Anthony Campbell

How to Tell if You Live in a Simulation

Last revised 9 May 2021

"[The Red King is] dreaming now," said Tweedledee: "and what do you think he's dreaming about?"
Alice said: "Nobody can guess that."
"Why, about you! Tweedledee exclaimed, clapping his hands triumphantly. "And if he left off dreaming about you, where do you suppose you'd be?"
"Where I am now, of course," said Alice.
"Not you!" Tweedledee retorted contemptuously. "You'd be nowhere. Why, you're only a sort of thing in his dream!"
"If that there King was to wake," added Tweedledum, "you'd go out—bang!—just like a candle!"
"I shouldn't!" Alice exclaimed indignantly. "Besides, if I'm only a sort of thing in his dream, what are you, I should like to know?"
"Ditto", said Tweedledum.
"Ditto ditto," cried Tweedledee.
He shouted this so loud that Alice couldn't help saying, "Hush! You'll be waking him, I'm afraid, if you make so much noise."
"Well, it's no use your talking about waking him," said Tweedledee, "when you're only one of the things in his dream. You know very well you're not real."
"I am real!" said Alice, and began to cry.
"You won't make yourself a bit realler by crying," Tweedledee remarked: "there's nothing to cry about."
"If I wasn't real," Alice said—half-laughing through her tears, it all seemed so ridiculous—"I shouldn't be able to cry."
"I hope you don't suppose those are real tears?" Tweedledum interrupted in a tone of great contempt.

[Lewis Carroll: Through the Looking-Glass]

An ancient dilemma given a modern twist by the simulation hypothesis

Alice's dilemma is a very ancient one. The seventeenth-century Spanish playwright Calderón used it in his play Life is a Dream, and long before him the Chinese Taoist sage Chuang Tzu said on waking that he couldn't be sure if he was a man who had dreamt he was a butterfly or a butterfly who had dreamt he was a man.

Such ideas find their modern technological counterpart in the simulation hypothesis, which proposes that the whole of reality—the entire universe—is an computer simulation.

Taking the simulation hypothesis seriously

The simulation hypothesis is not just science fiction; recently published papers by mainstream philosophers and scientists, including Nick Bostrom,1 David Chalmers,2 and Martin Rees3 among others, have taken it seriously, and it was recently discussed in the BBC popular science programme The Infinite Monkey CageΓΈ .

Who is thought to be responsible for the simulation? The usual answer is: our own remote descendants, who are supposed to have taken computing power far beyond what exists today. It's equally conceivable that the simulators could be non-human beings on other planets, in other galaxies, or even in other universes.

There doesn't seem to be an obvious way of testing the simulation hypothesis, but is there any positive reason to believe that it might be true? I think there may be.

Anomalous events in our world

In general, the universe follows what we describe as laws of nature. Science depends on assuming this. And yet some people claim there are exceptions to this lawfulness. Most religions postulate miracles, for example, and then there are claims for the paranormal. As far back as written records go there have been such reports. Hauntings, premonitions, apparitions, and similar phenomena have been described throughout history. And there is a wealth of anomalous events, some involving thousands of witnesses, in the religious literature; see, for example, the Wikipedia article Marian apparition. And then there is the huge volume of UFO literature.

In the nineteenth century a group of British intellectuals came together and founded the Society for Psychical Research (SPR) to study such phenomena; the American Society for Psychical Research soon followed (the philosopher and psychologist William James was a prominent member).4 These organisations still exist although they attract less attention than they did in earlier times; sceptics generally reject the paranormal out-of-hand, as due to superstition, fraud, or misreporting. But not all scientists are so dismissive; for example, Bernard Carr, professor of mathematics and astronomy at Queen Mary University of London, is a past President of the SPR.5

A particularly good example of a hard-to-explain anomaly of this kind is the poltergeist phenomenon. Currently BBC Radio 4 is providing a dramatised account of a fairly recent case, The Battersea Poltergeist. For an extensive academic treatment of the topic, see the book by Alan Gauld and A.D. Cornell.6. The cases they describe seeem impossible to explain in any rational manner, yet there is no reason to reject them except their intrinsic incredibility. But is that enough? Gauld and Cormell are critical thinkers and have a lot of first-hand experience of the matter while I have none. I therefore have to keep an open mind about it, but if they are right, the world must be a much stranger place than we rationalists like to think it is. Books like this,I find, induce in me a state of uncomfortable cognitive dissonance,

The main reason why most sceptics ignore studies like that of Gauld and Cornell is simply that the alleged phenomena are inexplicable in a scientifically based world view. They don't make sense. But if the simujlation hypothesis is true, this difficulty disappears. The phenomena have been inserted by the simulators for reasons of their own.. This solves the problem; it allows us to accept the reports of strange phenomena at face value without compromising our scientific rationality. But at a price, of course; we have to accept that we are computer avatars, creatures in someone else's dream.


I gave this piece the title 'How to tell if you live in a simulation', but I have to admit that I haven't done that, in the sense of providing a definitive test. On the other hand, I have suggested a reason why the simulation hypothesis may be true: it explains something that is otherwise difficult to understand. This doesn't make it true, of course, but at least it seems to me better than alternatives which demand belief in discarnate spirits or the like. On my hypothesis, poltergeists are as real, or unreal, as everything else, including you and me.


  1. Nick Bostrom: Are you living in a computer simulation?
  2. Chalmers D: The Matrix as Metaphysic.
  3. Martin Rees: In the Matrix.
  4. Gauld A, (1968): The Founders of the Society for Psychical Research. Routledge and Kegan Paul, London.
  5. Wikipedia: Bernard Carr.
  6. Gauld A, Cornell AD (1979) Poltergeists, Heinemann, London. ]s]s]]s[s[s[sff/html>