# Wikipedia:Reference desk/Archives/Science/2011 January 3

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# January 3

## Quantum Electrodynamics

I suspect I worked out the special relativity version of the Schrödinger equation. I want to check it, but I want another stab at it if I was wrong.

Is it some variation of ${\displaystyle -\left(\hbar {\frac {\delta \Psi }{\delta t}}\right)^{2}=\hbar ^{2}c^{2}{\frac {\delta ^{2}\Psi }{\delta x^{2}}}+m^{2}c^{4}-U^{2}\Psi ^{2}}$?

I'm pretty sure it's on the Schrödinger equation equation page, but I can't look myself for obvious reasons. If I just flipped a sign or something, go ahead and tell me the answer. But if it's completely wrong, don't.

While I'm at it, I have another question. I was trying to work out how the whole nothing -> particle + antiparticle thing works. Is nothing made up of particle-antiparticle pairs? That would require that, for example, the binding energy of positronium is about one MeV. I'm pretty sure it's supposed to be a quarter of a Rydberg energy or something like that. Does the weak force make another ground state when they're really close to each other or something? — DanielLC 02:03, 3 January 2011 (UTC)

The Dirac equation (don't look) page says "... the necessary equation is first-order in both space and time ...", so I don't think yours is correct. For the second part of the question, you may be interested in Dirac sea 157.193.175.207 (talk) 12:33, 3 January 2011 (UTC)

I don't think the Dirac sea thing helps. My problem is that there's three dimensions for each particle, so if you added a particle antiparticle pair, you'd add six dimensions. I'm pretty sure the laws just give how to change the amplitude of a given point in configuration space. You can't have it change the number of dimensions. Not unless you use the Copenhagen interpretation, and there has to be a better answer than that. — DanielLC 22:14, 3 January 2011 (UTC)
changing the QM framework to allow for creation and destruction of particles was historically a problem that was solved using Canonical quantization, especially second quantisation. 157.193.175.207 (talk) 12:27, 4 January 2011 (UTC)

If you drop the U, what you've come up with has a fair amount of similarity to a one-dimensional version of the Klein–Gordon equation, but there are a couple of important differences. I think you might as well just look at the article, since I think the Klein–Gordon equation isn't really all that important of a stepping-stone toward QED anyway, mainly because it describes a spin-0 particle, so it's not worth knocking yourself out over. Red Act (talk) 19:10, 3 January 2011 (UTC)

## Size of Casimir effect vs observed dark energy

One thing the Casimir effect page seems to be missing is a comparison vs the observed Dark energy level. So do the microscopic and cosmic measurements about "the state of nothing" agree or are they vastly different? Hcobb (talk) 06:18, 3 January 2011 (UTC)

The Casimir effect vastly increases at distance scales shrink, whereas dark energy is in the biggest size scales and seems to increase as size increases. They are very different. Graeme Bartlett (talk) 08:09, 7 January 2011 (UTC)

## Recording sound from a moving car?

Ordinarily, of course, one hears relatively little from the window of a moving car, since the background sound of rushing wind is so loud. But is it possible to design some sort of microphone pods that completely avoid turbulence, or cancel or filter all white noise, so that if they were connected to speakers inside the (well-soundproofed) car you could hear everything around the car while moving at highway speed as if you were parked? Wnt (talk) 06:50, 3 January 2011 (UTC)

