I really agree with you here. Superdeterminism is much weirder and harder to accept than non-locality. Of course, with enough non-locality you'll end up with something just as awkward as superdeterminism. I'm trying learn more about decoherence as an alternative to wave-function collapse.

I'm listening to the Into to QM course from mit's open courseware [0] and I have to say that QM represents a complete break with the classical past, not because of a scientist's ambition or a quirk of history, but because the experimental evidence demands it. The evidence results in a few postulates, and QM is really the only theory that satisfies the postulates, in the sense that any theory that satisfies those postulates will look like Schroedinger's eq. The story is not over at all, we're still very much at the beginning of understanding it.

[0] https://ocw.mit.edu/courses/physics/8-04-quantum-physics-i-s...

To me decoherence always seemed so obviously the solution to these 'problems in QM' that I genuinely don't understand why are still having these quasi-scientific discussions. Am I missing something or is there a ton of uninformed arm-chair science going on?

What are the scientific arguments against decoherence? What do up-to-date theoreticians think?

Think of it this way - decoherence depends on regions of the wave function more or less becoming isolated from one another in such a way that the results of experiments for classical things in those regions match our results. The wave function is still fundamental, but classical physics emerges as a limit.

The problem with decoherence is that the underlying physics of the wave function is still profoundly non-local in the sense that regions of the wave function don't have a simple relationship with regions of physical space.

And yet, classically, the notion of locality pertains precisely to physical space and is deeply related to fundamental physics. In fact, locality is still fundamental to the formulation of quantum mechanical theories, even if the quantum mechanical description ends up having some non-local features. And there isn't any philosophical or physical intuition that resolves this disconnect.

Decoherence has a variety of other philosophical issues. In particular, it requires that we accept the idea of the wave function (something we never see or interact with directly, for which we have no direct evidence) as fundamental and real AND that we take our day to day experiences, upon which all of our physical sciences are based, as derived, perhaps even, in important ways, not really real. In any case, the actual theoretical terms in which decoherence actually resolves the measurement paradox aren't fully understood either mathematically or in terms of the fundamental ontological status of things.

Thank you for this very well articulated response.

I don't see why locality is a requirement. What is it that makes a theory with particles being points in a six-dimensional position-momentum space acceptable, but particles being complex-valued functions over a three dimensional space unacceptable?

> it requires that we accept the idea of the wave function (something we never see or interact with directly, for which we have no direct evidence) as fundamental and real AND that we take our day to day experiences, upon which all of our physical sciences are based, as derived, perhaps even, in important ways, not really real.

I see no issue in pure quantum states being fundamental. Our day to day experiences are not compatible with a number of things we hold to be true. Take the physics of fluids for example, it suggests that liquids are infinitely dividable, which we know to be false. In that sense, fluid physics is decidedly not real. But it can also be derived as a very good approximation of the underlying reality on larger scales, similarly to how classical theories are good approximations of the underlying quantum reality on larger scales.

I do realize that my interpretation requires decoherence to work such that the pure quantum states reduce to ones that are well approximated by classical theories, and I'm not sure if we have evidence that decoherence works this way.

No mainstream physicist really objects to decoherence - it is obvious. But just decoherence doesn’t give you single outcomes - it gives you many worlds.

And people do debate how to derive our single world experience from many worlds. It can’t be done without more assumptions.

Many in this field do accept it, but say the other worlds are not real (QBism, dBB).

But that position is philosophically weak, so those against many worlds still look for alternatives.

Decoherence does not give you Many Worlds, or at least not unless you interpret it that way.

Decoherence or more strongly environmental super-selection from something like electromagnetic scattering, results in a Classical probability distribution over the macroscopic observables or more accurately renders the algebra of classical properties Boolean. This means there is no interference between the terms and the probabilities are simply ignorance of facts which have occurred.

Once this superselection process has occurred the mathematical structure of macroscopic observables is just as it is in classical statistical mechanics. There's no need to read this as multiple worlds, although you can if you want to. If interference terms persisted you might have more of a case for Many Worlds. Even then though there are other ways of reading the formalism.

