Stress is a complicated adversary. It is a silent killer, but a little bit is good for you. You can be stressed without knowing it, or feel more stressed than you are. Genetic and environmental factors combine in obscure ways to predispose some of us to stress, but not others.

Stress isn’t so straightforward elsewhere, either. Organisms facing rapid environmental change might adapt by turning genes on and off, but we don’t know if these epigenetic signals are inherited. Immense pressures inside stars and diamond anvils produce exotic states of matter whose physics are unclear.

All of which may be just as it should be. Pushing things and people past their usual boundaries has made the world the way it is, and naturally involves the unknown. Would we want it any other way?

Welcome to “Stress.”