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Arcane
2010-Nov-26, 11:17 PM
What is stopping light from traveling faster, and can we really count on the speed of light as being consistent?

Atmosphere limits the speed of objects on earth (i.e. Drag). It has also been proven that light can be slowed to 38mph given the right conditions... http://www.news.harvard.edu/gazette/1999/02.18/light.html

Given that light has been proven to be slowed through experiments here on earth, is it also not possible that light could be slowed while going through space? Is this why there is a speed limit on light? If there is a speed limit, could there not also be light that hits pockets of super cooled super dense space and is therefore slowed?

I only ask because it seems that most of our science is based on the assumption that the speed of light is always constant regardless of any sort of interference...but if that is true, why is there a speed limit? And how does one explain the experiment mentioned above?

Hlafordlaes
2010-Nov-27, 03:09 AM
My limited understanding is that light speed does not slow in a material, rather it is absorbed and re-emitted by atoms in the medium. There was a recent post on BAUT explaining this (in far better terms) that you can search for. As for the speed of light in a vacuum, it does not go faster because that is its speed, simply. Why? Because. The basics of our (anthropic?) universe are what they are. (Personally, I'd like light to go much faster, so the limit on how fast we can go would be higher and we could play Star Trek without FTL.)

Arcane
2010-Nov-27, 03:34 AM
Does not absorbed and reemitted with a delay in between = slowed? The point is, if light can be absorbed and reemitted, with a delay in between (i.e. slowed), does that not affect how we see light? For instance, if a light particle is coming from a few billion light years ago, is it not safe to say that the light may have been absorbed and reemitted, with a delay, a few times on its path to Earth?

If so, then how can we assume the distance the light was emitted from?

RelativityWorks
2010-Nov-27, 03:42 AM
In space, there is no medium an therefore it is not being absorbed and reemitted. Space is a vaccum. When light reaches other masses, it is either hitting the mass or being diverted from the original path due its gravity or curvature in space-time.

Strange
2010-Nov-27, 10:59 AM
Also, the speed of light comes out of theoretical considerations as well such as Maxwell's equations of electromagnetism. In fact (as I understand it) this was one more piece of evidence that light was electromagnetic in nature (because it travelled at the speed predicted by the equations).

Relativity then imposes this speed as a limit for any objects with non-zero mass.

Note that this is an upper limit and interactions with matter can (effectively) slow light. This is what causes refraction, for example. I suspect the experiment you refer to is something subtler to do with the slowing the group velocity (the speed of the laser pulses) rather than the phase velocity (the speed of the light itself).

forrest noble
2010-Nov-27, 06:56 PM
What is stopping light from traveling faster, and can we really count on the speed of light as being consistent?

Atmosphere limits the speed of objects on earth (i.e. Drag). It has also been proven that light can be slowed to 38mph given the right conditions... http://www.news.harvard.edu/gazette/1999/02.18/light.html

Given that light has been proven to be slowed through experiments here on earth, is it also not possible that light could be slowed while going through space? Is this why there is a speed limit on light? If there is a speed limit, could there not also be light that hits pockets of super cooled super dense space and is therefore slowed?

I only ask because it seems that most of our science is based on the assumption that the speed of light is always constant regardless of any sort of interference...but if that is true, why is there a speed limit? And how does one explain the experiment mentioned above?

The speed of light is thought to be related to the true nature of space and the Zero Point Field (ZPF) which occupies space. For most of the 1800's this was thought to be the particle density of an omnipresent field then called the luminiferous aether. Now it is thought by many to be related to the energy nature/ density of the ZPF. With the present proposals of dark matter, gravitons, Higgs particles, quantum foam, etc. the "true" nature of the ZPF might be described as being both particle and energy related. It's "density" or related characteristics could be the controlling factors concerning the speed of light in a vacuum.


If there is a speed limit, could there not also be light that hits pockets of super cooled super dense space and is therefore slowed?

If there were a variation in the speed of light due to the factors which you mentioned or others, it would seem to violate Special Relativity (the mainstream model) which asserts that the speed of light in a vacuum is the same in all directions/ locations.

caveman1917
2010-Nov-27, 10:01 PM
What is stopping light from traveling faster

Technically, the absence of a way for it to acquire imaginary mass.

cjameshuff
2010-Nov-27, 11:48 PM
There's a maximum speed at which any effect can propagate through the universe, and without the effects of some medium, light travels at that speed. It's probably more meaningful to ask why all the things that happen at less than lightspeed happen at the speed they do. If atoms were smaller (all else remaining the same), the speed of light would be faster by our standards, if the various physical processes our sense of time is ultimately based on occurred faster, it'd seem slower.

Rather than looking at the speed of light in vacuum as 299792458 m/s and wondering why it's that exact value, think of it as c, with other speeds being some fraction of that...x*c with x being <1. Earth's orbital speed being about 0.0001*c, for example. c looks a lot less mysterious this way.

John Xenir
2010-Nov-28, 12:33 AM
However that would be more confusing for ordinary people, because we measure speed based from time an object needs to reach some distance. Unless we adjust measures for distances (m) and time (s) to make readable in everyday life....

