Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

The Zen anti-interpretation of quantum mechanics (2021)

scottaaronson.blog

Post reply on HN
Print view View original

161–170 of 170 posts

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

#161

Post by layer8 »

goatlover wrote: post #159
Vecr wrote: post #60

Earlier quoted context omitted.

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).

The two cats are what the Schroedinger equation implies. The fact that you don't observe the dead cat is perfectly consistent with the Schroedinger equation. To deny the dead cat means that the Schroedinger equation doesn't describe physical reality, and that it has to be modified or added to in some way. There are ways to do so, but it makes the underlying model more complicated and more awkward. Occam's razor would suggest that the Schroedinger equation is the simplest and most parsimonious explanation for what we observe, despite it also predicting the unobservable (for us) other branches of the wave function.

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

#162

Post by _0w8t »

lmm wrote: post #155
_0w8t wrote: post #133

Earlier quoted context omitted.

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…

What is necessary is to find in the big wave function a subsystem consisting of, say, a particle with a spin and something approximating a classical measurement device.

Such 2-part subsystem should explain then how the classically-looking part gets the value it measures and the nature of probabilities.

Despite attempts nobody was able to find such subsystem.

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

#163

Post by lmm »

_0w8t wrote: post #162
lmm wrote: post #155

Earlier quoted context omitted.

> 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…

What is necessary is to find in the big wave function a subsystem consisting of, say, a particle with a spin and something approximating a classical measurement device. Such 2-part subsystem should explain then how the classically-looking part gets the value it measures and the nature of probabilities. Despite attempts nobody was able to find such subsystem.

For a sufficiently simplified model of a measuring device you can do that. I mean there's no getting away from having to use the Born rule, and I'm not as sanguine as Aaronson about the idea that that's adequately justified, but it's not like there's a better alternative.

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

#164

Post by _0w8t »

lmm wrote: post #163
_0w8t wrote: post #162

Earlier quoted context omitted.

What is necessary is to find in the big wave function a subsystem consisting of, say, a particle with a spin and something approximating a classical measurement device. Such 2-part subsystem should explain then how the classically-looking part gets the value it measures and the nature of probabilities. Despite attempts nobody was able to find such subsystem.

For a sufficiently simplified model of a measuring device you can do that. I mean there's no getting away from having to use the Born rule, and I'm not as sanguine as Aaronson about the idea that that's adequately justified, but it's not like there's a better alternative.

So far nobody was able to get such model unless I missed something. And the whole point of the decoherence exercise is to avoid Born rule as it implies a truly classical subsystem and we are back to where we started.

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

#165

Post by goatlover »

layer8 wrote: post #161
goatlover wrote: post #159

Earlier quoted context omitted.

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).

The two cats are what the Schroedinger equation implies. The fact that you don't observe the dead cat is perfectly consistent with the Schroedinger equation. To deny the dead cat means that the Schroedinger equation doesn't describe physical reality, and that it has to be modified or added to in some way. There are ways to do so, but it makes the underlying model more complicated and more awkward. Occam's razor would…

I understand, but Schrodinger himself came up with the cat thought experiment to demonstrate that he felt something was obviously wrong. A version of the Copenhagen interpretation would just say the wave equation is a useful tool for predicting experimental outcomes. We can't say what's really happening when we're not observing. So you don't need to add anything, you just give up on saying what's real. Which seems defeatist or anti-realist, but then one can always hold out hope for better experiments to one day show us what is really going on.

As for parsimonious interpretations, what does superdeterminism add?

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

#166

Post by Eupraxias »

still_grokking wrote: post #150
Eupraxias wrote: post #97

Earlier quoted context omitted.

All of this makes more sense when understood in terms of Field theory: David Tong: Quantum Fields https://youtu.be/zNVQfWC_evg?t=1168 "All the electrons that are in your body are not fundamental. All the electrons that exist in your body are waves of the same underlying field." The next question is, if there are no individual things, what does math count? http://www.katabane.com/mt/ontology.html

Differences. You can only measure (compare) something in relation to something else. If everything is homogeneous there are no measures, no clocks, and no way you could count anything.

Rephrased, what do numbers represent, if there are no discrete, fundamental things?

And if numbers represent the things we seem to perceive (discrete, fundamental things), though our science demonstrates that individual things are illusory.

The fun part is that the science which demonstrates the illusory nature of the things that math counts is dependent on the math.

