Wikipedia:Reference desk/Archives/Science/2013 November 4

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November 4

Why blind army ants do not hunt at night?

Why blind army ants do not usually hunt at night? — Preceding unsigned comment added by 67.71.98.182 (talk) 02:53, 4 November 2013 (UTC)

I suspect the underlying assumption of your Q is "Since it's dark at night, nothing can see, therefore the blind ants would suffer no disadvantage". However, nocturnal animals have eyes adapted to see in dim light, so your assumption is incorrect. StuRat (talk) 03:09, 4 November 2013 (UTC)

I suspect that underlying assumption of your reply is that "everyone out there is a debil who have no clue of what nocturnal animals are" and that you are the most smart guy in the world and only one who is aware of nocturnal animals. But your assumption is incorrect. 67.71.98.182 (talk) 06:47, 5 November 2013 (UTC)

The alternative is to assume that everyone who posts a Q here is a genius. Based on past experience here, that is definitely not the case and Q's are often posted which are based on faulty assumptions. Also, if you don't want us to make any assumptions, then you need to post your Q more clearly. In this case, you needed to state exactly why you expected blind army ants to hunt at night. StuRat (talk) 08:00, 5 November 2013 (UTC)

I guess you are referring to Dorylus. Which blind army ant species that don't forage both day and night are you referring to ? Or do you mean, why don't they only hunt at night ? I suppose a response to that might be, why should they ? I think army ants primary concerns when it comes to foraging are things like avoiding other army ant colonies, temperature/weather and food supply and they continuously adjust their foraging accordingly. The same colony may forage continuously, or only at certain times if it's too hot during the day or too cold at night for example. They're subject to predation both day and night. Sean.hoyland - talk 04:25, 4 November 2013 (UTC)

(ec) Hmmm... I'm guessing you mean some species of Dorylus? It seems like people have observed them anecdotally to forage at night. [1] It's hard to research such a general characterization - best to have a specific species and locale in mind. I'd presume that the habits of army ants have a great deal to do with the temperature and related weather conditions. Wnt (talk) 04:33, 4 November 2013 (UTC)

I was watching BBC documentary about army ants. Not sure exact spice they have filmed. But they claimed that both soldiers and workers are blind. And in one episode ants came close to termite nest, but stopped their raid becose of sunset/evening, returned to temporarily nest and only reached termites next day and attacked them. Yes, I do not see disadvantages for them to hunt at night. Even more important - I do not see advantage for blind insects to hunt/raid/explore new hunting territory during day only. 67.71.98.182 (talk) 04:59, 4 November 2013 (UTC) EDIT: About temperature: documentary was filmed in what looked like jungle. And while not direct evidence of hunting only in the daylight, whole documentary was filmed in natural light setting. But again, story about attack on termites clearly stated that they stopped their raid because of nightfall. 67.71.98.182 (talk) 05:16, 4 November 2013 (UTC)

Most army ants are actually partly to exclusively nocturnal. The army ants in BBC documentary are most probably the most widely studied army ant species exhibiting nomadic raiding behavior - Eciton burchelli. And they're widely studied precisely because they primarily raid during the day in massive columns and thus are easier to observe. Though they typically still avoid direct sunlight and temperature extremes and stay beneath the shadows of heavy forest canopies or else only raid during overcast days.

The daily and seasonal "schedules" of different ant species depend largely on the conditions they have evolved to tolerate as well as their specific "niche" in the ecosystem, and they differ from species to species. The temperature ranges (as well as other factors) where they still consider it "worth it" in terms of potential loss of colony members versus the chances of finding food is usually clearly delineated. This is more generally known as the optimal foraging theory. While I can't find any specific studies on what affects raiding behavior in army ants (though there are plenty on bivouac formation), I suspect this is the reason. It's not related to the availability of light. Just ingrained instinctive behavior shaped by competition, prey and predator diel cycles and distribution, and general abiotic factors. They simply don't consider it worth it to raid beyond the specific time/condition they have adapted to. Though if they had reached the termite nest before nightfall, the attack may have occured earlier.-- OBSIDIAN†SOUL 06:22, 4 November 2013 (UTC)

Thank you Obsidian Soul, this explanation is very good. And very helpful. I mean optimal foraging theory makes sense. Plus in fact BBC mentioned that ants were trying to stay "under cover" using dead leafs and shadows placing their routs in shades whenever possible. 67.71.98.182 (talk) 06:38, 5 November 2013 (UTC)

