"Does the moon exist when no one is looking at it?"
    —Albert Einstein, asked of Niels Bohr

    Suppose you were just starting to work out a theory of quantum mechanics.

    You begin to encounter experiments that deliver different results depending on how closely you observe them. You dig underneath the reality you know, and find an extremely precise mathematical description that only gives you the relative frequency of outcomes; worse, it’s made of complex numbers. Things behave like particles on Monday and waves on Tuesday.

    The correct answer is not available to you as a hypothesis, because it will not be invented for another thirty years.

    In a mess like that, what’s the best you could do?

    The best you can do is the strict “shut up and calculate” interpretation of quantum mechanics. You’ll go on trying to develop new theories, because doing your best doesn’t mean giving up. But we’ve specified that the correct answer won’t be available for thirty years, and that means none of the new theories will really be any good. Doing the best you could theoretically do would mean that you recognized that, even as you looked for ways to test the hypotheses.

    The best you could theoretically do would not include saying anything like, “The wavefunction only gives us probabilities, not certainties.” That, in retrospect, was jumping to a conclusion; the wavefunction gives us a certainty of many worlds existing. So that part about the wavefunction being only a probability was not-quite-right. You calculated, but failed to shut up.

    If you do the best that you can do without the correct answer being available, then, when you hear about decoherence, it will turn out that you have not said anythingincompatible with decoherence. Decoherence is not ruled out by the data and the calculations. So if you refuse to affirm, as positive knowledge, any proposition which was not forced by the data and the calculations, the calculations will not force you to say anything incompatible with decoherence. So too with whatever the correct theory may be, if it is not decoherence. If you go astray, it must be from your own impulses.

    But it is hard for human beings to shut up and calculate—really shut up and calculate. There is an overwhelming tendency to treat our ignorance as if it were positive knowledge.

    I don’t know if any conversations like this ever really took place, but this is how ignorance becomes knowledge:

    Gallant: “Shut up and calculate.”
    Goofus: “Why?”
    Gallant: “Because I don’t know what these equations mean, just that they seem to work.”
    five minutes later
    Goofus: “Shut up and calculate.”
    Student: “Why?”
    Goofus: “Because these equations don’t mean anything, they just work.”
    Student: “Really? How do you know?”
    Goofus: “Gallant told me.”

    A similar transformation occurs in the leap from:

    Gallant: “When my calculations show an amplitude of for this photon to get absorbed, my experiments showed that the photon was absorbed around 107 times out of 1,000, which is a good fit to the square of the modulus. There’s clearly some kind of connection between the experimental statistics and the squared modulus of the amplitude, but I don’t know what.”
    Goofus: “The probability amplitude doesn’t say where the electron is, but where it might be. The squared modulus is the probability that reality will turn out that way. Reality itself is inherently nondeterministic.”

    And again:

    Gallant: “Once I measure something and get an experimental result, I do my future calculations using only the amplitude whose squared modulus went into calculating the frequency of that experimental result. Only this rule makes my further calculations correspond to observed frequencies.”
    Goofus: “Since the amplitude is the probability, once you know the experimental result, the probability of everything else becomes zero!”

    The whole slip from:

    The square of this “amplitude” stuff corresponds tightly to our experimentally observed frequencies


    The amplitude is the probability of getting the measurement


    Well, obviously, once you know you didn’t get a measurement, its probability becomes zero

    has got to be one of the most embarrassing wrong turns in the history of science.

    If you take all this literally, it becomes the consciousness-causes-collapse interpretation of quantum mechanics. These days, just about nobody will confess to actually believing in the consciousness-causes-collapse interpretation of quantum mechanics—

    But the physics textbooks are still written this way! People say they don’t believe it, but they talk as if knowledge is responsible for removing incompatible “probability” amplitudes.

    Yet as implausible as I find consciousness-causes-collapse, it at least gives us a picture of reality. Sure, it’s an informal picture. Sure, it gives mental properties ontologically basic status. You can’t calculate when an “experimental observation” occurs or what people “know,” you just know when certain probabilities are obviouslyzero. And this “just knowing” just happens to fit your experimental results, whatever they are—

    —but at least consciousness-causes-collapse purports to tell us how the universe works. The amplitudes are real, the collapse is real, the consciousness is real.

