Entanglement

'Entanglement' by Amir D. Aczel is a very interesting read, I highly recommend it to anyone interested in Physics (more specifically, in the subject of quantum philosophy). The author is quite successful in explaining this very complicated subject in such a manner that it does not limit his audience to just physics-savvy folks. I feel completely comfortable in recommending this book to a non-nerd. The phenomena of entangled particles has always fascinated me and I happened to stumbled upon this book right as my curiosity in this subject was peaking. So obviously, this is going to be a slightly biased review.

Born in Einstein's brain as a thought experiment to disprove the validity of Quantum Theory, entanglement grew up to become Einstein's most famous failure. While Einstein was a major contributor to the development of Quantum Theory, he was also considered it's harshest critic. He did not believe that it was the final description of particle interactions on the microscopic scale. Many exchanges through so-called thought experiments with Neils Bohr left the universal acceptance of Quantum Theory in limbo. Einstein left this world with a smile though, thinking he had proven Bohr's theory wrong by stating that locality was violated by the formulation of Quantum Theory and therefore it cannot possibly be correct. A spooky thing labeled "action at a distance" couldn't possibly exist - not relative to Einstein's universe any way. But at the time, this experiment could not be tested empirically only intuitively. Einstein's argument makes tremendous sense to the lay person. But as we discover, there is actually very little in Quantum Theory that is intuitive. And as it turns out, Quantum Theory has eluded even Einstein's intuition.

A brilliant physicst/scientist, John S. Bell, devised a method for bringing Einstein's thought experiment into the laboratory. With the help of Clauser, Horne, Shimony and finally the brilliant Alain Aspect experimental evidence started clearly showing support for Bohr's theory rather than Einstein's. The violation of locality is an actual phenomena, meaning that if two particles somehow become "entangled" i.e. they are formulaically indistinguishable, a change in one will instantaneously have an effect on the other. No matter how large the distance between them. This is a pretty heavy concept to swallow. How can an entangled particle react to something that isn't happening locally to itself? Intuitively, one would think that somehow they must communicate with one another by exchanging some sort of message via a particle or by exchanging energy. But this phenomena has been proven to take place instantaneously which violates the fundamental laws of known physics. More specifically it violates the laws of Einstein's most famous work, his Theory of Relativity which states that nothing can travel faster than the speed of light. If the two particles are communicating instantaneously then they must not be exchanging particles, so how does one know when something happens to the other? We simply don't know, but we do know that the formulation of Quantum Theory is still the undisputed champion of the microscopic world.