Does space expansion theory obey relativity laws?

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Discussion Overview

The discussion centers around the concept of space expansion in the context of cosmology and its relationship with the laws of relativity. Participants explore whether the idea of space expanding to explain redshift effects aligns with general and special relativity, and they express varying interpretations of what space expansion entails.

Discussion Character

  • Debate/contested
  • Conceptual clarification
  • Technical explanation

Main Points Raised

  • One participant questions if space expansion contradicts relativistic principles, seeking clarification on the concept.
  • Another participant asserts that the term "space expansion" is consistent with general relativity and, without a cosmological constant, also aligns with special relativity.
  • Some participants argue against the notion of space "propelling" matter, suggesting instead that matter remains stationary while space itself expands.
  • A participant expresses confusion about the implications of space growing, noting that it results in relative motion between objects without a causal force, and proposes that this motion might be influenced by external gravitational forces.
  • Concerns are raised about the constancy of spacetime, with a participant mentioning that gravity distorts spacetime, suggesting that it cannot be considered constant.

Areas of Agreement / Disagreement

Participants exhibit disagreement regarding the terminology and conceptual understanding of space expansion, with no consensus reached on whether it aligns with the principles of relativity.

Contextual Notes

Some limitations in the discussion include differing interpretations of the term "space expansion," the role of gravity in spacetime, and the implications of relative motion between objects as space expands.

azzkika
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Does space expansion theory obey relativity laws??

I've been wondering about the idea of space expansion that's been used to explain red shift effects in most of our universe, which forgive me if i am wrong is nothing(space) propelling matter.

Please could someone tell me if i am misunderstanding space expansion and give a correct explanation of it for me.

Or if i have understood it correctly, surely it goes against relativistic principals?
 
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What you call space expansion, which I find an inaccurate and confusing phrase, is in full agreement with general relativity. And in the absence of a cosmological constant it is also locally in agreement with special relativity.
 


I think the really inaccurate phrase is "propelling". Azzikika, you shouldn't think of it as space moving matter. It's more accurate to think of it as matter staying in the same place (at approximately constant spatial coordinates) while space grows. I'm not sure why Jennifer doesn't like the term "space expansion", but I'm guessing that it has something to do with the fact that GR is a theory about spacetime, not space, and spacetime doesn't change. It just "is".
 


Fredrik said:
I think the really inaccurate phrase is "propelling". Azzikika, you shouldn't think of it as space moving matter. It's more accurate to think of it as matter staying in the same place (at approximately constant spatial coordinates) while space grows. I'm not sure why Jennifer doesn't like the term "space expansion", but I'm guessing that it has something to do with the fact that GR is a theory about spacetime, not space, and spacetime doesn't change. It just "is".


but if 'space grows', as it were, then 2 separate objects are moving relative to each other in this process, with no causal force. i personally cannot get my head around this concept.

i probably need to learn a lot more, but for now i choose to believe the motion is caused by a substantive force, probably massive external gravity beyond our current horizons. i think space expansion is a result, not a cause of whatever is occurring in our universe.

i also thought that gravity distorts space time, thus it isn't constant.
 
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