Nature of Gravity

I spend a lot of time thinking about the gravitational interaction and nature of spacetime. During my masters thesis I tried to understand the notion of emergent phenomena in Physics. Since gravitational field equations have same conceptual status as equations of fluid mechanics, how much can we learn about nature of gravitational interaction if it is an emergent phenomena like fluid mechanics?

What is the essential role of quantum mechanics in explaining gravitational interaction? Is the world fundamentally quantum mechanical? Is gravity, same as hydrodynamics, manifestly classical? If so, such a quantum theory of gravity is very different from theory of quantized gravity. Is theory of quantized gravity similar to phonon-physics? As phonons won’t provide any information about fundamental structure of atoms, would theory of quantized gravity not provide us any information regarding fundamental structure of spacetime? These are few of the questions that keep me up at night.

I think, in order to find a complete theory of quantum gravity, we need to pay attention to three main theoretical constructs, viz.,

• Black-hole singularity
• Big-bang singularity
• Cosmological constant problem

about which both gravitational and quantum theory has something to say. Any theory of quantum gravity must find a resolution to the aforementioned constructs.