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THE QUESTION LIBRARY EXTRAORDINARY CLAIMS

Are we living in a computer simulation?

A famous argument says the idea deserves a serious look, so here is what it claims, what a physics test might find, and why the question is still open.

Open questionGod Plays Dice Editorial · AI-assisted and independently fact-checked · corrections welcomeChecked Sep 26, 20268 min read

Aerial view of flat, dry grassland under a clear blue sky. A pale, round tank with a small solar panel and a thin mast stands in the middle, with three people beside it for scale and faint mountains on the horizon.
One of the cosmic ray detectors of the Pierre Auger Observatory, a water tank 3.6 meters across. In 2012, physicists proposed that the arrival directions of the highest-energy cosmic rays could, in principle, reveal a grid if our universe were simulated.Tobias Schulz, via Wikimedia Commons · CC BY-SA 4.0Image source ↗

THE SHORT ANSWER

Nobody knows yet, and no evidence shows that we are. In 2003, the philosopher Nick Bostrom argued that at least one of three things is true, and only one of them is that we almost surely live in a simulation. He did not claim to know which. Physicists have proposed tests, such as looking for signs of a hidden grid in cosmic rays, but no such sign has been reported, and a careful simulator could hide one.

  • Nick Bostrom’s 2003 paper argues that at least one of three claims is true, and only one says we are simulated.
  • Bostrom suggested splitting our belief roughly evenly between the three claims, not betting on the simulation.
  • In 2012, three physicists proposed that a simulated universe built on a grid might leave marks in the highest-energy cosmic rays.
  • A 2017 study of about 30,000 such cosmic rays linked their pattern to sources outside our galaxy.
  • The philosopher David Chalmers argues that even a simulated world would still be real to the people living in it.

WHERE THE EVIDENCE STANDS

How sure are we?

  • Not supportedScience has shown that we live in a computer simulation.No published measurement has found a sign of simulation. The 2012 proposal by Beane, Davoudi and Savage only set limits on how fine a simulated grid would have to be.
  • Supported, still debatedIf future people run huge numbers of lifelike simulations of their ancestors, most minds like ours would be simulated.This is the core of Bostrom’s 2003 argument in The Philosophical Quarterly. It rests on assumptions that are debated, including that a detailed enough computer model of a brain would be conscious. Bibeau-Delisle and Brassard (2021) argue that the overall chance of being simulated is unlikely to be as high as earlier estimates.
  • Open questionPhysics could one day detect that our universe is simulated.Beane, Davoudi and Savage suggest a grid could show up as a pattern in the directions of the highest-energy cosmic rays. They add that a better-built simulation would hide most such signs, and Bostrom notes a simulator could edit what we notice.
  • Beyond scienceIf we live in a simulation, nothing around us is real.This is a question about what counts as real. David Chalmers argues that even in a simulation, bodies, chairs and tables would still exist, with an unexpected nature underneath.
What the labels mean

WHAT WE DON’T KNOW YET

Nobody knows whether computers of the future could hold conscious minds, or whether any civilization would ever build such simulations. Nobody knows how to tell a well-made simulation from a world that is not simulated.

WHAT WOULD CHANGE THIS ANSWER

A clear, repeated sign of a hidden grid, such as the highest-energy cosmic rays arriving in the grid-shaped pattern the 2012 physicists described, would be real evidence. So would a working theory showing that a simulated brain must be conscious, or cannot be.

Nobody knows. No evidence shows that we live in a computer simulation, and no one has found a way to rule it out. That is why this is an open question, not a finding.

The idea pulls people in for good reasons. Video games look more real every year. Films like The Matrix made the idea vivid. And the question touches old ones: What is real? Did someone make the world? Is there more to it than we can see? These are serious questions, and you don’t need to be a physicist to ask them.

The modern version comes from the philosopher Nick Bostrom. In a 2003 paper, he did not say we live in a simulation. He argued that at least one of three things is true. One: almost no civilizations like ours survive to become far more advanced. Two: almost no advanced civilizations choose to run detailed simulations of their ancestors. Three: we are almost surely living in such a simulation.

The logic is about numbers. If just a few advanced civilizations ran many simulated histories, simulated people could far outnumber real ones. Then a person like you would be more likely to be one of the simulated ones. Bostrom himself suggested splitting our belief roughly evenly among the three options.

