The redshift from recession or expansion

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    Expansion Redshift
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Discussion Overview

The discussion centers on the nature of cosmic redshift, specifically whether it arises from cosmic expansion or the recession of celestial objects. Participants explore the implications of abandoning the Copernican Principle and the mathematical frameworks used to describe these phenomena.

Discussion Character

  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • Some participants argue that the conclusion that cosmic redshift is due to expansion relies on the Copernican Principle, which posits no favored position in the universe.
  • Others suggest that if one abandons the Copernican Principle, it may be possible to interpret the redshift as resulting from recession instead of expansion.
  • It is noted that the choice of coordinate system can affect the description of cosmic redshift, with some systems making the expansion appear as recession.
  • A participant acknowledges understanding this perspective after a clarification from another member.

Areas of Agreement / Disagreement

Participants express differing views on the interpretation of cosmic redshift, with no consensus reached on whether it is fundamentally due to expansion or recession.

Contextual Notes

The discussion highlights the dependence on the choice of coordinate systems and the assumptions underlying the interpretations of cosmic phenomena.

micomaco86572
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Almost all textbooks tell us that the cosmic redshift is arised from the cosmic expansion rather than the recession of the celestial objects. I think the conclusion is basically based on the assumption of Copernican Principle, i.e. there is no favored position in the whole universe. But what if we give up this assumption? Can we still lead to the conclusion that the redshift is caused by expansion?

thx.
 
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micomaco86572 said:
Almost all textbooks tell us that the cosmic redshift is arised from the cosmic expansion rather than the recession of the celestial objects. I think the conclusion is basically based on the assumption of Copernican Principle, i.e. there is no favored position in the whole universe. But what if we give up this assumption? Can we still lead to the conclusion that the redshift is caused by expansion?

thx.
It's largely just a matter of the description of reality rather than actually being a physical discrepancy. If you so choose, you can select a different coordinate system where the expansion appears to be primarily due to the recession instead of the expansion. The math is just easier in the coordinate system where the expansion is the cause of the redshift.
 
Chalnoth said:
It's largely just a matter of the description of reality rather than actually being a physical discrepancy. If you so choose, you can select a different coordinate system where the expansion appears to be primarily due to the recession instead of the expansion. The math is just easier in the coordinate system where the expansion is the cause of the redshift.

Thank u, Chalnoth. I understand it, now.
 

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