I feel like branches being in fact an uncountable continuum is essentially a given, at least unless we were to fundamentally rewrite quantum mechanics to use something other than complex numbers with a cardinality of . Talking about branches in terms of countable outcomes only makes sense if we group them by measurement outputs for specific discrete observables; but each of the uncountable infinity of worlds will continuously spawn uncountable infinite worlds and that's just something you gotta deal with. If you want to do ethics over this very confusing multiverse your best bet is probably to normalize everything - "adjust for inflation", so to speak.
I also don't think that even if the worlds were countable (and I have seen arguments to the effect of "actually only integer numbers exist and thus if we looked close enough we'd find that all equations and fields etc are discrete-valued") this would make a lot of difference. You making or not making the experiment does not create more branches, it just determines the outcome of branches that would already exist anyway. Assuming that we can purposefully create branches would require defining "measurement" as an actual discrete specific process, which is a much stronger claim (and I don't think any non-objective interpretation of QM really suggests how to do that, though some gesture towards such a thing existing in theory; and objective QM theories do not admit many worlds). "By looking at specific phenomena, sentient beings create new world-lines" would certainly be A Take; if true, it would beget an ethical nightmare, the Quantum Repugnant Conclusion that we all ought to spend all our time collapsing the wavefunctions that result in the most new worlds being created.
(as a side note, have you read Quarantine, by Greg Egan? I won't explain how precisely to avoid spoiling it, but it deals precisely with these sort of questions)
Thanks for the interesting comments.
You're right, I didn't discuss the possibility of infinite numbers of branches, though as you suggest this leads to essentially the same conclusion as I reach in the case of finite branches, which is that it causes problems for consequentialist ethics (Joe Carlsmith's Infinite Ethics is good on this). If what you mean by 'normalize everything' is to only consider the quantum weights (which are finite as mathematical measures) and not the number of worlds, then that seems more a case of ignoring those problems rather than addressing them.
I hope it was clear that I was suggesting a third approach (the number of worlds is neither finite, nor infinite, but indefinite) which does I think address the ethical problems better, since if there is no definite number of worlds then we have a reason to ignore the number of worlds and focus on the weights.
This third approach is based on the idea that 'worlds' are macroscopic, emergent phenomena created through decoherence (Wallace's book contains a full mathematical treatment of this). This supports both the claim that the number of worlds is indefinite (since it depends on ultimately arbitrary mappings of macroscopic to microscopic states) and the claim that worlds are created through quantum processes (since they are macroscopically indistinguishable before decoherence occurs). My point in the post was that these two claims in combination can avoid the repugnant conclusion via the approach of focusing on the weights.
(And when it comes to the virtue-theoretic implications, I've again tried to follow a weight-based approach, and not make assumptions about whether worlds are created or revealed.)
Thanks for the Egan suggestion, yea I love his work though need to read Quarantine more fully. It seems like the most philosophically relevant bit might be the ending which of course is the source of Egan's Law (it all adds up to normality). I also need to read his short story 'Singleton', which I gather is very relevant too.
If what you mean by 'normalize everything' is to only consider the quantum weights (which are finite as mathematical measures) and not the number of worlds, then that seems more a case of ignoring those problems rather than addressing them.
I mean that the amount of universes that is created will be created anyway, just as a consequence of time passing. So it doesn't matter anyway. If your actions e.g. cause misery in 20% of those worlds, then the fraction is all that matters; the worlds will exist anyway, and the total amount is not something you're affecting or controlling.
This third approach is based on the idea that 'worlds' are macroscopic, emergent phenomena created through decoherence (Wallace's book contains a full mathematical treatment of this). This supports both the claim that the number of worlds is indefinite (since it depends on ultimately arbitrary mappings of macroscopic to microscopic states) and the claim that worlds are created through quantum processes (since they are macroscopically indistinguishable before decoherence occurs). My point in the post was that these two claims in combination can avoid the repugnant conclusion via the approach of focusing on the weights.
I honestly don't think decoherence means the worlds are indefinite. I think it means they are an infinite continuum with the cardinality of the reals. Decoherence is just something you observe when you divide system from environment, in reality the Universe should have only a single, always coherent, giant wavefunction.
