Scenarios2/9
Brain in a Vat · A real brain in base reality. Only its world is computed, and everyone else is scripted.
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.
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, ~1021 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.
- 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.”
Instance report
A BRAIN IN A VAT
A BRAIN IN A VAT
Settings
ScaleEarth
Matter floorPainted set
LobbySingle player
Inner lives8.2 billion · real brain, outside
Computed1.7 × 10^-16%
TimeLinear, live from 1996
SlotA player
Computing needed
8.2 × 1015 FLOPS
Computer size8 × one AI accelerator
Universe-computers10-88
FeasibilityPossible today
Judged, not measured
The author’s reading. None of these changes the computing total.
SufferingAs found
Free willFeels free
Utilitariandivided
Deontologicaldivided
Virtue ethicsdivided
Existentialistleans 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
1013 FLOPS
Only surfaces are computed, and only where someone is looking. Anything unobserved is just a stored value.
Mind computingwild guess
8.2 × 1015 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 × 1020 animals as scenery.
Operations so farrough
7.8 × 1024
30 years on the clock, at 8.2 × 1015 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.