NEW VIEW ON QUANTUM GRAVITY:MICRO-STRUCTURE OF SPACETIME AND ORIGIN OFTHE UNIVERSE

摘要

It is generally agreed that the primary goal of quantum gravity is to find themicroscopic structure of spacetime. However, for the last half a century thecardinal principle upheld by most general relativists has been to find ways toquantize Einstein's general theory of relativity, a theory which has proven tobe highly successful in describing the macroscopic structure of spacetime welive in today. A tacit assumption in this existing paradigm is that doing sowill yield the micro-structures of spacetime. We challenge this supposition andpresent a different view. If general relativity is an effective theory valid onlyat the long wavelength and low energy limits, and the metric and connectionforms are collective variables, then quantizing a classical theory such as generalrelativity valid in the macroscopic domain is unlikely to yield a theory of themicroscopic structures of spacetime. To uncover the microscopic structures oneneeds to find ways to unravel the underlying microscopic structures from ob-served macroscopic phenomena rather than naively quantizing the macroscopicvariables, two very different paradigms. This task is similar to deducing themolecular constituents or even their quantum features from hydrodynamics oruniversalities of microscopic theories from critical phenomena. The macro tomicro road poses a new and perhaps more difficult challenge to the next gener-ation of theorists, phenomenologists and experimentalists in quantum gravity.Here we need to address issues at the quantum-classical and micro-macro in-terfaces familiar in mesoscopic physics, focusing on quantum fluctuations andcorrelations, coarse-graining and backreaction, and adopt ideas of nonequilib-rium statistical mechanics and techniques from quantum field theory to exploretheories built upon general relativity in a 'bottom-up' approach or a 'grass-root'road to quantum gravity. This view also provides us with a natural resolutiontowards the 'Origin of the Universe' issue, viz, the 'origin' is merely the com-mencement of a new phase where spacetime began to take shape and assume amanifold structure.