At Los Alamos in 1950, over lunch, Fermi listened to cheerful estimates of how many civilizations the galaxy should hold, did the arithmetic on how fast even slow starships spread, and asked the question that has embarrassed every estimate since: where is everybody? The proposed answers — we are first, we are rare, they hide, they destroy themselves — each carry their discomforts. This essay's candidate has a different flavor, and it is the least gloomy on the menu: run chapter five's arithmetic as any maturing civilization must, and outward travel is the most expensive possible way to have experiences, while inward computation is the cheapest. A species that completes its swarm finds the interesting frontier is no longer where but what. Why cross four light-years to stand on a dead rock in a pressure suit, when for the same joules you can live a thousand full lives in a thousand worlds of your own design? On this account the galaxy is quiet for the best imaginable reason: everyone's home is bigger on the inside. Expansion is what a civilization does with its energy until it learns what energy is for.
The counterargument at full strength, because honesty requires it: for this to explain total silence, essentially every civilization must turn inward — one expansionist exception fills the galaxy anyway — and universal behavior is a strong claim about minds we have never met. The inward turn has been seriously proposed and seriously criticized in the astrobiology literature, and it remains a candidate, not a verdict. It is ranked here as the candidate requiring the fewest miracles and the least despair, and the ledger in chapter eleven files it accordingly.