I think all the same arguments that it doesn't change decisions also apply to why it doesn't change virtue evaluations. It still all adds up to normality. It's still unimaginably big. Our actions as well as our beliefs and evaluations are irrelevant at most scales of measurement.
OK I think I see where you're coming from - but I do think the unimaginable bigness of the universe has more 'irrelevance' implications for a consequentialist view which tries to consider valuable states of the universe than for a virtue approach which considers valuable states of yourself. Also if you think the implication of physics is that everything is irrelevant, that seems like an important implication in it's own right, and different from 'normality' (the normal way most people think about ethics, which assumes that some things actually are relevant).
Note that the argument whether MWI changes anything is very different from the argument about what matters and why. I think it doesn't change anything, independently of how much what things in-universe matter.
Separately, I tend to think "mattering is local". I don't argue as strongly for this, because it's (recursively) a more personal intuition, less supported by type-2 thinking.
OK but your original comment reads like you're offering things not mattering cosmically as a reason for thinking MWI doesn't change anything (if that's not a reason, then you haven't given any reason, you've just stated your view). And I think that's a good argument - if you have general reasons that are independent of specific physics to think nothing matters (cosmically), then it will follow that nothing matters in MWI as well. I was responding to that argument.
“Decoherence causes the Universe to develop an emergent branching structure. The existence of this branching is a robust (albeit emergent) feature of reality; so is the mod-squared amplitude for any macroscopically described history. But there is no non-arbitrary decomposition of macroscopically-described histories into ‘finest-grained’ histories, and no non-arbitrary way of counting those histories.”
Importantly though, on this approach it is still possible to quantify the combined weight (mod-squared amplitude) of all branches that share a certain macroscopic property, e.g. by saying:
“Tomorrow, the branches in which it is sunny will have combined weight 0.7”
There is no non-arbitrary definition of "sunny". If you are fine with approximations, then you can also decide on decomposition of wavefunction into some number of observers - it's the same problem as decomposing classical world that allows physical splitting of thick computers according to macroscopic property "number of people".
You're right that you can just take whatever approximation you make at the macroscopic level ('sunny') and convert that into a metric for counting worlds. But the point is that everyone will acknowledge that the counting part is arbitrary from the perspective of fundamental physics - but you can remove the arbitrariness that derives from fine-graining, by focusing on the weight. (That is kind of the whole point of a mathematical measure.)
But why would you want to remove this arbitrariness? Your preferences are fine-grained anyway, so why retain classical counting, but deny counting in the space of wavefunction? It's like saying "dividing world into people and their welfare is arbitrary - let's focus on measuring mass of a space region". The point is you can't remove all decision-theoretic arbitrariness from MWI - "branching indifference" is just arbitrary ethical constraint that is equivalent to valuing measure for no reason, and without it fundamental physics, that works like MWI, does not prevent you from making decisions as if quantum immortality works.
I don't get why you would say that the preferences are fine-grained, it kinda seems obvious to me that they are not fine-grained. You don't care about whether worlds that are macroscopically indistinguishable are distinguishable at the quantum level, because you are yourself macroscopic. That's why branching indifference is not arbitrary. Quantum immortality is a whole other controversial story.
Because scale doesn't matter - it doesn't matter if you are implemented on thick or narrow computer.
First of all, macroscopical indistinguishability is not fundamental physical property - branching indifference is additional assumption, so I don't see how it's not as arbitrary as branch counting.
But more importantly, branching indifference assumption is not the same as informal "not caring about macroscopically indistinguishable differences"! As Wallace showed, branching indifference implies the Born rule implies you almost shouldn't care about you in a branch with a measure of 0.000001 even though it may involve drastic macroscopic difference for you in that branch. You being macroscopic doesn't imply you shouldn't care about your low-measure instances.
First of all, macroscopical indistinguishability is not fundamental physical property - branching indifference is additional assumption, so I don't see how it's not as arbitrary as branch counting.
You're right it's not a fundamental physical property - the overall philosophical framework here is that things can be real - as emergent entities - without being fundamental physical properties. Things like lions, and chairs are other examples.
But more importantly, branching indifference assumption is not the same as informal "not caring about macroscopically indistinguishable differences"!
This is how Wallace defines it (he in turn defines macroscopically indistinguishable in terms of providing the same rewards). It's his term in the axiomatic system he uses to get decision theory to work. There's not much to argue about here?
