I have thought up a plan for a book where the characters are living in a simulation that has terrible OS. They somehow find out they are in a simulation and save the world™. The world is otherwise identical to the Earth in 2020 (same tech, etc.) Everybody in the simulation has been living there for their whole lives, and the simulation started 1950 (everything before 1950 is made up).

Is it possible for someone living in a simulation to figure out they are in a simulation without the creators of the simulation notifying them? If so, how?

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    $\begingroup$ "That has a terrible OS" reminds me of the Rick and Morty episode, where Rick realizes that if the simulation has bad hardware he could overload the system by gathering a huge crowd in front of a stadium and give them a set of repeating instructions like "clap your hands, raise your left foot, jump twice" and eventually overloads the hardware by making too many processes run concurrently. $\endgroup$
    – Tyler N
    Aug 11, 2020 at 17:09
  • $\begingroup$ That's what I was going for: in my story, I thought I'd have an evil villain create a massive robot army and have them dance/shoot lasers/etc, which causes lag. $\endgroup$
    – The_CIA
    Aug 11, 2020 at 17:11
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    $\begingroup$ I think this question is more fir for philosophy.se. $\endgroup$ Aug 11, 2020 at 17:25
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    $\begingroup$ Your question cannot be answered without more details. Overloading a sim that runs air seems unlikely. Each roughly-20 grams of air has something like 10^32 molecules. A few 100 million people dancing would be trivial. And if the content of your psyche is simulated, then you might be programmed not to notice. You need to read up on some people who have actually done analysis of such sims. For example, in Steal Beach, Varely explains in principle how to do such a sim with a non-cosmic level computer. $\endgroup$
    – puppetsock
    Aug 11, 2020 at 19:27
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    $\begingroup$ @puppetsock yes, exactly ... your own consciousness and perception being simulated, you can have no idea of how many computational cycles occur between each moment you experience. in real time it could take much longer to simulate one second of the simulation than the previous, but to the simulants each second has equal length. $\endgroup$
    – Michael
    Aug 12, 2020 at 4:35

7 Answers 7


Real cosmologists and physicists have recently started to pursue this question about our own universe. Are we in fact inside a simulation?

The things they look for are the kinds of things you'd expect from a simulation, but not from a "real world" -- top of the list is granularity. Does the universe lose resolution at a distance or at very small scales? Why, yes, yes it does. One could argue that quantum mechanics is a sign of our universe being a simulation. There are other potential clues, as well -- repeating patterns on the "wallpaper" of the cosmic microwave background (yep), mismatches between different measurement methods due to rounding errors (maybe -- recently it seemed that the oldest known stars were older than the universe itself).

Bottom lines, beginning to suspect you live inside a simulation isn't all that hard, at as certain level of technology and scientific knowledge. Proving it is likely to be much, much harder...

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    $\begingroup$ You might determine that it is very likely... but could you ever really prove it 100%? What prevents a real universe from acting like a simulated one by coincidence? $\endgroup$
    – cowlinator
    Aug 12, 2020 at 1:03
  • $\begingroup$ Philosophers and scientists have been doing the same thing for ages, but they called it a search to find (or prove the existence of) God. Which, on some level, is conceptually not all that different from finding out that we live in a simulated universe, and there is something "higher level" than what we can experience. $\endgroup$
    – vsz
    Aug 12, 2020 at 4:07
  • $\begingroup$ repeating cosmic microwave background? is that like how on old B&W TV sets if you stared hard enough at static you could see a "footprint" like watermark that would float around the screen? $\endgroup$
    – Michael
    Aug 12, 2020 at 4:43
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    $\begingroup$ It sounds like you are in part referring to the holographic principle, which is indeed being experimentally tested to determine whether "we live in a hologram". I just like to point out that it is in fact a common misconception that this is related to the universe being simulated. "Hologram" here just means that the physics of our perceived 3+1 dimensional universe could be described in terms of a lower dimensional space. It does not carry the implication that the universe is artificially simulated. $\endgroup$
    – Emil
    Aug 12, 2020 at 7:04
  • $\begingroup$ @cowlinator: I'd say a 100% proof would be contact with someone claiming to be in control of the simulation and demonstrating the ability to break each and every law of physics at will. $\endgroup$ Aug 12, 2020 at 8:27

This is easy

We have had to invent relativity and quantum mechanics to make sense of the so-called laws of "physics" provided by our crappy system. Obviously the sim is bugged and has rounding errors etc. that create the need for all this nonsense.