Maybe the ants were taking advantage of the termites' vulnerability to sunlight... Ssscienccce (talk) 19:21, 5 November 2013 (UTC)

gases and pressure

I was reading a news article about helium-filled HDDs, and in the comments section people raised doubts about the hard disks' longevity, because helium (as is hydrogen) are notorious for diffusing through solids. But one person said that because helium is at atmospheric pressure inside the hard disk's casing, it won't "diffuse out" because air cannot "diffuse in" to compensate pressure. Are they right? I think, intuitively, that diffusion will continue even after the helium is below atmospheric pressure, because helium atoms have no way of knowing what pressure is outside and they don't care. They simply get caught in the metal's bulk and some manage to wiggle their way outside. Asmrulz (talk) 14:17, 4 November 2013 (UTC) or am I confusing diffusion and permeation? Asmrulz (talk) 14:35, 4 November 2013 (UTC)

That would make a hard drive into a great diffusion pump! Unfortunately, even while "wriggling" through intermolecular spaces, the statistics that aggregate into macroscopic concepts like pressure and temperature still apply to individual atoms. If the partial pressures are equal, then gas will flow in both directions - even across a barrier. So, if the gas chamber (the hard drive enclosure) is so perfectly sealed as to be totally impermeable to everything except helium, the steady state will equalize the internal pressure to the external partial pressure of helium (not to atmospheric pressure). The time it would take to reach such an equilibrium would be immensely slow - because the diffusion through the metal enclosure is very slow. If you did something to speed that process up, you'd increase permeability to other gases, and therefore, increase the steady state value for the pressure inside the enclosure.

When we create ultra high vacuums - the sort of crazy contraptions that need clean-rooms and labs full of equipment - the sort of place we build semiconductors and optical materials - the simple solution is to cool the vacuum chamber to low temperature. First we pump to low vaccuum; then a secondary stage pump (say, a turbine) pumps out the gas to high vacuum. Then we chill the vacuum chamber to, say, the boiling point of liquid nitrogen (which is convenient and cheaply available). This freezes or condenses the very few gas molecules that are left: they condense to liquid or gas and drop to the walls of the chamber. Finally, we can ionize the chamber, and almost everything else flows to the anode or cathode - like the hydrogen gas.

All that is usually left are the very tiny, neutrally-charged helium atoms: they're difficult to ionize until fairly high voltages are applied, and they won't condense unless we get the chamber much much colder (which we can do, at great cost and with much effort). This is why you hear about helium, and it's also why we know it can permeate through solid steel: helium is pretty much the last pesky gas molecule left in the chamber after we've used our best technology to clear everything else away.

So that's probably why they're putting it in hard disk enclosures; nitrogen or argon are also inert, but if some manufacturing stage requires low temperature vacuum, you'd end up with nitrogen ice crystals on the substrate. We want to avoid that: we need to get rid of the pesky gas molecules. It can be easier and cheaper to flood the chamber with high pressure helium, instead of creating an ultra-low vacuum - both processes have the effect of getting rid of the other gas species. Once assembled, there's no good reason why helium is any better for the hard drive platter than any other mostly-inert gas. As long as there is no particulate gunk or anything to scrape the platter, and as long as there's some gas between the disk head and the platter, and as long as you're not strongly oxidizing (or otherwise chemically reacting), helium serves the same role as "regular old (clean)room air." Nimur (talk) 14:39, 4 November 2013 (UTC)

Helium has excellent thermoconductive properties. A helium filled hard drive will dissipate heat more efficiently than other common gases. --DHeyward (talk) 15:50, 4 November 2013 (UTC)

Fact of the day: almost 15% of the internal heat dissipation for a hard-disk drive is conveyed by convective air-flow, according to IBM research published in this 1994 IEEE paper: Thermal and heat-flow aspects of actuators for hard disk drives. That is significantly higher than I expected. Yet, "These values show that convective heat transmission in the IIDD actuator is not the major cooling mechanism." The overwhelming majority of heat is conducted through the metal struts to the enclosure. Nimur (talk) 18:20, 4 November 2013 (UTC)

Interesting... But can some atoms still "wriggle through" against the pressure drop? Also, I didn't know the thing about partial pressure. Does this mean that if a gas were at 1 atm inside a container which is only permeable to that one gas, but there being actually very little of that gas in the surrounding air, that it is actuallt at excess pressure and will try to ooze out if the container isn't properly sealed? (Actually, if I think about it in terms of concentration, it does make sense) Asmrulz (talk) 17:11, 4 November 2013 (UTC)

