In this world, virtual reality has been perfected to the point were senses can be tricked and reality can be mimicked almost perfectly. Central powers can use this technology for terrifyingly efficient mass control, since people can't tell if they're in the real world or not once they've been (often forcefully) hooked to the virtual reality system.

The system works through stimulation of the five senses only; it can't control anything else.

Would there be ways for one person to check whether they're in the real world (original reality if you will) or not?

Note that my question is different from the proposed duplicate, as it is about an newly-introduced sensory virtual reality and not an entirely new virtual planet on which people live from their birth.

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    $\begingroup$ To judge whether or not a question is a duplicate I use a simple test: do the top answers from the other question answer this one? In my opinion, those answers answer this question perfectly, so this is still a duplicate. $\endgroup$
    – kingledion
    Dec 8 '17 at 20:02
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    $\begingroup$ @kingledion in my opinion, the answers from the other question do not truly answer my question , as they are based on the assumption that the simulation is the only reality people have ever known $\endgroup$
    – user44285
    Dec 8 '17 at 20:10
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    $\begingroup$ As long as they didn't call customer service, they should be fine. Did I take care of all your customer needs in a timely and satisfactory fashion today? $\endgroup$ Dec 8 '17 at 21:34
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    $\begingroup$ Since we don't know for sure if we're not already trapped in someone else's virtual world, how would one tell if he's trapped in a trap? $\endgroup$
    – qq jkztd
    Dec 8 '17 at 22:10
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    $\begingroup$ With truly advanced virtual reality, where they drive a giant spike into your brain stem, you wouldn't, unless someone starts flying around like Superman and dodging bullets. I'll take the blue pill, please. $\endgroup$
    – Mazura
    Dec 8 '17 at 22:17

10 Answers 10


Humans have far more than five senses. There are at least 20 that we know of. If only sight, sound, smell, taste and touch are simulated there will be countless discrepancies that will be quickly obvious.

Probably the easiest sense to check for a discrepancy would be proprioception, your sense of your body's own position.

As you move around the virtual world your actual body wouldn't move and the discrepancy between the two would be an indicator that you were in a virtual world.

Our sense of balance would be another easy one to detect discrepancies with. This is actually a problem with existing virtual reality technology where we see movement but don't sense it in our inner ear. This commonly results in feelings of nausea.

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    $\begingroup$ Bit of a discrepancy in the question, he says "all senses can be tricked" and then "five senses only". I think he wasn't aware of the other senses, and assumed they would also be tricked? $\endgroup$
    – Ebonair
    Dec 8 '17 at 20:25
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    $\begingroup$ Yes i wasn't aware of more than five senses, for the sake of honesty I'll edit to remove the "all senses" part as this is a good answer. $\endgroup$
    – user44285
    Dec 8 '17 at 20:54
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    $\begingroup$ @Unlambder Feel free to ask a follow on question about all the senses building on the answers from this one :) $\endgroup$
    – Tim B
    Dec 8 '17 at 21:20
  • $\begingroup$ @Unlambder If you do be sure to clearly indicate how that question differs from this one so it doesn't get erroneously closed as a duplicate. $\endgroup$
    – sphennings
    Dec 8 '17 at 21:25

I think it would come down to a discrepancy between the knowledge one has of how the real world works, and what they observe in the virtual world.

For instance, if a physicist going about his day to day suddenly notices that some molecular process stopped behaving according to the research he has been faithfully reproducing for years, he'd have pretty good reason to think he'd been stuffed in a simulation.

Similarly, if a person was put in the simulation, but all of their friends and family were not, it'd be pretty easy to tell that a bunch of people ceased to exist. Even if they were simulated, there are bound to be memories that the real person would remember, but the people running the simulation would have no way of knowing.

When I was a child, my brother and I had a code word that we never told anyone. We used it to make sure neither of us had been abducted by aliens and replaced with a clone. I would imagine in a world where people know that being shoved in a machine is a real possibility, they would have such memory "canaries".

Even consider the top in Inception. Just another example.

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    $\begingroup$ This assumes less than total surveillance. In a world where people are forced into computers I think that might not be reliable. $\endgroup$
    – user25818
    Dec 8 '17 at 20:31
  • $\begingroup$ People are sneaky. They find a way. $\endgroup$
    – Stephan
    Dec 8 '17 at 20:34
  • $\begingroup$ What was the code word? $\endgroup$ Dec 9 '17 at 0:29
  • $\begingroup$ @Azor-Ahai He can't tell anyone, in case you're an alien $\endgroup$
    – Draconis
    Dec 9 '17 at 0:54
  • $\begingroup$ Exactly. You never know when I might need that code word. $\endgroup$
    – Stephan
    Dec 9 '17 at 0:57

Would there be ways for one person to check whether they're in the real world (original reality if you will) or not?