Astrowannabe
2010-Nov-28, 12:49 AM
Arcane I think I see a mistake your making, and it's a very common one so I'll adress that and hopefully it'll clear some things up for you.

What your doing (and nearly everyone does this by mistake) is confusing the "speed of light" with "c". Most people think of "c" as being the speed of light, when in fact thats not entirely true. It's a subtle difference, but an important one.

Yes, light does travel at c in a vaccum, but the value of c was actually discovered in Maxwells equations first, and only later on did people realize that light happen to travel at this mysterious value. You see, one interesting thing about velocity is that every velocity you've ever heard mentioned was always relative to something else. So you where driving at 65 mph relative to the surface of the Earth. Or the Earth orbits at about 65,000 mph relative to the sun. Simply stating a velocity, by itself, is utterly meaningless. Velocities HAVE to be compared to something, always. And depending on what you compare it to will change the apparent velocity of the object.

C, however, was different. When c was discovered in Maxwells equations it did not depend on anything else. Er....let me explain a bit more. When an electric charge is accelerated, it will give off an electric wave. This wave will travel through space, and when you try to determine what it's velocity is you get c (the exact same thing is true for a magnetic wave). And c was not dependant on anything at all. It didn't depend on the strength of the charge, didn't depend on the charges motion, or the force of the acceleration, ect. It was simply 186,000 miles per second, and so was a magnetic wave. In fact, c was only dependant on 2 things, both of which are universal constants: The permeability of free space and the permativity of free space. These are fundamental constants of the universe, and they determine the value of c, nothing else.

It was then later discovered that light was, in fact, an EM wave and it also moved at 186,000 miles per second. And even though yes there are times when light can move slower then c (as in the experiments your talking about), even in those experiments the value of c stays the same while the speed of light is reduced. Light might not be traveling at c, but c is unchanged.

So the only way to change the value of c would be to alter either the permeability or permativity of free space. However you'd have about the same luck trying to change the gravitational constant of the universe, so it's not likely to happen anytime soon unless some ground breaking discovery is made. Also keep in mind that these constants effect the strength of protons and electrons, so even if you did manage to change these constants inside some experiment, any atoms inside (like say, a person or a spaceship) would most likely break down.

Hope that was helpful, and feel free to ask more questions if something wasn't clear.

cjameshuff
2010-Nov-28, 02:25 AM
However that would be more confusing for ordinary people, because we measure speed based from time an object needs to reach some distance. Unless we adjust measures for distances (m) and time (s) to make readable in everyday life....

I was not suggesting that you use it to measure everyday speeds. Doing so is not useful or helpful for understanding what I was trying to get across, that asking why the speed of light isn't faster or slower is looking at it backwards. It's c, the maximum local velocity, the maximum velocity at which information can travel between any two points in the universe. It's speed is what it is in human terms because the physical processes we measure length and distance with are what they are.

Ken G
2010-Nov-28, 07:12 PM
However that would be more confusing for ordinary people, because we measure speed based from time an object needs to reach some distance. Unless we adjust measures for distances (m) and time (s) to make readable in everyday life....Actually, we often already do that-- that's the basis of the "light year" distance scale. When distances are measured in light years, and time in years, then the speed of light is 1, and all other speeds are a fraction of 1.

Ken G
2010-Nov-28, 07:18 PM
If there is a speed limit, could there not also be light that hits pockets of super cooled super dense space and is therefore slowed?
Anything is possible. The goal of science is not to rule out what is not possible, but rather to build theories from what is seen to be possible, and try to explain everything we observe. If it succeeds at that, there is no reason in asking "is something else possible." That question, however, is a very important question to ask when we observe things we cannot explain, or even in anticipation of such observations. So the question is not "is it possible", but, "what would it look like if...?" That's a question that spurs much great theoretical science, but in the absence of observational motivation, it can also be a dead end.


I only ask because it seems that most of our science is based on the assumption that the speed of light is always constant regardless of any sort of interference...but if that is true, why is there a speed limit? Behind any scientific theory is the "why" question, that the theory itself does not answer. Sometimes a deeper theory comes along and answers that for the shallower theory, but not for the deeper theory. But the deeper theory has to have some explanatory advantages over the shallower one to be considered deeper at all. So far, there is no explanatory theory that explains why vacuum supports a speed of light, it just does. Maybe someday there will be one, and someone can return to your question on that forum!

JustAFriend
2010-Nov-29, 04:08 PM
You forget the important phrases implied in every scientific theory:

In this region of the Universe and as far as we know with current knowledge the speed of light is X.

Until we can run tests in other corners of the Universe of course we cannot
know for certain but this is the way we THINK the Universe operates....

forrest noble
2010-Nov-29, 11:38 PM
You forget the important phrases implied in every scientific theory:

In this region of the Universe and as far as we know with current knowledge the speed of light is X.

Until we can run tests in other corners of the Universe of course we cannot
know for certain but this is the way we THINK the Universe operates....

Although most here realize that such assumptions are implied, I think it is a great idea that it is reiterated from time to time (as you have done here) as a sobering reminder that other possibilities might exist concerning how the universe actually operates.