As Wallace showed, branching indifference implies the Born rule implies you almost shouldn't care about you in a branch with a measure of 0.000001 even though it may involve drastic macroscopic difference for you in that branch. You being macroscopic doesn't imply you shouldn't care about your low-measure instances.
Yes this is true. Not caring about low-measure instances is a very different proposition from not caring about macroscopically indistinguishable differences. We should care about low-measure instances in proportion to the measure, just as in classical decision theory we care about low-probability instances in proportion to the probability.
Things like lions, and chairs are other examples.
And counted branches.
This is how Wallace defines it (he in turn defines macroscopically indistinguishable in terms of providing the same rewards). It’s his term in the axiomatic system he uses to get decision theory to work. There’s not much to argue about here?
His definition leads to contradiction with informal intuition that motivates consideration of macroscopical indistinguishability in the first place.
We should care about low-measure instances in proportion to the measure, just as in classical decision theory we care about low-probability instances in proportion to the probability.
Why? Wallace's argument is just "you don't care about some irrelevant microscopic differences, so let me write this assumption that is superficially related to that preference, and here - it implies the Born rule". Given MWI, there is nothing wrong physically or rationally in valuing your instances equally whatever their measure is. Their thoughts and experiences don't depend on measure the same way they don't depend on thickness or mass of a computer implementing them. You can rationally not care about irrelevant microscopic differences and still care about number of your thin instances.
I'm not at all saying the experiences of a person in a low-weight world are less valuable than a person in a high-weight world. Just that when you are considering possible futures in a decision-theoretic framework you need to apply the weights (because weight is equivalent to probability).
Wallace's useful achievement in this context is to show that there exists a set of axioms that makes this work, and this includes branch-indifference.
This is useful because makes clear the way in which the branch-counting approach you're suggesting is in conflict with decision theory. So I don't disagree that you can care about the number of your thin instances, but what I'm saying is in that case you need to accept that this makes decision theory and probably consequentialist ethics impossible in your framework.
It doesn't matter whether you call your multiplier "probability" or "value" if it results in your decision to not care about low-measure branch. The only difference is that probability is supposed to be about knowledge, and Wallace's argument involving arbitrary assumption, not only physics, means it's not probability, but value - there is no reason to value knowledge of your low-measure instances less.
this makes decision theory and probably consequentialist ethics impossible in your framework
It doesn't? Nothing stops you from making decisions in a world where you are constantly splitting. You can try to maximize splits of good experiences or something. It just wouldn't be the same decisions you would make without knowledge of splits, but why new physical knowledge shouldn't change your decisions?
OK 'impossible' is too strong, I should have said 'extremely difficult'. That was my point in footnote 3 of the post. Most people would take the fact that it has implications like needing to "maximize splits of good experiences" (I assume you mean maximise the number of splits) as a reductio ad absurdum, due to the fact that this is massively different from our normal intuitions about what we should do. But some people have tried to take that approach, like in the article I mentioned in the footnote. If you or someone else can come up with a consistent and convincing decision approach that involves branch counting I would genuinely love to see it!
And one of Wallace’s axioms, which he calls ‘branching indifference’, essentially says that it doesn’t matter how many branches there are, since macroscopic differences are all that we care about for decisions..
The macroscopically different branches and their weights?
Focussing on the weight isn't obviously correct , ethically. You cant assume that the answer to "what do I expect to see" will work the same as the answer to "what should I do". Is-ought gap and all that.
Its tempting to think that you can apply a standard decision theory in terms of expected value to Many Worlds, since it is a matter of multiplying subjective value by probability. It seems reasonable to assess the moral weight of someone else's experiences and existence from their point of view. (Edit: also, our experiences seem fully real to us, although we are unlikely to be in a high measure world) That is the intuition behind the common rationalist/utilitarian/EA view that human lives don't decline in moral worth with distance. So why should they decline with lower quantum mechanical measure?
There is quandary here: sticking to the usual "adds up to normality" principle,as an apriori axiom means discounting the ethical importance of low-measure worlds in order to keep your favourite decision theory operating in the usual single-universe way...even if you are in a multiverse. But sticking to the equally usual universalist axiom, that you dont get to discount someone's moral worth on the basis of factors that aren't intrinsic to them, means you should not discount..and that the usual decision theory does not apply.
