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# Joe Henson

University of Bristol - Department of Physics

Area of Research:

## Research Interests

My research focuses on the search for a quantum theory of gravity (QG), and foundational questions in quantum mechanics that relate to that. I have most recently been interested in "causal dynamical triangulations", in which spacetimes are approximated using "gluings" of equilateral triangles (or tetrahedra, etc.), making it possible to define a QG theory and find some physically relevant observable quantities by computer simulations. I have benn involved with reformulating this theory in 2 dimensions, and in investigating whether the theory approximates to Einstein's theory of gravity in the appropriate regime, using simulations. I am also working on the causal set approach, in which spacetime is replaced at a more fundamental level by a discrete set of elements'' distinguished only by their causal relations with one another. I have been searching for observational consequences of this hypothesis. In foundations, I have been investigating definitions of causality and how they relate to quantum theory in the light of Bell's theorem.

## Positions Held

• October 2005 - September 2007 : Postdoctoral researcher, Spinoza Institute, University of Utrecht, the Netherlands.
• October 2003 - September 2005: Postdoctoral researcher, Mathematics department of the University of California, San Diego, USA.

## Recent Publications

• Luca Bombelli, Joe Henson, Rafael D. Sorkin, Discreteness without symmetry breaking: a theorem, accepted for publication in Mod.Phys.Lett., arXiv: gr-qc/0605006v1
• Joe Henson, Coarse graining dynamical triangulations: a new scheme, accepted for publication in Class. Quant. Grav., arXiv: 0907.5602v1 [gr-qc]
• Dario Benedetti, Joe Henson, Imposing causality on a matrix model, Phys. Lett. B678 (2009) 222-226, arXiv: 0812.4261
• Graham Brightwell, Joe Henson and Sumati Surya, A 2D model of Causal Set Quantum Gravity: The emergence of the continuum, Class. Quant. Grav. 25 (2008) 105025, arXiv: 0706.0375 [gr-qc].
• David Craig, Fay Dowker, Joe Henson, Seth Major, David Rideout, Rafael D. Sorkin, A Bell inequality analog in quantum measure theory, J. Phys. A: Math. Theor. 40 (2007), arXiv: quant-ph/0605008
• Joe Henson, Constructing an interval of Minkowski space from a causal set, Class.Quant.Grav.23:L29-L35,2006, arXiv: gr-qc/0601069
• Joe Henson, Comparing causality principles, Stud.Hist.Philos.Mod.Phys.36:519-543,2005, arXiv: quant-ph/0410051
• Fay Dowker, Joe Henson, Rafael D. Sorkin, Quantum Gravity Phenomenology, Lorentz Invariance and Discreteness, Mod.Phys.Lett. A19 (2004) 1829-1840, arxiv:gr-qc/311055
• Graham Brightwell, H. Fay Dowker, Raquel S. Garcia, Joe Henson, Rafael D. Sorkin,'Observables' in causal set cosmology, Phys.Rev.D67:084031,2003, arXiv: gr-qc/0210061
• Fay Dowker, Joe Henson, A Spontaneous collapse model on a lattice, J. Stat. Phys. 115 (2004) 1349, arXiv: quant-ph/0209051
• Joe Henson, Quantum Histories and Quantum Gravity, proceddings of the DICE conference on Quantum Gravity and Quantum Foundations, Castiglioncello (Tuscany) Sept 2008, J.Phys.Conf.Ser.174:012020,2009, arXiv: 0901.4009 [gr-qc]
• D. Craig, H. F. Dowker, J. Henson, S. Major, D. Rideout, and R. D. Sorkin, Noncontextuality in quantum measure theory". In proceedings of `On the present status of quantum mechanics', 7-9 September, 2005, Mali Losinj, Croatia.
• Graham Brightwell, H. Fay Dowker, Joe Henson, Raquel S. Garcia, Rafael D. Sorkin, General Covariance and the "Problem of Time" in a Discrete Cosmology, proceedings of the Alternative Natural Philosophy Association meeting, held August 16-21, 2001, Cambridge, England
• The Causal set approach to quantum gravity, in 'Approaches to Quantum Gravity: Towards a New Understanding of Space and Time'. Edited by D. Oriti. Cambridge University Press, 2006. arXiv: gr-qc/0601121

## Seminars

• Causal sets: Discreteness without symmetry breaking, Foundations of Space and Time (reflections of quantum gravity), Cape Town, August 2009
• Quantum Histories and Quantum Gravity, DICE conference, Castigioncello, Tuscany, Sept 2008
• Causal sets, New Directions in the Foundations of physics, Washington DC, August 2009
• PIRSA:06120039, A Bell inequality Analogue in quantum measure theory, 2006-12-07, Young Researchers Conference - 2006
• PIRSA:04100035 Consequences of Space-Time Discreteness on Wave Propagation Speaker(s): Joe Henson 30/10/2004, Workshop on Quantum Gravity in the Americas: Status and future directions