Hi,

 

I've read on several forums and websites there there is no such thing as absolute speed or movement, it's always relative because there is no fixed frame of reference.

But, if the speed of light is constant and thus independent of the speed/movement of it's source, than this must mean that the direction or vector of a light beam is also constant once it is generated.

 

If the vector (x,y,x) of a light beam is not influenced by the movement/speed of its source (lets say a laser diode) than a light beam in it self is a fixed frame of reference.

 

So this would mean that if I can somehow capture a light beam and measure the (apparent) change in its direction, I can measure my own absolute movement.

 

Any thoughts on why this is not correct? (Because, as far as I know, according to modern science this is not true).

 

Thanks,

Dennis

No matter what frame you are in, you will measure c, so that measurement means nothing. And we can never be in the same frame as a photon.

The speed of light is considered a constant because no matter how fast you are moving, in any direction, you will always observe light to be moving at the same speed, c (standing for 'constant'), which is 299,792,458 meters per second. This implies that time and distance are actually variable depending upon relative speed, which is what Special Relativity deals with.

Yes I know this.

But I'm not talking about measuring the speed of light. I'm talking about measuring the direction of the light. Or rather, the change in direction.

 

Maybe I haven't been clear. Basically what I'm saying is that not only the speed of light is constant but also the direction is fixed.

Edited July 12, 201312 yr by Nimleth

 

If the vector (x,y,x) of a light beam is not influenced by the movement/speed of its source (lets say a laser diode) than a light beam in it self is a fixed frame of reference.

Actually, the direction of the light beam IS influenced by the relative motion between source and receiver. The phenomenon is called "relativistic aberration". It is the speed of light that is not influenced by relative motion, the direction IS influenced.

Edited July 12, 201312 yr by xyzt

The direction does not determine an absolute frame. Photons can go in any direction.

Actually, the direction of the light beam IS influenced by the relative motion between source and receiver. The phenomenon is called "relativistic aberration". It is the speed of light that is not influenced by relative motion, the direction IS influenced.

Hi xytz,

 

Thanks for the tip about relativistic aberration, this was very helpful. So, if I understand it correctly, the photons do actually take on the velocity components of the source. I hadn't seen any explicit reference to this before.

So the fact that the source still sees the light having the velocity c comes purely from the variability in time.

 

Thanks a million,

Dennis

Hi xytz,

 

Thanks for the tip about relativistic aberration, this was very helpful. So, if I understand it correctly, the photons do actually take on the velocity components of the source. I hadn't seen any explicit reference to this before.

So the fact that the source still sees the light having the velocity c comes purely from the variability in time.

 

Thanks a million,

Dennis

Here is a decent reference that you can read on. The wave vector changes direction based on the frame of reference. The photons do NOT "take on the velocity of the source".