as well. I wonder which classical metal will be turned dangerous next: iron, copper, silver, or gold? – b_jonas 19:40, 28 September 2011 (UTC)

combustion

can you tell me the gases which support and do not support combustion?--Krishnashyam94 (talk) 17:47, 27 September 2011 (UTC)

The article Combustion is a good place to start your search. Cuddlyable3 (talk) 18:04, 27 September 2011 (UTC)

In general, you need an oxidizer and a reducing fuel with sufficient free enthalpy at whatever concentrations and pressures to support a sustained reaction. 69.171.160.139 (talk) 19:47, 27 September 2011 (UTC)

Reddish brown gas

Does NaNO₃ and KNO₃ react with sulphuric acid to liberate reddish brown NO₂ gas?--Krishnashyam94 (talk) 17:50, 27 September 2011 (UTC)

If it did, it would have reduced the nitrogen atom from the +5 oxidation state to the +4 oxidation state, which would mean that something else would have had to have been likewise oxidized. Look at the oxidation states of all of the elements in your mixture, and see if any is likely to be oxidized. --Jayron32 18:23, 27 September 2011 (UTC)

From personal experience, no. Potassium nitrate and excess sulfuric acid is reacted to produce nitric acid, which can be disilled off as an azeotrope. No brown gas is evolved, the nitrate ion is preserved in the substitution reaction. Plasmic Physics (talk) 01:28, 28 September 2011 (UTC)

As an aside, this is how medieval alchemists used to make nitric acid; in fact, this is the very method described in Agricola's De Re Metallica. 67.169.177.176 (talk) 05:35, 28 September 2011 (UTC)

Colour of compounds

What are the colours of Fe(CNS)₂ and Fe₃[Fe(CN)₆]₂--Krishnashyam94 (talk) 17:53, 27 September 2011 (UTC)

Please do your own homework.

Welcome to the Wikipedia Reference Desk. Your question appears to be a homework question. I apologize if this is a misinterpretation, but it is our aim here not to do people's homework for them, but to merely aid them in doing it themselves. Letting someone else do your homework does not help you learn nearly as much as doing it yourself. Please attempt to solve the problem or answer the question yourself first. If you need help with a specific part of your homework, feel free to tell us where you are stuck and ask for help. If you need help grasping the concept of a problem, by all means let us know. --Sean 17:55, 27 September 2011 (UTC)

The first is called "iron (II) isothiocyanate", and the second is called "iron (ii) ferricyanide". Google those terms. --Jayron32 18:21, 27 September 2011 (UTC)

It does not sound like it is necessarily a homework problem. A sensible homework problem would be more likely to ask how the color changes when the compound reacts with something. It is not a violation of the rules to just answer a question here with a referenced answer. I see lots of sites with discussion of similar sounding compounds; maybe there are various nomenclature conventions. Is "iron(II) thiocyanate", also discussed here as an indicator, different from "iron (II) isothiocyanate?" The latter site discusses Fe(SCN)_x compounds; are these different from the OP's "CNS" compounds? Edison (talk) 18:40, 27 September 2011 (UTC)

Thiocyanate is an ambidentate ligand (I took freshman chemistry with the guy who discovered this general property in organometallic chemistry). Thus, SCN is different from NCS in that SCN bonds to the iron at the sulfur, while NCS bonds at the nitrogen. I just noticed that the OP is asking about CNS, which I am unfamiliar with, but doing a quick search indicates that CNS is an alternate way of notating the thiocyanate ion (I always use SCN), apparently used in applications where the actual bonding is irrelevent or unknown. --Jayron32 18:48, 27 September 2011 (UTC)

I remember a ton of similar problems when I took inorganic chemistry, based on ligand field theory. Different geometries and numbers of ligands, and different orbital energies of the ligands and different oxidation states of the metal all play a role in predicting the energies of the transitions among electronic states. That's the same as saying "what are the UV/vis spectral characteristics?", which is really just "what color is it?". One could even analyze this pair based on HSAB (different iron charge and effect of added "S" have on the nitrile ligand)? That latter is sort of like Edison's idea, except the "reaction" is the removal/addition/electronic-tuning of the ligands on one to get to the other:) DMacks (talk) 02:18, 28 September 2011 (UTC)

