Stephen Hawking and determinism

The success of Newton's laws and other physical theories led to the idea of scientific determinism, which was first expressed at the beginning of the nineteenth century by the French scientist the Marquis de Laplace . Laplace suggested that if we knew the positions and velocities of all the particles in the universe at one time, the laws of physics should allow us to predict what the state of the universe would be at any other time in the past or the future.

In other words, if scientific determinism holds, we should in principle be able to predict the future and wouldn't need astrology. Of course, in practice even something as simple as Newton's theory of gravity produces equations that we can't solve exactly for more than two particles. Furthermore, the equations often have a property known as chaos, so that a small change in position or velocity at one time can lead to completely different behaviour at later times. As those who have seen Jurassic Park know, a tiny disturbance in one place can cause a major change in another. A butterfly flapping its wings in Tokyo can cause rain in New York's Central Park. The trouble is the sequence of events is not repeatable. The next time the butterfly flaps its wings, a host of other factors will be different and will also influence the weather. That is why weather forecasts are so unreliable.