The World as Program
If the hardware fantasy is that you can build a computer out of anything in the world, the software version is that you can make a world inside any computer. Indeed, the sense of personal omnipotence, of creating a domain where you are master, is part of programming's seductive charm. But playing God is dangerous. When you manufacture worlds at will, you become vulnerable to the awful surmise that your own world might be someone else's whim.
As the creator of a computer-simulated world, you decree the laws of nature. If you think gravity should be proportional to the cube of the distance rather than the square, then write the equation F = Gmm/r3. Invent water molecules that freeze into eight-pointed snowflakes. Build proteins out of right-handed amino acids. Let the universe expand every Monday through Friday and contract on the weekends.
Does the programmer of a simulated universe have total freedom of design? I don't know. If I invent a world, I'm fairly sure I can make the speed of light whatever I please, but it might be harder to tinker with the value of pi, or to make five-pointed snowflakes (allowing regular pentagons to tile the plane). Similarly, I don't know how to create a universe where the commutative law of addition fails to hold. But maybe these difficulties just reflect the weakness of my imagination. In any case, even if there are limits to the variety of simulated worlds, the programmer clearly has a lot of latitude. And if the laws of simulated nature are so arbitrary, how can we be sure the ground truth of our own world is not the invention of some sleep-deprived programmer?
The fear that the world we know—or think we know—might be nothing but a computer simulation is a nerdish version of a much older idea. In Through the Looking Glass we are figments of the Red King's dream; a Taoist parable has a monk dreaming of a butterfly dreaming of a monk. But the computer has put a sharper edge on these musings. Now we have a technology of artificial reality.
The theme turns up frequently in fiction and film. A recent movie by Andy and Larry Wachowski, The Matrix, portrays a future in which 1990s urban life is a computer simulation created to mollify an enslaved humanity. (One amusing scene reveals that the phenomenon of déjá vu betrays a "glitch in the Matrix," where the illusion momentarily fails.)
The most sophisticated play with these ideas is found in the fantasies of the Polish writer Stanslaw Lem, whose "constructors" Trurl and Klapaucius build a variety of computers, machines and worlds. One of Trurl's disasters is the machine that can make anything starting with the letter n—"nimbuses, noodles, nuclei, neutrons, naphtha, noses, nymphs, naiads. . ." The disaster comes when the skeptical Klapaucius asks the machine to make Nothing, and whole categories of objects begin disappearing from the universe.
In another story Trurl builds a toy kingdom for a deposed tyrant. Klapaucius is appalled:
"Have I understood you correctly?" he said at last. "You gave that brutal despot, that born slavemaster, that slavering sadist of a painmonger, you gave him a whole civilization to rule and have dominion over forever? . . . Trurl, how could you have done such a thing?"
"You must be joking!" Trurl exclaimed. "Really, the whole kingdom fits in a box three feet by two by two and a half . . . it's only a model. . . ."
"A model of what?"
"What do you mean, of what? Of a civilization, obviously, except that it's a hundred million times smaller."
"And how do you know there aren't civilizations a hundred million times larger than our own? And if there were, would ours then be a model? . . ."
The story has a happy ending, more or less. Trurl's Lilliputians escape their confinement, overthrow the tyrant and begin playing with nuclear weapons, like any self-respecting civilization.
Hans Moravec of Carnegie Mellon University offers another perspective on the theme in his book Mind Children. He imagines a Game of Life where after many ticks of the master clock some of the patterns in the cellular automaton develop consciousness. "The cellular intelligences (let's call them the Cellticks) deduce the cellular nature and the simple transition rule governing their space and its finite extent. They realize that each tick of time destroys some of the original diversity of their space and that gradually their whole universe will run down." So the Cellticks make contact with their creator by spelling out a message on the computer screen. Then the Cellticks and the programmer go off together to explore the programmer's universe, hoping to find another level of reality before this one too runs down.
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