The causal set theory is an approach to quantum gravity. But don't understand what it claims spacetime to be made of. What is a causal set? Is it a physical object or just a spacetime event? I read the wiki page and watched a few videos on it, but I still just don't understand it.
A causal set builds a universe from just two things: particles and actions. This means that spacetime is made up of particles and each particle has a family history of causes from which it emerged.
Light traveling through space is a set of causally linked particles even though we think of space as empty. Of course, quantum space is actually chock full of vacuum oscillators and so space is already a causal set. All matter comes from other matter and so matter is also a causal set.
The real issue is what exactly does a causal set do for explaining reality. Quantum charge is already a causal set and so making quantum gravity a causal set seems to set the stage for unification of charge and gravity. However, that has not yet been the case.