pcalau12i

People love to be pedantic as an “own” because they think it makes them look smart. And a lot of the times it actually works / is rewarded.

This is sadly pseudoscience, that only gets talked about because one smart guy endorsed it, but hardly anyone in academia actually takes it seriously. What you are talking about is called Orch OR, but Orch OR is filled with problems.

One issue is that Orch OR makes a lot of claims that are not obviously connected to one another. The reason this is is an issue is because, while they call the theory “falsifiable” because it makes testable predictions, even if the predictions are tested and it is found to make the correct prediction, that wouldn’t actually even validate the theory because there is no way to actually logically or mathematically connect that experimental validation to all of its postulates.

Orch OR has some rather bizarre premises: (1) Humans can consciously choose to believe things that cannot be mathematically proven, therefore, human consciousness must not be computable, (2) you cannot compute the outcome of a quantum experiment ahead of time, therefore there must be an physical collapse that is fundamentally not computable, (3) since both are not computable, they must be the same thing: physical collapse = consciousness, (4) therefore we should look for evidence that the brain is a quantum computer.

Argument #1 really makes no sense. Humans believing silly things doesn’t prove human decisions aren’t computable. Just look at AI. It is obviously computable and hallucinates nonsense all the time. This dubious argument means that #3 doesn’t follow; there is no good reason to think consciousness and “collapse” are related.

Argument #2 is problematic because physical collapse models are not compatible with special relativity or the statistical predictions of non-relativistic quantum mechanics, and so they cannot reproduce the predictions of quantum field theory in all cases, and so they aren’t particularly popular among physicists, and of course there is no evidence for them. Most physicists see the “collapse” as an epistemic, not a physical, event.

Orch OR also arbitrarily insists on using the Diósi–Penrose model specifically, even though there have been multiple models of physical collapse proposed, such as GRW. There is no obvious reason to use this model specifically, it isn’t connected to any of the premises in the theory. Luckily, argument #2 does present falsifiable claims, but because #2 is not logically connected to the rest of the arguments, even if we do prove that the Diósi–Penrose model is correct, it doesn’t follow that #1, #3, or #4 are correct. We would just know there are physical collapses, but nothing else in the theory would follow.

The only other argument that propose something falsifiable is #4, but again, #4 is not connected to #1, #3, or #4. Even if you desperately searched around frantically for any evidence that the brain is a quantum computer, and found some, that would just be your conclusion: the brain is a quantum computer. From that, #1, #2, and #3 do not then follow. It would just be an isolated fact in and of itself, an interesting discovery but wouldn’t validate the theory. I mean, we already have quantum computers, if you think collapse = consciousness, then you would have to already think quantum computers are conscious. A bizarre conclusion.

In fact, only #2 and #4 are falsifiable, but even if both #2 and #4 are validated, it doesn’t get you to #1 or #3, so the theory as a whole still would remain unvalidated. It is ultimately an unfalsifiable theory but with falsifiable subcomponents. The advocates insist we should focus on the subcomponents as proof it’s a scientific theory because “it’s falsifiable,” but the theory as a whole simply is not falsifiable.

Also, microtubules are structural. They don’t play any role in information processing in the brain, just in binding cells together, but it’s not just brain cells, microtubules are something found throughout your body in all kinds of cells. There is no reason to think at all they play any role in computations in the brain. The only reason you see interest in them from the Orch OR “crowd” (it’s like, what, 2 people who just so happen to be very loud?) is because they’re desperate for anything that vaguely looks like quantum effects in the brain, and so far microtubules are the only things that seem quantum effects may play some role, but this role is again structural. There is no reason to believe it plays any role in information processing or cognition.

Among philosophy academics, it’s somewhat popular to reject the Copenhagen Interpretation of quantum physics – the one we all have an ambient familiarity about that says that the universe is random

It doesn’t, though. The Copenhagen interpretation is not the strong claim that the universe is random, nor is it the strong claim that the universe is predeterministic. Bohr rejected an axiom called that of statistical independence, arguing that in reality it is physically impossible to separate yourself from what you are trying to measure, as you are yourself a physical system that acts on the system through trying to observe it and it acts back on you. He believed this inability to separate yourself from the system creates a limitation in the maximal amount of human knowledge one can gain about a system as gaining knowledge about some parts of a system inherently disturbs and thus erases knowledge about another part, a principle he called the principle of complementarity.

Bohr thus saw quantum mechanics as kind of a “final theory” at the limitations of what is possible for humanity to know about nature, rather than as a direct description of nature as it really is. He once stated that “physics is not about nature, but what we can say about nature.” It wasn’t meant as a strong claim about the underlying ontology of the universe, but instead a position that the underlying ontology is fundamentally unknowable due to the principle of complementarity. Heisenberg agreed due to his uncertainty principle. He did not outright dismiss the possibility that there are hidden variables, but said that even if they exist, the uncertainty principle makes it impossible to measure them, so it is pointless to speculate on them.

