You are getting there. But first, I want to be sure I understand you.
Your example is perfect. Fire causes heat. I mean, everyone knows that. So, if I show you a movie of a bunch of heat collecting itself to a point in order to magically form a fire, you will know that I cheated. You will know that I played the movie in reverse. And you know that, because fire does not form magically through the concerted and synchronous collection of energetic particles into a point. The same with a hammer hitting an egg. We know that shattered eggs do not assemble themselves to form a full egg and cause a recoil on a hammer.
Therefore, it is because of that that fire caused that heat and not the other way round. Is that correct?
But suppose now that I show you a movie where you cannot say whether I cheated or not. For instance the decay of a photon into two antiparticles. If I play the movie in reverse, I see two antiparticles disappearing and generating that photon, time reversed. Since both processes are equally possible, how do you know what caused what?
Ciao
- viole