Where the energy goes

There is exactly one currency in this world and every organism is always spending it. Not metaphorically. Energy is counted, in seven audited places, and if the books do not balance at the end of a tick the universe stops rather than carry on quietly leaking. Everything an organism does, including nothing, has a price.

The bill for existing

Start with the item nobody expects. Doing absolutely nothing is not free. Every living organism pays a basal upkeep on every tick regardless of behaviour, and on top of that pays continuously for capacities it is not currently using.

Sensing costs energy in proportion to the square of how far it can sense, whether or not there is anything out there. Running its controller costs a flat amount every tick it is used. If it has an active plastic learning mechanism, that costs too. An organism sitting perfectly still in an empty field, thinking about nothing, is running down its reserve the entire time.

The shape of each energy cost as effort increases Three curves on the same axes. A flat line shows fixed costs like basal upkeep and running a brain, unchanged by effort. A rising straight line shows costs proportional to effort, such as signalling. A steeply rising curve shows squared costs, such as movement speed, sensing range, and thermal or moisture stress, which are nearly free when small and ruinous when large. how much of it you do energy cost flat linear squared basal upkeep, running a brain signalling, reaching out to touch movement speed, sensing range, heat and moisture stress
The squared curve is the one that shapes lives. Mild discomfort is nearly free, so there is no pressure to avoid it. Real stress is ruinous, so there is enormous pressure to avoid that. The gap between those two is where a population's tolerances end up settling.

That squared shape matters more than any individual number. It means being slightly too hot costs almost nothing and being properly too hot is fatal, and the same for dryness, for light, and for moving quickly. A world where every cost rose in a straight line would be a world where organisms drifted anywhere, because nowhere would be sharply worse than anywhere else. The curve is what gives the map teeth.

You pay for trying, not for succeeding

This is the rule that catches people out, and it is worth stating on its own because it explains a great deal of what you will see if you watch closely.

Movement is charged on the attempt, not on arrival. An organism that walks into an obstruction pays the full cost of the walking. Trying to eat costs energy whether or not there was anything on the cell. Reaching out to make contact costs energy even when the reach hits empty air. Grasping costs the same whether the grasp works or fails.

Nothing in this world refunds a failed action, and nothing warns an organism in advance that an action will fail. The only feedback available is four of its fifty-three sensory channels reporting what happened when it last acted, which arrives after the money is gone.

Put that together with the ordering of a tick, where the whole bill is deducted after every action has been taken, and you get something that looks a lot like a real constraint: a creature can spend itself to death in a single tick, doing things that did not work, and find out at the end. The ordering is laid out in what happens in one tick.

Seven places, and the total never moves

Now the part that makes this more than a cost table. The energy in this world is conserved, and it is checked.

The seven audited energy reservoirs and the flows between them Energy enters from a cumulative influx into environmental resource. Resource passes into an organism's gut when it eats, from the gut into its body, and from the body it is either spent on living, which dissipates it, or invested in offspring. Dead organisms pass into detritus, which returns to resource. Matter in the world holds energy in objects. Influx and dissipated totals are tracked cumulatively so the sum across all seven is constant. influx arriving resource in the world gut eaten, not yet used soma the body itself detritus the dead, decaying objects held in matter dissipated spent, gone eat digest live die decay the sum of all seven is checked every tick, and must not drift
Nothing is created. An organism's body is energy that used to be resource, and will be detritus, and will be resource again. Reproduction is not creation either: a parent pays part of itself into the offspring, so the two together hold what the parent alone held a moment before.

At the start of every tick the total across all seven reservoirs is measured. At the end it is measured again, along with how much arrived and how much was spent. If those do not reconcile within tolerance, the simulation raises an error and halts.

It does not log a warning and continue. It does not correct itself. It stops, because a world that is quietly leaking energy is a world producing results that mean nothing, and running it for another hundred thousand ticks would only produce more of them.

Why an executable invariant beats a comment

Every rule in this list could have been a paragraph in a design document saying energy ought to balance. Written that way, it holds until the first change that breaks it, and then it holds in the document and not in the world, and nobody finds out for months. Written as a check that halts the universe, it cannot silently stop being true. The full accounting is on energy, metabolism and death.

What dying actually is

Given all of the above, death here has a precise and slightly deflating definition. An organism dies when its stored energy reaches zero, or when it reaches the end of a lifespan set by a gene it inherited. The overwhelming majority go the first way, and most of those go early, before they are old enough to have reproduced at all.

Nothing is lost when that happens. The energy in the body becomes detritus, and detritus decays back into the resource pool, and something else eats it later. The seven reservoirs are exactly as full the tick after a death as the tick before. Only the arrangement changed.

This is not a comforting thought dressed up as physics. It is the physics. In a closed world with a fixed influx, every living thing is a temporary arrangement of a fixed quantity, and the whole of the drama, the entire population, every lineage, is that quantity moving between seven columns of a ledger that always sums to the same number.

Where you can see it

The energy story is the most watchable thing in this world, once you know it is what you are looking at.

Empty regions are places where the bill exceeds what can be found. The grain that develops across the map over thousands of ticks is a cost gradient made visible. A population crash is the moment the resource pool was drawn down faster than it regrew, and the recovery afterwards is that pool refilling while very few things are eating from it. None of that requires anything to want anything, which is the subject of nothing in this world wants anything.

Select any organism on Watch and you get its actual energy reserve and gut contents, on this tick. Watch that one number for a few minutes and the whole essay becomes concrete: it falls when the creature does nothing, falls faster when it moves, and occasionally jumps when it lands somewhere with something on it.

Keep going

Watch the universe