The Copenhagen interpretation isn’t the strong claim that the universe is random or not random, but instead the viewpoint that fundamental physical limitations prevent the construction of a measurement device that could actually prove nature in such a way to reveal how it actually is at a fundamental level, and so any speculation regarding that is unfalsifiable and there is no possibility to choose which is correct vs incorrect, so there is no point in such an endeavor. It does leave open the possibility of hidden variables, but does not leave open the possibility (if the interpretation is correct) that there are knowable hidden variables, if an underlying ontology exists, we can’t know it. It’s a claim about epistemic limitations rather than an ontological stance.

When it came to the US, this was largely during WW2 when the Manhattan project was going on. Americans were much more practically minded and not philosophical because they were trying to build something rapidly for a war effort. This led the Copenhagen interpretation to morph from an argument based on physics and philosophy as to why we cannot meaningfully know the universe’s ontology to a purely utilitarian argument that we should “shut up and calculate” because metaphysics is “a waste of time.”

I think a lot of proponents of objective collapse would pick a bone with that, haha, although it’s really just semantics. They are proposing extra dynamics that we don’t understand and can’t yet measure.

Any actual physicist would agree objective collapse has to modify the dynamics, because it’s unavoidable when you introduce an objective collapse model and actually look at the mathematics. No one in the physics community would debate GRW or the Diósi–Penrose model technically makes different predictions, however, and in fact the people who have proposed these models often view this as a positive thing since it makes it testable rather than just philosophy.

How the two theories would deviate would depend upon your specific objective collapse model, because they place thresholds in different locations. For GRW, it is based on a stochastic process that increases with probability over time, rather than a sharp threshold, but you still should see statistical deviations between its predictions and quantum mechanics if you can maintain a coherent quantum state for a large amount of time. The DP model has something to do with gravity, which I do not know enough to understand it, but I think the rough idea is if you have sufficient mass/energy in a particular locality it will cause a “collapse,” and so if you can conduct an experiment where that threshold of mass/energy is met, traditional quantum theory would predict the system could still be coherent whereas the DP model would reject that, and so you’d inherently end up with deviations in the predictions.

What’s the definition of interact here?

An interaction is a local event where two systems become correlated with one another as a result of the event.

“The physical process during which O measures the quantity q of the system S implies a physical interaction between O and S. In the process of this interaction, the state of O changes…A quantum description of the state of a system S exists only if some system O (considered as an observer) is actually ‘describing’ S, or, more precisely, has interacted with S…It is possible to compare different views, but the process of comparison is always a physical interaction, and all physical interactions are quantum mechanical in nature.”

The term “observer” is used very broadly in RQM and can apply to even a single particle. It is whatever physical system you are choosing as the basis of a coordinate system to describe other systems in relation to.

Does it have an arbitrary cutoff like in objective collapse?

It has a cutoff but not an arbitrary cutoff. The cutoff is in relation to whatever system participates in an interaction. If you have a system in a superposition of states, and you interact with it, then from your perspective, it is cutoff, because the system now has definite, real values in relation to you. But it does not necessarily have definite, real values in relation to some other isolated system that didn’t interact at all.

You can make a non-separable state as big as you want.

Only in relation to things not participating in the interaction. The moment something enters into participation, the states become separable. Two entangled particles are nonseparable up until you interact with them. Although, even for the two entangled particles, from their “perspectives” on each other, they are separable. It is only nonseparable from the perspective of yourself who has not interacted with them yet. If you interact with them, an additional observer who has not interacted with you or the three particles yet may still describe all three of you in a nonseparble entangled state, up until they interact with it themselves.

This is also the first I’ve heard anything about time-symmetric interpretations. That sounds pretty fascinating. Does it not have experimenter “free will”, or do they sidestep the no-go theorems some other way?

It violates the “free will” assumption because there is no physical possibility of setting up an experiment where the measurement settings cannot potentially influence the system if you take both the time-forwards and time-reverse evolution seriously. We tend to think because we place the measurement device after the initial preparation and that causality only flows in a single time direction, then it’s possible for the initial preparation to affect the measurement device but impossible for the measurement device to affect the initial preparation. But this reasoning doesn’t hold if you drop the postulate of the arrow of time, because in the time-reverse, the measurement interaction is the first interaction in the causal chain and the initial preparation is the second.

Indeed, every single Bell test, if you look at its time-reverse, is unambiguously local and easy to explain classically, because all the final measurements are brought to a single locality, so in the time-reverse, all the information needed to explain the experiment begins in a single locality and evolves towards the initial preparation. Bell tests only appear nonlocal in the time-forwards evolution, and if you discount the time-reverse as having any sort of physical reality, it then forces you to conclude it must either be nonlocal or a real state for the particles independent of observation cannot exist. But if you drop the postulate of the arrow of time, this conclusion no longer follows, although you do end up with genuine retrocausality (as opposed to superdeterminism which only gives you pseudo-retrocausality), so it’s not like it gives you a classical system.

