Does superdeterminism save quantum mechanics?

http://backreaction.blogspot.com/2021/12/does-superdeterminism-save-quantum.html

by nsoonhui • 5 years ago

77 118 5 years ago

backreaction.blogspot.com

Strilanc• 5 years ago

From watching the video and reading one of the papers, I get the sense that the theory being described doesn't work in the usual way. For example, reading the paper it talks about "future inputs" determining what happens, which seems impossible if you need to have the entire state specified for each time slice without need to reference other time slices. Instead of having a specific state for time t, and being able to evolve it forward/backward to other times, it is instead applying constraints across spacetime?

In principle, allowing yourself that kind of flexibility could be enough to model quantum mechanics. But I'm not sure why I'd want to do it that way instead of the existing ways. It's not particularly philosophically appealing to me, and objectively speaking it looks like they don't yet have a concrete mathematical model that actually reproduces quantum mechanics. But maybe I'm just ignorant of the latter part's existence.

SuoDuanDao• 5 years ago

I'm no expert in this field, but aren't the existing assumptions around time being independent at the slice we want to take a major reason why QM and General Relativity can't be reconciled? If so, that would seem like a good reason to look at alternative ideas in this space.

naasking18• 5 years ago

I think that's more or less correct. GR suggests "time" isn't independent, we instead have 4-dimensional "spacetime". The idea that future inputs can influence past configurations can be perfectly sensible in this context. It's like a restricted form of consistent closed timelike curves.

There was some development in this direction years ago:

The Logic of Quantum Mechanics Derived from Classical General Relativity, https://arxiv.org/abs/quant-ph/9706018

evanb• 5 years ago

I think you may be over-simplifying. We have relativistic quantum-mechanical theories, and we can formulate quantum field theories on curved background spacetimes.

323• 5 years ago

You might want to read about "block time" or "block universe". In this theory, everything is already pre-computed, like an uncompressed video file. So you can skip to whatever frame you want since there is no state.

It is sometimes referred to as the "block time" or "block universe" theory due to its description of space-time as an unchanging four-dimensional "block", as opposed to the view of the world as a three-dimensional space modulated by the passage of time.

https://en.wikipedia.org/wiki/Eternalism_(philosophy_of_time...

zikzak• 5 years ago

People who meditate often begin to slowly realize that ideas arise without concious thought. We imagine we are "thinking" but there really is no break in causality where we somehow choose how we want the future to unfold. Our brains are no more exempt from cause and effect than a marble rolling downhill is.

It is a mistake to confuse the finger pointing at the moon with the moon itself. We don't preceive everything, our senses are a filter that allows us to navigate but there's no more free will here than a plant turning to follow the sun. Fortunately, we don't experience reality this way. If we did, life would cease to be meaningful.

d--b• 5 years ago

I can’t agree more with the OP about free will and stuff. The main problem of superdeternimism though is that it both explains everything and nothing. It’s like giving up.

astrange3• 5 years ago

The explanation of superdeterminism she gives here isn’t a “full” superdeterministic theory (nothing actually happens over time, there are no physics, the universe is just a movie being played back, etc) and she does say it only applies at the quantum level. So there’s still room for science.

midjji2• 5 years ago

Just means she hasn't thought of the inevitable consequences. Besides, the paradox she is resolving isn't a paradox, she just does not understand the answer in standard QM.

midjji2• 5 years ago

Exactly so, its an interesting philosophical idea,but its by definition invalidates the scientific method, and all forms of meaningful reason. The correct answer to the question of if you are dreaming a dream from which you could never wake up isnt perhaps that explains why my math doesnt make sense, its: by premise that can not matter.

naasking18• 5 years ago

Exactly so, its an interesting philosophical idea,but its by definition invalidates the scientific method, and all forms of meaningful reason

It doesn't, and Sabine specifically addresses this point.

naasking18• 5 years ago

The main problem of superdeternimism though is that it both explains everything and nothing.

Not sure why you think that. You still have to explain precisely what is superdeterministic and what isn't, and elaborate how this works in a coherent way, and that process will end up telling you a lot. Is that really any different that accepting non-locality to explain spooky action at a distance?

thinkski2• 5 years ago

It’s also an inconvenient idea. For instance, how can one be guilty of a crime if one had no choice in committing it? Why try at anything if you have no choice — everything that will happen was decided at the universe’s origin and is merely playing out. It’s nihilism to the extreme.

Then again, the quantum idea of true randomness isn’t much better — if human choice stems from a coin flip, can you really call it a conscious choice?