    Contrast to this argument schema:

    Student: “Wait, you’re saying that this amplitude disappears as soon as the measurement tells me it’s not true?”
    Goofus: “No, no! It doesn’t literally disappear. The equations don’t mean anything—they just give good predictions.”
    Student: “But then what does happen?”
    Goofus: (Whorble. Hiss.) “Never ask that question.”
    Student: “And what about the part where we measure this photon’s polarization over here, and a light-year away, the entangled photon’s probability of being polarized up-down changes from 50% to 25%?”
    Goofus: “Yes, what about it?”
    Student: “Doesn’t that violate Special Relativity?”
    Goofus: “No, because you’re just finding out the other photon’s polarization. Remember, the amplitudes aren’t real.”
    Student: “But Bell’s Theorem shows there’s no possible local hidden variable that could describe the other photon’s polarization before we measure it—”
    Goofus: “Exactly! It’s meaningless to talk about the photon’s polarization before we measure it.”
    Student: “But the probability suddenly changes—”
    Goofus: “It’s meaningless to talk about it before we measure it!”

    What does Goofus even mean, here? Never mind the plausibility of his words; what sort of state of reality would correspond to his words being true?

    What way could reality be, that would make it meaningless to talk about Special Relativity being violated, because the property being influenced didn’t exist, even though you could calculate the changes to it?

    But you know what? Forget that. I want to know the answer to an even more important question:

    Where is Goofus getting all this stuff?

    Let’s suppose that you take the Schrödinger equation, and assert, as a positive fact:

    This equation generates good predictions, but it doesn’t mean anything!

    Really? How do you know?

    I sometimes go around saying that the fundamental question of rationality is Why do you believe what you believe?

    You say the Schrödinger equation “doesn’t mean anything.” How did this item of definite knowledge end up in your possession, if it is not simply ignorance misinterpreted as knowledge?

    Was there some experiment that told you? I am open to the idea that experiments can tell us things that seem philosophically impossible. But in this case I should like to see the decisive data. Was there a point where you carefully set up an experimental apparatus, and worked out what you should expect to see if (1) the Schrödinger equation was meaningful or (2) the Schrödinger equation was meaningless; and then you got result (2)?

    Gallant: “If I measure the 90° polarization of a photon, and then measure the 45° polarization, and then measure 90° again, my experimental history shows that in 100 trials a photon was absorbed 47 times and transmitted 53 times.”
    Goofus: “The 90° polarization and 45° polarization are incompatible properties; they can’t both exist at the same time, and if you measure one, it is meaningless to talk about the other.”

    How do you know?

    How did you acquire that piece of knowledge, Goofus? I know where Gallant got his—but where did yours come from?

    My attitude toward questions of existence and meaning was nicely illustrated in a discussion of the current state of evidence for whether the universe is spatially finite or spatially infinite, in which James D. Miller chided Robin Hanson:

    Robin, you are suffering from overconfidence bias in assuming that the universe exists. Surely there is some chance that the universe is of size zero.

    To which I replied:

    James, if the universe doesn’t exist, it would still be nice to know whether it’s an infinite or a finite universe that doesn’t exist.

    Ha! You think pulling that old “universe doesn’t exist” trick will stop me? It won’t even slow me down!

    It’s not that I’m ruling out the possibility that the universe doesn’t exist. It’s just that, even if nothing exists, I still want to understand the nothing as best I can. My curiosity doesn’t suddenly go away just because there’s no reality, you know!

    The nature of “reality” is something about which I’m still confused, which leaves open the possibility that there isn’t any such thing. But Egan’s Law still applies: “It all adds up to normality.” Apples didn’t stop falling when Einstein disproved Newton’s theory of gravity.

    Sure, when the dust settles, it could turn out that apples don’t exist, Earth doesn’t exist, reality doesn’t exist. But the nonexistent apples will still fall toward the nonexistent ground at a meaningless rate of 9.8 m/s2.

    You say the universe doesn’t exist? Fine, suppose I believe that—though it’s not clear what I’m supposed to believe, aside from repeating the words.

    Now, what happens if I press this button?

