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The experimental confirmation of quantum mechanics
Murray Gell-Mann Scientist
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The widespread foolishness associated with the Einstein, Podolsky, Rosen, Bohm effect and its experimental… the experimental confirmation of quantum mechanics; I treat that at some length in my book. It's very strange. It has to do perhaps with the fact that John Bell, although he did very good work and didn't make any mistakes, as far as I know, actually didn't like quantum mechanics and introduced words that are sort of prejudicial like 'non-local', and when people say that the EPRB effect is… shows that quantum mechanics is non-local, what they mean is that a classical interpretation of what's happening would have to be either non-local or involved negative probabilities or both. That's not the same as saying that it actually is non-local, but that's the vocabulary that has been introduced, to say that quantum mechanics is non-local. And sort of—it's… it’s a matter of giving a dog a bad name and hanging him, as far as I can tell. When the quantum mechanical predictions for this experiment were fully verified, I would have thought everybody would say, great and go home. Instead they say, there is something seriously peculiar here. Well the only thing that's seriously peculiar there is quantum mechanics!

Now, as I explained in the book, when you have a situation in which say, two photons are produced in a single event, for example by a spins decay of a spin-zero meson, they move in opposite directions. An observer makes a measurement on one of them and thereby learns some property of the other one even though the other one is far away. That's not any sort of affront to locality or special relativity or anything. The point is that classically this could happen to… to a single kind of measurement and John Bell referred to this as Bertelsmann's socks, talking about a mathematician who I assumed was fictitious but apparently was a real mathematician who wore one pink sock and one green sock, and if you saw the pink sock you would know that the other foot had a green sock. Well, similarly with these two photons: since you know their correlation, if you measure a property of one, you learn the property of the other. There's nothing peculiar about that. As John Bell emphasized, in quantum mechanics the entanglement of the two photons can be deeper than it can be classically, in the sense that you could then, you could instead measure a different property of one of the photons and you would learn that property of the other photon. Well that's peculiar to quantum mechanics, but it still doesn't give rise to any sort of non-locality. People say, loosely, crudely, wrongly, that when you measure one of the photons it does something to the other one; it doesn't. All that happens is, you measure a property of one and you learn the corresponding property of the other one. Now, what these people who try to confuse us will say is, yes, but you choose which property and thereby you choose what state the other one will be in. Well, the point is that the different measurement, say, of linear polarization of one revealing the linear polarization of the other, or circular polarization of one revealing the circular polarization of the other; those measurements are made on different branches of history, decoherent with each other, only one of which occurs. So it's simply not true!  And Einstein's point of view, which was that if some variable could ever be measured with certainty it should have some sort of physical reality and a definite value, that's just wrong, that's just in contradiction to quantum mechanics. When two variables at the same time don't commute, any measurement of both of them would have to be carried out with one measurement on one branch of history and the other measurement on another branch of history and that's all there is to it. I… I presented that in my book, and of course Jim and I have argued for that, and some other people, but it doesn't seem to get across. People are still mesmerized by this confusing language of non-locality. What they do isn't necessarily wrong, lots of people do correct work on this subject, but the vocabulary makes it sound like something very different from what it is.

New York-born physicist Murray Gell-Mann is 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: Albert Einstein, Boris Podolsky, Nathan Rosen, John Bell, Einstein, Jim Hartle

Duration: 4 minutes, 43 seconds

Date story recorded: October 1997

Date story went live: 29 September 2010