Comment by lupire

It's a poorly worded way of saying, if heat doesn't exist, and objects don't gain or lose energy, but only change configuration in a controlled way, physics is reversible. This is traditional time-symmetric Newtownian physics before thermodynamics. "What does down bounces back up."

Entropy is measure of information. If an object changes state according to some law or data that you don't know, then you can't predict the result, and you can't set up conditions to undo the changes. Thus you can't reverse it, because you don't know the original state. If you can explicitly model every particle, you can reverse it.

You can't uncrack an egg, because you don't know an egg works. But you can unopen a door, because you know how a door works. All you need is a perfectly elastic mirror, carefully placed to bounce the swinging door off of.

An expert egg mechanic can uncrack an egg with a precise arrangement of mirrors.