I think when you add in the word "experience" you turn the physics problem into a philosophical one, and every pragmatic scientist wanders off to work on something else. Many worlds is totally sufficient for every question except for the nature of consciousness, and there are some very good reasons to believe that consciousness is non-empirical.

I don't see many-world arising from decoherence, please elaborate.

Decoherence doesn't give you single outcomes, but it gives you a classical probability distribution (like an enthropic ensemble) over pure quantum states, with the pure quantum states having reduced coherence (i.e. they 'look classical').

Classical probability distributions are nothing new, we don't need a many worlds interpretation to explain the butterfly effect.

Quantum states with a small amount of residual superposition also seem fine to me, as long as you are willing to accept that the world is ultimately quantum and not classical. That we don't see any quantum effects in daily life is just because the scales are too small, similar to how we don't observe relativistic effects because the scales are too large, or how we don't observe the atomicity of water. But in all these cases we can do experiments to reveal the true nature.

So during decoherence you don’t have classical worlds - the probabilities interfere so you can’t ignore the other terms. Over time that interference reduces, but as you say never disappears completely.

But at no point does one world even approximately emerge - it’s always many. I can say only the one I experience is real, but there’s no justification for it.

Your main problem though is thinking classically - you can't justify your theory by saying it can be reduced (after an infinite amount of time) to an old way of thinking. Classical probability is fraught with issues; just saying it’s always been acceptable isn’t true nor a rational argument.

What are the issues with Classical probability relevant to accepting there being a single world?

But, uh, a single world experience is trivially compatible with many worlds — in every world, the human is in a pure state that corresponds to a normal human experience of continuously living in a single world. If we don't require the conscience to be a single supernatural entity that flows along the timeline, selecting a world to visit at every branching point, then... that's it? Nothing else that still needs to be explained?

I apologize for the naivite of my line of thinking but wouldn't the locality of Relativity slot in at that point? Other realities could all be real, but only a subset could be real/accessible from the perspective of a given measurement device. As a guy who reads popular books on the subject to fall asleep, that seems like the obvious place for the two theories to couple. What am I missing?

Decoherence on its own still has a basis problem. You need superselection to reduce that to one basis. However this has been shown long ago (1980s) so in essence decoherence + superselection does solve these problems.

If you're not familiar with these terms I can explain.

There's intuition built on copenhagen interpretation, like probabilities and such, and people want to elaborate on that intuition.

Just out of curiosity, what is weird about non-locality? From my super naive perspective that's just saying that things don't necessarily work underneath the hood the way they appear to work. For me (super naive, remember ;-) ), that seems completely reasonable even if it might be very inconvenient. What am I missing?

You're missing special theory of relativity. Nature is local. When you add nonlocality, contradictions arise, you can try to just ignore them or patch them with ad hoc hypotheses, such things were tried before and turned out to be failures indicating that the premise is wrong.

Interesting. If you have some pointers for something to read that discusses why special relativity requires locality, I'd love to read it. I have no real idea where to start searching.

Edit: Just to be clear, I'm aware that Bell's theorem says that QM must either break locality or realism, but I don't really understand why it can't break locality. While incredibly inconvenient, wouldn't that solve the problem? Again, I realise I'm naive, so I don't actually suppose my line of reasoning is correct ;-)

Special relativity is essentially an explanation of why the speed of light is a constant regardless of how you measure it. That is, if you're in a train moving at half the speed of light relative to the ground, and someone fires a laser in the same direction as the train from the last station you passed through, that laser beam will move towards you at at the speed of light. If you fire a laser back, it will reach the station at the same time as the laser from the station reaches you (as seen by an observer in the station).

This makes no sense unless the speed of light is a fundamental physical constant, so that motion in general depends on the speed of light, which is what special relativity postulates.

Now there are ways to have a special kind of non-locality that do not violate special relativity - you can have phenomena that happen at infinite speed, but only if they do not carry mass or energy or any information at all. The common interpretation of wave-function collapse is an example of such a phenomenon.

