Amongst philosophers in general... what exactly is meant by the universe or reality itself being a simulation?

Simulation is fairly clear to me, when works "within" the assumptions of the framework of our physical world... ie: simulations like video games, VR games... these things are entities within our "normal" world. The existence of these things isn't puzzling.

What does it mean to say the universe is a simulation vs the universe is not a simulation? Are we talking about the existence of a controller/god... like the evil genius God Descartes was referring to or Berkeley's god? I don't think it's this, because atheists are also making these simulation claims.

What distinguishes a non-simulated reality from a simulated one (in meaning)?

EDIT: As an example maybe... what does Nick Bostrom mean exactly by "simulation" in his simulation hypothesis? What is he arguing for?

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    Bostrom was arguing for the plausibility that our universe is a computer simulation run by an advanced civilization living in a universe with the same laws of nature as we perceive. I discussed some of the details of his argument in this answer.
    – Hypnosifl
    Dec 18, 2020 at 3:55
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    I don't know anything about the different types of simulation you mentioned. Any way if you are looking for an answer about simulation you could use this link. You will see my answer also regarding this. I don't know whether it would be useful to you. philosophy.stackexchange.com/questions/48769/… Dec 18, 2020 at 4:44
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    @AmeetSharma - Yes, at least from reading the writings of his that I cited in that answer, I think he is just using Bayesian arguments to judge the relative probability of several alternate hypotheses which all take for granted that the physics of the base-level universe match what we observe.
    – Hypnosifl
    Dec 18, 2020 at 4:57
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    It means we are the data of someone else's information processing system.
    – J D
    Dec 18, 2020 at 7:43
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    @Hypnosifl It always struck me that this makes Bostrom's argument pragmatically self-defeating. He argues that our world, with all of its physics, is a made up simulation. If true, it leaves us with no apparent reason to suppose that this made up physics has anything to do with physics in the simulator's world. After all, we do not replicate our physics in World of Warcraft and the like. And without that there is nothing to base the simulation argument on to begin with.
    – Conifold
    Dec 18, 2020 at 9:26

3 Answers 3


Speaking as a computer engineer, having another "human" civilization "simulate" ours seems highly implausible. The computer power to simulate one human brain would require one of the largest computers in existence, and this computer would run on the order of 1000 times slower than the brain, and require on the order of 15 megawatts to operate. I'm not able to find hard numbers on physical size, but some clues I've found suggest that the physical size of this would be around 1000 cubic meters.

So to simulate the brains of 7.6 billion people on earth would consume over 100 billion megawatts of power, while the earth's electrical power production is on the order of 2 million megawatts. And the computer would occupy 7 trillion cubic meters, whereas the volume of earth is around 1 trillion.

Of course advances in technology would reduce these numbers, but, given the currently-known limits of physics, probably by not much more than about a factor of 10. And remember that the simulation would still be incredibly slow (though, again, it might speed up by a factor of 10).

So clearly the simulation of earth and its population by another earth-sized civilization is beyond impractical. Of course a larger civilization on a larger planet might attempt it, but it still would only be simulating earth's brains, not any of the environment, and not the rest of the universe as known to human brains. (Though partially simulating the rest of the universe does introduce some interesting parallels to "known" physics principles such as those surrounding quantum mechanics).

(Note: Some of my back-of-the-envelope computations above may be wrong, but likely not dramatically, in terms of the implications.)

  • You could just only simulate the levels of detail needed, ie only fine details when people are looking, and give statistically correct outputs elsewhere. It is obvious that a lump of meat the size of 7 billion human brains can simulate our world, because that's our current best model - and do so only using a tiny bit of the suns energy, cycling a few gases & some carbon and minerals, same reason. It's estimated biosphere uses 1% of solar hitting Earth, so could expect 100 simulations just use that, using 6" slabs of meat size of Isle If Wight. Without leaving Earth, with tech we have, in us
    – CriglCragl
    Dec 21, 2020 at 0:17

You might wish to read the discussion here Are we living in a simulation? The evidence

I quote from my answer there:

"David Chalmers has argued that we should consider the 'simulation hypothesis' not as a skeptical hypothesis that threatens our having knowledge of the external world but as a metaphysical hypothesis regarding what our world is actually made of. " http://philosophycommons.typepad.com/flickers_of_freedom/2014/08/the-case-for-libertarian-compatibilism-a-brief-overview.html

Although we are nowhere near creating fully realistic simulations, and probably don't even know how far we are off, it does seem it's inevitable in our future. Just like we cannot transfer minds, yet, but we will, has profound implications for identity, so simulation does for understanding what 'real' means.

I would describe simulstion-thinking as an iteration of the same sceptical thinking of Zhuangzhi's question whether he 'dreamed he was a butterfly or whether he was a butterfly now dreaming he was a man', Buddha's analysis of samsara, & Descartes scepticism. But, with the frisson of our expanding understanding of our future/s.