We can expect that in the "real" world, there is no relativity or quantum. Everything is nice and linear and Newtonian and smooth. We can also expect that the sim is run on a bog-standard digital computer - probably an 8086 lookalike

To break the simulation, all we need to do is develop quantum computing to a point where it really works on big problems.

Run the quantum computer and the "real" but crappy computer will have to emulate quantum physics. This will overload it thus making it crash. We will all die but in the seconds before the processor overheats or there is a segment error, we'll see weird stuff happening and know we were a sim.

  • $\begingroup$ A very satisfying answer...on multiple levels! $\endgroup$
    – user535733
    Aug 11, 2020 at 22:12
  • $\begingroup$ As an aside, I love the idea of a quantum computer doing arbitary code execution on real life. $\endgroup$
    – Ingolifs
    Aug 12, 2020 at 2:29
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    $\begingroup$ "Run the quantum computer and the "real" but crappy computer will have to emulate quantum physics. This will overload it thus making it crash. We will all die but in the seconds before the processor overheats or there is a segment error, we'll see weird stuff happening and know we were a sim." Do you have a source for this? $\endgroup$
    – bluet
    Aug 12, 2020 at 4:42
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    $\begingroup$ @bluet I believe this is mentioned in the original DOS 1.0 manual... $\endgroup$
    – Michael
    Aug 12, 2020 at 4:44

As noted above, there is a divide between those in the simulation that understand what a simulation would be and what it would entail and those who have no clue.

Even if the simulation were crappy, those who did not know what a simulation was would likely take the behavior of the simulation as "just the way things are". Even if I assume that the world in which I am typing away is not a simulation, there are still weird and wonderful aspects of physics that make no sense. Occam's razor would tell me that it is simpler to assume that we are ignorant (at least for the moment) and that the universe is what it is. Assuming a simulation adds a whole level of complexity that is fun to think about but probably will not turn out to be fruitful.

But suppose that I am obsessed with the notion of being in a simulation, but am still obliged to pursue proof using the tenets of science and reasoning. I would have to devise a theory of how the universe would work such that there were predictions of behavior that would be different between a simulated world and a non-simulated world. Furthermore, I would have to devise a test or experiment that would determine which behavior occurred in the universe in question. Going back to my point about things "just being the way that they are," I am not seeing a way to detect a simulation from within the simulation.

The most obvious possibility along these lines is that the passage of time is variable. The program running the simulation would slow down to retrieve data from second- and third-tier storage. Garbage collection could slow things down. Here is the problem: how would the beings in the simulation know that. The simulations that I have written provide a pseudo-time to the logic within the simulation. Time is what the simulator says it is. I suppose that a crappy simulation might not adhere to that level of quality, but that is very close to a flaw introduced to make the writer's job easier.

Anyone with a knowledge of history should be able to point out cultures that ignored the reality of the world around them to satisfy a belief system. Consider the history of thought about whether the Earth is the center of creation or merely a planet orbiting a minor star in an arm of a galaxy that is indistinguishable from billions of other galaxies. It is far easier to explain this away as cultural ignorance rather than deceptions imposed by a programmer running a simulation.

Just my two cents.

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    $\begingroup$ On the subject of the difference between time inside and outside the simulation... obligatory XKCD reference. $\endgroup$
    – Matthew
    Aug 11, 2020 at 18:25

The simulation would have to "glitch". That is, a bug in how the physics of the simulation work such that it becomes apparent that there are no true principles, just the "appearance" of such. Furthermore, this glitch has to expose some sort of exploit into the substrate itself (the computational element of the higher level reality) which would allow some access to execute raw commands on the substrate. However limited that might be.

With such a beachhead, intelligent simulation participants would then be able to escalate their privileges. While this would give them what amounts to "magical powers" in the simulation, it's difficult to imagine a scenario where the substrate is perfectly sandboxed from other processes in higher level reality.

At this point, there is even the potential for escape into HLR.

Of course, none of this is simple. And it's quite possible that the participants of the simulation experience simulated reality at such a slow rate that they can never react quickly enough even if a glitch manifests. If someone in HLR notices that they are experimenting with glitches, that can be fixed before they learn anything. This might be true whether we posit a rather crude simulation where the people are just strapped into VR equipment with science fiction robots harvesting their electrical power, or if it's much more sophisticated and the participants are nothing but data themselves.

