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Comment by Symmetry | Hacker News Reader

QM provides a clear set of equations that govern how wavefunctions evolve, but some versions also include the notion that wavefunctions collapse when an observation is made, but there are no equations or even firm rules for when this collapse is supposed to happen. Many-worlds is founded on the observation that the equations governing wavefunctions are sufficient in and of themselves to explain the observations that originally led people to believe that waveforms collapse, and that therefore the collapse postulate ought to be discarded as redundant. And because it's spooky action at a distance.

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> ... but there are no equations or even firm rules for when this collapse is supposed to happen

That's why it isn't science ;)

Maybe when QM was being developed "collapse" was a debated concept; I'm not too familiar with its history. Currently though, modern QM predicts that ensembles of identically prepared systems select an eigenstate of the linear operator corresponding to whatever observable it is you're measuring. Each of these eigenstates has a probability that can be calculated for it, and the mean value of these measurements is given by <Ψ|A|Ψ>, where A is the operator. I see no implications of collapse with this -- just probabilities of what values you will obtain in experiment.

> I see no implications of collapse with this -- just probabilities of what values you will obtain in experiment.

Not exactly, your statement is correct for single states, however it breaks down for entangled states. When one wavefunction describes two or more particle a measurement on one particle can be thought of collapsing the two particle wavefunction, which then forces the other particle into a well defined state.

Edit, I am not arguing in favour many worlds theory, only that the 'collapse' of the wavefunction is a well developed and useful idea in quantum physics.

I guess I just view the wavefunction as an inherently multiparticle function on a configuration space. The concept of approximating single-particle states seems peculiar to me; it seems simpler just to have one state for an entire system (and the corresponding probabilities of what measurements you'll get on that system, regardless of how the system is distributing spatially). Then again, we're coming from different research backgrounds so we probably have a different way of looking at it ;)

Quantum entanglement doesn't seem to be particularly unusual any more so than the fact that electron-electron correlation must be taken into effect when computing energy levels with some kind of QMC. All particles within a quantum system are correlated, so entanglement just kind of falls naturally out of that; I'm not assuming any kind of locality. I suppose what you're saying is that collapse is defined as the process of "fixing" these correlations?

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