Does it come with a 14-Gyr warranty?

As many of you probably saw, John Tierney of the New York Times thinks there’s a ~50% chance we’re living in a computer simulation, having been persuaded by Nick Bostrom’s infamous simulation argument.

(This argument, incidentally, is something that occurred to me as a teenager, and I’m guessing to many others of nerdly leanings as well. I didn’t consider it a profound metaphysical discovery, just a sign I needed to get out more.)

Peter Woit feels strongly that debates about whether the universe is a computer are not science and therefore have no place in the Times science section. Robin Hanson retorts that “rather than complain that something is not ‘science,’ or not ‘philosophy,’ it is much better to just say more specifically what it is that you don’t like about it.” Peter Shor points out that if we’re living in a simulation, then the incompatibility of quantum mechanics with general relativity might simply be a bug, in which case the universe will crash when the first black hole evaporates.

As for me, I tend to side with Woody Allen: yes, the universe might be a simulation, but where else can you get a decent steak?

The last word, however, goes to Bender Bending Rodriguez of Futurama.

Bender: “If that stuff wasn’t real, how can I be sure anything is real? Is it not possible, nay, probable that my whole life is just a product of my or someone else’s imagination?”

Clerk: “No, get out. Next!”

(Click here for the audio clip.)

97 Responses to “Does it come with a 14-Gyr warranty?”

  1. Raoul Ohio Says:

    Let’s have a quick vote: How many readers had a similar thought (our universe is a computer simulation) as a teenager? Not being aware of computer simulations (in the early 1960′s) I entertained the notion that we were an experiment, something like the glass walled ant farms that you used to see, with scientists in another dimension taking notes.
    Most of you know that Wolfram’s “A new kind of science”, claims that the universe is a simulation, and he graciously tells us how to track it with Mathematica. B.T.W., the new Mathematica has many cool features, of which “download on demand curated data” might change the way everyone works. Check it out: http://www.wolfram.com/products/mathematica/newin6/

  2. Joe Says:

    Certainly when I was younger I have had such thoughts, and it’s rather sad to think that there is no way of settling things one way or another.

    I haven’t really paid much attention to the simulation argument, as it’s always struck me as a little too antrocentric. Correct me if I’m wrong, but my understanding of the argument is that in the distant future someone or something is bound to build a computer sufficiently powerful to simulate a whole universe, and once that happens, there’ll be lots of virtual universes, in which case the odds are stacked in favour of us being a simulation.

    There seem to me to be two flaws in this reasoning. The first is that it assumes a high probability of such a computer being built, but it may not happen, in which case, there are no virtual universes. I’m not convinced that there is a definitive way to weight the odds.

    The other problem seems to me to be something which Scott spends a lot of time talking about, namely the computational power of physical systems. A computer capable of simulating our universe would be a very special machine, and perhaps we can say quite a lot about it.

    Assuming the point of the simulation is to get information out, then perhaps we can leverage the Holevo bound, and some of Seth Lloyd’s results about the computational capacity of the universe.

    If we assume the computer simulating us to obey the same laws of physics as we observe, then it is not clear at all to me that such a machine can exist. You need to both simulate the universe quickly enough that you get done before the end of the universe in which the computer resides, and avoid the Schwarzschild. Things are further complicated by a finite speed of light, which would essentially rule out a classical computer, as simulating long range quantum correlations would be hard to impossible.

    Well, I suppose I should read up on the arguments in favour of simulation, before I try shooting it down. Still, it seems to me that computation based on physics in the simulating universe must necessarily be as powerful or more powerful than it is in ours. If so, perhaps complexity heirarchies can tell us at which meta-level of simulation we sit.

  3. Joe Says:

    Oh, as a quick follow-up, surely any such computer could surely simulate spacetimes with closed timelike curves.

    Just a thought.

  4. Scott Says:

    If we assume the computer simulating us to obey the same laws of physics as we observe

    Of course that’s a massive, unjustified assumption. :-)

    On the other hand, if (as we believe) the laws of physics have the property of computational universality, then a computer obeying “our” laws really could simulate our universe. The only caveat is that the computer would have to be big: we’d probably want it to have significantly more than ~10122 qubits, the maximum number allowed in our causal region. (Any simulation incurs some overhead.)

    In other words, while the laws governing the “overlord universe” could be the same as our laws, constants like G, hbar, and Λ would presumably have to be set differently, to allow a larger cosmological horizon.

  5. James Says:

    Yes, I had thought about it as a teenager. But I might not have thought of it on my own — I might have been tipped off by the discussion of Conway’s game Life in Steven Levy’s book “Hackers”. I even wrote a little program hoping to simulate evolution, with little organisms with super-primitive genomes, but the outcome was, uh, not that interesting. A few years after that at university, I mentioned the simulation possibility to a super smart friend who was a political science student, and he thought it was some crazy mad-genius idea, when in fact it is perhaps the most vacuous idea there ever was.

  6. Michael Gogins Says:

    Does this argument not assume that in a simulated universe, simulations of conscious beings actually are conscious?

  7. Scott Says:

    Yes, it does assume that — and more specifically, it assumes that conscious beings in the simulated and simulating universes belong to the same “reference class” (so that when doing Bayesian calculations, you should equally well imagine yourself being any of them).

    Of course, the beings in the simulated universe might be videogame characters that are consciously controlled by overlord teenagers. But in that case you wouldn’t get the anthropic conclusion — at least, not unless the overlord teenagers can simultaneously play the videogame while living their lives in the overlord world, and do it so well that they effectively double the number of consciousnesses.

  8. Greg Kuperberg Says:

    Robin Hanson retorts that “rather than complain that something is not ’science,’ or not ‘philosophy,’ it is much better to just say more specifically what it is that you don’t like about it.”

    In order to be science, a proposal has to have some positive features of some kind. Ideally it should make new predictions or have new practical value. Of course, that is a common slogan aimed against string theory, quantum computing, and some other interesting things, so I’ll quickly jump to alternatives. If a research proposal does not offer (or does not yet offer) new predictions, it could provide a more rigorous or more parsimonious explanation of old experiments; or it could be an interesting rigorous or parsimonious extrapolation from old experiments. That is at least the intention of most of string theory and most of QC; by this measure they have both had at least some success.

    In any case string theory and QC are just two examples. Science has a huge reserve of parsimonious explanations that don’t directly predict anything, but from time to time are used to make new predictions.

    But the “universe as a simulation” idea does not offer any of these merits. It isn’t rigorous, or parsimonious, or predictive. Instead, it smacks suspiciously of theism and anthropomorphism. Rather like “multiverses”, unless someone explains it better, it’s a silly meme that could only distract from interesting science. Although it’s so silly that it’s not much of a distraction either, except maybe for science journalists.

  9. Moshe Says:

    I find Peter Shor’s comment absolutely brilliant, really a paradigm shift… Just imagine the amazing possibilities, the creative scenarios and opportunity to make quick advances if we no longer restrict our theories to be mathematically consistent…

  10. Moshe Says:

    That’s also a possible route to making falsifiable predictions from the simulation argument, which as we all know is the only true measure of good science.

  11. John Sidles Says:

    Nick Bostrom’s 2001 article does not reference David Deutsch’s 1997 book The Fabric of Reality , which (if memory serves) discusses the simulation issue at considerable length.

    This allows us to reason as follows. Deutsch and Bostrom are both at Oxford. Since a universal simulation would surely be rationally designed, and since it would be rational for Bostrom and Deutsch to talk with one another, Bostrom and Deutsch can both safely conclude, that neither of them are living in a rationally designed simulated reality.

    Hmmmm … maybe that “not rationally designed” part was obvious? :)

  12. Alejandro Rivero Says:

    The remark of R. Ohio is interesting: it seems we have passed from a lab experiment to a computer experiment. It could be said that it is actually a next step from the G-d wish argument, or better from Homeric gods, whose ability to manipulate Trojan war was somehow limited. Also, I suppose that psychiatry experts have some say in the topic, as well as humanists and experts on mythology. Nor to speak of theologians or readers of Tipler.

