5 ms·

I haven't read the new paper in enough detail to comment, but also mentioned is the Renner-Frauchiger paper, which Scott Aaronson heartily debunks here: https:/

I haven't read the new paper in enough detail to comment, but also mentioned is the Renner-Frauchiger paper, which Scott Aaronson heartily debunks here: https://www.scottaaronson.com/blog/?p=3975 https://www.scottaaronson.com/blog/?p=3975 The primary error there is one that people can't seem to stop making for some strange reason: if you don't measure a property X, and instead measure a (non-commuting) property Y, you are not free to say what X "would have been," and -- especially egregiously -- to use that to demonstrate a contradiction. There is no "would have been" in QM. Either you measure it or you don't, and even after you do, the value becomes invalid after it evolves or a complementary variable is measured. Secondly, Wigner's friend was not a single particle. Asking what a single particle "experienced" only makes sense if you are a panpsychist (or "panpsychic" as amusingly misspoken in the article). In any case, it has no bearing on the essence of Wigner's question.

TheOtherHobbes 6y ago
I think RF is a bit more subtle than that, and I'm not convinced that Scott Aaronson has really "debunked" it. "But clearly, even if no one literally measures Charlie in the {|0〉,|1〉} basis, he’s still there, thinking either the thought corresponding to |0〉 or the thought corresponding to |1. And likewise Diane. Just as much as Alice and Bob, Charlie and Diane both exist even if no one measures them, and they can reason about what they know and what they know that others know. So then we’re free to chain together the “certainties” of Alice, Bob, Charlie, and Diane in order to produce our contradiction." You can't use this argument without also explaining what "thinking" means - because in fact it makes no sense unless you assume consciousness exists as a quantum state which allows a phenomenon called "thinking." And philosophically and practically, that's a very, very large can of wormns. So this ends up in the usual place: it's not obvious how using an idea no one understands - like consciousness - to explain another idea no one understands - like QM - is supposed to solve any of these problems.
- Strilanc 6y ago
  In order to implement the measurement described in the thought experiment, you basically have to uncompute Charlie's state back to the start of the experiment (to disentangle him from the qubit you want to measure), do the measurement on the single qubit, then recompute Charlie forward. This means that when Charlie is making deductions about the current state of affairs, like "if my qubit is |0> then the other qubit is |+>, that thinking needs to be valid during the computation and during the recomputation. But the conclusions Charlie is making are not correct during the recomputation, e.g. it is no longer the case that if his qubit is |0> then the other qubit is |+> at that time, and as a result the whole argument (based on Charlie's reasoning being valid so that an outside agent can use his conclusions) falls apart. More details: https://algassert.com/post/1904 https://algassert.com/post/1904
NoodleIncident 6y ago
I'm going to be honest, and say that I have no idea if this comment on that page is relevant to the article in the OP. But if it is, it's hilarious: > OK, point taken. But if one has any experience with experiments in the foundations of QM, one knows full well what’s going to happen next. Namely: some experimental group will do a slightly souped-up test of Hardy’s Paradox, of course getting just the results that QM predicts, and will then market it in Science or Nature as “the first experimental probe of the logical contradiction at the heart of QM … who could’ve imagined that the ‘impossible’ outcome would occur with probability 1/12?” And then the science journalists will wet themselves with excitement. It’s all nearly as predictable as QM itself!

TheOtherHobbes 6y ago

I think RF is a bit more subtle than that, and I'm not convinced that Scott Aaronson has really "debunked" it. "But clearly, even if no one literally measures Charlie in the {|0〉,|1〉} basis, he’s still there, thinking either the thought corresponding to |0〉 or the thought corresponding to |1. And likewise Diane. Just as much as Alice and Bob, Charlie and Diane both exist even if no one measures them, and they can reason about what they know and what they know that others know. So then we’re free to chain together the “certainties” of Alice, Bob, Charlie, and Diane in order to produce our contradiction." You can't use this argument without also explaining what "thinking" means - because in fact it makes no sense unless you assume consciousness exists as a quantum state which allows a phenomenon called "thinking." And philosophically and practically, that's a very, very large can of wormns. So this ends up in the usual place: it's not obvious how using an idea no one understands - like consciousness - to explain another idea no one understands - like QM - is supposed to solve any of these problems.

Strilanc 6y ago
In order to implement the measurement described in the thought experiment, you basically have to uncompute Charlie's state back to the start of the experiment (to disentangle him from the qubit you want to measure), do the measurement on the single qubit, then recompute Charlie forward. This means that when Charlie is making deductions about the current state of affairs, like "if my qubit is |0> then the other qubit is |+>, that thinking needs to be valid during the computation and during the recomputation. But the conclusions Charlie is making are not correct during the recomputation, e.g. it is no longer the case that if his qubit is |0> then the other qubit is |+> at that time, and as a result the whole argument (based on Charlie's reasoning being valid so that an outside agent can use his conclusions) falls apart. More details: https://algassert.com/post/1904 https://algassert.com/post/1904

NoodleIncident 6y ago

I'm going to be honest, and say that I have no idea if this comment on that page is relevant to the article in the OP. But if it is, it's hilarious: > OK, point taken. But if one has any experience with experiments in the foundations of QM, one knows full well what’s going to happen next. Namely: some experimental group will do a slightly souped-up test of Hardy’s Paradox, of course getting just the results that QM predicts, and will then market it in Science or Nature as “the first experimental probe of the logical contradiction at the heart of QM … who could’ve imagined that the ‘impossible’ outcome would occur with probability 1/12?” And then the science journalists will wet themselves with excitement. It’s all nearly as predictable as QM itself!