Does an infinite universe contradict a Big Bang origin?

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SUMMARY

The discussion centers on the relationship between the Big Bang and the concept of an infinite universe. Participants clarify that if the universe is infinite now, it has always been infinite, albeit denser in the past. The observable universe, which is finite, is merely a small portion of the entire universe, which expanded uniformly. The Big Bang is described as a phenomenon that occurred everywhere in the universe, not limited to the observable region, and models like eternal inflation suggest that the universe may extend infinitely into the past without an initial singularity.

PREREQUISITES
  • Understanding of the Big Bang Theory and its implications.
  • Familiarity with the concept of the observable universe versus the entire universe.
  • Basic knowledge of cosmological models, including eternal inflation.
  • Grasp of general relativity and its role in cosmology.
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  • Study the implications of the cosmological principle in modern cosmology.
  • Explore the concept of eternal inflation and its significance in the universe's structure.
  • Investigate the mathematical models of the Big Bang and their observational predictions.
  • Learn about the observable universe's limitations and how they affect cosmological observations.
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Astronomers, cosmologists, physics students, and anyone interested in understanding the complexities of the universe's origin and structure.

  • #61
jackjack2025 said:
"Everyone else does"? You sure?
yes
 
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  • #62
jackjack2025 said:
This does not work in an infinite way.
yes, it does. You clearly haven't gotten your head around the concept of infinity and you apparently think it acts the same as a finite number. It doesn't.
 
  • #63
jackjack2025 said:
"Hilbert Hotel Expansion
@Ibix and the rest of us are quite comfortable with Cantor and transfinite cardinalities.

However, cardinality has nothing to do with metric expansion. No one is trying to say that the the cardinality of the set of stars now is less than the cardinality of the set of stars a moment from now.

We are not talking about counting rooms at all. We are talking about measuring the length of the carpet between rooms. The guests go to the beach for the day with 10 meters of carpet between adjacent rooms (for instance) and arrive back at the hotel to find 11 meters of carpet between adjacent rooms.

The guests do not have to run a measuring tape from one end of the hall to the other to observe such a change. They only have to measure one pair of rooms. Or enough to get a statistically significant sample.

In practice, the measurements that are made are not done with measuring tapes, of course. We use spectra, luminosity, time delays and various other hints to put together a coherent model for the shape of the universe and the distribution of stars, galaxies and clusters within it. The shape has a feature that is commonly referred to as metric expansion.

If this "metric expansion" does not fit with the meaning that you intuitively expect for "expanding universe" then that is not a problem with the idea of "metric expansion". The problem is with your non-standard interpretation of the meaning of the phrase.
 
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  • #64
jbriggs444 said:
If this "metric expansion" does not fit with the meaning that you intuitively expect for "expanding universe" then that is NOT a problem with the idea of "metric expansion". The problem is with your non-standard interpretation of the meaning of the phrase.
I think the word I added in red is what you had in mind.

EDIT: I see you beat me to it.
 
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  • #65
jackjack2025 said:
From the first stake to the last is the same length
No, it isn't, because in a spatially infinite universe there is no "last stake". You simply can't apply this intuitive picture to the case under discussion.
 

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