Describing here his invention of the differential and integral calculus, and his discovery of the law of gravitation, he had been a clever fellow indeed. His above-mentioned proof that gravity, the force responsible for an apple's fall, holds the moon in her orbit as well, united in a single stroke heaven and earth, and showed that both obey a single set of universal laws. He elucidated the laws of motion , and humankind, for the first time, was given precise predictive power over nature. We can calculate, for example, the solar eclipse schedule centuries into the future. But things are never as simple as we'd like for them to be.
Some physical systems seem to defy our ability to predict.
Repeat an experiment with identical initial conditions, and very soon the body's position and velocity do not even come close to those obtained the first time. After a very short time, the state of the system will be essentially unknown. It is virtually impossible to predict when the next drop will fall. It is not our ability to calculate that does us in, it is our inability to measure. To repeat an experiment, we must start the system off with precisely the same initial conditions.