The measure problem in many worlds quantum mechanics

Written by: Stephen Hsu

Primary Source:  Information Processing

I am a Quantum Engineer, but on Sundays I have principles. — J.S. Bell

My own conclusion … there is no interpretation of quantum mechanics that does not have serious flaws. — Steve Weinberg

I wrote this paper mainly for non-specialists: any theorist should be able to read and understand it. However, I feel the main point — that subjective probability analyses do not resolve the measure problem in many worlds quantum mechanics — is often overlooked, even by the experts.

The measure problem in no-collapse (many worlds) quantum mechanics
arXiv:1511.08881 [quant-ph]

We explain the measure problem (cf. origin of the Born probability rule) in no-collapse quantum mechanics. Everett defined maverick branches of the state vector as those on which the usual Born probability rule fails to hold — these branches exhibit highly improbable behaviors, including possibly the breakdown of decoherence or even the absence of an emergent semi-classical reality. An ab initio probability measure is necessary to explain why we do not occupy a maverick branch. Derivations of the Born rule which originate in decision theory or subjective probability do not resolve this problem, because they are circular: they assume, a priori, that we reside on a non-maverick branch.

To put it very succinctly: subjective probability or decision theoretic arguments can justify the Born rule to someone living on a non-maverick branch. But they don’t explain why that someone isn’t on a maverick branch in the first place.

It seems to me absurd that many tens of thousands of papers have been written about the hierarchy problem in particle physics, but only a small number of theorists realize we don’t have a proper (logically complete) quantum theory at the fundamental level.

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Stephen Hsu

Stephen Hsu is vice president for Research and Graduate Studies at Michigan State University. He also serves as scientific adviser to BGI (formerly Beijing Genomics Institute) and as a member of its Cognitive Genomics Lab. Hsu’s primary work has been in applications of quantum field theory, particularly to problems in quantum chromodynamics, dark energy, black holes, entropy bounds, and particle physics beyond the standard model. He has also made contributions to genomics and bioinformatics, the theory of modern finance, and in encryption and information security. Founder of two Silicon Valley companies—SafeWeb, a pioneer in SSL VPN (Secure Sockets Layer Virtual Private Networks) appliances, which was acquired by Symantec in 2003, and Robot Genius Inc., which developed anti-malware technologies—Hsu has given invited research seminars and colloquia at leading research universities and laboratories around the world.
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