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You're right, there are interpretations that do not require a conscious observer: "consistent histories" for instance. But here's the thing: most of these interpretations address primarily the problem of decoherence, that is, the passage from quantum-mechanical interference of complex amplitudes to classical addition of real (and positive) probabilities. What none of them address is the (not quantum-mechanical but probabilistic) problem of actuality (which of the actual histories is realised), which is basically the (probabilistic, not quantum mechanical) problem of assigning a probability to a single event.

Finally, there's an additional twist to this whole discussion which is that decoherence is supposed to be about breaking entanglement, a concept which figures prominently in gaianne's writeup and seems central to the "everything is connected" woo-woo (excuse me) narratives. Now the twist is that entanglement itself is not well defined. It is possible to write down a state of three particles such that depending on the result of a measurement made on A, B and C may or may not be entangled (and cyclic permutations of A, B and C). So, "connectedness" of A, B and C means that "connectedness" of B and C depends on what happens to A far away. This state is called sometimes a Borromean state, by analogy with the borromean rings which are not linked pairwise, but are linked as a set of three.

Back to the beginning, consciousness is not essential but unless a conscious observer is involved, philosophical problems with quantum mechanics seem rather mild to nonexistent, which again suggest a philosophical problem, not a problem with quantum mechanics. The central question is: how are entanglement or interference perceived? Remember Bohr's "no phenomenon is a phenomenon unless it is an observed phenomenon".

We have met the enemy, and he is us — Pogo

by Migeru (migeru at eurotrib dot com) on Wed Jan 2nd, 2008 at 09:20:25 PM EST
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