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If anyone wants to learn more about Bell's inequality, the simplest (real, no bullshit) explanation I've ever seen is by David Griffiths. You can follow it if you know the basics of calculus:

http://www.physics.umd.edu/courses/Phys270/Jenkins/Griffiths...




And if you don't know calculus, there's Mermin's version:

http://kantin.sabanciuniv.edu/sites/kantin.sabanciuniv.edu/f...


IAAP, but that is still a great article to drive home how fundamental and simple this property of our universe is.


The afterword seems kind of weak as it tries to return to the question of what quantum mechanics "means" and then... sort of doesn't really do that. It goes on to describe an "ethereal" influence distinct from causal influence, which is to say an "influence" that doesn't actually do anything at all. That's pretty disappointing.

The simplest explanation of what measurement actually is, in a quantum sense, is that it's the act of entangling your brain with whatever amplitude configuration represents the experiment we're interested in looking at. Basically the amplitude goes from looking like "brain * (result A + result B)" to "brain A * result A + brain B * result B". Brain A at that point can't communicate in any meaningful way with brain B because there isn't any causal relationship between the two anymore, so in a sense the brain has "split" and this is what we call decoherence. But for brain A to suppose that brain B has vanished in a puff of smoke, that is to say to privilege brain A over brain B, needlessly complicates the theory. It is the same as saying that since you can't see a thing anymore, it must not exist, and trying to build an entire physics based around what happens after you close your eyes.


I'm not sure if you realize, but you've described the Many-Worlds Interpretation.


it's funny i read this years ago (at the end of second semester qm) and it never clicked. guess i've gotten smarter since then. thanks.


I'll say that most of my physics classes lasted 2 years. 1 quarter in the class room and a year and a half before it really clicked. Wouldn't it be nice if you could retake classes again.


For a longer exposition that also covers the historical context more deeply, Jim Baggott's "The Meaning of Quantum Theory: A Guide For Students Of Chemistry and Physics" covers Bell's Theorem in Chapter 4 and also requires only basic knowledge of calculus.


Interesting to observe the lack of Many Worlds as an interpretation of quantum mechanics in Griffiths excellent explanation.




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