Mental illness in non-human animals

Has it ever been documented? LANTZY^TALK 19:04, 27 September 2011 (UTC)

See mental disorder. There is a section on animals. -- kainaw™ 19:06, 27 September 2011 (UTC)

(edit conflict) Yup, see Stereotypy (non-human) for but one example. --Jayron32 19:07, 27 September 2011 (UTC)

Back in the 1980's my brother had a neurotic border collie. Roger (talk) 19:12, 27 September 2011 (UTC)

Also take a look at feather-plucking for a specific condition. Some parrot species (e.g. Umbrella Cockatoo, African Grey Parrot) are notorious for their tendency to start plucking. --Kurt Shaped Box (talk) 19:28, 27 September 2011 (UTC)

Anecdotally, I know several people who have adopted small dogs from shelters, and many such small "rescued" dogs have a pathological fear and hate of strange men, maybe due to their life experiences, or maybe because they're nuts. I've known several dogs whose owners got tranquilizers prescribed for the animals to calm them down so they don't bounce off the walls. I have known several nutty cats which go berserk and start scratching or biting for reasons known only to themselves. Maybe behavior which seems nutty to us makes perfect sense to the animal. Edison (talk) 19:51, 27 September 2011 (UTC)

Many types of mental illness make perfect sense to the afflicted humans, as well. --Mr.98 (talk) 20:47, 27 September 2011 (UTC)

Most of the cases of 'animal mental illness' I've come across inevitably have the animal kept under the close auspices of, you guessed it, humans. Cf. dogs, zoo animals. Nietzsche wrote a little about how he thought animals would regard humans as the 'sick animal, the laughing animal'. Vranak (talk) 00:56, 28 September 2011 (UTC)

Here's the full quote:

I fear animals regard man as a creature of their own kind which has in a highly dangerous fashion lost its healthy animal reason – as the mad animal, as the laughing animal, as the weeping animal, as the unhappy animal. The Gay Science. Vranak (talk)

Are you kidding? The only dogs I have known that did not go into kill mode when hearing or seeing a person riding a bicycle are those who have been trained and conditioned by a loving owner to accept such persons as friends. Dogs come into this world as completely neurotic killing machines until guided by their owner with love through the most normal of human activities and situations. --DeeperQA (talk) 03:19, 28 September 2011 (UTC)

What you call neurotic Cesare Millan might called 'prey drive' -- which would be very useful if a dog had to go feral and catch its own dinner. Vranak (talk) 03:55, 28 September 2011 (UTC)

In terms of prey most domesticated dogs (family pets) are too well fed for food to be the driving force behind their neurosis. Rather their neurosis is to establish dominance over the territory they inhabit in the mind of anything and everything that enters it, right up to the point of who shares their food bowl. What love and conditioning and training and food do is merely raise the trigger point to a higher level. For a feral dog or cat that level may be only slightly above that of a wild animal. Check news articles for the past month and you will find one in which a family pet mauled and killed a new born because the parents were expecting the dog to automatically accept it as a family member without introducing the dog to the child. For the dog the infant was something that had entered its territory without introduction and anyone's demonstrated approval and in need of being killed and eaten like a person cuddling a rabbit they are about to set down in front of a pet snake for its next meal. --DeeperQA (talk) 05:51, 28 September 2011 (UTC)

You make a good point. It may be more to do with territoriality than hunting instinct. Vranak (talk) 14:55, 28 September 2011 (UTC)

How does that mean neurosis? Human beings usually automatically kill any snake or spider they find in hysteria that it might be venomous. Does that make humans neurotic as well? You are making the classic anthropocentric mistake of classifying animal behavior by how they relate to humans. -- Obsidi♠n Soul 06:37, 28 September 2011 (UTC)

