Thought Experiments


Do Computers Dream of Electric People?

Are we living in someone else’s fantasy?

The Chinese philosopher Zhuangzi posed this question more than two thousand years ago when he recalled waking from a dream unsure whether he was a man who dreamed he was a butterfly or a butterfly dreaming that he was a man. Today, with the advent of computers that can simulate cells, cities, and even solar systems, philosophers and scientists are asking this ancient question in a new way: Are we living in a computer simulation?

This question is more than just the premise of “The Matrix.” It’s a conjecture that lives at the intersection of humanity and technology—and though it might seem like philosophy, it spurs ambitious new questions about what computers are capable of and about the nature of reality itself. As theorists begin to think of our universe as nothing more than a vast collection of information, can we ever truly know whether our reality is as “real” as we think it is?

The philosopher Nick Bostrom, director of the Future of Humanity Institute at the University of Oxford, posed the latest iteration of this ancient question in a 2003 paper. His “simulation argument” begins with the observation that modern computers have improved at an exponential rate since their invention. If computing power continues to grow at this pace, advanced civilizations will one day be able to build titanic, densely-packed supercomputers capable of doing everything from beating the stock market to predicting the weather months or years in advance. “Post-human” programmers might even use these machines to simulate entire civilizations, vast electronic worlds that would put today’s computer games to shame.

What would it take to create this kind of simulation?

When it comes to simulating a person, scientists estimate it might take 1017 operations per second—that’s one followed by 17 zeroes—to simulate a human brain, based on the number of neurons in the brain and rate of which those neurons “talk” to each other. Assuming that simulating the sensory events a person experiences—every taste, sound, smell, touch and sight that is coded in our neurons—takes about 100 million bits per second, and that approximately 100 billion humans have lived on Earth to date, Bostrom estimates it might take 1036 calculations in total to create a simulation of the whole of human history that is indistinguishable from reality.

That’s just to simulate the parts of the universe that humans can sense. What about the microscopic structure of the Earth’s interior or the subtle features of distant stars? These little details could be safely omitted until a simulated person needed to observe them. In addition, to save computing power, maybe not every person in a simulation would be fully simulated. Perhaps some of the characters in the simulation would be “zombies or ‘shadow-people’—humans simulated at a level sufficient for the fully simulated people to not notice anything suspicious,” Bostrom writes in his paper.

So how close are we to achieving this dream (or nightmare)? Today’s most powerful supercomputers are capable of operating at roughly 10 petaflops per second—that is, 1016 calculations per second. A planet-sized computer based on current electronics might carry out 1042 operations per second. Bostrom also notes that quantum physicist Seth Lloyd of MIT has calculated that a 1-kilogram “ultimate laptop” that operates at the known limits of physics might be capable of 5 × 1050 operations per second. So, the planet-sized computer might be able to simulate all of human history in a millionth of a second; the ultimate laptop, a hundredth of a billionth of a second.

Given that fully simulating every person who has ever lived might only take a tiny fraction of an advanced civilization’s resources, Bostrom reasons that the number of computer-generated minds buzzing away inside simulations could vastly outnumber the total sum of real minds that have ever lived. If that is true, the odds are that we are simulated, not real. It may even be possible that our simulators are themselves simulated, and their simulators are simulated, and so on. “Reality may thus contain many levels,” Bostrom says.

This does not prove that we live in a simulation, Bostrom emphasizes. There are a number of caveats that could stop this bizarre future before it starts. One glum possibility is that civilizations might very well go extinct or collapse—say, by annihilating themselves in a nuclear war—before they can develop supercomputers of such immense power. Another thought is that civilizations simply have no desire to commit the vast resources needed to create supercomputers. Or perhaps advanced civilizations might not indulge in such simulations—maybe they would be ethically opposed to simulating minds and their suffering, or they might prefer to entertain themselves with machines that directly stimulate their brain’s pleasure centers. “Personally, I assign less than 50 percent probability to the simulation hypothesis—rather something like in the 20 percent region, perhaps, maybe,” Bostrom writes, although he describes this as a gut feeling rather than part of his logical argument.

