Black hole at the beginning of time

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Discussion Overview

The discussion centers on the nature of the universe at its inception, specifically addressing why the matter present at the beginning did not collapse into a black hole. Participants explore the implications of the Big Bang theory, the distribution of matter and energy, and the terminology used to describe these concepts.

Discussion Character

  • Exploratory
  • Debate/contested
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • Some participants propose that the Big Bang did not originate from a single point, but rather occurred uniformly throughout space, which may explain the absence of a black hole.
  • Others argue that the uniform distribution of matter and energy at the universe's inception did not create the necessary conditions for a gravitational collapse into a black hole.
  • A participant mentions that the term "Big Bang" may not accurately describe the early universe, suggesting that it is often misinterpreted in popular science.
  • There is a discussion about the use of comoving coordinates in general relativity and how they relate to the understanding of time in the context of the universe's history.
  • Some participants express uncertainty about the nature of time and observer dependence in cosmological models, particularly in relation to the Friedmann-Lemaître-Robertson-Walker (FLRW) model.
  • There are technical discussions regarding the properties of geodesic worldlines and the absence of a timelike Killing vector field in FLRW spacetime.

Areas of Agreement / Disagreement

Participants express differing views on the adequacy of the Big Bang description and the implications of terminology used in cosmology. There is no consensus on whether the Big Bang is a suitable term or on the specifics of time and observer definitions in cosmological models.

Contextual Notes

Participants note that the discussion involves complex concepts from general relativity and cosmology, with some assumptions and definitions remaining unresolved. The implications of isotropy and the nature of gravitational collapse are also highlighted as areas of ongoing exploration.

  • #61
PeterDonis said:
Is impossible as you state it here since, as @vanhees71 has correctly pointed out, isotropy about only one point does not imply homogeneity.
It's clear from the context that "isotropic" means isotropic at every point. That must be the default terminology in any case.
 
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  • #62
Well, it's obvious that isotropy around only one point is not enough. It's however also pretty intuitive that isotropy around all points implies homogeneity (but not the other way, i.e., homogeneity does not imply isotropy around any point). Weinberg's definitions and proofs in Gravitation and Cosmology (Chpt. 13) is also not too difficult to follow.
 
  • #63
PeterDonis said:
No global chart in any curved spacetime can be inertial.
Yes that's is true in general, in the particular case of chart described in #56 the reason behind it should be that pointed out there, I believe.
 
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