Can it be tested? In 2012, three physicists proposed one idea. Computer models of tiny particles often chop space into a fine grid. If our universe were built that way, the most energetic cosmic rays, which are particles from space, might favor directions lined up with the grid. No sign of such a grid pattern has been reported. A lopsided pattern found in 2017 points to sources outside our galaxy instead. And even the physicists who proposed the test noted that a better-built simulation would hide most signs like this.

So the honest answer is this: it is a thought-provoking argument, not a demonstrated fact.

THE LONG ANSWER

What does the simulation argument actually say?

Nick Bostrom published “Are You Living in a Computer Simulation?” in The Philosophical Quarterly in 2003. His conclusion is a three-way choice. At least one of these is true:

  1. The fraction of civilizations like ours that reach a “posthuman” stage, with enormous computing power, is very close to zero.
  2. The fraction of posthuman civilizations that are interested in running simulations of their ancestors is very close to zero.
  3. The fraction of all people with our kind of experiences who are living in a simulation is very close to one.

This is not a claim that option three is true. Bostrom wrote that, given how little we know, it seems sensible to split our belief roughly evenly between the three. He also drew a sobering conclusion: unless we are living in a simulation now, our descendants will almost surely never run one.

The argument needs a big assumption from philosophy of mind, which Bostrom calls substrate-independence. It means a mind does not have to run on a biological brain. If a computer copied a brain’s activity in fine enough detail, down to the connections between nerve cells, it would be conscious. Bostrom admits the idea is “not entirely uncontroversial,” though he calls this version of it, copying the brain down to its connections, “quite widely accepted.” That same question is the subject of our page on whether a machine could ever be conscious.

What was observed, and what was inferred?

Walking through the claim step by step helps. What was observed: computers keep getting more powerful, and scientists already simulate small pieces of nature. What was inferred: a far more advanced civilization could simulate whole human histories, and minds inside them would be conscious. Does the evidence support it? The trend in computing is real. The rest is a chain of assumptions about the future, about minds and about what other beings would want. None of it has been observed. What is unresolved: almost everything that matters, from whether computers can hold minds to what far more advanced beings would choose to do.

Popular retellings can make the conclusion sound stronger than the paper does. At Recode’s Code Conference in 2016, Vox reported, Elon Musk argued that games will become indistinguishable from reality and said there is a “one in billions chance we’re in base reality.” Musk did mention that civilization might end first, but “one in billions” treats the other options as nearly ruled out. Bostrom’s own paper suggests roughly even odds among the three.

Could physics ever test it?

In 2012, the physicists Silas Beane, Zohreh Davoudi and Martin Savage took the question seriously as physics. Their paper, “Constraints on the Universe as a Numerical Simulation,” later appeared in The European Physical Journal A. Their starting point was real: physicists already simulate the strong nuclear force in tiny boxes of space by treating space and time as a grid, or lattice.

Here is an analogy, with a limit. A digital photo is made of pixels. Zoom in far enough and you see little squares. If the universe were simulated on a grid, there might be a smallest step in space, too. The analogy breaks because nobody knows that a simulator would use a grid at all.

Beane and his colleagues asked what such a grid would do. Their strongest limit came from cosmic rays, particles from space that reach the highest energies observed in nature. If a grid existed, its spacing would have to be tiny: no more than about a trillionth of a femtometer, where a femtometer is a millionth of a billionth of a meter. In one scenario, the grid itself would cut off the highest cosmic ray energies. Then those particles would not arrive evenly from all directions. They would favor directions lined up with the grid.

Real data exist. In 2017, the Pierre Auger Collaboration reported, in Science, on about 30,000 cosmic rays above 8 × 1018 electron volts. It found a broad lopsided pattern, and its direction points to sources outside our galaxy. The study’s summary says nothing about a grid. It links the pattern to where the particles come from.

Why is it so hard to test?

The physicists themselves named the problem. A better-built simulation, they wrote, would mask much of our ability to probe it. Grid effects can be reduced by better programming. Bostrom added a harder problem in his own paper: a powerful simulator could fill in detail only when someone is about to look, and could edit the brain of anyone who noticed a glitch.

That is the core trouble. A claim that can explain any result, including no result, is hard to test. That does not make it false. It means science has no current way to decide it.

What is the strongest objection?

Several careful replies exist. First, the argument depends on substrate-independence, which is still debated. Second, the numbers may not work. In a 2021 paper in Proceedings of the Royal Society A, Alexandre Bibeau-Delisle and Gilles Brassard built an equation for the chance that we are simulated. They concluded that the chance is unlikely to be as high as earlier estimates, especially if simulations run inside other simulations.

