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According to quantum theory, physical variables in general do not have definite values unless measured. Yet, the time and causal order of events are assumed definite. A natural question is whether the latter reflects a fundamental physical restriction or it is an artefact of our formulation of the theory. Is it possible that, in suitable circumstance, the causal order of events can be indefinite similarly to other physical variables, how would this be described formally, and what testable consequences would it entail. To investigate these questions, we recently introduced a theoretical framework for correlations between separate quantum experiments that does not assume a causal structure from the outset, but only the validity of standard quantum theory locally. This framework unifies all correlations between local quantum experiments in space-time via a mathematical object called the ‘process matrix’, which generalises the standard density matrix. Remarkably, the framework also reveals the in-principle possibility for a new kind of correlations incompatible with any definite causal structure. In this talk, I review these results and discuss recent progress in understanding whether such acausal scenarios could have a physical realisation within standard quantum mechanics.

Offering up to £55,000 over 3 to 24 months for experienced researchers to conduct a programme of research in any discipline.

Research Fellowships are open to experienced researchers, particularly those who are or have been prevented by routine duties from completing a programme of original research. Awards are not limited to those holding appointments in higher education.

Value

The maximum value of a Fellowship is £55,000. The awards provide research expenses over and above normal living costs and/or provide a contribution towards reasonable replacement costs or loss of earnings.