> how can you prove that both particles were not having the same state from the start?
But this is exactly what these experiments aim to prove. That kind of predeterminism is precisely a form of local hidden variable theory. Such a theory is disproved if we can prove the violation of a Bell inequality. The standard reference for understanding the connection is this laymans-terms paper by Mermin:
If we accept that this experiment is indeed a standard-loophole-free violation of Bell's inequality, we then conclude that we must give up one of three things: locality, realism, or all free will. This rules out any local hidden-variable theory. The mainstream view is then to keep locality and free will. Some alternative theories (notably Bohmian ones) give up locality and keep realism, but this is strongly at odds with what we know from special relativity, and indeed locality is assumed in all work on quantum field theory (through Lorenz invariance) which has been verified to match experiments to a precision above that of any other physical theory. The third option, which essentially no-one supports, is that free will is impossible in our universe and that everything everywhere is predetermined.
Is there any chance that you can expand on the precise meaning of "free will" in a quantum physics context? My understand of the usual common-sense interpretation is roughly "The actions that I take are supernatural, and are not a consequence of physical laws", which seems quite absurd to me, and I'd expect that to have very little support in the physics community. If not this, then what does "realism" and "free will" mean here?
Free will is typically defined to mean you[n+1] != classical_function(you[n]), at least sometimes or with some probability. That does not necessarily imply anything supernatural, though if the supernatural (or any kind of dualism) exists that would explain it. It could also arise due to quantum noise or any other process that violates classical determinism.
There are those who define free will a bit differently though. It's not a precise term. Another definition is that you[n+1] cannot be computed from any function other than you or something isomorphic with you -- in other words you are not coarse-grainable or predictable using any subset of your state. Someone would have to literally make a copy of you to predict your behavior, possibly down to the atomic or quantum level.
I've heard functions/processes with this property called computationally irreducible:
Basically the computational irreducibility definition of free will just means nothing outside of you can predict what you're going to do unless it has an exact copy of you or something functionally equivalent (uploaded mind, etc.).
Another variation on the same idea is the "arrow of time" view put forward by Ilya Prigogine:
This is IMHO very close to if not identical to Wolfram's computational irreducibility, but framed a bit differently.
Obviously humans are somewhat predictable, but somewhat predictable doesn't imply deterministic. My personal opinion is that the second theory (irreducibility/arrow of time) is almost certainly true, and the first is also probably true. So we are probably both irreducible and indeterminate. I'd say the same is likely true of any living thing and possibly other complex natural processes.
My opinion is that we are predictable and deterministic, but we choose to cling to the idea of us being more than that because we can't deal with the other option. The other option is quite simple, from what I see: we'll never manage to completely read, simulate and predict a complex system like our body, so in reality nobody will be able to predict what we'll do - and for me that's enough to feel comfortable. From what I see free will is defined by others as some kind of magic process through which our decisions are based on some random factor which is unpredictable. I'd say the randomness doesn't need to exist as long as the unpredictability holds.
> My understand of the usual common-sense interpretation is roughly "The actions that I take are supernatural, and are not a consequence of physical laws", which seems quite absurd to me, and I'd expect that to have very little support in the physics community.
I can't speak for the physics community, but most philosophers are ok with a purely physical being having free will.
> Finally we need to assume that we have complete freedom to choose which of several measurements to perform - this is the third principle, also called the no-conspiracy principle.
> Freedom refers to the physical possibility to determine settings on measurement devices independently of the internal state of the physical system being measured.
No, that's not sufficient. Since the observables are represented by self-adjoint linear operators on a Hilbert space which for some observables is infinite-dimensional, there is an infinite number of states for each particle, so Graham's numbers are insufficient.
As the wikipedia page mentions, physicists who work in the field and who believe there are hidden variables agree that experiments show these must be non-local.
You are confusing a model with reality. We have no way to observe the difference between a sufficiently large number and infinity.
For an overly pedantic counter example, each particle could simply simulate the rest of the universe to some finite precision.
PS: That's not to say you can't rule out specific theory's that use local variables. And we should use the simplest theory that works, however it's counter productive to suggest we can rule out all forms of local variables.
Nope. Entanglement has been observed for particles that have never coexisted in time [1]. This would mean that even your overly pedantic counter example requires that we give up free will: since we choose what property to measure, the first particle is unable to simulate the outcome of the second measurement unless it can simulate what we choose. (And yes, it's generally accepted that assuming superdeterminism, aka. no free will, allows a local hidden variable theory.)
In other words it still works. Note, it needs not be 100% accurate simulation. If it's good enough we can't tell.
Not that I think reality works this way, but the goal is to look for ways that a theory falls down, not look for evidence in support of a theory.
PS: FTL communication also works as a means to sidestep the need for a lot of quantum weardness. Sure, we don't like it but that does not mean it can't be happening.
"The third option, which essentially no-one supports, is that free will is impossible in our universe and that everything everywhere is predetermined."
Well, not just "everything everywhere is predetermined" (which some people do support) but quite specifically predetermined so that every scientist that has so far made a decision on what to measure in these quantum experiments has had that decision correlate strangely with the underlying physical result.
Might it be that Lorenz invariance breaks down when Bell's inequality is violated? Is that what Bohmian theories postulate? Or is there independent evidence for Lorenz invariance under the conditions of the present experiment?
No. Bohmian theories are non-relativistic to begin with, so they don't have anything to say about Lorentz invariance.
> is there independent evidence for Lorenz invariance under the conditions of the present experiment?
If you mean, has Lorentz invariance been tested for photons and electrons, yes, it has, to high accuracy. The Wikipedia article has a good summary of experiments:
But this is exactly what these experiments aim to prove. That kind of predeterminism is precisely a form of local hidden variable theory. Such a theory is disproved if we can prove the violation of a Bell inequality. The standard reference for understanding the connection is this laymans-terms paper by Mermin:
http://web.pdx.edu/~pmoeck/pdf/Mermin%20short.pdf
If we accept that this experiment is indeed a standard-loophole-free violation of Bell's inequality, we then conclude that we must give up one of three things: locality, realism, or all free will. This rules out any local hidden-variable theory. The mainstream view is then to keep locality and free will. Some alternative theories (notably Bohmian ones) give up locality and keep realism, but this is strongly at odds with what we know from special relativity, and indeed locality is assumed in all work on quantum field theory (through Lorenz invariance) which has been verified to match experiments to a precision above that of any other physical theory. The third option, which essentially no-one supports, is that free will is impossible in our universe and that everything everywhere is predetermined.