What is spacetime made of?

Fay Dowker (Imperial)

Physicists are like the annoying child who keeps asking questions: What is this piece of chalk made of? What are molecules made of? What are atoms made of? and so on. Since the beginning of the 20th Century, we have had,
in addition to matter, another “something” to ask questions about: spacetime. Spacetime bends, warps and ripples and carries energy.

Does it make sense to ask what it is made of? I will argue that it does and that the proposal that it is made of smallest possible events — literally “atoms of spacetime” — leads to new ways of thinking about some central questions in the quest to unify our understanding of gravity and quantum theory, including, What accounts for the entropy of a black hole? and Why does the cosmological “constant”, Lambda, have the value it has? This “atomic” approach to the problem of quantum gravity may even throw light on the ancient philosophical question of why we experience time passing.