Yes, but everything would be doppler shifted. Ariel. (talk) 08:40, 3 January 2011 (UTC)
Noise-canceling microphone, Anti-noise, and Noise-cancelling headphones may be relevant. Perhaps with well-chosen locations of several microphones and the right circuitry, you might be able to cancel out much of the motor, tyre, and wind noise and be left with the car-less noise. 92.15.31.128 (talk) 13:54, 3 January 2011 (UTC)
I don't think that approach would work well, here, as such systems require a way to distinguish between the noise to be canceled and the sound to let through. When listening to music from the radio, is straight-forward, the sounds coming out of the radio are the ones to keep and the rest need to be canceled. However, in this case, the noise from wind turbulence around the car probably sounds identical to that from wind blowing through the trees. Reducing the background noise, by streamlining the car, would assist you, as would putting a (streamlined) microphone outside the car and driving as slowly as possible. StuRat (talk) 16:02, 3 January 2011 (UTC)
Well it could do if the target is well separated from the vehicle. Adding noise in antiphase to cancel it requires pickup mics close to the noise source (ie the engine, tyres, body) and the target to be away from the car. Noise cancelling mics work by rejecting noise from the rear and sides. This is going to work best if the mic is on a boom pointing away from the car, or at least pointing out the window. Not terribly practical for an everyday vehicle, what's your intended application? some kind of espionage? SpinningSpark 16:57, 3 January 2011 (UTC)
Nay, just curiosity during a long drive - though I was thinking that if an answer existed it might be based on some existing spy tech perhaps for airplanes. I understand that the Doppler shift would be noticeable, but that is just part of the curiosity. The noise cancelling approach is interesting, but I think that any air turbulence directly at the microphone would be unique and could not be cancelled against any other microphone. Though the engine and tire noise could be dealt with so, I was supposing that a well insulated stalk on a microphone could do the same. The real question to my mind is whether a moving object can be designed aerodynamically so that there is a region of perfect laminar flow over part of it, which can be insulated acoustically from the rest, and whether a microphone membrane can be placed there so as not to interfere with the airflow but which can pick up the sound. Wnt (talk) 17:45, 3 January 2011 (UTC)
Streamlining can be far better than it is now, but it requires compromises like less ground clearance and passenger room. Also, the radiators we use now that rely on air smashing headlong into them have to go. Instead, a larger radiator along the inside of the hood might make sense. Windshield wipers and door handles also need to go (or at least should be covered up when not in use). Instead of being open at the bottom, the car must have a panel underneath. Then there's the gaps between body panels. A single shell that's lowered onto the frame (and driver) would fix that. StuRat (talk) 17:58, 3 January 2011 (UTC)
The usual idea for microphones in wind is not to encourage laminar flow, but rather to break it up to something less energetic. This is the reason for the fur covering seen on microphones used by outside broadcast crews. See here also. SpinningSpark 18:40, 3 January 2011 (UTC)
It's essentially impossible. If you know the spectral characteristics of the signal you want to receive, you can amplify in a way that focuses on that spectral range, but because white noise covers the entire spectrum and is completely unpredictable, you will still pick up the part of it that overlaps with your signal. If you don't know the spectral characteristics of the target, it is completely hopeless. (As StuRat said, the noise-canceling principle can't be applied in this situation.) Looie496 (talk) 19:50, 3 January 2011 (UTC)
I don't think the OP really means white noise, I am reading that as merely a substitute for all the various sources of noise found in a vehicle. SpinningSpark 20:37, 3 January 2011 (UTC)
I think what you are wondering is if you can make the car "slip" through the external sounds, so they would flow around the car and you wouldn't hear them. This would only happen if the local section of air was traveling faster than the speed of sound - and that would be quite noticeable due to the sonic boom. A concorde is quieter to its own passengers because it outraces its own noise. Ariel. (talk) 20:42, 3 January 2011 (UTC)
I am skeptical of the statement that the Concord was quieter because it was outpacing its sound. Sound from aircraft engines is easily conducted through the aircraft itself. Googlemeister (talk) 21:01, 3 January 2011 (UTC)
Some sound is, but most isn't. A jet engine is extremely loud (over 140db) - if a lot of sound was conducted you'd need ear protection on flights. Also a lot of noise is turbulence from the wings and other surfaces, and that noise is generated slightly removed from the wings. Ariel. (talk) 21:34, 3 January 2011 (UTC)
Edit: I tried to find a ref for it. The best I info I found was a forum post that said that the back of plane was much louder than the front ('And the very back of the cabin was dubbed "rocket class".'[1]), but otherwise the sound level was mostly normal/typical. Apparently they also worked hard when designing it to minimize sound, so it's hard to separate that from speed of sound quietness. Ariel. (talk) 21:47, 3 January 2011 (UTC)

## where did all the mass go?

If the infant universe had infinite volume and infinite density, then it must have had infinite mass (since density is a function of mass and volume). However, our present universe does not have infinite density, so where did all the mass go?thank you. —Preceding unsigned comment added by 117.201.161.237 (talk) 11:05, 3 January 2011 (UTC)

This question has already been answered above. --Plasmic Physics (talk) 11:12, 3 January 2011 (UTC)
Where? And to answer your question, it did not have infinite volume. It was a singularity, so it was just a point with infinite density. When it rapidly expanded, it didn't have infinite density anymore. --T H F S W (T · C · E) 18:28, 3 January 2011 (UTC)
Here [[2]]. As I understand it infinite density is a backward extrapolation of the expansion of the universe we have observed. If this is true our observable universe started as a infinitesimal point, but we do not know how big the whole universe are and if it is infinite it is possible that the volume was infinite even when the density was infinite. The obvious answer to the question is that the mass is outside the observable universe and that every volume has expanded an infinite number of times so the density can be finite. --Gr8xoz (talk) 21:48, 3 January 2011 (UTC)

