Loschmidt's paradox

Loschmidt's paradox is about time reversal. Imagine there's a jar full of sand, and you have a wind-up toy car that can drive around in the jar and poke the sand. If you turn the car on, it will move around, leaving tracks in the sand. If you turn it backwards, it would look like time was running backwards, like the tracks were being erased. Loschmidt's paradox is about what would happen if you reversed the direction of time altogether. Would the car start going against the grain, erasing all the tracks it made originally, or would the sand actually start flowing uphill, re-arranging the grains so that it was the same as it was originally? Loschmidt's paradox says that it would be impossible for the sand to move uphill, which means time is not actually reversible.