The scientific method and human free will rely on a possible fiction of choice that is neither 100% deterministic, nor 100% random.

temp4385• 5 years ago

For instance, how can one be guilty of a crime if one had no choice in committing it?

Guilty is a social concept derived from the assumption that some events in the universe are "bad"

Why try at anything if you have no choice — everything that will happen was decided at the universe’s origin and is merely playing out.
It’s nihilism to the extreme.

Realising that there is no free will is not smth negative or positive. It's just smth which sets your further path which had no other purpose but spreading Life in the universe

naasking18• 5 years ago

For instance, how can one be guilty of a crime if one had no choice in committing it?

Why do you think you had no choice in committing it? Are you saying these people don't have any reasons they think justified committing a crime? That seems clearly false in general. Certainly if someone was literally forced to commit a crime, ie. they didn't want to do it, then they are not guilty, but why wouldn't they be guilty if they wanted to commit the crime and then did so?

This is a common confusion in thinking about moral responsibility under determinism.

"Choice" is a process whereby a set of options is reduced to one. This process is typically driven by an individual's reasons for acting, ie. there existed a hypothetical set of possible actions Y, but I did action X from Y because of reason Z. Z counterfactually describes why X was selected from Y, and when Z is an internally held value/justification for acting, this is a person's "will".

When a person is "free" to use their will to make choices, then they are acting of their own free will. If they are instead coerced into choosing W from Y instead of Z, where W is defined by somebody else's values, then they are no longer free to act on their will. This is Compatibilism, where free will and moral responsibility are compatible with determinism.

I also think it's important to distinguish "free will" as used in ethics and "free will" as used in science, where they speak of the experimenter's freedom. They are simply not the same thing, because one is compatible with determinism where the other may not be.

Why try at anything if you have no choice — everything that will happen was decided at the universe’s origin and is merely playing out.

What you're describing is fatalism, not nihilism or determinism. Given some tragedy is caused by a person, consider two scenarios:

1. they wanted that tragedy to happen

2. they fought tooth and nail to prevent it from happening

It's very clear to most people that the person in scenario #1 should be held responsible, where in #2 they should not. #2 is fatalism and absolves a person of moral responsibility, but this does not describe what happens under determinism. Under determinism, the people who make bad choices wanted to make those choices, and being held responsible is the moral feedback they need to correct their flawed decision process.

graycat3• 5 years ago

Uh, the OP frequently mentions "statistical independence", and I am uncomfortable with that: Independence is a property of a set of more than one random variable and is defined in probability, often used in statistics, but not defined in statistics. There is a polished, elegant, and thorough treatment of such independence, including of uncountably infinite sets of random variables, in J. Neveu, Mathematical Foundations of the Calculus of Probability.

PeterWhittaker• 5 years ago

In the context of Bell’s Theorem, statistical independence is understood to mean that, if extant, hidden variables are not correlated with how measurements are being performed.

Bell’s Theorem is only correct if this assumption holds. Hossenfelder is arguing that the assumption is incorrect: that Bell’s Theorem is incorrect precisely because there ARE hidden variables and that these ARE correlated with measurement settings.

She also argues that all mentions of free will in all related discussions are meaningless red herrings that have distracted physicists from properly interpreting Bell’s Theorem and observed violation of Bell’s Inequality.

Superdeterminism, arguably misnamed, simply argues that QM is deterministic, where Bell and others have argued it is not.

graycat3• 5 years ago

At least for now, I'm willing to f'get about issues of "free will".

Thanks, I will keep trying to make sense out of Bell's work.

I keep getting stuck trying to read quantum mechanics: One place was the claim that the wave functions form a Hilbert space. Nope: As I read in W. Rudin, Real and Complex Analysis, a Hilbert space is a complete inner product space where complete means that every Cauchy convergent sequence is convergent. Well, while the wave functions are likely points in a suitable Hilbert space, they can't be complete, e.g., they can converge to a point in the space, i.e., a function, that is not continuous and, thus, not differentiable in contradiction to the assumption that all wave functions are differentiable. I admit that this is a small point, but I was trying to take quantum mechanics seriously and be careful.

Closer to the OP, another place I got stuck was in the approaches of physics to independent and uncorrelated: In probability theory those two are not the same: For two real valued random variables, independence implies uncorrelated. As in W. Feller, in the case of two real valued random variables with joint Gaussian probability density function, uncorrelated implies independence. Generally, however, uncorrelated does not imply independence. Independence is a much stronger property than uncorrelated. Maybe eventually I will figure out what physics means by "uncorrelated", especially for Bell's work.