I'd also note that the famous E=mc^2 is also a limit on speed, since kinetic energy (mv^2/2) is part of the total energy of an object.

There are interpretations of quantum mechanics that give up on locality, most notably the Pilot Wave Theory[1]. It does work, and it is compatible with relativity.

I think that may be the reason it's not very popular: ok, so we've got these faster-than-light pilot waves, but we can't actually use them to do anything faster than light. They're just there for bookkeeping. (That said, Many Worlds suffers from the same problem, but it's very popular. They're two different ways of slicing up the same equation. You pick whichever one suits you.)

[1] https://en.wikipedia.org/wiki/Pilot_wave_theory

Physics is trying to fit reality to an equation, it is not reality itself. We don't know what an atom "is", we just know how it behaves with high precision.

If the simplest and most consistent math is a non-physical pilot wave, I don't think this really matters if it lets you calculate something more easily or correctly. I don't personally know how to use them (my five QM courses used traditional techniques) but if they give useful results it hardly matters if they're "real".

My good friend did his undergraduate thesis by noticing that Clebsch–Gordan coefficients could be used to describe grain boundary orientations in polycrystalline materials. Doesn't mean grain boundaries have spin. It's just math that was convenient and worked well.

There's a lot to be said for shutting up and calculating. If I were a physicist, I might subscribe to that myself. Since I can't calculate myself, I try to remain agnostic even to that extent.

That said, physics advances do sometimes come from asking "What if X is real?" The positron and electron spins are both poster children for that. Instead of just shutting up and calculating, people focused on the part of the calculation that seemed to imply the existence of an unobserved thing. We could, in fact, have kept going with a physics in which positrons were merely calculation conveniences; that physics is valid. But we might not have discovered the Standard Model that way.

So I'm of two minds... and in a lot of ways, I'm not really entitled to be of any minds, since my formal education stopped at undergrad, and I'm no longer capable of doing even that much math. I get leery when people with even less education want to "understand" without doing any of the math, because I fear that the best of explanations will only mislead them.

I'm not sure I understand why you see this as a dichotomy. Sometimes inspiration comes from a weird idea, sometimes it falls out of mathematical analysis.

It's not like it is exclusive, everyone thinks a bit different thankfully. Like your example of the positron and electron seems fine; math and experiment in a cycle of discovery. You wouldn't know to look for a positron if you didn't study the electron experimentally and try to come up with some math for it.

Contradictions are inconsistency in the theory, i.e. the theory can give different results depending on how you compute. To evade this you need to apply abstract reasoning outside of theory to decide how to compute in every situation. This means theory doesn't work by itself, i.e. it's not an objective theory. Also by realism Bell means hidden variables, not realism at large.

I can't see what's so hard about it either. Nor what would be the problem with something like hidden states/variables. Why would it be so hard to assume that there could be hidden states in partcles which we simply can't measure (maybe not yet)? Why does the world has to be directly measurable? Who told people that they ought to be able to measure every single variable directly (like hidden state of a quantum particle), why are they assuming that?

You should look into Bell's theorem. It is mathematical proof that (discounting superdeterminism) there is no way to explain QM observations with local hidden variables. You could have hidden variables, but only if they produce effects at infinite speed.

The big problem with infinite speeds is that, somewhat like superdeterminism, they mean that you can't do fully controlled experiments. If effects can propagate at infinite speeds, the whe universe has an impact on any experiment, including the state of your measuring apparatus and so on. That doesn't make them impossible, but it explains why they are disliked in theories.

I know that they cannot be local. My point of view is "just let them be global, build theories from there", global hidden variables don't interfere with any intuitions about the world for some reason.

The problem is you can't really build theories from global hidden variables. If the details of any experiment depend significantly\* on the state of the entire universe, until we can account for the entire universe in our measurements, we might as well stop measuring.

\* even with Newtonian physics, the universal attraction of any object does have non-0 values everywhere, but we know that the influence is negligible. However, with global hidden variables, the speed a billiard ball will take when I hit it may depend on the size of a planet in a different galactic cluster.

