Does an infinite universe contradict a Big Bang origin?

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Discussion Overview

The discussion revolves around the relationship between the concept of an infinite universe and the Big Bang theory. Participants explore whether the Big Bang, which is often described as originating from a finite volume, can coexist with the idea of an infinite universe. The conversation touches on theoretical implications, observational limitations, and the nature of spacetime.

Discussion Character

  • Debate/contested
  • Conceptual clarification
  • Exploratory

Main Points Raised

  • Some participants suggest that if the universe is currently infinite, it must have always been infinite, albeit denser in the past.
  • Others argue that the Big Bang theory applies to the entire universe, which may be finite or infinite, but the observable universe is a finite portion of it.
  • A participant questions how the Big Bang can apply to an infinite volume if it is described as having a finite volume, proposing a model where properties of spacetime emerged everywhere simultaneously.
  • There is a discussion about the observable universe being limited by the speed of light, leading to questions about the uniformity of the universe and the implications of the cosmological principle.
  • Some participants express confusion regarding the concept of "the universe before the Big Bang," with assertions that such a state does not exist in the discussed models.
  • A mathematical analogy involving the infinite real number line is presented to illustrate the relationship between infinite volume and density of matter over time.
  • Concerns are raised about the ability to explain these concepts clearly, indicating a perceived complexity in the discussion.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the relationship between an infinite universe and the Big Bang. Multiple competing views are presented, with some asserting that the Big Bang applies universally while others question the implications of an infinite universe on the Big Bang model.

Contextual Notes

Limitations in understanding arise from the complexity of the concepts discussed, including the nature of spacetime, the definition of the observable universe, and the implications of different cosmological models. Some assumptions about the initial conditions of the universe and the nature of the Big Bang remain unresolved.

  • #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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