Does time effect slowed light or not?

  • #1

Main Question or Discussion Point

I really wanted to know if we have managed to slow down light so its speed is not c ?
and if when its slowed down, if time effects the light or not?
Thanks
 

Answers and Replies

  • #2
russ_watters
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Welcome to PF.

No, the speed of light in a vacuum is what it is. It is constant.
 
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  • #3
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I really wanted to know if we have managed to slow down light so its speed is not c ?
Yes, that is how refraction works.

and if when its slowed down, if time effects the light or not?
I am not sure what you mean by this. Classically, light obeys Maxwell's equations both in and out of refractive materials, and Maxwell's equations certainly can be written in a manner which includes time. So I would say that time affects light both in vacuum and in matter. But it is hard to say without some more information about your meaning.
 
  • #4
So mean, that given light when it is travelling at its normal speed is not subject to time. So time doesn't effect light.
Is this still true if we slow down light?

So, you take a light beam, slow it down, then see if time still effects it.
This is important because if time does effect slowed light then time is separate from light.
But if it doesn't then it means that time is more universal.

Hope that is clear
 
  • #5
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So mean, that given light when it is travelling at its normal speed is not subject to time. So time doesn't effect light.
Maxwell's equations disagree.
 
  • #6
I think what he's trying to say is:

Since photons travel at c, they do not do not experience time and distance. But if they could be slowed down would this still be the case?
 
  • #7
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Since photons travel at c, they do not do not experience time and distance.
How can that be true?

-Photons oscillate at some frequency.

-The path of a photon is affected by strong gravitation fields.

How can a thing have frequency and change of directional without time and distance?
 
  • #8
Good point, but wouldn't the changes for the photons only apply for an observer?
 
  • #9
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Since photons travel at c, they do not do not experience time and distance.
That statement has no meaning as there is no inertial reference frame for light....you can't have clocks and rulers travel at 'c' is one way to look at it.... Here are a few recent comments I saved from another discussion about that:

Reference frame for a photon?

atyy

There is something called "light cone coordinates". However, the reference frame defined by these coordinates do not form an inertial reference frame, which is the sort of reference frame in which the "standard formulas" hold.
Fredrik
The standard definition of "a particle's point of view doesn't work". You can of course choose todefine a photon's "point of view", but then the question is, why would you want to call what you just defined a "point of view" (or "perspective" or whatever)?
Fredrik

The problem with the above is that it's not a valid coordinate system. It assigns the same coordinates to many points. Unlike the actual coordinate systems, such functions are not part of the mathematical structure that defines the theory, and they don't need to be.
In other words, length contraction and time dilation formulas don't apply to massless particles; the Lorentz transforms don't apply at velocities of c and greater.
 
  • #10
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Here is the discussion on 'reference frame for a photon'??

https://www.physicsforums.com/showthread.php?t=315122

About the only way to think about issues such as the one posed by the op, is to consider particles moving close to the speed of light.....but you can't extrapolate exactly to 'c'.

PS: If you observe light approaching a black hole, it will appear to slow down when viewed from a great distance, like earth. But actually that is a coordinate effect, that is a mathematically based appearance; locally, light always moves at velocity c'.

Another phenomena is phase and group velocity of waves:
http://en.wikipedia.org/wiki/Phase_velocity

Refraction is a change in the phase velocity of light...but individual photons always move a speed 'c'.....
There is some current experimental work at Harvard U., I believe, about 'slowing light' quantum mechanically, I can't remember the professors name....

edit: Her name is Prof. Hau.....three minute youtube video here....

seems like absorption and emission....individual photons appear to still move at 'c'...but maybe a Bose-Einstein condensate person here can clarify.....
 
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  • #11
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There is some current experimental work at Harvard U., I believe, about 'slowing light' quantum mechanically,
That's really remarkable! (that there's scientific work put towards that goal)

I've seen the "Light slowed down" video of light "propagating" through a coke bottle. That of course was remarkable camera work, not remarkable physics.

Tickles the (very small) sci-fi geek in me, of course "harnessing" the dimensions is the only route to acceleration without any work being done :tongue2:
 
  • #13
5,601
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That's really remarkable! (that there's scientific work put towards that goal)
Not sure just what your mean by that, but if you do a Google type search you'll find she
began 'slowing light' about 15 years ago.....

I wonder if anyone has been able to devise a practical application..
 

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