The Clock and the Quantum: Time and Quantum Foundations - 2008

I will identify six \'problems of time\' that arise in connection with quantum gravity and review the extent to which some of them can be regarded as solved, highlighting the very different aspects that they assume depending on one\'s starting point: Hamiltonian vs. path-integral, discrete vs continuous.

I discuss how we can give a satisfactory account of theory confirmation for theories with random data, such as Copenhagen quantum theory, despite the lack of a completely satisfactory definition of probabilistic theories of nature. I also explain why neither this nor any other proposed account of scientific confirmation works for many-worlds theories

There are a number of arguments in the philosophical, physical and cosmological literatures for the thesis that time is not fundamental to the description of nature. According to this view, time should be only an approximate notion which emerges from a more fundamental, timeless description only in certain limiting approximations. My first task is to review these arguments and explain why they fail. I will then examine the opposite view, which is that time and change are fundamental and, indeed, are perhaps the only aspects of reality that are not emergent from a more fundamental, microscopic description. The argument involves several aspects of contemporary physics and cosmology including 1) the problem of the landscape of string theory, 2) cosmological inflation and the problem of initial conditions, 3) the interpretation of the “wavefunction of the universe,” and the problem of what is an observable in classical and quantum general relativity. It also involves issues in the foundations of mathematics and the issue of the proper understanding of the role of mathematics in physics. The view that time is real and not emergent is, I will argue, supported by considerations arising from all these issues It leads finally to a need for a notion of law in cosmology which replaces the freedom to choose initial conditions with a notion of laws evolving in time. The arguments presented here have been developed in collaboration with Roberto Mangabeira Unger .