So saying we stick with objective collapse or multiple worlds, what I mean is, could you define a non-Lipschitz continuous potential well (for example) that leads to multiple solutions to a wave equation given the same boundary?

I don’t know, but that is a very interesting question. If you figure it out, I would be interested in the answer.

Many of the interpretations of quantum mechanics are nondeterministic.

1. Relational quantum mechanics interprets particles as taking on discrete states at random whenever they interact with another particle, but only in relation to what they interact with and not in relation to anything else. That means particles don’t have absolute properties, like, if you measure its spin to be +1/2, this is not an absolute property, but a property that exists only relative to you/your measuring device. Each interaction leads to particles taking on definite states randomly according to the statistics predicted by quantum theory, but only in relation to things participating in those interactions.

2. Time-symmetric interpretations explain violations of Bell inequalities through rejecting a fundamental arrow of time. Without it, there’s no reason to evolve the state vector in a single time-direction. It thus adopts the Two-State Vector Formalism which evolves it in both directions simultaneously. When you do this, you find it places enough constructs on the particles give you absolutely deterministic values called weak values, but these weak values are not what you directly measure. What you directly measure are the “strong” values. You can interpret it such that every time two particles interact, they take on “strong” values randomly according to a rule called the Aharonov-Bergmann-Lebowitz rule. This makes time-symmetric interpretations local realist but not local deterministic, as it can explain violations of Bell inequalities through local information stored in the particles, but that local information still only statistically determines what you observe.

3. Objective collapse models are not really interpretations but new models because they can’t universally reproduce the mathematics of quantum theory, but some serious physicists have explored them as possibilities and they are also fundamentally random. You assume that particles literally spread out as waves until some threshold is met then they collapse down randomly into classical particles. The reason this can’t reproduce the mathematics of quantum theory is because this implies quantum effects cannot be scaled beyond whatever that threshold is, but no such threshold exists in traditional quantum mechanics, so such a theory must necessarily deviate from its predictions at that threshold. However, it is very hard to scale quantum effects to large scales, so if you place the threshold high enough, you can’t practically distinguish it from traditional quantum mechanics.

Arguably, if we insist on trying to come up with the simplest way to explain non-relativistic quantum mechanics, that is to say, if we are very conservative and stick to classical explanations unless we absolutely are forced not to (rather than throwing our hands up and saying it’s all magic that’s impossible to understand, as most people do), then we find that it comes naturally to explain non-relativistic quantum mechanics by treating particles as excitations in a classical field. This alone can explain the interference-based paradoxes in completely classical terms, like double-slit or Elitzur-Vaidman paradox, without altering any of the postulates of the theory in any way. The extension to quantum field theory then becomes more natural and intuitive. imo

For any physical theory, you can always just ask “why x”, like a child who constantly asks “why” over and over again to every answer, but you will always hit a bottom. There seems to be a popular mentality that “why x” is always a meaningful question, and from that, we can conclude that we don’t know anything at all, because all our beliefs rely on a “why x” we don’t know the answer to, an so they are all baseless. We can’t make any truth claims about the behavior of particles, galaxies, or anything, because you can just infinitely ask “why” until we hit a bottom and then you would say “I don’t know.”

But, personally, I find this point of view rather bizarre, because, again, it can make it seem like we don’t know anything at all and have no foundations for truth claims in the slightest, and are completely ignorant about everything. I think it makes more coherent sense to just allow for to be a bottom to the questioning. Eventually a string of “why” questions will reach a bottom, where that bottom shouldn’t be answered with “I don’t know” but it should be answered with “it is what it is,” because, for all we know, it is indeed an accurate description of reality at a fundamental level and there is nothing beneath it.

That shouldn’t be taken as a strong claim that there definitely isn’t anything beneath it, as if we should just accept our current most fundamental theories are the end of the line and stop searching. It should be taken as the weaker claim that as far as we currently know it is the bottom, and so we can indeed make truth claims upon that basis. The child might ask, “why do things experience gravity?” You might say, “time dilation near matter.” The child then may ask, “why does time dilate near matter?” In my opinion, the appropriate response to that is just, “as far as we know, it is what it is.” That could change in the future, but, given our best scientific models at the present moment, that is the end of the line of the explanation.

That seems to be a fairly controversial point, though. Most people in my experience disagree, but I don’t see how you can have a basis for truth claims at all if you claim that “why gravity” does indeed have an answer but you can’t specify it, because then it would also be baseless to claim that gravity is caused by time dilation near matter, because you’ve not established that time actually does dilate near matter, as you would be claiming that this relies on postulates which you’ve not defined. It seems, again, simpler to just take the most fundamental theories as the postulates themselves, as the fundamental axioms.