    Can we find a good name for the “boringanthropic principle”? Meaning, the fact we live in the dullest of the allowed anthropic simulations. No godzillas around, no superheros. Perhaps “antronic principle”?

  13. Nick Tarleton Says:

    “~10122 qubits”

    This is if it simulates the entire observable universe at Planck resolution, no? Couldn’t it use much less computing power by taking shortcuts, like giving less resolution to things nobody is looking at?

    On falsifiability, see this.

  14. random stranger Says:

    Could we use a quantum computer to simulate the laws of physics to the same level that we can observe them, with a constant-bounded slowdown factor over time? (The distinctions about continuous versus discrete probabilities that were mentioned in an earlier post seem to actually matter here…)

    ((well, excepting that we don’t have a model that covers everything, then, if that doesn’t completely invalidate the question))

    Otherwise, there is a clear and immediate danger in performing too many experiments with quantum entanglement: Obviously, if we entangle too many particles, the simulators’ computer will start slowing down its time ticks. While we won’t notice the difference, its operators will probably get very annoyed and may very well intervene destructively.

  15. Jonathan Vos Post Says:

    Re Comment #11: “… Nick Bostrom’s 2001 article does not reference David Deutsch’s 1997 book The Fabric of Reality…”

    If Bostrom followed standard academic protocol and cited all prior publications germane to his, it would immediately be obvious that he had precisely ZERO original content to contribute.

    Nice job, if you can get it.

  16. Scott Says:

    Couldn’t it use much less computing power by taking shortcuts, like giving less resolution to things nobody is looking at?

    Nick, you may have stumbled on a new argument for Bishop Berkeley’s idealism. A tree falling in an observerless forest might very well make no sound, if the universe uses lossy compression.

  17. Scott Says:

    Could we use a quantum computer to simulate the laws of physics to the same level that we can observe them, with a constant-bounded slowdown factor over time?

    Random stranger: It’s consistent with what we know that the answer is yes. But a full answer will have to wait for (among other things) a quantum theory of gravity.

  18. John Baez Says:

    Scott writes:

    As many of you probably saw, John Tierney of the New York Times thinks there’s a ~50% chance we’re living in a computer simulation, having been persuaded by Nick Bostrom’s infamous simulation argument.

    Hmm, I only got to the part where Bostrom says there’s about a 20% chance when I quit reading that article. So Tierney thinks it’s a 50% chance? Over at the n-Café we were chatting about this and nobody deigned to guess a probability. But, I did make some jokes about the subject. Namely:

    If you think our universe is being simulated with probability p, you might guess the universe simulating us is itself being simulated with the same probability, giving a probability around p2 that we’re in a 2-level tower of simulations. And so on: a p3 probability of being in a 3-level tower, etc.

    Of course, this is a bit naive. The correct figures could be higher. After all, once the whole wacky idea was proved right the first time, it would seem a lot less surprising the second time around! On the other hand, the correct figures could be lower. After all, the universe simulating ours would need to have computers that dwarf ours, so it might harder to simulate them than us!

    But anyway, once you buy into this simulation theory with a fairly high probability, you really need to take seriously the idea that we’re part of a multi-level tower of simulations. This isn’t a reductio ad absurdum in the technical sense, but you might say it’s a reductio ad nauseum.

    However, things get even more complicated than this. After all, this “simulation theory” is just one of many scenarios where our universe is part of a bigger meta-universe. A classic one is the Gnostic myth, where our Yahweh is just some jerk who got out of hand and created this universe as part of a cosmic power trip. There are lots of others.

    So, besides straightforward towers that I just described, the people who take this stuff seriously should also estimate probabilities for “mixed” towers. For example, our universe could have been created by an omnipotent deity that’s being simulated on a computer run by a mad scientist who’s just a character in an online role-playing game!

    That’s a theory that would actually explain some things.

  19. John Baez Says:

    Hey! My superscripts, which worked so nicely in the previewer, died when I hit “Submit Comment”.

    Could the overlords please change the dorky-looking p2 and p3 up there to something that looks a bit more like p squared and p cubed?

  20. John Sidles Says:

    For those of a literary turn of mind, there is also Ian Watson’s 1988 chess novel, Kingmagic, Queenmagic, whose characters experience the rules of chess as the natural laws of their universe.

    As Watson’s characters slowly realize their predicament, their goal becomes … escape to the next level up in the cognitive hierarchy. At which they succeed! Or do they?

    Gosh, now that I think of it, there is also a collection of Stanislaw Lem stories (was it possibly titled non servium ? ) that had a very similar theme.

  21. Scott Says:

    But the “universe as a simulation” idea does not offer any of these merits.

    Greg, we basically agree for once :-). The trouble with debating whether the universe is a computer is not so much that it’s “unscientific” as that it’s boring: it doesn’t explain anything, or generate serious predictions, or even lead to nontrivial theorems. As we’ve known since Turing, the notion of computation is so general that it encompasses pretty much anything.

    Or to put it differently, there’s very little to say about the idea that wouldn’t occur to a nerdy 12-year-old.  (The idea can, however, be played for entertainment value, and to their credit Bostrom, Hanson, and Tierney all write in a way that suggests they don’t take themselves quite seriously.)

    Now, there’s a crucial caveat, which might be causing some of the confusion. Even though “Is the universe a computer?” is itself a boring question, it happens to be extremely close in ideaspace to lots of rich, nontrivial, interesting questions. E.g. supposing we choose to regard the universe as a computer, what kind of computer is it? How many bits can it store? How many operations can it perform per second? Does it have efficient universal machines? Can it solve NP-complete problems in polynomial time?

  22. I BLOG THAT I BLOG Says:

    Could the overlords please change the dorky-looking p2 and p3 up there to something that looks a bit more like p squared and p cubed?

    As thou wisheth, so be it done, on the browsers as it is on the servers. Thus saith the Blogger.

  23. Greg Kuperberg Says:

    The trouble with debating whether the universe is a computer is not so much that it’s “unscientific” as that it’s boring

    It’s strongly boring: not just expressed boringly but destined to be boring. I make no distinction between that and unscientific.

    Or to put it differently, there’s very little to say about the idea that wouldn’t occur to a nerdy 12-year-old.

    Indeed, many 12-year-olds like icing without cake. That is a big problem with John Tierney’s web site in general. He deserves some credit for not taking himself too seriously, but only so much. Because he still lampoons good science to the point of misrepresentation.

    Even though “Is the universe a computer?” is itself a boring question, it happens to be extremely close in ideaspace to a huge number of rich, nontrivial, and interesting questions.

    I agree that it is a cloying caricature of some good questions, and that that is better than if it were only a self-caricature.

    For example: supposing we choose to regard the universe as a computer, what kind of computer is it?

    Yes, in some interpretations this is a good question. However, it is should be understood that computational power is a set of attributes of the laws of physics, and not a law of physics itself. So it is much better as a secondary question than as a fundamental question.

  24. John Sidles Says:

    Scott remark: Even though “Is the universe a computer?” is itself a boring question, it happens to be extremely close in ideaspace to lots of rich, nontrivial, interesting questions.

    This is IMHO a very cogent and broad-ranging remark. Surely, it is true not only in mathematics and science, but equally in other spheres such as engineering and art.

    E.g., it is very close in ideaspace (a fine & useful word!) to the question “Will Boeing new 787 Dreamliner fly successfully?”

    The answer being “Yes, provided Boeing’s CFD computations are a good match to nature’s CFD computations (meaning, turbulent flow itself).”

    The global community is so confident in a “yes” answer, that they have placed 100 billion dollars in advance orders to Boeing, betting upon “yes.” And these advance orders are themselves a rather amazing phenomenon … tens of thousands of recently evolved primates, cooperating peacefully in a productive, rational, global enterprise.

    This kind of success doesn’t happen too often, does it?

    The enticing prospect of extending such computations to the quantum domain accounts for much of the engineering interest in the quantum information theory literature.

    Well, it accounts for my interest, anyway! :)

  25. Michael Bacon Says:

    John Sidles said: “Nick Bostrom’s 2001 article does not reference David Deutsch’s 1997 book The Fabric of Reality , which (if memory serves) discusses the simulation issue at considerable length.”

