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The Zen anti-interpretation of quantum mechanics (2021)

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Re: The Zen anti-interpretation of quantum mechanics (2021)

#151

Post by goatlover »

DiogenesKynikos wrote: post #146
goatlover wrote: post #143

Earlier quoted context omitted.

I don't see why that has to be the case other than mathematically it looks like QM "infects" everything as the theory stands now. But nature doesn't have to play along. Also, I forgot about spacetime. Is it quantum mechanical, relativistic or something else? And saying the universe began at al low entropy doesn't explain why it started out in that state.

You cannot construct a logical theory of physics in which some aspects of physics are quantum and others aren't. That's what I mean by Quantum Mechanics infecting the rest of physics. This is why after the discovery of Quantum Mechanics, there was a drive to formulate quantum versions of all fundamental theories.

And what if we fail to formulate quantum versions of all fundamental theories? Again, nature doesn't have to play along.

Re: The Zen anti-interpretation of quantum mechanics (2021)

#152

Post by DiogenesKynikos »

goatlover wrote: post #151
DiogenesKynikos wrote: post #146

Earlier quoted context omitted.

You cannot construct a logical theory of physics in which some aspects of physics are quantum and others aren't. That's what I mean by Quantum Mechanics infecting the rest of physics. This is why after the discovery of Quantum Mechanics, there was a drive to formulate quantum versions of all fundamental theories.

And what if we fail to formulate quantum versions of all fundamental theories? Again, nature doesn't have to play along.

Nature does have to play along, because whatever the correct theory of physics, it has to be logically coherent.

Either everything is quantum, or nothing is. Given that we are pretty darn sure that most of physics is quantum, we're pretty sure the answer is that everything is quantum, not that nothing is quantum.

There are different ways of formulating quantum theories of gravity (in fact, you can derive the Einstein equations fairly straightforwardly by trying to formulate a quantum theory of a massless spin-2 boson). We don't know which of those theories is correct yet, but it's not as if there's no way to quantize gravity.

Re: The Zen anti-interpretation of quantum mechanics (2021)

#153

Post by lmm »

goatlover wrote: post #144
lmm wrote: post #88

Earlier quoted context omitted.

The other cat is being observed by the other you. When you open the box and look, you entangle your state with the cat's, and the wavefunction describing both of you becomes one that could be decomposed as a superposition of two "worlds", one with a live cat and a you who's observed a live cat, the other with a dead cat and a you who's observed a dead cat. As far as I can see people's objection to this tends to be th…

But the other me isn't observed. There's no empirical evidence for that other world. It's an interpretation of the mathematical formalism that there would be other mes making different observations. But there's nothing observational saying I have to choose the MWI interpretation as the correct one.

There's no empirical evidence that the world continues to exist when you close your eyes, it's just the most natural interpretation of our best available mathematical formalism.

Re: The Zen anti-interpretation of quantum mechanics (2021)

#154

Post by lmm »

Jensson wrote: post #129
lmm wrote: post #87

Earlier quoted context omitted.

Decoherence of a system happens when the entropy of entanglement is maximal, so if you want a formula then it's S(Tr_a(p_ab)) -> N/e. In practice a complex system is probably never fully decoherent, but the separability is small enough to not matter; if we're being truly rigorous we work with it as a limit, similar to how we use the "classical limit" in other parts of QM or other contexts. (Analogy: imagine saying "R…

Relativity is a real formula, you just say that decoherence seems to correlate with entropy and then gave a formula for entropy. We don't have a formula for decoherence. Any explanation for decoherence that doesn't help us find a formula for it is nonsense. Here is a better theory than MWI: We live in a simulation, the computer is optimized so when there are too complex interactions in an area it simplifies the state…

> Relativity is a real formula

Relativity is a real formula and the classical limit is a real phenomenon, but there's no formula for when a relativistic situation "becomes classical".

> you just say that decoherence seems to correlate with entropy and then gave a formula for entropy

If the observed system and the observer/external universe are fully entangled (i.e. their entropy of entanglement is maximal) then decoherence has occurred and all observations of the observed system by that observer will be indistinguishable from if the system were not in superposition. That is a mathematical fact that falls right out of the equations. So I don't know what else you're asking for.

Re: The Zen anti-interpretation of quantum mechanics (2021)

#155

Post by lmm »

_0w8t wrote: post #133
lmm wrote: post #118

Earlier quoted context omitted.

> This notion does not explain how the thermal bath appears. The point of the bath is it's a generic model of a large system with lots of states and interactions. > I.e. why the system interacts with a particular bath and not a superposition of such baths? The bath can be in a superposition state at the start, that's fine. (Indeed the whole model would be pretty useless otherwise).

Again, models of decoherence assume existence of an external bath resembling classical state. By interacting with it the system becomes classical itself if it is and the bath is sufficiently big. But it does not explain how that external bath appears. In universe-as-a-wave-function there is no external bath. The system as whole is always coherent and is described by a single wave function. Then the idea of the decohe…

> models of decoherence assume existence of an external bath resembling classical state

They don't assume it's classical. They assume it's a system with lots of states and interactions, because if you want to have a model of "the external universe" then you have to have some kind of concept of what that looks like.