Yes, and any spontaneous process allows you to extract work from it. In this case you could extract work from the system using membranes that allow through only oxygen and nitrogen. Then oxygen and nitrogen would move into the enclosure until the partial pressures of these gasses are equalized, which means that the total pressure would increase to 2 atmospheres. You then have a total pressure difference, so you can then extract meachnical work by allowing it to expand and e.g. use that expansion to lift a weight. Count Iblis (talk) 17:50, 4 November 2013 (UTC)

VY Canis Majoris

What is the age of the star? 'Age' should be part of a template that gives data in a box. The box is there, but contents vary from star to star. If data is not available, use 'not available', 'not ascertained' etc.

49.15.202.34 (talk) 15:52, 4 November 2013 (UTC)rajankanjirakunnel

Here's the link to our article: VY Canis Majoris. I don't see any info there on whether the age is known or unknown. Your question is appropriate here, but requests to change an article belong on the talk page of that article. Or, you can simply edit the article yourself (although "Age ? We're not ass-certain." has a definite ring to it). :-) StuRat (talk) 20:48, 4 November 2013 (UTC)

Our article Stellar age estimation mentions in the lead that there is no method to get an accurate age of all types of stars. Perhaps it is not really known. Richard-of-Earth (talk) 21:01, 4 November 2013 (UTC)

Empirical evidence for length contraction?

I have repeatedly asked this encyclopedia reference desk to clarify the standard SR claim that physical objects and the distances between them contract, based on different frames of reference measuring the same object or distance differently, as if it is a given that different measurements equate to different physical lengths. My primary example has been the claim of a changing shape of Earth (with all varieties of different diameters), varying drastically with different observations from relativistic frames. The alternative "explanation" given has been that it doesn't change but *IS all different shapes at the same time*, just "depending on how you look at it" with no objective measurement of the physical body Earth possible ("all frames being equally valid."

This science reference desk continues to evade my question, most recently citing "argumentum ad lapidem... a logical fallacy that consists in dismissing a statement as absurd without giving proof of its absurdity." The burden of proof that Earth's shape changes, or that it has an infinite variety of shapes ("for" all possible observing frames) is on the theorists who make that claim. *There is no empirical evidence for length contraction.* The "length contraction" section should at least mention this fact, but the editors will not allow it. (I've tried.) Instead we have folks at this “desk” (assumed to be experts) denying the absurdity of an Earth changing shapes or having multiple shapes. Will someone here *please* address the question about Earth changing shapes or having a multitude of shapes. Btw, I protest the policy here of allowing only five days for discussion of questions before the discussion is buried in the archives. This is my third attempt to get clarification on this issue. LCcritic (talk) 19:06, 4 November 2013 (UTC)

See WP:NOTFORUM. There is nothing to be gained by asking the same question again because you don't like the answers you have already been given. I suggest that you pursue this elsewhere. AndyTheGrump (talk) 19:15, 4 November 2013 (UTC)

The evidence here is the evidence that Lorentz invariance is valid. You may say that this is indirect evidence, but you have to realize that all measurements are always indirect to some degree. If you measure the length of an object using a rod, you are invoking certain physical properties of that rod (e.g. that the length does not change when it is rotated). The validity of those assumptions can in turn be tested in the lab (e.g. that the assumption of rotational invariance is indeed valid). Count Iblis (talk) 19:21, 4 November 2013 (UTC)

We are a reference desk - we're here to present evidence from reliable sources. We've done that. We're simply not here to execute watertight logical disproofs of things you come here to say or to debate things that you don't happen to believe. We're not "evading" anything - it's simply not our responsibility to convince you. If the available reliable sources don't convince you - then we're done here. We aren't going to try to "prove" or "disprove" a damned thing.

To answer your question directly, as Length_contraction#Experimental_verifications points out, direct verification of length contraction is almost impossible:

"Any observer co-moving with the observed object cannot measure the object's contraction, because he can judge himself and the object as at rest in the same inertial frame in accordance with the principle of relativity (as it was demonstrated by the Trouton-Rankine experiment). So Length contraction cannot be measured in the object's rest frame, but only in a frame in which the observed object is in motion. In addition, even in such a non-co-moving frame, direct experimental confirmations of Length contraction are hard to achieve, because at the current state of technology, objects of considerable extension cannot be accelerated to relativistic speeds. And the only objects traveling with the speed required are atomic particles, yet whose spatial extensions are too small to allow a direct measurement of contraction."