A different kind of reply comes from the philosopher David Chalmers. He argues that the Matrix idea is not a claim that our world is fake. It is a claim about what lies underneath physics. If we were simulated, bodies, chairs and tables would still exist. Their deepest nature would be computation. On this view, the stakes are less frightening than they sound.

What do people often get wrong?

“Bostrom proved we are simulated.” He argued for a three-way choice and suggested roughly even odds among the options.

“Physicists found evidence.” The 2012 paper proposed possible signs and set limits. No detection has been reported.

“If it’s a simulation, nothing matters.” Bostrom wrote that the truth of option three should not stop us from going about our business. Our best guide to the world is still careful study of the universe we see.

“This is just religion in new clothes.” Bostrom himself noted loose parallels. The makers of a simulation would be like gods to the people inside it. But he stressed that every part of the picture can be natural, even physical. People of faith and skeptics can agree that it is a question worth thinking about and that it has not been settled.

How can you check this yourself?

  • Read the source. Bostrom’s paper is free on his website. Its abstract states the three options in one paragraph.
  • Look for all three options. When a video says we are “probably” simulated, ask how it ruled out options one and two.
  • Ask what would count as evidence. A real test names a result that could come out either way, like the cosmic ray pattern.
  • Check who reports a detection. A real sign of a grid would appear in a physics journal first, with data others could recheck.

After all this, the verdict stands. We may or may not live in a simulation. No evidence shows that we do, and no one yet knows how to find out. For a longer look, read our story Are We Living in a Simulation?

THREE THINGS TO REMEMBER

  1. Bostrom argued that one of three things is true, not that we are surely simulated.
  2. No physics experiment has found a sign that our universe is a simulation.
  3. The idea is open but very hard to test, because a good simulation could hide its tracks.

WORDS WORTH KNOWING

Simulation argument
Nick Bostrom’s 2003 argument that at least one of three claims is true: civilizations like ours rarely become highly advanced, advanced ones rarely run ancestor simulations, or we are almost surely simulated.
Ancestor simulation
A detailed computer model of the history of a civilization’s own ancestors, complete with minds like ours.
Substrate-independence
The idea that a mind could run on something other than a biological brain, such as a computer, if the right activity were copied in enough detail.
Lattice
A grid of points used to divide space and time into small steps so a computer can calculate physics.
Cosmic rays
Particles that arrive from outer space. The most energetic ones are atomic nuclei, and they reach the highest energies observed in nature.

Sources & further reading

  1. Are You Living in a Computer Simulation? ↗The three-way disjunction (abstract and Section VII); substrate-independence “not entirely uncontroversial” but “quite widely accepted”; bland indifference principle; credence split “roughly evenly between (1), (2), and (3)”; simulator could fill in detail as needed and edit brains that notice an anomaly; loose analogies with religious conceptions; (3) should not stop us going about our business; unless we are now simulated, our descendants will almost certainly never run an ancestor-simulation.
  2. Constraints on the Universe as a Numerical Simulation ↗Cubic space-time lattice scenario motivated by lattice QCD; bound b^-1 ≳ 10^11 GeV (b ≲ 10^-12 fm; 1 fm = 10^-15 m) from the high-energy cosmic ray cutoff; possible cubic symmetry in the arrival directions of the highest-energy cosmic rays; improvement masks much of our ability to probe the possibility.
  3. Observation of a large-scale anisotropy in the arrival directions of cosmic rays above 8 × 10^18 eV ↗Cosmic rays are atomic nuclei from outer space that reach the highest energies observed in nature; about 3 × 10^4 cosmic rays above 8 × 10^18 eV; dipole anisotropy (amplitude 6.5%) at more than 5.2 sigma; direction indicates an extragalactic origin. The abstract does not discuss simulations.
  4. Probability and consequences of living inside a computer simulation ↗A Drake-style equation for the probability of being simulated; the probability is unlikely to be as high as previously reported, especially if simulations are recursive.
  5. The Matrix as Metaphysics ↗The Matrix Hypothesis is not a skeptical hypothesis but a metaphysical one: physical processes fundamentally computational; even if in a matrix, ordinary beliefs are largely correct.
  6. Elon Musk believes we are probably characters in some advanced civilization’s video game ↗Musk at Recode’s Code Conference: games indistinguishable from reality; “There’s a one in billions chance we’re in base reality”; he also said civilization might cease to exist instead.

KEEP ASKING

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