    Perhaps this is because Deutsch isn’t good support for Bostrom’s views. If I’m not mistaken, Deutsch’s take on the question generally involves two points:

    1. in the distant future simulating physical systems with very high accuracy so that they look perfectly real to the user of virtual reality will become common place and trivial; but

    2. from the point of view of science Bostrom’s view is a catastrophic idea, because the purpose of science is to understand reality, and if we’re living in a virtual reality we are forever barred from understanding nature.

  26. Arun Says:

    …and if we’re living in a virtual reality we are forever barred from understanding nature.

    What nature?

  27. Michael Bacon Says:

    What nature?

    The material world and its phenomena, forces and processes that produce and control all the phenomena of the material world

  28. root@matrix.net Says:

    I am the sysadmin responsible for running the simulation.

    First, I would like to apologize for having to resort to this quantum stuff after the late 1800’s. You see, with you starting to observe more and more of the “universe” we started to run out of computational power so doing monte-carlo became a necessity and this still manifests itself as what you known as quantum phenomena.

    Second I would also like to apologise for that glitch in Utah regarding cold fusion. They were right, but it was a glitch (known for some time I might add) that was confined to Utah so we never though that people would pick it up. We were wrong and the guy who debugs had a hard time fixing that one. We still don’t know whether we introduced some unexpected side-effect elsewhere so if you guys discover something that later turns out not to be reproducible you can always suspect what happened.

    Regarding the LHC we are still debating what we will show you. I don’t make these calls (upper management does) but due to lack of resources we might not introduce anything new. Having or not having a Higgs is still under heated debate. SUSY is just way too complicated (too many free parameters) and we are running low on storage as I write so wouldn’t count on that for now.

    Regarding quark confinement, forget it. It’s just a kludge the programmers introduced so you won’t be able to figure that one out. You can’t, there is really no reason for it. The guy devising the theory that explains matter really messed things up and we had to solve it this way. Sorry.

    By the way, I almost forgot to mention. Of all the ~6E9 humans most are not really “sentient” and have no “free will”. They are just extras we added to keep things interesting for the others and to accommodate the population grows laws. Plus extras are very easy to simulate and sometimes we just simulate the whole group and add a bit of random noise in each “individual”. The real people never even suspect the end-result.

    Roughly there are as much “sentient” and “cogent” humans now as in the beginning (roughly 5% now). The world/Earth is really 6 thousand years old and the entire fossil record was just a way for you guys to believe there was something before and to add more fun to the simulation. Religions fall under this category also and the afterlife if existed would be being stored o tape.
    Reincarnation does exist but only for those 5% I mentioned. What you usually feel as past memories are pieces of reused storage blocks that weren’t completely erased, just recycled. Allocating the memory at birth with calloc instead of a simple malloc would solve this but we like the fun factor due to the current implementation.

    Finally, as for you being afraid of us pulling the plug, I must say so far the ratings have been very good and as long as Lubos is around and has a blog I will personally run a subset of the simulation out of my own pocket as long as I can just for the fun of it.

    If you guys have any questions feel free to ask me, no one will actually believe me so I don’t think I’ll mess the simulation. Besides, humans are not the crux of this experiment. I bet you didn’t see that one coming.

    If anything goes wrong, I’m root and I can always delete things, logs included and management would remain oblivious.

  29. Scott Says:

    Rootuser: And here I was, worried that Woit’s was the only mortal blog you deigned to comment on…

  30. Rettaw Says:

    If you are root how come you have such a boring top domain?

  31. Bram Cohen Says:

    Although for any statement it and its antithesis both appear somewhere in writing, they each only have a 1/3 chance of being right, not the 1/2 as stated earlier. If you wish to find that other 1/3, please find where the subject comes up in my writings. Make sure to give my opinion its due 1/3 weight.

    And, contrary to modern journalism’s regular statements, there aren’t two sides to every story, there are five. Please come to me if you wish to get the remaining three missing ones. Again, make sure to give each opinion equal weight, as they’re all equally valid as opinions.

  32. root@matrix.net Says:

    “If you are root how come you have such a boring top domain?”

    Well, even root can’t escape IANA…

    I could erase them, but just think about the havoc that would create.

  33. Greg Egan Says:

    I think Bostrom’s main error is the phony quantification, backed up with fairly poor arguments. Yes, it’s impossible with our present state of knowledge to rule out the simulation hypothesis completely, but pretending to be able to put a figure on “the probability that it’s true” is just kidding yourself.

    There’s an awful lot of nonsense that gets taken seriously these days just because people jump up and down and shout “Bayes’s theorem!” (Sean Carroll at Cosmic Variance recently mentioned this nice paper, which might be a useful antidote to certain kinds of faux-Bayesian cosmology.)

    At the risk of boring people I might already have bored over at The n-Category Café, I think a far more interesting question than “Are we in a simulation?” is “If we ever are able to simulate, say, evolution, or history, with such fidelity that the creatures we create in the process would genuinely have subjective experiences (and if you don’t believe that can happen inside a standard digital computer, feel free to vary the underlying substrate), then what are our responsibilities towards them?” Theologians have already spent several centuries inventing lame excuses for the amount of suffering in our own universe, but I’m hoping we’d do rather better at taking our responsibilities seriously.

    In my view, if any good comes out of Bostrom’s PR blitz, it will be people noticing that anyone who was responsible for creating/simulating our own universe would have to be utterly depraved, or utterly incompetent, to end up subjecting us to hundreds of thousands of years of the kind of brutality and suffering that they themselves had finally escaped.

  34. Greg Kuperberg Says:

    There’s an awful lot of nonsense that gets taken seriously these days just because people jump up and down and shout “Bayes’s theorem!”

    I agree. But it’s an ironic turn of events, given that quantum mechanics (in the explanation that I prefer) is fundamentally Bayesian. Or you could say “neo-Bayesian”, given that frequentism is of course excluded by violation of Bell’s inequalities.

  35. Michael Bacon Says:

    “In my view, if any good comes out of Bostrom’s PR blitz, it will be people noticing that anyone who was responsible for creating/simulating our own universe would have to be utterly depraved, or utterly incompetent, to end up subjecting us to hundreds of thousands of years of the kind of brutality and suffering that they themselves had finally escaped.”

    How true.

  36. root@matrix.net Says:

    “to end up subjecting us to hundreds of thousands of years of the kind of brutality and suffering that they themselves had finally escaped.”

    You assume too much. How do you know we escaped it?

    Your world is the best world out of all possibilities, rest assured. We made sure of it (modulo minor fun factors :) )

    In fact, sometimes I wish I lived there…

  37. Greg Egan Says:

    Your world is the best world out of all possibilities, rest assured.

    Ah, Doctor Pangloss I presume. I thought Voltaire had already disposed of you.

  38. dave tweed Says:

    I know I’m really bringing down the tone of discussion, but when I saw the reference to Bender from Futurama, my first thought was “How can I transfer from this simulation to his simulation?”. You know, the one that’s “…just like yours, but with blackjack and hookers”.

    BTW, I’m unsure about the characterisation of David Deutsch’ position. I seem to recall a section in his book where he basically says “you might figure out you’re in a simulation if as you probe you find more and more discrepancies in the laws of the ‘universe’ that make most sense if you’re in a simulation, but that the way to do this is to actually try harder to empirically and theoretically probe the the universe rather than engage in non-observational philosophising”.

  39. Coin Says:

    Peter Woit feels strongly that debates about whether the universe is a computer are not science and therefore have no place in the Times science section. Robin Hanson retorts that “rather than complain that something is not ’science,’ or not ‘philosophy,’ it is much better to just say more specifically what it is that you don’t like about it.”

    Um, isn’t that it isn’t science specifically what Woit doesn’t like about it?

    What’s so bad about unasking the question? :P

    A tree falling in an observerless forest might very well make no sound, if the universe uses lossy compression.

    So, here’s a question that actually has nothing to do with the reeks-of-ID “simulation” concept. I am not sure if I’m asking it right:

    Is the fact that renormalization works consistent with the idea that [at least with regards events governed by renormalizable theories] possibly the universe actually is only “computing” the results of events to some finite approximation and then giving up?