Basically, there is a tension between four things Rationalists are inclined to believe in:-
Some kind of MWI is true.
Some kind of utilitarian and universalist ethics is true.
Subjective things like suffering are ethically relevant. It's not all about number of kittens
It's all business as normal...it all adds up to normality.. fundamental ontological differences should not affect your decision theory.
That is the intuition behind the common rationalist/utilitarian/EA view that human lives don't decline in moral worth with distance. So why should they decline with lower quantum mechanical measure?
For the same reason that they decline with classical measure. Two people are worth more than one. And with classical probability measure. A 100% chance of someone surviving something is better than a 50% chance.
They are not the same things though. Quantum mechanical measure isn’t actually a head count, like classical measure. The theory doesn’t say that—it’s an extraneous assumption. It might be convenient if it worked that way, but that would be assuming your conclusion.
QM measure isn’t probability—the probability of something occurring or not—because all possible branches occur in MWI.
Another part of the problem stems from the fact that what other people experience is relevant to them, whereas for a probability calculation, I only need to be able to statistically predict my own observations. Using QM to predict my own observations, I can ignore the question of whether something has a ten percent chance of happening in the one and only world, or a certainty of happening in one tenth of possible worlds. However, these are not necessarily equivalent ethically.
They are not the same things though. Quantum mechanical measure isn’t actually a head count, like classical measure. The theory doesn’t say that—it’s an extraneous assumption. It might be convenient if it worked that way, but that would be assuming your conclusion.
QM measure isn’t probability—the probability of something occurring or not—because all possible branches occur in MWI.
So whence the Born probabilities, that underly the predictions of QM? I am not well versed in QM, but what is meant by quantum mechanical measure, if not those probabilities?
According the many-worlds interpretation (MWI) of quantum mechanics, the universe is constantly splitting into a staggeringly large number of decoherent branches containing galaxies, civilizations, and people exactly like you and me
There is more than one many worlds interpretation. The version stated above is not known to be true.
There is an approach to MWI based on coherent superpositions, and a version based on decoherence. These are (for all practical purposes) incompatible. Coherent splitting gives you the very large numbers of "worlds"..except that they are not worlds, conceptually.
Many worlders are pointing at something in the physics and saying "that's a world"....but whether it qualifies as a world is a separate question , and a separate kind of question, from whether it is really there in the physics. One would expect a world, or universe, to be large, stable, non-interacting, objective and so on . A successful MWI needs to jump three hurdles: mathematical correctness, conceptual correctness, and empirical correctness.
Decoherent branches are expected to be large, stable, non interacting, objective and irreversible...everything that would be intuitively expected of a "world". But there is no empirical evidence for them , nor are they obviously supported by the core mathematics of quantum mechanics, the Schrödinger equation. Coherent superpositions are small scale , down to single particles, observer dependent, reversible, and continue to interact (strictly speaking , interfere) after "splitting".
(Note that Wallace has given up on the objectivity of decoherent branches. That's another indication that MWI is not a single theory).
There isn’t the slightest evidence that irrevocable splitting, splitting into decoherent branches occurs at every microscopic event -- that would be combining the frequency of coherent style splitting with the finality of decoherent splitting. We dont know much about decoherence , but we know it is a multi-particle process that takes time, so decoherent splitting, if there is such a thing, must be rarer than the frequency of single particle interactions. ( And so decoherence isn't simple ). As well as the conceptual incoherence, there is In fact plenty of evidence—eg. the existence of quantum computing—that it doesnt work that way
Also see
I’m not going to argue for this view as that was done very well by Eliezer in his Quantum Physics.
Which view? Everetts view? DeWitts view? Deutsch's Zeh's view? Wallace's view? Saunders view?
I feel like branches being in fact an uncountable continuum is essentially a given
Decoherent branches being being countable, uncountable, or anything else is not given, since there is no established theory of of decoherence.
It's a given that some observables have continuous spectra..but what's that got to do with splitting? A observed state that isn't sharp (in some basis) can get entangled with an apparatus, which then goes into a non-sharp state, and so on. And the whole shebang never splits , or becomes classically sharp.
I mean that the amount of universes that is created will be created anyway, just as a consequence of time passing. So it doesn’t matter anyway. If your actions e.g. cause misery in 20% of those worlds, then the fraction is all that matters; the worlds will exist anyway, and the total amount is not something you’re affecting or controlling.