So you are saying that puppies are completely neurotic killing machines. Seems harsh. :) For interest, in my area there are several packs of feral dogs and my experience of their behavior doesn't really match your descriptions. They are effectively wild. They live, move, hunt/scavenge as packs and they are rather good at finding snakes it seems. They invest a lot of time establishing their dominance hierarchy or playing (...hard to tell the difference) and sleeping of course (..it's hot) to the extent that they are almost nocturnal. They don't really interact with people or seem very interested in people at all. They seem to reserve barking for ritualized, quite rare interactions with neighboring packs and encounters with potentially dangerous snakes. They are oddly quiet. Their territories seem to be rather fluid and change quite rapidly over time. The area is rural so there isn't really any kind of population pressure. I cross various pack's territories on foot quite often and if anything, I think the packs tend to react with indifference or moderate fear when they see a large primate crossing their territory. They certainly don't go into fight or flight mode or act aggressively. Sean.hoyland - talk 06:50, 28 September 2011 (UTC)

Trigger Point Ally, Trigger point... I am saying is that all that changes is the threshold. For puppies it is not until the first really painful bite on the nose by a litter mate that reveals puppy love may not be the only thing a puppy is made of. Dogs that have not been conditioned, trained, and reinforced with food and shelter to tolerate others and even strangers in their environment may have a very low Trigger Point of becoming neurotic over the presence of undesired guests. Even those which have been conditioned may "loose it" if their mind is in control and not their owners when faced with the need for action. Dogs which are left on their own forced to rely upon their own decisions may have no threshold of tolerance at all. Hence dead baby brought to you by an otherwise loving pet. --DeeperQA (talk) 07:52, 28 September 2011 (UTC)

How many fields?

I am guessing : electromagnetic, gravitational , weak , strong, possibly higgs.

Also do they all expand at the speed of light? :) — Preceding unsigned comment added by 92.30.216.128 (talk) 20:47, 27 September 2011 (UTC)

Every particle is made up of fields and the relationship is not one to one. Most of those fields have components that may or may not be counted as separate fields depending on how you choose to count them so counting fields is not a trivial matter. For instance, quarks come in three different colors and each color possibility should be counted separately for some purposes such as statistical mechanics where the number of independent states of an ensemble must be accurately calculated. Often times though identical quarks with different colors are not counted separately since they are so similar. Dauto (talk) 21:31, 27 September 2011 (UTC)

The second question has an even more subtle answer. Most of those fields are believed to be massless at high enough energies, but at low energies, after electroweak symmetry breaks, many of them acquire mass through the Higgs mechanism. Only massless particles propagate at the speed of light. Dauto (talk) 21:35, 27 September 2011 (UTC)

The real answer is that fields are a concept which act as a model that allow us to probe the details of how the universe works in a mathematically consistent way, and which best approximates the actual behavior of "reality". (It should be noted that, in this way, fields are not any different than "particles" or any other physical concept). Fields can be said to exist for any force or property which propagates through space (or space-time) and decays. We use fields because they work. --Jayron32 21:41, 27 September 2011 (UTC)

In modern physics "field" has a pretty clear definition and it is reasonable to ask how many there are (though, as Dauto said, there are different ways of counting them). -- BenRG (talk) 07:16, 28 September 2011 (UTC)

The number may increase dramatically if supersymmetry is discovered. And since supersymmetry is broken, there then likely exists hidden sector fields corresponding to particles that unlike the supersymmetric particles don't interact with Standard Model particles at all (except via gravity). Count Iblis (talk) 22:18, 27 September 2011 (UTC)

There are non-supersymmetric theories that introduce a lot of new fields too. For example, it's been proposed that there are 10³² copies of each of the Standard Model fields. This has probably been ruled out by the LHC, since every interesting idea seems to have been ruled out by the LHC. -- BenRG (talk) 07:16, 28 September 2011 (UTC)

Yeah, LHC has been pretty hard on some of the more creative ideas, but supersymmetry is still alive and well despite the rumors of its demise. Dauto (talk) 13:18, 28 September 2011 (UTC)

Although, if the Higgs is not found soon, that is then evidence for new physics. E.g. there could exist many different types of dark matter particles to which the Higgs can decay. That then hugely broadens the resonance signal for the Higgs, making it much more difficult to extract from the background. Count Iblis (talk) 15:52, 28 September 2011 (UTC)

The LHC has closed many windows in the mass spectrum for the Higgs, but the range from 115 to 130 GeVs is still open because of the large amount of background. There seems to be a peek forming in that region but it is still too early to tell. That peek seems broader then expected which goes along with your remark about peek broadening. That broadening might be spurious though. - Heck, the whole peek might be spurious. We may have to wait at least another year before things become more clear. Dauto (talk) 18:31, 28 September 2011 (UTC)

See Fundamental interaction.