There is a popular point of view that we shouldn’t do this because scientific theories often change, so something you believe today can be proven wrong tomorrow. But then we end up never being allowed to believe anything at all. We always have to pretend we’re clueless about nature because if we believe in any of our most fundamental theories, then our beliefs could be overturned. But personally, I don’t see why this to be a problem. A person who believed Newtonian mechanics was fundamental to how nature worked back in the 1700s were shown later to be wrong, but that person’s beliefs were still closer to reality than the people who rejected it and upheld outdated Aristotelian physics, or people who refused to belief in anything at all. It is fine to later be shown to be wrong, nothing to be upset about, nothing negative about that. We are better off, imo, as treating our best physical theories as indeed fundamentally how reality works, the “bottom” so to speak, until we find new theories that show otherwise, and we change our minds with the times.

That doesn’t disallow speculation or research into potentially more fundamental theories. Theories of quantum gravity are such a speculation. They remain in the realm of speculation because no one has demonstrated in the real world that it’s actually possible to construct a device such that quantum effects and gravitational effects are both simultaneously relevant and necessary to make predictions. The theories thus describe separate domains, and there isn’t a genuine need for a new theory until we can figure out how to bridge the two domains in reality.

We don’t actually know what would happen if we bridge the two domains. We may find that our theories of turning gravity quantum are all wrong and that in fact it is quantum theory that needs to be abandoned. We may also find that the domains aren’t even bridgeable. We already know of certain physical limitations that make the domains unbridgeable, such as, building an interferometer sensitive enough to detect both gravitational and quantum effects simultaneously would collapse into a black hole. There may be more things like this we will discover later on that just render the two theories unbridgeable in physical reality.

Many physicists are convinced that the bridging will end up turning gravity quantum, but this is just a complete guess, there’s no actual empirical evidence for it other than a complete historical coincidence that when studying the strong interaction physicists happened to accidentally stumble upon mathematics that also seemed to be able to also predict a particle that could explain gravity, giving birth to String Theory. People thought it must be correct because it wasn’t intentional but discovered by accident, but this isn’t a good criterion at all for suggesting it’s correct, and ultimately the theory never went anywhere.

If we are to talk about theories replacing quantum mechanics and general relativity, we don’t have a clue what these would look like because it’s just speculation, and so it could go either way.

That’s not true. If you read Schrodinger’s original paper “The Present Situation in Quantum Mechanics” he’s pretty clear that he was attempting to show how ridiculous it is to treat a superposition of states as if a particle is actually smeared out in multiple locations at once, because you could use that particle as the basis of a chain reaction that would eventually affect a macroscopic object, and then you would have to say the macroscopic object is smeared out in multiple places at once. The argument was a reductio ad absurdum for treating microscopic objects as if they are smeared out in multiple places at once. Its fundamental point was simply not a commentary on macroscopic objects but microscopic objects.

You don’t need the wave function to do quantum mechanics, it’s just a mathematical convenience, and so Schrodinger had insisted it shouldn’t be interpreted as a literal physical object as if particles are actually spreading out as waves. In his book “Science and Humanism” he says that the reason he invented the wave formalism is because he didn’t like Heisenberg’s formalism which, even though it made all the right predictions, it didn’t give intermediate states for particles, so it is as if they just hop around from interaction to interaction probabilistically, and the wave formalism was meant to “fill in the gaps” between the interactions.

However, in that book he also says that he believes this project was a failure because all the wave formalism does is move the gap between interactions to a gap between the evolution of the quantum state and observation, which made even less sense, and so he changed his mind and argued that we should abandon the notion of filling in the gaps between interactions, and the illusion of continuous transitions between states is only a macroscopically emergent feature.

I think it’s boring honestly. It’s a bit strange how like, the overwhelming majority of people either avoid interpreting quantum theory at all (“shut up and calculate”) or use it specifically as a springboard to justify either sci-fi nonsense (multiverses) or even straight-up mystical nonsense (consciousness induced collapse). Meanwhile, every time there is a supposed “paradox” or “no-go theorem” showing you can’t have a relatively simple explanation for something, someone in the literature publishes a paper showing it’s false, and then only the paper showing how “weird” QM is gets media attention. I always find myself on the most extreme fringe of the fringe of thinking both that (1) we should try to interpret QM, and (2) we should be extremely conservative about our interpretation so we don’t give up classical intuitions unless we absolutely have to. That seems to be considered an extremist fringe position these days.

You are just straight-up not reading my posts.

The specific article mentions QSDC which doesn’t actually exchange a key at all, QKD does exchange a key, but both operate on similar concepts. To measure something requires physically interacting with it, an interaction has to be specified by an operator in QM, and the rules of constructing physically valid operators don’t allow you to construct one that is non-perturbing, so you inevitably perturb the qubits in transit if you measure them in a way that can later be detected.

But, again, we are talking about “in transit,” that is to say, between nodes. If you and I are doing QKD, and are node A and B, we would exchange the qubits over a wire between A and B, and anyone who sniffs the packets in transit would perturb them in a detectable way. But if someone snipped the wire and setup an X and Y node in the middle, they could make X pretend to be you and Y pretend to be me, and so I would exchange a key with X and you would exchange a key with Y, and so the key exchange occurred over nodes A-X and B-Y and not over A-B.