To me, we can take the Ace of Hearts and the Ace of Spades, shuffle them, and deal them out, face down, one each to Bob and Sally. Bob can go a light year away. Sally then looks at her card and knows right away, nothing faster than the speed of light needed, what Bob's card is.

We know all the associated probability distributions for Bob and Sally. And we know that as soon as the cards are dealt what each of Bob and Sally have is determined -- so far unknown but still determined.

I'm guessing that this Bob-Sally thought experiment may have something to do with entanglement, the EPR (Einstein, Podolsky, Rosen) paradox, "spooky action at a distance", collapse of quantum mechanics wave functions, and Bell's results -- but I need to keep studying.

akvadrako• 5 years ago

Superdeterminism, arguably misnamed, simply argues that QM is deterministic, where Bell and others have argued it is not.

No, this is completely wrong. Super-determinism is more than determinism. Super-determinism is about conspiratorial coincidences – so the measurement settings you choose just happen to be the ones which will make it look like the world is quantum.

Other quantum interpretations are also deterministic, like many worlds and pilot wave theory. Bell's theorem doesn't assume determinism, but most importantly (1) locality (2) counterfactual definiteness (3) a single classical world (4) no retro-causality and (5) no super-determinism.

myridium11• 5 years ago

Superdeterminism, arguably misnamed, simply argues that QM is deterministic

This is incorrect. QM is already deterministic. Where oh where do people get the idea that it is not?

kgwgk2• 5 years ago

I guess the whole field of statistical mechanics would make you uncomfortable.

graycat3• 5 years ago

What I have seen so far for statistical mechanics is uses of integral calculus notation that has nothing to do with anything in any version of calculus, advanced calculus, measure theory, the Riemann integral, Lebesgue integration, etc.

6gvONxR4sf7o2• 5 years ago

Superdeterminism needs some kind of simplicity, for lack of a better word. To take her vaccine trial analogy further, imagine that you randomly assign a group of 100 people to a treatment and control cell (50-50). It could happen that all 50 people in the control cell just happened to be the 50 most a priori healthy people in the group. But it’s extremely unlikely. Following the analogy, superdeterminism says it happens anyways. But the level of coincidence involved invokes such an absurdly complex series of coincidences, that your coin flip comes up heads on these particular people, that occam’s razor might as well spontaneously cease to exist.

Are there any superdeterministic theories that maintain the level of simplicity that the universe is posited to have without it?

candiodari• 5 years ago

The point is that it's only unlikely (or other situations likely) if the events, even from patient to patient, are random. If whether a patient is sick or not determined if they're in the placebo group or the healthy group, you would be testing exactly nothing. The randomness in placing the patient is a required part of the experiment. And more than random, the patient placement must be random and independent from their disease status (misdiagnosed healthy patients get treated too, after all. Generally it works quite well, as there isn't any problem to solve) and whether the treatment will work.

And of course superdeterministic theories are "simple". In the same sense that you can model any sequence as a function: just list all observed values for all time. Very simple, very little predictive power when you need it.

That also gives you the criticism of superdeterminism: if we do things that way, nothing needs an explanation, as it just can't be simplified from that full specification that we observe ... so there's no point to science. Note that it can still be more complex than we'll ever usefully realise, so whilst it means everything is determined, it does not necessarily (in fact quite unlikely imho) make it predictable for us limited beings.

But, in at least one meaning of the word, it's certainly simple. Every function in physics, whether quantum gravity or electroweak forces or the number of puppies your cat will have next year: f(x) = the x'th entry in the table ... (tables, of course, that you generally don't have access to)

Which isn't to say this is a strategy that can't work and perform useful functions. Take a robot for example, and look at inverse kinematics. That comes with 3d calculus, volume intersection (robot mustn't self-intersect), and there's not just limits in position but in speed, acceleration and torque as well. You can fully develop this theory. Or you can move the robot, observe all variables and save them to disk, then use nearest neighbour to figure out robot movement. Works like a charm, and doesn't even need to know how many arms the robot has. And while it takes a while, I bet it's a hell of a lot faster than building the theory for even the simplest of robots, never mind multi-armed or nonlinear robots. Plus it's trivial to make a machine learning algorithm do it for you, and the same can't be said of developing the correct theory for a new robot model.

