Quantum theory survives latest challenge

  

 

 

 

The concept of entanglement, which describes how a collection of quantum particles have a closer bond than permitted by classical physics, has caused discomfort for a number of physicists since the inception of quantum mechanics, including Albert Einstein. Some physicists have therefore put up substitute theories that do not require quantum mechanics and permit such intimate connections. Although testing these theories has been challenging, UK researchers have made a significant measurement that supports quantum theory using "twisted light." Since quantum theory contradicts our notion of "realism," which holds that objects have certain characteristics whether or not we are looking at them, it appears alien to our everyday reality. 

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 The principle of locality, which prohibits communication faster than the speed of light, appears to be violated by quantum theory, which also seems to demand for entities that may respond instantly to an event happening elsewhere. In his well-known inequality, physicist John Bell provided a mathematical expression for these peculiarities. Bell demonstrated that all physical theories that adhere to locality and realism would give a numerical bound (or inequality) if a specific set of measurements were made on identically prepared pairs of particles. However, he also demonstrated that the predictions of quantum physics for pairs of entangled particles break this bound. For instance, in Bell experiments, two distant observers compute the correlations between entangled particles by measuring their polarization along various directions. John Clauser and Stuart Freedman completed this in the 1970s, and in the 1980s