Research on Quantum Gravity and Quantum Foundations

这个项目是针对量子引力的，这是物理学家如何将两者统一起来的问题

This project is directed to quantum gravity, which is how physicists refer to the problem of unifying the two main pillars of physical theory in its current state of development: Quantum Theory and General Relativity. A solution of this problem is generally expected to tell us about the structure of spacetime on the smallest length scales, and also to help answer questions about why the cosmos is as it is on the largest scales. My approach to this problem is based on causal set theory, which hypothesizes that the deep structure of spacetime is that of a causal set, a kind of generalized family tree, known technically as a "partial order". To formulate a theory of quantum gravity on this basis is difficult, because the basic concepts are so unfamiliar. Instead of equations of motion, one has a growth process describing the continual birth of causal set elements --- the "atoms of spacetime". Nevertheless, two major strides forward have been taken in the last couple of years, the first being a formulation of a quantum field theory on a causal set, the second being the discovery of an analog of the Einstein-Hilbert action- functional for the causal set itself. The project will follow up on these two pieces of progress. Based on the former, we will study the effect of spacetime atomicity on Hawking radiation by a black hole. Based on the latter, we will perform computer simulations to learn whether the causal set is able to give rise to an approximate spacetime, not only in principle but also in practice. A related strand of this research-proposal concerns Quantum Foundations, an endeavor which I believe to be intertwined with Quantum Gravity to the extent that progress in the one will ultimately depend on progress in the other. The defining question here is, To what sort of microscopic reality does the quantum formalism refer? The projected research would develop further a proposed answer to this question which some of us have put forward, according to which a quantum reality is "built out of classical realities" in much the same way that a polynomial like x(y+z)+w is built out of the indeterminates x, y, z, and w.