it isn’t scientifically accurate…

That’s a classical ambiguity, not a quantum ambiguity. It would be like if I placed a camera that recorded when cars arrived but I only gave you information on when it detected a car and at what time and no other information, not even providing you with the footage, and asked you to derive which car came first. You can’t because that’s not enough information.

The issue here isn’t a quantum mechanical one but due to the resolution of your detector. In principle if it was precise enough, because the radiation emanates from different points, you could figure out which one is first because there would be non-overlapping differences. This is just a practical issue due to the low resolution of the measuring device, and not a quantum mechanical ambiguity that couldn’t be resolved with a more precise measuring apparatus.

A more quantum mechanical example is something like if you apply the H operator twice in a row and then measure it, and then ask the value of the qubit after the first application. It would be in a superposition of states which describes both possibilities symmetrically so the wavefunction you derive from its forwards-in-time evolution is not enough to tell you anything about its observables at all, and if you try to measure it at the midpoint then you also alter the outcome at the final point, no matter how precise the measuring device is.

Let’s say the initial state is at time t=x, the final state is at time t=z, and the state we’re interested in is at time t=y where x < y < z.

In classical mechanics you condition on the initial known state at t=x and evolve it up to the state you’re interested in at t=y. This works because the initial state is a sufficient constraint in order to guarantee only one possible outcome in classical mechanics, and so you don’t need to know the final state ahead of time at t=z.

This does not work in quantum mechanics because evolving time in a single direction gives you ambiguities due to the uncertainty principle. In quantum mechanics you have to condition on the known initial state at t=x and the known final state at t=z, and then evolve the initial state forwards in time from t=x to t=y and the final state backwards in time from t=z to t=y where they meet.

Both directions together provide sufficient constraints to give you a value for the observable.

I can’t explain it in more detail than that without giving you the mathematics. What you are asking is ultimately a mathematical question and so it demands a mathematical answer.

I am not that good with abstract language. It helps to put it into more logical terms.

It sounds like what you are saying is that you begin with something a superposition of states like (1/√2)(|0⟩ + |1⟩) which we could achieve with the H operator applied to |0⟩ and then you make that be the cause of something else which we would achieve with the CX operator and would give us (1/√2)(|00⟩ + |11⟩) and then measure it. We can call these t=0 starting in the |00⟩ state, then t=1 we apply H operator to the least significant, and then t=2 is the CX operator with the control on the least significant.

I can’t answer it for the two cats literally because they are made up it a gorillion particles and computing it for all of them would be computationally impossible. But in this simple case you would just compute the weak values which requires you to also condition on the final state which in this case the final states could be |00⟩ or |11⟩. For each observable, let’s say we’re interested in the one at t=x, you construct your final state vector by starting on this final state, specifically its Hermitian transpose, and multiplying it by the reversed unitary evolution from t=2 to t=x and multiply that by the observable then multiply that by the forwards-in-time evolution from t=0 to t=x multiplied by the initial state, and then normalize the whole thing by dividing it by the Hermitian transpose of the final state times the whole reverse time evolution from t=2 to t=0 and then by the final state.

In the case where the measured state at t=3 is |00⟩ we get for the observables (most significant followed by least significant)…

• t=0: (0,0,+1);(+1,+i,+1)
• t=1: (0,0,+1);(+1,-i,+1)
• t=2: (0,0,+1);(0,0,+1)

In the case where the measured state at t=3 is |11⟩ we get for the observables…

• t=0: (0,0,+1);(-1,-i,+1)
• t=1: (0,0,+1);(+1,+i,-1)
• t=2: (0,0,-1);(0,0,-1)

The values |0⟩ and |1⟩ just mean that the Z observable has a value of +1 or -1, so if we just look at the values of the Z observables we can rewrite this in something a bit more readable.

• |00⟩ → |00⟩ → |00⟩
• |00⟩ → |01⟩ → |11⟩

Even though the initial conditions both began at |00⟩ they have different values on their other observables which then plays a role in subsequent interactions. The least significant qubit in the case where the final state is |00⟩ begins with a different signage on its Y observable than in the case when the outcome is |11⟩. That causes the H opreator to have a different impact, in one case it flips the least significant qubit and in another case it does not. If it gets flipped then, since it is the control for the CX operator, it will flip the most significant qubit as well, but if it’s not then it won’t flip it.

Notice how there is also no t=3, because t=3 is when we measure, and the algorithm guarantees that the values are always in the state you will measure before you measure them. So your measurement does reveal what is really there.

