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Why Quantum Mechanics?

scottaaronson.blog

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Re: Why Quantum Mechanics?

#181

Post by stared »

kgwgk wrote: post #173
stared wrote: post #145

Earlier quoted context omitted.

To elaborate on this a bit: One may argue that "a state" is a simpler concept than "a superposition of all state". Even in pure mathematics [1], I don't think that (say) real numbers are less fundamental than natural (unlike Kronecker in "Natural numbers were created by God, everything else is the work of men"). What's true for the set theory route, does not need to be true for any possible mathematics, including tho…

> One may argue that "a state" is a simpler concept than "a superposition of all state". What would that mean in the context of QM? "A superposition" is "a state".

Here by "a state" I meant "a classical state". E.g. a particle with fixed (x, p), or a binary state 0 or 1.

Re: Why Quantum Mechanics?

#182

Post by HotHotLava »

trixie_ wrote: post #27
EMM_386 wrote: post #24

Earlier quoted context omitted.

I strongly feel that the mystery of consciousness is somehow deeply tied into why we have things like QM and not classical physics. If it was just classical physics, then you get yourself into the thinking that you can rewind time and all the "billiard balls" knock into each other the same way, which is why you order a soup and not a sandwich every single time on that day. That eliminate free will. There is something…

That's why physicists are so opposed to super determinism because like you say it would make life 'utterly meaningless' (I dont agree, a bit dramatic). Super determinism is the unpopular answer that solves many problems in quantum mechanics and relativity. It also makes a lot of sense if you think of the universe as pre-rendered, just like you would a CGI movie. Determine where all the particles land upfront througho…

But superdeterminism in the sense that Scott uses it doesn't just mean life is completely predetermined (I think that would be a fairly unobjectionable theory), it means that specifically the whole universe is predetermined in a way that just happens to cause human experimenters to choose measurement settings that accidentally reproduce the the values predicted by Bell's inequality.

It's that mind-blowingly unlikely coincidence with no explanation that scientists object to.

Re: Why Quantum Mechanics?

#183

Post by platz »

breuleux wrote: post #165
platz wrote: post #138

Earlier quoted context omitted.

This assumes a differnt universe could have been possible. What pool are you sampling from? What notion of probability are you relying on? scott is not asking what other universes were possible. he's asking to explain why QM must be true in the universe that we do observe.

I mean, if QM wasn't true we would observe something else, wouldn't we? I don't understand how this is a meaningful question.

No, he's asking how to fit the data we do observe, and why QM is the obvious conclusion compared to other theories that fit the data that we do observe.

Re: Why Quantum Mechanics?

#184

Post by platz »

Koshkin wrote: post #158
platz wrote: post #138

Earlier quoted context omitted.

This assumes a differnt universe could have been possible. What pool are you sampling from? What notion of probability are you relying on? scott is not asking what other universes were possible. he's asking to explain why QM must be true in the universe that we do observe.

A trivial answer is that the question is moot, as this universe is the way it is precisely due to the laws of QM themselves. (Conceivably, in other universes, ones that we do not observe, the laws could be different.)

You're begging the question by asserting the universe = QM. QM is just a description. He's asking the if there is an alternative to QM that also fits the data, that could make the universe the way it is; if there isn't an obvious answer that could update our understanding of QM.

Re: Why Quantum Mechanics?

#185

Post by breuleux »

hansbo wrote: post #70
breuleux wrote: post #34

Earlier quoted context omitted.

> If it was just classical physics, then you get yourself into the thinking that you can rewind time and all the "billiard balls" knock into each other the same way, which is why you order a soup and not a sandwich every single time on that day. I don't understand this line of reasoning. If I ordered a soup for lunch, and then time is rewound and I order a sandwich instead, it would appear that my choice is in fact r…

I view this the same way. Determinism vs randomness says nothing about free will. I think the problem with arguments regarding free will is that it's very hard to define (like consciousness for that matter). I am my brain. My brain controls what I do. Therefore, I control what I do. Only if we lift up our consciousness or free will as something higher than our brain does this become a problem. The fact that my free w…

Yes, to me that seems the only sensible way to interpret free will.

I think that the whole determinism vs randomness debate boils down to the fact that when we make a choice, for example whether to order soup or a sandwich, we have to hold the belief that either choice is possible. We can simulate ourselves in our mind taking either decision, evaluate pros and cons, and use the results to act. In that sense, because it is compatible with many counterfactuals, our internal self-model is decidedly non-deterministic. And if you think about it, it has to be non-deterministic in order to be a useful decisional tool: considering what would happen if you did X or Y is the foundation of deliberation.