—Wavelength (talk) 16:07, 28 September 2011 (UTC)

humongous voice coil

Suppose I was to wind a coil of wire around the equator lots and lots of times. In this configuration with the Earths magnetic field the coil takes on the same (albeit linear rather than "U" shaped) voice coil or solenoid. Could I do anything useful with this coil such as listening to the Earth's magnetic field or sending dance tunes to aliens in the far reaches of space? --DeeperQA (talk) 20:57, 27 September 2011 (UTC)

During geomagnetic storms it might produce a powerful current, but most of the time the internal resistance at such lengths would dampen any possible application. See Geomagnetically induced current. 69.171.160.139 (talk) 22:43, 27 September 2011 (UTC)

Not that I'm aware, although you could use up the world's copper output for a while. Electricity is generated when a wire loop moves with respect to a magnetic field. Yours would be pretty static. Regards, RJH (talk) 22:50, 27 September 2011 (UTC)

You could probably pick up fluctuations in the field, such as from geomagnetic storms, though. Of course, you could probably do almost as well with a much smaller coil... --Carnildo (talk) 01:14, 28 September 2011 (UTC)

Silver mining

My crew of dwarves that I'm running a dnd quest for is about to liberate a silver mine from a band of marauding orcs who took it over from the human kingdom recently. They've mentioned desire to actually take it over and manage it during down time from adventuring so I thought I'd investigate what would be involved. I've taken a look at the silver mining page and have decided that the mine is actually a lead mine and the silver is extracted by melting the lead with zinc. My question is this: About how much lead could one expect to need in order to get a measure of silver? Are we talking about a tonne of lead for a pound of silver type ratios or would it be much greater than that? Thanks for any insight :) 142.244.35.91 (talk) 21:21, 27 September 2011 (UTC)

If it helps any, an example on pg. 41 in Principles of Mining by a certain former president gives 20 ounces of silver per ton, of which 15 ounces is recovered. You could just use 2d20 ounces/ton. Regards, RJH (talk) 22:08, 27 September 2011 (UTC)

Awesome, thanks for the rapid response. Now to figure out how much ore a dwarf can move with a pick axe in a 12 hour day! :) 142.244.35.91 (talk) 22:38, 27 September 2011 (UTC)

Coolest question ever. Sorry I don't have a clue as to the answer myself. You might try Comstock Lode for leads. μηδείς (talk) 22:12, 27 September 2011 (UTC)

Make sure you ask your DM for the maximum rainfall in the local climate so you can take precautions against flooding (e.g. dig out lower levels under your main shafts so your miners have time to escape.) Also you should be able to hire some low level henchmen magic users or clerics to help locate the mineral seams and maybe set up some kind of a magic smelting furnace to cut down on operating costs. 69.171.160.139 (talk) 22:59, 27 September 2011 (UTC)

I like the “liberate” part of the question. – b_jonas 19:28, 28 September 2011 (UTC)

Crystallization of the Earth's core

I'm able to track down information on the past and current crystallization of the Earth's outer core along the boundary with the inner core, but I can't find anything about future projections for inner core expansion and the freezing out of the magnetic dynamo process. If memory serves, there was a story about that in the press a while back (perhaps in a science magazine), but I can't find it anywhere. Does anybody have a reference I could use, or recall where that story appeared? Thank you. Regards, RJH (talk) 22:01, 27 September 2011 (UTC)

Earth's Missing Ingredient; June 2010 Scientific American? Bus stop (talk) 22:09, 27 September 2011 (UTC)

I remember there being interesting speculation concerning the Perovskite layer and the Postperovskite layer. Bus stop (talk) 22:12, 27 September 2011 (UTC)

Yes I think that might be it. Thank you. Unfortunately, in skimming through it, that doesn't appear to answer the question I'm trying to resolve. I.e. how long it will take for the core to freeze solid. I guess then that may be just too difficult to model at the moment. Regards, RJH (talk) 22:43, 27 September 2011 (UTC)

The back of my envelope suggests that it would be roughly 30 billion years to freeze solid, give or take a factor of a few. Dragons flight (talk) 18:33, 28 September 2011 (UTC)