    Or are the results we measure from such events only consistent with renormalization calculations where the “cutoff” (or whatever it’s called) is taken to the infinite limit?

  40. James Says:

    I actually think there is one use of the simulation idea, and that is on a meta level as a foil. The idea is obviously vacuous, maybe even intentionally so, but sometimes vacuous ideas wear the clothing of interesting sheep. And sometimes it’s useful to ask ourselves how much more our current pet theories buy than some vacuous ones. And to do this exercise, it’s nice to have a few canonical examples of vacuous ideas sitting around to serve as foils. Sometimes we’ll decide that our idea isn’t that interesting after all, and sometimes we’ll have to think hard to put our fingers on the true reason why our idea is interesting.

    For example, as I’ve mentioned before here, heliocentricity of the solar system sounds really great until you realize that it actually buys you nothing. On the other hand, I have found it interesting to think about what exactly the theory of evolution buys. It is obviously correct in some sense, but in what sense, exactly?

    Of course, this position has been filled before by other famous vacuous ideas, like the one that says we were all created 65 minutes ago with all our memories intact, or the one that says 472393 angels can dance on the head of a pin. (Just in case, let me add that I’m not trying to attack anyone’s research program with truisms. I know science moves slowly, etc.)

  41. Scott Says:

    The idea is obviously vacuous, maybe even intentionally so, but sometimes vacuous ideas wear the clothing of interesting sheep.

    Well put!

    I have found it interesting to think about what exactly the theory of evolution buys. It is obviously correct in some sense, but in what sense, exactly?

    In the sense that all life on Earth did in fact evolve via natural selection from a common ancestor?

  42. Niel Says:

    For example, as I’ve mentioned before here, heliocentricity of the solar system sounds really great until you realize that it actually buys you nothing.

    Well, I would argue that it makes it more likely that you will formulate useful theories of inertia and gravitation, and then eventually develop the physical and mathematical sophistication to realize that the question of which orbits around which really doesn’t matter.

    Some ideas are unscientific, but yet manage to provoke ideas which are.

  43. serafino Says:

    It seems that J.L. Borges isn’t so popular here. (BTW, is there a difference between Simulator and God?).
    -serafino

    “With relief, with humiliation, with terror, he understood that he also was an illusion, that someone else was dreaming him.” (J.L.Borges, Las Ruinas Circulares).

    “We (that indivisible divinity that operates within us) have dreamed the world. We have dreamed it as enduring,
    mysterious, visible, ubiquitous in space and stable in time;
    but we have consented to tenuous and eternal intervals
    of illogicalness in its architecture that we might know it is false.” (J.L.Borges, Avatares de la Tortuga).

  44. Me Says:

    Borges is quite nice, in particular http://en.wikipedia.org/wiki/The_Library_of_Babel

    I like it very much. What is at stake here isn’t whether it’s nice or not but whether there is any knowledge from the world that derives from this idea and so far nothing even remotely tangible came out of it and apparently never will.

    ” Yo me atrevo a insinuar esta solución del antiguo problema: La biblioteca es ilimitada y periódica. Si un eterno viajero la atravesara en cualquier dirección, comprobaría al cabo de los siglos que los mismos volúmenes se repiten en el mismo desorden (que, repetido, sería un orden: el Orden). Mi soledad se alegra con esa elegante esperanza.”

    This is nice literature but that doesn’t mean it should be printed in the science section of the NYT.

    “Some ideas are unscientific, but yet manage to provoke ideas which are.”

    True, let them come and give credit to this if they come. I for one can barely wait.

  45. John Sidles Says:

    Serafino says: It seems that Borges isn’t so popular here.

    He’s popular with me, and I think with many others … all we need is a little encouragement (too little, some think :) ).

    For example, in his story The Zahir Borges describes a Persian astrolabe of such marvelous wonder and beauty, that all who saw it could never again think of anything else, but became useless for all practical enterprises, so that the Shah orders the astrolabe to be thrown into the sea.

    Could Borges be talking about … string theory? complexity classes? pure mathematics? Doh! :)

    On the other hand, in my experience, roughly one person in three strongly dislikes Borges’ writing … since I’m married to one such person (a writer herself), I’ve learned tolerance. :)

  46. Scott Says:

    Borges is one of my favorites — lots of misses, but Library of Babel, Garden of Forking Paths, Circular Ruins, Borges and I, … more than make up for them. That he didn’t get a Nobel in literature is a commentary on the prize rather than him.

  47. ExPrePhysicist Says:

    this might be mentioned in the zillion pages linked from here, but still it might be worth to mention that the question whether the known universe is real predates computers. At least this is how *I* always understood Plato’s cave.

    http://en.wikipedia.org/wiki/Allegory_of_the_cave

  48. Coin Says:

    For example, as I’ve mentioned before here, heliocentricity of the solar system sounds really great until you realize that it actually buys you nothing.

    I imagine that it becomes very useful whenever you decide to start building space probes.

    On the other hand, I have found it interesting to think about what exactly the theory of evolution buys.

    It offers, for example, a meaningful set of predictions as to how pests or contagious diseases will likely adapt in the face of attempts to eradicate them; it also offers ways of building models that predict how closely “related” that different species are, and such models have a variety of real uses.

  49. Funes Says:

    For example, as I’ve mentioned before here, heliocentricity of the solar system sounds really great until you realize that it actually buys you nothing.

    Unless I’m missing some important technical detail, it buys you an inertial system, or nearly so, and that’s a lot, me thinks.

  50. Funes Says:

    Sorry, I meant “inertial frame”. That’s what happens when I read quotations from Borges in his mother tongue…

  51. Raoul Ohio Says:

    Scott sez: In the sense that all life on Earth did in fact evolve via natural selection from a common ancestor?

    I’m not sure “common ancestor” is essential. For example, I think the following are plausible if not likely:
    1. Lots of “Level 0″ organisms started at about the same time with biochemistry either the same, or similar and evolved to the same.
    2. Multiple inheritance: Many subsystems (mitochondrea and so on) evolved separately and were subsequently incorporated. In some cases there is surely a common base class, but who knows about things we have yet to recognize as incorporated? Maybe the DNA/RNA system started on its own and was incorporated into many existing roots, so we think there is a common ancestor.
    3. Roll your own “no common ancestor” theory.

  52. GeniusNZ Says:

    > but pretending to be able to put a figure on “the probability that it’s true” is just kidding yourself.

    Still,m if you want to defeat Bostrom’s argument you needto play by his rules and demonstrate that his conclusion does not emerge from those rules. Otherwise you just argue past each other. I think that in this case that can be done and why Bostrom gets away with it is because peopel either dont bother to seriously tackle it OR they are too busy defending it.

  53. zevans Says:

    Yes, I too have thought about whether or not my life is just a simulation. But as well all know, the question is pretty meaningless. If the universe is “just a simulation”, that changes nothing. My life is still my life. The laws of physics are still the laws of physics. Everything is still exactly as we know it. So it makes no difference.

    As for “The Simulation Argument”, of the possible options in the abstract, I think it’s pretty clear that #2 is the most likely. Running simulations of our evolutionary history would be an enormous computational task to say the least.

  54. serafino Says:

    Scott writes: ‘That he [Borges] didn’t get a Nobel in literature is a commentary on the prize rather than him.’

    When he got the Swiss ‘Premio Balzan’ (maybe richer than Nobel) somebody asked him (I was there, in Rome) about why he didn’t get the Nobel. “It is the evidence of their wisdom.” he said. He also said that he was going to buy (with that money, coming from the Balzan Foundation) the long desired monumental ‘Treccani’ encyclopedia. And he was completely blind, of course.

  55. Not even right Says:

    Root: please reveal us all the physical laws so that the physicists don’t need to chase them anymore! But they will become jobless then!

  56. Greg Egan Says:

    GeniusNZ (comment #52), if you want some arguments from me that engage with Bostrom’s claims directly, here they are over at Not Even Wrong … assuming they haven’t been deleted from that blog.

  57. Nagesh Adluru Says:

    So Scott what are your criteria for a possible “unified theory” not to be boring? If at all discovered it would (by definition) explain everything right?

