So far, there hasn't been much physics in Wine, Physics, and Song---nor much song, for that matter, though there's been plenty of wine, and some economics and politics.  I guess wine is easier and more relaxing to write about.  But it's time to redress that balance.

I arrived in Ponta Delgada, the main town of the island of São Miguel in the Portuguese archipelago of the Azores, courtesy of the Foundational Questions Institute, to attend and speak at their second annual conference.  We were treated to dinner and an after-dinner talk.  (The wines, especially a white called  something like Tierra de Lavas that was served before dinner, were tasty.)  The talk was by Peter Byrne, who is writing a biography of Hugh Everett III, the originator (unless you want to ascribe it to Schrödinger in his cat paper) of what he called the "relative state" interpretation of quantum mechanics, often called the "many worlds interpretation" (MWI).  I was particularly interested in this talk because a fascination with the problem of how to interpret quantum theory is a large part of what got me into physics.  In 1989--1990 I wrote a paper (unpublished), "The Many-Worlds Interpretation of Quantum Mechanics: Psychological versus Physical Bases for the Multiplicity of "Worlds", arguing that Everett's interpretation had often been misunderstood as involving a "physical" splitting of the universe into different branches, whereas Everett was actually fairly clear that the "branching" into parts of the universe involving different outcomes of a quantum experiment was associated with different subspaces of a single Hilbert space of the world, subspaces defined by which of the different macroscopic outcomes of the experiment an observer had experienced.  So I was very interested to hear from Peter Byrne that among the boxes of Everett's paper that he has been sorting and studying, were drafts of Everett's thesis in which there is much more extensive discussion of splitting minds than was available even in the long version of his thesis published by Princeton.  If I'm reporting Byrne correctly, one of these drafts compares the splitting minds to splitting amoebas, noting there is no fact of the matter as to which of the amoebas is the original one.  The whole thing, he says, had much more extensive discussion of splitting, which his advisor John Wheeler made him take out (partly, if I understood correctly, because of negative comments by Bohr, relayed by Stern who was on Everett's thesis committee).   It will be interesting to see the details of these drafts, and find out more about how Everett understood this "splitting".

My early paper was to some extent a "devil's advocate" exercise---I did not then, and do not now, believe in Everett's interpretation in the sense that a macroscopically entangled wavefunction, describing me having all kinds of different conscious experiences, is a real entity.  But I did believe, and still do, that pushing Everett's idea as far as possible is one good way of getting a better understanding of what is weird about quantum theory, and of the unexpected difficulties we've encountered in figuring out what quantum physics has to tell us about the world, and our place in it.

My reasons for not accepting many worlds are in part tied up with the fact that there don't seem to be probabilities of measurement outcomes on this interpretation, as there are indeed not definite classical outcomes.  More on this later---it is something that I've been thinking about for years, and before Byrne's talk, I had a long discussion about it with Alan Guth at dinner.   But one last thing:  it was therefore striking to hear from Byrne that one of a myriad of titles Everett considered for his dissertation was "Wave mechanics without probability".