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

#167

Post by DoctorOetker »

dekhn wrote: post #24

The right frame of mind is not "shut up and calculate", it's "shut up and make testable hypotheses and then invalidate them experimentally".

(self-)censorship has seldom brought progress, especially in science.

consider the question: is the distinction between theory A vs B testable?

if we can not yet verify that a distinction is untestable, it might still be testable, but we might just be missing the insight on how to construct the experimental setup to test a distinction.

if in fact a hypothesis eventually turns out to be testable, there is no guarantee that a single person or single group would have come up with such a test, perhaps devising the test requires careful and deliberate thought by a lot of people separated by location and or generations.

in that case, the prescription to "shut up and make testable hypotheses and then invalidate them experimentally" would be counter-productive advice, eliding the agressive "shut up" might do wonders...

as an aside, perhaps we fail to see the forest for the trees:

consider Youngs double slit experiment, the quantum mechanical version, perhaps with single photons or alternatively electrons, self-interfering with single particle detection on a screen.

according to the path integral formalism the particle is taking all possible paths, and the complex amplitudes are added together with their respective path-length-delays, i.e. "simple interference", except I only see course notes picturing the paths through slit A and B, and I never see the quantum mechanics books picturing the infinite number of topological loops: through slit A -> [back through slit B, through slit A again] x N -> to screen...

are many worlds interpretations truly untestable, or are we refusing to acknowledge their having been measured a long time ago?

what prevents a physicist from claiming all of the paths in the path integral formalism correspond to the system histories of the universe splitting over the (continuous or discrete) paths, and then merging by interference on the same final measurement point on the screen.

one can not explain the interference as long as one refuses to recognize the particle passed both slits.

if something so basic to the theory of quantum mechanics such as the single particle equivalent to Youngs double slit experiment could be recognized as not just proof of splitting histories, but also proof of merging histories, that might be seen as a paradigm shift.

what makes self-interference of a particle exploring all paths so much more palatable than simply claiming all these paths correspond to different histories of the photon, and those same histories merging through the laws of interference?

That would render the acceptance of interference into an acceptance of not just many worlds, but also the possibility of diverging histories interacting (at least in setups where interference takes effect).

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

#168

Post by chias »

consilient wrote: post #94
TedDoesntTalk wrote: post #86

Earlier quoted context omitted.

> There are no little billiard balls … electrons don't actually orbit Wait, what? What do they do then? My physical science education ended in high school.

The next useful falsehood on the ladder is that electrons in an atom exist as probability densities around the nucleus. Fire a photon here, and knock an electron off with this probability; fire it there, and get that probability instead. But before they interact with something, electrons aren't anywhere in particular. https://en.wikipedia.org/wiki/Atomic_orbital The real answer is that constituent parts of bound stat…

Thank you, this is the first time I've read a description of what an electron probability density means that has made real sense to me.

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

#169

Post by whatever1 »

graycat wrote: post #58

Sure, I'd like to read Aaronson and tried. My difficulty with quantum mechanics is much earlier, that is, more elementary and basic than what Aaronson considers. I've watched MIT lectures, looked into books by experts, ..., and I get nothing I can believe in. Right in the first hour, I get questions with no answers. E.g., (1) Wave Function. Okay. I can't find a definition of a wave function. Nothing subtle but just t…

.

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

#170

Post by lmm »

_0w8t wrote: post #164
lmm wrote: post #163

Earlier quoted context omitted.

For a sufficiently simplified model of a measuring device you can do that. I mean there's no getting away from having to use the Born rule, and I'm not as sanguine as Aaronson about the idea that that's adequately justified, but it's not like there's a better alternative.

So far nobody was able to get such model unless I missed something. And the whole point of the decoherence exercise is to avoid Born rule as it implies a truly classical subsystem and we are back to where we started.

> So far nobody was able to get such model unless I missed something.

If you model it as e.g. a quantum system with a state space that describes what you're measuring, coupled to a thermal bath, then it works. What kind of model are you looking for? Real measuring instruments are probably too big to ever model the full quantum state space of all the particles they're made up of, for example.

> And the whole point of the decoherence exercise is to avoid Born rule as it implies a truly classical subsystem

What do you mean by "truly classical"? The Born rule implies that our experience is the same as if we found ourselves within one of an ensemble of possible classical-like states with a certain probability, but, well, experimentally that's what we do; any interpretation of quantum mechanics needs to be able to recover that reality.

Post reply on HN