Mysteries of the Quantum World

Quantum mechanics has fascinating and sometimes weird consequences. The so-called EPR conundrum first raised by Einstein, Podolsky and Rosen in 1935 questions the completeness of quantum mechanics. The problem has its roots in the uncertainty principle, which prevents quantum states from describing simultaneously certain complementary elements of reality, such as position and momentum. The resolution was provided by John Bell in the mid-1960s and confirmed experimentally in 1981. Bell proved that no theory more complete than quantum mechanics can be formulated without violating special relativity. Remarkably, the feature of quantum mechanics that leads to this behaviour, namely quantum entanglement, has been turned into a resource that allows the construction of super fast quantum computers and provides in principle absolutely secure data encryption. We describe the nature of quantum entanglement and the workings of quantum computers, with examples. Finally, we address the question “what does this all mean” by describing various interpretations of quantum mechanic, each of which may be satisfying, or not, depending on one’s taste.