In a simulation everything is known which makes any apparent random event a pre-calculated event.

Taking that into account is it possible to simulate the universe with absolute accuracy in a way that results of jumping forward at any point in the simulation are pre-determined.

PS: This question is not about to simulate it is more like 'if universe was a simulation' or if it can be simulated assuming that it is possible to know everything.


To be clear on what I am asking. If everything was known, will there be any randomness which can make it impossible to simulate the universe with absolute accuracy, and make knowing everything incorrect?

Actual question I had was "if universe was sent back in time and resumed from there will it reach exactly the same state from where it was sent back?"

If two exactly same isolated universes were started in parallel, will the remain exactly the same in course of their duration?

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    $\begingroup$ I'm unclear on your question. Are you asking whether the universe is deterministic? Or are you asking this in a more practical sense?- $\endgroup$ – lemon Apr 7 '15 at 10:57
  • $\begingroup$ I would think, at some level the uncertainty principal would make a full simulation impossible since we can't even simulate a single particle, but that possibly might average out to a pretty good predictability, in theory, though perhaps impossibly difficult in practice. - just speculating. $\endgroup$ – userLTK Apr 7 '15 at 10:58
  • $\begingroup$ @lemon Not in practical sense. I had actually a broader question quora.com/Physics/… and it all came down to randomness and simulation of universe. $\endgroup$ – SMUsamaShah Apr 7 '15 at 11:30
  • $\begingroup$ @lemon I may be actually asking about determinism of the universe. But this will lead to another question of cause and effect. $\endgroup$ – SMUsamaShah Apr 7 '15 at 11:35
  • $\begingroup$ If your question is to find a proof that the universe is a simulation then sorry there isn't, not even the universe knows the future outcomes unless it is being observed and this will act will interfere with the outcome. Whether we are a simulation or not I'll still treat you to a drink cheers. $\endgroup$ – user6760 Apr 7 '15 at 11:56

To my taste, the most coherent way to think about it is to realize that the whole concept of "randomness" is strongly related do lack of information.

It only makes sense to talk about randomness when we have a small "agent", who is a part of a large "universe" -- thus he cannot have a complete knowledge about that universe. But he needs to make some decisions to achieve some goals. And that requires some intelligent way of embracing uncertainties -- he needs to control randomness by manipulating probabilities.

One might still try to ask "but what if that agent really knows everything?" To that I'd like to note that the "agent" we are talking about is still a part of the universe. He is follows the same physical rules as all the rest of it. Thus it is not only looks highly improbable that a bunch of silicon crystals (or a kilogram of brain tissue) can embrace whole complexity of the universe around it. It is actually self-contradictory since that agent needs to have a complete description of himself as a part of the universe.

Finally one still try to object with "but quantum mechanics!" That is a territory of opinionated debate on interpretations of quantum mechanics. But it is still possible to interpret quantum mechanical randomness also as a lack of some knowledge.

  • $\begingroup$ If two exactly same isolated universes (at any point) were started in parallel, will the remain exactly the same in course of their duration? $\endgroup$ – SMUsamaShah Apr 8 '15 at 16:47
  • $\begingroup$ @LifeH2O Yes if you are talking about the total wavefuncion of your your system. $\endgroup$ – Kostya Apr 8 '15 at 17:21

We don't know is probably the right answer to this question.

With current knowledge of quantum mechanics it is believed that randomness is inherent in quantum mechanics. Or we may simply do not yet know the mechanics behind.

In conclusion if randomness is real than there is no way for a universe to produce exactly the same result when started multiple times with same initial conditions.


The premise of your question is flawed.

It is not possible to know everything with perfect accuracy, even in a non-quantum fully deterministic system. (In a quantum system, even if you do know its state with perfect accuracy, you can't predict it accurately.)

Ever hear of chaos? the butterfly effect? the three-body problem?

No matter how well you know the state of a system, your knowledge has a finite number of bits (it is rational), while the state of the system has an infinite number of bits (it is irrational). When those leftover bits become significant, the simulation will no longer be accurate.

Related: The Incompleteness Theorem can be seen as saying that any deterministic simulation has blind spots, where it cannot follow possible realities, even in a sub-universe as simple as arithmetic over the integers.

  • $\begingroup$ If two exactly same isolated universes (at any point) were started in parallel, will the remain exactly the same in course of their duration? $\endgroup$ – SMUsamaShah Apr 8 '15 at 16:45
  • $\begingroup$ @LifeH2O: That's a problematic hypothetical. $\endgroup$ – Mike Dunlavey Apr 8 '15 at 16:46
  • $\begingroup$ @LifeH2O You can't ask that question without understanding the ambiguity in saying that you are starting two identical universes in parallel. And upon understanding the ambiguity, you need to define what is meant by "starting", "parallel", and "exactly the same at any point". Even then, I can almost always use the same definitions as you to show how any universes you create do not fulfill the definitions without being uninterestingly trivial. $\endgroup$ – Jim Apr 8 '15 at 16:54
  • $\begingroup$ @Jimnosperm I am taking the universe as an object. Or in a more simple way can I ask that if a replica of this universe is created right on this moment. Will everything in that universe take the same course of action? I am only trying to understand this quora.com/Physics/… I don't know the right way to ask this question on SE $\endgroup$ – SMUsamaShah Apr 8 '15 at 17:03
  • $\begingroup$ @LifeH2O: Even if the hypothesis of copying the universe were possible, quantum randomness would make them diverge. Take a simpler example: two entangled electrons with opposite spins. As soon as you learn the spin of one you know the spin of the other, but from that point on, they evolve independently. $\endgroup$ – Mike Dunlavey Apr 8 '15 at 17:10

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