Determinism - the belief that all events (including animal behavior and human actions) are fixed or ordained by antecedent conditions or external forces before they happen - doesn't keep me up at night, but it seems to be something of a bogeyman for many people. To my mind, it's a fantastical notion. Here's how I perceive the argument for this belief:
One could provide many sophisticated philosophical arguments against the determinist fantasy, involving Gödel's Incompleteness Theorem, the epistemology of explanation and prediction, the nature of time, etc. Because I like to keep things short and sweet, instead I'll use a homely example: the honeybee.
What would our all-knowing entity need to know in order to precisely and accurately predict every event in the life a single honeybee? And I do mean every: its exact lifespan, its exact physiological activity at every moment, exactly how many times each day it flies out of the hive for pollen, its exact flight paths, exactly which flowers it visits and for how long, exactly what messages it exchanges with its hivemates, exactly what obstacles and conditions it experiences and exactly how it reacts, and so on. Even if the bee never flies more than a mile from the hive and the hive contains only one hundred bees and there are only a thousand flowers within a one-mile radius (of course these things change with the seasons and the weather and the passage of time), the possible event-trees for prediction purposes must number in the trillions or more.
And that's just one little honeybee! Consider that, even in that one square mile of earth, we'd need to multiply by a hundred of bees in the hive, a thousand flowers, thousands of other insects, hundreds of birds and quadrupeds and bushes and trees, hundreds of thousands of blades of grass, and so on - not to mention the exact composition and condition of the soil and the constantly moving and changing air (including every weather event), etc. Oh, and let's multiply all that by hundreds of millions of square miles of the earth's surface area, or cubic miles of land mass and ocean. And then multiply again by hundreds of billions of galaxies and their constituent solar systems. How would our all-knowing entity learn about the exact condition of all these things, and do so at the same time? (We must of course factor in the speed of light, not to mention undefined methods of measurement.) How indeed would all these events throughout the universe not merely be roughly modeled but precisely and accurately predicted? Leaving aside gods and demons, how enormous would a computer need to be in order to formulate such predictions - and what impact would such an enormous computer have on the universe itself? (This impact, too, would need to be predicted because, after all, the computer itself would be part of the universe.)
This brief thought experiment leads me to conclude that determinism is not a serious hypothesis, but a groundless fantasy. And I have much more important things to spend my time on than groundless fantasies!
(Cross-posted at philosopher.coach.)
FOR FURTHER EXPLORATION
Peter Saint-Andre > Journal