One of the more interesting potential answers to this question is quantized spacetime: http://einsteinsintuition.com/what-is-qst/overview/
Is Spacetime Real?
61–70 of 103 posts
Re: Is Spacetime Real?
#62Earlier quoted context omitted.
>We can sense them directly What does this even mean? Unless you're talking about some supernatural "atomic sense", there's obviously no way to "sense them directly" - we sense them through their interaction with other things combined with our model of those things and the interaction.
Okay, that's fair. But taken to its extreme, we sense everything through its interaction with other things. But obviously, things exist; not everything can be just a mathematical model.
Check out Max Tegmark's writings on the mathematical universe, some very interesting stuff in that direction.
Re: Is Spacetime Real?
#63Earlier quoted context omitted.
We have a photo of a building that makes accurate and measurable predictions of things like the roof being above the door, and how far, and which parts are transparent (windows) and which parts opaque (walls), and how many people could fit inside it. Is that picture as real as buildings get?
Is your claim that the picture is the building? Because that's the equivalent of claiming that the a Penrose diagram is spacetime, instead of a representation of the model. The photo of the building is an accurate diagram of the model of that one individual building. It describes the building, it is not actually the building. However, your model (roof height, walls, location, etc) is the building. If that building is…
> "Is your claim that the picture is the building?"
You said "a model which makes accurate predictions is as real as real gets". That the picture is the building is your claim here, that there's nothing more real than an accurate model, which I'm countering by absurdum. Wind can turn a turbine, a weather predicting model of wind cannot. You say "the differentiation [between a model and reality] is meaningless", I say a model is a leaky abstraction - when you send a single atom through a Young's double slit experiment and it interferes with itself and generates a wave interference pattern, that's leaking a reality outside the billiard-ball model of atoms, that's one time when the distinction between model and non-model is meaningful.
> "If that building is destroyed in a fire and remade to those exact specs, do we not say it is still a building?"
If the building is destroyed in the fire, and your model of it isn't, how can you say there is no difference between the building and the model?
Re: Is Spacetime Real?
#64Spacetime is a vector in Hilbert space. Entanglement yields locality. Space emerges. I'm not convinced time is emergent, though (I give the idea low credence). I'm not a scientist, I just listen to Sean Carroll's podcasts.
> Entanglement yields locality Could you please expand on that?
In trying to derive spacetime from quantum field theory, some working theories show that minimum "energy" fields that are highly entangled with each other are "near" each other. That gives you locality, therefore space. That is, locality arises in the model from certain kinds of entanglement.
Better explanation here: http://www.preposterousuniverse.com/blog/2016/07/18/space-em...
Re: Is Spacetime Real?
#65Earlier 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? I'd add: is it something one can develop an intuition for? I don't think there is anyone who says gluons or general relativity are intuitive. You have to do the calculations (or memorize heuristics) to get something useful. Atoms, on the other hand…
I don't believe anybody can intuitively "visualize" an atom which leads to accurate predictions, especially the electron cloud and it's collapse. Atoms which manage to stay isolated for long enough are not even localized in space.
Re: Is Spacetime Real?
#66The question is meaningless.
The question is a fine journey whose path as such could be profitable.
But practically, we behave as though reality, consciousness, and freewill have substantial basis.
Re: Is Spacetime Real?
#67Earlier quoted context omitted.
> So then the Aether was real for a while and stopped being real 200 years ago? Yeah, pretty much. > If we discover a new model that makes better prediction than our current spacetime based model, just like relativity was to Newton's theory, will spacetime stop being real? In so far as Newtonian gravitation is also not-real. We still use that model for a lot of things of course. I don't know much about Aether theory…
I do agree with your point, but I think we are seeing the limit of language: when we don't attach the exact same definition to words, we can misunderstand each others while trying to convey the same thing. The way you use "real" is the way I would use "valid": A theory is valid until proven otherwise. And the way I use "real" (and I think it is the same way the article used it), is whether something has any grounding…
> And the way I use "real" (and I think it is the same way the article used it), is whether something has any grounding in our universe (some pattern as you said before).
Many of the things you described as "real" don't have grounding in our universe, i.e. things like "chair". It's possible I misunderstand your usage of the term "grounding".
> For example, wormholes are possible following the theory of general relativity, but we don't know if they are "real", e.g. can there actually be a wormhole in our universe. If we do end up finding one, then they are real. If we however find conclusive evidence that they cannot exist in our universe, then they are not real, but only an artifact of our (incomplete) theory of general relativity.
Sure, but how does that apply to spacetime? We know, so far as anything can be known, that space and time are two different perspectives of the same thing. Relativity described it, and we have measured and the effects it predicts with startling accuracy.
Here's a question: It matters if wormholes can or cannot exist regardless of if the current model permits them or not. Does it matter if spacetime fits your definition of "real" or not?
Re: Is Spacetime Real?
#68Define "real"
"Reality is that which, when you stop believing in it, doesn't go away." --PKD
Re: Is Spacetime Real?
#69Earlier quoted context omitted.
Is your claim that the picture is the building? Because that's the equivalent of claiming that the a Penrose diagram is spacetime, instead of a representation of the model. The photo of the building is an accurate diagram of the model of that one individual building. It describes the building, it is not actually the building. However, your model (roof height, walls, location, etc) is the building. If that building is…
> " Is your claim that the picture is the building? " You said "a model which makes accurate predictions is as real as real gets". That the picture is the building is your claim here, that there's nothing more real than an accurate model, which I'm countering by absurdum. Wind can turn a turbine, a weather predicting model of wind cannot. You say " the differentiation [between a model and reality] is meaningless ", I…
> You said "a model which makes accurate predictions is as real as real gets". That the picture is the building is your claim here, that there's nothing more real than an accurate model, which I'm countering by absurdum.
My claim is that the model describes a real thing, not that it itself is a real thing, and the extent to which that thing being described is real is a matter of the accuracy of the model. You can model the motion of planets with geocentric epicycles, but that is less real than a model that uses heliocentric ellipses.
Let me turn this around for a second:
> when you send a single atom through a Young's double slit experiment and it interferes with itself and generates a wave interference pattern, that's leaking a reality outside the billiard-ball model of atoms, that's one time when the distinction between model and non-model is meaningful.
Now ask yourself: if we have a 100% accurate model of physics that employs a concept of spacetime such that there are no leaks, no unaccounted for observations whatsoever, then would you say that it matters if spacetime is just some mathematical concept and the real mechanism works differently but produces exactly the same results?
I submit that it doesn't. A model that produces perfectly accurate descriptions describes reality in so far as any description of reality can be said to. We don't have perfect models of reality, that is known, however lacking a more accurate model it is meaningless to say that our current ones (which are astonishingly accurate despite being imperfect) don't describe reality.
Re: Is Spacetime Real?
#70Earlier quoted context omitted.
"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 t…
> It's clear if you read many of the comments here that there is no such agreement I guess I should have said "all experts agree" instead? Lack of knowledge about something by some people doesn't change the definition of that thing. I would add however, that you can reach out and touch an atom with a certain definition of touch (as touch is mostly a macroscopic concept). > I'm certainly not claiming that atomic theor…
Touch isn't any different than measuring radiation interacting with something. These are metaphysical questions, not scientific ones.
Scientists, like everyone, have a realist perspective. They consider reality to correspond with appearences. But this is a convention or a metaphysical belief or even a religous belief, it's not scientific.