> If the details of any experiment depend significantly\* on the state of the entire universe, until we can account for the entire universe in our measurements, we might as well stop measuring.

Every experiment does depend on the entire state of the universe, even in QM, but those influences are typically small due to symmetries. At the quantum level, many of these symmetries no longer apply.

I also have a hard time disbelieving in global variables. We have a lot of evidence validating quantum field theories, and the fields in QFT are global.

Only in a trivial sense. Quantum Field theories are explicitly local theories, constructed from Langrangians which purposefully have and express Lorentz invariance, exactly to maintain locality.

In any case, quantum field theories are good at predicting stuff but almost certainly not descriptions of the true fundamental dynamics of the universe, given their known and relatively well understood divergences.

Those hidden variables have to violate known physics in order to exist. So that's a pickle.

well, that's the point isn't it? They're saying that "known physics" is wrong

incomplete

> Superdeterminism is much weirder and harder to accept than non-locality.

I disagree, with the following example to back up why I believe it is less weird.

Superdeterminism can mean that faraway events can be correlated by a common ancestry. For instance: if you suddenly create a massive object, it will attract massive objects indiscriminately spherically; most points in space will be eventually affected, and so, they all are limited in the space of possibilities, no matter whether you can actually detect gravity.

In the case of quantum mechanics, there may well be some currently-undetectable field similar to the gravitational one, which is very chaotic at a nanoscopic level, but that is severely constrained in the shape it can form, even across large distances.

It is similar to how a large-space LCG (the PRNG) may look extremely random, but if you plotted consecutive numbers as coordinates across the complete cycle, you would get a lattice. Locally chaotic, but globally constrained.

On the other hand, non-locality means superluminar information, which really breaks the common understanding of spacetime and of causality.

How would this field work with Bell's inequality (the no-local-hidden-variables theorem)?

Here's that previous discussion, for the curious. https://news.ycombinator.com/item?id=21802674

"The implications of superdeterminism, if it is true, would bring into question the value of science itself by destroying falsifiability, as Anton Zeilinger has commented" [1]

[1] https://en.m.wikipedia.org/wiki/Superdeterminism

> The implications of superdeterminism, if it is true, would bring into question the value of science itself by destroying falsifiability, as Anton Zeilinger has commented

Except Zeilinger is wrong. The freedom of the experimenter is not fundamental to the scientific process, rather the nature of the experimenter's complexity is what matters. Even simple deterministic algorithms can explore an entire state space, and given we are capable of simulating such algorithms with our brains (Turing completeness), we are therefore also capable of exploring the full state space of physical theories.

Furthermore, it is not a false picture of nature at all. It very clearly describes the behaviour of that which is observable, which is exactly what science is designed to do.

A simple description of superdeterminism would be that it's a theory of hidden variables where those hidden variables evolve with intelligence level complexity. It's a traditional method to evade falsifiability, yes :)

These criticism sound quite convoluted and hyperbolic when its really just saying some kind of intrinsic selection bias is a possible explanation.

Yep. Superdeterminism as a particular physical hypothesis has nothing to do with a philosophical notion of determinism or debates about free will. The latter is really the subject of metaphysics which by definition is not physics.

It is like mixing implementation details of a particular Python script with a theory of programming languages.

Someone who knows, that determinism can be a metaphysical concept (depending on which determinism one is talking about). Not many people get that. Good to see some people actually read about it or thought about it. This is what I always try to explain to people trying to counter it with quantum mechanics, as if it was a proof against determinism.

I'm interested. Could you expand a bit more on this? You imply there are different types (levels?) of determinism. Which are those?

I can try for grandparent. In physics all equations including quantum mechanics are deterministic in the sense that if one knows the initial state of the universe then one knows evolution of the universe after and before. Moreover, in classical physics the assumption was that if one knows the state of some local patch of the universe at some moment, then one in principle can tell the near future and past of that local patch without knowing the state of the rest of the universe.