Unless the simulators decide to make themselves known, there may be no way to prove or disprove the simulation argument. Some have suggested looking for “glitches” in the simulation, but such glitches would be more plausibly explained as hallucinations, visual illusions, fraud or self-deception. Even if errors did pop up, a smart simulator could simply wipe any memory of the anomaly from our simulated brains.

If we are living in a computer simulation, how should we live our lives? “The simulation hypothesis currently does not seem to have any radical implications for how one should live,” Bostrom said. Still, “it helps to shed light on, among other things, the prospects of our species.”

Also, thinking of the universe as a computer may actually be a helpful approach in science. “You can start thinking about what kind of computer it is, what kind of operations can it do, what kinds of problems can it solve,” said theoretical computer scientist Scott Aaronson at MIT. “That’s an extraordinarily fruitful way of thinking about the universe that has led to the whole field of quantum computers—devices based on the quantum physics that explains how the fundamental building blocks of the universe behave.”

We may never know whether we are living in someone else’s fantasy; whether we’re the man or the butterfly. But if we do one day develop supercomputers capable of simulating minds and universes, perhaps our creations will be able to answer the question for us.

Tell us what you think on Twitter, Facebook, or email.


Charles Choi

    Charles Q. Choi has written for Scientific American, The New York Times, Wired, Science and Nature, among others. In his spare time, he has traveled to all seven continents, including scaling the side of an iceberg in Antarctica, investigating mummies from Siberia, snorkeling in the Galapagos, climbing Mt. Kilimanjaro, camping in the Outback, avoiding thieves near Shaolin Temple and hunting for mammoth DNA in Yukon.

    • Dana79


    • As humans we possess the ultimate feedback loop as we are aware of our fate and possess consciousness…then I read this…

    • Frenchiefrie

      If we WERE in computer simulations, would the computers really let us discover this? Would they let this thought come into our minds? I don’t think they would. so 😛

    • sean s.

      This seems to be the modern version of the late nineteenth century error of thinking that brain volume equates to intelligence; that to be smarter you just need “more” brains. Now we have “more operations per second”; computational rate replacing computational mass. Ridiculous.

      What makes us mysterious is what “program” is running in our minds, or more properly: what suite of programs is running. We are not lacking fast enough computers, even if we had them, we don’t know how to program them to do the things we do. That’s the bottleneck.

      Can we even simulate the mind of a cockroach?

      • Steve Meaney

        Yes, we can even remote control the brain of a cockroach by feeding it back captured brain waves

    • Kurtis Erikson

      This reminds me of an argument about the nature of reality I once had. If a simulated reality is so comprehensive and consistent as the one which we experience, than it really might as well just be referred to as reality since the distinction becomes meaningless at some point. If that simulated paycheck gets simulated groceries to alleviate my simulated hunger, there’s not much point in fighting it or trying to see past it.

    • Anonymous

      If we are the result of some super computer running simulations, then we sure are taking our time getting to the next generation of simulations?

    • Anonymous

      Isn’t Bostrom forgetting something in estimating a simulation of human history at 10^36 operations? To arrive at that all he does is extrapolate the average number of neural operations made over the lifetime of a human, but this doesn’t account for any sort of external world which would massively boost the number of operations needed.

    • Matthew Reed

      One method of testing this occurs to me, regarding quantum computers. If we were to ever build one, we could use it to perform calculations that would be impossible for any classical computer, no matter how advanced, to simulate. Running Shor’s factoring algorithm on a few thousand digit number would consume the resources of any conceivable classical computer that may be simulating us. That is, simulating every human that has ever lived perfectly would be trivial compared to a single execution of Shor’s algorithm.

      I suppose the obvious answer to this is that our simulators would also have quantum computers that could simulate our own, if it became necessary to do so. But we could at least make our simulation much more taxing for our alien overlords.

      • ==
        So you’re first sentence was wrong; this is NOT a way to test if we’re a simulation. It’s just a way to p1ss off whoever runs the computers we rely on for our very existence, or its a complete waste of time.

