[danbruc]

Do I get this right? Wave function collapse due to measurements is not real, the wave function evolves unitarily all the time. But as quantum states get amplified into the macroscopic world, superposition states are somehow amplified asymmetrically which makes it look like wavefunction collapse.

[jfengel]

Pretty close.

The wave function is still symmetric, but it takes on a bimodal distribution, with very little overlap. For any given event, it will be affected only by the half of the distribution that it's in. The other half has basically zero effect. The further time evolves, that effect becomes even smaller -- as in, the odds of an experiment demonstrating it quickly go towards 1 in 10^googol^googol.

You can round that down to exactly zero and call it "collapse". Or you can keep thinking about the entirety of the wave function, and call it a "multiverse". That rounding is technically invalid, but it simplifies the conceptualization (and the math) to a massive, massive degree without affecting the outcome in any pragmatically measurable way.

(One more caveat: "symmetry" implies we're talking about a wave function with a 50-50 superposition. That's not a requirement, but it simplifies an already complex explanation.)

[superposeur]

Yes, except for the “asymmetrically” part. In other words, Many Worlds.

[danbruc]

But isn’t it conceivable, because the original quantum state contains probabilities of different outcomes, that one imprint might correspond to “up” and another to “down,” [...] [Zurek’s theory] predicts that all the imprints must be identical.

Does this not imply that there is an asymmetry, one half of the state gets imprinted, the other half neglected? This however also raises the question about the basis, what is a superposition and what is not depends on the choice of basis. Is there a special basis just as pointer states are somehow special?