> In universe-as-a-wave-function there is no external bath. The system as whole is always coherent and is described by a single wave function.

Sure; the point is that if you split the universe into "these two entangled particles" and "the rest of the universe", because you want to understand how we observe that entanglement "decaying" as the particles interact with the rest of the universe, then you can model that as "these two entangled particles" interacting with "a thermal bath".

> The trouble is that so far nobody came up with a model where such temporary approximately classical subsystem appears.

This is nonsense? Wavefunctions generally have a lot of structure and decomposing them into smaller subsystems and functions happens all the time.

Re: The Zen anti-interpretation of quantum mechanics (2021)

#156

Post by goatlover »

DiogenesKynikos wrote: post #152
goatlover wrote: post #151

Earlier quoted context omitted.

And what if we fail to formulate quantum versions of all fundamental theories? Again, nature doesn't have to play along.

Nature does have to play along, because whatever the correct theory of physics, it has to be logically coherent. Either everything is quantum, or nothing is. Given that we are pretty darn sure that most of physics is quantum, we're pretty sure the answer is that everything is quantum, not that nothing is quantum. There are different ways of formulating quantum theories of gravity (in fact, you can derive the Einstein…

What makes you so sure reality is fundamentally quantum and not something else we've yet to discover/formulate that underpins QM and everything else?

Re: The Zen anti-interpretation of quantum mechanics (2021)

#157

Post by goatlover »

lmm wrote: post #153
goatlover wrote: post #144

Earlier quoted context omitted.

But the other me isn't observed. There's no empirical evidence for that other world. It's an interpretation of the mathematical formalism that there would be other mes making different observations. But there's nothing observational saying I have to choose the MWI interpretation as the correct one.

There's no empirical evidence that the world continues to exist when you close your eyes, it's just the most natural interpretation of our best available mathematical formalism.

Other than the fact your other senses are working, the ground continues to hold you up, gravity is still at play, you're still breathing, etc. That's a ridiculous standard for empirical. MWI isn't the only interpretation, and there isn't a current experiment which can determine which if any of the interpretations are correct. This is the same problem String Theory has had. You can't just base reality on the math.

Re: The Zen anti-interpretation of quantum mechanics (2021)

#158

Post by lmm »

goatlover wrote: post #157
lmm wrote: post #153

Earlier quoted context omitted.

There's no empirical evidence that the world continues to exist when you close your eyes, it's just the most natural interpretation of our best available mathematical formalism.

Other than the fact your other senses are working, the ground continues to hold you up, gravity is still at play, you're still breathing, etc. That's a ridiculous standard for empirical. MWI isn't the only interpretation, and there isn't a current experiment which can determine which if any of the interpretations are correct. This is the same problem String Theory has had. You can't just base reality on the math.

> Other than the fact your other senses are working, the ground continues to hold you up, gravity is still at play, you're still breathing, etc.

Sure; I was being poetic. We could talk about when you sleep, or distant regions of the universe that you simply can't measure within a human lifetime.

> MWI isn't the only interpretation, and there isn't a current experiment which can determine which if any of the interpretations are correct. This is the same problem String Theory has had. You can't just base reality on the math.

When other "interpretations" require extra assumptions, you can, and should. Otherwise you can never rule out theories that add extra epicycles that have no observable consequences.

Re: The Zen anti-interpretation of quantum mechanics (2021)

#159

Post by goatlover »

Vecr wrote: post #60
goatlover wrote: post #56

Earlier quoted context omitted.

But we only observe the cat being alive or dead. Where is the other cat? Are the many worlds hiding in the equation?

You are "in" the wave function still associated with the live cat, but not with the dead cat wave function. Obviously neither you or a cat is a single wave function, but that's basically the explanation.

I understand that's the interpretation, but I don't observe the dead cat, so I don't feel compelled to accept MWI. I'm not saying it's wrong (who knows), only that it's not scientific (lacking empirical evidence for the dead cat) and one of the other interpretations could be correct (again who knows if any of them are representative of the true state of affairs).

Re: The Zen anti-interpretation of quantum mechanics (2021)

#160

Post by DiogenesKynikos »

goatlover wrote: post #156
DiogenesKynikos wrote: post #152

Earlier quoted context omitted.

Nature does have to play along, because whatever the correct theory of physics, it has to be logically coherent. Either everything is quantum, or nothing is. Given that we are pretty darn sure that most of physics is quantum, we're pretty sure the answer is that everything is quantum, not that nothing is quantum. There are different ways of formulating quantum theories of gravity (in fact, you can derive the Einstein…

What makes you so sure reality is fundamentally quantum and not something else we've yet to discover/formulate that underpins QM and everything else?

You should read about Bell's theorem to understand what the alternatives are. Experimental data now makes the alternatives vanishingly likely.
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