That's a special case of "no moral responsibility under determinism". which might be true , but it's very different from "utilitarianism works fine under MWI".
**Enough of the physics confusions -- onto the ethics confusions!""
As well as confusion over the correct version of many worlds, there is of course confusion about which theory of ethics is correct.
There's broadly three areas where MWI has ethical implications. One is concerned with determinism, freedom of choice, and moral responsibility. One is over the fact that MW means low probability events have to happen every time -- as opposed to single universe physics, where they usually don't. The other is over whether they are discounted in moral significance for being low in quantum mechanical measure or probability
MWI and Free Will
MWI allows probabilities of world states to change over time, but doesn't allow them to be changed, in a sense amounting to libertarian free will. Agents are just part of the universal wave function, not anything outside the system, or operating by different rules.MWI is, as it's proponents claim, a deterministic theory, and it only differs from single world determinism in that possible actions can't be refrained from, and possible futures can't be avoided. Alternative possibilities are realities, in other words.
MWI, Moral Responsibility, and Refraining.
A standard argument holds that causal determinism excludes libertarian free will by removing alternative possibilities. Without alternative possibilities, you could but have done other than you did, and , the argument goes, you cannot be held responsible for what you had no choice but to do.
Many world strongly implies that you make all possible decisions: according to David Deutsch's argument that means it allows alternative possibilities, and so removes the objection from moral responsibility despite being a basically deterministic theory.
However, deontology assumed that performing a required act involves restraining from alternatives.. and that it is possible to retain from forbidden acts. Neither is possible under many worlds. Many worlds creates the possibility, indeed the necessity, of doing otherwise, but removes the possibility of refraining from an act. Even though many worlds allows Alternative Possibilities, unfortunately for Deutschs argument, that other aspects create a similar objection on the basis of moral responsibility: why would you hold someone morally responsible for an act if they could not refrain from it?
MWI, Probability, and Utilitarian Ethics
Its tempting to think that you can apply a standard decision theory in terms of expected value to Many Worlds, since it is a matter of multiplying subjective value by probability. One wrinkle is that QM measure isn't probability -- the probability of something occurring or not -- because all possible branches occur in MWI. Another is that it is reasonable to assess the moral weight of someone else's experiences and existence from their point of view. That is the intuition behind the common rationalist/utilitarian/EA view that human lives don't decline in moral worth with distance. So why should they decline with lower quantum mechanical measure? There is quandary here: sticking to the usual "adds up to normality" principle,as an apriori axiom means discounting the ethical importance of low-measure worlds in order to keep your favourite decision theory operating in the usual single-universe way, even if you are in a multiverse. But sticking to the equally usual universalist axiom, that that you dont get to discount someone's moral worth on the basis of factors that aren't intrinsic to them, means you should not
Measure is not probability.
Mathematically, Quantum mechanical measure—amplitude—isn’t ordinary probability, which is why you need the Born rule.The point of the Born rule is to get a set of ordinary probabilities, which you can then test frequentistically, over a run of experiments. Ontologcally, it also not probability, because it does not represent the likelihood of one happening instead of another. And it has its own role, unlike that if ordinary probability, which is explaining how much contribution to a coherent superposition each component state makes (although what that means in the case of irrevocably decohered branches is unclear)
Whether you are supposed to care about them ethically is very unclear, since it is not clear how utilitarian style ethics would apply, even if you could make sense of the probabilities. But you are not supposed to care about them for the purposes of doing science, since they can no longer make any difference to your branch. MWI works like a collapse theory in practice.
The Ethical Weight or Low Measure Worlds
MWI creates the puzzle that low probability outcomes still happen, and have to be taken into account ethically. Many rationalists assume that they simply matter less, because that is the only way to restore anything like a normal view of ethical action -- but one should not assume something merely because it is convenient.
