Is the universe discrete? If it is, then doesn't that mean

>>8282705
>If it is, then doesn't that mean there are only a finite number of positions a particle can be in?

no, you can also have an infinite descrete grid

I don't believe that our universe is discrete in such a simple sense. If it is compact, particles would have descrete energy states but it is very likely that we could never measure these because of its size.

>>8282705
In this case, discrete means there's a smallest, indivisible unit for time,distance, and therefore energy.

This would break quantum physics in the sense that at that scale, position and momentum could be known exactly.

The universe most likely is not discrete.

>>8282705
>Is the universe discrete?
No. All models of physics depend on the infinite differentiability of space-time.

>>8282732
>If [the Universe] is compact, particles would have descrete energy states
[citation needed]

>>8282750
>No. All models of physics depend on the infinite differentiability of space-time.

actually many models work if spacetime (metric) is only two times differentiable, but in this case it doesn't matter

sorry i thought it was trivial (just quantum mechanics on a sphere/torus/whatever) but I didn't consider that the universe is expanding so I don't really know if that statement is correct

>>8282763
The first part of your post seems to indicate you aren't the OP. The second part of your post doesn't relate to anything previously mentioned in this thread. I'm confused.

You're right though, the models don't necessarily need an infinitely differentiable spacetime. However, a discrete spacetime isn't differentiable at all, by definition. Basically everything in modern physics relies on the proposal that spacetime is a manifold (at least Pseudo-Riemannian, with a few more specifications about the metric). If you get rid of that, you have no formal basis for establishing conservation laws or gauge theories or any of the fun wonderful stuff that inspires this board to make threads without doing their homework first.

No physicist is considering the "quantization of space-time." This is also not what they mean when they discuss quantum gravity.

>>8282841

The second part should describe, what I thought when writing about descrete energy states.

I think physicists are considering the quantization of space time since the graviton is an excitation of the metric as a quantum field. Also there are people trying to find some kind of Hamilton function for spacetime and grind it through the quantum apparatus although there are many problems, like the Pauli uncertainty principle causing increasing curvature the smaller your structures become.

>>8282748
I'm not so sure about that, the Universe could easily be discrete, if you also subscribe to superdeterminism.
It's not a particularily interesting cosmology, but it satisfies the Occam' razor pretty well for me.

>>8282866
Quantizing the excitations of the metric on small scales is not the same thing as making spacetime discrete. Well, maybe if you're Lee Smolin, but fuck that guy.

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

>When the canonical quantization procedure is applied to a field, such as the electromagnetic field, the classical field variables become quantum operators. Thus, the normal modes comprising the amplitude of the field become quantized, and the quanta are identified with individual particles or excitations. For example, the quanta of the electromagnetic field are identified with photons. Unlike first quantization, conventional second quantization is completely unambiguous, in effect a functor.

>>8282896
I know that, I just didn't know we were still talking about discrete spacetime lol

>>8282900
your own post:
>>8282866
>I think physicists are considering the quantization of space time
What do you think "quantization of space time" means?

The head of a drum is continuous, but the oscillations available when you strike it are discretely available Bessel functions. Now, I clearly don't work in the field of quantum gravity, but I do know a thing or two about quantum physics. The premise of this thread - that there are discrete points of space and time - is not a property of any promising research effort to describe gravitation with quantum mechanics.

At the moment at the smallest experimental scales there is no evidence of a discrete structure of spacetime. Indeed in most theories spacetime is most often thought of as a continuous structure. However there is one approach to quantum gravity that I know of that tries to use a discrete spacetime as a starting point https://en.wikipedia.org/wiki/Causal_sets however it's a pretty niche area of research. You might be able to find some review papers on it if you are interested.

>>8282705
this will probably help

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

>>8282878
Occams razor is shit.

I could argue the simplest explanation is that god did it.

If the universe is discrete, eisenberg uncertainty won't hold

Read up on nassim haramiens swartz child radius

Guy is a crack pot, but he still correctly predicted the radius of a proton using the idealisms you're discussing here OP

>>8283715
You clearly don't know what Occam's razor is.

>>8282906
>The head of a drum is continuous, but the oscillations available when you strike it are discretely available Bessel functions.
First of all, aren't there an infinite amount of Bessel functions? Sure the oscillations are discrete in the way that they can only occupy certain modes but there are an infinite number of them. Just like how energy levels are discrete but there are still an infinite amount of them.

Secondly, the head of a drum is not continuous. Mathematically speaking, a continuous drum can only oscillate in certain modes because of the boundary condition we set on it. But an actual drum is composed of atoms and thus cannot be continuous. If this isn't what you meant by continuous, please clarify.

I really don't know whether I'm arguing for or against a discrete spacetime, but We need to be clear about how we use our words and whether we're working in a mathematically ideal universe or the actual universe. Because there is a difference.

>>8282705
>What does the "movement grid" look like?

No one really knows. People speculate about quantum foams or causal sets as mentioned, but again there is no evidence for them. The problem is, they should result in (Lorentz?) symmetry being broken but we see nothing of the kind. In fact it has been tested to an extremely high level of accuracy.

Most likely it's just our ability to measure things that is discrete.

>>8283715
And you'd be an idiot. A god would be the most complex explanation. Don't talk shit.