In the beginning was the bit
And after that came the rest of the weird world, says Hans Christian von Baeyer
"NOBODY understands quantum mechanics," lamented Richard Feynman. But Anton Zeilinger at the University of Vienna aims to prove him wrong. His research group has demonstrated the futuristic phenomena of quantum teleportation and quantum encryption, and these successes have encouraged Zeilinger to search for the essence of quantum mechanics--the irreducible kernel from which everything else flows. He believes that he has found it. If he is right, all the mysteries of the quantum world will turn out to be inescapable consequences of a single, simple idea.
Quantum theory describes the world with astonishing precision, whether applied to elementary particles a hundred thousand times smaller than atoms or to currents in superconducting rings a billion times larger. And yet it seems to present a catalogue of intertwined conundrums. The most fundamental is quantisation, the notion that energy, spin and other quantities only come in discrete steps. Another enigma is the probabilistic nature of the quantum world, at odds with the classical world of definite physical properties. Then there is entanglement, the profound connectedness of objects and processes across large distances, and superposition, the astonishing proposition that an electron can be both here and there, a current can flow simultaneously clockwise and anticlockwise, and a cat can be both dead and alive, until you look to see which.
Physicists have anxiously devised one philosophical interpretation of quantum mechanics after another. In the Copenhagen interpretation, the outcome of an experiment is only revealed when the quantum system interacts with a macroscopic apparatus in the laboratory, which eliminates all possibilities but one. The many-worlds interpretation insists that all possible outcomes of an experiment actually occur in as many parallel universes, but as we only occupy a single branch of the hydra-headed multiverse, we experience only one outcome. Or, if you prefer, there's the guiding wave interpretation, which assigns an undetectable "pilot wave" to each particle to steer it along a perfectly determined path. Altogether there are at least eight serious and reputable interpretations of the theory, which implies that no single one is convincing.