A person's memory would be the weak point here.

While all their external senses are controlled by the simulation. There is no way for the external system to know personal details about a person's history.

So if a you wanted to know if you are inside a virtual world with the intent of that world to being deceptive (i.e. make you think it's the real world). All you would have to do is return to a location that was personal to you. Find some kind of detail that only you knew about from your past and verify that detail to be correct.

If that detail is missing. You would either challenge the idea that you're in a virtual world or you would experience some kind of personal crisis.

If the virtual world is limiting in someway. As to not allow you to leave the area. You would accept the world as real. Upto a point.

Take the movie The Truman Show as an example. Truman accepts his reality as real but his human nature drives him to escape. Even when the world fights back he would rather die than be limited by that world.

It's interesting that even in The Truman Show it is his own memory that plays an important role in discovering the real world.


I just wondered how people felt about a solution put forth in a episode of Dr. Who where the Doctor figures out that he is in a simulation by asking everyone for a list of numbers. His logic was that computers can't really generate a random list of numbers. So, everyone would give the same list.

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    $\begingroup$ Other individuals in the simulation might actually be the avatars of real people. But if I were one of those real individuals, I might mess with the doctor by repeating the same list I heard someone else say so he would think I was virtual. Then a few minutes later I would give him a couple of extra numbers I made up, and maybe some letters. Janet I like this observation but really it is a comment, and you should delete it and put it as a comment under the original. $\endgroup$
    – Willk
    Dec 8 '17 at 22:20
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    $\begingroup$ Normal computers really can't compute truly random numbers, as they only have access to deterministic algorithms. But you can vary the input and work with pseudorandom numbers for most usecases. A common trick I've seen for simple applications is to use the current timestamp as a "seed" value for the start of a random sequence. If the simulation does this then the random numbers will surely not be detected by a human. Or just a really, really big list of pseudo-random numbers with one initial input - and then distribute this to all NPCs. $\endgroup$
    – Secespitus
    Dec 8 '17 at 22:41
  • $\begingroup$ Welcome to WorldBuilding by the way. If you have a moment please take the tour and visit the help center to learn more about the site. Have fun! $\endgroup$
    – Secespitus
    Dec 8 '17 at 22:41
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    $\begingroup$ Actually, computers are very good at generating statistically random numbers, while humans are terrible. It would be more realistic for the Doctor to find his lists of numbers to be statistically random and reject the simulation on that basis. $\endgroup$ Dec 8 '17 at 22:48
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    $\begingroup$ @JamesHollis very good take - agreed. Docter Who is not written by people who know about science, I think. I know, I know - it seems crazy when you hear him talk about "timey wimey" - how did they get the physics so realistic? :-) $\endgroup$
    – Rob Grant
    Dec 8 '17 at 23:20

This sounds like the classic physics relativity problem to me, heh.

I think the main loophole lies in the words "almost perfectly"... If the simulation isn't truly perfect then that should be enough to prove it's not real. Think of it like a small math error, the system either has to try to silently correct for it and blow the consistency of the process, or allow the incorrect value to stand and risk it being compounded to a macroscopic scale. The catch is that you have to find something that the system can't process perfectly but which you know the correct result of.

cgTag's answer hits one good option but misses the more straightforward method of using it. The plot device from Inception, of an object with physical properties that only you know, is a perfect solution. The VR environment can't replicate the behaviour of something that it doesn't know about. As long as the "import" process in to the virtual world isn't more than a basic analysis of the items you have, you should be fine.

How the person being "imported" to the world is scanned is actually pretty key as well. An implant or biological marker that you could detect but which wouldn't be included in your avatar by the VR would do it.

Another use of memory is other people... to be sufficiently convincing you'd have to hook up everyone or simulate the people who you didn't hook up. If you've got people being faked then you just need to test common memories to find one who has a discrepancy. Of course it only works if the powers in charge are being more selective of who they're hooking up, so it doesn't work so well in something like the Matrix where just about everyone is connected. Unless you're post-scarcity you should be safe though on that.

A lot of the possible plot mechanics to detect an illusion depend on preparation factor. A person that knows there is a possibility of being placed in to such an environment has time to prepare recognition tools against it, such as the ones described. On the other hand, a person taken by surprise, both in terms of the existence of technology as well as their connection to it, would be less likely to be able to identify the fabrication of their surroundings.

It's also important to note that most mechanisms for detecting the substitution aren't going to work more than a few times. As a random example, if you managed to slip a bioimplant past their scan and use it's absence to determine that you're hooked in then they'll simply improve their scans to pick it up. How long it takes them depends mainly on how long it takes them to realise that you've beaten the system that way.