Experimental observations of violations of Bell equations tell that no, one cannot tell the evolution of the local patch from the patch alone. Standard interpretation of quantum mechanics and physical super-determinism are just different ways to explain this.

In particular the standard quantum mechanics assumes that things are still local, but the wave function is not observable in principle so we can only talk about statistical properties. Super-determinisme assumes that things are not local and tries to explain how.

In philosophy determinism is essentially the opposite of free will. It implies that what people perceive as personal free will is an illusion. But this has nothing to do with the determinism of physical models. In particular, free will is compatible with physical determinism of what one perceives as an external world. One possible explanation of how this is possible is that the act of free will changes both future and past. So it looks like the future state reflecting the choice of will is deterministically follows from the past. It is just the past is different from what would be if the choice would be different. Stanford encyclopedia entry on free will has more splendid explanations.

Thanks, this was very clearly written, though I'm already familiar with it. If I got it right, you're saying that the levels of determinism refer to the difference between physical determinism and metaphysical ideas (of which the idea that a conscious being's will influences both the past and the future is an example)?

> But this has nothing to do with the determinism of physical models.

It seems rather confusing to state it has nothing to do with determinism of physical models. More accurately, it does have to do with determinism of physical models if you assume a physicalist perspective, but it might not, though then you have to resort to much more involved and comprehensive models of what consciousness and will are (like changing both the future and past).

Physics cannot address the question of free will at all, as all our experiences tell that at least globally universe is 100% deterministic. So one need to go beyond physics to address that.

This is similar with the notion of time. A typical perception is that only now exists. Yet according to physics there is no now. All our physical models based on experience imply that the universe is 4-dimensional static something. There is no now and all points across the time dimension have same properties just as points across space.

One needs metaphysics to try to explain this discrepancy between perception and very successful physical models.

> as all our experiences tell that at least globally universe is 100% deterministic.

I'm not sure what you mean by this so I'm also not sure how to address it, but it does seem reasonable to assume free will simply does not exist exactly because phenomena is either deterministic or stochastic, not some third option which would allow free will. This view is informed by physics.

> There is no now and all points across the time dimension have same properties just as points across space.

This is a much more interesting problem and one that has kept me up many times.

I meant all our fundamental physical models are fully-deterministic globally. The only exceptions are singularities of General Relativity, but even for those the believe is that a proper accounting of quantum effects should resolve this. We build those models based on experience. So here is comes the contradiction with personal perception. One can always say that it just implies that free will is an illusion. But as there are other ways to resolve this that keeps free will and are compatible with apparent determinism of external world, the inevitable conclusion is that physics cannot resolve the issue of the free will.

As for the problem of now, for me it is similar to the problem of free will. Starting from Parmenides and Buddha one way to resolve this was to declare that the perception of now and movement is an illusion similar to the notion of free will. And as with free will, that will be compatible with physical models and the opposite cannot be expressed within physical models.

Evolution of the local patch is predictable from the patch alone. Violation of inequation is when this evolution has correlation with a distant patch. Copenhagen interprets this correlation as causation, hence FTL.

> Evolution of the local patch is predictable from the patch alone.

How do you know, that there is no non-local influence, that makes your predictions "from the patch alone" incorrect? I don't think this can be easily excluded as a possibility.

We can assume that there is no non-local influence and try to make progress from there, but we might be wrong about it, which is what the article is getting at, if I understand it correctly.

The article describes nonlocality, but doesn't support it. Instead it supports superdeterminism, which is local.

> Evolution of the local patch is predictable from the patch alone.

Only if you take the experimenter and his decision as part of the local patch, and take the decision to be determined by the same state which also determines the experiment's outcome, which is essentially what superdeterminism is, no?

Predictability is essentially determinism, not necessarily superdeterminism.

Every time I search for it, I seem to need to go through many websites with wishy-washy explanations. Then I found: http://catdir.loc.gov/catdir/samples/cam051/2004045179.pdf where it lists 4 types in the table of contents (just search for "determinism" in the document). However, some other websites list more types, where some of them imply the others. For example: https://www.philosophybasics.com/branch_determinism.html Recently I had an interesting discussion with a coworker, but I cannot find the website we shared to clarify, what I meant by "deterministic".

