What is the simulation hypothesis, and is there any evidence for it?

The simulation hypothesis is the idea that our reality might be a computer simulation run by a more advanced civilisation. There's currently no scientific evidence that we live in one, and most physicists regard it as untestable for now. The best-known version, philosopher Nick Bostrom's simulation argument, doesn't actually claim we're simulated; it argues that at least one of three possibilities must be true.

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Where the idea comes from

People have wondered whether the world is real for thousands of years, from Plato's cave to Descartes' deceiving demon. The modern, computer-based version took shape in 2003, when Oxford philosopher Nick Bostrom published a paper titled "Are You Living in a Computer Simulation?" in The Philosophical Quarterly. Films, video games and fast-improving computer graphics have kept the question popular since.

Bostrom's argument: three doors

The argument is often summarised as "we're probably in a computer". That's not what it says. It's a probability argument which claims that at least one of these is true:

1. Almost no civilisation reaches the technology needed to run realistic simulations of conscious minds, perhaps because it's impossible or because civilisations destroy themselves first.
2. Civilisations that reach that level almost never choose to run such simulations, perhaps because it's forbidden, considered cruel or simply uninteresting.
3. We're almost certainly living in a simulation, because if the first two are false, simulated minds would vastly outnumber original ones, and a mind that can't tell which it is should bet on the majority.

The strength of the argument is that it relies on counting rather than physics. Its weakness is that nobody knows how to put probabilities on the first two options. If consciousness can't be simulated at all, as some philosophers argue, the argument falls away.

Is there any evidence?

You'll often see claims that physics has "found evidence" of a simulation. Here's a more careful picture.

Some features of physics do rhyme with computation:

• Quantities such as energy and electric charge come in discrete units.
• The Planck length marks a scale below which current theories stop working.
• Physicist John Wheeler's phrase "it from bit" captured the idea that physical things might ultimately be made of information.
• The holographic principle in theoretical physics suggests the information in a region of space is limited by its surface area rather than its volume.

None of these is evidence of a simulation. Each is equally consistent with a universe that simply is the physics we observe. "The world has structure" is a different claim from "the world is computed". Some researchers have proposed experiments to look for tell-tale artefacts, but as of now the hypothesis hasn't been tested in a way that could confirm or rule it out, which is why it sits in philosophy rather than settled science.

What philosophers say it would mean

Philosopher David Chalmers, who takes the idea more seriously than most, argues in his book Reality+ that even if we were in a simulation, the things in it would still be real in every way that matters. A simulated table still holds up a simulated cup, and your life is still the only one you have.

Why the question is still useful

Here's a practical way to look at it. Suppose you learned tomorrow, beyond doubt, that reality is a simulation. What would you actually do differently?

For most people the honest answer is: nothing much. You'd still get hungry, rent would still be due, and actions would still have consequences by the same rules. The one thing that might change is your attention. You'd start looking for the rules, the way you would in a game.

That "player's stance" is useful whatever the truth is:

• Notice the rules that never change, such as compounding, incentives and probability.
• Choose your own scoreboard instead of inheriting one, whether that's money, health, freedom or meaning.
• Act deliberately rather than reacting to every prompt, notification and offer.
• Focus on what you control: your attention, your next action, what you say, who you spend time with and what you're aiming for. The Stoic philosopher Epictetus made the same point nearly two thousand years ago.

A note on feeling unreal

Thinking about the simulation hypothesis is usually fun. But if you ever feel that the world, or your own body, isn't real in a way that's frightening or won't go away, that's a recognised experience with good treatments. Please speak to a doctor.

Key takeaways

• The simulation hypothesis says reality might be a computer simulation.
• Bostrom's argument says one of three possibilities must be true; it doesn't prove we're simulated.
• Features of physics that resemble computation are not evidence of a simulation.
• The hypothesis is currently untestable, so it remains a philosophical question.
• Treating life as a game with learnable rules can be useful whatever the answer.

We Are in a Simulation uses the hypothesis as a lens rather than a scientific claim: a player's manual for strategy, risk, leverage and attention, with a 30-day plan for starting to play on purpose.

FAQ

Who came up with the simulation hypothesis?

The idea has old roots in philosophy, but the modern simulation argument was set out by Oxford philosopher Nick Bostrom in a 2003 paper.

Can the simulation hypothesis be proven?

Not with current methods. Some experiments have been proposed to look for signs of a simulated universe, but none has produced evidence either way, and many scientists consider it untestable for now.

Do scientists believe we live in a simulation?

Most scientists treat it as an interesting idea rather than a likely description of reality. Even those who find it compelling usually stress that it's unproven.

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