Why does redshift indicate that space-time is expanding

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Discussion Overview

The discussion revolves around the interpretation of redshift in the context of cosmology, specifically whether redshift indicates that space-time is expanding or if it is simply a result of galaxies moving away from each other. The scope includes conceptual understanding and historical context related to Hubble's observations.

Discussion Character

  • Conceptual clarification
  • Debate/contested
  • Historical

Main Points Raised

  • Some participants suggest that the observation of redshift correlates with the distance of galaxies, implying that space-time itself is expanding rather than galaxies merely moving away.
  • Others argue that the interpretation of redshift as an indicator of expanding space-time requires the absence of an edge to the universe and a uniform distribution of galaxies, which they claim is not observed.
  • One participant questions the necessity of observing certain conditions (like the universe's edge) to explain redshift as a result of galaxies flying away, expressing a desire to understand the historical context of Hubble's conclusions.
  • Another participant mentions that both cosmological redshift and Doppler redshift can yield similar results on small scales, but on larger scales, Doppler redshift may provide incorrect values.

Areas of Agreement / Disagreement

Participants express differing views on the interpretation of redshift, with no consensus reached on whether it is primarily indicative of expanding space-time or simply the motion of galaxies. The discussion remains unresolved.

Contextual Notes

There are references to historical observations and interpretations that may not be fully understood by all participants, indicating a potential gap in knowledge regarding the evolution of cosmological theories.

LSulayman
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Since nobody answered my last question I''l try it this way:

Why does redshift indicate that space-time is expanding and not that galaxy's are just flying away from each other?
 
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Its the fact that the further away it is, the faster a galaxy appears to be travelling, and this points towards space-time itself expanding, rather than the galaxies moving away and nothing else.
 


LSulayman said:
Since nobody answered my last question I''l try it this way:

Why does redshift indicate that space-time is expanding and not that galaxy's are just flying away from each other?

What you suggest requires that the universe have an edge and a non uniform distribution of galaxies and neither are observed.
 


russ_watters said:
What you suggest requires that the universe have an edge and no such edge is observed.

How come? Maybe this is something we know now but when Hubble presented his observations of redshift people did not know. (I think)
 


What does that have to do with anything? (...and see my late edit...)
 


russ_watters said:
What you suggest requires that the universe have an edge and a non uniform distribution of galaxies and neither are observed.

Why do you have to observe these things in order to explain that redshift is not from expanding space-time but from galaxy's flying away from each other?
Or do I need heavy phisics to understand (I'm not a physisist or stronomer so)?

I'm trying to understand what made people (Hubble) back then think that the redshift was because of expanding space-time, that's why I asked.
 


Btw, you'll need to be more patient - this place isn't continuously staffed and activity can be highly variable.
 


LSulayman said:
Why do you have to observe these things in order to explain that redshift is not from expanding space-time but from galaxy's flying away from each other?
Or do I need heavy phisics to understand (I'm not a physisist or stronomer so)?

I'm trying to understand what made people (Hubble) back then think that the redshift was because of expanding space-time, that's why I asked.

LS, you should search this site for threads adressing cosmological redshift vs doppler redshift. On small enough scales they can both give same results, on large scales doppler redhift gives wrong numbers, although there are ways of treating cosmological as doppler, it only unnecessary complicates things.
 

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