Emergence of Space-time Structures

Abhay Ashtekar

The term emergence has many facets and is often used rather loosely. In this talk, I will use it in the following precise sense: Physics of interest is emergent if it is formulated in terms of notions which can be derived from a fundamental theory based on entirely different degrees of freedom. (An obvious example is provided by QCD where the directly observable physics involves hadrons and mesons but it is derived from equations governing completely different fundamental entities, namely quarks and gluons.) In this sense, I believe that space-time structures of general relativity are emergent: the fundamental degrees of freedom of quantum gravity are likely to be very different from notions that are most directly useful in classical general relativity. However, this does not mean that one cannot use general relativity as a starting point to construct quantum gravity. That is, although in the final picture classical space-time structures will only be emergent, Einstein's theory can nonetheless serve as a powerful guide in our search of the fundamental degrees of freedom. I will illustrate these ideas through several examples.

The talk will be addressed primarily to non-experts.