My question is slightly philosophical, so be warned. If we could only experience the world through a recording played backward, what laws would we form? I am asking, because the strangest thing occured to me: at least some of these laws would be exactly like ours. Say, you have two coins. They travel through void. They hit. Bounce off. Now they travel in different directions. Now imagine you record the whole thing happening and you play it backwards. The funny thing is, your recording still makes sense. As much sense, as the 'proper' recording. Energy preserved. Cause and effect just "traded places". Cause and effect (= time?) is "symmetric". Earth revolves around Sun. We play it backwards. Still makes as much sense. But, obviously, not all causes and effects can be reversed like this. Let's say an asteroid hits the Moon and it explodes. Little pieces fly in all directions and come to rest at the surface of the Moon. If we reverse this, we get small pieces detaching themselves, for no apparent reason, from the surface; jumping together; forming the asteroid and then flying away into the space. It's hard to imagine what set of alternate-physics laws would it take to do that. Gravity working in opposite direction, that's for one (or maybe the void working as the source of gravity-like force). I am not sure if it could be explained by any laws... but maybe? What of entropy? In our world, it increases with time. In alternate reverse-time world, the laws would have to state "entropy decreases with time". Ironically, it appears just as logical as our "increases with time". After all, physics is generally like mathematics. It has equations... Symmetric, reversible. 2+2 is 4 and therefore 4 is 2+2. E=mc2 and mc2=E. And yet in real life, in physics, when we get to cause and effect, this symmetry gets broken. Does it? If we tried to form laws of physics for a "recording-played-backward world", where exactly would they lose symmetry with our laws? Or wouldn't they?