dimreepr Posted January 3, 2016 Posted January 3, 2016 Perhaps a little of topic but what is the theoretical slowest speed of light?
dimreepr Posted January 3, 2016 Author Posted January 3, 2016 (edited) 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 January 3, 2016 by dimreepr
John Cuthber Posted January 3, 2016 Posted January 3, 2016 That’s like saying whatever speed I’m doing is my speed, which is, of course, true but it doesn’t answer the question. No, it's like saying that light always travels at the same speed, which it does.
swansont Posted January 3, 2016 Posted January 3, 2016 No, it's like saying that light always travels at the same speed, which it does. Photons travel at c. Light travels as slow as you can make it.
John Cuthber Posted January 3, 2016 Posted January 3, 2016 Photons travel at c. Light travels as slow as you can make it. Very deep.
Delta1212 Posted January 3, 2016 Posted January 3, 2016 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.
John Cuthber Posted January 3, 2016 Posted January 3, 2016 The problem seems to me to be that light is never not in a medium. If there's a medium present then it goes through it to see how long it takes. How else does it manage the "least time" principle?
fiveworlds Posted January 3, 2016 Posted January 3, 2016 (edited) 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 January 3, 2016 by fiveworlds
Fuzzwood Posted January 3, 2016 Posted January 3, 2016 You do realize the c in your example stands for concentration, right?
Strange Posted January 3, 2016 Posted January 3, 2016 Thus the speed of light traveling through the atmosphere constantly changes speed. It is slowed by about 0.03%.
fiveworlds Posted January 3, 2016 Posted January 3, 2016 Sorry need to change this again should be p=(a/el)rt
swansont Posted January 3, 2016 Posted January 3, 2016 Sorry need to change this again should be p=(a/el)rt Still not relevant to the discussion. 1
dimreepr Posted January 4, 2016 Author Posted January 4, 2016 (edited) 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 January 4, 2016 by dimreepr
Strange Posted January 4, 2016 Posted January 4, 2016 Presumably the light can’t be stopped using this method, which would suggest there is a lower limit. "Bringing light to a halt: Physicists freeze motion of light for a minute" http://www.sciencedaily.com/releases/2013/08/130806111151.htm 1
swansont Posted January 4, 2016 Posted January 4, 2016 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. 1
Strange Posted January 4, 2016 Posted January 4, 2016 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.
swansont Posted January 4, 2016 Posted January 4, 2016 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.
StringJunky Posted January 4, 2016 Posted January 4, 2016 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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