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

It is generally agreed that the primary goal of quantum gravity is to find the microscopic structure of spacetime. However, for the last half a century the cardinal principle upheld by most general relativists has been to find ways to quantize Einstein's general theory of relativity, a theory which has proven to be highly successful in describing the macroscopic structure of spacetime we live in today. A tacit assumption in this existing paradigm is that doing so will yield the micro-structures of spacetime. We challenge this supposition and present a different view. If general relativity is an effective theory valid only at the long wavelength and low energy limits, and the metric and connection forms are collective variables, then quantizing a classical theory such as general relativity valid in the macroscopic domain is unlikely to yield a theory of the microscopic structures of spacetime. To uncover the microscopic structures one needs to find ways to unravel the underlying microscopic structures from observed macroscopic phenomena rather than naively quantizing the macroscopic variables, two very different paradigms. This task is similar to deducing the molecular constituents or even their quantum features from hydrodynamics or universalities of microscopic theories from critical phenomena. The macro to micro road poses a new and perhaps more difficult challenge to the next generation of theorists, phenomenologists and experimentalists in quantum gravity. Here we need to address issues at the quantum-classical and micro-macro interfaces familiar in mesoscopic physics, focusing on quantum fluctuations and correlations, coarse-graining and backreaction, and adopt ideas of nonequilibrium statistical mechanics and techniques from quantum field theory to explore theories 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 resolution towards the ‘Origin of the Universe’ issue, viz, the ‘origin’ is merely the commencement of a new phase where spacetime began to take shape and assume a manifold structure. This realization would push us to ask the more challenging question: How do we characterize the phase before? Was it a foam-like structure of multiply-connected spactime? How did the phase transition take place – first or second order, discrete to continuum, stochastic to deterministic? An even more difficult question: How and ‘when’ did our concept of time and an arrow of time emerge whence we can ask how the universe came into being and evolved as far back as we can trace it?