It's not quantum mechanics, it's just an analogy.
In the followup chapter, you e.g. get the following hypothetical:
"Why not just let the 'degree of existence' be a complex number, while you're at it?"
Bo'ma rolls his eyes. "Please stop mocking me. I can't even imagine any possible experimental evidence which would point in the direction of that conclusion. You'd need a case where two events that were real in opposite directions canceled each other out."
Which hypothetical is actually a reference to an element of real QM -- as the amplitudes of configurations are indeed complex numbers, and can indeed cancel each other other. (if I'm not mistaken)
Today's post, Where Physics Meets Experience was originally published on 25 April 2008. A summary (taken from the LW wiki):
Discuss the post here (rather than in the comments to the original post).
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