That’s not true. (Or, at best, it’s misleading for present purposes.)
First, it’s important to keep in mind that if MWI is “untestable” relative to non-MWI, then non-MWI is also “untestable” relative to MWI. To use this as an argument against MWI, you’d need to talk specifically about which hypothesis MWI is untestable relative to; and you would then need to cite some other reason to reject MWI (e.g., its complexity relative to the other hypothesis, or its failures relative to some third hypothesis that it is testable relative to).
With that in mind:
1 - MWI is testable insofar as QM itself is testable. We normally ignore this fact because we’re presupposing QM, but it’s important to keep in mind if we’re trying to make a general claim like ‘MWI is unscientific because it’s untestable and lacks evidential support’. MWI is at least as testable as QM, and has at least as much supporting evidence.
2 - What I think people really mean to say (or what a steel-manned version of them would say) is that multiverse-style interpretations of QM are untestable relative to each other. This looks likely to be true, for practical purposes, when we’re comparing non-collapse interpretations: Bohmian Mechanics doesn’t look testable relative to Many Threads, for example. (And therefore Many Threads isn’t testable relative to Bohmian Mechanics, either.)
(Of course, many of the things we call “Many Worlds” are not fully fleshed out interpretations, so it’s a bit risky to make a strong statement right now about what will turn out to be testable in the real world. But this is at least a commonly accepted bit of guesswork on the part of theoretical physicists and philosophers of physics.)
3 - But, importantly, collapse interpretations generally are empirically distinguishable from non-collapse interpretations. So even though non-collapse interpretations are generally thought to be ‘untestable’ relative to each other, they are testable relative to collapse interpretations. (And collapse interpretations as a rule are falsifiable relative to each other.)
To date, attempts to test collapse interpretations have falsified the relevant interpretations. It is not technologically possible yet to test the most popular present-day ones, but it is possible for collapse theorists to argue ‘our views should get more attention because they’re easier to empirically distinguish’, and it’s also possible for anti-collapse theorists to try to make inductive arguments from past failures to the likelihood of future failures, with varying amounts of success.
I don’t have an argument against MWI specifically, no.
and you would then need to cite some other reason to reject MWI
No, that is not how it works: I don’t need to either accept or reject MWI. I can also treat it as a causal story lacking empirical content. Nothing wrong with such stories, they are quite helpful for understanding systems. But not a part of science.
MWI is testable insofar as QM itself is testable.
By that logic, if I invent any crazy hypothesis in addition to an empirically testable theory, then it inherits testability just on those grounds. You can do that with the word “testabiity” if you want, but that seems to be not how people use words.
If some smart catholic says that evolution is how God unfolds creation when it comes to living systems, then any specific claims we can empirically check pertaining to evolution (including those that did not pan out, and required repairs of evolutionary theory) also somehow are relevant to the catholic’s larger hypothesis? I suppose that is literally true, but silly. There is no empirical content to what this hypothetical catholic is saying, over and above the actual empirical stuff he is latching his baggage onto. I am not super interested in having catholic theologians read about minimum descriptive complexity, and then weaving a yarn about their favorite hypotheses based on that.
so it’s a bit risky to make a strong statement right now about what will turn out to be testable in the real world
I like money! I am happy to discuss bet terms on this.
collapse interpretations generally are empirically distinguishable from non-collapse interpretations
Yes if you have an interpretation that gives different predictions than QM, then yes that will render that interpretation falsifiable of course (and indeed some were). That is super boring, though, and not what this argument is about. But also, I don’t see what falsifiability of X has to do with falsifiabiliity of Y, if X and Y are different. Newtonian mechanics is both falsifiable and falsified, but that has little to do with falsifiability of any story fully consistent with QM predictions.
My personal take on MWI is I want to waste as little energy as possible on it and arguments about it, and actually go read Feynman instead. (This is not a dig at you, I am just explaining where I am coming from when it comes to physics).
No, that is not how it works: I don’t need to either accept or reject MWI. I can also treat it as a causal story lacking empirical content.