If we say |0⟩ = no sleepy gas is released and the cat is awake, and |1⟩ = sleepy gas is released and the cat go sleepy time, then in the case where both cats are observed to be awake when you opened the box, at t=1: |00⟩ meaning the first one’s sleepy gas didn’t get released, and so at t=2: |00⟩ it doesn’t cause the other one’s to get released. In the case where both cats are observed to be asleep when you open the box, then t=1: |01⟩ meaning the first one’s did get released, and at t=2: |11⟩ that causes the second’s to be released.

When you compute this algorithm you find that the values of the observables are always set locally. Whenever two particles interact such that they become entangled, then they will form correlations for their observables in that moment and not later when you measure them, and you can even figure out what those values specifically are.

To borrow an analogy I heard from the physicist Emily Adlam, causality in quantum mechanics is akin to filling out a Sudoku puzzle. The global rules and some “known” values constrains the puzzle so that you are only capable of filling in very specific values, and so the “known” values plus the rules determine the rest of the values. If you are given the initial and final conditions as your “known” values plus the laws of quantum mechanics as the global rules constraining the system, then there is only one way you can fill in these numbers, those being the values for the observables.

“Free will” usually refers to the belief that your decisions cannot be reduced to the laws of physics (e.g. people who say “do you really think your thoughts are just a bunch of chemical reactions in the brain???”), either because they can’t be reduced at all or that they operate according to their own independent logic. I see no reason to believe that and no evidence for it.

Some people try to bring up randomness but even if the universe is random that doesn’t get you to free will. Imagine if the state forced you to accept a job for life they choose when you turn 18, and they pick it with a random number generator. Is that free will? Of course not. Randomness is not relevant to free will. I think the confusion comes from the fact that we have two parallel debates of “free will vs determinism” and “randomness vs determinism” and people think they’re related, but in reality the term “determinism” means something different in both contexts.

In the “free will vs determinism” debate we are talking about nomological determinism, which is the idea that reality is reducible to the laws of physics and nothing more. Even if those laws may be random, it would still be incompatible with the philosophical notion of “free will” because it would still be ultimately the probabilistic mathematical laws that govern the chemical reactions in your brain that cause you to make decisions.

In the “randomness vs determinism” debate we are instead talking about absolute determinism, sometimes also called Laplacian determinism, which is the idea that if you fully know the initial state of the universe you could predict the future with absolute certainty.

These are two separate discussions and shouldn’t be confused with one another.

In a sense it is deterministic. It’s just when most people think of determinism, they think of conditioning on the initial state, and that this provides sufficient constraints to predict all future states. In quantum mechanics, conditioning on the initial state does not provide sufficient constraints to predict all future states and leads to ambiguities. However, if you condition on both the initial state and the final state, you appear to get determinstic values for all of the observables. It seems to be deterministic, just not forwards-in-time deterministic, but “all-at-once” deterministic. Laplace’s demon would just need to know the very initial conditions of the universe and the very final conditions.

Many Worlds is an incredibly bizarre point of view.

Quantum mechanics has two fundamental postulates, that being the Schrodinger equation and the Born rule. It’s impossible to get rid of the Born rule in quantum mechanics as shown by Gleason’s Theorem, it’s an inevitable consequence of the structure of the theory. But Schrodinger’s equation implies that systems can undergo unitary evolution in certain contexts, whereas the Born rule implies systems can undergo non-unitary evolution in other contexts.

If we just take this as true at face value, then it means the wave function is not fundamental because it can only model unitary evolution, hence why you need the measurement update hack to skip over non-unitary transformations. It is only a convenient shorthand for when you are solely dealing with unitary evolution. The density matrix is then more fundamental because it is a complete description which can model both unitary and non-unitary transformations without the need for measurement update, “collapse,” and does so continuously and linearly.

However, MWI proponents have a weird unexplained bias against the Born rule and love for unitary evolution, so they insist the Born rule must actually just be due to some error in measurement, and that everything actually evolves unitarily. This is trivially false if you just take quantum mechanics at face value. The mathematics at face value unequivocally tells you that both kinds of evolution can occur under different contexts.

MWI tries to escape this by pointing out that because it’s contextual, i.e. “perspectival,” you can imagine a kind of universal perspective where everything is unitary. For example, in the Wigner’s friend scenario, for his friend, he would describe the particle undergoing non-unitary evolution, but for Wigner, he would describe the system as still unitary from his “outside” perspective. Hence, you can imagine a cosmic, godlike perspective outside of everything, and from it, everything would always remain unitary.

The problem with this is Hilbert space isn’t a background space like Minkowski space where you can apply a perspective transformation to something independent of any physical object, which is possible with background spaces because they are defined independently of the relevant objects. Hilbert space is a constructed space which is defined dependently upon the relevant objects. Two different objects described with two different wave functions would be elements of different Hilbert spaces.

