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Is Spacetime Real?

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Re: Is Spacetime Real?

#21

Post by sailingparrot »

thisiscorrect wrote: post #5

“What exactly is spacetime? Is it a real thing like an atom, or just a mathematical construct that is used to describe how mass 'generates' gravity?” This is a false dichotomy. Atoms too are "just" a mathematical construct used to describe how certain observable, physical systems behave. It's even called the atomic _theory_, and like all other good theories it knows its limits. At low enough energies, it's too fine a…

I disagree with you. Your argument could be made about anything, there is no such thing as a "human" either, it's just a big bunch of wave-particles that does not have some clear limits. Yet when we talk about a human, we all know what that is, and when a human is seating on a chair we don't think the chair is part of it.

The same applies to atoms, we all agree on what they are, and we can show pictures of them etc.

The question here is whether spacetime is something like that, or if it is a proxy concept with no grounding whatsoever in the universe, but with good predictive powers?

For example, for a long time we believed that Aether filled space, and although we now know this is not the case, the mathematical model provided by the Aether theory was pretty useful. You could very well imagine a world where we know Aether is not real, but continue using it for lack of a better theory as it is a useful framework.

> It's even called the atomic _theory_

Theory, in scientific theory, means the opposite of theory in our everyday language though. Theory does not mean a guess, it means a body of work accepted as valid and robustly tested.

Re: Is Spacetime Real?

#22

Post by Q_is_4_Quantum »

codeulike wrote: post #10
thisiscorrect wrote: post #5

“What exactly is spacetime? Is it a real thing like an atom, or just a mathematical construct that is used to describe how mass 'generates' gravity?” This is a false dichotomy. Atoms too are "just" a mathematical construct used to describe how certain observable, physical systems behave. It's even called the atomic _theory_, and like all other good theories it knows its limits. At low enough energies, it's too fine a…

I dont agree its a false dichotomy. Yes every theory is just a model to fit observations etc etc. But Atoms are conceivable - they work as a model, but we can also imagine how to fit into the reality that we experience. We can 'see' them to an extent with special instruments. And their abilities/behaviours are evident in all the physical world of compounds and elements around us. You can disolve salt in water, you ca…

Agree with this - the jury is still out on "reality" or otherwise of a wavefunction, and people expend their "real" research efforts differently according to their opinion! Saying "well everything is just mathematics" is a bit like advocating solipsism: people will roll their eyes and stop inviting you to cocktail parties, its a boring position.

Another historical example would be electric and magnetic field lines. My impression is that even Faraday originally had doubts about their reality; others certainly did. They could have just been forever considered a useful mathematical construct. At some point it became clear that thinking of them as really existing, permeating space, and having physical properties akin to those of accepted real stuff (momentum etc) was more useful. Many years after GR was formulated there were arguments about similar mathematical objects (dynamical components of a tensor, or "gravitational waves") should be considered real or not. The story is that Feynman convinced many with a simple thought experiment about how they transmit energy.

Re: Is Spacetime Real?

#23

Post by invalidtaxonomy »

This raise a bunch of interesting questions, but the first one that comes to mind is "should approving such cookie popup for your business be considered a clear sign of mental illness?". This is clearly the work of a dangerous and deranged mind that I would not feel comfortable letting my family hang out with.

Re: Is Spacetime Real?

#24

Post by mmcconnell1618 »

Does anyone else see a logical flaw in explaining the distortion of spacetime with examples like a weight on a rubber sheet or too many actors on a stage causing it to warp? It seems that the easiest way to explain how gravity is created by spacetime is to use a self referential example of gravity itself.

Re: Is Spacetime Real?

#25

Post by acd »

Yes but you can warp space time with gravity according to Einstein.

https://en.wikipedia.org/wiki/Spacetime

But you need to warp space as in curve it. If you would fly close to a black hole space might be warped.

https://www.space.com/1976-black-hole-puts-dent-space-time.h...

You probably need to think of space in higher dimensions than three for example four dimensions.

Re: Is Spacetime Real?