It does go on to produce five different indirect experiments - one of which is the consequences of muon decay - which we've already discusssed with you at length.

But no matter what - we're not here to convince you. Go and read the references we've given you - and if you're not convinced, then bad luck. Either way, your repeated insistance on proof here is becoming annoying, trollish and disruptive - and you should cease further questions on this subject before someone decides to apply editing restrictions to prevent you from posting here. SteveBaker (talk) 19:45, 4 November 2013 (UTC)

As far as I can tell, he seems to be suggesting that the observer affects the observed. While this happens at a quantum level[2], such macroscale changes are frankly unprovable. A possible example would be saying that ancient maps (see History of cartography for a range) represented the true shape of the world at the time and that subsequent revisions caused the changes. In reality they were simply a result of new technology and greater understanding of the world.--Auric talk 23:28, 4 November 2013 (UTC)

Auric said, "As far as I can tell, he seems to be suggesting that the observer affects the observed. I have been challenging the SR claim that the observer effects the observed (that the length of objects changes with how they are observed.) Please at least understand that before "someone decides to apply editing restrictions to prevent (me) from posting here." Earth's diameter does not change with how it might be observed from relativistic perspectives. Censoring that statement does not serve science. (And censoring, by whatever name, is not a legitimate part of science.) LCcritic (talk) 00:29, 5 November 2013 (UTC)

Yes it does. You're wrong. Go away. Tevildo (talk) 00:36, 5 November 2013 (UTC)

We are under no obligation whatsoever to provide a platform for 'challenges'. That is not the purpose of this reference desk. AndyTheGrump (talk) 00:42, 5 November 2013 (UTC)

I agree. SteveBaker (talk) 02:27, 5 November 2013 (UTC)

I get into my car, drive off at 50 km/s, and measure the speed of the trees on the side of the road. Wow, I get 50 km/s! How can that be? A minute ago, I did the same measurement and got 0 km/s!

Then, I get onto a highway and accelerate to 100 km/s. Wow, now my tree-speed-reader is saying 100 km/s! But that's impossible...how can the tree be travelling at 3 different speeds at the same time! The speed of a tree does not change with how it might be observed with relativistic principles. The burden of proof that a tree's speed changes, or that it has an infinite variety of speeds ("for" all possible observing frames) is on the theorists who make that claim. We have folks at this “desk” (assumed to be experts) denying the absurdity of a tree changing speeds or having multiple speeds. Will someone here *please* address the question about a tree changing speeds or having a multitude of speeds. --Bowlhover (talk) 04:16, 5 November 2013 (UTC)

Going somewhere which does not welcome whatever you're trying to do uninvited, telling them they're wrong and refusing to leave or repeatedly coming back when it's been made clear what you're doing is not welcome (and never were, no matter whether people believe you're right or wrong) is not part of "legitimate science" no matter how much you may throw around words like "censoring".

What does "serve science" is knowing where and when you should present your "science" and doing so in the places where it would be welcome rather than trying to force other people to let you present your "science" in other places where it's unneeded and unwanted.

To put it a different way, I don't think I know enough about physics to understand what you're trying to say, but it's easy to see enough to dismiss your views. Anyone who comes to the RD or elsewhere on wikipedia (or anywhere where what they're doing is clearly offtopic) to try to prove their own theory and then throws around words like 'censorship' when people tell them to bugger off clearly does not have any good argument or real science to back them up.

Nil Einne (talk) 04:18, 5 November 2013 (UTC)

The point is that the experimental evidence and the mathematics say that this is without doubt what happens. The size of an object is indeed different for observers moving at different speeds relative to it - it does have a different size depending on who is looking at it. That is the truth. It's really not deniable after rational examination of the experimental evidence. The fact that your own "common sense" can't make head or tail of what the "reality" of that is doesn't make it any the less real. It is not the responsibility of nature to conform to what human "common sense" can make of it. This is perhaps more subtly so for relativity than for the bizarro-world of quantum mechanics - but it is still the case. One of the joys of physics (for me at least) is when you come across something like this that stretches your mind to try to imagine how this "really" is. So embrace the weirdness of our universe rather than railing against it. The rules of physics don't appeal to human common sense - they are what they are and it is for us to find ways to incorporate them into the world-view of our somewhat evolved monkey-brains. SteveBaker (talk) 06:16, 5 November 2013 (UTC)