That means perspective transformations are only possible to the perspective of other objects within your defined Hilbert space, you cannot adopt a “view from nowhere” like you can with a background space, so there is just nothing in the mathematics of quantum mechanics that could ever allow you to mathematically derive this cosmic perspective of the universal wave function. You could not even define it, because, again, a Hilbert space is defined in terms of the objects it contains, and so a Hilbert space containing the whole universe would require knowing the whole universe to even define it.

The issue is that this “universal wave function” is neither mathematically definable nor derivable, so it only has to be postulated, as well as its mathematical properties postulates, as a matter of fiat. Every single paper on MWI ever just postulates it entirely by fiat and defines by fiat what its mathematical properties are. Because the Born rule is inevitable form the logical structure of quantum theory, these mathematical properties always include something basically just the same as the Born rule but in a more roundabout fashion.

None of this plays any empirical role in the real world. The only point of the universal wave function is so that whenever you perceive non-unitary evolution, you can clasp your hands together and pray, “I know from the viewpoint of the great universal wave function above that is watching over us all, it is still unitary!” If you believe this, it still doesn’t play any role in how you would carry out quantum mechanics, because you don’t have access to it, so you still have to treat it as if from your perspective it’s non-unitary.

Yes they are both particles and waves, but “collapse” is also purely a mathematical trick and isn’t something that physically occurs. Quantum theory is a statistical theory and like all statistical theories, you model the evolution of the system statistically up until it gets to the point you want to make a prediction for. But state vector notation (the “wave function”) is just a mathematical convenience that works when you are dealing with a system in a pure state that is only subject to Schrodinger evolution. It doesn’t work when a system undergoes decoherence, which follows the Born rule, and that says to compute the square magnitude of the state vector. But if you compute the square magnitude of the state vector, you get a new vector that is no longer a valid state vector.

Conveniently, whenever a system is subject to decoherence/Born evolution, that happens to be a situation when you can acquire new physical information about a system, whereas whenever it is subject to Schrodinger evolution, that corresponds to a situation when you cannot. People thus do this mathematical trick where, whenever a system undergoes decoherence/Born evolution, they take pause their statistical simulation, grab the new information provided about the system, and plug it back into the state vector, which allows them to reduce one probability amplitude to 1 and the rest to 0, which gives you a valid state vector again, and then they press play on their statistical simulation and carry it on from there.

This works, yes, but you can also pause a classical statistical simulation, grab new information from real-world measurements, and plug it in as well, unpause the simulation, and you would also see a sudden “jump” in the mathematics, but this is because you went around the statistical machinery itself into the real world to collect new information to plug into the computation. It doesn’t represent anything actually physically occurring to the system.

And, again, it’s ultimately just a mathematical trick because it’s easier to model a system in a pure state because you can model it with the state vector, but the state vector (the “wave function”) is simply not fundamental in quantum mechanics and this is a mistake people often make and get confused by. You can evolve a state vector according to Schrodinger evolution only as long as it is in a pure state, the moment decoherence/Born evolution gets involved, you cannot model it with the state vector anymore, and so people use this mathematical trick to basically hop over having to compute what happens during decoherence, and then delude themselves into thinking that this “hop” was something that happened in physical reality.

If you want to evolve a state vector according to the Schrodinger equation, you just compute U(t)ψ. But if you instead represent it in density matrix form, you would evolve it according to the Schrodinger equation by computing U(t)ψψᵗU(t)ᵗ. It obviously gets a lot more complicated, so in state vector form it is simpler than density matrix form, so people want to stick to state vector form, but state vector form simply cannot model decoherence/Born evolution, and so this requires you to carry out the “collapse” trick to maintain in that notation. If you instead just model the system in density matrix form, you don’t have to leave the statistical machinery with updates about real information from the real world midway through your calculations, you can keep computing the evolution of the statistics until the very end.

What you find is that the decoherence/Born evolution is not a sudden process but a continuous and linear process computed with the Kraus operators using ΣKᵢ(t)ρKᵢ(t)ᵗ and takes time to occur, cannot be faster than the quantum speed limit.

While particles can show up anywhere in the universe in quantum mechanics, that is corrected for in quantum field theory. A particle’s probability of showing up somewhere doesn’t extend beyond its light cone when you introduce relativistic constraints.

For some reason I can’t get the “reallyreallyrandom” link to work it just endlessly loads for me. I want to know how they actually know it’s quantum randomness and not just thermal noise. If they can genuinely prove it’s quantum random then they should throw it on a PCIe card and sell it. There is a small market for it, I own one from Quantis and that cost me like two grand, it’s optics based QRNG and has a bunch of papers proving it is quantumly random. I’d want to see something like that for that transistor diode method if it’s really that cheap to build a QRNG.

