I don’t think it works the other way either, I don’t see why anything in quantum mechanics specifically would give any more credence to determinism than classical mechanics which is also deterministic.

Bob is a scientist, they have hooked a computer to the R vs T experiment and when R occurs the screen flashes red. When the screen flashes red, red photons collide with Bob’s skin and eyes, signals enter their brain and they observe a red screen, and they remember it. So, given the state of redbob, I think it’s reasonable to say that perceived R.

These are all classical assumptions which Many Worlds denies. Again, you keep repeating classical descriptions to explain Many Worlds. I do not know how I can explain it as I’ve already went over this several times. You do not get discrete events out of the Schrodinger equation, there is no “redbob,” there is no photons colliding with Bob’s skin and eyes. None of this happens if all you have is the Schrodinger equation.

If R or T never happen from an external perspective doesn’t really matter to us though.

I am not sure what you mean by “an external perspective.” The point is that R or T never occur in physical reality, so you have to then explain how it is that we actually perceive R or T if it’s literally something that doesn’t occur in the real world.

If we accept many worlds as true for a second, then it follows that the total quantum states describes quite a lot, your exact configuration is somewhere within the total state.

There is no “your exact configuration” if Many Worlds is true because discrete objects like “you” don’t even exist.

At a large scale you depend on your parents having existed. So you can only perceive the parts of the total state where your parents existed, because any parts of the state where they didn’t exist does not contain a you to perceive.

This analogy, again, doesn’t work. My parents existing could be said to be R and my parents not existing can be said to be T, and if I have a limited perspective where I only see R (due to the anthropic principle) then it naturally follows I would see R and not T, so that explains why I see one and not both.

But this is not applicable to Many Worlds at all because Many Worlds does not claim two events happen and that a limited perspective makes us just see one of them. Many Worlds claims no events happen. You cannot take the subset of the null set and get a non-empty set from it. The rest of your comment, again, stems from this misconception, which I did try to clearly address in my previous comment yet it still seems to not be understood.

What is meant by “determinism” here? If you mean nomological determinism in the sense of the “free will vs determinism” debate, quantum mechanics is still a nomologically deterministic theory, so it does not strengthen the “free will” position at all. If you mean predetermination in the sense of the “randomness vs determinism” debate, if you interpret quantum mechanics to be fundamentally random, then of course it is incompatible with predetermination. But this is still ultimately an interpretation as it is empirically impossible to distinguish between true randomness and a significantly chaotic system.

One might justify the former position on philosophical grounds, such as, Occam’s razor: it’s simpler to believe there is no cause than to posit a cause we cannot (currently) demonstrate, but that is still ultimately a philosophical argument. Take Plato’s cave, for example. If all they could see is the shadows, they might build theories about the shadows themselves, and then someone might posit that we should believe that the shadows are all that exists and nothing causes them because of Occam’s razor. They would clearly arrive at the incorrect conclusion using Occam’s razor, so Occam’s razor itself is debatable whether or not it is a reliable rule of thumb in cases like this.

In many worlds, it’s not so much that the classical world is an illusion

Again, I think you have a false picture in your mind that Many Worlds is like an objective collapse model but where the “collapse” leads to a split into different parallel branches of all possible outcomes, and the reason we see just one discrete outcome and not all of them is because of a “limited perspective.”

But that’s not what Many Worlds is, in Many Worlds there are no discrete outcomes at all. If a photon hits a beam splitter and there is a 50% chance it will be reflected and show up on detector R and a 50% change it will be transmitted and show up on detector T, Many Worlds says that it will never show up on detector R or T at all. The discrete events of R or T simply never occur in Many Worlds.

Just saying there is a “limited perspective” does not get you anywhere. “Limiting a perspective” does not somehow get you to an eigenstate. Note that I am not saying in Many Worlds there are no “singular events.” Of course, if there are only “plural events,” i.e. if R and T both happen, then limiting your perspective to just one of them will give you a singular event. The point is more complicated than that: in Many Worlds there are simply not discrete events at all, so it is not as if R and T both happen in Many Worlds. Neither R or T happen, so there is no “limited perspective” that could give you R or T if neither the events R or T ever happen at all.

I don’t think there’s much difference between many worlds and random selection in the end, at least from our perspective. Either way we experience only state contingent on our state, so any quantum superposition that contains us (ok, sure, contains our brain) we can experience only one concrete resolution to, since the others would require our brain to be in a different state.

