Jump to content

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


dimreepr

Recommended Posts

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
Link to comment
Share on other sites

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
Link to comment
Share on other sites

 

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.

Link to comment
Share on other sites

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.

Link to comment
Share on other sites

 

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.

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.