## Theory of everything

Haven't electromagnetism and both nuclear forces already been unified? Why is it still so hard to unify gravity with a single force instead of three forces? --75.60.13.19 (talk) 15:03, 3 January 2011 (UTC)

Because gravity isn't even well explained by itself, never mind how it fits into a possible Theory of Everything. One of the key problems with gravity is that it is ignored by the standard model, which holds that forces are propagated by Force carriers; that is particles which transport the "force" between the things so affected by the force. EM is mediated by photons, the strong nuclear force by gluons, and the weak nuclear force by the W and Z bosons. There has not yet been any confirmed existance of a graviton, or even a consistant theory which predicts its existance, beyond the "the other forces have one, so gravity must too". General relativity gets around this problem by making gravity a pseudoforce, much like Centrifugal force; that is gravity represents objects moving in straight lines at constant speeds (and thus, unaffected by forces), but doing so in a curved 4D spacetime, a concept known as Geodesics. The problem is that, so far, both General Relativity and the Standard Model are really good, working theories, but they resist incorporation with each other. --Jayron32 15:30, 3 January 2011 (UTC)
Have you (the OP) read our article on the modern theory of everything? Electricity and magnetism were united as they were researched during the enlightenment forming electro-magnetism. Electro-magnetism and the weak force were united between 1979 and 1983 forming the electroweak force. There are several (related) theories to unite the electroweak force and the strong force forming the grand unified theory, however they are not fully resolved. Once this is done, the next stage is to unite GUT and gravity, forming the theory of everything. On a tangential note, special and general relativity explain how large objects move at speeds approaching the speed of light, and quantum mechanics explains how very small objects move. However, there is no working relativity and quantum mechanics theory to unite them. CS Miller (talk) 00:10, 6 January 2011 (UTC)

## Coloured light

I know that if I look at, for example, a picture of a yellow object on my monitor, what I'm really looking at is nothing yellow, but instead little red and green lights packed so closely together that my eyes can't tell the difference and think they're seeing yellow. But if I'm looking at an actual physical object that really is yellow, am I correct that the light coming into my eyes really is yellow?

This caused me to imagine a situation where this blending of different-coloured lights didn't exist. We could only see pure hues of the entire spectrum, at different brightnesses. An easy way to simulate this is by loading a picture in your favourite graphics editor and setting the saturation in the entire image to 100%. I tried this on a couple of photographs, and it didn't look that much unrealistic. JIP | Talk 19:25, 3 January 2011 (UTC)

