What is life, physically?
Physically, life is a pattern that keeps itself the same at its own expense. In 1865 Claude Bernard described fasting rabbits that held the sugar and salt of their internal fluid steady while their livers took their bodies apart to do it. A stone persists for free, its readings sitting where they sit. Leave a rabbit alone for a week and its readings walk off, because holding them was work. The criterion is bounded homeostatic persistence, meaning maintenance under disturbance, paid for out of a finite budget. What a living thing defends is what it shows its neighbors, kept consistent with some possible world, while its interior travels a long way to keep it so. When the spending stops, every atom is where it was a minute earlier. The reading is what stops.
Also in Chapter 39: Why Is a Bacterium Freer Than an Atom?.
This answer comes from OPH, Observer Patch Holography. OPH is a rigorous, consistent and complete description of the unified, self-creating computational Universe we inhabit. Its consistency is machine-checked: the fixed point at its core is constructed explicitly, and a theory with a model contains no contradiction.
To understand OPH and check every step yourself, start with the free book Reverse Engineering Reality. It builds the theory from the ground up, and the OPH Notebook answers your questions while you read.
read the free bookask the notebookor ask sage:read chapter 38: Why Does Anything Try to Persist?watch a universe make its own particles