To say that MWI lacks empirical content is also to say that the negation of MWI lacks empirical content. So this doesn’t tell us, for example, whether to assign higher probability to MWI or to the disjunction of all non-MWI interpretations.
Suppose your ancestors sent out a spaceship eons ago, and by your calculations it recently traveled so far away that no physical process could ever cause you and the spaceship to interact again. If you then want to say that ‘the claim the spaceship still exists lacks empirical content,’ then OK. But you will also have to say ‘the claim the spaceship blipped out of existence when it traveled far enough away lacks empirical content’.
And there will still be some probability, given the evidence, that the spaceship did vs. didn’t blip out of existence; and just saying ‘it lacks empirical content!’ will not tell you whether to design future spaceships so that their life support systems keep operating past the point of no return.
By that logic, if I invent any crazy hypothesis in addition to an empirically testable theory, then it inherits testability just on those grounds. You can do that with the word “testabiity” if you want, but that seems to be not how people use words.
There’s no ambiguity if you clarify whether you’re talking about the additional crazy hypothesis, vs. talking about the conjunction ‘additional crazy hypothesis + empirically testable theory’. Presumably you’re imagining a scenario where the conjunction taken as a whole is testable, though one of the conjuncts is not. So just say that.
Sean Carroll summarizes collapse-flavored QM as the conjunction of these five claims:
Quantum states are represented by wave functions, which are vectors in a mathematical space called Hilbert space.
Wave functions evolve in time according to the Schrödinger equation.
The act of measuring a quantum system returns a number, known as the eigenvalue of the quantity being measured.
The probability of getting any particular eigenvalue is equal to the square of the amplitude for that eigenvalue.
After the measurement is performed, the wave function “collapses” to a new state in which the wave function is localized precisely on the observed eigenvalue (as opposed to being in a superposition of many different possibilities).
Many-worlds-flavored QM, on the other hand, is the conjunction of 1 and 2, plus the negation of 5 -- i.e., it’s an affirmation of wave functions and their dynamics (which effectively all physicists agree about), plus a rejection of the ‘collapses’ some theorists add to keep the world small and probabilistic. (If you’d like, you could supplement ‘not 5’ with ‘not Bohmian mechanics’; but for present purposes we can mostly lump Bohm in with multiverse interpretations, because Eliezer’s blog series is mostly about rejecting collapse rather than about affirming a particular non-collapse view.)
If we want ‘QM’ to be the neutral content shared by all these interpretations, then we can say that QM is simply the conjunction of 1 and 2. You are then free to say that we should assign 50% probability to claim 5, and maintain agnosticism between collapse and non-collapse views. But realize that, logically, either collapse or its negation does have to be true. You can frame denying collapse as ‘positing invisible extra worlds’, but you can equally frame denying collapse as ‘skepticism about positing invisible extra causal laws’.
Since every possible way the universe could be adds something ‘extra’ on top of what we observe—either an extra law (e.g., collapse) or extra ontology (because there are no collapses occurring to periodically annihilate the ontology entailed by the Schrodinger equation) -- it’s somewhat missing the point to attack any given interpretation for the crime of positing something extra. The more relevant question is just whether simplicity considerations or indirect evidence helps us decide which ‘something extra’ (a physical law, or more ‘stuff’, or both) is the right one. If not, then we stick with a relatively flat prior.
Claims 1 and 2 are testable, which is why we were able to acquire evidence for QM in the first place. Claim 5 is testable for pretty much any particular ‘collapse’ interpretation you have in mind; which means the negation of claim 5 is also testable. So all parts of bare-bones MWI are testable (though it may be impractical to run many of the tests), as long as we’re comparing MWI to collapse and not to Bohmian Mechanics.
