Theories of Everything and Hawking's Wave Function of the Universe

TL;DR

This paper discusses the limitations of a 'theory of everything' in predicting all phenomena, emphasizing that fundamental laws explain universal regularities but not specific outcomes in complex systems.

Contribution

It clarifies that a fundamental theory of physics does not fully predict complex phenomena and highlights the distinction between laws governing regularities and specific events.

Findings

A theory of everything is not a complete quantum mechanical universe.

Short laws are unlikely to predict everything.

Regularities in various fields are consistent with but not derived from fundamental physics.

Abstract

If a cat, a cannonball, and an economics textbook are all dropped from the same height, they fall to the ground with exactly the same acceleration under the influence of gravity. This equality of gravitational accelerations of different things is one of the most accurately tested laws of physics. That law, however, tells us little about cats, cannonballs, or economics. This lecture expands on this theme to address the question of what features of our world are predicted by a fundamental ``theory of everything'' governing the regularities exhibited universally by all physical systems. This may consist of two parts: a dynamical law governing regularities in time (e.g superstring theory) and a law of cosmological initial condition governing mostly regularities in space (e.g. Hawking's no-boundary initial condition). The lecture concludes that: (1) ``A theory of everything'' is not a theory of everything in a quantum mechanical universe. (2) If the laws are short enough to be discoverable then they are probably too short to predict everything. (3) The regularities of human history, economics, biology, geology, etc are consistent with the fundamental laws of physics but do not follow from them. (Public lecture given at The Future of Theoretical Physics and Cosmology: Stephen Hawking 60th Birthday Symposium.)