Forks in the Road, on the Way to Quantum Gravity
Rafael D. Sorkin (ICN-UNAM, Syracuse University)

TL;DR
This paper discusses key decision points in developing a quantum gravity theory, advocating specific approaches like sum-over-histories and causal sets, and explores implications for cosmology and black hole entropy.
Contribution
It presents a reasoned argument for particular choices in quantum gravity frameworks, emphasizing the causal set approach and its implications for cosmology and black hole physics.
Findings
Support for sum-over-histories framework
Proposal of causal sets as fundamental structure
Insights into black hole entropy and cosmological constant
Abstract
In seeking to arrive at a theory of ``quantum gravity'', one faces several choices among alternative approaches. I list some of these ``forks in the road'' and offer reasons for taking one alternative over the other. In particular, I advocate the following: the sum-over-histories framework for quantum dynamics over the ``observable and state-vector'' framework; relative probabilities over absolute ones; spacetime over space as the gravitational ``substance'' (4 over 3+1); a Lorentzian metric over a Riemannian (``Euclidean'') one; a dynamical topology over an absolute one; degenerate metrics over closed timelike curves to mediate topology-change; ``unimodular gravity'' over the unrestricted functional integral; and taking a discrete underlying structure (the causal set) rather than the differentiable manifold as the basis of the theory. In connection with these choices, I also mention…
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