The middle-man would then have two keys, they would decrypt the messages sent from A-X with one and re-encrypt them using the second key to transmit from B-Y, and vice-versa. Messages sent from A to be B would still arrive at B and messages sent from B to A would still arrive at A, but A wouldn’t know the key they established was with X and not B, and B wouldn’t know the key they established was with Y and not A. From their perspectives it would appear as if everything is working normally.

You have to have some sort of authentication of the nodes in any security infrastructure. That’s what public key infrastructure is for. Man-in-the-middle attack is basically a form of impersonation, and you can’t fight impersonation with encryption or key distribution algorithms. It’s just a totally different kind of problem. You authenticate people’s identities with signatures. Similarly, on the internet, you authenticate nodes on a network with digital signatures. Anyone can make up a random signature on the spot, so you have to compare a provided signature to one provided by a trusted database of signatures called certificate authorities. That’s what public key infrastructure is, and it’s one of the major backbones of the internet.

Both QKD and QSDC are vulnerable to man-in-the-middle attacks. It doesn’t allow eavesdroppers, but that is not the same thing. An eavesdropper simply sniffs the packets of information transmitting between two nodes. A man-in-the-middle attack sets up two nodes in a network, let’s call them X and Y, and then if A and B want to communicate, then they have X pretend to be B and Y pretend to be A, so A and B talk to X and Y and think they are talking to A and B.

You then perform either QKD or QSDC twice between nodes X and A and Y and B, which are both valid implementations of the protocol as B would expect the data to become readable at Y because they falsely think Y is A, and A would expect the data to become readable at X because they falsely think X is B. This, however, allows for the data to pass through in a completely readable form between nodes X and Y, which the man-in-the-middle could then read it at those points.

It is sort of like if I took your computer and then pretended to be you. It doesn’t matter how good the encryption algorithm is, if everyone thinks I am you, they will send me information meant for you in a way that they intend for it to be readable when I receive it. A man-in-the-middle attack doesn’t really exploit a flaw in the algorithm itself, but a flaw in who the algorithm is intended for / directed at. Even classical algorithms have the same problem, you can defeat Diffie-Hellman with a man-in-the-middle attack as well.

You can only solve it through public key infrastructure. My biggest issue with the “quantum internet” is that I’ve seen very little in the way of scalable quantum PKI. The only algorithm I’ve seen is fundamentally not scalable because the public keys are all consumable. If the intention really is to replace the whole internet, that’s kind of a big requirement. But if the intention is just small-scale secure communication like for internal government stuff, that’s not as big of an issue.

The double-slit experiment doesn’t even require quantum mechanics. It can be explained classically and intuitively.

It is helpful to think of a simpler case, the Mach-Zehnder interferometer, since it demonstrates the same effect but where where space is discretized to just two possible paths the particle can take and end up in, and so the path/position is typically described with just with a single qubit of information: |0⟩ and |1⟩.

You can explain this entirely classical if you stop thinking of photons really as independent objects but just specific values propagating in a field, what are sometimes called modes. If you go to measure a photon and your measuring device registers a |1⟩, this is often interpreted as having detected the photon, but if it measures a |0⟩, this is often interpreted as not detecting a photon, but if the photons are just modes in a field, then |0⟩ does not mean you registered nothing, it means that you indeed measured the field but the field just so happens to have a value of |0⟩ at that location.

Since fields are all-permeating, then describing two possible positions with |0⟩ and |1⟩ is misleading because there would be two modes in both possible positions, and each independently could have a value of |0⟩ or |1⟩, so it would be more accurate to describe the setup with two qubits worth of information, |00⟩, |01⟩, |10⟩, and |11⟩, which would represent a photon being on neither path, one path, the other path, or both paths (which indeed is physically possible in the real-world experiment).

When systems are described with |0⟩ or |1⟩, that is to say, 1 qubit worth of information, that doesn’t mean they contain 1 bit of information. They actually contain as much as 3 as there are other bit values on orthogonal axes. You then find that the physical interaction between your measuring device and the mode perturbs one of the values on the orthogonal axis as information is propagating through the system, and this alters the outcome of the experiment.

You can interpret the double-slit experiment in the exact same way, but the math gets a bit more hairy because it deals with continuous position, but the ultimate concept is the same.

A measurement is a kind of physical interaction, and all physical interactions have to be specified by an operator, and not all operators are physically valid. Quantum theory simply doesn’t allow you to construct a physically valid operator whereby one system could interact with another to record its properties in a non-perturbing fashion. Any operator you construct to record one of its properties without perturbing it must necessarily perturb its other properties. Specifically, it perturbs any other property within the same noncommuting group.

When the modes propagate from the two slits, your measurement of its position disturbs its momentum, and this random perturbation causes the momenta of the modes that were in phase with each other to longer be in phase. You can imagine two random strings which you don’t know what they are but you know they’re correlated with each other, so whatever is the values of the first one, whatever they are, they’d be correlated with the second. But then you randomly perturb one of them to randomly distribute its variables, and now they’re no longer correlated, and so when they come together and interact, they interact with each other differently.

