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Slowest speed of light (split from why is c constant)

dimreepr
in Quantum Theory

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That’s like saying whatever speed I’m doing is my speed, which is, of course, true but it doesn’t answer the question.

Edited by dimreepr

Very deep.

But true if we're talking about the propagation speed of light in a medium that slows it down rather than its speed in a vacuum.
No, it's like saying that light always travels at the same speed, which it does.

 

 

Take two formulas.

pv=nrt

 

Molar attenuation coefficient

a=ecl

 

From here we see that c and n are the same provided we convert to the same units.

Therefore

 

n=a/el

pv=(a/el)rt

 

Thus the speed of light traveling through the atmosphere constantly changes speed.

Edited by fiveworlds

You do realize the c in your example stands for concentration, right?

  • Author
One laser is shot across the width of the cloud of condensate. This controls the speed of a second pulsed laser beam shot along the length of the cloud. The first laser sets up a "quantum interference" such that the moving light beams of the second laser interfere with each other. When everything is set up just right, the light can be slowed by a factor of 20 million.
Slowing light this way doesn't violate any principle of physics. Einstein's theory of relativity places an upper, but not lower, limit on the speed of light.

 

 

 

Presumably the light can’t be stopped using this method, which would suggest there is a lower limit.

Edited by dimreepr

 

Presumably the light can’t be stopped using this method, which would suggest there is a lower limit.

 

Speed is a non-negative scalar, so the limit of zero is already baked into the discussion.

"Bringing light to a halt: Physicists freeze motion of light for a minute"

http://www.sciencedaily.com/releases/2013/08/130806111151.htm

 

 

Absorption is not stopping, in my book. It's a really neat experiment to recreate the light with all the same properties, but there was no point where a photon existed at rest. Similarly, talking into a voice recorder is not "freezing sound" unless you are using your poetic license.

Absorption is not stopping, in my book. It's a really neat experiment to recreate the light with all the same properties, but there was no point where a photon existed at rest. Similarly, talking into a voice recorder is not "freezing sound" unless you are using your poetic license.

 

Isn't the same true of the experiment in the OP? I.e. there was no point where a photon was travelling slower than c, but the overall speed of light (group velocity?) was reduced?

 

But I can see there may be a difference between light slowing because photons are "just" interacting with atoms, compared to being completely absorbed and then recreated.

 

Isn't the same true of the experiment in the OP? I.e. there was no point where a photon was travelling slower than c, but the overall speed of light (group velocity?) was reduced?

 

But I can see there may be a difference between light slowing because photons are "just" interacting with atoms, compared to being completely absorbed and then recreated.

 

That's true, since the photons move at c. In the "stopped light" experiment it's an absorption in a real state. It's more stored light than stopped light.

Photos only travel in a vacuum and always at c. True, given that a vacuum exists even in media; between particles?

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