Can speed of light be changed ?

[aby001234]

I mean to say that can the speed of light differs in various media?
Can we do any thing to change or alter speed of light?
According to the theory of varying speed of light (VSL),
the speed of light in the earlier satges of university were different from what
they are today?
How is this possible?
or is it just another theory with no proof?

 

[phinds]

where did you read that the speed of light was different in the early universe? References please.

 

[aby001234]

where did you read that the speed of light was different in the early universe? References please.

It is a theroy called variable speed of light
http://en.wikipedia.org/wiki/Variable_speed_of_light

 

[Lsos]

Absoultely speed of light differs through media. It goes slower through glass or water, for example.

This is Cherenkov Radiation...it's what happens when charged particles travel faster through water than the speed of light (in water). I guess it's the light-equivalent of a sonic boom, although I'm sure that's an oversimplification.

I think they even managed to slow light down to human-scale speeds in some experiments...

 

[phinds]

It is a theroy called variable speed of light
http://en.wikipedia.org/wiki/Variable_speed_of_light

Hadn't heard that one before. Thanks.

 

[l470594464]

Maybe you'd better learn the Maxwell's equation first to see how light's speed comes from and why it travels slower in some media.Wikipedia is not science book. lol

 

[faizin]

Maybe you'd better learn the Maxwell's equation first to see how light's speed comes from and why it travels slower in some media.Wikipedia is not science book. lol

couldn't agree more..

 

[my_wan]

What needs to be realized in these VSL theories is that when you talk about a speed it has no absolute meaning whatsoever. Even the speed of your car is meaningless except in relation to the road, or whatever else you want to compare it to.

As an example from a post I just made on gravity in a hollow sphere, when GR invoked a variance in the apparent mass of Mercury to explain the perihelion precession you could just as easily say that it was not the apparent mass that changed but the apparent value of the gravitational constant (big G). Mathematically this has exactly the same empirical result. Yet keeping these constants constant in this way keeps the formalism defining the laws of physics consistent in a straightforward manner. Arguing one or the other is 'absolutely' the true definition of what occurred is meaningless and physically absurd.

So when VSL theories are talking about changes in the speed of light they are not referring to any actual change in absolute speed. Rather they are talking about its speed relative to some other constant. You could also say it was the other constant that changed rather than light speed, but then that involves a rather pedantic argument over what constitutes an absolute speed or metric. Coordinate independence is almost certainly a fundamental property of the Universe.

 

[vinniewryan]

Yes, light can be slowed down. In fact, the technology to do so will soon be found in a silicon chip. I just found this out about 2 weeks ago:

http://news.harvard.edu/gazette/1999/02.18/light.html
http://www.sciencedaily.com/releases/2008/03/080327172255.htm

 

[rcgldr]

The speed of light in a media is slowed down because of the lag between absorption and emission of photons by the electrons in the media. The speed of light remains the same as it travels from electron to electron as it would in a vacuum.

The speed of light is affected by gravity under general relativity:

http://en.wikipedia.org/wiki/Shapiro_delay

 

[my_wan]

The speed of light in a media is slowed down because of the lag between absorption and emission of photons by the electrons in the media. The speed of light remains the same as it travels from electron to electron as it would in a vacuum.

The speed of light is affected by gravity under general relativity:

http://en.wikipedia.org/wiki/Shapiro_delay

Absolutely correct on the speed through a medium, but the gravitational effects need a bit more explanation. At the local point by point position the photon tracks through space the speed of light always remains constant relative to that point. The problem is that for an inertial observing this track each point the photon occupies has a slightly different clock rate relative to that observer. Hence to that observer it 'appears' that the speed of light changes as it progresses through the gravitational field. Yet relative to the clock rate defined at the points the photon occupies it never changes.