The Shalimar Treaty

[AngleWyrm]

These guys seem to think red shift and Doppler shift describe the same phenomenon:
http://www.answers.com/topic/redshift
http://zebu.uoregon.edu/~soper/Light/doppler.html
http://hyperphysics.phy-astr.gsu.edu...ro/redshf.html

If light is being emitted from a source at 3x10^8m/s and I travel away from that source at 1x10^8m/s, then the light will approach me at 3x10^8m/s - 1x10^8m/s = 2x10^8m/s.

[Spoo]

AngleWyrm_2 said:
These guys seem to think red shift and Doppler shift describe the same phenomenon:
http://www.answers.com/topic/redshift
http://zebu.uoregon.edu/~soper/Light/doppler.html
http://hyperphysics.phy-astr.gsu.edu...ro/redshf.html

Using "red shift" and "Doppler effect" interchangably is a common mistake. While it is true that a Doppler effect is measurable for stars in our galaxy and for nearby galaxies (the shift can be "red" or "blue"), in most cases, when an astronomer refers to "red shift" they mean the stretching of photons by the expansion of the universe. To quote your first source,
"...all distant galaxies show a red shift proportional to their distance from the earth as a result of the general expansion of the universe (see Hubble's law)..."
In other words, the Doppler effect is an example of red shift, but not all red shifts are caused by the Doppler effect.

But this is getting off topic.

If light is being emitted from a source at 3x10^8m/s and I travel away from that source at 1x10^8m/s, then the light will approach me at 3x10^8m/s - 1x10^8m/s = 2x10^8m/s.

Wrong. "The speed of light is the same for all observers, no matter what their relative speeds."

[AngleWyrm]

If light is being emitted from a source at 3x10^8m/s and I travel away from that source at 1x10^8m/s, then do you believe that it will still approach me at 3x10^8m/s? What about the guy I pass along the way; does it approach him at 3x10^8m/s also?

It seems to me that the light will reach the guy I pass before it reaches me.

[douglas]

AngleWyrm_2 said:
If light is being emitted from a source at 3x10^8m/s and I travel away from that source at 1x10^8m/s, then do you believe that it will still approach me at 3x10^8m/s? What about the guy I pass along the way; does it approach him at 3x10^8m/s also?

It seems to me that the light will reach the guy I pass before it reaches me.

The stationary observer will indeed measure that the light's velocity relative to you is only 2x10^8m/s. For you, however, time will pass more slowly. When you measure the speed of light, you might come up with the same distance covered as the stationary guy measured, but your figure for the time will be lower. As a result, your measurement of light speed relative to yourself will come out exactly the same as the stationary observer's measurement of light speed relative to himself. Actually, your measurement of the distance will be somewhat off as well, but the net effect is that no matter what your speed, any attempt to measure the speed of light in a vacuum relative to yourself will always give the same result.

[AngleWyrm]

So I'm zooming away from an pulsar, and pass a stationary witness, who observes me travelling at 1/3c and the light from the pulsar flying along at c, closing the gap between itself an myself at a rate of 2/3c (twice my speed).

On the one hand, the pulses would reach me with longer gaps between (from the stationary witness point of view), because I am racing away from them (doppler effect). Does this time compression thing say the amount of time between pulses would be the same to me as it was when I was stationary, because time has slowed down for me?

This seems to say that I cannot perceive a change in pulsar timing, no matter what my speed.