But the success of mechanics spawned the idea that nature as a whole might be deterministic. And reality is counter-intuitive: If I can know exactly where one thing will be at some point in the future, what’s keeping me from knowing where everything will be at some point in the future? Only my ignorance, right? This view is most often expressed in Laplace’s famous, but ultimately delirious fantasy that if one knew the precise position and momentum of every particle in the universe then it would be possible to predict absolutely all future states of the universe. This is the limit case of the view that the nature is fundamentally made up of little billiard balls whizzing around in space, somehow brought into a kind of clockwork regularity at the level of stars and planets by an absentee God who wound up the clock, wrote down Newton’s laws of motion, and then left it to mankind to discern the inscrutable meaning behind the contraptions resulting from the accumulation of God’s pure reason.
To be clear, I don’t think anyone ever really believed this, maybe not even Laplace himself, but the public understanding of why nature is non-deterministic is often incorrectly associated with quantum mechanics. While it’s true that the quantum theory was also a decisive blow to the belief in mechanistic determinism, the reality is that this view was discredited long before the development of quantum theory. Again right at the end of the 19th century, Poincare demonstrated decisively that Newtonian mechanics itself was never deterministic to begin with. I hope to devote a post at some point in the future to Poincare’s ideas, because they are a model of both beauty and subtlety.