    In The Simple Truth, I said:

    Frankly, I’m not entirely sure myself where this “reality” business comes from. I can’t create my own reality in the lab, so I must not understand it yet. But occasionally I believe strongly that something is going to happen, and then something else happens instead… So I need different names for the thingies that determine my predictions and the thingy that determines my experimental results. I call the former thingies “belief,” and the latter thingy “reality.”

    You want to say that the quantum-mechanical equations are “not real”? I’ll be charitable, and suppose this means something. What might it mean?

    Maybe it means the equations which determine my predictions are substantially different from the thingy that determines my experimental results. Then what doesdetermine my experimental results? If you tell me “nothing,” I would like to know what sort of “nothing” it is, and why this “nothing” exhibits such apparent regularity in determining e.g. my experimental measurements of the mass of an electron.

    I don’t take well to people who tell me to stop asking questions. If you tell me something is definitely positively meaningless, I want to know exactly what you mean by that, and how you came to know. Otherwise you have not given me an answer, only told me to stop asking the question.

    The Simple Truth describes the life of a shepherd and apprentice who have discovered how to count sheep by tossing pebbles into buckets, when they are visited by a delegate from the court who wants to know how the “magic pebbles” work. The shepherd tries to explain, “An empty bucket is magical if and only if the pastures are empty of sheep,” but is soon overtaken by the excited discussions of the apprentice and the delegate as to how the magic might get into the pebbles.

    Here we have quantum equations that deliver excellent experimental predictions. What exactly does it mean for them to be “meaningless”? Is it like a bucket of pebbles that works for counting sheep, but doesn’t have any magic?

    Back before Bell’s Theorem ruled out local hidden variables, it seemed possible that (as Einstein thought) there was some more complete description of reality which we didn’t have, and the quantum theory summarized incomplete knowledge of this more complete description. The laws we’d learned would turn out to be like the laws of statistical mechanics: quantitative statements of uncertainty. This would hardly make the equations “meaningless”; partial knowledge is the meaning of probability.

    But Bell’s Theorem makes it much less plausible that the quantum equations are partial knowledge of something deterministic, the way that statistical mechanics over classical physics is partial knowledge of something deterministic. And even so, the quantum equations would not be “meaningless” as that phrase is usually taken; they would be “statistical,” “approximate,” “partial information,” or at worst “wrong.”

    Here we have equations that give us excellent predictions. You say they are “meaningless.” I ask what it is that determines my experimental results, then. You cannot answer. Fine, then how do you justify ruling out the possibility that the quantum equations give such excellent predictions because they are, oh, say, meaningful?

    I don’t mean to trivialize questions of reality or meaning. But to call something “meaningless” and say that the argument is now resolved, finished, over, done with, you must have a theory of exactly how it is meaningless. And when the answer is given, the question should seem no longer mysterious.

    As you may recall from Semantic Stopsigns, there are words and phrases which are not so much answers to questions, as cognitive traffic signals which indicate you should stop asking questions. “Why does anything exist in the first place? God!” is the classical example, but there are others, such as “Élan vital!”

    Tell people to “shut up and calculate” because you don’t know what the calculations mean, and inside of five years, “Shut up!” will be masquerading as a positive theory of quantum mechanics.

    I have the highest respect for any historical physicists who even came close to actually shutting up and calculating, who were genuinely conservative in assessing what they did and didn’t know. This is the best they could possibly do without actually being Hugh Everett, and I award them fifty rationality points. My scorn is reserved for those who interpreted “We don’t know why it works” as the positive knowledge that the equations were definitely not real.

    I mean, if that trick worked, it would be too good to confine to one subfield. Why shouldn’t physicists use the “not real” loophole outside of quantum mechanics?

    “Hey, doesn’t your new ‘yarn theory’ violate Special Relativity?”
    “Nah, the equations are meaningless. Say, doesn’t your model of ‘chaotic evil inflation’ violate CPT symmetry?”
    “My equations are even more meaningless than your equations! So your criticism double doesn’t count.”

    And if that doesn’t work, try writing yourself a Get Out of Jail Free card.

    If there is a moral to the whole story, it is the moral of how very hard it is to stay in a state of confessed confusion, without making up a story that gives you closure—how hard it is to avoid manipulating your ignorance as if it were definite knowledge that you possessed.