Basically the metaphysical determinism says, that everything is predetermined and if something seems random, it is simply because of something we do not know yet or something that is too complex to be calculated, so that we cannot predict the event that seems random. Whatever physicists come up with, for example quantum whatever, one can always say: Well, it seems random, but I believe, that there is something we have not yet discovered or don't yet know about, which makes things behave exactly as they are, completely deterministic.

At that point it becomes a believe, not a science. You can always add an unknown (or "hidden variable"). Personally, I do not think this believe is in any way worse, than the believe, that something "simply happens at random" with "no theoretical way of explaining why". Probably metaphysical determinism in one way or another has always been a big motivator for scientists to continue research.

Agreed. This line:

> But because of the historical legacy, researchers who have worked on or presently work on Superdeterminism have been either ignored or ridiculed.

is too strong. I would say that the historical legacy does not have much to do with it - the reason that superdeterminism is ignored or ridiculed is that it looks absolutely wild to most physicists - much more mind-bending than the vanilla story of the Bell test, which is mad enough to begin with. That's not to say that it is ruled out - just that we have avoided it for pretty sensible reasons, rather than stupidity or some sort of blind spot.

> That's not to say that it is ruled out - just that we have avoided it for pretty sensible reasons, rather than stupidity or some sort of blind spot.

I have to question the validity of this argument, because generations of physicists have been taught to give up realism in order to accept QM. Superdeterminism is no weirder than giving up realism, it's just a weirdness to which you've grown accustomed.

I think of superdeterminism not as a theory but as a barometer - the Bell's Theorem world we live in is baffling enough that people are willing to consider superdeterminism as an explanation.

I was curious so I looked up your comments.

> There is no such thing as a controlled experiment

> The superdeterministic explanation is: "well, there's nothing to explain. You were simply determined to lose by the initial conditions of the universe. It couldn't have gone any other way."

This eventually led me to a quote from Anton Zeilinger about his dislike for it.

> I suggest, it would make no sense at all to ask nature questions in an experiment, since then nature could determine what our questions are, and that could guide our questions such that we arrive at a false picture of nature.

My question is, does it matter if we are seeing a false picture as long as the result of experiments within it are consistent and lead to new discoveries that themselves are actionable? If everything we experience is in this “false picture” is it really false or simply a different set of rules based on underlying circumstances.

I think the whole point being made by the authors here is that QM is dead-ending and that superdeterminism could give us more answers, not less. Why not see if it leads somewhere?

Superdeterminism is like the whole existence being a Haskell program without I/O. To get anything actionable we'll have to logically separate parts of it...

first discoveries were done without a sound theory, it's certainly possible :)

>authors here is that QM is dead-ending

Copenhagen is dead-ending, not QM.

In general all these interpretations are more popular on the technically literate web going culture than in actual research in physics where Copenhagen style views still predominate.

For the simple reason that all of the other interpretations (Many Worlds, Bohmian, Transactional) only somewhat work with Non-Relativistic QM not with QFT. Only Copenhagen works with QFT.

What even is superdeterminism? Determined determinism? What?

What is need is less arguing and more experimenting. That's how this will be resolved.

No no, arguing is important. It lubricates an essential step in the scientific process. No one can design experiments, let alone predict results or even understand results, without understanding.

Let me clarify. In this particular case there has been plenty of arguing already and no progress in more than 50 years. So I'm suggesting it is time to start experimenting more.

The authors don't argue that there's not enough experiments, though. They argue it's wrong type of experiments that are conducted.

To quote Dr. Hossenfelder directly: "In standard quantum mechanics the measurement outcomes will be non-correlated. In a superdeterministric hidden variables theory, they'll be correlated - provided you can make a case that the hidden variables don't change in between the measurements." [1]

That last sentence is the catch here: in case the experiment fails to show any correlation, it can always be argued that the hidden variables changed for whatever reason. If the calculated theoretical boundaries (e.g. temperature & measurement time) are insufficient, there's still no way of telling systematic errors from falsifying the initial hypothesis. It's little details like this that theorists can hide behind while still shouting "Foul!" from the peanut gallery.