There’s a paper on this here and also a lecture on this here. You don’t have to go beyond the visualization or even mathematics of classical fields to understand the double-slit experiment.

Why interpret it as either? The double-slit experiment can be given an entirely classical explanation. Such extravagances are not necessary. As the old saying goes “extraordinary claims require extraordinary evidence.” We should not be considering non-classical explanations unless they are genuinely necessary, and the only become necessary in contextual cases, which the double-slit experiment is certainly not such a case.

My impression from the literature is that superdeterminism is not the position of rejecting an asymmetrical arrow of time. In fact, it tries to build a model that can explain violations of Bell inequalities completely from the initial conditions evolved forwards in time exclusively.

Let’s imagine you draw a coin from box A and it’s random, and you draw coins from box B and it’s random, but you find a peculiar feature where if you switch from A to B, the first coin you draw from B is always the last you drew from A, and then it goes back to being random. You repeat this many times and it always seems to hold. How is that possible if they’re independent of each other?

Technically, no matter how many coins you draw, the probability of it occurring just by random chance is never zero. It might get really really low, but it’s not zero. A very specific initial configuration of the coins could reproduce that.

Superdeterminism is just the idea that there are certain laws of physics that restrict the initial configurations of particles at the very beginning of the universe, the Big Bang, to guarantee their evolution would always maintain certain correlations that allow them to violate Bell inequalities. The laws don’t continue to apply moment-by-moment, they just apply once when the universe “decides” its initial conditions, by restricting certain possible configurations.

It’s not really an interpretation because it requires you to posit these laws and restrictions, and so it really becomes a new theory since you have to introduce new postulates, but such a theory would in principle then allow you to evolve the system forwards from its initial conditions in time to explain every experimental outcome.

As a side note, you can trivially explain violations of Bell inequalities in local realist terms without even introducing anything new to quantum theory just by abandoning the assumption of time-asymmetry. This is called the Two-State Vector Formalism and it’s been well-established in the literature for decades. If A causes B and B causes C, in the time-reverse, C causes B and B causes A. if you treat both as physically real, then B would have enough constraints placed upon it by A and C taken together (by evolving the wave function from both ends to where they meet at B) to violate Bell inequalities.

That’s already pretty much a feature built-in to quantum theory and allows you to interpret it in local realist terms if you’d like, but it requires you to accept that the microscopic world is genuinely indifferent to the arrow-of-time and the time-forwards and the time-reversed evolution of a system are both physically real.

However, this time-symmetric view is not superdeterminism. Superdeterminism is time-asymmetric just like most every other viewpoint (Copenhagen, MWI, pilot wave, objective collapse, etc). Causality goes in one temporal direction and not the other. The time-symmetric interpretation is its own thing and is mathematically equivalent to quantum mechanics so it is an actual interpretation and not another theory.

The problem with pilot wave is it’s non-local, and so it contradicts with special relativity and cannot be made directly compatible with the predictions of quantum field theory. The only way to make it compatible would be to throw out special relativity and rewrite a whole new theory of spacetime with a preferred foliation built in that could reproduce the same predictions as special relativity, and so you end up basically having to rewrite all of physics from the ground-up.

I also disagree that it’s intuitive. It’s intuitive when we’re talking about the trajectories of particles, but all its intuition disappears when we talk about any other property at all, like spin. You don’t even get a visualization of what’s going on at all when dealing with quantum circuits. Since my focus is largely on quantum computing, I tend to find pilot wave theory very unhelpful.

Personally, I find the most intuitive interpretation a modification of the Two-State Vector Formalism where you replace the two state vectors with two vectors of expectation values. This gives you a very unambiguous and concrete picture of what’s going on. Due to the uncertainty principle, you always start with limited information on the system, you build out a list of expectation values assigned to each observable, and then take into account how those will swap around as the system evolves (for example, if you know X=+1 but don’t know Y, and an interaction has the effect of swapping X with Y, then now you know Y=+1 and don’t know X).

This alone is sufficient to reproduce all of quantum mechanics, but it still doesn’t explain violations of Bell inequalities. You explain that by just introducing a second vector of expectation values to describe the final state of the system and evolve it backwards in time. This applies sufficient constraints on the system to explain violations of Bell inequalities in local realist terms, without having to introduce anything to the theory and with a mostly classical picture.

Quantum mechanics becomes massively simpler to interpret once you recognize that the wave function is just a compressed list of expectation values for the observables of a system. An expectation value is like a weighted probability. They can be negative because the measured values can be negative, such as for qubits, the measured values can be either +1 or -1, and if you weight by -1 then it can become negative. For example, an expectation value of -0.5 means there is a 25% chance of +1 and a 75% of -1.

If I know for certain that X=+1 but I have no idea what Y is, and the physical system interacts with something that we know will have the effect of swapping its X and Y components around, then this would also swap my uncertainty around so now I would know that Y=+1 without knowing what X is. Hence, if you don’t know the complete initial conditions of a system, you can represent it with a list of all of possible observables and assign each one an expectation value related to your certainty of measuring that value, and then compute how that certainty is shifted around as the system evolves.

