Time machines and quantum theory

Wormholes, Time machines and Energy conditions: would Einstein have come to this parallel session? If it was held in 1950, I don’t think so. Einstein had a strong belief in preserving causality as a fundamental principle that contributed to his work on relativity. But if Einstein was at MG11 in 2006, this is where Einstein would be. Einstein would be attracted not so much for his interest in general relativity but for his desire to find an explanation for quantum theory. The difference between the two dates is our understanding of quantum theory, particularly Bell’s inequalities which showed that quantum theory could not be explained by any local hidden variables theory. Or in other words; if an underlying explanation for quantum theory is ever to be found it must involve time travel in a technical sense. The intervening years have also seen experimental verification of the violation of Bell’s inequalities. Unlike Einstein’s EPR thought experiment, the conclusion cannot be that the equations are deficient, but that quantum theory is either inexplicable or requires a non local unifying theory. Perhaps quantum theory is telling us something about spacetime. If so, where better to look for a deeper understanding than the best theory of space and time that we have general relativity. In fact, it is our only theory of space and time, so the choice of where to start is obvious! We already know: