Liquidrage

As we know the speed of light in a medium is less then the speed of light in a vacuum.
This is due to the absorbtion and emissions of photons by electrons in the medium.

Is c a limited speed and not infinite (as would logically be the case) because of quantum vacuum energy?

If so does this make the speed of light through a system a direct measure of the amount of energy available in a given system?

We know it takes eons for a photon to emerge form the sun.
It takes just 8 minutes for that photon to reach the earth once it leaves the surface of the sun.

Could I rightfully say that the amount of energy available in the path taken between the sun and the Earth by the photon is equal to an 8 minute journey of that photon while in the sun?

Mind you I'm not stating all mass between the sun and the Earth nor all mass within 8 minutes from a point within the sun. Only matter on a path as taken by a photon.

Likewise, if one could somehow prevent quantum fluctuations from occuring in a given system would light be able to travel instantaneously through that system?

Also, if this were the case, what would it say about quantum fluctuations? It would appear that they would be constants as well.

[ August 17, 2002: Message edited by: Liquidrage ]</p>

Bill

No. <a href="http://www.cnn.com/2000/TECH/space/07/20/speed.of.light.ap/index.html" target="_blank">Recent experiments have demonstrated that a particular medium can conduct light faster than the speed of light in a vacuum.</a> As a laser pulse begins to enter the medium, the medium immediately issues an equivalent (but less intense) pulse out the other side.

== Bill

{Edited to add the URL...}

[ August 17, 2002: Message edited by: Bill ]</p>

Shadowy Man

I thik this has been addressed before as being a phase velocity v. group velocity issue. It is typical bad reporting of science.

Liquidrage

I was under the assumption that what Shadowy Man says goes for what is claimed in the link posted by Bill.

And if light could travel faster in a medium then a vacuum one would still have to explain why the absorbtion/emission rate of photons has been lowered when compared to a vacuum.

Bill

That is not my understanding. Here is a direct quote from one of the researchers from within the article I linked to, above: If the trailing edge of an "almost identical light pulse" is truly 60 feet away at the same instant when the trailing part of the exciting pulse finally enters the chamber, then that is not what is meant by the distinction between "phase velocity v. group velocity."

I am not an expert on this sort of thing by any means, but I read that as a real scientific advance demonstrating a real "breaking" of the "speed of light" limit (at least, in some sense of those words ).

== Bill

Jesse

I'm fairly certain that these experiments did not involve "breaking the speed of light" in the sense that information could actually have been transmitted faster than light. Transmitting information faster than light necessarily involves transmitting information backwards in time in some reference frame, which is why breaking the light barrier is a bit more serious than, say, breaking the sound barrier. If this experiment involved an actual causality violation I think we'd have heard more about it.

In general it is possible for waves to travel faster than the causal interactions between the bits of matter/energy which make them up. Think of a long row of sports fans doing the wave, except instead of waiting till they see the person before them standing up they stand up according to a prearranged schedule--in this case the wave could potentially exceed light speed (imagine that the bench is two light seconds long, but the schedule dictates that the last person on the bench stands up only one second after the first person). This is why the "velocity" of a wave can be a bit misleading. <a href="http://www.mathpages.com/home/kmath210/kmath210.htm" target="_blank">This</a> page on wave velocities gives a technical explanation for why both phase velocity and group velocity can exceed light speed without any information (or matter/energy) doing so.

edit: I just found an article about the experiments Bill referred to, explaining why "In short - and in spite of appearances - no energy or information has travelled faster than the speed of light in vacuum." It can be found at:

<a href="http://plus.maths.org/issue12/news/fasterThanLight/" target="_blank">http://plus.maths.org/issue12/news/fasterThanLight/</a>

[ August 18, 2002: Message edited by: Jesse ]</p>

Shadowy Man

I guess the scientists themselves may not be above the sensationalist reporting that passes for science reporting these days... sigh.

Jesse

I don't think the scientists are guilty of any sensationalism here. In the article I posted above there is a link to an <a href="http://www.neci.nj.nec.com/homepages/lwan/faq.htm" target="_blank">FAQ</a> on the experiment written by the scientists themselves, and they make it clear that this does not violate relativity:

Also, at the end of the FAQ they try to explain the experiment in an intuitive way in terms of treating the light wave as a sum of component waves of different frequencies, which as they exit the medium "add to produce the exact form of the incoming pulse."

Shadowy Man

But in the article that Bill referred to I found the following quotes, which are at best only misleading, and at worst deceptive of what they really achieved:

Jesse

The first quote you mention was actually in the section of the FAQ I quoted, if you look back at my last post (it's one of the sentences in italics). In the context of that reply I don't find it particularly misleading--they make it very clear that relativity was not violated--so I'd guess the real fault here is with the media who took that one sentence out-of-context. The same would probably go for the second quote, if you could find its context (it might be from the FAQ as well, I'm not sure).