Infinite Universe: What does it mean?

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SUMMARY

The discussion centers on the implications of an infinite universe, specifically under the assumption of an "open" universe with a density less than the critical density. Participants reference standard cosmological models, including the definitions of open, flat, and closed universes as per Carroll and NASA. Key conclusions include that an open universe suggests infinite spatial volume, and while matter/energy may extend beyond the observable universe, the exact nature of that extension remains uncertain. The consensus emphasizes that the observable universe can expand indefinitely without necessitating a center or finite boundaries.

PREREQUISITES
  • Understanding of standard cosmological models (open, flat, closed).
  • Familiarity with critical density and its implications for universe geometry.
  • Knowledge of the observable universe and its limitations.
  • Basic grasp of cosmological principles such as homogeneity and isotropy.
NEXT STEPS
  • Research the implications of an open universe on cosmic expansion.
  • Study the FLRW metric and its role in understanding universe geometry.
  • Explore the concept of non-trivial topology in cosmology.
  • Investigate the relationship between observable and unobservable regions of the universe.
USEFUL FOR

Astronomers, cosmologists, physics students, and anyone interested in the fundamental nature of the universe and its expansion dynamics.

  • #31
marcus said:
... The Hubble radius is just a handle on the speed of expansion of distances. Expansion speed is proportional ...

Can I just confirm, if something sent a signal today, & it was greater than the Hubble radius from us, could it reach us?
 
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  • #32
Lino said:
Can I just confirm, if something sent a signal today, & it was greater than the Hubble radius from us, could it reach us?

Yes! and there is a nice reason! The Hubble radius is reciprocal to the percentage rate of distance growth, so as the growth rate declines the Hubble radius increases.

It is not a physical distance between definite things, so it is to subject to cosmological metric expansion. But it can increase.

So it can REACH OUT AND GATHER IN light which may be struggling to reach us but being carried slowly back by the expansion of distance.

If the light starts out a little bit outside the Hubble radius TODAY, and at first is being swept slowly back, it still may be inside TOMORROW'S Hubble radius.

Once a flash of light is safely within the Hubble radius it is home free, it will eventually make it.
 
  • #33
marcus said:
Yes! and there is a nice reason! ...
Wow! Thank you ... it reads correctly & sense-aguilie (?), but I need to think about it :)

Thanks Marcus.
 

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