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    41 comments, sorted by Click to highlight new comments since: Today at 6:20 AM

    Egan's law is one the most dangerous biases I've ever heard of. It prevents a person from facing reality in those cases in which it turns out that it isn't normal.

    How would reality go about being not normal? Or more specifically, what is normal, if not reality?

    Well, I suppose reality could get pretty abnormal. And yet, it would still all add up to normality - that is, my model of reality should explain my observations, even if that model was "it's all a big acid trip." Getting around that would need something like a violation of causality.

    Hypotheses non fingo

    Unknown, I don't think Egan's Law has anything to do with facing reality. If I read it correctly, Egan is saying that any theory (e.g. quantum mechanics, general relativity, the standard model) ought to predict normal events on the level of normal events. If relativity predicted that a ball dropped from a height of 4.9 meters would take 5.3 seconds to hit the ground, relativity would be disproven. It all must add up to normality.

    1) Can someone tell me to what extent this many-worlds interpretation is really accepted? I mean, nobody told me the news that the collapse interpretation was no longer accepted, and I think I read such things in a recent physics textbook. So, can physicists remark on their experience?

    2) I think the notion that the QM equations don't mean anything refers to the fact that nobody knows what the real substrate is in which QM takes place. It's a bit analogous to the pre-QM situation with light. People asked, what does light travel in? But since nobody was able to identify any substrate for light, they had to treat the wave-like nature of light as simply an empty metaphor. At least, that's how the classical theory of light was taught to me.

    So in the same way, you say that the amplitudes and configurations are the "reality." But where do the configurations "exist"? Unless you believe that the universe is being simulated in a computer (which seems like a highly unparsimonious not to mention anthropocentric assumption), the equations must be a model of something that's out there. But it doesn't seem like we really know anything that the equations are models of.

    Eli: You are writing a lot about physics recently. Why?

    Shane, it's a series. See "Quantum Explanations."

    "My curiosity doesn't suddenly go away just because there's no reality, you know!" Eliezer, I want to high-five you.

    Does this "Many worlds" thing imply that there exists (in some meaningful sense) other worlds alongside us where whatever quantum events didn't happen here happened? (If not, or if this is a wrong question, disregard the following.)

    What are the moral implications? If some dictator says "If this photon passes through this filter (which it can do with probability 0.5), I will torture you all; if it is absorbed, I will do something vaguely nice.", and the photon if absorbed, should we rejoice, or should we grieve for those people in another world who are tortured?

    Should we try quantum suicide? I think I'm willing to die (at least once, but maybe not in a lot of worlds, my poor little brain can't grasp the concept of multiple deaths) to let one world know whether the MWI is true.

    What about other events? A coinflip isn't really a quantum random event (and may even be not random at all if you know enough), but the coin is made out of amplitudes - are there worlds where the coin lands on the other side? We won WW2 by the skin of the teeth, are there any worlds where the Earth is ruled by Nazi Germany?

    should we rejoice, or should we grieve for those people in another world who are tortured?

    People were, in fact, tortured. You can grieve for them if you wish.

    Should we try quantum suicide?

    That is also a question of how branching world-lines work.

    I'd say no. Identity is an illusion. Everyone only exists for an instant, and a "person" is actually a world-line composed of tons of different people who all think they're the same person. If you perform the experiment, there will be fewer people who think they're you.

    are there any worlds where the Earth is ruled by Nazi Germany?

    Every world exists, but some exist more than others. Don't take that at face value. All it means is that not all of the worlds are equally likely. I have no idea why. Just rest assured that the other worlds exist somehow.

    People were, in fact, tortured. You can grieve for them if you wish.

    If you grieve for everyone tortured in every branch not your own, not singling out your own branch for special treatment out of the literal infinity of branches, then I understand you have your work cut out for you just managing the mathematical infinities involved to specify a utility function. (The solutions I've seen all start by putting in the desired conclusion as an arbitrary assumption.)

    No-one can or will mourn literally infinite people. (Even if you ignore people in other branches, what about people in our own in case our universe is spatially infinite and everything possible happens infinitely many times?) This is not how mourning works in humans.

