Mark_Eichenlaub comments on Frugality and working from finite data - Less Wrong

27 Post author: Snowyowl 03 September 2010 09:37AM

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Comment author: Mark_Eichenlaub 04 September 2010 06:31:15PM 1 point [-]

But a photon emitted by object A would not be going fast enough to outrace the >expansion of space, and would never reach B. So B would never obtain any >information about A if they are flying apart faster than light.

I think that was the point, but since the expansion is accelerating this was not always the case.

A and B are retreating faster than light now (in our reference frame), so the light they are emitting now will not reach each other.

However, the A and B are far apart, say 5 billion light years. 5 billion years ago A and B were receding more slowly - perhaps half the speed of light, so the light emitted 5 billion years ago from A is now reaching B. Hence, B currently sees light from A.

Five billion years in the future this will not be the case. Sometime in the next 5 billion years B will observe A to redshift all the way to zero and wink out.

Comment author: Snowyowl 04 September 2010 11:54:57PM 1 point [-]

Agreed. Thanks.