Can there be a theory of everything?
5th December 2000
In your recent book What Remains To Be Discovered you expressed some pessimism about the progress being made at the frontiers of science. I want to explain, as a scientist at one frontier, why I am so optimistic about our progress-especially on the fundamental issue of the unification of quantum theory (understanding the ultimate nature of atoms) with general relativity and cosmology (understanding the nature of space and time) to make a combined quantum theory of gravity.
The problem of quantum gravity is how to complete the revolution initiated by Max Planck’s overthrow of Newtonian physics exactly 100 years ago. Quantum theory, general relativity, modern cosmology and elementary particle physics are all steps in the construction of the new theory. The objective is to explain how the rules (or laws) that regulate the smallest entities in the world, particles of matter and radiation, also account for the large-scale behaviour of the universe and the strange phenomena within it, black holes for one thing. To put it another way, the issue is how to make the mathematics that describes things that come in bits (“quanta”) compatible with general relativity’s treatment of space-time as a continuum.
Some people call this the problem of achieving a “theory of everything.” I prefer to call it, a bit more modestly, a theory of all physical phenomena we currently know about. Why does it matter? Because it addresses our basic idea of what the universe is, and what space and time are. A revolution in our understanding of what the universe is must have profound consequences for our understanding of who we are and what meaning we can give to our existence.
Moreover, there are clear connections between how we understand the organisation of the universe and how we understand the organisation of our societies. People who lived in strict hierarchical societies imagined a universe organised on strict hierarchical lines, as in Ptolemy and Aristotle. The classic liberal conception of society is not unlike the notion of a world of atoms with properties defined by their relation to an absolute background of space and time. There is also some connection between the struggle of modern legal theorists to define what law is in the absence of an absolute notion of rights and scientists’ attempts to understand how the universe could exist without an…