    You can mourn the general fact that suffering happens, without letting the (probably infinite) amounts of it directly establish the amount of mourning done. It wouldn't be productive in any sense, because in a universe where everything happens somewhere - whether via quantum branches or sheer size or both - you can't reduce the suffering, it'll always be infinite. So mourning in this case does not serve any purpose; I would wish to stop feeling such mourning if I felt it.

    Just rest assured that the other worlds exist somehow.

    And that you cannot interact with them ever again and therefore should not mourn them.

    And that you cannot interact with them ever again and therefore should not mourn them.

    If people leave on a spaceship to colonize another galaxy, and between their speed and the expansion of the universe it is physically impossible to interact with them ever again, surely they still have moral weight. If the spaceship company had constructed the spaceship to collapse the moment they could no longer ever interact with us, to cut costs, then surely when we discovered this from their internal documents we would prosecute them as criminals, even though the consequences of their crime occurred somewhere as fundamentally separate from us as another world.

    I don't think you have, in your morality, an exception for everyone who is causally isolated from you.

    surely they still have moral weight.

    You're just stating your conclusion again. Such a moral belief is possible, but it's a choice. I choose not to care morally about people I cannot even in principle interact with.

    then surely when we discovered this from their internal documents we would prosecute them as criminals

    Note that punishment for crime isn't the same as grief, and works on different rules.

    Why punish people? To reduce future similar crime. (I don't accept moral propositions of punishment for punishment's sake.) I could board such a ship in the future myself, and would not wish it to be sabotaged. So I want these saboteurs to be punished to deter future crime.

    Here's another reasoning for the same conclusion: their action reduced the (expected) utility of the people on the ship while they were still in contact with us. We just didn't find out about it until later. This is analogous to a case where we discover that two years ago, Jane wounded Alex. We know that a year ago, Alex died from unrelated causes. We still want to punish Jane today even though Alex cannot be reimbursed himself anymore.

    I don't think you have, in your morality, an exception for everyone who is causally isolated from you.

    My morality comes from two main sources. One is how I feel (due to nature and nurture): such as grief. Sometimes I find this is not how I want to feel, and then I try to change myself - as I would with any other feelings. So if I discovered myself grieving for people outside my universe, I would try to stop doing so.

    Luckily I, like most people I think, don't grieve for such people: grief falls off rapidly for more distant suffering (in space and/or time). People outside the future light cone, or in other quantum branches, are as far as they can be from me and still exist in some sense.

    The second source of my morality is practical ethics: how do I want to behave, and want others to behave, to achieve certain things? Here too, grieving or expending any other resource (time, effort, thought) on people I cannot interact with doesn't benefit me or them or anyone else, so I would prefer not to do it.

    Can you clarify why you choose to grieve for people at all?

    I mean, you seem to classify grieving as an example of expending resources on someone. So if person A dies and person B grieves, B is expending resources on someone. Who benefits from those resources? It certainly isn't A; A is dead.

    There seem to be a number of possibilities.

    1) Nobody actually benefits from those resources being expended. In which case your reasoning seems to equally well reject all grief, not just grief over hypothetical superluminal travellers.

    2) Some surviving person benefits from B's grief... maybe B themselves, maybe A's family members, maybe somebody else. In this case rejecting grieving for A may have costs, and perhaps those potential costs should be understood before rejecting it.

    3) A benefited, while alive, from the fact that B runs algorithms that reliably result in B grieving for A once A is dead. In this case rejecting grieving for A may have the consequence of also rejecting those algorithms, which would perhaps otherwise have been beneficial to someone in the same way that were in the past beneficial to A. Here again, perhaps those potential costs should be understood before rejecting grief.

    Is there a fourth option?

    A combination of all three options is true; I don't know of a fourth. Grief is mostly a waste because there's more of it than I'd like (option 1), but also helps to prevent future causes of grief (option 3) and possibly helps the griever cope (option 2).

    I see grief as analogous to pain. It's an evolved response. Its primary function is conditioning by negative reinforcement. To avoid grief, people try to prevent grief-causing situations, e.g. protecting their loved ones more. Just as with pain, we have to live with grief today but we may wish to self-modify to grieve less.