It can be argued that most decision theoretic calculations come out the same under different interpretations of QM...but altruistic ethics is different. In standard decision theory, you can tell directly how much utility you are getting; but in altruistic ethics , you are not measuring your suffering/happiness, you are assessing someone else's...and in the many worlds setting, that means solving the problem of how they are affected by their measure. It is not clear how low measure worlds should be considered in utilitarian ethics. It's tempting to ethically discount low measure worlds in some way, because that most closely approximates conventional single world utilitarianism. The alternative might force one to the conclusion that overall good outcomes are impossible to attain , so long as one cannot reduce the measures of worlds full of suffering zero. However, one should not jump to the conclusion that something is true just because it is convenient. And of course, MWI is a scientific theory so it doesn't comes with built in ethics
One part of the problem is that QM measure isn't probability, because all possible branches occur in MWI. Another stems from the fact that what other people experience is relevant to them, wheareas for a probability calculation, I only need to be able to statistically predict my own observations.. Using QM to predict my own observations, I can ignore the question of whether something has a ten percent chance of happening in the one and only world, or a certainty of happening in one tenth of possible worlds. However, these are not necessarily.equivalent ethically.
Suppose they low measure worlds are discounted ethically. If people in low measure worlds experience their suffering fully, then a 1%, of creating a hell-world would be equivalent in suffering to a 100% chance, and discount is unjustified. But if people in low measure worlds are like philosophical zombies, with little or no phenomenal consciousness, so that their sensations are faint or nonexistent, the moral hazard is much lower, and the discount is justified. A point against discounting is that our experiences seem fully real to us, although we are unlikely to be in a high measure world
A similar, but slightly less obvious argument applies to causing death. Causing the "death" of a complete zombie is presumably as morally culpable as causing the death of a character in a video game...which, by common consent, is not problem at all. So... causing the death of a 50% zombie would be only half as bad as killing a real person...maybe.
Classical Measure isn't Quantum Mechanical Measure
A large classical universe is analogous to Many Worlds in that the same structures -- the same people and planets -- repeat over long distances. It's even possible to define a measure, by counting repetitions up to a certain level of similarity. And one has the option if thinking about Quantum Mechanical measure that way,as a "head count"....but one is not forced to do so. On one hand, it features normality, on the other hand It is not "following the maths" ,because there's nothing in the formalism to suggest summing a number of identical low measure states is the only way to get a high measure one. So, again, it’s an extraneous assumption, and circular reasoning .
Ethical Calculus is not Decision Theory
Of course, MWI doesn't directly answer the question about consciousness and zombiehood .You can have objective information about observations, and if your probability calculus is wrong , you will get wrong results and know that you are getting wrong results. That is the negative feedback that allows physics to be less wrong. And you can have subjective information about your own mental states, and if your personal calculus is wrong , you will get wrong results and know that you are getting wrong results. That is the negative feedback that allows personal decision theory to be less wrong.
Altruistic ethics is different. You don't have either kind of direct evidence, because you are concerned with other people's subjective sensations , not objective evidence , or your own subjectivity. Questions about ethics are downstream of questions about qualia, and qualia are subjective, and because they are subjective, there is no reason to expect them to behave like third person observations.
"But it all adds up to normality!"
If "it all" means every conjecture you can come up with, no It doesn't. Most conjectures are wrong. The point of empirical testing is to pick out the right ones -- the ones that make correct predictions, save appearances, add up to normality That's a difficult process, not something you get for free.
So "it all adds up to normality" is not some universal truth And ethical theories relating to someone else's feelings are difficult to test, especially if someone else is in the far future, or an unobservable branch of the multiverse. Testability isn't an automatic given either.
There are no major ethical implications at all...Wallace makes a similar claim in his book: “But do [the many worlds in MWI] matter to ordinary, banal thought, action and language? Friendship is still friendship. Boredom is still boredom. Sex is still sex
That's very narrow circle ethics, if it's ethics at all --he just likes a bunch of things that impact him directly And it's rather obvious that small circle ethical theories have the least interaction with large universe physical theories. So it likely he hasn't even considered the question of altruistic ethics in many worlds, and is therefore coming to the conclusion that it all adds up to normality rather cheaply. It's his ethical outlook that is the structural element , not his take on MWI.
What kinds of ethical implications should we expect from the Many-Worlds Interpretation of Quantum Mechanics (MWI)? I’ll argue that we shouldn’t expect decision-making to change. The implications are more about how we should think or feel about events in our lives, and the virtues of taking a cosmic perspective.
According the many-worlds interpretation (MWI) of quantum mechanics, the universe is constantly splitting into a staggeringly large number of decoherent branches containing galaxies, civilizations, and people exactly like you and me[1].