Since experiments cost time, money, and pin down talent, research facilities need to be picky about what they test. "Because I like it." [2] is not the most compelling argument when trying to make your case ;)

I wonder whether crowd-funding would work in this case...

[1] https://backreaction.blogspot.com/2013/10/testing-conspiracy...

[2] https://www.fetzer-franklin-fund.org/wp-content/uploads/2014...

This has been the mainstream position for most of those 50 years. Working on the "foundations of physics", which is what you call "arguing" was considered disreputable and career-destroying for a long time. Read, for example, "Something Deeply Hidden" by Sean Caroll for more about this.

A lot of really really smart people tried to solve this by experimenting more. It didn't work. It's time for philosophy again, and in my view, also to accept that the weirdness is not going away. Nature doesn't care about what we find weird or not.

I've been partial to superdeterminism for a long time, but I have no idea how one would go about testing it. In fact, it seems as unfalsifiable as many-worlds or other theories. Do you have a suggestion?

The kind of superdeterministic theories proposed by t'Hooft are falsifiable. From [0] "If engineers ever succeed in making such quantum computers, it seems to me that the CAT is falsified; no classical theory can explain quantum mechanics." By "such quantum computers" he means computers that can run Shor's algorithm. "...but factoring a number with millions of digits into its prime factors will not be possible – unless fundamentally improved classical algorithms turn out to exist."

As for the author of the article I've never seen a clear proposal but it appears the idea is to do repeated measurements that display quantum effects while reducing noise as much as possible and check if there are deviations from quantum theory.

EDIT: found a more concrete proposal http://backreaction.blogspot.com/2013/10/testing-conspiracy-...

[0] - https://arxiv.org/abs/1405.1548

My understanding was that many-worlds could be tested experimentally if we were able to set up large objects in superpositions, and I thought that there is no reason to expect that it isn’t physically possible to do so (we just don’t know how at the moment).

You can’t get any information from that because the main interpretations all make the same predictions from an outside perspective, which is what you’ll expect to see.

Besides to put a person in a superposition may require a machine as large as the universe, so you get issues with the speed of light.

The only way to test MWI is multiverse immortality - many worlds means you should expect to always have some future experience - there is no real death.

Some version of you will expect it, some versions won't.

>set up large objects in superpositions

EPR experiment does exactly that. In fact, it's a good experiment to get intuitive understanding of MWI.

Hossenfelder proposes[1] to measure non-commuting variables in identical systems in as noise-free an environment as possible.

In standard QM says the measurements should be completely uncorrelated, but she argues that in a superdeterministic theory results somewhat correlated.

[1]: https://arxiv.org/abs/1105.4326

The progress is stiffled by belief that this is not a problem and there should be no arguing and no experimenting and everybody should shut up and calculate.

Superdeterminism says that arguing is a part of the experiment anyway.

You can't.

Not just the way it's arbitrarily hard from an engineering perspective to design an experiment to disprove string theory. It is theoretically impossible, the way it's impossible to distinguish between Copenhagen and many worlds.

No, you actually can. The authors of this article discuss the issue more in their longer paper here: https://arxiv.org/abs/1912.06462

The idea is that superdeterminstic theories are deterministic, while quantum mechanical measurements are random, so you should be able to set up an experiment where QM predicts you would just get random results, but actually you get the same result each time.

There are many classical physics experiments you could do where you understand all the physics and formulas to excruciating detail and you control every variable but you still can't get the same results everytime. Things like throwing dice, as mentioned in the article, or the chaos generated by flowing fluids. Given that any superdeterministic mechanisms would be even even more complex and weird and unknown it seems impossible to disprove. Any failed experiment could be excused by saying that there are more unknown uncontroled variables.

Well, the determinist would argue, that, if you cannot predict the result reliably every time, you do not actually know all the variables, even if you think you do.