    Because it's an evolved mechanism, it tends to be entangled with other processes; thus it is claimed to have a secondary purpose - to help with "healthy psychological coping" of the grieving person in accepting reality. I've heard this claim but have not looked into its sources and don't have a good estimation of how true or important this is.

    I suffer from experiencing grief a lot more than I am willing to suffer in order to get these benefits. If it was just a matter of choice, I would choose to grieve a lot less or maybe not at all, in all situations. That would require a level of modification of my psychology that would also enable me to get the above benefits without grieving. In reality I don't have that level of control.

    However, we do have some control over how much we grieve. In particular, grieving for very distant people seems to be off-by-default in most people, and only activated by deliberate thinking about those distant people; i.e. this kind of grief may be avoided a lot of the time. It also happens to be the kind of grief where the above benefits are least (or nonexistent). So of course I focus my efforts and advise others to practice grieving less first of all in such circumstances.

    Note: "grief" can be read broadly, as in "feeling sad through empathy with suffering distant others".

    Given this, I am very confused by what you think is special about the esoteric possibilities you discuss with alex_zag_al above.

    That is, given my understanding of your position, it seems you should reject or endorse grieving over those doomed intergalactic explorers to basically the same degree that you would either reject or endorse grieving over a boat full of tourists who drown on their way to Greece. (I'm not really sure what degree that is... what I get from your explanation is that you endorse some amount of grief, but not as much of it as people actually demonstrate.)

    Does it matter at all that they're in a spaceship etc. etc. etc.? Or does that just happen to be the example under discussion?

    It matters that I'm not going to interact with them again (or with their dead bodies). For people who are still entangled with me, like tourists in Greece, I allow more grief because in principle my grief (and by TDT-like reasoning, the grief of others) may help prevent other drowning accidents in the future. But you're right that the actual grief I experience in practice for tourists drowning in Greece is for practical purposes zero.

    The example of a spaceship is esoteric; I wasn't the one who chose it, but I responded to people discussing exotic propositions like grieving for "acausal" people like those in other quantum branches. I can't even afford to grieve for everyone who suffers on this Earth, in my own branch - 150,000 people die daily and I haven't got that much grief to spend even if I tried to grieve as much as possible (which I don't want to).

    [+][comment deleted]2y1

    We won WW2 by the skin of the teeth

    We did?

    No. Well actually there are semi defensible scenarios where the Nazis could have won Europe but they're extremely unlikely. I was going to answer just "No." but the following factors suggest an even more freakishly lucky Nazi regime could have beaten the Soviet Union and the war in Europe was in reality the Soviets versus the Nazis because that conflict was existential once it began.

    Evidence the Soviets could have lost

    • At one stage over 100% of Soviet GDP was going to the military.
    • The Soviets came quite close to losing 10% of their male population in WW2.

    The GDP point means that all non-military economic activity was being supported by external subsidy, i.e. the USA and lendlease. The casualties as a percentage of population are suggestive because it took killing 30% of the male population to convert the Afghans to Islam and this seems a reasonable upper bound on the proportion of a population you need to kill to make a cultural change in a non state society permanently at war. Any more complex society, like the Soviets had will be less robust than that.

    But in all seriousness the Soviets could have won the war without the British Empire or Americans committing combat troops, maybe not without economic support. The Nazis were not getting nukes so once anyone on the other side did they were doomed. The Japanese were doomed absent extraterrestrial intervention. I mean that literally. If a meteorite of sufficient size had landed on a major US city maybe the US would have pulled out. Otherwise the Japanese were fucked from the word go. The Italians are irrelevant.

    For the easiest data point against the possibility of WW2 being lost by the Allies consider this; the Allies had over 50% of World GDP and had integrated battlegroups, command and control and economic planning. The Nazis had the Italians for allies and could not meaningfully link up with the Japanese.

    Absent rocks from space the maximal surviving Nazi state is one of

    • Hitler dies after annexing Czechoslovakia.
    • Hitler dies after dividing Poland with Stalin.

    I don't think Stalin would have started a war with a post Hitler Nazi regime so scenario 2 is plausible but scenario 1 is overwhelmingly probable.