LCcritic, if you bring references supporting suggested content to the article's talkpage that you can quote or paraphrase you are likely to get better responses. Often suggested text can be modified so as to be more accurate and to take into account different views per the policy here: wp:NPOV. --Modocc (talk) 07:01, 5 November 2013 (UTC)

The length contraction section needs a clarification of the difference between observer/frame velocity/direction effects, seldom challenged, and actual physical shrinkage of objects and the distances between them. It is well established in science that Earth's diameter is not in fact physically 4000 miles or less, so the claim that all frames are equally valid, including one approaching at .866c and measuring it to be 4000 miles is simply not true. LC critics have no problem with applying the Lorentz transformation to that measurement to translate it to the proper (actual, physical) diameter length (7901 miles for polar and 7926 for equatorial.) The problem is with claiming that 4000 miles is an equally valid and accurate description of Planet Earth's diameter. Modocc, I cited (in the LC text edit section) the conclusion of Delbert Larson, renowned physicist and designer of particle accelerators, that there is no evidence for LC, but that was rejected. There are many others, but the problem is that anyone who denies physical length contraction is called a "relativity denier" and labeled a crank (or worse) in spite of the fact that there is no explanation in physics for a contracted Earth, "squished" in all possible directions which relativistic observers might be traveling and contracted in proportion to the observer's speed) LCcritic (talk) 20:10, 5 November 2013 (UTC)

SR's use of the word "observer" is unfortunate, because that word normally refers to a person who makes an observation, which is not at all what the word means in the context of SR. In the context of modern SR, all an "observer" is is just a particular kind of coordinate system (an inertial frame of reference), not something that physically exists. Objects that physically exist are more conveniently analyzed in some coordinate systems than in others, because a more convenient choice of coordinate system lets you take certain shortcuts, but it certainly isn't necessary to analyze any object in any particular coordinate system. All laws of physics, when appropriately expressed without using any shortcuts, remain the same regardless of what coordinate system is being used. So in the following, I'll stick to the phrase "coordinate system", to emphasize that no humans are being discussed at all, or even any non-human objects that somehow affect things by "observing" them.

As is common sense, none of Earth's geometric properties change at all due to what coordinate system the geometric properties are expressed in, if any, or what velocity some human or some inanimate object is travelling at relative to the Earth, or what's going on in the brain of some human. Completely consistent with that common sense, special relativity does not claim that Earth's geometric properties change for any of those reasons.

The Earth only has one geometric property pertaining to its polar diameter, but that geometric property is a 4-vector, not a scalar. I'll call that 4-vector Earth's "polar 4-vector" and define it as being a 4-vector whose magnitude is the proper (rest) polar diameter, and whose direction in the Earth's rest frame points from the south pole to the north pole. The Earth's polar 4-vector is very nearly constant over moderate periods of proper time. Like any vector, the polar 4-vector as a geometric object doesn't change if you express it using a different coordinate system; the vector's geometric properties of magnitude and direction remain unchanged.

Similar to polar diameter, the Earth only has one geometric property pertaining to speed, but that geometric property is a 4-vector (the Earth's 4-velocity), not a scalar. There is also a scalar that I'll call "relative speed", but that's not a geometric property of the Earth per se, but rather a geometric relationship between the Earth and a 4-velocity that has nothing to do with the Earth. There is no self-contradiction with the Earth having an infinite number of different relative speeds, because there are obviously an infinite number of different 4-velocities that have nothing to do with the Earth. Mathematically, the Earth's relative speed as a function of an arbitrary 4-velocity V is

$s(V)={\sqrt {(g_{\mu \nu }+V_{\mu }V_{\nu })U^{\mu }U^{\nu }}}$,

where g is the metric tensor, U is the Earth's 4-velocity, sub/superscripts indicate co/contravariance, and the Einstein summation convention is being used. The part of that equation within the parentheses is a projection tensor; see MTW page 565.

