Physical determinism is the idea that everything in the world happens because of the physical laws that govern it. It means that if we knew everything about the physical world, we could predict exactly what will happen in the future.
Think of it like a really big domino set up. If you set up all the dominoes just right, you can predict exactly when and where each one will fall. And if you had all the information about the dominoes, like their size and weight and how much force you used to push them over, you could predict exactly where the last domino will land.
In the same way, everything in the world is like a big domino set up. Every action and reaction is determined by the physical laws that govern it. And if we knew everything about the physical world, we could predict exactly what will happen next.
Of course, the world is much more complicated than a domino set up. There are lots of things we don't understand yet, like how tiny particles interact with each other or how the human brain works. So, while physical determinism is a really cool idea, we can't actually predict everything that will happen in the future...yet.