--- title: "Brain in a Vat · a universe that takes 8.2 × 10¹⁵ FLOPS · Simulation Hypothesis" url: https://simulation-hypothesis.com/builds/vat description: "A real brain in base reality. Only its world is computed, and everyone else is scripted." license: https://creativecommons.org/licenses/by/4.0/ credit: "Ross Allan Dahl, Simulation Hypothesis (simulation-hypothesis.com)" --- [Scenarios](https://simulation-hypothesis.com/builds)2/9 # Brain in a Vat · A real brain in base reality. Only its world is computed, and everyone else is scripted. Open in the sandbox ▸ A real brain, kept alive in a vat in base reality and wired to a computer. The brain isn’t simulated. Its own neurons do the thinking. The computer supplies everything it senses and responds to everything it does. That means a present-day Earth, drawn in only where the brain looks, with every other person scripted. Only the world counts toward the total, which makes this the cheapest build in the sandbox. Required computing power rough 8.2 × 10^15 FLOPS Our computers could run this today. [The countdown ▸](https://simulation-hypothesis.com/countdown) Data-centre scale. Our computers already run this. Computer sizerough 8 × one AI accelerator One of today’s data-centre accelerators at low precision. Training a large language model takes thousands of them. Feasibility Possible today Data-centre territory: a rented GPU cluster would do. Universe-computerstextbook 10^-88 One universe-computer is every kilogram in the observable universe computing at Lloyd’s bound. Power draw, Landauer floortextbook 0.000024 W The thermodynamic minimum for flipping bits at room temperature. The best real hardware uses about five billion times more energy than that. At the thermodynamic minimum, a wall socket would do. On every computer on Earthrough faster than real time How long it takes, on a clock, to compute one second of simulation on all of humanity’s computers, \~10^21 FLOPS. Real time, on computers we have today. World actually computedwild guess 1.7 × 10^-16% 1.7 × 10^-16% of the mass is watched by one observer. The observation dial sets how much of the remainder is computed at the full floor. ## Questions this scenario asks * If only one mind really exists, does ethics still apply? * How could you know that other people are real? * Can meaning be built from input alone? * If a memory is of something that never happened, is it still yours? “Worked out a brain in a vat: a real brain in base reality, with only its world computed. 8.2 × 10^15 FLOPS, or 8 × one AI accelerator.” ## Report card Instance report A BRAIN IN A VAT Settings Scale Earth Matter floor Painted set Lobby Single player Inner lives 8.2 billion · real brain, outside Computed 1.7 × 10^-16% Time Linear, live from 1996 Slot A player Computing needed 8.2 × 10^15 FLOPS Computer size 8 × one AI accelerator Universe-computers 10^-88 Feasibility Possible today Judged, not measured The author’s reading. None of these changes the computing total. Suffering As found Free will Feels free Utilitarian divided Deontological divided Virtue ethics divided Existentialist leans against “Worked out a brain in a vat: a real brain in base reality, with only its world computed. 8.2 × 10^15 FLOPS, or 8 × one AI accelerator.” Two of these are rough and three are wild guesses, and each is tagged that way. Change any one dial and you get a different universe. Matter computingrough 10^13 FLOPS Only surfaces are computed, and only where someone is looking. Anything unobserved is just a stored value. Mind computingwild guess 8.2 × 10^15 FLOPS none, by definition: the brain runs on its own neurons, outside the simulation One real brain in base reality, which does its own thinking, and 8.2 billion scripted characters. Inner liveswild guess 8.2 billion 1 real mind, 8.2 billion scripted, 4.5 × 10^20 animals as scenery. Operations so farrough 7.8 × 10^24 30 years on the clock, at 8.2 × 10^15 per second. History that is only storedrough 99.9999998% Computing begins in 1996\. 5.77 billion humans are present at the start, with preinstalled memories. [◂ The Matrix](https://simulation-hypothesis.com/builds/sleepers)Open in the sandbox ▸ [Solipsism ▸](https://simulation-hypothesis.com/builds/solipsism)