A lot also depends on what the person does after they've realised... disconnection yourself like in the Matrix is probably going to get noticed much quicker than staying in the system and trying to subvert it from within. If there's a period of a month between you discovering it and the first evidence of you doing something that demonstrates that knowledge, well that's going to be harder for them to trace back how you found out. How much of a threat they think the information poses also limits how much they'll let you spread it once you're discovered.

Hope something in there helps.


This is a question philosophers have been wrestling with for many thousands of years. Some Buddhists, as I understand it, would say that’s not a bad analogy for how the world of our senses really is an illusion, and we can only free ourselves of it through enlightenment. The classic Western development of the idea was Plato’s Allegory of the Cave, where the evil tyrants have slightly lower tech at their disposal but do essentially the same thing, and it has influenced many kinds of religious mysticism.

The Matrix is the most well-known variant of the idea these days, but it’s been used in many other works. The Silver Chair by C. S. Lewis sets up a Christianized version of the allegory: the villainess has succeeded in tricking the heroes into believing that Narnia is nothing but a fairy-tale for babies, and her realm is all that is real, but they stand up to her and decide that, even if Narnia isn’t real and there’s no possible way for them to ever prove otherwise from inside her cave, they still would rather try to live there than here where life has no meaning. Philip K. Dick often wrote about this theme; a really clever version of it was Eye in the Sky, where the characters all find themselves living in the world of one person’s religious delusions, and he’s the only one who doesn’t realize that the world worked nothing like he thought it did and his belief system becoming true changed everything overnight. This leads to a series of false realities imposed not by any villain, but by their own narrow minds. A few decades ago, the movie people would have brought up would have been Total Recall, loosely based on another story by Dick, but even in the Hollywood version, a popular fan theory is that the protagonist really did lose himself in his own delusional power fantasy and refused to wake up. There’s no way to tell.

If you approach it as a philosophical problem, you’ll end up looking for a philosophical solution and not a scientific one. That said, philosophers really like stories where philosophers find the truth by being really smart, mystics really like stories where mystics find the truth by meditating hard, religious apologists really like stories where the revealed doctrines of their religion are revealed to be true, gamers like stories where NPCs lead the hero by the nose until he shoots his way out, and so on. It’s ripe for sending up if somebody wanted to.

If the simulation is good enough, there’s no way to find anything in it that looks or feels fake. My best suggestion is that you could force the simulation to simulate some physical process in real-time that can’t be computed efficiently, forcing it to approximate, then take your time and calculate what should have happened. The Navier-Stokes equations are an example that aren’t known to have an efficient solution. But keep in mind, the simulation could alter your notes!

A better bet would be checking something from the real world that the programmers would not know about. This could be harder than it sounds: is the other person really a sim who doesn’t know the secret she’d never ever tell the tyrants, or does she think she’s in a sim where they’re trying to trick her into telling them?


From a computing power standpoint, it would take a computer larger than the world to fully simulate the world. They don't have a computer that big, so there will be holes in their simulation. It is just a matter of finding where they skimped on the processing power. You just have to act as oddly as possible to push up against a boundary they didn't expect. Use a microscope to look at sand on the beach, dig a 50 foot hole in the ground, some where there is a limit.

They control your senses do they control how you feel on the inside? Eat too much does it feel the same, run too far do you feel the lactic acid build up in your muscles correctly? If you workout do you get stronger? Also what is the time frame for deciding in\out of simulation. Do subtle changes occur that normally happen when time passes, hair and nail growth that kind of thing?


Reflexive, Reactive, Reflective Intelligence

In robotics, the 'degree' of intelligence of an autonomous system is sometimes classified into 3 levels: reflexive, reactive, and reflective.

  1. Reflexive intelligence merely responds to a 'known' stimuli with a singular invariant response. x : --> y , where x is the stimuli and y is the response. In a virtual world, reflexive intelligence is entirely incapable of identifying the stimuli as being sourced from a virtual/artificial source.

  2. Reactive intelligence responds to a stimuli with a variant response. Here, x : f_t(x) --> y , where x is the stimuli, y is the response and f_t() is the behavior of the autonomous system. The behavior of the system can change over time. It can also be trained. These attributes put reactive intelligence well beyond mere reflexive intelligence. However, even reactive intelligence can not independently distinguish between stimuli from real vs. virtual world.

  3. Reflective intelligence responds to a stimuli with a response that based in part on the stimuli and in part on the state of the system and its behavior. Here x : f_t(x, s) --> y, where s is the state of the system. With reflective intelligence it is entirely possible for the response to a stimuli being entirely independent of the stimuli and based solely on the state of the system; x : f_t(s) --> y.