Given the current rate of 0.5 mm/yr and assuming that rate stays constant (which is probably not a good assumption as the proportion of iron drops and the radius increases), I get (3,480 − 1,220 km) × (1,000,000 mm/km) / 0.5 mm/yr. = 4.5 gyr. But either way it's not something I can reliably cite, alas. Regards, RJH (talk) 21:47, 28 September 2011 (UTC)

It's an energy loss problem, so the scaling factor ought to be change in volume rather than change in linear scale, but yeah I don't see any thing one can cite either. Dragons flight (talk) 22:05, 28 September 2011 (UTC)

September 28

Zero-point energy

Could zero-point energy be used for clean, limitless power generation? --70.134.53.27 (talk) 01:28, 28 September 2011 (UTC)

No. Dauto (talk) 02:02, 28 September 2011 (UTC)

No, please read the definition of zero point energy. Plasmic Physics (talk) 02:48, 28 September 2011 (UTC)

In case it's not immediately obvious, specifically the section on Claims in Pseudoscience.Vespine (talk) 06:17, 28 September 2011 (UTC)

Rechargeable batteries

I took the wrapping off several sets of batteries and now I can't tell which ones are rechargeable (and some of them are) and which ones are not. Not one of them says "rechargeable". I think the Energizer Lithium AA 03 2023 batteries are the rechargeable ones, but I can't seem to find anything on Google that says they are or they aren't, just lots of specs about their uses in cameras. Anybody out there know? Thanks Bielle (talk) 03:04, 28 September 2011 (UTC)

Having kept looking at batteries in general, I have concluded that if they don't say "rechargeable" writ large, then they are not. Thus, the Energizer Lithiums are not rechargeable. Comments appreciated. Bielle (talk) 03:15, 28 September 2011 (UTC)

The chemistry in rechargable batteries is very different than the chemistry of other batteries. Attempting to recharge a non-rechargable battery involves unfun events like "leakage" and "overheating" and "explosion". Don't do it. Every rechargable battery is always clearly and unambiguously labeled as such, so if it doesn't say "rechargable" in a giant freindly font on the side of the battery, don't stick it in a recharger. --Jayron32 03:37, 28 September 2011 (UTC)

Lithium-ion batteries are rechargeable, but Lithium batteries like Energizer Lithium aren't. -- BenRG (talk) 07:20, 28 September 2011 (UTC)

Lithium is a violently excitable substance if it is abused. A lithium fire would probably ruin your day. It cannot be put out by common extinguising substances such as water or carbon dioxide. Roger (talk) 09:26, 28 September 2011 (UTC)

In other words, say hello to the new battery-sized hole in your table. And to the huge blackened areas in your floor and ceiling. And I bet that any smoke entering your lungs will be completely healthy and won't leave you coughing for weeks. --Enric Naval (talk) 10:31, 28 September 2011 (UTC)

As a further note, the only common rechargable AA batteries are NiMH, NiCd and NiZn. Of these, NiMH are what you're most likely to encounter, NiCd are rare nowadays for various reasons including them containing cadmium, their general low capacity, the memory effect etc. NiZn are still relatively new and should be used with care since their nominal voltage is fairly high, may be too high for some devices. NiMH and NiCd batteries can usually be charged in the same chargers but NiZn need their own chargers. You can get rechargable Lithium-ion batteries (there are actually several kinds of rechargable lithium ion batteries) in AA size equivalent, more commonly called 14500 but these are not intended to be used with most devices accepting AA batteries because of the much higher voltage. These need special chargers and aren't really intended for the consumer market (although are popular in some circles) and instead are generally used for packs and in devices where they aren't intended to be removed, and you will not find Duracell ones. Because of the risks, I wouldn't recommend them if you don't know what you're doing. As has been noted, lithium batteries should be treated with care, even primary ones. Nil Einne (talk) 12:41, 28 September 2011 (UTC)

