There are people who believe we live in a world, simulated on a computer. That computer must have been built in either another computer-generated world or a real world (by which I mean a non-simulated world). If it has been made in another computer-simulated world then the (simulated) computer on which the simulation (program) for "the next" simulated world is run must be a subset (by which I circumvent the notion of size) of the "previous" computer, which means that the computers on which the next-world simulations are run will be ever-decreasing subsets of the previous computer.
Doesn't this mean that there has to be a first real world because if the "stack of turtles" would be infinite there would be no limit to the increasing subset connected to a computer in a previous simulated Universe, sending the subset to infinity, when the simulated Universe gets more and more down the stack of turtles?
If the simulated Universe grows to an infinite subset (when tracing back the track of subsequent simulations or going down the stack of turtles) of the previous computer, whatever the programmers program into it, wouldn't it take an infinite time to program this infinite set, so the next simulated Universe never gets finished (and neither the preceding simulation) and the process stops. In this case, there has to be a first, infinite real-world (because such a world can't be programmed in an infinite computer). Programmers in this real infinite world can make a finite-world simulation.
This is a crude (but essential) outline of my thoughts on this subject, of which I clearly think that a real world has to be there.

By the way, I think it's a waste of time to elaborate on the idea that we live in a simulated world (which indeed, as written below only shifts the problem of explaining Nature to an alleged previous simulated world, etc.). I'm satisfied with the world I live in and it's my gut feeling that the world I live in is real. So in my eyes, there isn't a first world that's real but it's the world we live in that's real (I think it's a creepy thought that we live in a simulated world, just I think it's a creepy thought that we're made by (a) god(s) or by evolution for that matter). But despite all that, I'm still curious how others on this site think about this subject.

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    Each world is a simulation of the one above it. There is no ultimate simulation. "It's turtles all the way up."
    – user4894
    May 19, 2016 at 4:27
  • We have to think it that way, but we have to be agnostic towards the objective reality. Welcome to Kant.
    – Philip Klöcking
    May 19, 2016 at 8:40
  • Welcome to my world! Is that Kant guy the one who said something about Das ding an sich? May 19, 2016 at 10:21
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    "That Kant guy" is the one that proclaimed an Ding an sich as something we have to think, because we cannot think experience of objects otherwise at all, but always has been agnostic towards the ontological status, not to speak of any description of it. The main reason is that all that we can possibly know of is objects as they appear to us mediated through our mind and the way our mind mediates them.
    – Philip Klöcking
    May 19, 2016 at 10:39

6 Answers 6


We can not carry the argument past the first step because if our physical laws are simulated then we know nothing about the "physics" of the world that does the simulating. In particular, it may make no sense to say that one computer is "bigger" than another if they function by completely different principles, space or time as we know them may not apply to our simulator either. For that matter, the chain of simulations if it comes to that, doesn't have to be finite, there might be a simulator that simulates an infinite chain of other simulators each one simulating the next, and on and on.

But before we get into turtles all the way down let me point out that your question exposes the main weakness of "universe as a simulation" proposals, they lack explanatory value. The simulation idea is supposed to explain how our universe functions, but all it does is shift all the questions to the simulator: what kind of reality does it reside in, what kind of physics does it obey, what kind of intelligence is behind it? We do not need to deal with the infinite regress here, the first step is already superfluous. This is like the homunculus theory of how the mind works, there is a little man in the head that does the thinking, it does nothing to explain how the thinking is done. We might as well cut out the little man, and simulations.

This said, there is a school of thought that argues that one can have a "simulation" without a simulator, pixelated world which is already "real", not run by another one. This is usually phrased differently, e.g. Lloyd's universe as a quantum computer, or Tegmark's universe as a mathematical structure. However, something always seems to be missing in such accounts, namely how such a "simulation" manages to implement itself while lacking physical powers (in the ordinary sense), I even asked a question about it: How can the physical world be an abstract mathematical structure? But it seems that explanations provided always appeal to some sort of implicit physical implementer, i.e. the underlying "real" world, or simply God. The root problem is that we do not know how to leap either from mathematics to physics, i.e. from inert idealities to physical action, nor from physics to psychology, i.e. from physical action to perception and awareness. And without "simulating" those it is hard to see how self-simulation proposals can get off the ground.

