Laplace's Demon

Suppose there were an all-knowing being that knew the position and momentum of every particle in the universe. If this demon (or angel if you prefer) knew this information and the equations of motion, the future would be deterministic. That is of course if he were incredible at computation. The future would immediately be known as well as the past.

Over the years, many thinkers contributed to our understanding of the world. For example, Isaac Newton discovered that force is equal to mass times acceleration and Galileo and Kepler discovered the equations of the heavenly bodies. The laws of physics seem to be written in a way that makes it possible to plug in values for time and see where objects are in the future if all initial conditions are known.

Along comes Pierre-Simone Laplace, who took this idea to the extreme. Who is to say there couldn't be an all-powerful computer operated by some otherworldly entity that could then calculate the future? Not just the future of where a ball will land, but where everything goes at any point in the future.

Do you believe this is possible, at least in theory? If so, you are at odds with what most physicists know to be true. According to our best understanding, particles obey the Heisenberg uncertainty principle, which makes deterministic predictions impossible to this degree. Werner Heisenberg, a great thinker of the 20th century, realized that it is actually impossible to know with 100% certainty, the position and momentum of any particle. You may know exactly where something is, or the velocity of something, but never both at the same time.

Laplace (1749-1827) was a great contributer to our understanding of how the world works. He is also famous for Bayesian probability, which is a different way to view what is mean by the probability of an event. He was also close to realizing the possibility of black holes.

So many great insights, paradoxes, realizations, and discoveries, have been made by thought. Even as a kid I thought that the reason why we perceive time differently as an adult vs. as a child is due to our perception to time in relation to our existence. Wouldn't it be reasonable to think a year is a long time when you are only 6 years old? Would it have the same weight as someone in their 80's? Look at the world around you, what questions or insights do you have?

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