[choeger]

QM is obviously very true in the sense that it makes useful predictions (in that sense, truth is somewhat a quantity). But it is arguably very inelegant in its seemingly ad-hoc introduction of probability. Naturally, one would hope to one day get a more principled explanation of this randomness.

What would be needed to make physicists search for such an explanation? Some kind of pattern in the "randomness"? Say, photons behave more like particles on Monday mornings?

[vecter]

What you want is a theory of local hidden variables. [0]

They are at odds with what quantum mechanics predicts (and what we have observed).

On a semi-related note, I might be reading too much into your comment, but I very much dislike when people imply that scientists haven’t thought outside or the box or tried other non-mainstream theories. They try all the time, but fail because those theories often aren’t true. What we’re left with are the best extant theories, even if they’re obvious incomplete.

[0] https://en.wikipedia.org/wiki/Local_hidden-variable_theory?w...

[choeger]

It is true that at my level of understanding I would intuitively prefer hidden variables. But that's not my point.

My point is that the notion of "measurement" or "wave function collapse" simply don't seem to explain anything. Instead they are just different words for what we observe. So yes, that is certainly useful but it also seems to be limiting.

A simple question would be: What is "measurement", i.e. what is the fundamental thing that forces a probability distribution to yield a concrete value? And why does it exist separately from said probability distribution?

Edit: to make things even clearer: I am not lamenting that there is no one working on mathematically consistent interpretations of QM. I know people are doing that and I know that this is difficult. Instead I am asking what would be a clearly visible limit of QM. Where would we, as a society, encounter a situation where we say: "We really need to explain the reasons behind QM or we won't get that problem here solved."

[zackees]

No.

Correct theories are suppressed all the time by oligarchs. See the electric car.

This assumption that the best is chosen is part of the problem of the scientific institution - the assumption that corruption doesn’t play a major role in what is allowed through the gate keepers.

[AgentME]

If you go with the Many-Worlds Interpretation, then trying to remove the randomness is nonsensical: the world just branches (in proportions as described by the Schrodinger equation), people on every branch have experience, and "randomness" is just what branch you find yourself on. The randomness of what branch you find yourself in is just like the randomness of what person you find yourself born as.

All classical theories and interpretations of QM already have indexical uncertainty (the randomness of what person you find yourself born as). MWI avoids adding any new kinds of entities not implied by the Schrodinger equation and effectively explains away quantum randomness by implying that it's the same thing as indexical uncertainty, instead of being a separate kind of randomness.

[tsimionescu]

On the contrary, it is still an open problem to rigorously derive the Born rule probabilities in MWI just from this perspective. Either way, the response will be equivalent to the Born rule: instead of positing that a measurement'outcome is proportional to the amplitude of the state, we posit that the number of branches in which an outcome happens is proportional to the amplitude of that outcome. Not sure why these are fundamentally different.

Also, the MWI idea of branching is no more satisfying or intuitive than the wave function collapse, which at least doesn't require an infinity of universes out of which some are much more probable than others.

Note also that there is only 1 of you in MWI, you just exist with different amplitudes in different states, but when interacting with another object, you become entangled with a single outcome and thus can no longer perceive the other states that other versions of you perceive. This is important, as otherwise physical quantities would not be properly conserved.

[GoblinSlayer]

The Born rule is statistical distribution, and statistics is certainly computable in MWI. It's a matter of converting the wave function into distribution basis, where it will have the Born rule distribution with amplitude close to 1, which means that observations have the Born rule distribution in most cases.

[kanzenryu2]

This is one thing I love about MWI... it has at least some kind of explanation for randomness. For every other interpretation they do some stuff and then choose a random outcome, and I want to ask "and how does that random step happen?"

[l33tman]

But it isn't that simple. There isn't a "proportional split" that can depend on the Schrödinger Equation. This is exactly why QM behaves non-intuitively in the first place - you can't add up probabilities from individual events, you have to add complex numbers and only at the "end" you square them and get probabilities. So it's would be a nice analogue in MWI that the world just splits up and that's why probabilities arise, but it doesn't fit.. :/

[pishpash]

This is a misunderstanding of QM. Probability isn't what's unusual, it's the Born rule and the fact that the world doesn't use probability laws over real numbers but over complex numbers. That's what gives waves some sense of reality.

[frongpik]

The probability waves may be regular real waves, it's just convenient to describe amplitude and phase at every point with a complex number. We could describe water surface the same way, but it wouldn't mean water is complex.

[pishpash]

The point is that waves are inherent in the description, whether it's complex numbers or amplitude + phase.

[diegoperini]

> What would be needed to make physicists search for such an explanation?

I'd say confirmation of a failed prediction by QM is what's needed.

[nojs]

Local hidden variables as an explanation has been experimentally refuted: https://en.m.wikipedia.org/wiki/Bell%27s_theorem

[pessimizer]

The probabilities spawned QM, not the reverse. The modern interpretation of QM is a reification of those probabilities - an insistence that they aren't the results of a process, but are just probabilities, irreduceably.

[AgentME]

And it's not just like people found these probabilities and then decided to stop trying to explain things and said "what if these are just how physics worked". Instead, people found that any attempts at removing the probabilities (through local hidden variable theories) ended in contradictions, and then accepted that they must be fundamental.

[chii]

> explanation of this randomness

what if randomness is an inherent property of nature?

[tsimionescu]

The problem is that QM doesn't allow randomness at the fundamental level. The Schrodinger equation is a linear differential equation, systems that evolve according to it evolve just like classical mechanics.

However, when you measure the state of such a system after however many steps of perfectly deterministic interactions you want, you find the system takes only one of the many possible states predicted by the Schrodinger equation, with a probability that depends on the amplitude of that state.

It is this discrepancy between the deterministic nature of the quantum world and the classical world, but the probabilistic nature of the crossing between them, that people find disconcerting.

MWI even does away with this to solve extent, explaining it as a kind of observation bias: as a particle interacts with a very independent system, it loses its ability to interact with itself (decoherence), and so we get many versions of the system each interacting with a single version of the particle, which stimulates classical physics for each version. From the perspective of any particular version of this system it is random with which particular version of the particle it interacts, even though at the universal level there is no randomness.