### Project Description

RESEARCH AREAS:

General Relativity and Cosmology

Foundations of Quantum Theory

Conceptual Issues in Particle Physics and Cosmology

CONTACT:

# MARC HOLMAN

**Postdoctoral Fellow;**

Department of Philosophy, Western University

A theoretical physicist by education, Marc Holman has a longstanding interest in the history and conceptual foundations of modern physics. Concretely, this interest is strongly shaped by the idea that, at an elementary level, obtaining a better understanding of these aspects of modern physics is a necessary condition for further theoretical progress to be made – in particular when it comes to the still elusive theory that would somehow unify quantum theory and general relativity.

Quite remarkably, the two physical theories that describe extremely well physical phenomena on the largest and smallest distance scales in our universe, viz. general relativity and quantum theory, respectively, are radically disparate. Both theories are now almost a century old and have passed with flying colours every test to which they have been put, but they seem to be telling us completely different stories about the nature of physical reality. Loosely formulated, general relativity is a local, deterministic, background independent theory, while quantum theory is fundamentally nonlocal, non-deterministic and background dependent, with experiments moreover putting very strong constraints on any *interpretation* of the theory that is more akin to general relativity in the first two respects.

My doctoral dissertation (Utrecht University; 2014) is essentially a detailed and critical review of both these fundamental theories, as well as the further developments they spawned. Regarding the first aspect, issues such as the historical emergence and conceptual foundations of both theories are crucially dealt with, while notions such as black holes, the thermodynamic arrow of time, applications of quantum theory to field systems, renormalization theory, and the standard models of modern cosmology and particle physics are key to the second aspect. Two other equally important and related, but so far critically unresolved issues in this latter regard revolve around the question of how to interpret the quantum formalism and the problem of how to integrate both theories into an overall unified framework – a so-called theory of “quantum gravity’’. In dealing with these issues, the discussion includes fairly comprehensive and critical treatments of constructs as esoteric as string/M-theory, the anthropic landscape and parallel quantum universes, as well as apparently somewhat more worldly ideas, such as loop quantum gravity, Bohmian beables, and the quantum-classical cut. Although the upshot of these discussions is that there are good reasons to think that *both *quantum theory and general relativity will have to undergo subtle, but profound revisions before a successful, even-handed quantum gravity scheme can be formulated, the status of quantum theory is specifically focussed upon. Indeed, one of the main conclusions of the work is that quantum theory, in spite of all its triumphant empirical confirmations, is most presumably an approximate theory.

My present, post-doctoral research phase comprises two essential strands. First and foremost, I will be continuing my investigations into modern cosmology and its conceptual underpinnings in a more systematic way. Cosmological research has made spectacular advances over the past several decades on the observational side of things (as exemplified for instance by the increasingly more detailed maps of the CMB-spectrum provided by successive space satellites such as WMAP and PLANCK), but in spite of these advances, *no* direct observational evidence has so far been found for any of the three forms of stress-energy postulated by the so-called “cosmological concordance model’’, i.e., “dark energy’’, (cold) dark matter and the “inflaton’’, each of which allegedly explains a specific discrepancy between essentially standard Newtonian/Einsteinian cosmology and certain observations (i.e., the accelerated expansion of the presently observable universe, the dynamic-luminous mass discrepancy for (clusters of) galaxies and the so-called horizon problem, respectively). Furthermore, for all three components alternatives exist which may well be closer to the truth. An important aim of the current project is to assess the state of cosmological research in this regard. A second line of investigation is the refinement of certain arguments put forward in earlier work, pertaining, for instance, to so-called naturalness problems and the foundations of quantum gravity.

__Articles__

*On Arguments for Linear Quantum Dynamics*, (2006), arXiv quant-ph/0612209

*LEP, LHC en het Higgs Effect – Enkele Feiten en Mythes* (2008), Nederlands Tijdschrift voor Natuurkunde [Dutch Journal of Physics], **74**, 9, 319

*Physical Degrees of Freedom in Higgs Models*, (2009), arXiv 0910.4054

*Generalized Noether Theorems for Field Theories Formulated in Minkowski Spacetime*, (2010), arXiv 1009.1803

*Het Higgsdeeltje : Baanbrekende Ontdekking of Pyrrusoverwinning? *(2013) Nederlands Tijdschrift voor Natuurkunde [Dutch Journal of Physics]*, ***79***, *9, 319 (correspondence : **79**, 5, 163)

*Foundations of Quantum Gravity : The Role of Principles Grounded in Empirical Reality* (2014) Stud. Hist. Phil. Mod. Phys., **46B**, 142-153, arXiv 1308.5097

*Electroweak Symmetry Breaking, Intermediate Regulators and Physics Beyond the Standard Model* (2015), arXiv 1507.08214

*On the So-Called Flatness Problem of FLRW Cosmologies* (2016; forthcoming)

*Issues of Unity, Uniqueness and Universality in the Quest for Quantum Gravity* (forthcoming)

__Doctoral Thesis__

*The Quest for a Fundamental Theory of Physics. Rise and Demise of the Field Paradigm.* Department of Mathematics, Utrecht University (2014)

__Invited Talks__

Quantum Theory : its Geometry, Possible Extensions and Causality, Institute of Theoretical Physics, Utrecht, the Netherlands, November 2003

__Conference Presentations__

*The Significance of Empirical Principles for Quantum Gravity*, International Conference on the Foundations of Physics, LMU, Munich, Germany, July 2013

*The Significance of Empirical Principles for Quantum Gravity*, Conceptual and Technical Challenges for Quantum Gravity, Sapienza, Rome, Italy, September 2014

*How Problematic is the Near-Euclidean Nature of the Universe’s Spatial Geometry *? Fourth International Conference on the Nature and Ontology of Spacetime, Varna, Bulgaria, June 2016

Fall, 1998, Classical Mechanics, Physics Department Pennsylvania State University (TA)

Spring, 1999, Waves & Optics, Elementary Thermodynamics and Quantum Mechanics, Physics Department PSU (TA)

Summer, 1999, Waves & Optics, Elementary Thermodynamics and Quantum Mechanics, Physics Department PSU (TA)

Fall & Winter, 2000-2001, Advanced Quantum Mechanics (MSc level), Physics Department, Utrecht University (TA)

Fall & Winter, 2001-2002, Advanced Quantum Mechanics (MSc level), Physics Department, Utrecht University (TA)