Our eyes and brain interpret colors by the amount of stimulation received by the three types of cone cells in our eyes. Light that is true yellow, that is say about 580 nm wavelength, will tend to equally stimulate the "red" and "green" photoreceptors roughly equally. However, so won't light which is 50% red and 50% green; the result is that we cannot actually tell the difference between "spectral yellow" and "non-spectral yellow". See also Color vision and Spectral color for more. --Jayron32 19:39, 3 January 2011 (UTC)
"So won't"? Do you mean "so will", or what? JIP | Talk 19:44, 3 January 2011 (UTC)
So will. --Tagishsimon (talk) 20:31, 3 January 2011 (UTC)
Sorry, "So won't" is part of my New England dialect. The "positive negative" is a regionalism present in that area. It means the same thing as "So will". --Jayron32 20:40, 3 January 2011 (UTC)
I could care less about that.  :) -- Jack of Oz [your turn] 21:19, 3 January 2011 (UTC)
Is that just a New England thing? I had no idea. From here in Connecticut, when I saw JIP's objection I thought "What's the big deal? It means the same either way." APL (talk) 23:07, 3 January 2011 (UTC)
It certainly doesn't mean the same here in England. "So won't" is not idiomatic here in any meaning, but it never occurred to me that it might mean "so will". --ColinFine (talk) 00:08, 4 January 2011 (UTC)
The negative form of will is will not, for which the contraction is won't.[3], literally woll not where woll is an obsolete or dialectical form of will.[4] Cuddlyable3 (talk) 21:57, 4 January 2011 (UTC)
Obviously. However, This side-discussion was about the specific construction "Something will verb, so won't something else" which (in some regions) is identical in meaning to "Something will verb, so will something else", despite the literal meanings of the individual words. "So don't" is occasionally used for "So do" as well. I suppose it's wicked confusing to people not from this area. APL (talk) 23:12, 4 January 2011 (UTC)
Having the same (apparent) color, but made up of different combinations of frequencies is called Metamerism. If you want to see the pure color in your photo, use a magnifying glass. Just changing the saturation won't do that because the ratio between the colors stays the same. Ariel. (talk) 20:39, 3 January 2011 (UTC)
Many objects that you believe are "really yellow" are just reflecting similar amounts of red and green light, plus frequencies in between, but very little blue light. I don't think I can distinguish between "true yellow" and normal reflective "yellow" (except in the extreme cases such as sodium lamps where the frequency range is very narrow), though looking at "pure red" and "pure green" objects by the reflected light should enable an estimate of the range of frequencies being reflected. I remember doing an experiment nearly fifty years ago, in which I held a pure red filter to one eye and a pure green to the other, and could see yellow perfectly normally, proving that it is in the brain that the signals are combined.Dbfirs 22:04, 3 January 2011 (UTC)
But I thought Binocular rivalry proved that each eye is separate! Maybe it only applies to shape and not color? (It mentioned something called "binocular colour rivalry", although without details.) Or maybe only if the images are very different? Ariel. (talk) 22:45, 3 January 2011 (UTC)
Some anaglyph images are "true color" in the sense that all the R information comes in one eye and the G and B data comes in the other eye. It never feels quite right, but it's close. APL (talk) 23:10, 3 January 2011 (UTC)
I think the brain always tries to combine the images, but can be forced to concentrate on just one set of signals, either at will, or involuntarily if there is a big discrepancy. The variation in density of cones and pigment suggests that we all see colour differently, but we adjust our perception to match that of others, so there is an enormous amount of pre-processing goes on in the visual cortex before the conscious mind "sees". Dbfirs 09:08, 4 January 2011 (UTC)
Another practical example involves the so-called "white light" emitted by fluorescent lamps, which is actually made up of various bands of color. Many things don't really show the proper coloration that they would under genuine sunlight, or a good natural-frequency incandescent bulb for that matter, because they aren't reflecting or absorbing real yellow light. Wnt (talk) 14:51, 4 January 2011 (UTC)

## Chimney drought or draft

The article on Chimney drought or draft (Chimney#Chimney_draught_or_draft) confused me a little. It says that "the combustion flue gases inside the chimneys or stacks are much hotter than the ambient outside air and therefore less dense than the ambient air. That causes the bottom of the vertical column of hot flue gas to have a lower pressure than the pressure at the bottom of a corresponding column of outside air."

I'm confused by the claim that the hotter air would be at a lower pressure. Wouldn't the pressure be higher, because it's hotter? 65.92.7.244 (talk) 20:27, 3 January 2011 (UTC)

In a closed system, hotter air would be at a higher pressure, assuming the same sized container and the same quantity of gas. The deal is, the chimney is open at both the bottom and the top, so it isn't a closed container. As the hot air rises out of the chimney, this creates a lower pressure at the bottom of the column of air in the chimney, essentially because as the warm air leaves via the top, it removes air faster than it can be replaces by cold air at the bottom. What you have in this case is that the quantity of air is actually lower, proportionally, than the temperature of the air is higher. Mathematically, considering the ideal gas law PV=nRT, the "n" term is droping faster than the "T" term is rising, resulting in a lower overall "P" term. --Jayron32 20:31, 3 January 2011 (UTC)
The missing link in your description is that you havn't explained why hot air is less dense than cold air. Hot air has faster-moving air molecules which ricochet off each other and their container and spread out the same mass over a larger volume, and hence has lower density. Edit: reading it again I don't think its true: "as the warm air leaves via the top, it removes air faster than it can be replaces by cold air at the bottom" - its only a chimney, not a jet engine! The cold air should have no problems entering the chimney easily. The warm air rises like something lighter than water floats upwards from the bottom of the sea. 92.15.22.77 (talk) 20:46, 4 January 2011 (UTC)
This is how hot air balloons work. 92.29.114.99 (talk) 20:53, 3 January 2011 (UTC)
Is there an equation that would tell how much thrust (downward) a chimney generates if the volume of air intake, and its temperature and pressure is known? Googlemeister (talk) 20:55, 3 January 2011 (UTC)
I'm sure their is; its a question of fluid dynamics, however I have a background in chemistry, and not chemical engineering. A chemical engineer would likely be able to work out such a problem, and/or have an equation at hand. --Jayron32 20:59, 3 January 2011 (UTC)
If the chimney is in a steady state, then the volume and average density of the hot air in it will be constant. The difference between the mass for that volume of hot air, and the same volume of cold air, should allow you to calculate the force involved. At least that's my guess - its a long time since I did A-level physics. Edit: I understand the thrust is to do with the net momentum difference between what's entering and what's leaving. At a steady state the mass entering and leaving should be the same. If you knew the amount by which the cold air expanded its volume into hot air (although the pressure should be nearly the same since the hot and cold air are interconnected), then you could calculate the relative speeds at which the air entered and left the chimney, and thus calculate the net momentum and therefore thrust. Or you could use smoke to estimate the speed of the entering and leaving air directly. 92.28.251.68 (talk) 00:25, 5 January 2011 (UTC)

