Would the universe be the same if it was reset?

nonequilibrium

Dave, the indeterministic interpretation of QM is just as much a "speculation" as the deterministic one.

I agree that not all interpretations are on equal footing a priori, but you seem to be implying that there are no arguments for the deterministic interpretation except taste (or even a sort of unwillingness to accept indeterminism). Am I interpreting you correctly? If so, I disagree on that one. There are a lot of respectable physicists who support the pilot-wave theory (if I really have to throw out one name, it's J.S. Bell; his name seems most obvious to say first since he's the most famous) and their arguments are all but poor in my view. The arguments concern matters such as a minimal set of axioms, or for example an absence of ambiguity (the main problem with the orthodox interpretation), even pratical issues like new (and sometimes better!) numerical approximations. Another argument might be that the pilot-wave theory was actually one of the very first versions of QM, implying it's not at all far-fetched (de Broglie put it forward, but Schrödinger -when writing down his equation- only afterwards left out the point particle, but for reasons we now know are wrong (at that time Schrödinger was not aware of the phenomenon of collapse which destroyed his interpretation) and Born, when putting forth his probabilistic law, for some unknown reason only based himself on Schrödinger's research, although the probabilistic law was already a consequence/theorem from de Broglie's theory).

Literally the same, as in for example a Newtonian world view: if the laws are deterministic, then a certain set of fixed initial conditions (this is of course very important; even the slightest change in initial conditions will lead to a dramatically different universe) will lead to exactly the same evolution.

mfb

This is wrong.
The Copenhagen interpretation (and some others) says no. Other interpretations say yes.

Count me in. And the ~60 others here, too (multiply a "physicist fraction" to this number of you like). And of course all other physicists supporting these interpretations.

DragonPetter

I'm not speaking on behalf of the validity of his statements, because it is very much an opinion and string of unfounded conclusions he seems to be talking about.

But, I think entropy was relevant to his opinion because entropy is a way to describe systems that we cannot account for microscopically because they simply have too much information and too many variables and interactions. We describe it statistically, much as random events are described statistically. His point is that even though we can treat it as randomness, it is more as a result of our inability to account for all possible interactions, variables, etc. than it is that the universe is truly random.

I think he is missing the mark though, because we have shown that single particles and interactions are only described mathematically using probability at best. My thought is that the universe would not be identical at small detail, but perhaps macroscopic properties such as total energy and entropy in the universe could be the same at a given time.

ResolutE

The big bang was a result of an infinitely small particle exploding in all directions, forming the universe.

I have never taken a QM course, what I'm about to say is speculation, and I would like to hear your (anyone reading this) input.

Newtonian physics seems deterministic, and probably the reason for that is it's on a much bigger scale than the quantum level. If I were to stamp a piece of paper with the same stamp, it would make the same mark every time, it is deterministic because of it's properties.

However, QM and HUP say that things on a very small scale, such as electrons, are non deterministic. If this means that they are truly random, and not that we just can't describe it so we label it random, but truly random, then I believe if the universe was reset it would look much different.

Because the big bang resulted from a very very small particle, and QM and HUP says that very small things act very strangely, and randomly. So the slightest change, and the slightest chance of the tiny particle being different or random would result in a different explosion resulting in a different universe.

Assuming this is correct, then what is the chance of the universe being exactly the same?

Well, if you have a red object and blue object in a bag, there is 1/2 chance of picking one of them. If you have a very small particle, what are the chances of it being in one spot rather than another? Well 3D space is infinite, the particle can be at point (1,1,1) or point (1,1,0.999999999999999999999999). So if there are an infinite amount of possibilities for a particle, then 1/ infinity = 0, which I speculate would mean that there is a 0% chance of the universe being the same if it was reset.

Thoughts?

DaveC426913

This is an inaccurate description of the Big Bang, though it does not change your depiction of the probabilities.

nonequilibrium

@ResolutE:
As discussed above, this is actually not true. At the moment we don't know whether QM implies nature is determinstic or not. It is often said that QM implies nature is non determinstic, but these are speculations promoted by the accidental history of physics. We need to invent new experiments to get a better clue of what's going on.

pgardn

Not at all convinced based on what I have read about Bell. Imo he is getting into the realm of a Goedel like analysis with a dash of "I dont want to look at the world" as it will ruin my ability to reason. The logic and reasoning applied becomes highly philosophical in nature and I find too many ways to approach the math. I have to remain an ape and go with math that fits models that best fit what is observed and measured in what I presume (after reading up) are feeble (observing and measuring) efforts. I feel handicapped by not being able to directly observe gravitational fields with my antennae but thats the way it is.

I have to go with No.

DaveC426913

OK, I'll accept that.

Not all interpretations of QM call for a non-deterministic universe.

nonequilibrium

I honestly have to say that despite the effort I have no idea what you're talking about.

pgardn

This becomes more about the philosophy of logic and reasoning. This is the way I see the whole thing headed. The math needed to describe this gets into the aforementioned realm.

Because humans are quite obviously limited we scrape and scratch to make sense of things in what are heroic but suspect methods to describe certain phenomena as pointed out by Bell and more fundamentally Goedel (basic logic flaws in math). So because I fail to see any experiments to prove Bells ideas I will at this time say no.

DaveC426913

He is looking at Bell's Theorem, which asserts that there are (there can be) no hidden variables involved in why QM works the way it does, for example whether particles decay truly randomly. Bell's theorem (to be oversimplistic) asserts that the OP's friend is wrong when he says "there's nothing random, just properties we can't observe yet". Bell's Theorem says "these properties cannot exist, else we would not see what we see."

pgardn is struggling with that. I think. Though I'm not sure if he accepts or if he rejects Bell's Theorem.