Is Spacetime a Real Physical Entity or Merely a Conceptual Framework in Physics?

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Discussion Overview

The discussion centers around the nature of spacetime, questioning whether it is a real physical entity or merely a conceptual framework within physics. Participants explore its implications in the context of general relativity, measurement, and the physical world.

Discussion Character

  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • Some participants question the characterization of spacetime as a "real world thing," suggesting that the term itself may be vague and requires clearer definition.
  • Others propose that spacetime is a geometric framework that describes the relationships between time and space, as utilized in general relativity.
  • There are claims that spacetime can be viewed as a curved medium or "fabric" that guides the movements of masses, though this characterization is challenged by some participants.
  • One participant emphasizes that the physics of spacetime is encapsulated in the Einstein field equations, which describe how spacetime interacts with mass and energy.
  • Another viewpoint suggests that the understanding of spacetime relies on measurement, with time being defined by clocks and distance by rulers, leading to a discussion on the nature of physical reality.

Areas of Agreement / Disagreement

Participants express differing views on whether spacetime is a tangible entity or a conceptual tool, indicating that multiple competing perspectives remain without consensus.

Contextual Notes

Participants highlight the need for precise definitions when discussing concepts like "real world thing," and the discussion reflects a range of interpretations regarding the nature of spacetime and its implications in physics.

Michael Ray Mooney
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Given that physics is the study of the physical world, what exactly is spacetime if it is an actual "real world thing", a curved medium or "fabric" guiding the movements of masses, and what is the physics of how this guidance works. As far as I know, space is a vacuum (where not occupied of course) and time is a human concept designating the duration of any specified movement, like Earth's periods of rotationand orbit. Thanks.
 
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Michael Ray Mooney said:
Given that physics is the study of the physical world, what exactly is spacetime if it is an actual "real world thing", a curved medium or "fabric" guiding the movements of masses, and what is the physics of how this guidance works. As far as I know, space is a vacuum (where not occupied of course) and time is a human concept designating the duration of any specified movement, like Earth's periods of rotationand orbit. Thanks.
Modern physics (since Newton) is generally about finding a mathematical model that can be used to predict the outcome of experiments. Spacetime is part of the mathematics of relativity and maps to the experimental concept that events take place at a time and a spatial location.

If you want to study Relativity, you could start with Morin's book, the first chapter of which is available free online:

https://scholar.harvard.edu/files/david-morin/files/cmchap11.pdf

This includes an introduction to the concept of spacetime.
 
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Michael Ray Mooney said:
what exactly is spacetime if it is an actual "real world thing"
Spacetime is the geometry of the “real world”.

Michael Ray Mooney said:
a curved medium or "fabric"
Why should geometry be a fabric or medium?

Michael Ray Mooney said:
what is the physics of how this guidance works
The physics of how spacetime works is described by the Einstein field equations.
 
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Michael Ray Mooney said:
Given that physics is the study of the physical world, what exactly is spacetime if it is an actual "real world thing", a curved medium or "fabric" guiding the movements of masses, and what is the physics of how this guidance works. As far as I know, space is a vacuum (where not occupied of course) and time is a human concept designating the duration of any specified movement, like Earth's periods of rotationand orbit. Thanks.
We won’t have a productive discussion unless we can say what a “real world thing” is, and the fact that we are compelled to use scare-quotes around the term is a strong hint that we aren’t there.

When we’re studying the physical world we have to start with things that we can (at least in principle) measure. Thus we start with Einstein: time is what a clock measures and distance is what a ruler measures. Observation finds relationships between these that are most effectively described using the methods of differential geometry applied to a pseudo-Riemannian manifold; we have to call that manifold something and “spacetime” is the name that has stuck. Does that make it a “real physical thing”? Who knows? How could we tell? Would the answer affect any measurement or experimental result?

Please take a moment to review this forum’s mission statement. We will gladly work with you if are here to advance your understanding of general relativity and/or to help others do so, but an uncrisp discussion of vaguely defined terms is not what we’re here for.

This thread is closed.
 

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