(You can, of course, object that affirming 3-5 as fundamental laws has the advantage of getting us empirical adequacy. But ‘MWI (and therefore also ‘bare’ QM) isn’t empirically adequate’ is a completely different objection from ‘MWI asserts too many unobserved things’, and in fact the two arguments are in tension: it’s precisely because Eliezer isn’t willing to commit himself to a mechanism for the Born probabilities in the absence of definitive evidence that he’s sticking to ‘bare’ MWI and leaving almost entirely open how these relate to the Born rule. In the one case you’d be criticizing MWI theorists for refusing to stick their neck out and make some guesses about which untested physical laws and ontologies are the real ones; in the other case you’d be criticizing MWI theorists for making guesses about which untested physical laws and ontologies are the real ones.)
I am not super interested in having catholic theologians read about minimum descriptive complexity, and then weaving a yarn about their favorite hypotheses based on that.
Are you kidding? I would love it if theologians stopped hand-waving about how their God is ‘ineffably simple no really we promise’ and started trying to construct arguments that God (and, more importantly, the package deal ‘God + universe’) is information-theoretically simple, e.g., by trying to write a simple program that outputs Biblical morality plus the laws of physics. At best, that sort of precision would make it much clearer where the reasoning errors are; at worst, it would be entertainingly novel.
To say that MWI lacks empirical content is also to say that the negation of MWI lacks empirical content.
Yes.
So this doesn’t tell us, for example, whether to assign higher probability to MWI or to the disjunction of all non-
MWI interpretations.
Right. But I think it’s a waste of energy to assign probabilities to assertions lacking empirical content, because you will not be updating anyways, and a prior without possibility of data is just a slightly mathier way to formulate “your taste.” I don’t argue about taste.
[spaceship example]
One can assume a reasonable model here (e.g. leave a copy of the spaceship in earth orbit, or have it travel in a circle in the solar system, and assume similar degradation of modules). Yes, you will have indirect evidence only applicable due to your model. But I think the model here would have teeth.
But realize that, logically, either collapse or its negation does have to be true.
Or we are thinking about the problem incorrectly and those are not exhaustive/mutually exclusive. Compare: “logically the electron must either be a particle or must not be a particle.”
it’s somewhat missing the point to attack any given interpretation for the crime of positing something extra.
I am not explicitly attacking MWI, as I think I said multiple times. I am not even attacking having interpretations or preferring one over another for reasons such as “taste” or “having an easier time thinking about QM.” I am attacking the notion that there is anything more to the preference for MWI than this.
To summarize my view: “testability” is about “empirical claims,” not about “narratives.” MWI is, by its very nature, a narrative about empirical claims. The list of empirical claims it is a narrative about can certainly differ from another list of empirical claims with another narrative. For example, we can imagine some sort of “billiard ball Universe” narrative around Newtonian physics.
But I would not say “MWI is testable relative to the Newtonian narrative”, I would say “the list of empirical claims ‘QM’ is testable relative to the list of empirical claims ’Newtonian physics.”
The problem with the former statement is first it is a “type error,” and second, there are infinitely many narratives around any list of empirical claims. You may prefer MWI for [reasons] over [infinitely long list of other narratives], but it seems like “argument about taste.” What’s even the point of the argument?
Let’s say I prefer some other interpretation of ‘QM’ than MWI. What does that say about me? Does it say anything bad? Am I a ‘bad rationalist?’ Do I have ‘bad taste?’ Does it matter what my favorite interpretation is? I think this lesswrongian MWI thing is belief-as-attire.
Full disclaimer: I am not a professional philosopher, and do not think about testability for a living. I reviewed a paper about testability once.
Could you restate your response to the spaceship example? This seems to me to be an entirely adequate response to
it’s a waste of energy to assign probabilities to assertions lacking empirical content, because you will not be updating anyways, and a prior without possibility of data is just a slightly mathier way to formulate “your taste.” I don’t argue about taste.
Favoring simpler hypotheses matters, because if you’re indifferent to added complexity when it makes no difference to your observations (e.g., ‘nothing outside the observable universe exists’) you may make bad decisions that impact agents that you could never observe, but that might still live better or worse lives based on what you do.
