Can Spacetime Truly Have an Outside?

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Discussion Overview

The discussion revolves around the question of whether spacetime can have an "outside." Participants explore this concept in the context of theoretical physics, particularly General Relativity and possibly other theories like Brane theory. The inquiry includes considerations of experimental implications and the nature of spacetime geometry.

Discussion Character

  • Debate/contested
  • Conceptual clarification
  • Experimental/applied

Main Points Raised

  • Some participants question the existence of an "outside" to spacetime, suggesting that General Relativity does not support this notion as it describes an intrinsic geometry.
  • One participant asks for specific references to the concept of an "outside" of spacetime, indicating a need for more substantial sources than general mentions.
  • Another participant inquires about potential physical experiments that could measure an "outside" of spacetime, emphasizing the importance of testability in scientific discussions.
  • There is mention of embedding theorems and pseudo-Riemannian geometry as relevant mathematical frameworks, although their implications for the concept of an "outside" are not fully explored.
  • One participant suggests that discussions about entanglement may relate to the idea of an "outside" of spacetime, though this connection remains vague.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the existence of an "outside" to spacetime. Multiple competing views are presented, particularly regarding the implications of General Relativity and the nature of theoretical discussions versus experimental inquiries.

Contextual Notes

The discussion highlights the ambiguity surrounding the concept of an "outside" of spacetime and the challenges in framing it within testable scientific theories. There are unresolved questions about the definitions and assumptions underlying the concept.

fanieh
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Can spacetime have an outside? I sometimes read stuff where it is mentioned. Is it true?
 
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fanieh said:
Can spacetime have an outside? I sometimes read stuff where it is mentioned. Is it true?
Please provide a specific reference. "Stuff where it is mentioned" is not enough to go on.

You may wish to read about embedding theorems and pseudo-Riemannian geometry.
 
fanieh said:
Can spacetime have an outside? I sometimes read stuff where it is mentioned.

Where did you read such "stuff"?

Zz.
 
What physical experiment would you do to measure an "outside" of space-time? Do any of the things you "sometimes read" describe such an experiment that could be carried out to answer the question - i.e. an experimental result that gives one answer if there is an 'outside' and a different result if there is not? Lastly, are such discussions that you "sometimes read" in the context of General Relativity, or in some other theory (for example, some sort of Brane theory).

In the context of General Relativity, there's no reason to assume that there is anything "outside" space-time, in fact the geometry is carefully set up to be an intrinsic geometry. Many popularizations use an embedding diagram to illustrate the concept of curvature, but this is more or less a visual aid, it's not part of the theory itself.

I don't necessarily have a good answer outside the context of GR - the question though is rather broad, if you think you have some specific theory that requires an "outside of space-time", it would probably be a good idea to identify that particular theory more closely, and then find the appropriate forum to talk about that question. It's always worth asking the question if you're thinking about something that is testable by physical experiment - or if you are asking about something that can never be tested. Sometimes the tests may not be obvious, but if you realize you're asking about something that can never be experimentally decided, you're asking yourself a philosophical question and not a scientific one.
 
ZapperZ said:
Where did you read such "stuff"?

Zz.

I forgot.. but maybe something about entanglement using traffic outside spacetime..
 
With that this thread is closed and will remain closed.
 

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