Time & Space Expansion: What Does It Mean?

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Discussion Overview

The discussion revolves around the concept of the expansion of space and its implications for time, particularly in the context of spacetime as described by Einstein's theories. Participants explore the relationship between space and time, questioning the conventional understanding of space expansion and its effects on time.

Discussion Character

  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • One participant asserts that if space is expanding, then timespace must also be expanding, questioning the meaning of time expansion.
  • Another participant argues that the statement "space is expanding" relies on a specific separation of spacetime into space and time, suggesting that other separations may not support the idea of space expansion.
  • A third participant expresses confusion about the concept of expanding space and its compatibility with spacetime, referencing a lecture on dark energy that raises questions about the validity of general relativity (GR) and gravity.
  • A later reply emphasizes that the chosen division of spacetime into space and time does not necessarily imply that time itself is expanding, despite the convention of describing space as expanding over time.

Areas of Agreement / Disagreement

Participants do not reach a consensus; multiple competing views regarding the relationship between space and time remain, with ongoing debate about the implications of spacetime separation.

Contextual Notes

The discussion highlights limitations in the conventional understanding of spacetime separation and the assumptions underlying the expansion of space. There are unresolved questions about the implications of dark energy and the correctness of general relativity.

earamsey
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Physicists say that space is expanding. Well, Einstein says that space and time can not be separated so I can assume that timespace is expanding. What does it mean for time to expand?
 
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"Space is expanding" depends on a particular separation of spacetime into space and time - quite contrary to the spirit of spacetime - spacetime can be separated into space and time many other ways, and in some of those ways, space is not expanding. Anyway, the particular separation of spacetime into space and time used in "space is expanding" is convenient and conventional.
 
pardon my ignorance, but what is the answer? I asked question because I keep hearing theory of expanding space and some how it start to not sound correct when one thinks about spacetime. I guess I should not worry about this since I saw a lecture about dark energy that questions the correctness of GR and gravity anyways so maybe I have to wait and see what is the final consensus about it.
 
First divide spacetime into space and time - there are many ways to do it - but by convention we choose a way in which space is expanding with time. Since we already chose a division of spacetime into space and time, that space is expanding does not imply that time is expanding.
 

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