    Also on the other note, it’s probably in the “later” stages of life too that people might get ideas like this right Newton drifted to Alchemy after he did actual science and Einstein too toward Unified Theory right?

  58. Scott Says:

    So Scott what are your criteria for a possible “unified theory” not to be boring?

    At a minimum, it needs to have some explanatory or predictive content.

    If at all discovered it would (by definition) explain everything right?

    Even a quantum theory of gravity would “merely” describe the machine language of the universe, leaving infinitely many other questions unanswered. I don’t think there’s any finite theory to explain all Aleph0 facts. Nor do I hope for one. It’s hard enough to explain something that no one else has, so why worry about explaining everything?

  59. Michael Gogins Says:

    Responding to comment 33 by Egan, advising forbearance in creating simulations in which sentient beings suffer, you are free to commit suicide at any time to end your pain. But if you would rather be alive, which obviously you do since you haven’t jumped off the bridge yet, perhaps those in your simulation also would prefer to exist. I believe this shows that creating simulations in which sentient beings exist, even if they are in considerable pain, is a very great good.

  60. Greg Egan Says:

    Michael Gogins (#59) wrote:

    I believe this shows that creating simulations in which sentient beings exist, even if they are in considerable pain, is a very great good.

    There are lots of problems with this kind of argument even in more general settings; that most beings would prefer to continue to exist once they exist is not in itself a good reason for bringing them into existence, it’s merely a good argument against murder. But for the specific hypothesis under consideration it’s especially poor, because the simulators are likely to have the means to create vast numbers of spectacularly happy, near-immortal beings, rather than rehashing versions of their miserable ancestors.

    Most of us who have children do so in the hope that they will lead lives as good as, or better than, our own. Running a simulation which you know (unless you’re an idiot) will contain Auschwitz and worse — and then declining to intervene if any of this took you by surprise — is not about creating a great good. If these hypothetical simulators wanted to create a great good, they would do what we do: they’d have kids, and do their best to make them happy.

  61. Nagesh Adluru Says:

    Thanks Scott. Very reasonable opinions.

  62. zeddeff Says:

    That a computer has simulated our universe assumes there can be such things as a computational device in the “real” universe.
    In fact, any talk of the real universe in such a context assumes that the “real” universe has some regularities (How could an universe which did not exhibit anything remotely law-like ever have any science?)
    And so, like turning a sock inside out, the “real” universe becomes very like our universe.
    Perhaps, then, it is exactly what we call our “universe.” (What evidence can there possibly be that laws can be different? You can work out the consequences of a different law, but that is not evidence.)
    Finally, we have trouble simulating fluid flow, let alone the universe.

  63. Michael Bacon Says:

    Scott,

    I think any theory of everything worth the name should have explanatory AND predictive content . . .

  64. Robert Leigh Says:

    Way off topic, but…I have always thought Stephen Jay Gould’s “Wonderful Life” was the worst example of reviving a teenage nerd idea and trying to turn it into science. The nerd idea is “hey, look at the odds against me existing – my mum meeting my dad and their mums meeting their dads and…” varied to apply to the human race. To be fair it hadn’t occurred to me prior to reading the book to generalise the idea to the human race; but the correct response to Jay Gould is “I hadn’t thought of that” followed immediately by “so what?”

    Message: if your title and theme are taken non-ironically from a cheesy Hollywood movie, your book is probably not interesting science.

  65. Ze Says:

    Greg Egan says:
    I think Bostrom’s main error is the phony quantification, backed up with fairly poor arguments. Yes, it’s impossible with our present state of knowledge to rule out the simulation hypothesis completely, but pretending to be able to put a figure on “the probability that it’s true” is just kidding yourself.

    Being able to assign probabilities without making unreasonable assumptions about how the universe came to exist is exactly why I’m an agnostic and not an atheist.

    In my experience just about every atheist will say there is a tiny probability that god exists they just find it highly improbable.

    I’m an agnostic because we simply can’t work out that probability to any reasonable degree and hence our guess doesn’t really give us any information.

    I’ll delay making a guess at that probability till it’s actually useful to do so , or there is enough information to calculate it , till then saying yes or no with some probability doesn’t give me anything useful over treating it as unknown.

  66. Will Says:

    Also on the other note, it’s probably in the “later” stages of life too that people might get ideas like this right Newton drifted to Alchemy after he did actual science and Einstein too toward Unified Theory right?

    Lead can be turned into gold with a sufficient amount of work. Maybe Newton was merely too far ahead of his time?

  67. Nagesh Adluru Says:

    Lead can be turned into gold with a sufficient amount of work.
    Then, are people using the technique to get more gold? I thought Alchemy did not fit modern science standards.

  68. Jonathan Vos Post Says:

    Re: #58:

    It’s not obvious to me, without qualification, that there are Aleph-null facts. In a Platonic sense, if there is at least one fact for each real number in [0,1] then there are at least C facts.

    Now, constructively, using countable strings over a finite alphabet to represent these facts, there are only Aleph-null representable facts.

    But all that means is that the facts that you can describe with the finite alphabet in countable strings is of measure zero over the larger set of all facts.

    It was about here that Cantor started getting weird, with assigning different cardinals to the human mind and to the mind of God.

    But I half-way see his point, Theomathematically speaking.

    This ties together omniscience and undecidability.

    When I was a little boy, thinking about this, I concluded as follows.

    The universe is either finite or infinite. Human beings are either finite or infinite. Let’s look at the 4 combinations.

    (1) Cosmos infinite, humans finite — we’re screwed, science is useless, or at least hopelessly limited;
    (2) Cosmos finite, humans infinite — seems contradictory;
    (3) Cosmos finite, humans finite — leads to Friedrich Nietzsche’s version of the Doctrine of Eternal return (also known as “eternal recurrence”) — boring;
    (4) Cosmos infinite, humans infinite — interesting. But which infinity?

  69. Will Says:

    “Then, are people using the technique to get more gold?”

    Well, no. But it can be done!

  70. Job Says:

    If this simulation were to use a binary matrix for storing the state of the universe at time t, in what order would each bit be read/written when processing the matrix to obtain the t+1 state? Left to right, top to bottom, random?
    Order should have a big impact on what t+1 turns out to be, or no? If the order were to be non-random, would this be detectable?

  71. Greg Egan Says:

    Job (#70), if the simulation is being done correctly, it should make no difference exactly how it is being done in external time. It might be massively parallel, with, say, one processor allocated to every cubic metre of our universe, or it might be completely serial (with, as you note, an awful lot of choice about the order in which different locations’ time evolution are computed).

    One point that remains unclear to me (and I suspect to everyone) is what it even means to have computed “the state of the universe at time t”. There are an infinite number of different ways that the simulation’s information could be encoded in binary data, and although all the different possible forms for the data, and all the different algorithms that might be used to manipulate it, would in some sense be isomorphic, it’s very peculiar and counter-intuitive to ponder how identical subjective content can (presumably) arise from such wildly different physical processes in the external world.

    I wrote a novel about this many years ago (Permutation City), which has a computer copy of the protagonist experimenting on himself by being run on geographically scattered processors, then having his data “canonically represented” at different time increments, and then in random order. And of course, none of this can possibly change his behaviour or memories (given that both have clear “physical” correlates within the simulation), and hence (presumably) none of it can change his subjective experience either.

    But this seems to lead to some very strange conclusions. If a simulated person (with a simulated environment, and no contact with the outside world) really can’t tell what the actual spacetime distribution of the bits that represent his or her brain states at successive times are, why wouldn’t a pile of random bits in any order and any physical form do the job just as well? In which case, it’s completely up to the simulated person to make “internal sense” of the bit heap, and we can do away with any computer. This means that any algorithm that would entail consciousness is effectively “executed”, whether or not any computer does so.

    I should add that, personally, I’m not convinced that all this follows unavoidably from the hypothesis that software can be conscious … but I’ve never heard a really convincing refutation of this line of argument either, and many people, including the roboticist Hans Moravec have argued essentially the same thing.

