What Is Space in Physics?

  • Context: Undergrad 
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Discussion Overview

The discussion centers around the concept of space in physics, particularly in the context of general relativity and cosmology. Participants explore theoretical implications of space existing independently of matter, the nature of space-time, and the characteristics of different models of the universe, including open, closed, and flat universes.

Discussion Character

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

Main Points Raised

  • One participant questions the nature of space by proposing a scenario with two large masses moving apart and asks what exists at their initial location.
  • Another participant suggests that at the initial point, a vacuum exists and defines space as a framework for describing the universe.
  • Discussion on general relativity indicates that space-time is not merely a backdrop but can have curvature influenced by mass and energy.
  • Some participants express uncertainty about whether space exists without matter, with one suggesting that without matter, space-time is unbent.
  • There is a debate about the characteristics of open, closed, and flat universes, with differing views on whether the universe is definitively flat or if it could be otherwise.
  • One participant mentions that the concept of a closed universe implies that space loops back on itself, while an open universe expands infinitely.
  • Another participant challenges the idea that the universe is "pretty darn flat," citing literature that suggests the density of the universe has not been conclusively measured to be at critical density.
  • There is mention of non-trivial solutions in a universe without matter, specifically referencing a 'de Sitter universe'.

Areas of Agreement / Disagreement

Participants express multiple competing views regarding the nature of space, the existence of space without matter, and the characteristics of the universe. The discussion remains unresolved, with no consensus on several key points.

Contextual Notes

Limitations include the dependence on definitions of space and time, the unresolved nature of certain mathematical models, and the varying interpretations of cosmological observations.

Who May Find This Useful

This discussion may be of interest to students and enthusiasts of physics, particularly those exploring concepts in general relativity and cosmology.

  • #31
Light Bearer said:
"Space has no objective existence whatsoever in the same way that ponderable matter does.

In GR, it does.

Light Bearer said:
It is also a void through which force carriers can propagate, but it is the characteristics of the force carriers which determine the way in which they behave and interact with ponderable matter. I believe that this is the most modern view and it replaces the older concepts of space being an aether with properties of its own."

You're talking about the idea of graviton fields replacing spacetime? Certainly a modern treatment of space and gravity, though we haven't found any gravitons, nor come up with one widely accepted theory yet.
 

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