stupid physics questions

[pogo]

You want to look at Quantum Mechanics for that one. QM itself for how the universe is quantised, the Pauli exclusion principle for why things spread out, so you get only so much information in a finite space. Not that it’s a really meaningful result: the universe is finite, and contains only finite information, but it is also so incredibly vast that it might as well be infinite.

[gravy]

Is that true?

Pauli exclusion doesn't apply to boson iirc

[zip accident]

Without (as everyone here has probably noticed by now) being an expert, I'd think it's the Planck lenght being finite, and the universe being a finite number of Planck lengths across that makes it non infinite.

[pogo]

Pauli exclusion explains atoms, e.g. why atoms have electrons in electron shells. By extension it explains how matter such as we are made of is formed, and how it is remarkably stable even under extreme conditions. E.g. you take rock to the depths of outer space, or bury it deep under 1000 atmospheres of pressure, and it is still rock. At most atoms rearrange themselves, so graphite becomes diamond under extremes of pressure. Even if you heat it so it melts the atoms stay the same distance apart.

It’s not until you gather it together in such quantities that gravity overcomes the forces keeping electrons apart and you get a neutron star. But you need a lot of mass, more than is in our Solar System. And even that obeys the same laws of exclusion, just on a smaller scale as now neutrons are kept apart.

Yes this does not apply to bosons, but not just any old bosons. Helium for example, but only very cold ones. Or possibly you could achieve the same effect at a higher temperature and pressure in the heart of a star, but good luck finding one that is mostly helium.

[gravy]

So you can have an infinite amount of information in the universe and the pauli exclusion principle isn't a limiting factor.

Maybe. Planck length probably affects that.

[gravy]

Without (as everyone here has probably noticed by now) being an expert, I'd think it's the Planck lenght being finite, and the universe being a finite number of Planck lengths across that makes it non infinite.

We posted at the same time

Apparently:

There is no concensus on the physical significance of the Planck length. Some theories treat it as a physical limit, but realize that there has been no experiment that can get anywhere close to probing space at this scale. It may be nothing more than a combination of other fundamental constants that has units of length.

A bit of further reading says this is a good case where GR and QM clash. Planck length would put a hard limit on maximum light frequency but light frequency is dependent on difference of inertial frames and tends to infinity.

In short: no one knows.

[pogo]

So you can have an infinite amount of information in the universe and the pauli exclusion principle isn't a limiting factor.

Maybe. Planck length probably affects that.

In theory, but where would you get it from? I mean you can have as many photons as you like in one place, and they being massless, charge free, do not do odd things like form neutron stars when you put more and more of them in the same place. But photons come from atoms mostly and there are only a finite number of them.

I still feel, and it is just a feeling not something I can justify formally, that QM stops you having infinite information density. At the most fundamental level QM says “everything is quantised” – everything is divided up into small pieces. So there is not really a continuum you can divide over and over, like you can the real line. At some point you reach the quantum level where everything is quantised.

Another less direct argument is from Heisenberg’s uncertainty principle. You can’t divide over and over as that means measuring shorter and shorter lengths. Heisenberg’s uncertainty principle says that if you do so the uncertainty, so inaccuracy, of the other data you are reading increases. This means past a certain point, as you try and cram more and more information into your space, it becomes too inaccurate to be useful, putting a hard limit on the information you can store.

[gravy]

The core of this is whether spacetime is quantized or not isn't it?

Better minds that ours have spent decades on that so I'm not sure we're get anywhere substantial on YY

I think pauli exclusion is a red herring tho. Don't we have some actual physicists on here?

EDIT: full circle, just read the link darkflame posted on the previous page.

[gumboot]

If everything turns out to be deterministic, then there is zero information in the universe. It can express only a single state and you can't have a second one that is different.

In fact, by the very definition of 'universe', you cannot haveobserve a second one in a different state, so by definition there is zero information. It just "is what it is".

[zip accident]

In fact, by the very definition of 'universe',

Universe = one verse:

"In the beginning god created the heaven and the earth".

I thought there was going to be a bit more to it than that, but the next line is numbered two, so I guess that's the whole verse.

[funkstar]

In fact, by the very definition of 'universe',

Universe = one verse:

I don't think that's the actual etymology, though.

[zip accident]

In fact, by the very definition of 'universe',

Universe = one verse:

I don't think that's the actual etymology, though.

I don't say it's a good origin for the word, but it makes sense in the historical context, and it fits exactly.

[pogo]

“verse” is from the same root but from so long ago that both modern meanings have diverged greatly. It is from the word meaning “turn” in Latin, and is still used like that in English in words like “reverse”. It becomes the verse in poetry or prose as you read such by repeatedly turning, whether returning to the start of the line or turning the page. Universe is less clear, but it may be as “one turn”, i.e. a complete rotation, lets you take in everything around you. Without the benefit of modern telescopes, and without street lights, everything you could see was pretty much everything there was. That makes the modern connection largely a coincidence.

[zip accident]

That makes the modern connection largely a coincidence.

That is sort of vaguely what I was heading toward implying, you can't really make much sense of our modern understanding of what the universe is, by looking at the definition of what stone age sheep-herders, great guys though they may or may not have been, thought it might be.

[gumboot]

But its definition expands at exactly the rate our perception expands. Once we realised the stars weren't just painted onto the firmament, the universe grew to encompass them. If, for example, faster-than-light communication suddenly came about, then things beyond the wavefront of the first light leaving earth at the beginning of time could be brought into our universe as well.

As soon as we can perceive it, it can (and inherently does) alter our behaviour and consequently the behaviour of the universe. If that alteration was deterministic then the thing that altered it would have always been a part of the same universe even if we didn't know about it before.