Normally if batteries are not rechargeable they will say "do not recharge" on them in small print somewhere. I have plenty of batteries which are rechargeable but don't explicitly say "you can recharge this battery" on them 82.43.90.142 (talk) 09:54, 28 September 2011 (UTC)

solar wind movement and direction

solar wind is the current of ejected particles from sun corona , those particles have 250~750 km/s velocity , which is further than sun gravity field escape velocity (180km/s).In addition the particles obey electromagnetic field rules which make them to have spiral rotation , suppose any particle (for example proton)how will it move at its way in interstellar space?akbarmohammadzadeIRAN--78.38.28.3 (talk) 03:36, 28 September 2011 (UTC)

Presumably, once past the heliopause, the wind will join the general interstellar medium where the particle's motions are effected by the prevailing magnetic field. Regards, RJH (talk) 22:10, 28 September 2011 (UTC)

hydostatic pressure and core of stars

can the diffrence between liquid and plasma matter change our ideas about the pressure and density and temperature of core of stars??akbarmohammadzadeIRAN--78.38.28.3 (talk) 04:06, 28 September 2011 (UTC)

I don't think so. They are only related in the sense that plasma can sometimes behave like a type of liquid. The current, widely-accepted stellar model holds that the cores of hydrogen fusing stars are entirely composed of plasma matter. At the millions of Kelvin needed for nuclear fusion of hydrogen, how can it be otherwise? Ergo, the properties of liquid matter don't appear directly relevant. Regards, RJH (talk) 21:55, 28 September 2011 (UTC)

Remember, there is pressure also to contend with. Plasma is not a state of matter, at least it is not distinct from solids, liquids, or gases. After all, toyu do get solid plasma's, liquid plasmas, and the more familiar gaseous plasmas. Plasmic Physics (talk) 22:06, 28 September 2011 (UTC)

Jet Sound

When the fighter aircraft pass over our heads they make such terrible sound, but why does the big Jumbojet(or Airbus) don't make so much noise though it has more and far bigger engines, when it is landing or taking off near us at airport etc, though it is quite close. 124.253.129.113 (talk) —Preceding undated comment added 04:15, 28 September 2011 (UTC).

Supersonic aircraft like jet fighters create a sonic boom when they break the sound barrier. Subsonic aircraft like jumbo jets don't. --Jayron32 04:24, 28 September 2011 (UTC)

The planes don't always break sound barrier. Breaking sound barrier is a momentary phenomenon that last a fraction of a second...most of the time they are traveling below speed of sound 124.253.129.113 (talk) —Preceding undated comment added 05:02, 28 September 2011 (UTC).

Jumbo jets have high-bypass turbofan engines, which derive most of their thrust from pumping cold air through the bypass ducts and out the exhaust nozzle; this is for better efficiency at medium-high speeds (500-600 knots or so), but it also muffles the roar of the hot gases from the combustion section of the engine. Jet fighters, on the other hand, have straight turbojet engines that derive most if not all of their thrust from the hot gases; these produce more power at very high speeds (> Mach 1), but obviously don't have the same muffling effect from the cold air. 67.169.177.176 (talk) 05:32, 28 September 2011 (UTC)

The above is totally correct. If it's worth mentioning, this is not an accident, noise consideration is a considerable factor in commercial jet engine design. If anything, apart from absolute performance, fighter jets are, in complete contrast, designed to shock and awe. Vespine (talk) 06:15, 28 September 2011 (UTC)

Also, military jets sometimes use afterburning which makes them EVEN LOUDER! One civilian airliner with very loud engines was Concorde; her Olympus engines had been developed from those of a supersonic jet bomber. Alansplodge (talk) 17:47, 28 September 2011 (UTC)

I have always assumed that stealth aircraft are fairly quite though. Am I correct? Googlemeister (talk) 18:18, 28 September 2011 (UTC)

Not as a general statement; it depends on what kind of stealthing the aircraft is concerned with. For instance, a helicopter operates a low altitudes where being noticed by foot soldiers can be a threat. Thus, stealthing a helicopter reasonably includes sound-deadening measures. Stealth aircraft operating at high altitudes, on the other hand, won't care about sound output to nearly that extent. If they're quiet, it's more likely as the result of a happy design accident (perhaps aforementioned high-bypass turbofans are good for stealth purposes due to heat of exhaust) than intentional design methodology. — Lomn 18:50, 28 September 2011 (UTC)

Question about GRAVITY?

Galileo was first to demonstrate that all objects fall at the same rate in the absence of an atmosphere. As it is said that the earth and the apple fall toward each other but apple looks a lot to falls to the earth as compared to the falling of earth toward the apple which is so tiny to be detected.

