Rewind — will the scattered book come back together?
A clay book is made of forty-eight gold beads. Shake it and they scatter; rewind and they are a book again. But the further down the boards you go, the harder rewinding becomes.
Shake, then press Rewind, and the motion you just saw runs backwards.
The laws do not tell forwards from backwards. Play the collisions and bounces in reverse and nothing is out of place.
Shake, nudge one bead by a hair's breadth, and rewind. This rewind is not a film played backwards: every bead's velocity is reversed and the motion is actually run.
What blocks the rewind is not the law but a very small error. It grows at every collision.
A bead that reaches the gap at the top turns to light and flies out of the box. Shake, then rewind.
The light given off when the book burned has already flown into space. To rewind, you would have to call that light back too.
What you just did by hand is written up in these pieces.
There are countlessly more scattered arrangements than gathered ones. That is why scattering by itself is easy and gathering by itself is hard. The direction of time is set not by the laws but by this difference in the number of arrangements.