It is a personal peeve when any explanation of the Bell Inequality fails to mention the determinist Big Loophole: It rules out nearly all local hidden-variable theories, except those for which the entire universe is ruled by hidden variables. If you reject the assumption of counterfactual definiteness (the idea that there is a meaningful answer to the question “what answer would I have gotten, had I conducted a different experiment?”), local hidden variable theories are not ruled out. This leads to superdeterminism and theories which assume that, through either hidden variables stretching back to t=0 or backwards-in-time signals, the universe accounted for the measurement and the result was determined to match.
This is, in fact, what I held to be the most likely total explanation for years, until I better understood both its implications and MWI. Which, in fact, also rejects counterfactual definiteness. MWI does it one better; it rejects factual definiteness, the idea that there is a well-defined answer to the question “What answer did I get?”, since in alternate worlds you got different answers.
Sorry for being a pain, but I didn’t understand exactly what you said. If you’re still an active user, could you clear up a few things for me? Firstly, could you elaborate on counterfactual definiteness? Another user said contrafactual, is this the same, and what do other interpretations say on this issue?
Secondly, I’m not sure what you meant by the whole universe being ruled by hidden variables, I’m currently interpreting that as the universe coming pre-loaded with random numbers to use and therefore being fully determined by that list along with the current probabilistic laws. Is that what you meant? If not, could you expand a little on that for me, it would help my understanding. Again, this is quite a long time post-event so if anyone reading this could respond that would be helpful.
Firstly, I am not an expert in QM, so you should take everything I say with a whole serving of salt.
1) Yes, counterfactual = contrafactual. What other interpretations of QM say about counterfactual definiteness I don’t know. But wikipedia seems to give at least a cursory understanding to what is necessary for any interpretation to QM.
2) You could understand it that way, yes. Basically, the existence of hidden variables means ‘just’ that our current theory of QM is incomplete. So basically there is no collapsing wave function or decoherence or anything and all the seeming randomness we observe just comes from our not knowing which values those hidden variables take.
Again, if all I have said is complete and utter nonsense, please correct me!
The problem with superdeterminism it that it cannot be Turing-computable (in a practical sense, that we would be able to build a machine that would tell us what would happen in any simple quantum experiment.) To see this, imagine you have a machine which tells you before any experiment whether a photon will go through the filter or not. Run this computer, say, a thousand times, then decide which filter to use depending on the result. (If it predicts ~%20, then do the one that should give you ~5.8%, and vice-versa). Unless the machine affects the results, you will find that it is wrong.
I fail to see how that has any relevance whatsoever. I think you are very confused about something, though I’m not sure what.
Talking about “Turing computability in a practical sense” is nonsensical; computability is defined by an infinite-tape machine with arbitrarily large finite time to compute, neither of which we have in a practical sense, and most cases where computability is in doubt make use of both properties.
Superdeterminism also doesn’t need to care at all about the computer you’ve made to predict in advance what will happen. Unless you’ve found a way to “entangle” your computer with the hidden variables which determine the outcome of the result, the results it gives will know nothing about what the actual outcome will be, and just give you the Born probabilities instead.
And which other interpretation of quantum mechanics is Turing-computable, exactly?
In principle, you could (as mentioned) get some other process connected to the same hidden variables, in which case you could predict some events with perfect accuracy, which would be pretty definitive confirmation of the hidden variable theory.
It is a personal peeve when any explanation of the Bell Inequality fails to mention the determinist Big Loophole: It rules out nearly all local hidden-variable theories, except those for which the entire universe is ruled by hidden variables. If you reject the assumption of counterfactual definiteness (the idea that there is a meaningful answer to the question “what answer would I have gotten, had I conducted a different experiment?”), local hidden variable theories are not ruled out. This leads to superdeterminism and theories which assume that, through either hidden variables stretching back to t=0 or backwards-in-time signals, the universe accounted for the measurement and the result was determined to match.
This is, in fact, what I held to be the most likely total explanation for years, until I better understood both its implications and MWI. Which, in fact, also rejects counterfactual definiteness. MWI does it one better; it rejects factual definiteness, the idea that there is a well-defined answer to the question “What answer did I get?”, since in alternate worlds you got different answers.
That helps me. In his book Quantum Reality, Nick Herbert phrases it this way:
which is cutely aphoristic, but confused me. What does contrafactuality even mean in MWI?
Pointing out that MWI rejects factual definiteness clears things up nicely.
Sorry for being a pain, but I didn’t understand exactly what you said. If you’re still an active user, could you clear up a few things for me? Firstly, could you elaborate on counterfactual definiteness? Another user said contrafactual, is this the same, and what do other interpretations say on this issue?
Secondly, I’m not sure what you meant by the whole universe being ruled by hidden variables, I’m currently interpreting that as the universe coming pre-loaded with random numbers to use and therefore being fully determined by that list along with the current probabilistic laws. Is that what you meant? If not, could you expand a little on that for me, it would help my understanding. Again, this is quite a long time post-event so if anyone reading this could respond that would be helpful.
Firstly, I am not an expert in QM, so you should take everything I say with a whole serving of salt.
1) Yes, counterfactual = contrafactual. What other interpretations of QM say about counterfactual definiteness I don’t know. But wikipedia seems to give at least a cursory understanding to what is necessary for any interpretation to QM.
2) You could understand it that way, yes. Basically, the existence of hidden variables means ‘just’ that our current theory of QM is incomplete. So basically there is no collapsing wave function or decoherence or anything and all the seeming randomness we observe just comes from our not knowing which values those hidden variables take.
Again, if all I have said is complete and utter nonsense, please correct me!
Also not a QM expert, but this matches my understanding as well.
The problem with superdeterminism it that it cannot be Turing-computable (in a practical sense, that we would be able to build a machine that would tell us what would happen in any simple quantum experiment.) To see this, imagine you have a machine which tells you before any experiment whether a photon will go through the filter or not. Run this computer, say, a thousand times, then decide which filter to use depending on the result. (If it predicts ~%20, then do the one that should give you ~5.8%, and vice-versa). Unless the machine affects the results, you will find that it is wrong.
I fail to see how that has any relevance whatsoever. I think you are very confused about something, though I’m not sure what.
Talking about “Turing computability in a practical sense” is nonsensical; computability is defined by an infinite-tape machine with arbitrarily large finite time to compute, neither of which we have in a practical sense, and most cases where computability is in doubt make use of both properties.
Superdeterminism also doesn’t need to care at all about the computer you’ve made to predict in advance what will happen. Unless you’ve found a way to “entangle” your computer with the hidden variables which determine the outcome of the result, the results it gives will know nothing about what the actual outcome will be, and just give you the Born probabilities instead.
My point was that if superdeterminism is true, it is not testable, because we can never get a full description of the rules within our universe.
And which other interpretation of quantum mechanics is Turing-computable, exactly?
In principle, you could (as mentioned) get some other process connected to the same hidden variables, in which case you could predict some events with perfect accuracy, which would be pretty definitive confirmation of the hidden variable theory.