  72. Job Says:

    Taking the universe at some time t how would we apply the laws of physics to obtain t + 1sec? If i start with the particles at one end of my room and proceed to the other then this establishes a timeline of particle interactions (event propagation, chains) which completely define t + 1sec (in my room).
    What governs this timing? What is it a function of?

  73. Greg Egan Says:

    Job, suppose you model a system of many particles by updating their states in a loop that deals with them by index, i, inside a loop that advances time:

    for (t=0;t≤tmax;t+=tinc)
      for (i=0;i<nparticles;i++)
        [compute new state of particle i,
        based on old states of all particles]

    Yes, from an external point of view there is a definite order in which the particles adopt their new states. But nothing inside the simulation can “detect” that. Any simulated person made from these simulated particles will behave in a way that obeys only the internal physics and internal notion of time; they don’t have access to an external clock. They can’t tell the difference if we change the inner loop to:

      for (i=nparticles-1;i≥0;i--)
        [compute new state of particle i,
        based on old states of all particles]

    If I’m an observer inside the simulation, I don’t observe some kind of “wave of change” moving across the space around me as the inner loop executes. All I can experience is my own succession of brain states, which are based on information that comes in through my simulated senses, etc., all of which are obeying a model of physics that is independent of the order in which the detailed calculations are performed.

    To put it another way, if there is a single experiment within the simulation whose outcome is sensitive to the external-time order in which certain calculations are carried out, then this is not a simulation of any physical model, it belongs to a different class of programs.

  74. Greg Egan Says:

    WordPress declined to display my last reply to #72 … but also remembers it well enough to refuse to let me resubmit it verbatim! So here’s a shorter answer:

    Job, in the simplest simulations of say, Newtonian particles, you’d retain all the t=0 data while computing the updated positions and velocities for all the particles, based solely on the previous values. This makes it obvious that the dynamics will be independent of the order of updates. It’s not much harder to do the same thing with relativistic physics. But the real point is, unless your program’s results are independent of the order in which you update data structures, that’s a bug, and the program fails to be a model of physics.

  75. wolfgang Says:

    Greg,

    the simulation code would not be written in C, but either LISP (if there is a God) or FORTRAN (if not).

  76. John Sidles Says:

    It’s a little bit odd, that on a quantum information theory blog, no one seems to be worried that the notion of a quantum simulation of the universe is ill-defined.

    One difficulty being, what do you use as the starting state? No matter which state you choose, it will swiftly evolve to a state that is so intricately auto-correlated, that it might as well not be correlated at all!

    IMHO, this is a clue that the state-space of the ultimate simulation should not be a linear Hilbert space at all, but rather, should be some kind of reduced dimension Kahlerian state space, substantially much along the lines described by Ashtekar and Schilling in arXiv:gr-qc/9706069.

    What’s that? You don’t want to live without the glories of linear quantum mechanics? Just to play the role of tempter, there might be compensating physics and math glories in a Kahlerian quantumverse.

    For example, take our old friends, the quantum operators “p” and “q”. Each generates a flow in quantum state-space, and we can call the vector fields associated with that flow “V_p” and “V_q”.

    Then we recall, that associated with any pair of vectors is the Kahlerian sectional curvature S(V_p,V_q), which describes the intrinsic curvature of the quantumverse on the section sliced out by V_p and V_q.

    The Kahlerian sectional curvature is, of course, zero in a boring old Hilbert quantumverse. But it is non-zero in a Kahlerian quantumverse … it is in fact a dimensionless new constant of nature (or possibly even, a dynamical field itself).

    So I will ask this question. Since no one knows whether we live in a Hilbert quantumverse, or a Kahlerian quantumverse, what experiment(s) should we do to measure the quantum sectional curvature, and find out? :)

  77. John Sidles Says:

    Just as a follow-up to the above (somewhat tongue-in-cheek) post … and because I am doing a wet-bench sample preparation late into the night …

    By the way … Oh, tedium of wet-bench work! … part of the fun of an equation is, you can look at it, see whether its right, and if necessary, fix it … with wet bench work you can look at it, see that it’s not right, and realize you irretrievably scr*w*d up about eight hours ago.

    Anyway, for all you narrative thinkers, Kahlerian curvature measurements are interesting because (assuming they can be done at all), they show you what G*d’s simulation of Hilbert space looks like. Kinda like if the “Sims” figured out a way to create buffer overflows.

    For all you folks who just like to compute, and want to work a “toy” problem, one approach would be, not to use “x” and “p”, but instead use “s_x” and “s_y”; the spin operators. Then you can mess around in finite-dimensional spaces.

    I assure you, there’s lots of good math there (try a Google Books search for the exact phrase “Kahler manifold”).

    And where there’s lots of good math, isn’t good physics surely near at hand? Or is it vice versa? :)

  78. John Sidles Says:

    Jeepers, looks like the Kahler curvature topic was a thread-stopper. :(

    Perhaps this alternative topic will keep things alive until Scott launches a new thread … is there anyone (besides me) who is a huge fan of (Berkeley graduate student) Austin Grossman’s new novel Soon I Will Be Invincible ?

    If so, please post your favorite quote. Like …

    “Once you get past a certain threshold, everyone’s problems are the same: fortifying your island and hiding the heat signature from your fusion reactor.”

    Scott, a review of Grossman’s hilariously wonderful book would IMHO be a lively thread!

  79. John Faughnan Says:

    I read quite a bit of science fiction as a youth, and I’m fairly sure the life as a simulation theory came up there – it was certainly familiar to me. I didn’t read Hume, Descartes, or even Plato as a callow teen, but they considered the possibility fairly seriously (albeit not in terms of a simulation).

    As to whether this is science or not?

    1. It is one answer to the Fermi Paradox. We’re alone because that’s the way the simulation runs.

    2. We might be able to devise tests for simulation conditions. Certainly the universe as a simulation makes entanglement/spook action at a distance seem less peculiar. “Bugs” in reality could be legitimate science.

    Conversely, is this religion? In what way is life in a simulation similar to life with an omnipotent deity?

  80. Greg Egan Says:

    As to whether this is science or not?

    It is not science. Like religion, one can imagine spectacular interventions that would pretty much silence all doubters, but given reality as we’ve found it to date, the “science” of this subject consists of people listing conjectures of the form “Hey, they might be doing X, for reason Y!” There are versions of this to cover pretty much any X that takes your fancy, but we can attribute no meaningful likelihoods to any of these scenarios, because we have no good reason to assume that the laws of the simulator’s universe have anything in common with our own (or that we can trust our reasoning or our memory).

    As Scott noted back in #4, the possibilities include a complete and consistent simulation of our entire observable universe down to the quantum information limit … while at the other extreme, the simulation might just be your consciousness for the last three seconds, with everything else faked with false memories, and maybe even a deliberate corruption of your ability to reason about anything.

    Bostrom, BTW, denies that his argument is a form of “radical skepticism” (i.e. doubting pretty much everything), but I think ruling out all the possibilities that are toxic to reasoning while retaining the possibility that we are a simulation at all is just ad hoc. In fact in his original paper Bostrom explicitly raises the possibility that scientists’ perceptions, memories and thought processes might be the subject of specially targeted interventions by the simulators, in order to get around the practical difficulties of computing details to subatomic level. This is part of his program to stack the odds: trying to make it sound plausible that there would be vastly more “ancestor simulations” in the universe than real civilisations. But it also makes the creationists’ proposal that fossils have been “planted” (I can never remember if it’s God or Satan who’s supposed to be doing that) look positively benign in comparison.

  81. Kurt Says:

    Bostrom explicitly raises the possibility that scientists’ perceptions, memories and thought processes might be the subject of specially targeted interventions by the simulators

    All of this assumes that the simulators would somehow know or care about our existence. The thing that strikes me about this thread is not that it is so much that the anthropic principle is running amok, but rather anthrocentrism is. The beings running the simulation are interested in the formation of certain types of nebulae on the other side of the universe, and they have no clue that the initial parameters they typed in just happen to also lead to the creation of life on a very, very small subset of the stellar systems that evolved. This universe is just a big lava lamp to them.