The wave function then just becomes a compressed form of this. For qubits, the expectation value vector grows at a rate of 4^N where N is the number of qubits, but the uncertainty principle limits the total bits of information you can have at a single time to 2^N, so the vector is usually mostly empty (a lot of zeros). This allows you to mathematically compress it down to a wave function that also grows by 2^N, making it the most concise way to represent this.

But the notation often confuses people, they think it means particles are in two places at once, that qubits are 0 and 1 at the same time, that there is some “collapse” that happens when you make a measurement, and they frequently ask what the imaginary components mean. But all this confusion just stems from notation. Any wave function can be expanded into a real-valued list of expectation values and you can evolve that through the system rather than the wave function and compute the same results, and then the confusion of what it represents disappears.

When you write it out in this expanded form, it’s also clear why the uncertainty principle exists in the first place. A measurement is a kind of physical interaction between a record-keeping system and the recorded system, and it should result in information from the recorded system being copied onto the record-keeping system. Physical interactions are described by an operator, and quantum theory has certain restrictions on what qualifies as a physically valid operator: it has to be time-reversible, preserve handedness, be completely positive, etc, and these restrictions prevent you from constructing an operator that can copy a value of an observable from one system onto another in a way that doesn’t perturb its other observables.

Most things in quantum theory that are considered “weird” are just misunderstandings, some of which can even be reproduced classically. Things like double-slit, Mach–Zehnder interferometer, the Elitzur–Vaidman “paradox,” the Wigner’s friend “paradox,” the Schrodinger’s cat “paradox,” the Deutsch algorithm, quantum encryption and key distribution, quantum superdense coding, etc, can all be explained entirely classically just by clearing up some confusion about the notation.

This narrows it down to only a small number of things that genuinely raise an eyebrow, those being cases that exhibit what is sometimes called quantum contextuality, such as violations of Bell inequalities. It inherently requires a non-classical explanation for this, but I don’t think that also means it can’t be something understandable.

The simplest explanation I have found in the literature is that of time-symmetry. It is a requirement in quantum mechanics that every operator is time-symmetric, and that famously leads to the problem of establishing an arrow of time in quantum theory. Rather than taking it to be a problem, we can instead presume that there is a good reason nature demands all its microscopic operators are time-symmetric: because the arrow of time is a macroscopic phenomena, not a microscopic one.

If you have a set of interactions between microscopic particles where A causes B and B causes C, if I played the video in the reverse, it is mathematically just as valid to say that C causes B and B causes A. Most people then introduce an additional postulate that says “even though it is mathematically valid, it’s not physically valid, we should only take the evolution of the system in a single direction of time seriously.” You can’t derive that postulate from quantum theory, you just have to take it on faith.

If we drop that postulate and take the local evolution of the system seriously in both its time-forwards evolution and its time-reversed evolution, then you can explain violations of Bell inequalities without having to add anything to the theory at all, and interpret it completely in intuitive local realist terms. You do this using the Two-State Vector Formalism where all you do is compute the evolution of the wave function (or expectation values) from both ends until they meet at an intermediate point, and that gives you enough constraints to deterministically derive a weak value at that point. The weak value is a physical variable that evolves locally and deterministically with the system and contains sufficient information to generate its expectation values when needed.

You still can’t always assign a definite value, but these expectation values are epistemic, there is no contradiction with there being a definite value as the weak value contains all the information needed for the correct expectation values, and therefore the correct probability distribution, locally within the particle.

In terms of computation, it’s very simple, because for the time-reverse evolution you just treat the final state as the initial state and then apply the operators in reverse with their time-symmetric equivalents (Hermitian transpose) and then the weak value equation looks exactly like the expectation value equation except rather than having the same wave function on both ends of the observable, you have the reverse-evolved wave function on one end of the observable and the forwards-evolved wave function on the other. (You can also plug the expectation value vectors on both ends and it works as well.)

Nothing about this is hard to visualize because you just imagine playing a moving forwards and also playing it in the reverse, and in both directions you get a local causal chain of interactions between the particles. If A causes B and B causes C in the time-forwards movie, playing the movie in reverse you will see C cause B which then causes A. That means B is both caused by A and C, and thus is influenced by both through a local chain of interactions.

There is nothing “special” going on in the backwards evolution, the laws of physics are symmetrical so, visually, it is not distinguishable from its forwards evolution, so you visualize it the exact same way, so you can pretty much still maintain a largely classical picture in your head, just with the caveat that you have to consider both directions in order to place enough constraints on the system to explain the observed results. All the “paradoxes” suddenly evaporate away because you can just compute how the system locally evolves in any “weird” situation and look at exactly what is going on.