  • Frisson notwithstanding, doesn't the very contemporariness of simulation theory cast doubt on the idea? Like the mechanistic universe following the discoveries of Newton. Whatever's clever this week, we extrapolate to a grand philosophy of the world. Everyone has a smartphone so we must all be avatars in the great smartphone in the sky. I tweet therefore I am.
    – user4894
    Dec 20, 2020 at 1:57
  • I think the separation between the world of "phenomena" and some real word apart from it isn't really controversial... but I assume by simulation we mean something much more specific... ie: there's a world above ours somehow analogous to ours... where there are computers or something similar to them running programs on which we run. Dec 20, 2020 at 3:53
  • @user4894: On the contrary, it is familiarity with real mechanisms, which give physics insights. Clockwork helped us understand a heliocentric solar system. Steam engines created thermodynamics. Digital ideas of information underlie Loop Quantum Gravity, and blackhole thermodynamics & the holographic principle. Paradigms.
    – CriglCragl
    Dec 20, 2020 at 23:44
  • @AmeetSharma: That is certainly the approach people tend to take initially. But in philosophy, the focus is generally on 'in principle'. I'd compare arguments involving determinism, where pragmatic concerns are generally neglected. A series of imponderables about whether simulators would allow us to know their purposes, and whether the simulation has in fact just been switched on, and so on, just invite speculation, and risk halting useful thought. Like with teleportation paradoxes, which are actually about probing intuition about identity, ideas like substrate independence probe 'real'.
    – CriglCragl
    Dec 20, 2020 at 23:51
  • @CriglCragl, sure but without those specifics, I'm concerned that the simulation thesis is really indistinguishable from almost any other metaphysical view. I mean that there's some noumenal world that does information processing and produces the phenomena we experience which have all sorts of 'regularity'... If that's all simulation thinking is, couldn't almost any metaphysical view fit this? Dec 21, 2020 at 0:11

The simulation argument can't be referring to Descartes's cunning deceiver, for the reason Descartes points out. Even if everything I perceive, everything I experience, is an illusion created by the great computer in the sky, my "I", my subjective consciousness, exists and is separate from the deception. Simulation theory is incomplete. Perhaps my couch and my laptop and my room are an illusion; but the "I" that experiences these illusions is not. It's separate from the deceiver, separate from the deceptions. And what is my "I"? It's outside the simulation. So Cartesian simulation doesn't explain all of reality. It leaves the deepest mystery, the "I", unsolved.

So simulation theory must be saying that it's my "I" itself, my very consciousness, the thing (whatever it is) that experiences my experience, that is also being simulated. And there, Bostrom's argument fails. The premise is that 40 years ago we had crude video games like Pong, and today we have hyper-realistic video games, and in the future they'll be indistinguishable from reality. I have no doubt that's true.

But Bostrom does not explain how consciousness itself will be implemented by a computer. We have no idea how to do that, nor any theory that says it's even possible. Turing machines are extremely constrained. They do one discrete thing at a time and can't solve the Halting problem. That's an example of a problem that we can conceive that no computer can solve. There's no evidence, only a belief on the part of some, that the universe is so constrained. Some people think Turing machines can be conscious, but nobody knows how.

Bostrom's premise fails. In the future we'll have super-duper realistic experiences to enjoy. But there's no evidence or even a convincing argument that subjective consciousness can be implemented. The argument is just wrong. And it's a bit disingenuous, because it begins with the Pong versus modern video games analogy, but sneakily ignores the problem of subjective experience. Descartes did not miss that point. He noted that even if the great computer in the sky is programming my reality, it can't program my subjective experience. I exist separately from the simulation.

Bostrom's analogy from Pong to modern video games is false. The electronic paddles in Pong did not have subjective consciousness; nor do the avatars in modern video games. In terms of the core mystery of subjective experience, no progress at all has been made in the past 40 years. And that destroys Bostrom's premise.

Please see my other response to this question here, which makes similar points.

  • Ideas like Integrated Information Theory suggest Bostrom's argument is thoroughly plausible if they hold, surely? I'd locate Descartes squarely in considering simulations, because he implies a world of mind 'operating' matter, like from a more real world.
    – CriglCragl
    Dec 20, 2020 at 23:55
  • @CriglCragl (1) I'm aware of Tononi, I don't find his idea plausible.(2) Descartes's mind is DECEIVED by the deceiver, not the other way 'round. Yet he still has a mind that is separate from the deceiver/simulator. That's the point.
    – user4894
    Dec 21, 2020 at 0:17
  • In his dualism he gives subjectivity primacy, he considers it more real. On Tononi, you underline that your argument is one from incredulity, about us being unable to make progress, or that we have not made progress, on how subjectivity occurs. Which is the objectively more incredible claim. What magic can there be to it?
    – CriglCragl
    Dec 21, 2020 at 0:24
  • @CriglCragl Right. Subjectivity is more real. So simulation theory doesn't explain it. My point, and one already made in 1641 by Descartes. You're agreeing with me. Re Tononi I haven't studied his ideas in sufficient detail to offer a more nuanced response other than incredulity, so I'll provisionally accept your point (that I'm ignorant of Tonini) without agreeing with your conclusion (that he's explained consciousness). Turing machines can't be self-aware, this I believe. Penrose too FWIW.
    – user4894
    Dec 21, 2020 at 0:37
  • Subjectivity being more real = dualism, which is, untenable. Structural ideas like strange loops point to overcoming Godel Incompleteness & halting problems. I'm a big fan of OrchOR, but not because I see it a sprinkling magical quantum consciousness fairy dust, but because it points to the human brain being several orders of magnitude more complex than a classical picture (& explaining gas anaesthesia, and distributed memory in relation to brain damage)
    – CriglCragl
    Dec 21, 2020 at 16:23

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