Monday, December 22, 2014

Is Quantum Theory Complete?

Can quantum theory as currently formulated be all there is to the theory?

That was Einstein's greatest doubt, and many people doubt it today. Quantum theory seems to offer us probabilities for the results of well constructed experiments. But it does not offer us insight of the internal workings of those experiments. Can that really be all we can know about the quantum world?

That's what Randy and Jim discuss in this episode while talking about Aharonov and Rohrlich's Quantum Paradoxes, chapter 3: "Is Quantum Theory Complete?"

Einstein's Clock in a Box Paradox (last episode) failed to prove that quantum theory was inconsistent -- that the postulates of quantum theory have some contradictory implications. So, he turned to proving that they were incomplete: additional postulates were required to provide a full understanding of the physics of the theory (similar the necessity of Euclid's fifth postulate in geometry). So he and two others invented the Einstein-Poldosky-Rosen Paradox (this episode), which many years later would be formalized as Bell's Theorem and then shown to be consistent with measurements in the Aspect experiment.

Also discussed in this episode: quantum entanglement and the block universe.

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We're reading Quantum Paradoxes by Yakir Aharonov and Daniel Rohrlich. This is a technical book that is making an argument for a specific interpretation of quantum theory. The first half of the book uses paradoxes to explore the meaning of quantum theory and describe its mathematics, then after interpretations are discussed in the middle chapter, an interpretation of quantum mechanics is explored with paradoxes based on weak quantum measurements.

A popular, and short, introduction to quantum mechanics that includes a lot of the topics in the first half of this books is Rae's Quantum Physics. If the equations in Quantum Paradoxes get you down, this might perk you up.

Two other books that were mentioned in this podcast were:

Speakable and Unspeakable in Quantum Mechanics: Collected Papers on Quantum Philosophy: This is a collection Bell's papers that includes his formulation of the EPR in a way that there is a measurable difference between classical and quantum results.

Quantum Theory (Dover Books on Physics): David Bohm's classic text on quantum mechanics. In Chapter 14, he formulates the EPR paradox mathematically using electron spin and Stern-Gerlach devices.