    The problem of suffering presents no moral dilemma for the simulators because they don’t even know we exist, let alone that we suffer. Why should they? Maybe someday one of them will be browsing the log files and notice some little anomalies in the data corresponding to our existence…and the experiment will get shut down.

    We are such self-centered little beings.

  82. Greg Egan Says:

    Kurt (#81) writes:

    The beings running the simulation are interested in the formation of certain types of nebulae on the other side of the universe

    If the simulators can’t find a more efficient way to study structure formation in cosmology than a model that goes down to the femtometre level, then they belong to the class of civilisations who are very, very bad at both physics and computer science.

    and they have no clue that the initial parameters they typed in just happen to also lead to the creation of life on a very, very small subset of the stellar systems that evolved.

    If it can cross our minds that this might happen, why would it not cross theirs? Where did they come from themselves, that their origins would not make this possibility obvious? If they had no intention of creating life at all, why would they not take the relatively trivial steps needed to intervene to rule it out?

    Of course the reality is that the universe doesn’t care about us. The redundant part is positing someone out there to manifest this indifference, when the inanimate physical laws are already doing such an excellent job on their own.

  83. Kurt Says:

    Greg (#82) wrote:

    If the simulators can’t find a more efficient way to study structure formation in cosmology than a model that goes down to the femtometre level, then they belong to the class of civilisations who are very, very bad at both physics and computer science.

    Butterfly effect. The simulation overlords are really into butterflies. Specifically, trying to get horsehead nebulae to flare their nostrils by adding or subtracting electrons a billion years earlier in the simulation. And of course with CPU speed doubling every 18 months, it’s easy to get lazy about burning extra cycles.

    If it can cross our minds that this might happen, why would it not cross theirs? Where did they come from themselves, that their origins would not make this possibility obvious? If they had no intention of creating life at all, why would they not take the relatively trivial steps needed to intervene to rule it out?

    Of course it crosses our minds; we’re here. The simulators’ universe is very different and much more complex than ours (obviously); the universe we know is just a “toy” model to them. As far as not being able to anticipate all the consequences and outcomes of a complex system, is this not a truism for us?

    Of course the reality is that the universe doesn’t care about us. The redundant part is positing someone out there to manifest this indifference, when the inanimate physical laws are already doing such an excellent job on their own.

    And of course I agree with you on this point.

  84. Jonathan Vos Post Says:

    Greg Egan: “Of course the reality is that the universe doesn’t care about us.”

    This was, in the history of literature, the great contribution of H. P. Lovecraft. An amateur astronomer, and author of an Astronomy column in a local newspaper, he absorbed the “heat death of the universe” cosmology of his day. He then brilliantly followed Poe, merging Science Fiction, Fantasy, and Horror as genres, with the notion that one need not have anything supernatural or demonic as such to scare the reader ontologically and epistemologically.

    It suffices that the universe does NOT care about humans, nor life in any form, and that there is life of other forms within our own solar system (he wrote about a then-speculative planet beyond Neptune) and having to some extent colonized Earth in the distant past.

    He himself was not good at Math, albeit he refers to 4-dimensional geometry and Relativity in several stories.

    There is a sense in which H. P. Lovecraft influenced you, making up for the sad fact that HPL never seemed to have understood what Babbage had been up to. Some of your stories, in an alternate history, might have happened if Lovecraft had collaborated with von Neumann and Stan Ulam, except that your prose is vastly more straightforward.

    Without HPL there would have been no Robert Bloch of Fritz Lieber or Stephen King, at least in the way that we know them.

  85. KWRegan Says:

    For a question from “nearby ideaspace” (per Scott’s comment 21 above), (how) does the Many Worlds Interpretation help explain quantum complexity theory? Has anyone tried to flesh this out in greater detail than the last section of Scott’s Democritus Lecture 10 and comments in that blog entry?

    E.g. the MWI explanation of Shor’s algorithm on pp216-217 of Deutsch’s The Fabric of Reality strikes me as suggesting extra computational overheads in getting “10^500 universes” to interfere and collaborate, beyond what the standard quantum circuit model led me to expect.

    Concretely, I wonder if a state prep in which some 2-qubit gate g is applied to a pair of qubits entangled with many others, requires more effort than a prep that differs only in applying g to an unentangled pair. Has anything like this been tested?

    Any references to other MWI-specific quantum-complexity expositions (is the preferred basis problem relevant to complexity itself?), or opinions on whether attempting one is a reasonable and worthwhile MS thesis topic, are welcome.

  86. serafino Says:

    Does such a simulation decrease or increase the entropy – whatever it means – of the (sub-system of the) supposed Simulator? Does this question make any sense?

  87. John Sidles Says:

    Along the lines of what Ken Regan is saying, one could imagine a universe which at its birth was *very* quantum, but as it expands and ages, becomes less and less quantum (it is not quite clear to me, whether this is more fun to imagine as a theory, or as a story)

    In either case, the “heat death” of the universe then becomes the “classical death” of the universe.

    We can ask, what would it be like to live in a world in which the quantum state-space supported inexorably decreasing levels of entanglement?

    The first signs would be subtle … like unexpectedly and irreducibly high error rates in prototype quantum computers … Doh!

    Soon thereafter, it would become possible to eavesdrop on quantum key exchange protocols.

    Still later, the signs would be far more dramatic … continuous observation would no longer “collapse” states to exact eigenstates … because the state-space would no longer support exact eigenstates.

    Looked at from this perspective, high-order quantum correlations are an order-type resource that might irretrievably diminish, just like all other kinds of ordered resources.

  88. Bobby Says:

    Greg @71:
    I wrote a novel about this many years ago (Permutation City)…

    I apologize for the digression into philosophy, but I read Permutation City several years ago. It led to some minor panic and some more deep thought on my part. I finally did think I saw a refutation of the notion that “software can be conscious implies all possible conscious algorithms run without a substrate”.

    It’s not a refutation of the logic, but rather one that demonstrates some assumption must be incorrect.

    Assumptions:
    1) software can be conscious
    2) two bit-identical representations of a conscious entity are indistinguishable
    3) the algorithm for a conscious entity is valid with a wide array of input data (at least everything that is physically possible)
    4) Every possible algorithm (or at least a great many of them) is simulated given the appropriate filtering algorithm on normal physical processes/matter arrangements.

    Given those assumptions, there should be an indefinitely large number of simulations that include a conscious entity identical to me as I am now, each with wildly different input data. If you select one of those sets of input data arbitrarily, it is likely to be profoundly different from one’s normal experiences. Since one can’t distinguish between different ‘instances’ of the conscious entity, statistically speaking my next experience (and indeed my recent experiences) should be one of those experiences radically different from those that fall within the norms of our universe.

    Since my last few minutes have been consistent with the pretty narrow range of input data that comprises “normal experiences in our universe”, and this is fantastically statistically if you accept the assumptions, then one of the assumption must be wrong.

    To bring this back to QM, perhaps Penrose is right and there is a quantum component necessary to consciousness. Furthermore, perhaps this quantum component is not classically computable.

    Without something preventing either
    a) classical simulation of consciousness
    b) separation of a consciousness from its surrounding input data
    then it seems to me that everyone’s experiences should be almost random, based on the logic played out in Permutation City.

  89. Bobby Says:

    Typo correction:
    this is statistically fantastically unlikely if you accept the assumptions

  90. Greg Egan Says:

    Bobby (#88,89), I largely agree with you. I stated something similar to this myself on the Dust Theory FAQ:

    I think the universe we live in provides strong empirical evidence against the “pure” Dust Theory, because it is far too orderly and obeys far simpler and more homogeneous physical laws than it would need to, merely in order to contain observers with an enduring sense of their own existence. If every arrangement of the dust that contained such observers was realised, then there would be billions of times more arrangements in which the observers were surrounded by chaotic events, than arrangements in which there were uniform physical laws.

    But on the other hand, given that we don’t know how to characterise the class of algorithms that yield subjective experience, I have no great confidence in these kinds of counting arguments. There are some fairly persuasive arguments that consciousness could not exist without a certain level of consistency in physical laws (in the traditional sense), so it might be possible to leverage that kind of argument into something that carries through to algorithms, if we could show that in order for anyone to be conscious at all, it’s most likely that the algorithm creating them would be effectively simulating something like a spacetime with a set of universal physical laws.

