Spacetime doesn't really exist does it?

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    Spacetime
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Discussion Overview

The discussion centers around the nature of spacetime, particularly whether it exists independently or is merely a mathematical model used to describe physical phenomena. Participants explore the implications of general relativity (GR) and the conceptual understanding of spacetime in relation to mass and energy.

Discussion Character

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

Main Points Raised

  • Some participants propose that spacetime is a mathematical model useful for predicting interactions of mass-energy, lacking independent existence.
  • Others argue that spacetime must exist, as it is integral to the Big Bang and the expansion of the universe, suggesting it has a tangible nature.
  • A participant mentions gravitational waves as evidence that spacetime may have independent existence, contingent on their detection.
  • There is a reference to the "hole argument," which suggests that geometries are equivalence classes of manifolds and metrics, indicating a relational view of spacetime.
  • Some participants express skepticism about the ability to experimentally determine concepts like diffeomorphism invariance, raising questions about the empirical basis of spacetime theories.
  • One participant reflects on the philosophical implications, suggesting that if spacetime and wavefunctions are merely equations, it raises the possibility of a simulated universe or holographic projection.

Areas of Agreement / Disagreement

Participants express a range of views, with no consensus on whether spacetime exists independently or is merely a mathematical construct. The discussion remains unresolved, with competing perspectives on the nature of spacetime and its implications.

Contextual Notes

The discussion touches on complex concepts such as general covariance and the relationship between geometry and physical reality, with participants acknowledging the limitations of current experimental evidence regarding these ideas.

  • #31
Tanelorn said:
Personlly I dislike mathematical description of anything
Then you should probably avoid physics.
 
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  • #32
Tanelorn said:
what it really is

And how do we decide whether a certain description of something is what it "really is?"
 
  • #33
Well in reply, I would suggest that many of the concepts that we discuss in these posts are communicated mainly verbally and with charts and pictures and as a result we communicate a deeper understanding of all aspects of an issue, especially the fundermental concepts and where the emphasis or heart of the matter lies. Granted the Mathematics and equations are a tool for high precision. For those who are fully conversant with the specific mathematics it is also a form of language, but I don't believe that these ideas can only be communicated mathematically. In fact I frequently witness people having to resort to using words to explain the true meaning and intent of each mathematical statement. When was the last time that the conclusion of a paper was written in mathematics? Anyway I think this is off topic.
 
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  • #34
Phrak said:
Of course spacetime doesn't exist. I see this over and over again, ad nauseum. However, no explanations of this logical fallacy seems to penetrate the well educated mind.

DaleSpam said:
Please cite one experimental or cosmological observation that supports this statement.

It's a grammatical error.
 
  • #35
Tanelorn said:
Well in reply, I would suggest that many of the concepts that we discuss in these posts are communicated mainly verbally and with charts and pictures and as a result we communicate a deeper understanding of all aspects of an issue, especially the fundermental concepts and where the emphasis or heart of the matter lies. Granted the Mathematics and equations are a tool for high precision. For those who are fully conversant with the specific mathematics it is also a form of language, but I don't believe that these ideas can only be communicated mathematically. In fact I frequently witness people having to resort to using words to explain the true meaning and intent of each mathematical statement. When was the last time that the conclusion of a paper was written in mathematics? Anyway I think this is off topic.

I disagree. Though I mostly use words, handwaving etc. natural language are parables, math the 'reality' when it comes to physics.

So, another 'reality debate'. In physics, which is 'real' the words or the math? I guess my view is physics about constructing mathematical models that, combined with correspondence rules between mathematical objects and measurements, successfully predict observations.
 
  • #36
Phrak said:
It's a grammatical error.
"Spacetime" is a noun, "exist" is a verb, so "Spacetime exists." is not a grammatical error. You will have to do better than that. Again, please substantiate your claim with any observational evidence which supports it.
 
  • #37
DaleSpam said:
"Spacetime" is a noun, "exist" is a verb, so "Spacetime exists." is not a grammatical error. You will have to do better than that. Again, please substantiate your claim with any observational evidence which supports it.