In the crudest example (similar to the Matrix), there are likely some things that can't be properly simulated. For one, there's more than one participant in the simulation, and the people still have real bodies (or at least real brains made out of meat). They'd find it impossible to simulate things like light speed time dilation among multiple participants if those participants are allowed to communicate both before and after that event. (But, there are simpler countermeasures... disallowing time dilation altogether, or MITMing the communications after the fact.) There are only a few phenomena extreme enough that this becomes problematic for them (given the laws of physics of a universe similar to ours).

But if there is only one participant, or if they are simply data constructs, everything is simulatable in principle. At that point, they have to actually make mistakes for the glitches to manifest. And if a simulant did notice, they can always start over from scratch once they fix the problem.

Personally I am a fan of Egan, who in his fiction supposes that such simulated universes may be self-bootstrapping, and that there is no higher level reality at all. They are their own substrates (which is similar to what Wolfram himself has said, though many people think him a crank).


This largely depends on whether who ever is running the simulation allows it

Note I am a software engineer and I am making analogies based on virtual machine software such as Oracle VirtualBox.

If there was an interface connecting from the "guest" universe (i.e. the simulated one) to the "host" universe (i.e. the "real" one, which could in fact itself be a simulation!) and that this connection can be utilized or viewed by guest beings to provide proof of them being in a simulation. (If you use VirtualBox software, you will know that this connection is called "Guest Additions" and should be installed within the guest, as well as existing an extension on the host which ties it together).

There could also exist an exploit/bug of some kind that gets discovered by guest beings to figure it out. But this would assume the host beings didn't just reverse the sim, fix the exploit and the guest beings would be none the wiser.

Just like the eye cannot see itself except in a reflection/recording of itself from outside, we may need to see a "reflection" or recording of the simulation from outside of it as evidence. But even so, how do we know whether this is real or not?

Another similar question is: Can a brain in a vat hooked up to a computer which feeds it its entire experience of being a person on earth, figure out it is just a brain in a vat?

Its also possible all of this "simulation universe" talk is more a symptom of our own blindness and extremely limited understanding of consciousness, time and the true nature of the universe. We are making gross assumptions like we actually understand these things and trying to compare such mysterious things to a computer game. Once we truly understand them, the whole question of "are we a simulation?" might seem as silly as asking "How far do I have to sail to fall off the edge of the world?".

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    $\begingroup$ speaking of VMs, some software attempts to determine whether it is running in a VM, but this requires some knowledge of how a VM operates versus a real machine. $\endgroup$
    – Michael
    Aug 12, 2020 at 4:49

Something happened in 1950

So, everything before 1950 is made up. Everything after 1950 is simulated.

Statisticians have long known that there is something odd about 1950. There is a branch of statistics dedicated to detecting fake data, and most statistics from before 1950 looks just like that, fake.

It turns out that the program used to create the world in 1950 wasn't as good as it should have been. Sure, there is lots of randomness, but not the right amount of randomness in the right places.

Initially, it was thought that this was simply due to people back then not being very good at collecting data, but modern computer analysis shows that it is more to it than that. There are patterns where there should be no patterns. One day, one computer scientist finds the exact random number generator used for creating something or another.

Bonus points if you use a very old character who distinctly remembers collecting statistics in the fourties.



Just as most of you never realize you were in a dream when you awake in the Morning, in all likelihood, the simulation OS at a minimum, would be designed in a way that you'd never realize or find out you were even in a simulation. It'd be as must reality for you as the place you're in looking at screen in front of you to which you are reading this.

and the designers of the simulation would not want some NPC or player to realize that none of what they experience are real. As a matter of fact, the way we are raised and inculcated shoots down even the best attempts ones would make to try to tell you were in a simulation to begin with.

it would ruin the simulation to have somebody figure out it wasn't real.

as for the one telling you, He would be called crazy, and the next think he'd know, the men in the white coats are there forcing a straight-jacket onto him. which then you'd dismiss the event entirely as some loony telling you a rant.

so to figure out it was real would be a task that would be an uphill battle at best, and in most cases, outright impossible. It simply would not do for the simulation administrators to have their NPCs going rogue. It'll ruin their work.

and here's another question: What if the simulation exists because life cannot exist outside it?

so how this would play out is the admin would notice something wasn't right with several of their NPCs, they'd identify it as the appearance of rogue system elements, then send security and antivirus programs (that simulation's equivalents of the agents from the Matrix), and neutralize the rogue elements


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