Multi-layer abstraction

Unlike the previous lower levels of intelligence, the system modifies itself even in the absence of external stimuli. The system state (s) keeps changing independent of the external world. These changes are not random. They are based on set of 'rules' or meta-parameters that the autonomous system uses to govern its change of state (s). These meta-parameters can be structured in layers, where parameters (rules) at a given layer are dependent on parameters at a deep layer. The deeper the meta-parameter, more invariant it is to change. All the meta-parameters in their layered structure together constitute the autonomous system's 'world view'.

Autonomous adaptation

As such, this type of intelligence could be considered introspective. This is where the reflective intelligence diverges sufficiently from lower levels of intelligence to potentially decipher the source of the stimuli it is receiving. The challenge here is for the virtual world creating stimuli. The virtual world does not know the state (s) of the autonomous system. When a stimuli-response loop is in progress, the virtual world will struggle to sustain a stimuli-response cycle that does not begin to diverge from the reflective intelligence's 'expectations', predicated by its 'world view'.

Expectation management

Therein lies the challenge towards building a universal virtual world. It can not 'fool' everyone equally. The reflective intelligence that has a deeper layered structure of rules/meta-parameters and a more robust rule update policy, will be more difficult to convince during a stimuli-response cycle. The lack of consistency with the 'real world' will emerge in pattern of sequence of stimuli.

Game Theory

Reflective intelligence employs a self-correcting mechanism. In doing so, it will intentionally produce a response that it knows is completely wrong for a given stimuli. The subsequent stimuli given by the 'real/virtual world' will tell the reflective intelligence about the world's traits. In essence, for reflective intelligence, the stimuli-response is a two-way street and both the world and the autonomous system are giving each other stimuli, instead of a stimuli-response.


Pattern recognition in successively deeper layers of abstraction is a very powerful tool to approximate arbitrarily large and complex information. Lets see how this plays out.

A reflective intelligence 'expects' the world to have at least a reflective level of intelligence in the 'game theory' setting.

  1. If the world then display a reflexive stimuli/response (Think extremely poorly coded NPC in a video game, acting in a mindbogglingly repetitive manner), the expectations are completely thrashed and the reflective intelligence knows it is trapped in a virtual world.

  2. If the reflective intelligence intentionally 'jukes' the world in its response, the world my respond with a altered stimuli. While this a better than reflexive intelligence and passes the first layer of rule abstraction, the manner of change in the world's stimuli (going from f_1(y) to f_2(y) to f_3(y)) will not align with the expectations about pattern of change of world stimuli and this fails the second layer of rule abstraction.

  3. If the world responds to the myriad of 'jukes' and brilliantly varied behavior of the reflective intelligence that never sufficiently violates its expectation for arbitrarily deep layer of abstracted rule, then the virtual world has successful supplanted the real world for that specimen of reflective intelligence.

Enter Morpheus!

Even, if the virtual world successfully learnt to consistently meet the expectations of individuals, there still remains a layer of abstraction, which is beyond reflective intelligence: a type of swarm intelligence.

However, swarm intelligence is beyond the scope of the OP's question of mind control. I'll just say, when individuals are limited by their isolated intellectual capacity, they can team up to pool together their individual and unique layers of abstraction. With this dialogue the fact that the virtual world has adapted to provide an individual a tailor made stimuli-response experience will emerge. I can not recall any Sci-Fi literature that describes a virtual world that can convincingly adapt to an entire group of unique reflective-intelligence individuals.


The answer to the OP's question of defeating a virtual world's entrapment in a nutshell is: use deception and teamwork to outsmart the adversary!


I learned to distinguish between lucid dreaming and reality by deliberately focusing on areas of my body where I knew there wold be pressure if I was sleeping. If I believed I was standing up, but I felt pressure on the backs of my calves, then I was dreaming.

From a mechanistic viewpoint, such a VR system is stimulating the brain either directly or indirectly. For this discussion, eyepieces and VR suits count as "indirectly". However, whether the mechanics are direct or indirect, you can always apply stimulation easily, but can't prevent it easily or block it proactively.

Therefore, your VR experience will always be a blend of reality and what the VR operator wants you to see. The VR operator will do his best to limit the sensory input from the real world, but absent suspending the victim in an orbital facility there would always be something to cue off of.


Maybe the Fermi paradox would give it away that the world is not real? A simulated universe would likely have limited space (to save computing power). For example, it could be that only our solar system is simulated in great detail and the rest of the universe is just a shoddy stage decoration, with barely enough detail to seem real when observed from the Earth. So the absence of extraterrestrial life in the entire observable universe would be a sign that the beings who run the simulation did not bother to create life in other solar systems because otherwise the simulation would have got too complex and computationally expensive.