Chapter 4, Predicting the Future Summary and Analysis

Hawking begins chapter four by discussing the previous view of physicists that the universe was deterministic, meaning that any one state of the world plus the laws of nature would entail every future state. It looks like determinism is threatened by Heisenberg uncertainty. The problem is that uncertainty prevents us from even testing whether determinism is true. We can't get the data so we can't get an answer. Garbage in, garbage out.

Quantum mechanics partially restores determinism because we can accurately predict about half of what we could with full determinism. Particles don't have well-defined positions or velocities, but their states can be represented with wave functions, numbers at each point of space that list the probability that a particle can be found in that position. The Schrodinger equation specifies the rate at which the...