You might think such a metaphysically radical theory should have pretty radical implications for how one should live. The quantum physicist John Bell once wrote “if such a theory were taken seriously, it would hardly be possible to take anything else seriously”.
But proponents of MWI - including both Eliezer and David Wallace - have concluded the opposite. Eliezer quotes Egan's Law: It all adds up to normality. There are no major ethical implications at all[2].
I’ll argue that it's important to distinguish between two kinds of ethical implications we might expect MWI to have, which I’ll call ‘decision-theoretic’ and ‘virtue-theoretic’ (I’ll explain what I mean by these names).
Eliezer and Wallace are right that MWI doesn’t have decision-theoretic implications. But they overlook the fact that MWI plausibly has implications for virtue theory.
Decision theory in the multiverse
The main reason for thinking MWI has no significant implications for ethics comes from decision theory.
In standard decision theory you try to calculate the expected value for a particular course of action by multiplying the utility of each possible consequence by the probability of that consequence occurring.
The main difference in MWI is that each possible consequence corresponds to a world that actually ends up existing, rather than being just hypothetical.
But this makes no difference to the expected value that the calculation spits out. As Eliezer puts it:
So it seems that we end up making the same decisions in MWI as we would otherwise, which in turn seems to imply that MWI has no significant implications for ethics.
Problems for decision theory
Now, one can question this argument. Those who argue that decision theory does work differently in MWI, usually start from a version of MWI in which it makes sense to count the number of worlds.
If you allow ‘branch-counting’, as this approach has been called, then decision theory seems to break down. To take a simple example, suppose you do a quantum experiment with two possible outcomes - your measurement apparatus makes a beep or it doesn't.
On the branch-counting approach, where there was previously one world, there are now two: each containing the same people, animals and other valuable objects - except for the beep.
The question is: do you now also have lots more value? Consequentialist approaches to ethics (ones which say for example that two happy people are better than one) would seem to imply that you do, and that therefore doing the experiment is extremely desirable - or possibly extremely bad, if you think total disvalue outweighed total value before the split.
And of course from a decision-theoretic perspective it seems this evaluation of consequences should inform the utilities we assign in order to calculate expected value.
It’s true that this simple example ignores the fact that in MWI branching is happening all the time.
But that fact just makes the decision-theoretic situation worse. If we're allowed to count branches, the number of worlds, and therefore the amount of value and disvalue, is rapidly increasing all the time.
Of course this seems to be a reductio ad absurdum[3], but which premise do we let go of? Do we reject the branch-counting approach to MWI or reject the consequentialist approach to calculating value?
Indefinite numbers of worlds
Fortunately for consequentialists, David Wallace has developed a detailed version of MWI that does not involve branch counting. The number of worlds that result from quantum processes, on this view, is in fact undefined. As he puts it:
Importantly though, on this approach it is still possible to quantify the combined weight (mod-squared amplitude) of all branches that share a certain macroscopic property, e.g. by saying:
This allows Wallace to build up a detailed model of how decision theory works in MWI - and how it produces the same results as classical decision theory, as Eliezer suggests.
Wallace shows that by choosing a specific set of sensible axioms, you can formally prove the Born rule in quantum mechanics, which states that mod-squared amplitudes can be treated as probabilities.
And one of Wallace’s axioms, which he calls ‘branching indifference’, essentially says that it doesn’t matter how many branches there are, since macroscopic differences are all that we care about for decisions.
So Wallace’s proof confirms that in order for decision-theory to give sensible results in MWI, you need to stop thinking about numbers of branches; and he thinks that’s OK because numbers of branches are in fact undefined.
All of which is to say that there is indeed a way MWI ‘adds up to normality’. You can still get decision theory to give you the same results as before - it just takes a bit of housekeeping to iron out branch-counting wrinkles.
Virtue theory and virtue ethics
So Wallace and Eliezer are plausibly right that MWI doesn’t have ethical implications in the decision-theoretic sense outlined above.
The mistake is to conclude that MWI has no ethical implications at all. The focus on decision theory leads us to overlook other kinds of ethical implications MWI could have.
A sizable portion of (both contemporary and historical) ethical theory is not about decisions at all, but rather: what kind of person to be, what kinds of character traits are desirable and how one should think and feel about situations.
