Doubt about the relativity of simultaneity

[jartsa]

Since from the reference frame of observer B, radio telescope 1 is turned on first and then radio telescope 2, observer B expects that the measurement of the mean temperature of the cosmic microwave background of radio telescope 1 is higher than that of radio telescope 2. Without However this does not happen, both measures are identical.

So according to B the other beam travels for a very very very very long time, and then the beam is in a universe that is not very very old.

Is this perhaps a correct rephrasing of the problem?(Let's say B travels extremely fast relative to the telescopes, and also let's say the telescopes are not so far apart that expansion of universe matters.)

 

[PeterDonis]

the other beam

What "other beam" are you talking about?

The OP's scenario doesn't include any "beams". The radio telescopes are measuring the CMB at their location; they're not sending or receiving "beams".

 

[jartsa]

What "other beam" are you talking about?

The OP's scenario doesn't include any "beams". The radio telescopes are measuring the CMB at their location; they're not sending or receiving "beams".

OP said: "Right in the center is a light source, with no relative motion relative to radio telescopes. The light source sends a beam of light to each radio telescope, hits the switch, turns them on."

 

[PeterDonis]

OP said: "Right in the center is a light source, with no relative motion relative to radio telescopes. The light source sends a beam of light to each radio telescope, hits the switch, turns them on."

Ah, ok. But these "beams" have nothing to do with the actual measurements the radio telescopes are making. They're just a way of specifying in what frame the measurements made by the radio telescopes are simultaneous (the A frame, in which both telescopes are at rest).

Everyone appears to agree that in the B frame, the measurements are not simultaneous; explaining how that comes about is not the issue. The issue is how an observer at rest in the B frame explains the fact that both measurements still give the same result for the CMB temperature, which means that the "age of the universe" under the usual definition of that term (which is not the same as "coordinate time elapsed in the B frame") is the same at both measurements, even though they are not simultaneous in the B frame.