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Quantum Mechanics


Bohr-Einstein debates
 

EPR

why is it called a "paradox"

 


 

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Andrew Zimmerman Jones:

The reason that this is classified as a paradox is that it seemingly involves communication between the two particles at speeds greater than the speed of light, which is a conflict with Albert Einstein's theory of relativity...

The Paradox's Meaning

There are two key points at work here which make this troubling:

Quantum physics says that, until the moment of the measurement, the particles do not have a definite quantum spin but are in a superposition of possible states.

As soon as we measure the spin of Particle A, we know for sure the value we'll get from measuring the spin of Particle B.

If you measure Particle A, it seems like Particle A's quantum spin gets "set" by the measurement, but somehow Particle B also instantly "knows" what spin it is supposed to take on. To Einstein, this was a clear violation of the theory of relativity.

 

 

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