Quantum Spacetime and the Problem of Time in Quantum Gravity
Search for a unification of Einstein’s general relativity and quantum theory in quantum gravity theory is the most important and most difficult research programme in fundamental physics since early 1980’s. In this article we present motivation for the unification and some of main difficulties which prevent contemporary physicists from achieving the aim. We focus our attention on the conceptual problems regarding the notions of time, space and spacetime in quantum gravity. After explaining of why gravity should be quantized (section 1) we present the modem notions of time and spacetime according to general relativity (in section 2) and then compare them in section 3 with the concepts of time and space as they are necessary in quantum mechanics in order for the probabilistic interpretation of the theory to work. Since the concepts in both the theories are different and reconciling them in quantum gravity is extremely hard, we present in section 4 attempts to achieve a less ambitious aim, a fully quantum theory of matter in a classical gravitational field. The current idea that the conceptual problems of foundations of quantum theory may be solved with the help of quantum theory of the Universe is discussed in the last section.
Keywordsrelativity theory quantum theory time spacetime quantum gravity quantum cosmology
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