Let's imagine earth is a homogeneous sphere therefore in the following cases, what would be the direction of direction [falling] of earth in the absence of all other gravitational attraction including atmosphere?

1- If two apples start falling simultaneously from ANTIPODEAN trees from same altitude.

2- If two different masses [say one apple and other big asteroid] start falling simultaneously from same ANTIPODEAN altitude.

Also, would gravity "g" of two equal planets cancel each other if placed on each other?68.147.43.159 (talk)Eccentric Khattak#1 —Preceding undated comment added 04:55, 28 September 2011 (UTC).

Presumably this is a continuation of your question listed under "Question about the Galileo Statement"? ←Baseball Bugs ^{What's up, Doc?} carrots→ 05:01, 28 September 2011 (UTC)

I think there is some very fundamental goof here. He says apple and earth fall towards each other. The apple is OK, it falls i.e. it moves in a straight line towards earth, but does earth move towards apple ? I think no, as it is already "falling" - it is moving around the sun - that is technically falling, no ?. Now, how can something move towards two different directions at same time ? 124.253.137.182 (talk) —Preceding undated comment added 05:49, 28 September 2011 (UTC).

Different vectors. Any object in space is moving along a path that's the "sum" or "net effect" of its vectors (there may be a different word for that, but I can't think of it just now). Earth and moon orbit around a common point. That point orbits around the sun. The sun presumably orbits around the center of the Milky Way Galaxy. And the Milky Way is presumably heading along an approximately straight line away from wherever the Big Bang occurred. So the earth, viewed in isolation and relative to all these different forces, would be taking a very interesting path. As noted in the earlier section, the falling apple has a theoretical effect, but so small as to be negligible. ←Baseball Bugs ^{What's up, Doc?} carrots→ 05:52, 28 September 2011 (UTC)

Fair answer except for the moment where you talk about a place where Big Bang happened since Big Bang did not happen in a place. Big Bang is an expansion of the whole universe, not an event within the universe with specific time and space coordinates. Dauto (talk) 14:03, 28 September 2011 (UTC)

Again you are essentially setting up a Three body problem. What don't you understand? It's fairly simple. In scenario 1, given "perfect conditions, the earth will stand perfectly still, pulled equally by the two apples. For 2, assuming the asteroid is more massive then the apple, then it will have more of a gravitational effect on the earth then the apple, however unless the mass of the asteroid is a meaningful fraction of the mass of the earth, the effect will still be insignificant. I don't actually understand what you mean by Also, would gravity "g" of two equal planets cancel each other if placed on each other? No, if your adding their masses, their gravity would also add up, not cancel out. Note, the gravity would NOT double with a doubling of the mass, it's one of those inverse square law situations. Vespine (talk) 06:09, 28 September 2011 (UTC)

The force on an object due to gravity does double when the mass is doubled. This means that the acceleration due to gravity remains the same. Depends exactly what the OP meant, though, which isn't clear. Grandiose (me, talk, contribs) 09:42, 28 September 2011 (UTC)

With both planet's particles being present, the various forces these generate will be present too, but they can create a static equilibrium with forces opposed to each other. If you lived in the place where the two equal planets are joined together, the net force due to gravity is zero. See for instance Lagrangian point #L1. In a similar situation, gravitational acceleration decreases in a tunnel or well with increasing depth, see Gravity of Earth. Living between the two planets should be interesting, being nearly weightless and being able to easily move around but with a significantly greater rate of fall as you climbed out. The building materials on the surface would need to be progressively stronger too. The L1 position is unstable, so apples will fall towards the planet that is nearest, but one might become adapt at calculating the inertia needed to miss the surface in a fall (see Douglas Adams' novels, :-), for more detail). Once you reached either "end of the world" the gravity due to both masses will not be doubled on account of the one planet being further away. So locally, there is no doubling, but as you leave the system, the difference in the distances to each planet can become so insignificant that the gravitational acceleration due to both can be practically twice that of only one planet. --Modocc (talk) 17:54, 28 September 2011 (UTC)

faster than light question

Just to clarify the predominant understanding of traveling faster than the speed of light actually means I take it then that if I am traveling on the back of a light beam and a faster than light is coming up behind me that from my perspective it is in my past and when it passes me it is in the future while I remain in the present? --DeeperQA (talk) 07:37, 28 September 2011 (UTC)

