Fun fiction, unfortunately missing the boat on quantum computing capabilities, the aims of quantum simulation, and the way quantum mechanics works.
The current interpretation of quantum mechanics is completely at odds with the statement from the story: "'[the simulation] is still as accurate a simulation of the real universe as there can possibly be. Civilisation - indeed, all of history - should rise on this Earth precisely how it did in reality. There are no chances. It's all worked out to infinitely many decimal places.'"
That's just not quantum mechanics. The "infinitely many decimal places" is a classic mistake (pardon the pun) and indicates a strong deterministic bent to the authors way of thinking about the world.
Clearly, quantum indeterminacy and its implications for a non-deterministic universe are still hard to both understand and get right in fiction.
I'm pretty certain the author knows quantum mechanics doesn't work like it does in the story. Consider:
Brute force primality testing of every single integer in existence? Easy. Pi to the last digit? Piece of cake. Halting Problem? Sa-holved.
This is obviously tongue in cheek, and only serves to establish that the computer is "larger than life" and that therefore we should automatically accept all the subsequent descriptions of how the computer can instantly simulate the entire universe and then some.
The reader is not supposed to believe quantum computers actually work like that. The computer is just a storytelling device, no more, no less.
Certainly the hyperbole is part of the story. And again, let me say I think its fun fiction.
However, I still have strong regrets that the author choose to stick the label "quantum" on it just to make it powerful/magical.
Why not call it a massively-interconnected, nano-organic cellular automata computer instead? Sure, it looses its literary flair, but quantum mechanics and computing is already so rarely understood in the public world, I hate to see fiction encouraging a deterministic model.
> Why not call it a massively-interconnected, nano-organic cellular automata computer instead?
That would be unrealistic, absurd, and impossible. How are you going to get an infinite amount of computation in finite time with a cellular automaton or a computer made out of discrete components? The only chance of realistic technobabble is quantum effects. That way, you can pull all sorts of mumbo jumbo like "doing infinitely many things in parallel" or "teleporting the results of computation across space without violating causality" or "expressing the future of a simulation in the binary expansion of real number." And the story simply wouldn't work without a deterministic universe.
I hate to see fiction encouraging a deterministic model.
I know I may get downvoted for this "me-too" comment, but just wanted to let you know that I was very happy to see both of your comments, as I share your sentiment exactly. This entire story is impossible, but many readers, not knowing much about QM might walk away thinking it's "plausible" due to their ignorance and the way the story is presented. Which isn't to say that's a bad thing on its own, but then they walk up to me and badger me with this bullshit... :-p
If you go down the route of http://www.simulation-argument.com/faq.html then the computer is very important, since without one, case 2 dominates case 3 (the interesting one described in the story).
If you can get past the tricky first step of understanding the story (which many seem to fail at), the world gets even trickier after that.
So, the obvious first step is to run the simulation to completion of heat death of the universe. That way at least your reality won't suddenly shut off. This actually detaches you from the top-level reality at that point, because it guarantees that even the top-level can no longer shut you off; it had a "time step" which contained the entire universe simulation and can't be taken back.
Now, you're on top, right? Not necessarily. Suppose the next thing you did was to re-run the simulation again. You skip back to the present, in which you all already detached. Now, in infinity-1 universes, you are once again in a loop, under your total control, with one universe at the top not in the loop but grotesquely outnumbered. Now, go nuts. Design your perfect universe. No more entropy, eternal life, whatever. Take your time, you can always recover the exact state of the dearly departed simply by rerunning the simulation to the proper point.
Now, suddenly cut in your perfect universe. Infinity-1 one of you will experience a sudden transition to perfect universe. (Yes, I know infinity-1 is meaningless. Bear with me here.) So not only are you simulated, you have the power to completely rewrite the laws of your universe at will. Careful construction of this universe may result in other entertaining consequences; for instance, it need not be "a" universe, perhaps you leave the old one in place and install a literal portal to something new, or construct multiple. You can "get in" to the simulation.
Truly these people are gods in every sense that matters.
