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linuxhansl | on: I don't understand quantum physics (2018)
FWIW (and it's not worth a lot, since I'm a layperson), I think the interpretation that makes the most sense to me is Quantum Decoherence (https://en.wikipedia.org/wiki/Quantum_decoherence).

My interpretation of the interpretation is that the universe is a giant constraint resolution system. Particles are free to be anywhere randomly as long as they do not randomly interact with other particles. As soon as they interact they have fewer "degrees of freedom", since now they interacted. When they interact with anything macroscopic they have no freedom left. Makes sense to me anyway.

monktastic1 | parent | next
Decoherence isn't an interpretation, but an experimentally established fact. What makes interpretations interpretations is that they cannot be experimentally distinguished (or in some cases, can only be with great difficulty). That said, the study of decoherence has certainly made aspects of the measurement problem easier to come to terms with, which in turn has bearing on the intuitive draw of some interpretations over others. In particular, it helps answer when universes should be said to "split" in MWI (though, as many will rightly tell you, that's not a complete solution to the measurement problem, as decoherence is still unitary--i.e., there's no in-principle irreversibility there).
rcxdude | parent | next
Decoherence is how you get from "Maybe the wave function never collapses" to "Maybe there are many parallel 'universes' in QM.".
kgwgk | root | parent
Decoherence gets you a diagonal density matrix description of the world. It doesn't get you a single-state description of the world. Going from "There are many parallel universes" to "and we are in one of them" still takes a lot of handwaving.
mitthrowaway2 | root | parent
But we're not in one of them. We're in all of them. Yours is a misunderstanding of how it feels to be in a quantum superposition. There's no component of the wave function in which Schrodinger's cat experiences anything other than being alive or being dead. There's no component in which it feels like it's in some ghostly combination of both outcomes. Both components of the wave function exist in superposition, and to the extent that they are decoherent, they do not interact and do not even notice that they have company. I don't mean this only as an academic statement; it's also true of you and me, at this very moment.
tsimionescu | root | parent | next
> There's no component of the wave function in which Schrodinger's cat experiences anything other than being alive or being dead.

The problem is that this is not what Schrodinger predicts, though. If |alive> and |dead> are valid solutions to the Schrodinger equation of some system, then so is any linear combination of them whose norm is one, such as 1/sqrt(2) |alive> + 1/sqrt(2) |dead>. So the math of QM predicts that there should be infinitely many cats that should feel partly alive and partly dead, many times more than the one live cat and the one dead cat. And yet you don't find this in any classical experiment.

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monktastic1 | root | parent | next
It's a bit like:

"Doc, I feel pain in my toe."

"No, sorry, the math says you don't."

"Okay, but like... I do."

"Sorry, you're just not good at accepting math!"

Not a perfect analogy, of course, but people have competing intuitions of what to do when the map fails to match the territory. MWI abandons the latter, most prefer the former.

podocarp | root | parent | next
If that isn't absurd, then I don't know what is.
mitthrowaway2 | root | parent
I think the alternatives would be more absurd:

- That humans can't be put into quantum superpositions, or

- That a human being in a quantum superposition of two states A and B would feel at all to that human like being in a quantum superposition of two states A and B, when neither of those states is "a human feeling like they're in a superposition of two states A and B".

Follow this to its conclusion, and you end up with a superposition of A and B meaning: "the universe is in a superposition, containing a component where a human believes that they're in state A, and a component where a human believes that they're in state B. Within both branches, the human thinks their wavefunction collapsed in that state". This is exactly the way that all interpretations of QM already understand things to work with particles in superpositions.

diedyesterday | root | parent | next
Every state is a superposition. Even eigenstates (of some operator, e.g. X) are superpositions (of eigenstates of some other operator, e.g. P). So everything is a superposition and being superposition or not is relative.
kgwgk | root | parent
There's the handwaving.
goatlover | parent
Decoherence only hides entanglement by having the entire world go into a complex superposition. It's entirely compatible with MWI. Decoherence does not resolve the measurement problem on its own. It's not a separate interpretation. It only provides us a mathematical reason for why the world appears classical.
tsimionescu | root | parent
Specifically, decoherence provides a mathematical reason why we don't see self-interference and similar quantum phenomena on classical objects. It doesn't on its own explain why the single classical world arises from the infinitely many solution pairs to any quantum equation.