  • I´m sure we´re not living in a simulation, as sure I am if I´m dreaming or not. And like I said if we can´t build a human being outside the womb of the mother (and we´re even unable to build a single human cell), we certainly can not program human beings on a computer. Concerning the simulations without a computer, I have the same attitude. I think Tegmark is the ultimate follower of Plato. May 20, 2016 at 10:39
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    The universe a computer exists in does not have to be similar to the one we live in. Consider the many worlds generated by our computers that are nothing like our reality. So any explanation based on the fact that we cannot create such a device is fallacious. You should not limit yourself to "simulators" because the simulator may be you, just experiencing a very lucid dream or the delusional effects a psychotropic influence. The simulator and its mechanics cannot be discernibly ascertained from within it. May 22, 2016 at 0:05
  • @alampert22 Regardless the assumption that the worlds where the next level of a simulated world is computed on obeying different laws, one thing is sure: there has to be a way to create to construct on a physical material (I think material exists in all different kinds of physics), whether this material is simulated or not. If I´m dreaming the dream that has entered my mind, the things I see are all just a simulation, not the real thing. Do you believe that the persons I meet in a dream are real and have consciousness, emotions, thinking abilities etc? Dreams also, in connection with neural.. May 22, 2016 at 5:24
  • networks, neural activities that appear to go much faster than seeing, hearing, interpreting things, in the waking state. So if we take a clock in the waking world, there is a big difference in the time of the neural activity in the vision centre, in combination with the neural activity that resembles a flying bird in the memory (in wich the bird, as seen in the patterns of the memory, flies faster than in the waking world), But you actually don´t see thing moving faster. They appear just as in our daily lives. Somehow the brain manages it for us to see dreams as we do in the waking state. For May 22, 2016 at 5:38
  • In a dream you may believe that the people and things in your dream are real. It is only upon waking that we have the reference to acknowledge the dream for what it was. While there is such a thing as lucid dreaming, these are a specific type of dream and do not account for all dreams. I am under the impression that most people do not experience lucid dreaming. May 22, 2016 at 5:38

Also... as far as the Simulation Argument, you have to ask "what difference would it make?". If we're simulated, what would be different from if we're real? How would it affect things?

If it would make no observable difference, then it's not a question science can answer. There is no answer, nobody could ever know.

Of course, some clever soul might think up some way of testing our simulation. Perhaps run a really odd process on a quantum computer. Reality gets odd on the teeny-weeny scale, maybe there's a trick there... [but probably not]

Do you remember that Dr Who episode where it turned out they were simulated? All random numbers turned out the same. Up until the weird glowy door appeared, they had no idea about the simulation.


Yes, there does. Even if we're simulated by some computer, in a world that itself is simulated in a bigger computer, somewhere along the line there has to be a computer that actually exists.

Of course the nature of that computer, and the world it exists in, we can say nothing about. We can say nothing about the world one "level" above ours either.

That said, the simulation argument has strong tendencies towards being unprovable (and worse, undisprovable). It's currently undisprovable and likely always will be. Until one of our gods throws his joypad across the room and breaks it, after another inconceivable intelligence calls his mum gay.

  • I agree. But why is it ( in accordance with the views of Popper) so bad if a theory can't be disproved (or falsified, like Popper called it)? Everything (falsifiable or mot) can contribute to the progress of science. That theories have to be falsifiable is at the core of Popper's scientific method (which is embraced by most scientists) and we know since Feyerabend that in practice not one single method exists. It depends on the context which method we use or don't use one at all. By the way, I like your example a god throwing his joypad across the room. If our world is on it...KABOOM! Feb 4, 2018 at 14:48
  • Sure, some information might give a clue to something important. But when you're dealing with theories about reality and how it works (eg biology, chemistry and physics (in that order!) ), if you're going to say something, produce a theory, then it has to be disprovable. Theories are based on observation and experiment. If an experiment cannot fail, then it's pointless to do, you're not testing anything. If a theory can't be proved wrong, it's tautological. It says something only about itself, not the world behind it.
    – Greenaum
    Feb 17, 2018 at 1:51

Thats a pretty big if... Assuming that eventually, stepping up through the simulations there is a real world containing the first simulation, you are asking "Does Inifinity have an upper bound?" That being the case, and we are living in a simulation, it means the universe does not go on forever in all directions, nor does it cycle back on itself in a loop. I painted a picture called Deus et Machina that deals with this; a machine stands at the edge of the universe bearing a flag, in front of him is God's face (I used classical Methuselah imagery to depict the Creator), rubbing His beard as he pondered on the creation of his creation. By proposing that our simulations could ever be complete enough to simulate us, we're ignoring a hard fact about complexity itself. While a simulation of the universe could be Turing Complete, it could never contain itself, being an information system. To store a unit of information requires two things, itself and something to represent it with...

This means that the universe, being made of atoms that are all identical and only describe it by arrangement, is itself a representation of something; the question is what?

IMO, the universe is simulating itself, meaning there are no levels to it, which resolves the information system paradox.

Take a leaf from a tree. It is made of atoms lined up in a certain configuration that define it as what it is. It is alive because it is swapping some of its atoms for others but retaining a basic but changing form.

Take a rock. It is made of atoms lined up in a certain configuration that define it as what it is. It is not alive because it is not swapping some of its atoms for others, and is retaining a basic and unchanging form.