Completely analogous to the Earth's relative speed, there is a scalar that I'll call "relative polar diameter", that's not a geometric property of the Earth per se, but rather a geometric relationship between the Earth and a 4-velocity that has nothing to do with the Earth. There is no self-contradiction with the Earth having an infinite number of different relative polar diameters, because there are obviously an infinite number of different 4-velocities that have nothing to do with the Earth. In complete analogy to the Earth's relative speed, the Earth's relative polar diameter as a function of an arbitrary 4-velocity V is

$p(V)={\sqrt {(g_{\mu \nu }+V_{\mu }V_{\nu })P^{\mu }P^{\nu }}}$,

where P is the Earth's polar 4-vector, and everything else is identical to the definition of relative speed.

Note that the expression for the Earth's relative polar diameter has nothing whatsoever do with any particular choice of coordinate system. Indeed, the expression can be considered to not be using any coordinate system at all, if you consider the expression to be using abstract index notation. I.e., "length contraction" does not at all depend on there being multiple "observers", i.e. multiple coordinate systems in use.

"Length contraction" basically occurs because "length" is essentially a 3D "partial metric" that's only operating on 3 out of a 4-vector's 4 components. Given that, it shouldn't be the least bit surprising if two 4-vectors with the same interval don't happen to have the same length. The only way two lengths is comparing apples to apples is if the two 4-vectors in question point in the same direction in 4-space. The same exact issue occurs with using an n-1 dimensional "partial metric" on an n dimensional space even with a Euclidean metric instead of a Minkowski one, and even with using a smaller n than 4. For example, consider the following thought experiment involving using a 1D "partial metric" on a 2D Euclidean space:

Attach a piece of paper to a table. Draw a picture of a lizard as seen from above on the paper. Create a second 2D object on the paper by also drawing a canoe as seen from above. Holding one end of a ruler in each hand, put your elbows at your sides, and lower the ruler until it's on the piece of paper. This will establish a "left-to-right" direction on the paper. Holding the ruler in place, use a pencil and a steel square placed against the edge of the ruler to draw a series of parallel lines 1cm apart, that are perpendicular to the left-to-right direction you established with the ruler. Label those lines from left to right as x=0, x=1, x=2, etc. You have thus established a 1D coordinate system on the 2D space.

You can define a 1D metric using that 1D coordinate system that you've just defined. Make the definition that if two points that you care about on an object are on the lines x=x_a and x=x_b, then the "left-to-right size" of the object is √(x_a-x_b)². Using this definition, you find that, say, the left-to-right size of the lizard (measured from tip of the nose to tip of the tail) is 4cm, and the left-to-right size of the canoe (measured from bow to stern) is 3cm.

Now repeat your construction of a 1D coordinate system on the 2D space, except that this time, stand at an angle to how you were standing, so that the "left-to-right" direction is different from what it had been. Also, this time label the lines as x'=0, x'=1, x'=2, etc. Just as with the unprimed coordinate system, there is a concept of "left-to-right size" in the primed coordinates, which is √(x'_a-x'_b)². But when using the primed coordinates, you find that, say, the left-to-right size of the lizard is now 3cm, and the left-to-right size of the canoe is 4cm. So in changing from the unprimed to the primed coordinates, there's been a "left-to-right size contraction" from 4cm to 3cm for the lizard, and there's been a "left-to-right size dilation" from 3cm to 4cm for the canoe. Furthermore, you can construct as many different 1D coordinate systems as you want, and wind up with the lizard and the canoe each having an infinite number of different left-to-right sizes, all at the same time.

Just as with the relative polar diameter, the ambiguity can be resolved if you define a "relative left-to-right size" for any given object, which is not a geometric property of the object per se, but rather a geometric relationship between the object and a direction in 2-space (which is equivalent to specifying a 4-velocity in spacetime) that has nothing to do with the object. I'll leave the details of how to do that as an exercise to the reader. Red Act (talk) 22:28, 5 November 2013 (UTC)

Amazing explanation, Red Act. Thank you. Incidentally, Dr Larson's website makes for interesting reading - I note he has a perpetual motion machine to sell, inter alia. Tevildo (talk) 22:46, 5 November 2013 (UTC)

Yes, thanks for such an excellent and clear explanation. (I've been wanting to say something like that since this topic started, but I just don't have the expertise or clarity of thought to express it. ) I hope this explanation satisfies those of us who have argued about "reality". Dbfirs 23:34, 5 November 2013 (UTC)

