On Wed, Feb 12, 2020 at 3:55 AM Bruno Marchal <marc...@ulb.ac.be> wrote:
> On 10 Feb 2020, at 08:17, Bruce Kellett <bhkellet...@gmail.com> wrote: > > > That would not be the way most physicists would see it. They take > Everettian QM as basic. Unfortunately, Everettian QM has hit a catastrophic > train wreck -- it is clearly not viable as an understanding of quantum > physics. The reason for this is a clear corollary of Kent's argument. > Simply put, Everett takes the Schrodinger equation as basic. Acting on a > general quantum state with the Schrodinger equation gives the relative > states, and there can only ever be one relative state for each term in the > expansion in terms of some set of basis states. The amplitudes of interest > are the coefficients in this expansion. However, these coefficients or > amplitudes, are just ordinary complex numbers, so are completely > transparent to the SE. The set of sequences of outcomes of repeated trials > (measurements on replications of the initial state) is then all n^N > sequences of outcomes (labelled by 0 - n-1 for the n possible outcomes for > N trials). This set of sequences is independent of the amplitudes in the > original expansion of the state of interest in terms of the set of basis > states. Consequently, the data one obtains from this set of experiments is > one of the set of possible sequences of the integers 0 to n-1, is > completely independent of the amplitudes in the original expansion. One > can, therefore, gain no information about these amplitudes from the set of > N trials. The Born rule is irrelevant, because the data are necessarily > independent of the coefficients/amplitude. > > This proves that Everett's approach from the SE, where there is only one > branch for each possible outcome in a single trial, cannot account for the > way in which experimental results are used in practice. Given Everett, > experiments cannot reveal anything at all about the original state. So > Everett fails as a scientific theory. End of story. Period. Nothing more to > be said. > > > >> The main issue is unitary time evolution. This is a rather >> unambiguous thing that one can check in experiments. A breakdown of >> unitary time evolution has never been observed. >> > > As Brent has pointed out, unitary evolution breaks down every time we > observe a particular result for a measurement (to say nothing of black > holes). Your focus on unitary evolution is misplaced -- it is not > universally observed. > > > “Unitary evolution” is the theory, which has not an observable in any > reasonable sense of observable. > If that is what "unitary evolution" means, then it has no bearing on physics. To add a collapse is like saying that theory break down, but there no > observation indicating that it does, given that the theory explains, or is > supposed to explain, such an appearance. > I think "explaining the appearances" is what science is all about. You claimed above that unitary evolution does not have observable. In which case , by definition, it cannot explain experience. The problem I have pointed to is that unitary evolution via the Schrodinger equation leads to data that have no relation to the oriignal state under study. So the data can give no information about the underlying quantum state, and so your theory cannot explain experience -- because we see different results for measurements on different quantum states. Everett is essentially ruled out by the "no miracles" argument, since given that the data are independent f the original state, it would require a miracle for independent experiments on the same state to give the same answers. What you seem to say is that QM might be wrong, but to assume a theory is > wrong to satisfy an ontological commitment is not in “the normal scientific > practice” (as you said). > There is no ontological commitment here. The only commitment I see in others is that everything is unitary, and that a totally unitary theory can explain appearances. This has been shown to be wrong. No completely unitary theory can be consistent with our experience of the physical world. Many-worlds theory might be salvageable from the train wreck of Everett, > but it is not clear how. It seems to be widely assumed that there is more > than one branch for each basis state, even though that is not what Everett > or the SE say. It is not clear how this could ever happen in a principled > way: it certainly is not consistent with unitary evolution via the > Schrodinger equation. > > > On the contrary, Everett is the only one entirely consistent with unitary > evolution, > Have you simply ignored all the arguments that show that unitary evolution cannot explain appearances? and that is why cosmologist refers to it, when they are confronted to the > problem that the Copenhagen have necessarily when applying QM to the whole > universe, or to just a portion we inhabit. Everett’s idea is just an idea > already defended by Newton which is that the physicists obeys to the > physical law; and Everett has just realised that most paradox get away when > we apply the SWE to the couple observed - observer. > Everett's idea that one should apply quantum mechanics to the whole system -- and not make some arbitrary distinction between the classical and quantum worlds, such that the classical is necessary to make sense of the quantum (Bohr) -- was a valuable insight. The trouble was that the simplistic way he implemented this idea does not work. That leads to a complicated counter-intuitive ontology, but eventually, as > Everett used Mechanism, we know that eventually any simple Turing universal > ontology will do. > That is even more hopeless as an account of the phenomenal world as we experience it. Bruce -- You received this message because you are subscribed to the Google Groups "Everything List" group. To unsubscribe from this group and stop receiving emails from it, send an email to everything-list+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/everything-list/CAFxXSLRqC6VPKEH43ndY8zc4%3D2CpDtyQprj%2BPiFzG2e1mYGTpw%40mail.gmail.com.
