Does Flat Space Exist in the Context of General Relativity?

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Discussion Overview

The discussion revolves around the existence of flat space within the framework of general relativity, exploring the implications of mass on the curvature of space-time and the philosophical underpinnings of space and time measurement.

Discussion Character

  • Exploratory, Conceptual clarification, Debate/contested

Main Points Raised

  • One participant questions the existence of flat space if mass creates space-time, suggesting that if there is nothing, there cannot be flat space.
  • Another participant references Newton's postulates and contrasts them with Einstein's experimental approach, implying that space is defined by measurement.
  • A participant asserts that flat spacetime, according to general relativity, contains nothing, noting that special relativity's flat spacetime is only an approximation in small regions.
  • One participant proposes that space-time is equivalent to mass, suggesting that the absence of mass implies the absence of space-time.
  • A later reply mentions Mach's principle, expressing skepticism about its relevance in a universe with mass and questioning the utility of discussing an empty universe.

Areas of Agreement / Disagreement

Participants express differing views on the relevance and existence of flat space in the context of mass and space-time, indicating that multiple competing perspectives remain without consensus.

Contextual Notes

Some claims depend on philosophical interpretations of space and time, and there are unresolved implications regarding the definitions of flat space and empty universes.

yuanwei
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For understand general relativity, they tell me, there have flat space, add a sun, the flat space changed to curved space, so the Earth move around. There has a question, if we admit mass, space , time is created, how could exist flat space? there have space-time and there have nothing?
 
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Newton offered his famous postulates about time and space, and they served well for hundreds of years. Einstein came along and removed the taste of philosophy from them, and appealed to experiment. "Time is what a clock measures." So I suppose the answer to your question is: "Space is what a ruler measures."
 
Yes, according to general relativity, spacetime that is flat everywhere has nothing in it. Special relativity in which spacetime is flat and has stuff in it only holds as an approximation over small regions of spacetime.
 
I think space-time is same with mass, so there have nothing means there have no space-time.
 
That would be http://en.wikipedia.org/wiki/Mach_principle" in Bondi's classification. Personally I think it is a fairly useless principle, as are many of the Mach Principles. In this universe there is mass so any discussion of an empty universe is irrelevant to this one.
 
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