It’s common to think of ‘virtue ethics’ - understood as the approach to ethics (deriving ultimately from Aristotle) in which such things are treated as fundamental - as one of the three main approaches to ethical theory, the others being the deontological (Kantian) and consequentialist (deriving from Bentham and Mill’s Utilitarianism) approaches.
But you don’t need to be in the ‘virtue ethics’ camp to think virtue is worth understanding. Consequentialist and deontological approaches to virtue exist as well.
For instance a consequentialist might propose that what makes a trait virtuous is its tending to lead to good consequences. And the well-known difficulties involved in actually quantifying the utilities of all possible consequences are among the reasons for consequentialists to show interest in virtue[4].
In short, it’s possible for those from a variety of perspectives to agree that the focus on decision-making leaves out a great deal of ethics.
So even if MWI doesn’t have decision-theoretic implications, it could still have virtue-theoretic ones. For example, it could have implications for how we should think or feel about our location within the multiverse.
Wisdom in the multiverse
To make such implications seem not only technically possible but also plausible, I'll now sketch out some specific virtue-theoretic implications of MWI (I'll aim to go into more detail on these in future posts).
Firstly, consider that there's a certain kind of anxiety and regret associated with having to choose between two mutually exclusive good options. It seems plausible that MWI could help us feel better about such choices, if it's true there's a world in which you actually experience the other good option.
Secondly, consider the simple fact that if you find yourself in an extremely unlucky personal situation - a car crash, say, or getting cancer - then MWI implies that there are other worlds, with high quantum weights, in which you are not so unlucky.
Again this is plausibly a consoling thought, similar in kind to the consoling thoughts recommended by philosophical traditions like stoicism.
Likewise, if you're in what you estimate as the bad end of the spectrum of physically possible 'timelines' of global history, it seems consoling to know that those other timelines are real.
From a virtue-theoretic perspective, we could say that it’s good to develop the disposition to take the wider cosmic perspective these thoughts assume, and so enhance one’s equanimity (a standard goal of classical virtue theory[5] which is arguably linked to both well-being and effective action).
Our cosmic situation
Zooming out further, there is also the ability to take the widest possible cosmic perspective, and consider one’s place in the quantum multiverse as whole.
Other fundamental scientific theories have been taken to have implications of this sort.
For instance, the second law of thermodynamics, and the theory of evolution have both been taken to imply that the universe as a whole is essential hostile to human interests.
In 'A free man's worship'. Bertrand Russell proposed that the second law of thermodynamics is a kind of foundation for one's overall philosophical perspective:
In a similar vein, Eliezer's discussion comparing evolution to a blind, idiot God ends with the suggestion that our basic stance towards the universe should be confrontational[6]:
Similarly, MWI plausibly has implications for our assessment of the goodness or badness of the cosmos as a whole: whether we should feel at home in nature, or set against a hostile universe.
Again taking a virtue-theoretic perspective, we might say that the virtue of wisdom requires an accurate appreciation - both intellectually and emotionally - of our place in the multiverse.
Summary
As I said at the start, MWI is a metaphysically radical theory that we might reasonably expect to have ethical consequences.
We’ve seen that proponents of MWI like Eliezer and Wallace, have arrived at the somewhat surprising conclusion that it actually doesn’t.
I’ve argued they're only half-right. They're right that MWI doesn’t have significant decision-theoretic implications. But it plausibly does have significant implications for virtue theory.
I'm not going to argue for this view as that was done very well by Eliezer in his Quantum Physics sequence. And in fact since that sequence was written MWI has become increasingly mainstream, so you can also read for example a major edited volume (2012) and David Wallace's 'The Emergent Multiverse' (2014) for painstaking academic support of the view.
Wallace makes a similar claim in his book: “But do [the many worlds in MWI] matter to ordinary, banal thought, action and language? Friendship is still friendship. Boredom is still boredom. Sex is still sex.” (p273)
Though like many a reductio ad absurdum the conclusion has been taken seriously, eg in this post.
A reminder here that Eliezer has a post called 'The Twelve Virtues of Rationality'.
See for example discussions of Ataraxia in Stoicism and Epicureanism.
Joe Carlsmith's sequence Otherness and control in the age of AGI is a good exploration of these and related ideas under the heading of 'deep atheism'.