There is no way to “establish whether or not there is an objective reality.” It’s a philosophical position. You either take the reality which we observe and study as part of the material sciences to be objective reality, or you don’t believe it’s objective reality and think it is all sort of invented in the “mind” somehow. Either position you take, you cannot prove or disprove either one, because even if you take the latter position, no evidence I present to you could change your mind because to be presented evidence would only mean for that evidence to appear in the mind, and thus wouldn’t prove anything. The best argument we can make is just taking the reality we observe as indeed reality is just philosophically simpler, but that also requires you to philosophically value simplicity, which you cannot prove what philosophical principles we should value with science either.

Choosing between parties is arguably less democratic because in many countries with such a system, like the USA, you basically just have corporations/corporate media choosing the candidates, so your “choice” is between corporate candidates, so corporations always win. There is no option to reject the nominee entirely, while in China’s system you can reject the nominee. you can just straight up veto candidates.

Westerners often also look at the very end of the process and ignore everything leading up to it. They will say “there’s only one candidate on the ballot!” as proof it’s undemocratic (even though this happens all the time in the US too…). But this ignores the entire democratic process leading up to how the candidate gets on the ballot in the first place. In Cuba for example, candidates getting on the ballot is a two-year long process resulting from local elections and meetings with mass organizations, but they ignore this entire process and just focus on the final election at the very end.

There’s still a pattern in the results, so by one means or another we want to explain the results. Just calling it nondeterministic, if I understand right, would be just saying you can’t predict it from prior observations. So, whatever language you use to describe this puzzling situation, the puzzling situation thus far remains.

I mean nondeterministic in a more fundamental sense, that it is just genuinely random and there is no possibility of predicting the outcome because nothing in nature actually pre-determines the outcome.

A priori?

Through rigorous experimental observation, it’s probably the most well-tested finding in all of science of all time.

Or because it best fits with Relativity? It sounds about as strong as saying, “we know time is universal.” It’s obvious, has to be true, but apparently not how the universe functions.

So we can never believe anything? We might as well deny the earth is round because people once thought time is absolute now we know it’s relative, so we might as well not believe in anything at all! Completely and utterly absurd. You sound just like the creationists who try to undermine belief in scientific findings because “science is always changing,” as if that’s a bad thing or a reason to doubt it.

We should believe what the evidence shows us. We changed our mind about the nature of time because we discovered new evidence showing the previous intuition was wrong, not because some random dude on lemmy dot com decided their personal guesses are better than what the scientific evidence overwhelmingly demonstrates.

If you think it’s wrong show evidence that it is wrong. Don’t hit me with this sophistry BS and insult my intelligence. I do not appreciate it.

Maybe you are right that special relativity is wrong, but show me an experiment where Lorentz invariance is violated. Then I will take you seriously. Otherwise, I will not.

trvth nvke

Even though China gave up on most communist ambitions post-Dheng

No they haven’t.

Quantum nonlocality really is a misnomer. Nothing is nonlocal about it. We know from the No-communication Theorem that there is no physical interaction you could carry out with one particle in an entangled pair that would affect the state of the other particle, and we know it is compatible with special relativity, which is a fundamentally local theory, as such a unification of the two is how we get quantum field theory.

“Local realism” is also a nonsensical term. There is no agreed upon rigorous definition of “realism” and its introduction to the scientific literature has only served to confuse the discussion and promote quantum mysticism because people think because Bell’s theorem supposedly shows that “local realism” is false that you there have to choose between locality or realism, but not both, and since we know the universe is local, we have to conclude there is no objective reality, devolving into mysticism and idealism.

This isn’t just a problem in popsci articles but even in published scientific literature. This “local realism” hogwash has caused even otherwise respectable physics to publish nonsense about how reality doesn’t exist. The term “realism” is never used in Bell’s theorem and has tn relevance to it. Bell’s theorem is about local hidden variable theories, and it is complete nonsense to conflate hidden variables with “realism” as if your only choices are to believe the reality is deterministic or to deny reality even exists! What kind of options are those? What about a third option that reality exists and it is just nondeterministic?

What Bell’s theorem shows is that quantum mechanics cannot be replaced with a local hidden variable theory, and since we know the universe is local, that means it cannot be replaced with a hidden variable theory. It forces us to accept nondeterminism, it doesn’t force us to deny reality, nor does it prove there is nonlocality.

It can, under certain conditions, contain information about things at a distance, but a function is not a physical entity and its reduction is not a physical process, so none of this reflects anything superluminal actually going on in physical reality.