Setting up such an experiment means to control hidden variables, but then they aren't hidden.

That's the whole point right? The hope is to figure out what the hidden variables were, to make better predictions than quantum mechanics could. To un-hide them, as it were.

Determinism simply means the nature of things is deterministic, that's all. In other words, that is: given all initial conditions you can determine the exact resulting conditions.

Bell coined the term "Superdeterminism" to describe to others of theories that evade his own theorem - theories which are absolutely and completely deterministic. Theories that are only partially deterministic - don't hold up to his theorem. Hence he coined this term to highlight the difference (to those that fail to understand), which again is absolutely/completely vs partially deterministic theories.

As so there's no real difference here. If you understand determinism, then you know that a "partially" deterministic theory is not actually deterministic...

I see the difference between determinism and superdeterminism but it's unclear to me why, if you accept the former, why you might not accept the latter.

I think it's worth thinking through and delineating superdeterminism to its utmost limits even if I wouldn't necessarily say I find it compelling.

I do wonder why the authors are so quick to reject nonreductionism though, as nonreductionism seems fairly reasonable to me. Maybe I have a different idea of nonreductionism, but it seems to me that rejecting nonreductionism is akin to accepting Laplace's demon which as far as I understand has been disproved. Basically, at some point the information in a system supercedes that of any system that might represent it faithfully, in part because of measurement effects -- there's a lot of parallels with QM issues.

The problem is determining what determinism determines and how it determines it. And that's a precondition before you can even consider superdeterminism.

There is nothing in classical physics that suggests the universe is deterministic on cosmic scales. There's plenty in physics which suggests it isn't.

If you want to propose any form of determinism, be it superdeterminism, a bulk universe, or any of the other popular variations, you have to start by proving that causality is infinitely precise and absolute. Because otherwise your causality is partly random and therefore not truly causal at all.

Our experience of causality suggests that real measurements have limited precision, and predictions can only be made on limited timescales.

So anyone who is proposing superdeterminism is claiming that this can be fixed - by hidden variables, with noise-free super-realistic precision, which allow a universe-wide predictive horizon.

Free will is a side issue here, because the problem doesn't go away even if the universe has no observers.

The problem isn't whether free will hides super-predictive hidden variables, it's whether it's plausible that super-predictive hidden variables exist at all.

If you believe they do, you have a first-order universe in which these mysterious entities operate with effectively infinite precision behind the scenes, to create a second-order universe which has limited precision in practice.

Of course that may be happening. But it seems like quite unlikely.

You believe that magic ad-hoc random variables are more plausible? And that somehow for whatever non-causal (so magic) reason they follow the same probability distribution? This is clearly epistemologically weaker, but seduce more the wishful thinker mind.

I think for these people the detail just doesn't matter to them. They see near random behavior which is currently impossible to model and they shrug their shoulders and call it a magic, ad-hoc random variable.

And to a degree, they have a point: Does it really matter if we can predict the exact time and location of an alpha particle as is exits a black hole as hawking radiation? What good does modeling this phenomenon accurately give us?

At some point all that "nah what's the advantage of knowing that exactly?" would pile up and we throw away to many questions of how things work, limitting progress. I think that these kind of things are what scientists want to know. "We" want to know everything and how it works, no?

> you have a first-order universe in which these mysterious entities operate with effectively infinite precision behind the scenes, to create a second-order universe which has limited precision in practice

There are analogues to this in mathematics, for example, our formulation of the Fourier transform has limited precision but the physical phenomenon it relates to has no reason to be limited.

The limitations of the Fourier transform are intimately tied to the uncertainty principle: https://www.youtube.com/watch?v=MBnnXbOM5S4 Reality does appear to be limited by the limitations of the Fourier transform.

Not so fast. The uncertainty principle has narrow conditions outside which it doesn't apply. If you don't satisfy them, you can game the whole system and measure anything you want.

Did you watch the video?

If you can "fix" what that video describes, you'd better start preparing your Fields medal acceptance speech. That you can "get around" it sometimes doesn't remove the underlying math.