文档介绍：Bell's Theorem
Bell's Theorem
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INTRODUCTION
In 1975 Stapp called Bell's Theorem "the most profound discovery of science." Note that he says science,
not physics. I agree with him.
In this document, we shall explore the theorem. We assume some familiarity with the concept of wave-
particle duality; a document on this may be found here. We also assume considerable familiarity with the
Stern-Gerlach experiment and the concept of a correlation experiment; a document on these may be found
here.
A much simpler introduction to the theorem, with some loss pleteness, has been html
prepared. You may access an html or pdf version with the links to the right. pdf
The origins of this topic is a famous paper by Einstein, Rosen and Podolsky (EPR) in 1935; its title was
Can Quantum-Mechanical Description of Physical Reality be plete? They considered what
Einstein called the "spooky action-at-a-distance" that seems to be part of Quantum Mechanics, and
concluded that the theory must be plete if not outright wrong. As you probably already know, Einstein
never did accept Quantum Mechanics. One of his objections was that "God does not play at dice with the
universe." Bohr responded: "Quit telling God what to do!"
In the early 1950's David Bohm (not "Bohr") was a young Physics professor at Princeton University. He
was assigned to teach Quantum Mechanics and, as mon, decided to write a textbook on the topic;
the book is still a classic. Einstein was at Princeton at this time, and as Bohm finished each chapter of the
book Einstein would critique it. By the time Bohm had finished the book Einstein had convinced him that
Quantum Mechanics was at least plete. Bohm then spent many years in search of hidden variables,
unobserved factors inside, say, a radioactive atom that determines when it is going to decay. In a hidden
variable theory, the time for the decay to occur is not random, although the variable