In both cases, removing the atoms and replacing them with others does not affect the collection - it remains a leaf or a rock. Also in both cases, rearranging the atoms affects the collection, it is no longer a leaf or rock, it could be anything constructable from the units it is made of.

This demonstrates that the universe is only defined by arrangement, not atoms. It COULD be represented with anything that is unitary and indistinguishable from another unit - mathematics falls into this category, so theoretically mathematics could describe the universe but only if contained in a computer, an abacus, or a mind like a god - so it obvious that the arrangements we have are representing something. A leaf represents itself by being arranged like a leaf, or it would be something else.

This leads me to conclude that the universe is Cartesian in nature and thinks because it is, because the only other conclusion is that it was arranged by an external entity and is therefore proof of a Creator.


Turtles my dear boy, turtles.

This concern has been around since before the modern computer. René Descartes contested a similar concern in his Meditations, though for him the illusion was made by a mischievous demon. We have also seen portrayals of this in "The Matrix".

Unfortunately, the logical necessity for a Primary World cannot quite overcome the existence of an infinite regression. Much like aligning two mirrors towards each other, the image appears in an infinite regression. This is the plot of ##Spoiler Alert## "The Thirteenth Floor".

Another example that may put the concept into perspective is the old problem in cosmology posed by the "unmoved mover" paradox. As phased jokingly by Stephen Hawking:

A well-known scientist (some say it was Bertrand Russell) once gave a public lecture on astronomy. He described how the earth orbits around the sun and how the sun, in turn, orbits around the center of a vast collection of stars called our galaxy. At the end of the lecture, a little old lady at the back of the room got up and said: "What you have told us is rubbish. The world is really a flat plate supported on the back of a giant tortoise." The scientist gave a superior smile before replying, "What is the tortoise standing on?" "You're very clever, young man, very clever," said the old lady. "But it's turtles all the way down!" — Hawking, 1988

  • The turtle argument also holds in physics. Say you have found some ultimate theory. Example. The current universe we´re living in, wich came from those zillions (10exp500?) possible worlds, was it chosen randomly or with an intrinsic probability (I´m not a proponent of neither string theory nor intrinsic probability)? Both beg the question if there is un underlying theory, wich in my view should be a determinist one wich gave rise to this theory. And the same question can be asked for every turtle beneath each theory. Or for of god(s). Or simulation. But I think there is one at the bottom. May 22, 2016 at 5:03
  • Its not necessary to answer whether there is a first one, if you cannot differentiate reality from illusion. The reason I cited the movies is because they are actually decent illustrations of the concept. The Thirteenth Floor deals with a simulator machine in a simulator machine. And the challenge that exists from trying to identify reality in any way other than finding the "end of the road" where the illusion falls apart. May 22, 2016 at 5:08
  • Maybe one simulator exists today: one where you to put on a helmet, wear gloves and a special suit, all to provide you with the related sensory perceptions and which are in sync with the movements you make to let you, for example, picking up a ball. The gloves let you feel the opposing force the ball would give you in the real world, so it is as of you are really take the ball in your hand. Or when you hear something in your mask you focus and walk to it. If you´re only focusing on that sound maybe you don´t see the bee that thinks you are attacking and he stings, wich the suit makes you feel. May 22, 2016 at 13:39
  • Surely you can tell the difference between the simulated world, provided to you by gloves,a suit,a helmet, and a very strong computer to provide the visible world you can see in your helmet, the audible world and the sensory world of skin pressure (an itch seems to me more difficult to take part), and to synchronize your attention by reacting to your attention and let appear the right vision, sounds and pressure if you´re touching something. You can feel it's not the real thing. But trying to program reality on a supercomputer seems to me impossible because the programmed things aren´t real. May 22, 2016 at 13:57
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    Do you think a simulated human being, like the ones that appear in my dreams, have the same brains and body as a real person? -- Me personally? No, I don't personally believe in simulation at all, for many reasons we can't go into here. But if you allow ONE simulation, who says there aren't infinitely many; perhaps even arranged in a loop like a snake swallowing its tail? Why believe in ONE simulation then get squeamish about infinitely many? That's like believing in 1 but refusing to believe in 2, 3, 4, 5, ... You seem to be assuming the answer to the question you're asking.
    – user4894
    May 23, 2016 at 23:47

Simulation by definition means that it's a simulation of something. That 'something' should exist. So, if we assume there is a simulation, that by definition means there is a 'reality' which this simulation is a simulation (imitation) of. Even if there are many levels of simulations, there is the top-level 'actual' reality.

I cannot see why this is subject to an infinite regression. Top-level computer would have finite resources. Even if you are a simulation in a simulation (and so on) you are still bound by the actual 'real' hardware.

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