    It’s very easy for us to imagine a “game-world” scenario, where the physics can be very weird and bug-ridden without annihilating the characters completely … but that might be a false impression created by the fact that all our current virtual environments don’t need to be doing anything to support consciousness. If consciousness is possible under algorithm A, I’m sure it’s always possible to splice in a patch that turns the environment from high-resolution quantum gravity into Super Mario Brothers, without destroying the conscious entity itself, but perhaps the statistics are actually stacked against that kind of thing after all. I just don’t know … and at this point in history I don’t think anyone else does either.

  91. John Sidles Says:

    Hmmm … latest batch of samples looks no good … this makes me grumpy enough for a theoretical vent (`cuz why should theorists have life any easier than experimentalists, doh!).

    The folks on this thread have broad-ranging interests in physics, and in particular many will recognize Wheeler’s aphorism “Matter tells space how to curve, and curved space tells matter how to move.”

    Wheeler’s aphorism sums up a huge 21st Century cognitive jump in physics, in which static Newtonian state-space was replaced by a dynamical Riemannian state-space.

    In the process, a lot of cherished conservation laws were upgraded. For example, energy and momentum still are conserved … iff gravitational radiation is taken into account.

    Well, why shouldn’t old-fashioned Hilbert-space quantum mechanics be subject to a conceptually analogous 21st Century dynamical upgrade? In the sense that “Operators tell quantum state-space how to curve; and curved quantum state-space tells operators how to commute.”

    The strategy here is not to make gravity look more like QM, but to make QM look more like gravity.

    Of course, this makes for mathematics that is plenty hard. And the observable effects are presumably so small, relative to conventional QM, that definitive experiments are hard to conceive, much less accomplish.

    Still, the idea that quantum state-space is perfectly linear, seems as implausible as (in retrospect) the idea that Newtonian state-space is perfectly Cartesian.

    Plus, the Machian principle that “everything that exists is dynamical” is IMHO very effective at identifying enjoyable opportunities in physics and mathematics.

    So even if the sysop of our universe compiled the operating system with the flag “–Hilbert linear”, there is no reason that we can’t compile our own Egan-style simulations with “–Hilbert dynamical”. :)

  92. Greg Egan Says:

    I just wanted to add to what I said in #90 that it seems quite plausible to me that the shortest bit string (algorithm+input data) that gives rise to consciousness is one that simulates homogeneous physical laws acting on simple starting conditions.

    For example, it wouldn’t be all that surprising if the TOE and Big Bang could be specified in less than 2^10 bits. Generating consciousness in other ways, such as putting in the necessary structures “by hand” in the input data, would involve many more bits.

    I have no idea, though, how to justify a measure on the space of all bit strings that favours short ones. All I can say is that the version of the simulation argument that works best for me is the one where an infinite number of monkeys are typing on computer keyboards, and there’s a hot key for “Compile and execute everything that was typed so far; ignore all further input”. There is no interrupt key. That would explain our universe perfectly.

  93. John Sidles Says:

    Well, the spheres from last night’s batch came out looking pretty good! Not only does this put me in a good mood, it also is a chance to explain why a wet-bench experimenter would care so passionately about a quantum simulation thread.

    The smallest of the spheres we made last night are about 50 nm in diameter. Each sphere is doped with about 55,000 electron spins. These individual spheres are intended to serve as imaging targets for MRFM imaging experiments, where they will be placed in a large magnetic gradient (about 500 Gauss across the sphere), and subjected to complex RF pulses, while at the same time the electron spins interact with each other, and with the neighboring nuclear spins.

    The above parameters are not too different from a quantum computer, really!

    Needless to say, we are quite passionately interested to simulate the quantum dynamics of this imaging process: such simulations are the sine qua non of modern system engineering.

    From Greg Egan’s point of view, if humanity ever does achieve the ability to create self-aware quantum simulations, this ability will likely not arise de novo, but rather, will grow incrementally out of simulations that are motivated by purely prosaic considerations of quantum system engineering.

  94. John Sidles Says:

    Jeez, this thread is averaging just one post a day …

    OK, here’s a simulation-related technical question. Any simulation of an open quantum system is subject to a certain invariance … the question is, what is the name of that invariance?

    Here I am talking about the invariance indexed by Nielsen and Chuang under the unwieldy name “Theorem: unitary freedom in the operator-sum representation.”

    This is an elegant mathematical theorem, *and* a fundamental law of nature, *and* a very powerful tool for optimizing quantum simulations.

    Such a powerful concept deserves a short, cool name.

    What do your professors call it? What do you call it?

  95. Bobby Says:

    I read your Dust Theory FAQ and Moravec’s fascinating essay.

    At first I was floored by Moravec’s essay. I felt that he waved his hands at the statistical “why do our experiences follow physical laws” argument against the Dust Theory, but I also felt that he was very eloquent in describing and supporting the Dust Theory. He also thought of a few consequences that I hadn’t (and hadn’t seen before), e.g. the ethics of producing works of fiction in which conscious entities suffer.

    (If you haven’t read Moravec’s essay [I know you have, Greg, I mean other people], I heartily recommend it. He really does lead into the ethics question above in a way that isn’t completely laughable, which is a pretty impressive accomplishment in itself IMO.)

    However, now that I’ve slept on it, I am less impressed overall. The “ethics of fiction” section fails to point out that all such sky high “simulation summaries” are played out in any sufficiently large arbitrary dataset. This means that the author’s/game player’s work affects these entities not a whit, which tends IMO to make that whole argument a mockery.

    His hand waving at the consistency of experience as an argument against the dust theory bothers me more, especially since he doesn’t treat the argument with the self-doubt it deserves.

    That said, he certainly did a far better job illustrating the whole argument than I have.

    To elaborate further on the ‘quantum computing as a prerequisite for consciousness’ argument, I find myself a little confused about the power of quantum computing versus Turing machines.

    My understanding is that if you ignore measurement events, quantum theory is deterministic. Everything is just a big evolving dataset, with the next value in the dataset computable by a Turing machine from the previous, with the possible issue that the data may be analog.

    Further, our typical experience in “the real world” is deterministic.

    It also appears that the quantum world is just a composite of all possible “real worlds” (shown by Feynman’s path integral work) and that the real worlds are just a special kind of slice of the quantum world (shown by Hugh Everett’s PhD thesis).

    My point with all of this is it seems that in the pure quantum world, the most powerful computing engine is a Turing machine. In the everyday real world, the same appears to be true. It is only in the way the real world is a component of the quantum that allows quantum computing, which is demonstrably more powerful than a Turing machine. (Grover’s algorithm solves in n^1/2 what a Turing machine requires n/2 to solve).

    My further point is that if you make the rather large assumption that consciousness requires quantum computing, then perhaps you could apply the Dust Theory to the quantum world, and consciousness then falls out, but only within those thin slices (which appear to have some statistical normalcy forced on them, which invalidates the statistical argument against the Dust Theory).

  96. Bobby Says:

    OK, postulating a weak form of Moravec’s argument for eternal life at the end of his article… This weaker argument is essentially the almost tautological argument that you will only experience consciousness in the classical slices of the quantum universe in which you aren’t dead. Call it the “weak anthropomorphic quantum” (WAQ) theory.

    In that case, perhaps the answer to Fermi’s paradox is that every advanced civilization figures out WAQ is true, and arranges circumstances so that all conscious entities in the civilization are obliterated in every branch of the universe except the ones with extremely unlikely but extremely beneficial properties (quantum paradise). For example, by constructing an antimatter bomb that is set to explode unless some extremely salient and complex question is answered by a giant quantum computer that “just happens” to form from random quantum fluctuations in the particles composing a nearby moon.

    Since we don’t happen to live in one of those exceedingly unlikely paradise slices, we don’t see anyone “out there”. (Or, indeed, anyone stamping us out as exponential growth pushes them to expand at the speed of light).

  97. Daniel Says:

    I have to say, that I could not agree with you in 100% regarding Does it come with a 14-Gyr warranty?, but it’s just my opinion, which could be wrong :)