Spacetime consists of the past, present and future. The future will exist. The present exists. The past existed. Would you provide experimental evidence that the past exists?
 
  • #38
PAllen, perhaps consider a mathemetical simulation which models the weather. Is it really providing us with a full or complete understanding of the fundermental Physics of the weather? Or is it just using a bunch of equations that give us most of the time numbers close enough to the real world? Reminds me a little of the Turing test; if the computer responds with the right answers did it truly understand anything, is it truly alive? I don't believe so, and I suspect it never will with the current approach.

I think the method of understanding inside your head is the most important thing. Even with mathemetics I convert to pictures inside my head to see dependencies etc.
 
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  • #39
I doubt that the past still exists, or at least exists in our present. If time was like space then we could walk across the road to yesterday and enjoy that beer all over again.
 
  • #40
Tanelorn said:
I doubt that the past still exists, or at least exists in our present. If time was like space then we could walk across the road to yesterday and enjoy that beer all over again.

Now you're getting into personal beliefs, not science. Suppose yesterday exists but no known process allows you to 'get there'. How do you distinguish this from 'not existing'? Certainly, the image from a billion years ago exists - that's what astronomers see. There is no plausible process to get into the center of neutron star and out, so I suppose you might argue that a neutron star has no center?
 
  • #41
Tanelorn said:
PAllen, perhaps consider a mathemetical simulation which models the weather. Is it really providing us with a full or complete understanding of the fundermental Physics of the weather? Or is it just using a bunch of equations that give us most of the time numbers close enough to the real world? Reminds me a little of the Turing test; if the computer responds with the right answers did it truly understand anything, is it truly alive? I don't believe so, and I suspect it never will with the current approach.

I think the method of understanding inside your head is the most important thing. Even with mathemetics I convert to pictures inside my head to see dependencies etc.

Your head and mine can both do (I hope) mathematics. Our respective mathematics is more likely to coincide than natural language pictures.

As for the turing test, I have less than that to go on to believe that you are a real being with intelligence.

As for your weather example, all physics is approximation. Until we go well over (e.g.) 500 years without needing to modify any physics, we can assume that 'reality', whatever it is, is only aproximately modeled by our current physical theories, whether expressed with mathematics or parables.
 
  • #42
Phrak said:
Spacetime consists of the past, present and future. The future will exist. The present exists. The past existed. Would you provide experimental evidence that the past exists?
So you are concerned about the conjugation of the verb "to exist"? :rolleyes: I have to say that this is one of the weakest arguments I have ever seen on the subject. Many natural languages don't even have verb tenses. In any case, even a statement like "the past exists" is not grammatically incorrect, and I assume that resorting to this argument is a tacit admission that you have no supporting observations.

Regarding evidence, all of the accumulated evidence for SR and GR can be interpreted as evidence that the past exists in the sense of being part of spacetime. There is plenty of evidence that spacetime existed over the last century during the collection of that data. Absent any new evidence to the contrary, we will make the usual scientific assumption that it continues to exist and that it will continue to exist.
 
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  • #43
Tanelorn said:
PAllen, perhaps consider a mathemetical simulation which models the weather. Is it really providing us with a full or complete understanding of the fundermental Physics of the weather?
If you had a mathematical simulation which would accurately model every possible feature of the weather, then in what conceivable way could you say that our understanding of the weather is not "full or complete".
 
  • #44
jtbell said:
And how do we decide whether a certain description of something is what it "really is?"

Tanelorn said:
Well in reply, I would suggest that many of the concepts that we discuss in these posts are communicated mainly verbally and with charts and pictures and as a result we communicate a deeper understanding of all aspects of an issue, especially the fundermental concepts and where the emphasis or heart of the matter lies. Granted the Mathematics and equations are a tool for high precision. For those who are fully conversant with the specific mathematics it is also a form of language, but I don't believe that these ideas can only be communicated mathematically. In fact I frequently witness people having to resort to using words to explain the true meaning and intent of each mathematical statement. When was the last time that the conclusion of a paper was written in mathematics? Anyway I think this is off topic.

Indeed, I think this is off-topic for a physics forum. Maybe it is on-topic for a metaphysics or philosophy forum.
 

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