Randomness is not the problem. If fundamental randomness was the only difficulty in QM, there would not be so much debate around this subject. The issue is not randomness but that there is no possible way to construct a consistent statistical transition from the quantum state to a random classical outcome from the Schrodinger equation alone, you have to introduce some additional assumptions, and these additional assumptions inherently violate classical premises (such as locality or statistical independence).

Many Worlds does not escape this because it still posits the existence of a transition. To claim that the transition occurs only in our heads and not in physical reality is still positing the existence of a transition, and so there still needs to be some physical process by which the quantum state of waves in infinite-dimensional Hilbert space can be mapped onto the “limited perspective” that we consciously perceive. This mapping, again, requires additional assumptions, and these additional assumptions inherently violate classical premises, as all proposed assumptions for deriving Born probabilities in Many Worlds are manifestly nonlocal.

I’m not sure what it even means to say that you have a “limited perspective” in Many Worlds because you exist smeared out across all the possible branches and there is simply no discrete “you” localizable to a single branch.

Many worlds adds “but there is a disconnected copy of us experiencing the other valid states after we entered the superposition”, random chance says “and the other states disappeared when the superposition collapsed”, but without reaching past that horizon of our own state they’re measurably identical theories, so either both equally valid or both equally pointless speculation, depending on how strict you want to be.

Again, no, that is not Many Worlds. Many Worlds denies that we ever experience any outcome at all. Many Worlds is not a variant of an objective collapse model where all possible outcomes the quantum state could collapse to occur in a different branch of the multiverse. It denies that discrete events even occur at all. It does not argue that in the example of the photon that in one branch of the multiverse you perceive an event on detector R and another on detector T, but ultimately it is denying that the events associated with R and T even occur at all.

The problem that Einstein, Schrodinger, and Bell tried to point out is not “speculation” but that the orthodox interpretation and Many Worlds both make a claim about physical reality which they do not explain. They both take the form (1) there is an infinite-dimensional wave in Hilbert space, (2) you look at it, (3) a miracle happens, and (4) you perceive a discrete event localizable to 3D space. Both posit some sort of transition (which either occurs in external reality or in your head) which inherently implies a mapping from the invisible quantum state to observable reality yet neither actually provide this mapping.

Einstein first pointed this out with an example of radioactive decay, pointing out that the Schrodinger equation, no matter how much you evolve it, never gives you anything even with the appearance of a discrete event where an atom decays and emits a particle. It only gives you a quantum state for the emitted particle that its position spreads out over time.

Just saying abstract things like it’s a “limited perspective” does not address the issue because this is not a philosophical problem; you need a mathematical mapping or what the “interpretation” is claiming simply is not well-defined, i.e. it is not actually physically coherent. For many Copenhagenists they might argue being coherent doesn’t even matter because they only care about practical utility, and if a physical theory makes no physical sense, as long as this does not conflict with practical predictions it doesn’t matter, but Einstein wanted a physical theory that was coherent.

The gigantic, universal ψ wave that contains all the possible worlds is like Hegel’s dark night in which all cows are black: it does not account, per se, for the phenomenological reality that we actually observe. In order to describe the phenomena that we observe, other mathematical elements are needed besides ψ: the individual variables, like X and P, that we use to describe the world. The Many Worlds interpretation does not explain them clearly. It is not enough to know the ψ wave and Schrödinger’s equation in order to define and use quantum theory: we need to specify an algebra of observables, otherwise we cannot calculate anything and there is no relation with the phenomena of our experience. The role of this algebra of observables, which is extremely clear in other interpretations, is not at all clear in the Many Worlds interpretation.

— Carlo Rovelli, “Helgoland: Making Sense of the Quantum Revolution”

Yes, he was an Epsteinite, but his point was generally correct. Einstein, Schrödinger, and Bell all recognized that the orthodox interpretation of quantum mechanics makes no sense because it postulates a transition from quantum to classical with no explanation of how this actually occurs. They would not have liked Many Worlds either because it does not actually get rid of the transition, it just claims the classical world is an illusion so it shifts the transition to something happening in your brain, but then doesn’t explain how your brain could possibly create a world of discrete events happening in 3D space from a world where no discrete events ever happen that is just one giant continuous wave evolving in an infinite-dimensional space as there is no clear way to map the latter onto the former. Bell was around when Many Worlds was becoming popularized and so he did comment on it and pointed out it is nonsense and Everett never demonstrated any way to carry out this mapping consistently.

Don’t forget his contribution to paedomechanics.

real dragons? 🤔