Bostrom's argument in plain terms
Nick Bostrom's paper "Are You Living in a Computer Simulation?" (Philosophical Quarterly, 2003) makes a narrower claim than its reputation: one of three statements is almost certainly true.
- Nearly all civilisations at our stage go extinct before they can run realistic simulations of minds.
- Nearly all civilisations that can run them choose not to.
- We are almost certainly living in a simulation, because simulated minds would vastly outnumber original ones.
Which one is true depends on numbers nobody knows. The argument is logically neat and empirically empty until those numbers can be estimated.
Why the hypothesis is hard to test
A perfect simulation would reproduce physics exactly, so no experiment inside it could tell the difference. Any test has to assume an imperfect simulation with some specific shortcut.
The best-known proposal is by Silas Beane, Zohreh Davoudi and Martin Savage (2012). If the simulation runs on a space-time grid, like today's lattice calculations of quantum chromodynamics, the grid would impose a maximum energy and a preferred set of directions. The highest-energy cosmic rays would then arrive in a slightly non-uniform pattern tied to the grid's axes. No such pattern has been seen. That rules out only this particular kind of simulation.
Other suggested "glitches", from quantum measurement to the speed of light as a processing limit, are analogies. They explain known physics after the fact without predicting anything new.
Simulated versus computational
The simulation hypothesis bundles two different ideas:
- The universe is computational. Its laws describe how information is transformed. This needs no outside computer.
- Someone is running it. There is a simulator, a programmer and a purpose. This adds an agent for which we have no evidence.
The first idea has a long scientific history: Konrad Zuse's Calculating Space (1969), John Wheeler's "it from bit" (1989), Rolf Landauer's argument that information is physical, Seth Lloyd's view of the universe as a quantum computer, and Stephen Wolfram's hypergraph models (2020). It can be turned into mathematics, and mathematics can be tested.
The second idea is what makes the simulation hypothesis popular and what makes it untestable.
The testable version
The research programme on this site takes the first idea and drops the second. It treats the universe as a network that processes information, closer to Vanchurin's world-as-a-neural-network model than to a video game, and asks what that predicts for something measurable.
Its preprint builds such a network as working code, the Sixth language, and derives from it complexity results, correspondences with known models of distributed computation and a substrate-language version of the standard dark-energy estimate, each with falsifiers stated in advance.
The novel Bugs Academy plays the simulation idea out as fiction: a debugger who treats physical anomalies as bugs. The non-fiction The Celestial Code keeps to what can be measured.
Bottom line
Nobody knows whether we are in a simulation, and most forms of the idea cannot be tested. The part worth keeping is the claim that physics is information processing, because it leads to models that can be checked against data.