# Philipp Hoehn

Area of Research:
Phone: x7462

## Research Interests

My research interests concern multiple aspects at the interface of quantum theory and gravitational physics and in the foundations of quantum physics:

(1) One of my focuses is a novel reconstruction of quantum theory from information inference principles and operational arguments which solely concern the relation between an observer and an observed system. (For a brief blog report, see http://ilqgs.blogspot.nl/2014/11/quantum-theory-from-information.html.)

(2) A current project analyzes the surprisingly deep relation between elementary space-time structure and the possibility of certain abstract quantum communication tasks for observers contained in it.

(3) Discretization changing dynamics features generically in discrete gravity models underlying various approaches to quantum gravity. But a temporally varying discretization also arises in field theory on an evolving lattice. The discretization changing dynamics constitutes canonical coarse graining or refining operations on the discrete system. Recent work of mine develops a consistent classical and quantum formalism for such scenarios. It clarifies the notion of Dirac observables, symmetries, unitarity and symplecticity on such dynamical discretizations.

4) One of my research interests also concerns the notion of observables in gravitational theories. In a recent project I analyzed together with Bianca Dittrich, Tim Koslowski and Mike Nelson what the impact of chaos or non-integrability is on gravitational observables and what the consequences are for quantization. The repercussions are surprisingly strong, implying that standard methods of quantization -- if at all -- yield sick quantum theories.

CONFERENCE ORGANIZATION:

Together with Ryszard Kostecki and Markus Müller I was organizing the conference "Information theoretic foundations for physics" at Perimeter from May 11-15 2015. For more information see http://perimeterinstitute.ca/conferences/information-theoretic-foundations-physics

## Recent Publications

• Bianca Dittrich, Philipp A. Höhn, Tim A. Koslowski and Mike I. Nelson, Chaos, Dirac observables and constraint quantization, arXiv: 1508.01947
• P A Höhn, Toolbox for reconstructing quantum theory from rules on information acquisition (2014), arXiv: 1412.8323
• P A Höhn and M P Müller, An operational approach to spacetime symmetries: Lorentz transformations from quantum communication (2014), arXiv: 1412.8462
• P A Höhn, Canonical linearized Regge Calculus: Counting lattice gravitons with Pachner moves, Phys. Rev. D 91, 124034 (2015), arXiv: 1411.5672
• P A Höhn, Classification of constraints and degrees of freedom for quadratic discrete actions, J. Math. Phys. 55 (2014) 113506, arXiv: 1407.6641
• P A Höhn, Quantization of systems with temporally varying discretization II: Local evolution moves, J. Math. Phys. 55 (2014) 103507, arXiv: 1401.7731
• P A Höhn, Quantization of systems with temporally varying discretization I: Evolving Hilbert spaces, J. Math. Phys. 55 (2014) 083508, arXiv: 1401.6062
• B Dittrich, P A Höhn, Constraint analysis for variational discrete systems, J. Math. Phys. 54 (2013) 093505, arXiv: 1303.4294
• P A Höhn, E Kubalova and A Tsobanjan, Effective relational dynamics of a nonintegrable cosmological model, Phys. Rev. D 86 (2012) 065014, arXiv: 1111.5193
• B Dittrich and P A Höhn, Canonical simplicial gravity, Class. Quant. Grav. 29 (2012) 115009, arXiv: 1108.1974
• M Bojowald, P A Höhn and A Tsobanjan, Effective approach to the problem of time: general features and examples, Phys. Rev. D 83 (2011) 125023, arXiv: 1011.3040
• M Bojowald, P A Höhn and A Tsobanjan, An effective approach to the problem of time, Class. Quant. Grav. 28 (2011) 035006, arXiv: 1009.5953
• B Dittrich and P A Höhn, From covariant to canonical formulations of discrete gravity, Class. Quant. Grav. 27 (2010) 155001, arXiv: 0912.1817
• P A Höhn and S M Scott, Encoding cosmological futures with conformal structures, Class. Quant. Grav. 26 (2009) 035019, arXiv: 1001.2928
• P A Höhn and S M Scott, Quiescent cosmology and the final state of the universe, Int. J. Mod. Phys. D 17 (2008) 571, arXiv: 1001.2823

## Seminars

• Constraints, Dirac observables and Chaos' talk given at Loops '15', Erlangen
• Constraints, Dirac observables and Chaos' talk given at The problem of time in perspective' workshop, LMU Munich
• Quantum theory from questions,' seminar at CPT Marseille
• Quantum theory from rules on information acquisition', seminar at ITF Utrecht
• From gravitation to information - and back again', VCQ talk, Vienna, Austria
• Information and the architecture of physical theories: Two examples' talk at Emergence of space and time in quantum gravity' workshop, AEI
• Quantum theory from information inference principles', seminar at IQOQI Vienna
• Quantum theory from information inference principles,' Int. LQG phone Seminar, audio, slides and blog report available under http://ilqgs.blogspot.nl/2014/11/quantum-theory-from-information.html
• Discretization changing dynamics', Conceptual and Technical Challenges in Quantum Gravity, Rome
• Quantum formalism for systems with temporally varying discretization,' Frontiers of Fundamental Physics "14, Marseille
• Elements of quantum theory from limited information and complementarity,' Frontiers of Fundamental Physics "14, Marseille
• Elements of quantum theory from limited information and complementarity,' IQSA "14, Olomouc
• Elements of quantum theory from limited information and complementarity,' QTPA "14, Växjö
• Quantum formalism for systems with temporally varying discretization,' seminar at Universiteit Nijmegen
• Quantization of systems with temporally varying discretization,' seminar at University of Waterloo
• Breakdown of quantum relational dynamics in a nonintegrable cosmological model,' Spanish Relativity Meeting "13, Benasque
• Evolving Hilbert spaces and the quantization of systems with time varying discretization,' seminar at Albert Einstein Institut, Potsdam
• An information theoretic and operational reconstruction (attempt) of qubit quantum theory,' seminar at Free University Berlin
• Canonical dynamics of variational discrete systems,' 3rd Iberian Gravitational-Wave Meeting, Valencia, Spain
• PIRSA:15060050, Dirac Observables in Chaotic Systems, 2015-06-25, SD@Convergence - A Shape Dynamics Workshop
• PIRSA:15050079, Information and the architecture of quantum theory, 2015-05-12, Information Theoretic Foundations for Physics
• PIRSA:15030086, Quantum theory from rules on information acquisition, 2015-03-17, Quantum Foundations
• PIRSA:14050133, Elements of Quantum Theory from limited Information and complementarity, 2014-05-22, Quantum Gravity Day 2014
• PIRSA:13070075, Discrete Approaches - 2, 2013-07-25, Loops 13
• PIRSA:13060025, Discrete Approaches - 1, 2013-06-25, Loops 13
• PIRSA:11120050, Canonical Time Evolution in Simplicial Gravity , 2011-12-07, Quantum Gravity