## Sunday, November 11, 2007 ... //

### Hugh Everett: 77th birthday

Hugh Everett was born on November 11th, 1930. He proposed the many-worlds interpretation of quantum mechanics and because no one cared, he left physics right after his PhD. More precisely, the term "many-worlds interpretation" comes from DeWitt who interpreted Everett in this way in 1971.

Later, he applied Lagrange multipliers in the commercial sector and earned some big bucks. As a chain smoker and drinker, he died at the age of 51. However, he believed in quantum immortality so the death was probably not such a big issue. His daughter, Elizabeth, suffered from schizophrenia and committed suicide in 1996, claiming that she was moving into a parallel universe to spend time with her dad.

Everett's wife, born as Nancy Gore, died of cancer in 1998. Unless we deal with a closed time-like curve connecting different parallel universes, she shouldn't be confused with Nancy Gore Hunger, Al Gore's sister, who also died of cancer but in 1984. Everett's son, Mark Oliver Everett, is a rock musician with "Eeels" and some of his songs were inspired by the deaths in his family.

Everett's main contribution was written in the article called

'Relative state' formulation of quantum mechanics
See also a philosophical meditation about the paper at Stanford. OK, I have never understood how the branching tree of the parallel universes is supposed to look like when we measure many quantities at different points of spacetime, how it is reconciled with relativity, how it is guaranteed that the probabilities of different outcomes are what they should be, and what this breathtaking superconstruction is supposed to solve. Nevertheless, I think it is fair to say that Everett's picture was an ancient suggestion of decohering histories. He can also be credited with the elimination of the redundant concept of a "collapse of the wave function" from quantum mechanics.

The different parallel universes should be identified with decohering histories as studied in my favorite neo-Copenhagen interpretation of quantum mechanics due to Gell-Mann, Hartle, and others. If we adopt this interpretation, Everett needed to assume the existence of a privileged basis of the Hilbert space describing the whole Universe. But he correctly led physicists to understand that the preferred basis is not assigned to a microscopic object per se but it is only assigned relatively to the decision of the experimenters or another macroscopic object that interacts with the microscopic one.

Anyway, I still don't think that Everett really understood how decoherence works. That's why I would say that his work has much greater impact on the popular perception of science than science itself.

Also, 103 years ago, J.H.C. Whitehead (Henry) was born. This mathematician was one of the founders of homotopy theory and other disciplines of mathematical topology.