Could Spacetime be Causal Structure Alone?

7 February 2011
Fay Dowker
<em> Abstract: In the continuum the answer to the title question is "no". But if spacetime is atomic then the answer is yes. And it so happens that there is rather compelling circumstantial evidence that spacetime is actually discrete at the Planck scale. So now the question becomes, why if spacetime is discrete should it take the form of a discrete causal structure or *order*? The answer is that if you don't put causal order in fundamentally you don't get it out -- at least that's what known models of "emergent spacetime" indicate. If we want to make life easy for ourselves in quantum gravity, then, we should plump for discrete causal order (a "causal set") as the inner basis for spacetime. That, however raises the spectre of wild nonlocality. I will describe recent progress that shows that this wildness can be tamed. In particular we now have an approximately local action for causal sets and I'll explain what that means. </em>
  • String Theory Seminar