The trick, though, is that ultimately this is just epistemological non-determinism: you don't know what is going to happen, and you can't know, because you are in the process of figuring it out. When I am looking at the menu, I think it is possible that I will order a soup or a sandwich, just like I think it is possible that they are out of soup, even though there is a definite answer to whether they do or not. I just don't know it. Our misstep is to (intuitively) extrapolate that if we can't know what we will choose, then no one else can.

Re: Why Quantum Mechanics?

#186

Post by breuleux »

platz wrote: post #183
breuleux wrote: post #165

Earlier quoted context omitted.

I mean, if QM wasn't true we would observe something else, wouldn't we? I don't understand how this is a meaningful question.

No, he's asking how to fit the data we do observe , and why QM is the obvious conclusion compared to other theories that fit the data that we do observe .

What other theories fit the data that we do observe?

Re: Why Quantum Mechanics?

#187

Post by VirusNewbie »

stared wrote: post #145
stared wrote: post #135

> Why didn't God just make the universe classical and be done with it? What would've been wrong with that choice? I hear it over and over and still don't understand the premise. Classical mechanics is not something sacred. It is our first serious model of physics. Our first approximation is based on the scales at which we operate and our senses as humans. Furthermore, even "regular" quantum mechanics is a non-relativ…

To elaborate on this a bit: One may argue that "a state" is a simpler concept than "a superposition of all state". Even in pure mathematics [1], I don't think that (say) real numbers are less fundamental than natural (unlike Kronecker in "Natural numbers were created by God, everything else is the work of men"). What's true for the set theory route, does not need to be true for any possible mathematics, including tho…

Really interesting to read your post, despite half of it being a bit over my head. That is quite cool you got to have a long conversation with Penrose!

As to your statement about platonism or mathematical realism, I'm curious about something. Surely most axiomatic systems are a choice, so I can understand why we would say they're man made (euclidean geometry, ZFC, etc).

However we also know about 'meta axioms', which seem to go beyond being a choice. There are simply some axioms that don't seem optional. Do you hold those to be also man made or is that a separate phenomenon?

Re: Why Quantum Mechanics?

#188

Post by PaulDavisThe1st »

stared wrote: post #135

> Why didn't God just make the universe classical and be done with it? What would've been wrong with that choice? I hear it over and over and still don't understand the premise. Classical mechanics is not something sacred. It is our first serious model of physics. Our first approximation is based on the scales at which we operate and our senses as humans. Furthermore, even "regular" quantum mechanics is a non-relativ…

I consider "classical" in this context just to mean "very small things behave like very big things". That doesn't make it sacred, it just means that scale doesn't matter. The universe appears to not be that way, and SA is asking why.

Re: Why Quantum Mechanics?

#189

Post by guerrilla »

naasking wrote: post #178
lulantivaxxers wrote: post #156

Earlier quoted context omitted.

Thanks for this, hidden variable theories are very seductive but Bell's Theorem is definitive.

It's definitive that you have to give up locality (Bohmian mechanics), counterfactual definiteness (Copenhagen and others), or statistical independence (Superdeterminism). It's not definitive at all about local hidden variables.

> It's not definitive at all about local hidden variables.

What?

> To date, Bell tests have found that the hypothesis of local hidden variables is inconsistent with the way that physical systems do, in fact, behave.

Re: Why Quantum Mechanics?

#190

Post by IIAOPSW »

stared wrote: post #135

> Why didn't God just make the universe classical and be done with it? What would've been wrong with that choice? I hear it over and over and still don't understand the premise. Classical mechanics is not something sacred. It is our first serious model of physics. Our first approximation is based on the scales at which we operate and our senses as humans. Furthermore, even "regular" quantum mechanics is a non-relativ…

Why clouds?

Sure I understand the theory of the water cycle. But the whole precipitation and evaporation thing is a complex mess. It doesn't look at all like the simplest possible form that could achieve the same job. Why not just water above the firmament?

When something in nature seems needlessly complicated, one has to ask what purpose the complexity serves. Why would a hypothetical universe engineer (dare I say "god") sit down and decide to have a universe that is indistinguishable from a classical one on nearly every length scale but is still quantum at the bottom? There's only a few possibilities:

1. The complexity isn't actually needless but it is arbitrary. There are other self-consistent laws of physics that are possible, but all the alternatives are just as weird and complex as QM.

2. The complexity isn't actually needless because QM is inevitable. There's some deep logical principle that forces the hand of the hypothetical universe engineer.

3. There complexity actually is needless. Our universe is quantum because that's just how it is.

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