Why do things decay? Why can't things stay what they are?
Thermodynamic decay - why entropy increases, why ordered systems dissipate into disorder, what time's arrow actually is at a physical level.
Biological decay - why organisms decompose, what the decomposer ecosystem actually does, how death feeds life at the chemical level.
Structural decay - how buildings fail, how bridges crack, how load eventually wins.
Cultural decay - why institutions calcify, why languages shift?
Why do things decay? Why can't things stay what they are?
Material decay - corrosion, oxidation, fatigue, creep, why metals fail, why concrete cracks, why rubber hardens.
Ecological decay - nutrient cycling, carbon return, the mechanics of a forest floor.
Informational decay - why memories fade, why signals degrade, why copies of copies lose fidelity.
Physics gives you the second law of thermodynamics, entropy always increases in a closed system.
But that just restates the observation. It doesn't explain why the universe is built that way, why time has a direction at all, why the initial conditions were low-entropy enough that decay could happen in the first place.
Well, that's what statistical mechanics is for.
And it does it in a really, really elegant way.
Except for the time arrow, of course.