    My personal favorite theory is that the cold war was quantum suicide on a species-wide level. Since you seem versed in history: seen in counterfactual retrospective, how likely was our survival?

    I amn't that well versed in history but if we could somehow check all branches after V-J Day nuclear weapons being used in anger by one or both sides in 1/4 of them would not surprise me. Do keep in mind that it was the 80s before nuclear war would be civilisation ending. Europe and the Soviet Union were toast given nuclear war from '50 maybe, North America had to wait for ICBMs to be screwed given nuclear war and I can't remember if it was Brazil or Australia that were the last places to be targetted by civilisation ending numbers of bombs.

    Quantam species suicide I doubt. By the time we could end civilisation the Soviet union was a gerontocracy, albeit one that truly thought the US was an existential enemy when it was barely an enemy. but hey, Stanislav Petrov. I don't know.

    Disclaimer: I don't understand QM on a formal level. But here's what I got out of reading the Sequences and other LW discussions on the subject.

    Does this "Many worlds" thing imply that there exists (in some meaningful sense) other worlds alongside us

    They exist, in a special sense of the word. Instead of arguing about definitions of existence, measure of reality, etc., let's talk about the experimental consequences. Which are: you're not going to interact with them ever again. They exist at most as much as people in our own branch who are outside our Hubble radius.

    Should you still grieve for them? That's for you to decide, but I do make a suggestion: grief is in part a useful adaptation. It may help motivate you to prevent more future grief. If you cannot prevent future grief-causing events (because quantum torture branches will always keep splitting off, and to the extent you cannot influence their measure), then that grief is useless. Eliminating it (not grieving) makes you better off and no-one else worse off, so in such cases I suggest you do not grieve.

    Should we try quantum suicide?

    Again, there may well be good quantum theoretical arguments against quantum suicide. But here's a more practical one. Suppose it works. It has been suggested that it in the vast majority of the branches in which you survive, you do not survive unscathed: you survive hurt, reduced, as an invalid, etc. If you rig up a gun to shoot you, there are some branches where it fails to shoot entirely, but there are many more branches where it misses just enough that you live on as a cripple. Quantum suicide is dangerous like an outcome pump.

    are there any worlds where the Earth is ruled by Nazi Germany?

    In principle, any world whose past evolution does not contradict the laws of physics exists as a branch.

    Most people try to avoid the unpleasant implications by assigning significance to the weight of those branches. I find this a bit problematic when applied to branches that are not in our future: the Born probabilities govern the branch we expect to witness, but we don't understand why or how, so why should we say they govern some "reality measure" of branches we cannot interact with?

    @ Z. M. Davis.

    Yeah, but why? I mean, there's a rumbling noise coming from just over the horizon... the clock is ticking... the machines are coming...

    How is Eli turning into a (seemingly quite good) quantum theory philosopher going to save us?


    We need to simulate problems where human solutions deviate from what is observably optimal. With AI, the program must model both the underlying physics of a problem, and it must model a human response to this physical model.

    For both of these models we must decide how much detail to build in.

    These models include rules that often resemble or approximate equations from quantum mechanics. A particularly interesting similarity is the statistical nature of Bayesian calculations and the statistical representation of amplitude flows in quantum mechanics.

    Unless you believe that the universe is being simulated in a computer (which seems like a highly unparsimonious not to mention anthropocentric assumption)

    I can certainly see how it's an unparsimonious assumption, but how is it especially anthropocentric? Would you consider a given Conway Game of Life run to be "glidercentric"?

    Shane, maybe I'll do a post on the reasons.

    (Whorble. Hiss.) "Never ask that question."

    Hee. Funny coincidences, just rewatched that episode about, uhh, ten hours ago.

    ME, why should the configurations have to exist "somewhere", i.e. in some space? That's the real anthropocentrism. As you say, light doesn't actually travel in some medium.

    Manon: if you survived a quantum suicide experiment, it might convince you of MWI but wouldn't be evidence to others even in the worlds where you survived. This is confusing.

    Nick - sure it could. I killed myself in parallel universe #49237fkwmn(ii) not ten minutes ago, and here I am typing away. QED.

    how very hard it is to stay in a state of confessed confusion, without making up a story that gives you closure

    Is there a "heuristics and biases" term for this?