This matters when you’re making predictions about agents far from you in space and/or time. MWI is a special case of the same general principle, so it’s a useful illustrative example even if it isn’t as important as those other belief-in-the-implied-invisible scenarios.
I am not even attacking having interpretations or preferring one over another for reasons such as “taste” or “having an easier time thinking about QM.” I am attacking the notion that there is anything more to the preference for MWI than this.
Collapse and non-collapse interpretations are empirically distinguishable from each other. I’ve been defining ‘QM’ in a way that leaves it indifferent between collapse and non-collapse—in which case you can’t say that the distinction between bare QM and MWI is just a matter of taste, because MWI adds the testable claim that collapse doesn’t occur. If you prefer to define ‘QM’ so that it explicitly rejects collapse, then yes, MWI (or some versions of MWI) is just a particular way of talking about QM, not a distinct theory. But in that case collapse interpretations of QM are incompatible with QM itself, which seems like a less fair-minded way of framing a foundations-of-physics discussion.
Collapse and non-collapse interpretations are empirically distinguishable from each other.
You are not engaging with my claim that testability is a property of empirical claims, not narratives. Not sure there is a point to continue until we resolve the disagreement about the possible category error here.
There is another weird thing where you think we test claims against other claims, but actually we test against Nature. If Nature says your claim is wrong, it’s falsified. If there is a possibility of Nature saying that, it’s falsifiable. You don’t need a pair of claims here. Testability is not a binary relation between claims. But that’s not central to the disagreement.
Why do you think collapse interpretations are ‘narratives’, and why do you think they aren’t empirical claims?
Regarding testability: if you treat testability as an intrinsic feature of hypotheses, you risk making the mistake of thinking that if there is no test that would distinguish hypothesis A from hypothesis B, then there must be no test that could distinguish hypothesis A from hypothesis C. It’s true that you can just speak of a test that’s better predicted by hypothesis ‘not-A’ than by hypothesis A, but the general lesson that testability can vary based on which possibilities you’re comparing is an important one, and directly relevant to the case we’re considering.
There are two issues, what I view as non-standard language use, and what I view as a category error.
You can use the word ‘testability’ to signify a binary relation, but that’s not what people typically mean when they use that word. They typically mean “possibility Nature can tell you that you are wrong.”
So when you responded many posts back with a claim “MWI is hard to test” you are using the word “test” in a way probably no one else in the thread is using. You are not wrong, but you will probably miscommunicate.
An empirical claim has this form: “if we do experiment A, we will get result B.” Nature will sometimes agree, and sometimes not, and give you result C instead. If you have a list of such claims, you can construct a “story” about them, like MWI, or something else. But adding the “story” is an extra step, and what Nature is responding to is not the story but the experiment.
The mapping from stories to lists of claims is always always always many to one. If you have [story1] about [list1] and [story2] about [list2], and Nature agrees with [list1], and disagrees with [list2], then you will say:
“story1 was falsified, story2 was falsifiable but not falsified.”
I will say:
“list1 was falsified, list2 was falsifiable but not falsified.”
What’s relevant here isn’t the details of story1 or story2, but what’s in the lists.
When I say “MWI is untestable” what I mean is:
“There is a list of empirical claims called ‘quantum mechanics.’ There is a set of stories about this list, one of which is MWI. There is no way to tell these stories apart empirically, so you pick the one you like best for non-empirical reasons.”
When you say “MWI is testable” what I think you mean is:
“There are two lists of empirical claims, called ‘quantum mechanics’ and ‘quantum mechanics prime,’ a story ‘story 1’ about the former, and a story ‘story 2’ about the latter. Nature will agree with the list ‘quantum mechanics’ and disagree with the list ‘quantum mechanics prime.’ Therefore, ‘story 1’ is testable relative to ‘story 2.’”
That’s fine, I understand what you mean, and I think you are right, up to the last sentence. But I think the last sentence is a category error.
Because you are equating lists of claims with stories, you are carrying over the testability property of the list ‘quantum mechanics’ to your favorite story about this list, ‘MWI.’ But there is an infinite list of stories consistent with ‘quantum mechanics’. I can replace ‘MWI’ in your argument with any other consistent story, including those involving the flying spaghetti monster, etc.
