Imperial College London

Professor Halliwell

Faculty of Natural SciencesDepartment of Physics

Professor in Theoretical Physics



+44 (0)20 7594 7831j.halliwell




Mrs Graziela De Nadai-Sowrey +44 (0)20 7594 7843




H/521Huxley BuildingSouth Kensington Campus





My broad interests over my whole career are the foundations of quantum mechanics and quantum gravity with my present focus being on questions concerning time in quantum mechanics.

I started out in 1983 in the relativity group in Cambridge and worked on quantum cosmology -- the attempt to describe models of the early universe in completely quantum-mechanical terms -- for ten years or more and this area still remains one of interest to me and a source of interesting problems in quantum theory. I subsequentlybecame interested in the decoherent histories approach to quantum theory, which is a novel formulation of standard quantum theory which gives histories a central role. This is of particular interest in quantum gravity, where the notorious problem of time makes it difficult to define a time-evolving state. It also provides an extremely powerful framework in which to address the emergence of classical behaviour from quantum theory, another area on which I have worked for many years, mainly in the context of non-relativistic quantum mechanics.

In the last few years I have worked extensively on aspects of time in quantum mechanics and associated phenomena, including the quantum Zeno effect and also the intriuging phenomenon of backflow -- the (so far unobserved) fact that for a state of purely positive momenta the probability can flow in the opposite direction. I also wrote a paper recentlly offering a sensible interpretation of negative probabilities and another on looking at Fine's theorem, which is essentially the logical converse of Bell's inequalities.

In the next few years I anticipate that I will be continuing to work on time in quantum mechanics, emergent classicality and general issues in the foundations of quantum mechanics.



Dorronsoro JD, Halliwell JJ, Hartle JB, et al., 2017, Real no-boundary wave function in Lorentzian quantum cosmology, Physical Review D, Vol:96, ISSN:2470-0010

Halliwell JJ, 2017, Comparing conditions for macrorealism: Leggett-Garg inequalities versus no-signaling in time, Physical Review A, Vol:96, ISSN:2469-9926

Halliwell JJ, 2017, Incompatible multiple consistent sets of histories and measures of quantumness, Physical Review A, Vol:96, ISSN:2469-9926

Halliwell JJ, 2016, Leggett-Garg inequalities and no-signaling in time: A quasiprobability approach, Physical Review A, Vol:93, ISSN:2469-9926

Halliwell JJ, 2016, Leggett-Garg correlation functions from a noninvasive velocity measurement continuous in time, Physical Review A, Vol:94, ISSN:2469-9926

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