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10

Jun

2020

Beyond Spacetime

 
 

One of the greatest challenges in fundamental physics is to reconcile quantum mechanics and general relativity in a full theory of “quantum gravity”. It is a challenge that has by turns excited and frustrated physicists, for nearly a century. Much is known (or at least believed), but much remains uncertain. A successful theory will have profound consequences for our understanding of space, time and matter, and many researchers believe that a major impediment to progress is the very fact that attendant central concepts will have to be replaced — even quantum mechanics assumes that space is classical, for instance. We argue (making the case that history clearly teaches this) that such changes do not come after a formal theory is hypothesized and tested, but have to be made simultaneously with the development of such a theory: for instance, consider the conceptual reasoning that helped Einstein develop his theories of relativity.

To advance this work, two of us (Huggett and Wüthrich) founded the Beyond Spacetime project to bring together philosophers (especially philosophers of physics) and physicists working in quantum gravity; since 2013 we been organizing conferences, summer schools, and speaker series, and recruiting students, and pre- and post-doctoral fellows (including our co-editor, Matsubara) — and of course pursuing our own research. (With funding from both US and Swiss NSF, Foundational Questions Institute, and major support from the John Templeton Foundation.) You can find out more about our activities — and a complete video archive of talks, schools, and meetings — at www.beyondspacetime.net.

One of our activities was an annual essay contest, and the winning essays are collected — with other essays invited or chosen from our meetings — into two volumes. The first is just published by Cambridge University Press: Beyond Spacetime: The Foundations of Quantum Gravity. Its essays have a more technical orientation, and it is intended for an audience of physicists and philosophers of physics. (The second volume, Philosophy Beyond Spacetime, is forthcoming from Oxford University Press, and is aimed also to a more general philosophical audience.)

Beyond Spacetime is divided into three broad topics. ‘Spacetime Emergence’ asks in what senses classical spacetime might be missing from various theories of quantum gravity, and how its appearance might be recovered. For instance, Daniele Oriti argues that emergence comes in different degrees for different theories; while Robert Brandenberger and Daniel Harlow explore concepts of emergence in string theoretic accounts of the big bang and black holes.

The second section addresses the status of time specifically. For instance, both Carlo Rovelli and Fay Dowker see room for a conception of ‘temporal becoming’: the former in the form of transition amplitudes in loop quantum gravity, and the latter in the ‘birth’ of events in a causal set. In an essay synthesizing several decades of his work, Lee Smolin also points to clues that temporal becoming will be a key element of quantum gravity.

The final section addresses a variety of interpretational issues: for instance, essays on the significance of black hole evaporation, string duality, and the nature of final theories.

These essays represent some of the best recent work on the conceptual foundations of quantum gravity, the result of significant thought and discussion between some of the best physicists and philosophers in the field, as well as a number of rising scholars. We hope that it will help sustain that important conversation, and bring in new participants!

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About the Author: Christian Wüthrich

Université de Genève...

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About the Author: Keizo Matsubara

Uppsala Universitet, Sweden...

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About the Author: Nick Huggett

Nick Huggett is LAS Distinguished Professor at the University of Illinois, Chicago. He has worked in the field of the philosophy of quantum gravity for over twenty years. He is co-editor of Physics Meets Philosophy at the Planck Scale (Cambridge, 2001) and is Co-Director of the 'Beyond Spacetime' research project, funded by NSF, Foundational Questi...

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