6gvONxR4sf7o2• 5 years ago

The randomness here is a stand in for complexity. Substitute some other volume measure and the “probability” logic still works out, meaning that you can interpret “unlikely” as meaning “only happens in a teensy tiny sliver of phase space.” And with any reasonable way of trying to do randomness (coin flipping, PRNGs) it also means that it’s not just any sliver of phase space, it’s an extraordinarily complex sliver of it. Hence the original statement about how superdeterminism theories can potentially be. And hence the question about whether any of today’s superdeterministic theories avoid this extraordinary complexity issue.

naasking18• 5 years ago

But the level of coincidence involved invokes such an absurdly complex series of coincidences, that your coin flip comes up heads on these particular people, that occam’s razor might as well spontaneously cease to exist.

Sure, but the experiments you have to run to see these absurd coincidence are also absurdly contrived, so is that really surprising?

It's worth noting that Sabine's take on superdeterminism is also a bit different than past takes that are rife with "conspiracy", so I suggest reading her papers.

quantum_mcts• 5 years ago

I'm from the many-worlds interpretation camp, and this "superdeterminism" business always strikes me as ironic.

Proponents of hidden variables, in their desire to explain QM effects, arrived at the idea that there is something that permeates the Universe since the Big Bang and participates in every physical interaction. Existence of this something cannot be directly proven - since we are "inside" of it.

How about the "wave function of the Universe"?

effie• 5 years ago

Their goal is to find the deeper explanation behind wave functions, so obviously going back to wave function, even that of the Universe, is not very appealing to them.

myridium11• 5 years ago

Well if they insist on expressing the dynamics of the universe as the minimisation of a global (or local) action functional, then they are already throwing in the towel because that implies a wavefunction of the universe.

I'm suspicious that these fringe quantum-physics-deniers just don't understand the mathematics. They want to be relevant but they don't want to learn, so they post wordy, fluffy blog posts targeted at non-professionals. Like Sabine.

myridium11• 5 years ago

Totally agree. It's therapeutic to read this.

Last I checked, many-worlds is a consequence of current quantum theory, not a postulate or additional axiom. Yet people treat it like such. Probably because it's 'spooky'. Then indeed it's ironic that they search for alternative explanations which try to say the same thing as many worlds but without saying 'many worlds'.

naasking18• 5 years ago

Last I checked, many-worlds is a consequence of current quantum theory, not a postulate or additional axiom.

There is an additional postulate, namely that the state vector is the real world we inhabit. This may seem obvious to you and not amount to postulating much or anything with any substance, but that's a philosophical claim that isn't suggested by the physics.

There are also the problems of deriving the Born rule from the existing postulates of MWI. Last I checked, the existing derivations are not fully satisfactory to most physicists.

8note3• 5 years ago

There's is definitely an axiom built into many world's.

Something along the lines of "things we don't observe are as valid and exist as much as things we do observe"

That's an addition over the usual "things we observe exist"

naasking18• 5 years ago

Proponents of hidden variables, in their desire to explain QM effects, arrived at the idea that there is something that permeates the Universe since the Big Bang and participates in every physical interaction.

Actually that's not correct. In Bohmian mechanics the wave function is not actually real, it merely describes a law of motion. You're doing what many MWIers do, and applying the ontology of MWI to other ontologies and concluding they assume redundancies. That's just not how it works.

nimish• 5 years ago

There are other possible choices that reject superdeterminism but are still ok: https://arxiv.org/abs/1907.05607 -- you have to abandon either locality or the assumption that observed events exist absolutely

Personally I think it's easiest to reject the "absoluteness" of events and subscribe to RQM or QBism. Superdeterminism is a little boring if ultimately plausible.

meroes3• 5 years ago

"If statistical independence is violated, this means that what a quantum particle does depends on what you measure."

But in standard QM without superdeterminism, what a particle does already depends what you (i.e. the experimenters) measure - how you set the relative angles of your detectors determines the amount of correlation, even when setting them at spacelike distances after the entangled pair is released (say Alice chooses hers and Bob his without any communication between them.