Right, thanks. 65.92.7.244 (talk) 00:04, 4 January 2011 (UTC)

I do not think there would be much or any difference in pressure, at least in a cionventional chimney, at the hot and cold air is in contact and would share the same pressure. Rather the hot air is less dense than the cold air as explained above, and so floats upwards. 92.28.242.164 (talk) 15:00, 5 January 2011 (UTC)

## moons

Where might I find out the dates of various phases of the moon for the period June-February 1593? No lunar calendar I have been able to find online goes back anywhere near that far.

79.74.213.144 (talk) 21:00, 3 January 2011 (UTC)

The time between full moons is 29.530589 days. You could probably back-calculate from a known full moon to find the dates of the full moons in that time period. --Jayron32 21:24, 3 January 2011 (UTC)
I use a program called "stellarium" which shows you how the sky looks at any particular time and place and allows you to fast forward or rewind time. I've never tried to go back centuries though, not sure if it will accurately go back that far. I'm at work so can't check. It's free and easy to install if you want to give it a shot. Vespine (talk) 21:35, 3 January 2011 (UTC)
If you do the calculation yourself, don't forget the change from the Julian calendar to the Gregorian calendar. Dbfirs 21:48, 3 January 2011 (UTC)
I just came to write that. But that was 1582 which is before the 1593 date requested. But if you do go back farther be careful of that. Ariel. (talk) 21:50, 3 January 2011 (UTC)
Implementation of the Gregorian calendar varied by country (at as late as 1917), but in Western Europe the change was in 1582. Googlemeister (talk) 22:19, 3 January 2011 (UTC)
That's only correct for a few countries. Most Catholic contries changed within a few years after 1582, but most Protestant countries waited until the 18th century (1752 for Britain and its colonies, for example). See details here. --Anonymous, 07:04 UTC, January 4 (Gregorian), 2011.
List of 16th century lunar eclipses says that in 1593, partial lunar eclipses occurred on May 15, June 13, Nov 8, and Dec 8. Since lunar eclipses can only occur when the moon is full, this should do a pretty good job of pinning it down, assuming the dates are correct. Looie496 (talk) 22:49, 3 January 2011 (UTC)

The site you want is Fred Espenak's eclipse pages at NASA, and specifically the Catalog of the Phases of the Moon going back over 4,000 years (and almost 2,000 years into the future), and under that, specifically this page for the years 1501-1600. Note that he uses the Gregorian calendar beginning with the end of 1582, and assumes that all years start on January 1; if that's wrong for the location you're interested in, you need to correct the dates accordingly. Also note that times are given in UT; for dates of phases of the moon at some location other than the Prime Meridian, you need to correct to local solar time according to the longitude of the place at a rate of 15°/hour. For example, if it says "Jan 17 01:27", the date is January 16 for any location west of longitude 1h27m x 15°/hour = 21°45' W; if it says "Jan 17 23:27", the date is January 18 for any location east of longitude 0h33m (time until midnight) x 15°/hour = 8°15' ). --Anonymous, 07:17 UTC, January 4, 2011.

(The reason for "15°/hour" rather than using time zones, of course, is that they didn't have time zones in the 16th century.) --Anon, 10:58 UTC, January 4, 2011.

