Does the expanding universe contradict relativity?

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Discussion Overview

The discussion revolves around the relationship between the expanding universe and the principles of special relativity (SR). Participants explore whether the nature of the expanding universe presents a contradiction to SR, particularly in terms of reference frames and motion.

Discussion Character

  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • Some participants question whether the expanding universe creates a contradiction with special relativity, noting that in typical scenarios, motion can be described from either frame of reference.
  • One participant suggests that in the context of the expanding universe, all other frames appear to be moving away from a chosen frame, but the observer cannot claim to be moving away from all other frames, raising concerns about the implications for SR.
  • Another participant argues that regardless of the reference frame chosen, all other frames will appear to move radially outward, indicating that there is no preferred frame and thus no contradiction with SR.
  • One participant asserts that a dynamic universe is incompatible with SR, emphasizing that SR applies to flat spacetime rather than curved spacetimes.

Areas of Agreement / Disagreement

Participants express differing views on whether the expanding universe contradicts special relativity. Some see potential contradictions, while others argue that the principles of SR remain intact across different frames.

Contextual Notes

Participants note the distinction between flat and curved spacetimes, indicating that the discussion may hinge on the definitions and assumptions regarding the nature of the universe's expansion.

rede96
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I know this is probably a stupid question but I was wondering, with two frames that are moving wrt to each other, it is valid to say that ‘A’ is moving from ‘B’ OR that ‘B’ is moving from ‘A’

However with the expanding universe, I can say that all other frames are moving away from me, but I can’t say that I moving away from all other frames.

So is that a contradiction of SR?
 
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In our expanding universe you can fix any reference frame S and determine the motion of other frames X, X', X'', ... You will always find that these frames move radially outwards w.r.t. S. Now chosing a different frame T (with its origin at a different location) and determining the motion of other frames Y, Y', Y'', ... you will again find that these frames are moving radially outwards, therefore there is no difference between S and T, no preferred frame which located "in the center".
 
rede96 said:
I know this is probably a stupid question but I was wondering, with two frames that are moving wrt to each other, it is valid to say that ‘A’ is moving from ‘B’ OR that ‘B’ is moving from ‘A’

However with the expanding universe, I can say that all other frames are moving away from me, but I can’t say that I moving away from all other frames.

So is that a contradiction of SR?

Whichever frame you choose, you will see that ALL other points in space are moving away from you.
 
rede96 said:
I know this is probably a stupid question but I was wondering, with two frames that are moving wrt to each other, it is valid to say that ‘A’ is moving from ‘B’ OR that ‘B’ is moving from ‘A’

However with the expanding universe, I can say that all other frames are moving away from me, but I can’t say that I moving away from all other frames.

So is that a contradiction of SR?
A dynamic universe is indeed not compatible with SR. But the realm of SR is flat spacetime not curved spacetimes.
 

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