    "Need for closure". (I know, who'da thunk it?)

    Is there a missprint in this sentence? "Doing the best you could theoretically do, would mean that you recognized that, even as you looked for ways to test the hypotheses." I think [this sentence] should tell what to recognise, but it does not. (I.e., what is actually the second "that"?)

    Is there a missprint in this sentence? "Doing the best you could theoretically do, would mean that you recognized that, even as you looked for ways to test the hypotheses." I think [this sentence] should tell what to recognise, but it does not. (I.e., what is actually the second "that"?)

    If it is true that all possible outcomes actually happen in at least one of the many-worlds, then a global quantum suicide machine (such as the one that's just about to be activated under the Franco-Swiss border) could be used as a veritable genie.

    All possible outcomes happen if everything that happens or doesn't happen is determined at some point by a quantum event. If this is true, then the operators of the global quantum suicide machine can say "We'll activate it today if we don't win the lottery today." Then, only two types of world will exist: Those in which the experimenters all won the lottery, and those where the quantum suicide machine broke down (in which case, the experimenters can try again). From the point of view of the experimenters (and the rest of the world, too), it will seem like there's a certain probability of either their wish coming true before they hit the button, or the machine breaking down, every time they even consider pushing the button. For those outcomes that are less improbable than the machine breaking down, the experimenters would tend to get what they wanted. For other outcomes, the experimenters could try several times.

    If they can increase the reliability of the machine arbitrarily, then they can also increase the improbability of their wishes, along with the probability of their wishes coming true when they ask. For example, they could activate the machine only if a meteor shower doesn't etch their names on the Moon.

    If the wish can't be influenced by one or more quantum events, then the only worlds that would exist would be those in which the machine broke down.

    There's no telling how far the experimenters would be able to go. Is anything truly impossible, or are some things merely ludicrously improbable? Is there anything the experimenters could ask for but never get?

    "Is there anything the experimenters could ask for but never get?"

    Well, I'd guess they couldn't get anything incompatible with the actual laws of physics, like FTL (if that's impossible). Even so, the problem with this scenario as I see it is that there wouldn't just be the three types of world "wish granted"/"machine failed, nothing happened"/"earth disintegrated", but quite likely partial "successes" as well, where the machine failed in disastrous but not apocalyptic ways, e.g. only a third of humanity died. Whether or not that's ethical I'm not sure, but those surviving folks in the "a third of humanity died" world sure would be upset.

    I've been meaning to update my knowledge about quantum mechanics for a few years now. Last I did any real thinking on it, I was being introduced to it, and the Many Worlds interpretation was spoken of as a very interesting unlikelihood. I didn't even realize the non-realism was wrong, though I do remember that it struck me as highly bizarre that my mind had that kind of power over reality. Then again, I was a teenager and a theist back then, and got all my science info from the brain candy magazines.

    These past 4 hours, I've been reading this page and the various links (and sublinks). I was even half-convinced by the philosopher getting things wrong about experiments proving things, despite knowing that you were going to pull the rug from under his argument.

    Thanks, Eliezer, for your continued efforts to be less wrong, and to help others be so as well.

    There are a number of kinds and grades of non-realism.

    Well, obviously, once you know you didn't get a measurement, its probability becomes zero

    has got to be one of the most embarrassing wrong turns in the history of science.

    If you take all this literally, it becomes the consciousness-causes-collapse interpretation of quantum mechanics. These days, just about nobody will confess to actually believing in the consciousness-causes-collapse interpretation of quantum mechanics—

    It's not an inevitable slide. An interpretation that is anti-realist about collapse, will not attribute the cause of collapse to consciousness, since it does not acknowledge the reality of collapse in the first place. It nonetheless has to explain the process of disregarding unobserved possibilities. ...which it can do by saying that the observer is updating their subjective map on the basis of fresh information. Selective anti-realism about collapse is a consistent position. Sweeping anti-realism,might not be, but that is another issue. The subjective interpretation of collapse is posited on information becoming available to an observer from an external world, so it is not sweeping anti realism.

    "Shut up (−1/3)i and calculate." is a typo that isn't present in the original post.