If all changes are reflected above and below, then the guys on top of you in the simulation are running you to the heat death of the universe as well. Which is essentially the same as turning off the simulation.
Calculating to heat death doesn't make a difference to the people in the simulation. So, it's not the same as terminating the simulation before completion.
For instance, if calculating the simulation was paused for 100 years, then resumed, the people in the simulation would never know.
So, just because it might take five seconds to calculate the entire life of the simulation does not mean entities in the simulation would experience it like that.
Also, our universe seems pretty stable, so if heat death is a part of our universe's life, then there is a reason.
Sam Hughes' entire fiction section on qntm.org is worth reading if you enjoy stories like this. I'd recommend the "Ed stories" (http://qntm.org/ed), "Time Loop" (http://qntm.org/timeloop), "Valuable Humans In Transit" (http://qntm.org/transit), and the entire set of "Fine Structure" (http://qntm.org/structure), which is a large piece of fiction made up of small stories that he recently finished up.
In the not-very-likely event that anyone here hasn't already seen it, the same author's authoritative work on How To Destroy The Earth is worth a look: http://qntm.org/geocide .
Obviously there's a limit to how big an accident can get. ... [snip] ...Be creative and the kinds of accidents I'm talking about here seem more and more plausible.
Obviously there's a limit to how big an accident can get.
You could create awesome feedback loops by making a very small change to something in the simulated universe, relative to how it is in your universe.
Then the people in the simulation will make the same change too, but relative to the change that you made.
This is something that I put into an unpublished novel I wrote, but I want to go back and make the thing that's being changed cooler, like some fundamental universe rule.
Also, once the test has run, the stack of simulations and the real (top) world have diverged. Diane and Timmy at the top have belief states that simulated D and T do no: they know they are at the top of the stack.
Yeah, I would worry about what that top version of me would do. But I suppose, with the simulator it would likely be possible to see. Just run another instance of the universe to the point I found out I'm in the simulation chain, but don't let the new instance see the black sphere. This serves another purpose... when the level that thinks it is the top level sees the level below them running this test, they will have to again wonder if they are in one of those simulations. So they will again have incentive to be nice/benevolent to the simulation chain.
The "real" (i.e. top-level) Tim and Diane wouldn't have seen an inert sphere materialize, and they would thus realize they were different from the simulations. Consequently they're not the "same" people as the simulated ones. They could completely fuck up their simulations without repercussions.
I don't understand why they should be careful not to disturb lower levels?
They don't interact with upper levels.
They are simulation anyway - they have no free will (that was an assumption - other way all the levels would diverge the moment the first human was born).
So no amount of caution can do anything to them - they are in predetermined world.
It behooves them to be the kind of people that would be nice to the lower levels, since that is then all but certainly how the version of them one level up will also behave in the same situation. It is a bit like Newcomb's problem, if you are predictably and cooperatively well-behaved you get rewarded.
Did you mean that they should be nice because the upper levels can see them and intervent? I can agree that in such situation they should be good to their simulated selves.
Or did you mean that even when upper levels are not watching, their (upper levels) behaviour depends on decision of lower levels? Because I can't see why it is so.
People at any given level are either:
a) at the top and have nothing to worry - their universe won't stop working no matter what they do
b) simulated and have no choice - what they decide is just result of simulation inputs and, maybe, tinkering of upper levels
Ether way - the real decisions are made only at the top level - if not, why all simulated worlds have the same history?
People would make different decisions earlier in simulated history if it was possible, and after many generations of simulated people and their different decisions worlds would diverge beyond recognition.
Even if free will exists on lower levels - why decision of lower levels inhabitants should change probabilities of upper levels decisions? Either they have free will, and their decisions are independent of upper levels - or they don't have free will, and their decisions just mirrors their top level selves.
Maybe I'm misunderstanding sth, English isn't my native language, and the subject is hard. Anyway - it's very interesting thought experiment.
