Project

Discipline

emergent gravity; philosophy of physics; principles of physics; philosophy of quantum gravity

Lead
La formulation d'une théorie de la gravité quantique - une théorie qui réunit la physique quantique et la relativité générale - est un projet majeur de la physique resté inabouti depuis près d'un siècle. Étant donné l'absence de données empiriques à même de guider l'élaboration et la confirmation d'une théorie à venir, le projet présent étudie les présupposés d'une telle entreprise, questionne les hypothèses tacites que cachent les programmes de recherche et considère les alternatives qui émergent suite à l'abandon de certaines de ces hypothèses.
Lay summary
Objectif Ce projet propose d'élargir de deux manières le champ d'investigation sur lequel la philosophie travaille habituellement. Dans un premier temps il consiste en la réévaluation des principes physiques de base à l'oeuvre dans la physique fondamentale ainsi qu'à leurs justifications et à leurs rôles en gravité quantique. Ce projet vise à rendre compte de l'ensemble des principes susceptibles de jouer un rôle. Dans un second temps il analyse l'idée originale selon laquelle la gravité ne serait pas une force fondamentale, mais davantage le résultat d'interactions non-gravitationnelles collectives de la matière fondamentale. La confirmation d'une telle idée rabaisserait la théorie générale de la relativité au rang d'une théorie des champs effective, similaire en ce point à l'hydrodynamique. Contexte Comme diverses approches de la gravité quantique suggèrent que l'espace et le temps n'existeraient pas à un niveau fondamental mais plutôt émergeraient, tout comme d'autres caractéristiques de notre monde macroscopique, il devient urgent d'entreprendre un travail philosophique de ces approches de la physique fondamentale. Dans un esprit de pluridisciplinarité, ce projet comporte des volets philosophiques, physiques et mathématiques entrepris dans le but commun de clarifier les fondations de nos théories portant la réalité physique fondamentale.

Direct link to Lay Summary

Last update: 11.04.2016

Active participation

Self-organised

Title	Year

Number	Title	Start	Funding scheme

To articulate a quantum theory of gravity--a theory unifying quantum physics and general relativity--has remained an unfulfilled challenge in physics for almost a century. Proposals for how to approach the problem abound, but all research programs face major mathematical, physical, and philosophical obstacles. Recently, the frontrunners in the race to find the elusive theory--string theory and loop quantum gravity--have stalled in their progress and the field is disintegrating into myriad research programs pulling in divergent directions. No empirical data is available to guide the hunt in quantum gravity. The mathematical, physical, and conceptual disunity of quantum physics and general relativity renders the difficulty nearly insurmountable. One way to find guidance out of the quagmire is to revisit the very presuppositions of the enterprise, question the possibly tacit assumptions behind stalling research programs, and consider the alternatives that open up once some of them are dropped. This is precisely what the present project proposes to do. The fledging field of philosophy of quantum gravity is almost exclusively concerned with the philosophical foundations of the dominating approaches. We propose to leave the trodden paths in the hope to gain novel insights on the problem of quantum gravity. We will do this in two ways. First, we will step back to reconsider what precisely it would mean to succeed in articulating a quantum theory of gravity. This suggests a reevaluation of the basic physical principles such as unification, discreteness, background independence, general covariance, unitarity, correspondence, and holography, and a reconception of their justification and role in theory-building in quantum gravity. We aspire to developing an integrated account of candidate principles of quantum gravity. Second, we will examine the neglected--and iconoclast--possibility that gravity may not be a fundamental force, but instead the result of the collective non-gravitational interactions of fundamental degrees of freedom. This would degrade general relativity to an effective field theory, similar in status to hydrodynamics. We scrutinize two types of models in this 'emergent gravity' paradigm inspired by solid state physics and black hole thermodynamics, and evaluate to what extent their claims to generality can be upheld.Our project will be of great interest to a wider audience in philosophy. Quantum gravity, it is assumed--though this is not without detractors--, will eventually deliver a theory more fundamental than the current best theories, both of the fundamental constitution of matter (the standard model of particle physics), as well as of the large-scale structure of spacetime (general relativity). Hence, philosophers interested in the fundamental structure of the world will do well to pay attention to what happens in quantum gravity. The project is also of great interest to general philosophy of science, as it considers to what extent a methodology driven by principles can replace the usual empirical methods of science when these latter seem to become obtuse. To enter the fray and engage at short range in the scientific process of constructing a physical theory with deep implications for our conception of the world before the final theory gets inscribed into the textbooks for all to study is an exciting opportunity. By getting immersed in this process, we hope to contribute to this effort with our uniquely philosophical skill set and to draw valuable lessons for the larger fields of metaphysics and philosophy of science.