## Aspirin

hey all. Over the holidays I was over at my grandparents' house and my grandfather has high blood pressure. He explained to me that he takes aspirin to reduce his risk of heart attack. I'm only in pre-med, but I'm curious: how does this work? I've heard that if you think you're having a heart attack you should chew an aspirin but I assumed it was a blood thinner. Wouldn't regularly taking a blood thinner be dangerous, though? Thanks. 24.92.70.160 (talk) 22:28, 3 January 2011 (UTC)

See the "Prevention of heart attacks and strokes" section of our aspirin article and also our Mechanism of action of aspirin article. You're right that it can act as a blood thinner, but that may be the lesser of two evils (the other being having a heart attack) and may even be a direct benefit (reducing clotting or other flow inhibition that can lead to heart attack). DMacks (talk) 22:29, 3 January 2011 (UTC)
Asperin does thin the blood, yes. There are dangers to taking blood thinners, but it is a standard treatment for some heart problems. A aspirin a day is a very common prescription. If that isn't enough, Warfarin is taken for heart problems to thin the blood. --Tango (talk) 00:05, 4 January 2011 (UTC)
I haven't heard about chewing an aspirin if you think you are having a heart attack. In the movies they take nitroglycerin at the onset of a heart attack. At Nitroglycerin it states Nitroglycerin is also used medically as a vasodilator to treat heart conditions, such as angina and chronic heart failure. It is one of the oldest and most useful drugs for treating heart disease by shortening or even preventing attacks of angina pectoris. Nitroglycerin comes in forms of tablets, sprays or patches. Dolphin (t) 07:22, 4 January 2011 (UTC)
See Myocardial_infarction_management -- aspirin is a well known treatment for acute heart attacks as its antiplatelet activity can reduce the degree of thrombosis and potentially decrease the severity of the ischemic damage. --- Medical geneticist (talk) 12:24, 4 January 2011 (UTC)
Pet peeve - aspirin does not "thin" the blood; your blood does not somehow become more dilute with the ingestion of acetylsalicylic acid. Aspirin serves to reduce platelet aggregation; that is, it reduces the "clumping" action of platelets. While the meaning is generally understood, you'll note that our article carefully avoids the use of this phrase. Matt Deres (talk) 14:26, 4 January 2011 (UTC)
Moreover, the prescribed daily dose of aspirin for preventive antithrombosis is generally the baby aspirin -- 81mg BID (or QD). DRosenbach (Talk | Contribs) 04:17, 6 January 2011 (UTC)

## Light speed

I'm assuming that time and speed are inversely proportional. On that, I can predict the reason light speed can never be met is that you can't add more acceleration because you can't have a "0" time. Is this correct? Albacore (talk) 22:50, 3 January 2011 (UTC)

That doesn't make sense to me. I read your proposal as implying speed of light is infinite. That's obviously not true, it has a definite and measurable speed, so there is certainly time there for any given distance travelled. The light-speed problem is that you simply cannot reduce that time below a certain level. DMacks (talk) 23:00, 3 January 2011 (UTC)
(ec) No. Massive objects can not reach light speed, because as they accelerate arbitrarily close to light speed, it takes an increasingly larger amount of energy for each incremental unit of acceleration. This means that it would require an infinite amount of input energy to reach a finite velocity. It has nothing to do with "subtracting time", although the mathematical formulation of the Lorentz transform can be used to model the effect known as time dilation. Nimur (talk) 23:01, 3 January 2011 (UTC)
Note: I believe that when Nimur wrote "massive objects", he meant "objects with mass" and not "really large objects, like Jupiter". Comet Tuttle (talk) 23:05, 3 January 2011 (UTC)
Correct. I meant "objects with non-zero rest mass." That is, pretty much everything except photons. Nimur (talk) 00:10, 4 January 2011 (UTC)
Yeah you're talking about time dilation, and I'm not a physicist but I think this is one way you can look at it. Another factor to consider is Length contraction. I remember reading some mind bending stuff about how the universe is actually stationary in time from the reference of a photon, or any photon. So from a photon's perspective it's actually everywhere at once, or it's actually only one photon everywhere at once, or something like that, don't quote me I've probably got it wrong, but it was pretty far out. Vespine (talk) 23:34, 3 January 2011 (UTC)
Time dilation at light speed is infinite, which basically means time doesn't make sense for a photon. You could say that, from a photon's point of view, a photon is a line through spacetime rather than a point. If exists simultaneously at every point along its worldline, since without a concept of time everything is simultaneous. Mathematically, though, we just say the proper time for a photon is undefined and leave it at that. --Tango (talk) 00:10, 4 January 2011 (UTC)
Actually, what physicists say is that photon's do not have a point of view; that it is literally impossible to consider light itself as a reference frame, and thus it is nonsensical to even consider what the posibilities are. You generate far to many real paradoxes when you try to do so, it becomes kinda impossible to even think about it in those terms. --Jayron32 03:49, 4 January 2011 (UTC)