In many ways, FTL travel introduces many real paradoxes which cannot be resolved by a simple explanation in the English language (or indeed any language). --Jayron32 13:20, 28 September 2011 (UTC)

You keep asking the same question. Do you expect to get different answers? Speed is relative - that is: different observers can see objects moving differently. For someone in a train, their luggage is just sitting their on the floor, not moving at all, but that same piece of luggage is observed to be moving by someone at the train station. It turns out that the rules for transforming speed between different observers is more complex than believed by 19th century physicists and an object seen moving faster than light by one observer will be observed moving backwards in time by another observer leading to severe paradoxes. The simplest and most logical way to avoid those paradoxes is to assume that faster than light travel is not possible. Dauto (talk) 13:32, 28 September 2011 (UTC)

Also, if you are traveling on the back of a light beam, you have no past and no future since your time stops due to an infinite time dilation factor. From the point of view of a photon, the universe is flattened into a 2-dimensional pancake and the photon is created and absorbed in the same spot simultaneously. Dauto (talk) 13:57, 28 September 2011 (UTC)

The universe is fucking awesome. --Goodbye Galaxy (talk) 17:01, 28 September 2011 (UTC)

No, its more than that. Richard Avery (talk) 17:21, 28 September 2011 (UTC)

Growth

Is muscular exercise helpful in increasing height in adolescents? — Preceding unsigned comment added by 1.39.146.152 (talk) 11:26, 28 September 2011 (UTC)

Yes (or more accurately peak bone mass), with proper nutrition, of course. Though ultimately, height is determined by genetics, being in the best possible health while still young can have significant effects that carry on to adulthood. Health problems in the developing years can also lead to stunted growth. Also see Skeletal development during childhood and adolescence and the effects of physical activity (Kemper, 2000) and Bone development in young people (IOF).-- Obsidi♠n Soul 11:59, 28 September 2011 (UTC)

I can't see anything there that justifies answering this question with a yes. Nutrition does matter, but to my knowledge there is no evidence that muscular exercise affects height. Looie496 (talk) 16:27, 28 September 2011 (UTC)

I did explicitly say bone mass. While it does not (or at least only very slightly) affect bone length, surely you can agree that being a bit more healthy can make the difference? -- Obsidi♠n Soul 16:53, 28 September 2011 (UTC)

What manner of substance is this?

So, I was watching videos of shredders shredding things and found myself on this one, which shows large chunks of metal igniting and burning and popping and sparking whilst going through the machine. The video just calls it 'speciality metals' and there are a few guesses in the comments section - but does anyone here know for sure what the hell that stuff is? --Kurt Shaped Box (talk) 19:19, 28 September 2011 (UTC)

Looks a lot like magnesium to me; for liability purposes they may not want to name the metal, which is why they use the term "specialty metals". Magnesium is a fairly reactive metal, and it is flammable, even in pure CO2. (google "magnesium and dry ice" for some fun videos). The bright flashes look a LOT like magnesium when it burns, and grinding it up like that could easily produce enough heat via friction to ignite it. --Jayron32 19:28, 28 September 2011 (UTC)

A high alkaline phosphate level

A high alkaline phosphate level of over 200 - can this have a relationship to lipo phosphates and also to lipodema- — Preceding unsigned comment added by 94.13.166.2 (talk) 21:44, 28 September 2011 (UTC)

Power required for levitation

Mass M is required to be levitated (stationary) in a gravitational field of strength g by pumping out a fluid of density rho over a cross-sectional area A (e.g. a ducted fan blowing out air). Assuming no losses, how much power is required?

I get Power = (M g)^(3/2)/sqrt(2 rho A), which somehow is not quite what I was expecting. Can anyone verify (or correct) this? Regards, 86.179.118.99 (talk) 22:08, 28 September 2011 (UTC)

Clarification: In case unclear, I mean that the fan is attached to (part of) the mass M and is also hovering (as opposed to blowing upwards from the ground). 86.179.118.99 (talk) 22:16, 28 September 2011 (UTC)