That is enough to explain QM in local realist terms, doesn’t require any modifications to the theory, and has been well-established in the literature for decades, is easy to visualize, but people often seem to favor explanations that are impossible to visualize, like treating the wave function as a literal object despite the wave function being, at times, even infinite-dimensional for continuous observables, or even believing we all live in an infinite-dimensional multiverse. And then they all complain it’s impossible to visualize and so confusing and “no one understands quantum mechanics”… I don’t understand why people seem to prefer to think about things in a way that they themselves admit just leads to endless confusion.

Well, first, that is not something that actually happens in the real world but is a misunderstanding. Particles diffract like a wave from a slit due to the uncertainty principle, because their position is confined to the narrow slit so their momentum must probabilistically spread out. If you have two slits where they have a probability of entering one slit or the other, then you will have two probabilistic diffraction trajectories propagating from each slit which will overlap with each other.

Measuring the slit the photon passes through does not make it behave like a particle. Its probabilistic trajectory still diffracts out of both slits, and you will still get a smeared out diffraction pattern like a wave. The diagrams that show two neat clean separated blobs has never been observed in real life and is just a myth. The only difference that occurs between whether or not you’re making a measurement is whether or not the two diffraction trajectories interfere with one another or not, and that interference gives you the black bands.

This is an interference-based experiment. Interference-based phenomena can all be given entirely classical explanations without even resorting to anything nonclassical. The paper “Why interference phenomena do not capture the essence of quantum theory” is a good discussion on this. There is also a presentation on it here.

Basically, you (1) treat particles as values that propagate in a field. Not waves that propagate through a field, just values in a field like any classical field theory. Classical fields are indeed something that can take multiple paths simultaneously. (2) We assume that the particles really do have well-defined values for all of their observables at once, even if the uncertainty principle disallows us from knowing them all simultaneously. We can mathematically prove from that assumption that it would impossible to construct a measuring device that simply passively measures a system, it will always perturb the values it is not measuring in an unpredictable way.

A classical field has values everywhere. That’s basically what a field is, you assign a value, in this case a vector, to every point in space and time. The vector holds the properties of the particles. For example, the X, Y, and Z observable would be stored in a vector [X, Y, Z] with a vector value at any point. What the measuring device measures is |0> or |1>, where we interpret the former to meaning no photon is there and we interpret the latter to mean a photon is there. But if you know anything about quantum information science, you know that |0> just means Z=+1 and |1> just means Z=-1. Hence, if you measure |0>, it doesn’t tell you anything about the X and Y values, which we would assume are also there if particles are excitations in a field as given by assumption #1 because the field exists everywhere, and in fact, from our other assumption #2, your measurement of its Z value to be |0> must perturb those X and Y values.

It would be the field that propagates information through both slits and the presence of the measurement device perturbs the observables you do not measure, causing them to become out of phase with one another so they that they do not interfere when the field values overlap.

Interestingly, this requires no modification to quantum mechanics. If a system is physically redundant, we can often ignore parts of it in the mathematics to simplify our calculations, but if we do so, then the mathematics don’t directly reflect the physical character of the system because parts of it are ignored. All we have to do is assume that for these kinds of photon-based and interference-based experiments that we are making a mathematical simplification due to redundancies and then can mathematically expand the description where it is more clearly obvious what is going on, and doing so is mathematically equivalent as it leads to the same predictions and, if you simplify it, it would lead to the same traditional way of describing the experiment.

It’s sort of like if you have 4, you can expand it into 2+2. It means the same thing, but 4 and 2+2 have physically different meaning, because 2+2 suggests two separate things coming together, whereas 4 suggests only 1 thing. Expanding the double-slit experiment is a bit complicated because position is continuous, but it’s trivial to demonstrate it for something like the Mach-Zehnder interferometer. You just map |0> to |01> and |1> to |10>, and then all the paradoxes with that, including the “bomb tester” paradox, disappear.

Quantum mechanics is not complicated. It just appears complicated because everyone chooses to interpret it in a way that is inherently contradictory. One of the fundamental postulates of quantum mechanics is that it is time-symmetric, called unitarity, but almost everyone for some reason assumes it is time-asymmetric. This contradiction leads them to have to compartmentalize this contradiction in their head, which then leads to a bunch of a contradictory conclusions, and then they invent a bunch of nonsense to try and make sense of those contradictions, like collapsing wave functions, a multiverse, cats that are both dead and alive simultaneously, particles in two places at once, nonlocality, etc. But that’s all entirely unnecessary if you just consistently interpret the theory as time-symmetric. This has been shown in the literature for decades, called the Two-State Vector Formalism, yet it’s almost entirely ignored in the popular discourse for some reason.

But that wasn’t the thing I was even talking about when I said the game is not accurate. In real life, if you “take a picture” of an electron’s location while it is buzzing around the nucleus unpredictably, it doesn’t stay in that last position as long as you continue looking at the “picture”. It will continue buzzing around the nucleus unpredictability and your “picture” is just its location in an instantaneous moment. Also, the unpredictable movement of particles is not nonlocal, they cannot suddenly hop from one side of the solar system to the other. You can only find them in places that they would have had enough time to reach.

don’t mind me i have autism