It's the same physical facts and we either take superdeterminism or quantum nonlocality (or other interpretations not at issue here). To me the conspiracy of superdeterminism is too great.

mrjangles• 5 years ago

Yeah this seems like yet another attempt by someone to use different words to explain the exact same quantum theory we have always been using, then trying to claim because they used different words they somehow came up with a special new theory.

naasking18• 5 years ago

What you describe is "quantum contextuality". What Sabine is saying is that so-called superdeterminism/giving up statistical independence implies the contextuality that is needed to explain quantum mechanics using hidden variables, and it does so in a simple way if we accept future input dependence.

meroes3• 5 years ago

Bell nonlocality is not the exact same thing as contextuality from what I’ve been able to find.

rafaelero7• 5 years ago

This is the first time I've read some way of looking at quantum physics that actually make sense. I hope it is indeed correct and all those ~smart people who were putting their ridiculously complex theory of quantum physics at our throats end up being ridiculed.

myridium11• 5 years ago

You're exactly the target audience for her content :) .

rafaelero7• 5 years ago

I suppose. It does seem pretty logical that statistical independence between measurement and particles could be violated, and I am just a newbie. If someone could explain why people overlooked this fact I would be very interested.

sigmoid10• 5 years ago

This reminds me of Feynman's famous quote: "If you think you understand quantum mechanics then you don't understand quantum mechanics." Frankly, I'm baffled how some scientists still clinge to classical physics and absolute determinism, just because they describe our macroscopic world nicely. People have tried to argue against quantum principles 100 years ago and some still do it today, even going so far as to believe that the entire universe conspires against us since the big bang (which is what supetdeterminism boils down to in light of things like entanglement) rather than accept the inconvenient truth: our universe is much stranger than classical physicists could have envisioned.

rafaelero7• 5 years ago

Going with "if it is not weird enough, it can't be right" doesn't seem very scientific to me.

raylad6• 5 years ago

I got a bit lost at the double slit experiment with superdeterminism. Can someone clarify what is supposed to be going on?

* We send one photon at a time through a double slit, don't measure them, and an interference pattern is formed, presumably because the probabilities of the particle going through each slit interfere with each other.

* If we measure the position of the particle, it goes through only one slit, and there's no interference pattern created.

* Standard QM says that the probability wave function representing the position of the particle "collapses" when measured and the particle then goes through only one slit with no interference when we measure it.

* Superdeterminism says that the initial state of the universe determined that we would measure the particle, and therefore it goes through one slit and there's no interference.

* What I don't understand is: why would there ever be interference in that case? If it's not probabilities interfering with each other what causes single photon interference in the double slit experiment in superdeterminism?

Koshkin7• 5 years ago

Well, the thing is, neither the standard (non-local) quantum mechanics nor the superdeterminism answer this question, as they both simply talk about a wave function and its taking a different shape depending on what measurement is made; the only difference is that one completely gives up on futher clarification of what the wave function physically represents while the other encourages looking for hidden variables.

raylad6• 5 years ago

I've heard the interference discussed as an "interference of probability amplitudes".

But in superdeterminism, it seems as if there are no probabilities in that sense, or am I missing something?

rafaelero7• 5 years ago

Superdeterminism says that the initial state of the universe determined that we would measure the particle, and therefore it goes through one slit and there's no interference.

Where did you get this from? I don't think Sabine implied that. From what I understood, it is more like the measurement interacted with the particle and it changed its behavior. I don't see why we need to consider that it was always meant to be that way.

raylad6• 5 years ago

It seems that can't be true, because if you randomly decide after the particle is launched whether to measure it or not, the interference pattern still appears.

So it's not the measuring that does anything in superdeterminism apaprently, it's that if you do measure it, that was "known" in advance by the state of the universe.

If not that, what is supposed to be going on (physicists please respond).

8note3• 5 years ago

determinism implies that afaik?

8note3• 5 years ago

Nit: the single slit case still gives you an interference pattern. It's just that it's a single slit pattern and not a double slit one

alex_young2• 5 years ago

Once you understand what’s going on with the double slit, all the other quantum effects that are allegedly mysterious or strange also make sense. Take for example a delayed choice experiment. In such an experiment, it’s only after the particle started its path that you decide whether to measure which slit it went through. And that gives the same result as the usual double slit experiment.

Delayed choice seems pretty silly in relativistic terms to me. If photons are massless, and distances they travel are 0, then there is no such thing deciding to measure the slit after the photon is emitted but before it reaches the slit, right? That's just a figment of our reference frame.

Koshkin7• 5 years ago

But reference frames do have physical significance (and the distance traveled does depend on one).

alex_young2• 5 years ago

So, from the photon’s perspective (I know perspective isn’t right, but I’m not sure what else to call it), the distance traveled is 0, and the emitting and measuring happen instantaneously right?

What I’m struggling with is what it means to the experiment to move a measurement into the system between these events if they are at the same moment according to the thing being measured.

thyrsus• 5 years ago

The post suggests that carefully designed experiments could settle the question. I hope they get performed.

Does superdeterminism save quantum mechanics?

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