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Decoherent histories, realms (Part 2)

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Decoherent histories, realms (Part 1)
Murray Gell-Mann Scientist
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In the late '80s, Bob Griffiths and Roland Omnes, independently, worked on decoherent histories and they published the idea before Jim and I did. In fact I'd never written anything about quantum mechanics until the very end of the 1980s. But I'd thought a lot about it, and the thoughts, as I say, were sort of continuous. Jim Hartle and I have worked on decoherent histories with a particular point of view. Some people have tried to get the minimum conditions for consistency allowing probabilities to be assigned to course-grained histories, so they get a weaker and weaker form of decoherence. We have been interested in finding a stronger and stronger form of decoherence, trying to appreciate what actually happens in the real world where decoherence is far from minimal. The actual decoherent histories with which one conventionally deals are decoherent in a very strong manner, and it's that strong decoherence that we've tried to describe, approach and so on. But now if you consider a set of decoherent, course-grained, alternative histories of the universe, given the two fundamental principles; the unified theory of all the particles and forces, and the initial condition, initial density matrix or a wave function, then… the… let me see, what was I going to say… if… if you're given all that, there's a question of… of which set of decoherent histories you use. And we like to talk about a realm, which is a set of alternative decoherent histories subject to some condition. Usually it's a kind of maximality condition so that you… if you were to fine-grain further you would start to lose the… the decoherence, something like that; or if you fine-grained further you would start to lose either the decoherence or some other desirable property, and such a system we call a realm.

New York-born physicist Murray Gell-Mann (1929-2019) was known for his creation of the eightfold way, an ordering system for subatomic particles, comparable to the periodic table. His discovery of the omega-minus particle filled a gap in the system, brought the theory wide acceptance and led to Gell-Mann's winning the Nobel Prize in Physics in 1969.

Listeners: Geoffrey West

Geoffrey West is a Staff Member, Fellow, and Program Manager for High Energy Physics at Los Alamos National Laboratory. He is also a member of The Santa Fe Institute. He is a native of England and was educated at Cambridge University (B.A. 1961). He received his Ph.D. from Stanford University in 1966 followed by post-doctoral appointments at Cornell and Harvard Universities. He returned to Stanford as a faculty member in 1970. He left to build and lead the Theoretical High Energy Physics Group at Los Alamos. He has numerous scientific publications including the editing of three books. His primary interest has been in fundamental questions in Physics, especially those concerning the elementary particles and their interactions. His long-term fascination in general scaling phenomena grew out of his work on scaling in quantum chromodynamics and the unification of all forces of nature. In 1996 this evolved into the highly productive collaboration with James Brown and Brian Enquist on the origin of allometric scaling laws in biology and the development of realistic quantitative models that analyse the influence of size on the structural and functional design of organisms.

Tags: Bob Griffiths, Roland Omnes, Jim Hartle

Duration: 2 minutes, 25 seconds

Date story recorded: October 1997

Date story went live: 29 September 2010