I don't get no satisfaction. :-) RedAct your explanation is helpful and velocities are certainly relative and have nothing to do with the Earth and one does have to keep in mind that relativity works with four dimensions and string theories add a few more. I'll note too that classically we distinguish between time-dependent graphs and static maps of space. But with SR such maps differ with the reference frame. In fact, length contractions of the lattices of electric charges are modeled under SR when explaining the equivalence of the magnetic and electric fields. And I've seen plenty of manifolds twisting and turning the vacuum of space into incomprehensible pretzels and I ate an entire bag of these once before a 5k run, which was an unfortunate mistake (I was sweating salt), but I'm rambling now... Modocc (talk) 02:19, 6 November 2013 (UTC)

First, I don't understand the hierarchy of authority here by which Red Act was allowed to reply after the debate was supposedly forbidden to continue. Nevertheless, that was an amazing piece of work which explains the LC ambiguity in great detail (with the full-on math!... which remains beyond my expertise.) The short version still remains that planets, physical objects in general and distances between objects in space don't physically shrink/contract, regardless of presently prevailing LC "dogma." The length contraction section of Wiki is still in dire need of disambiguation on that issue. Thanks again to Red Act for an intelligent clarification. LCcritic (talk) 02:52, 6 November 2013 (UTC)

This is a reference desk for an encyclopaedia. You have been provided with the standard answer to your question. Disagreeing with it is your problem. It is evident you were not enquiring you were simply setting up a soapbox for your views. Wikipedia does not engage in original research and is not a forum for debate. There's other places for that sort of thing. Dmcq (talk) 13:33, 6 November 2013 (UTC)

Yes, that is what I said here a while ago. - DVdm (talk) 10:24, 7 November 2013 (UTC)

To further complicate the discussion, if you actually did a fly-by of the Earth at near light speed, you would see it as spherical. However, on its surface, you would only see a small portion of the Earth, perhaps only New Zealand. Look at the visualizations towards the end of this video: http://www.youtube.com/watch?v=JQnHTKZBTI4 51kwad (talk) 15:54, 7 November 2013 (UTC)

... in that case, New Zealand would appear to be stretched, not contracted, wouldn't it? Dbfirs 18:02, 8 November 2013 (UTC)

Drug use in the animal kingdom

This cracked article suggests Jaguars use MAOI'S found in Banisteriopsis Caapi to enhance their senses as well as to hallucinate. http://www.cracked.com/article_17032_7-species-that-get-high-more-than-we-do_p2.html Could someone please provide references from journals that support these claims, they are probably correct.

Catnip - Nepeta cataria - is apparently psychoactive in many felines. Roger (Dodger67) (talk) 21:49, 4 November 2013 (UTC)

---

There is a discussion here: http://www.reddit.com/r/askscience/comments/19bvzh/has_there_been_any_scholarly_work_done_on_jaguars/ — ...which includes link to following source: Electroencephalographic and behavioral effects of harmaline in intact cats and in cats with chronic mesencephalic transection

Psychopharmacologia 29. VI. 1970, Volume 17, Issue 4, pp 302-313

~E71.20.250.51 (talk) 23:08, 4 November 2013 (UTC)

• Our article on ayahuasca discusses the relevant pharmacology -- MAOI's by themselves are not usually considered to be very potent hallucinogenic agents, in humans at least. Their effect is to potentiate other drugs. Looie496 (talk) 23:21, 4 November 2013 (UTC)

Calculating impact depth for neutronium

I was looking at the #Impact depth section and I got to thinking. Assuming a free-floating plate of neutronium 1m thick, what velocity would a projectile have to reach to penetrate it? Conversely, what thickness of material would be required to stop a neutronium projectile traveling at that velocity? I checked Impact depth, but can't seem to figure out how the predicted density of neutronium (4×10¹⁷ kg/m³) could be input.--Auric talk 23:59, 4 November 2013 (UTC)

The speed has to be significantly larger than the speed of sound, which for neutronium is

c/sqrt(3). Therefore the projectile has to move at an extremely relativistic velocity, not only does it have to move at a hypersonic speed, it must also overcome the huge difference in the density. Count Iblis (talk) 00:54, 5 November 2013 (UTC)

Well neutronium is not even solid, and neutrons can easily penetrate many kinds of matter, so I suspect a projectile would sink in pretty well. Graeme Bartlett (talk) 10:53, 6 November 2013 (UTC)

Neutronium would be an antipycnal gas, even more so than helium, at STP conditions. At elevated pressures, it would form an extremely dense superfluid. Plasmic Physics (talk) 06:52, 7 November 2013 (UTC)