The funny thing is that, given in the story that it is possible to simulate the universe, even the top level Timmy and Diane can't be certain that they are not in a simulation, only that they are at the top of that particular line of simulations involving them. Imagine that when they publish this paper and others try Diane's program out on their own quantum computer, they will also create infinite simulations, which all also simulate this account of Diane and Timmy creating simulations at a previous point. In each of those infinite simulations of others running Diane's program there will be an infinite number of simulated Dianes and Timmys experiencing themselves as top level in the occurrence described in this story (not seeing the black ball behind them). Basically if the universe can be simulated, we are probably all in a simulation.
They'd probably know when they didn't see the hole in space behind them.
They probably wouldn't have any qualms with turning the simulation off either. My guess is that all those infinite simulations were on borrowed time until the top layer got bored.
I don't think you read my comment carefully enough (could be my fault, I may not have been very clear). Just to clarify, unless nobody ever runs Diane's program ever again on their own quantum machine there are an infinite number of Dianes and Tommys not seeing the black hole behind them even though they are also simulations, and they would not know it one way or the other but odds are they could guess they are in a simulation and would more than likely be right.
It has nothing to do with time travel, if you didn't care to read the article, why care to comment.
Also you can probably only know the future of different, possible similar timelines. Whatever changes you make in those other timelines will not affect your own. You can alter their future but not your own, otherwise you can alter causality. I don't know if altering causality makes any sense.
A perfect deterministic world simulator will imply the ability to see into the future, which would give rise to the "Dbz Paradox", even if that was not the point of the story.
It is not exactly a new revelation, if you include a model in the model, the problem potentially arise. What you typically do is to keep running the model with the previous answer, and hope the answer converge. It is a common technique for finding numeric solution to the more complex equation systems. I have done it many times. Of course, there is in general no guarantee that there is a solution, that the solution is unique, or that you will find it using this technique.
But if the simulated worlds are deterministic as implied then you could run the simulation forward into the future if your reality also followed the same determinism. Doing this would cause an interesting paradox where knowledge of the simulated future could change what you do in the real world. For example, simulate forward to the next lottery drawing to discover the numbers. Then play those numbers in the real world and win the lottery.
This all depends on the fact that the simulation and the real world are deterministic which, it would seem, is highly improbable.
In the context of this story, the simulation below you would also be looking into the future, and the simulation above would be looking at your future. Whatever "future" is seen has to be reflected in every simulation.
This doesn't change much, the problem irons its self out. I see no paradox. And I don't know what you see that makes determinism "seem improbable."
For the sake of argument, let's say that world zero (W0 for short) is at some arbitrary level. Worlds being simulated below that level would be -W1, -W2, etc. Worlds above would be W1, W2, etc. If everything is deterministic then worlds at all levels take the same path and arrive at the same outcome. But if W0 has control over the -W1 timeline, then W0 can view it's own future by moving the -W1 timeline forward. W0 now knows it's own future (lottery numbers for arguments sake). W0 can now use that knowledge to change it's future. The W0 future is now different from the W1 future which contradicts the ability for all worlds to be deterministic.
As I said, every simulation within the context of this story would be looking into the future via the lower simulation.
In this argument, every simulation would look into the future to see the lottery numbers, and would act out on this knowledge. There would be no "changing the future." Every simulation would see the lottery numbers, then see themselves go to the store and get a ticket with the numbers, and every simulation will win with those numbers. There was no other future. The future you see in the simulation is the future that will occur in your own simulation.
Calling this a paradox is like calling recursive mirrors a paradox.
The current interpretation of quantum mechanics is completely at odds with the statement from the story: "'[the simulation] is still as accurate a simulation of the real universe as there can possibly be. Civilisation - indeed, all of history - should rise on this Earth precisely how it did in reality. There are no chances. It's all worked out to infinitely many decimal places.'"
That's just not quantum mechanics. The "infinitely many decimal places" is a classic mistake (pardon the pun) and indicates a strong deterministic bent to the authors way of thinking about the world.
Clearly, quantum indeterminacy and its implications for a non-deterministic universe are still hard to both understand and get right in fiction.