Tripping the light fantastic

摘要

The only way to understand the quantum world is to measure it. This empirical view is dear to the heart of Anton Zeilinger, now at the University of Vienna, a leading figure in quantum physics through his work on correlated photons. In Dance of the Photons, he explores the phenomenon of quantum entanglement, the quantum correlations in the properties of particles. When two photons are made to interact, they share their quantum information and become 'entangled! If one travels off, it retains knowledge about its counterpart. So measuring one can determine the state of the other, even if they are far apart. Albert Einstein was worried by such reasoning: instant messaging between entangled particles contradicted his theory of relativity, which stated that signals cannot travel faster than the speed of light, unless you allow the crazy idea that particles do not have real properties independent of measurement.