Red/blue shift question.

[Severian]

Severian - this might be a clearer way to ask the question. If are in a space ship located 10 light-years from a star, and stationary wrt the star, when we start moving toward the star, will we immediately notice the bluse shift (asuming we are moving fast enough to produce an appreciable shift)? Or will we have to wait until the light from the star being emitted right now reaches us in order to notice the shift.

 

You will see it right away. The important thing in this case how frequently you pass through the wave peaks. Since you are travelling towards them you will hit them more frequently.

[Saint]

You will see it right away. The important thing in this case how frequently you pass through the wave peaks. Since you are travelling towards them you will hit them more frequently.

 

And I guess that ultimately where our disagreement comes from here. I don't see how you can approach the the wave peaks faster without approaching the beam of light faster. I mean, you have a beam of light, and the you have yourself. The only thing that changes the frequency in this case is your velocity wrt to the light beam. But that velocity is supposed to remain constant. It seems like you're saying that the relative speed will influence how often you encounter the wave peaks without inlfuencing your speed relative to the wave peaks. I don't see how that can be the case.

[Severian]

And I guess that ultimately where our disagreement comes from here. I don't see how you can approach the the wave peaks faster without approaching the beam of light faster. I mean, you have a beam of light, and the you have yourself. The only thing that changes the frequency in this case is your velocity wrt to the light beam. But that velocity is supposed to remain constant. It seems like you're saying that the relative speed will influence how often you encounter the wave peaks without inlfuencing your speed relative to the wave peaks. I don't see how that can be the case.

 

OK - I see what you problem is now. The difficulty is that the doppler shift looks like it has different causes in different frames.

 

You are correct that in your new frame (moving towards the source) the light will still be moving at a speed c towards you. So it looks like nothing has changed: previously you had the light moving towards you at relative speed c, and now you still do!

 

However, now you are moving fast all the distance scales will suffer a length contraction, so the distance to the next wavepeak becomes smaller and you will reach it more quickly. Hence the frequency goes up and the light is blue-shifted as before.

[MetaFrizzics]

What is most remarkable with spacial compression in the direction of motion (toward the star) is that while Special Relativity seems to limit the velocity of a massive object, there is a real gain in actual acceleration as the object is 'moved' closer by the act of compression of spacetime.

 

But here's the rub: rather than this extra boost allowing faster than light-speeds, the compression is normally interpreted as an illusion, explained by time dilation. That is, rather than getting a distance boost toward the star, your clock is actually slowing down. This avoids the absurdity of you being able to compress the entire universe by flapping your wings. Instead your own clock (and perception of time?) slows down.

 

An outside observer doesn't see you accelerating up to the speed of light, but rather notes your clock is slowing down as you speed up a 'normal' amount.

 

The 'red/blue shift' is best explained as your measurement device malfunctioning due to its internal 'time-clock' slowing down.

 

By keeping 'time' a local variable which is itself dependant upon your 'absolute' velocity (your angle relative to the 'time axis' through spacetime), relativists avoid more serious contradictions and paradoxes. The cost of doing business for Relativity is that a universal 'Time' and absolute planes of simultaneity are sacrificed to the God of 'Electromagnetic Relativity'.

[swansont]

By keeping 'time' a local variable which is itself dependant upon your 'absolute' velocity (your angle relative to the 'time axis' through spacetime), relativists avoid more serious contradictions and paradoxes. The cost of doing business for Relativity is that a universal 'Time' and absolute planes of simultaneity are sacrificed to the God of 'Electromagnetic Relativity'.

 

I guess I'm a little fuzzy on on your previous explanation. Whenever you spout nonsense, we are to interpret it as your wacky sense of humor?

[MetaFrizzics]

There: I've fixed my avatar. This should help you to understand when I am speaking about relativity.

[J.C.MacSwell]

(If you think about it' date=' of course you can cause a red/blue shift by independantly changing your speed relative to a source. The times between release of light and our reception of it are so great (measured in hundreds or thousands of light-years!) that we might as well view all light available to us as 'already been released'. [b']The red/blue shifts we observe are actually due to our motion relative to planes of propagation of EM waves now. [/b] If you couldn't create a shift by motion, we would never see any observable shifts now. All the shifts we see are based upon the earth's / solar system's current speed.

!

 

All the redshifts we observe cannot be due to the Earth's / solar system's current speed unless we are imploding pretty fast.

 

p.s. I'm sure you are aware that time is not measured in light years.

[Saint]

OK - I see what you problem is now. The difficulty is that the doppler shift looks like it has different causes in different frames.

 

You are correct that in your new frame (moving towards the source) the light will still be moving at a speed c towards you. So it looks like nothing has changed: previously you had the light moving towards you at relative speed c' date=' and now you still do!

 

However, now you are moving fast all the distance scales will suffer a length contraction, so the [b']distance[/b] to the next wavepeak becomes smaller and you will reach it more quickly. Hence the frequency goes up and the light is blue-shifted as before.

 

Thanks Severian - I appreciate the time. One more question. WRT what are you moving in order to observe a doppler shift in a beam of light.

[swansont]

One more question. WRT what are you moving in order to observe a doppler shift in a beam of light.

 

The source, or more specifically the reference frame in which the source is stationary, when the light was being emitted.

[Daecon]

*nevermind*