        Good luck getting research funds.

        — faye kane

    • How arrogant we are! To think that the universe is bound by our constraints of space and time, mere constructs we use to measure what we experience.

      • No, believing the most likely explanation for what we observe isn’t arrogance, it’s science.

        Arrogance is just making sh1t up and believing it, which is what you seem to advocate.

        -faye kane

    • Erik

      … and then you die.

    • Doodletoo1212

      idg that

    • No, they would have to let us do whatever we would if we were real, otherwise, in principle the difference would be detectable to us.

      That’s how the people in

    • Are we real or are we memorex?

      The ultimate answer was shown in an AMAZINGLY intelligent, deeply philosophical film, by, of all people, the Monkees. The film was called “Head”. Bob Nicholson and Peter Tork wrote it during a 3-day LSD trip.

      It was the only movie they ever made and it went completely over everybody’s head.

      When it starts out, the Monkees has just finished having sex with the same groupie, and are bored with being make-believe rock stars. They’re very distressed that they aren’t a real group, but only fictional characters created for a TV show that isn’t even on anymore. That made them angry, because they wanted to be taken seriously.

      Then they realized they’re not just fictional characters from TV, they’re also fictional characters in the film, saying what’s written in a script. That made them REALLY angry, so they kept trying to break out of the simulation. They deliberately flubbed lines, smashed through paper backgrounds of sets, suddenly punched other actors during scenes for no reason, argued with the director, and worse.

      But no matter what they did, it turned out that those actions were just part of the script anyway, and each time, they found themselves inside a large black box waiting to do their next scene. [I read that the “black box” idea came from RL. When making the film, they had to wait for their next scene in a large, quiet black room which had been constructed for them when they were shooting on location. They felt like they were trapped in it because they could hear people outside the room who were actually DOING things.]

      But near the end of the movie, Peter Tork discovers the ultimate meta-truth, one which can set them (and us) free.

      He realized:

      It doesn’t matter whether we’re fictional characters in a movie trapped in an inescapable, metaphorical box, or thoughtful, real people on a movie set in a black plywood box waiting for our next scene. Because the ultimate answer is that as long as we have free will, as long as we can do whatever we want, as long as the simulation is indistinguishable from reality, IT DOESN’T MATTER IF WE’RE IN A BOX.

      We can kick it open because it’s plywood, or we can kick it open per the script as a metaphor for this revelation, or we can kick it open because we’re the wacky, crazy Monkees. We can even continue to sit here in it. But no matter what, we’re not trapped in this box.

      …Even if we are and can never escape from it.

      Unfortunately, the other three thought this was just internally contradictory, meaningless stoner dorm-room philosophy, mere sophistry from a fellow prison inmate to cheer them up. They got angry at him (and at being trapped in a box), and they kicked it open. This made Peter feel silly for pondering questions known to be unanswerable when he could be DOING things, which are all that matters. Contemplating your navel does NOT matter, and it’s a waste of time. In reality, you’re free to do anything you want, even if it’s pointless, crazy or illegal. But the only things that actually happen are things you DO.

      So, outside and angry, they went on a killing spree. Then, being chased by dozens of police, they jumped off a very high bridge and crashed crashed into the water below—underwater and dead, but finally free.

      You think that’s the end, but in the final scene, Nicholson rolls a huge aquarium into a studio storage cabinet in case he wants to make another movie. As the storage room doors close, the Monkees are motionless, staring in amazement through the water.

      Ironically, it was the only movie they ever made because teeny boppers wanted the Monkees to be wacky, fictional characters from TV, and didn’t want to watch a serious film about deep philosophy by four intelligent, real people. And intelligent people didn’t want to watch a shallow movie by the Monkees because they’re four wacky, fictional characters from TV.

      Being an intelligent animal, is really, really strange, if you think about it too much.

      Which is why I stopped thinking too much, walked off my nuclear engineering job, and live naked in a cave in the woods with stolen electricity, books about hyperbolic topology, and festive, colored christmas lights.

      — faye kane homeless brain