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It addresses a related but slightly different question. You flip a coin: there is a 50/50 chance of heads or tails. These probabilities are due to our incomple
by millstone 10y ago
It addresses a related but slightly different question.
You flip a coin: there is a 50/50 chance of heads or tails. These probabilities are due to our incomplete knowledge: the coin knows which face is up, and it's only because we don't know that we assign probabilities.
Now if we have a particle that is 50/50 spin up or spin down, we may think that it is like a coin: the spin is already determined, we just don't know which it is. This is where Bell's Inequality comes in and shuts that idea down. Until the particle is observed, it simply does not have a spin, in the same way that a coin has an up face.
So if a pre-observed particle does not have a spin, what does it actually have? This is the core of the dispute in the article. There's two possible answers:
1. A wavefunction (psi), aka a quantum state. This is the psi-ontic view which argues the wavefunction is a real and physical thing that evolves in time regardless of any observations. MWI and Bohm are both psi-ontic theories.
2. Nothing. This is the psi-epistemic view which holds that it makes no sense to talk about a particle's reality in-between observations. In this view, only measurements and their results are real; the wavefunction is a state of knowledge. Copenhagen, Consistent Histories, and the minimalist ensemble interpretations are psi-epistemic.
- TheOtherHobbes 10y agoThe argument about what "a real and physical wavefunction" means boils down to this question: "Is there a science of the wavefunction beyond QM?" Can you ask more questions about it, break it down into constituent processes, maybe re-engineer it? Or is it opaque and closed and there is no possible way to do further science on it? My money is on option 1, because it's hard to imagine an organising principle you can't possibly do any science on. Wavefunction science may be weird and like nothing ever seen before - especially given non-locality and possibly non-realism. But it's a good rule of thumb in science that when nature becomes counterintuitive you're on the right track. If the answer was obvious and familiar you wouldn't need original and creative thinking to find it. Option 2 seems like an admission of total defeat. It would be the first time in science where we hit a wall and didn't even try to understand what it was made of. That doesn't mean it can't be correct. But it does mean we shouldn't give up without trying for quite a while longer. And if we do give up, it should only be after discovering some kind of meta-Bell theorem which proves there's no way to go further.
- yters 9y agoIf I understand it all correctly, the article describes an experiment to test your preferred option, but so far the evidence is in favor of option 2?