Gravity and Quantum Theory: Domains of Conflict and Contact

Understand

There are two strong clues about the quantum structure of spacetime and the gravitational dynamics, which are almost universally ignored in the conventional approaches to quantize gravity.

• The first clue is that null surfaces exhibit (observer dependent) thermal properties and possess a heat density.
• This suggests that spacetime, like matter, has microscopic degrees of freedom and its long wavelength limit should be described in thermodynamic language and not in a geometric language.
• Second clue is related to the existence of the cosmological constant.