Lloyd’s bound
Lloyd’s bound is the physical limit on computing found by Seth Lloyd (2000). He worked out from quantum mechanics that one kilogram of matter can do at most about 5 × 1050 elementary operations per second. For the observable universe that comes to roughly 10104 operations per second, and 10120 over cosmic history.
The universe-computer rung: all matter working at the physical maximum. It’s the top of the machine ladder.
Lloyd’s bound is the ceiling on the machine ladder. It makes a universe-scale computer a real physical object and not just a figure of speech. All the mass in the observable universe, computing at the physical limit, gives about 10104 operations per second. Several sandbox scenarios need more than that. That’s what “physics says no” means here.
14 short pages, one per thinker, each with its matching dial. See also the reading list.