Fotini Markopoulou

"Geometrogenesis. We do not know much about quantum gravity. We expect it to hold at Planck scale energies of 10²² MeV. This is 10²⁰ orders of magnitude higher than subatomic physics. Our best tests of quantum field theory are at settings of some 10²⁰ orders of magnitude cooler than the physics of quantum gravity. In all other cases we know of in physics, it suffices to change energy scales by much less than that for the studied system to undergo a phase transition. Then two things can happen. First, the system can acquire properties that did not exist previously. This is the subject of emergence. For example, if we cool water we get ice. The order of the crystalline structure of ice is an emergent property of the ice phase. Second, but related, almost always the degrees of freedom we use to describe the two phases are different. An example of this is the comparison of fluid dynamics to the underlying theory of quantum molecular dynamics. The first is governed by the continuity and Euler equations and we use notions such as waves to describe the system. At the molecular level we have the Schrödinger equation and the intermolecular potential. Waves are emergent notions, applicable only at the low energy phase. There are no degrees of freedom describing waves at the molecular level."

Space does not exist, so time can.

The disappearance of geometric time dictated by diffeomorphism invariance may be a statement about being inside the universe and not about whether fundamental time exists.

The ultimate background independent theory is not one where the physics is independent of the background but the one with no background. Background independence means to make no distinction between geometry and matter and to describe the dynamics of the universe as seen by observers inside it. Diffeomorphisms are not about timelessness but about being inside a dynamical universe, affecting it and being affected by it, constituting it.