Steven WeinsteinPerimeter Institute for Theoretical Physics
From classical mechanics to quantum field theory, the physical facts at one point in
space are held to be independent of those at other points in space. I propose that we can
usefully challenge this orthodoxy in order to explain otherwise puzzling correlations at both
cosmological and microscopic scales.
Despite radical differences in their conceptions of space, time, and the nature of matter, all of the physical theories we presently use | non-relativistic and relativistic, classical and quantum share one assumption: the features of the world at distinct points in space are understood to be independent. Particles may exist anywhere, independent of the location or velocity of other particles. Classical fields may take on any value at a given point, constrained only by local constraints like Gauss’s law. Quantum field theories incorporate the same independence in their demand that field operators at distinct points in space commute with one another.
The independence of physical properties at distinct points is a theoretical assumption, albeit one that is grounded in our everyday experience. We appear to be able to manipulate the contents of a given region of space unrestricted by the contents of other regions. We can arrange the desk in our office without concern for the location of the couch at home in our living room.
Yet there are realms of physical theory, more remote from everyday experience and physical manipulation yet accessible to observation, in which there appear to be striking correlations between the values of physical properties at different points in space. Quantum theory predicts (and experiment confirms) the existence of strongly correlated measurement outcomes apparently inexplicable by classical means. I refer, of course, to the measurements of the properties of pairs of particles originally envisioned by Einstein, Podolsky and Rosen (EPR) , measurements that suggested to EPR the incompleteness of the theory. Bell (1964) showed that no theory satisfying two seemingly natural conditions could possibly account for these correlations.