Spacetime same size during Big Bang up to now?

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Discussion Overview

The discussion revolves around the nature of spacetime during the Big Bang and its relationship to the current state of the universe. Participants explore concepts related to the expansion of the universe, the meaning of spacetime and its "size," and the implications of an infinite versus finite universe.

Discussion Character

  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • One participant suggests that spacetime during the Big Bang is the same size as it is now, despite the metric expanding, and questions why spacetime should get bigger.
  • Another participant argues that it is unknown whether the universe is finite or infinite, positing that if it is infinite, it was infinite during the Big Bang and remains so, while still expanding.
  • A third participant challenges the concept of spacetime having a "size," stating that in standard cosmological models, space has a "scale factor" that increases, but this does not imply a meaningful size for spacetime.
  • A later reply indicates that without a valid reference, the discussion lacks a foundation for meaningful engagement.

Areas of Agreement / Disagreement

Participants express differing views on the nature of spacetime and its expansion, with no consensus reached on the validity of the initial claim regarding spacetime size.

Contextual Notes

Limitations include the ambiguity surrounding the definitions of spacetime and size, as well as the unresolved question of whether the universe is finite or infinite.

mieral
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I read somewhere here (but couldn't find the exact message) where it was mentioned the size of spacetime during the Big Bang is the same size as it is now. But the metric expands. However semantically even though the metric expands, spacetime doesn't expand. But spacetime should get bigger now, no? why specifically?
 
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First, that's not known because it's not known whether the universe is finite or infinite. If the universe is infinite then yes, it was infinite then and it is infinite now AND it is expanding. As for how it can expand it if it infinite, Google "Hilbert Hotel"
 
mieral said:
I read somewhere here (but couldn't find the exact message)

Sorry, this is not a valid reference. Without a valid reference we can't have a meaningful discussion.

As far as spacetime having a "size", that's not a meaningful concept. In the standard cosmological models, space (not spacetime) has a "scale factor" that increases with the expansion of the universe. But that's not a "size" for spacetime in any useful sense.
 
In the absence of a valid reference in the OP, this thread is closed.
 

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