## Summary

A trio of dichotomies, Atomicity versus Continuity, Locality versus Global-ness and, Being versus Becoming, are persistent themes in our struggle to understand the physical world. In the present era, they are finding concrete expression in the attempt to create a theory of "quantum gravity", which phrase is a shorthand for a framework in which all of physics will find unified expression. In my research these ancient tensions reveal themselves to be intertwined one with another and I am attempting, not so much to resolve them but to put them to work as heuristics in discovering quantum gravity. Consider the first dichotomy: we now know that ponderable matter is atomic and, since the work of Einstein, we know that space-time is a physical, 4-dimensional substance which bends, warps and ripples, an apparent continuum. I work on an approach to unifying physics in which this material space-time fabric is itself fundamentally granular or `atomic' and in which the smooth continuum of our current theory of space-time is an approximation to a discrete substructure. Space-time discreteness appears in several approaches to the problem of quantum gravity; what sets the approach I work on apart is that the atomicity respects the relativistic causal principle that physical influence cannot propagate faster than light. This causal spacetime atomicity takes the concrete form of a discrete partial order or *causal set*.

The other dichotomies become entangled in the quest as causal sets both necessitate a radical non-locality in nature and potentially enable physics to reclaim the notion of Becoming that seemed to have been lost with the advent of relativity and the rise of the block universe view. In another thread, quantum causal set dynamics (QCD) requires that quantum theory be conceived in terms of the path integral. Path integrals are global in nature: they deal with whole spacetime histories. Only in the classical limit does exactly local physics emerge, as the Euler Lagrange equations arise in the stationary phase limit. In the full quantum theory, it is unlikely that locality can be exactly achieved and this adds another layer to the challenge of recovering approximately local physics and a notion of Becoming, from quantum gravity.

In this public debate I argue that the path integral (or sum over histories) approach to quantum mechanics provised a One World interpretation

Public lecture on my research Spacetime Atoms and the Unity of Physics

Short set of lectures on Causal Set Quantum Gravity

Seminar Counting the Entropy of Any Causal Horizon

Personal Website atomsofspacetime

## Publications

### Journals

Barton C, Counsell A, Dowker F, et al. , 2019, Horizon molecules in causal set theory, *Physical Review D: Particles, Fields, Gravitation and Cosmology*, Vol:100, ISSN:1550-2368, Pages:1-17

Wilkes H, Dowker H, Lewandowski C, et al. , 2017, A ``problem of time''' in the multiplicative scheme for the n-site hopper, *Journal of Physics A: Mathematical and Theoretical*, Vol:50, ISSN:1751-8113

Ahmed SN, Dowker F, Surya S, 2017, Scalar field Green functions on causal sets, *Classical and Quantum Gravity*, Vol:34, ISSN:0264-9381, Pages:1-19

Dowker F, Zalel S, 2017, Evolution of universes in causal set cosmology, *Comptes Rendus Physique*, Vol:18, ISSN:1631-0705, Pages:246-253