Light velocity independent of the source velocity.

[Vilas Tamhane]

There are many experiments that prove that light emitted by the moving source does not acquire velocity of the source. Only one I know is that of binary star. However in this it is proved that when the star moves in the direction of our sight or away from it, velocity of light is not c+v or c-v.

 

What is not given is that when the star moves across the line of sight, still it will not acquire velocity of the source. In short photons emitted by the star in the direction perpendicular to the motion of the star will not move along with the star. If this was not the case then we would miss the photons and we will not be able to see the star when it is moving perpendicular to the line of our sight.

 

Am I correct? Are there links which bring out experimental observations?

 

 

[Janus]

There are many experiments that prove that light emitted by the moving source does not acquire velocity of the source. Only one I know is that of binary star. However in this it is proved that when the star moves in the direction of our sight or away from it, velocity of light is not c+v or c-v.

 

What is not given is that when the star moves across the line of sight, still it will not acquire velocity of the source. In short photons emitted by the star in the direction perpendicular to the motion of the star will not move along with the star. If this was not the case then we would miss the photons and we will not be able to see the star when it is moving perpendicular to the line of our sight.

 

Am I correct? Are there links which bring out experimental observations?

 

 

http://en.wikipedia.org/wiki/Aberration_of_light

[J.C.MacSwell]

http://en.wikipedia.org/wiki/Aberration_of_light

 

Isn't that regarding velocity of the receiver?

 

The OP seems to be concerning velocity of the emitter.

[md65536]

What is not given is that when the star moves across the line of sight, still it will not acquire velocity of the source. In short photons emitted by the star in the direction perpendicular to the motion of the star will not move along with the star. If this was not the case then we would miss the photons and we will not be able to see the star when it is moving perpendicular to the line of our sight.

 

Am I correct?

Yes. The propagation of light is isotropic, meaning the same in all directions.

 

You can't directly observe signals sent perpendicularly to you, but you can receive information sent from different events (the simplest being if the light signals are also reflected to you at both the source and destination), and will always calculate the speed of light between any 2 points in a vacuum, to be c.

 

 

[Janus]

Isn't that regarding velocity of the receiver?

 

The OP seems to be concerning velocity of the emitter.

 

It is regarding relative velocity between emitter and receiver, it doesn't matter which one you consider as "moving".

[Vilas Tamhane]

http://en.wikipedia....ration_of_light

 

I have gone through this link earlier and was not satisfied. There is a following paragraph in it.

 

 

“In contrast, stellar aberration is independent of the distance of a celestial object from the observer, and depends only on the observer's instantaneous transverse velocity with respect to the incoming light beam, at the moment of observation. The light beam from a distant object cannot itself have any transverse velocity component, or it could not (by definition) be seen by the observer, since it would miss the observer. Thus, any transverse velocity of the emitting source plays no part in aberration. Another way to state this is that the emitting object may have a transverse velocity with respect to the observer, but any light beam emitted from it which reaches the observer, cannot, for it must have been previously emitted in such a direction that its transverse component has been "corrected" for. Such a beam must come "straight" to the observer along a line which connects the observer with the position of the object when it emitted the light.”

 

 

In the above, it is not clear what the author has to say about emitted light. At some other place I got the explanation that the photon emitted in the direction of line of sight are not received by earth as they have component of velocity of the star. They will of course miss the observer. However rays emitted at backward angle will reach the us.

 

If the second point is true, we have some problem. As the star goes on acquiring horizontal component of velocity w.r.t. line of sight, then we will receive the light rays at an angle (in contrast to what the author of the link says), in that case aberration seen by us throughout the year, will not be uniform. If we are to receive light in vertical direction (neglecting aberration) then our problem becomes bigger. Velocity of this component of the light will be less than ‘c’. In this case, taking time that takes for light to reach us, we will not be able to see uniform motion of star or in other words, motion of star will appear not to follow Kepler’s law.

 

 

In the experiment with aberration of light it is interesting to observe that all the way we assume that light received is vertical. Aberration then occurs due to velocity of earth with respect to vertical direction. Since aberration angle changes uniformly, it is safe to assume that we do receive light vertically. No where it is made clear if the direction or velocity of light changes when motion of the star is horizontal to line of sight.

 

 

Therefore it all points out to the fact that in whatever direction light is emitted by the star, it will not acquire any component of the velocity of the star. It is rather unacceptable that light will not acquire longitudinal velocity of the star but it will acquire transverse velocity.

 

 

Star propagates light in all directions. But if we have a well collimated light pulse then we can easily test, even in the laboratory, if the emitted pulse does move along the source or not.

 

Yes. The propagation of light is isotropic, meaning the same in all directions.

 

You can't directly observe signals sent perpendicularly to you, but you can receive information sent from different events (the simplest being if the light signals are also reflected to you at both the source and destination), and will always calculate the speed of light between any 2 points in a vacuum, to be c.

 

 

 

Your first sentence is very important but what does it convey? Suppose light acquires velocity of the source, then transverse radiation will move along the source. Thus if light is directed upwards by a source moving horizontally and if light moves along with the source, then actual path of light will be diagonal and along this diagonal path, velocity of light will be c. This does not violate principle of isotropy of light but it makes light change its direction of propagation. I am considering light not as a wave but as a photon packet.

 

Isn't that regarding velocity of the receiver?

 

The OP seems to be concerning velocity of the emitter.

 

 

It is but in the link there is a mention of velocity of light when star is in transverse motion to the line of sight. To me, author of the link appears confused. He does not state in very clear words, direction and speed of photon emitted by the star.

 

 

That velocity of light emitted by source is always ‘c’, is known to every body. What is not clear to me is, when light is emitted perpendicular to the motion of the source, if light changes direction.