#27

Post by AnIdiotOnTheNet »

sailingparrot wrote: post #21
thisiscorrect wrote: post #5

“What exactly is spacetime? Is it a real thing like an atom, or just a mathematical construct that is used to describe how mass 'generates' gravity?” This is a false dichotomy. Atoms too are "just" a mathematical construct used to describe how certain observable, physical systems behave. It's even called the atomic _theory_, and like all other good theories it knows its limits. At low enough energies, it's too fine a…

I disagree with you. Your argument could be made about anything, there is no such thing as a "human" either, it's just a big bunch of wave-particles that does not have some clear limits. Yet when we talk about a human, we all know what that is, and when a human is seating on a chair we don't think the chair is part of it. The same applies to atoms, we all agree on what they are, and we can show pictures of them etc.…

> The question here is whether spacetime is something like that, or if it is a proxy concept with no grounding whatsoever in the universe, but with good predictive powers?

Consider that "human", "chair", and "atom" are also just concepts are minds apply to certain patters of energy. We all "know what that is" because it is advantageous for our minds to place things in these categories for the purpose of modeling. You may know what a "chair" is, but there are an infinity of gradations between "chair" and any two other objects, like the beanbag chair sitting between "chair" and "pillow".

The concept of a chair has no grounding in the universe, it's all in the mind. There are no physics that only apply to chairs.

> For example, for a long time we believed that Aether filled space, and although we now know this is not the case, the mathematical model provided by the Aether theory was pretty useful. You could very well imagine a world where we know Aether is not real, but continue using it for lack of a better theory as it is a useful framework.

Yes, that's how it works. When we have a better model we use that unless a simpler one will do. Newtonian gravitation isn't "real" by your definition, but we still use it in a lot of circumstances even though we have more accurate models.

Re: Is Spacetime Real?

#28

Post by thisiscorrect »

sailingparrot wrote: post #21
thisiscorrect wrote: post #5

“What exactly is spacetime? Is it a real thing like an atom, or just a mathematical construct that is used to describe how mass 'generates' gravity?” This is a false dichotomy. Atoms too are "just" a mathematical construct used to describe how certain observable, physical systems behave. It's even called the atomic _theory_, and like all other good theories it knows its limits. At low enough energies, it's too fine a…

I disagree with you. Your argument could be made about anything, there is no such thing as a "human" either, it's just a big bunch of wave-particles that does not have some clear limits. Yet when we talk about a human, we all know what that is, and when a human is seating on a chair we don't think the chair is part of it. The same applies to atoms, we all agree on what they are, and we can show pictures of them etc.…

"The same applies to atoms, we all agree on what they are, and we can show pictures of them etc."

This is where you bury the lede. It's clear if you read many of the comments here that there is no such agreement. Some people _think_ of an atom as something you can reach out and touch, or grok in some deep sense distinct from performing specific experiments. Others take an approach that's more in line with theory in the sense I use it (https://en.wikipedia.org/wiki/Scientific_theory). Your definition of theory is too loose: it's not just a body of work. That sounds like a pile of experimental evidence to me. A theory is a robust model or family of related models that match the experimental evidence. Atoms exist in that sense: they're a well tested model of experimental phenomena.

I'm certainly not claiming that atomic theory is a wild speculative guess which you seem to imply I've done.

Re: Is Spacetime Real?

#29

Post by tim333 »

yesenadam wrote: post #4

TLDR: Article ends with > whether it’s “real” or not — that’s not a question that science has yet discovered the answer to.

Not sure that's even a question of science. It's a question of how you define real.

Re: Is Spacetime Real?

#30

Post by sailingparrot »

AnIdiotOnTheNet wrote: post #27
sailingparrot wrote: post #21

Earlier quoted context omitted.

I disagree with you. Your argument could be made about anything, there is no such thing as a "human" either, it's just a big bunch of wave-particles that does not have some clear limits. Yet when we talk about a human, we all know what that is, and when a human is seating on a chair we don't think the chair is part of it. The same applies to atoms, we all agree on what they are, and we can show pictures of them etc.…

> The question here is whether spacetime is something like that, or if it is a proxy concept with no grounding whatsoever in the universe, but with good predictive powers? Consider that "human", "chair", and "atom" are also just concepts are minds apply to certain patters of energy. We all "know what that is" because it is advantageous for our minds to place things in these categories for the purpose of modeling. You…

Right, and that was the point I was trying to make with the human analogy.

So the question is whether spacetime is one of those patterns we can point to, like a "human" a "chair" or an "atom", which is what we call "real" in our everyday language, or whether it is only a useful modelization tool, like the Aether. There are no pattern anywhere in the universe matching the Aether.

It is a valid question.

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