Then you get unintuitive statements like ‘the flying spaghetti interpretation of quantum mechanics is testable relative to X.’ This is a sufficiently weird use of the word “testable” that I think we should not use the word “testable” in this way. And indeed, I believe the standard usage of the word “testable” is not this.
At one point I started developing a religious RPG character who applied theoretical computer science to his faith.
I forget details, but among other details he believed that although the Bible prescribed the best way to live, the world is far too complex for any finite set of written rules to cover every situation. The same limitation applies to human reason: cognitive science and computational complexity theory have shown all the ways in which we are bounded reasoners, and can only ever hope to comprehend a small part of the whole world. Reason works best when it can be applied to constrained problems where clear objective answer can be found, but it easily fails once the number of variables grows.
Thus, because science has shown that both the written word of the Bible and human reason are fallible and easily lead us astray (though the word of the Bible is less likely to do so), the rational course of action for one who believes in science is to pray to God for guidance and trust the Holy Spirit to lead us to the right choices.
In so far as I understand what the “preferred basis problem” is actually supposed to be, the existence of a preferred basis seems to me to be not an assumption necessary for Everettian QM to work but an empirical fact about the world; if it were false then the world would not, as it does, appear broadly classical when one doesn’t look too closely. Without a preferred basis, you could still say “the wavefunction just evolves smoothly and there is no collapse”; it would no longer be a useful approximation to describe what happens in terms of “worlds”, but for the same reason you could not e.g. adopt a “collapse” interpretation in which everything looks kinda-classical on a human scale apart from random jumps when “observations” or “measurements” happen. The world would look different in the absence of a preferred basis.
But I am not very expert on this stuff. Do you think the above is wrong, and if so how?
First, it’s important to keep in mind that if MWI is “untestable” relative to non-MWI, then non-MWI is also “untestable” relative to MWI. To use this as an argument against MWI,
I think it’s being used as an argument against beliefs paying rent.
MWI is testable insofar as QM itself is testable.
Since there is more than one interpretation of QM, empirically testing QM does not prove any one interpretation over the others.
Whatever extra arguments are used to support a particular interpretation over the others are not going to be, and have not been, empirical.
But, importantly, collapse interpretations generally are empirically distinguishable from non-collapse interpretations.
No they are not, because of the meaning of the word “interpretation” but collapse theories, such as GRW, might be.
No, MWI is not unusually difficult to test. It is untestable.
That’s not true. (Or, at best, it’s misleading for present purposes.)
First, it’s important to keep in mind that if MWI is “untestable” relative to non-MWI, then non-MWI is also “untestable” relative to MWI. To use this as an argument against MWI, you’d need to talk specifically about which hypothesis MWI is untestable relative to; and you would then need to cite some other reason to reject MWI (e.g., its complexity relative to the other hypothesis, or its failures relative to some third hypothesis that it is testable relative to).
With that in mind:
1 - MWI is testable insofar as QM itself is testable. We normally ignore this fact because we’re presupposing QM, but it’s important to keep in mind if we’re trying to make a general claim like ‘MWI is unscientific because it’s untestable and lacks evidential support’. MWI is at least as testable as QM, and has at least as much supporting evidence.
2 - What I think people really mean to say (or what a steel-manned version of them would say) is that multiverse-style interpretations of QM are untestable relative to each other. This looks likely to be true, for practical purposes, when we’re comparing non-collapse interpretations: Bohmian Mechanics doesn’t look testable relative to Many Threads, for example. (And therefore Many Threads isn’t testable relative to Bohmian Mechanics, either.)
(Of course, many of the things we call “Many Worlds” are not fully fleshed out interpretations, so it’s a bit risky to make a strong statement right now about what will turn out to be testable in the real world. But this is at least a commonly accepted bit of guesswork on the part of theoretical physicists and philosophers of physics.)
3 - But, importantly, collapse interpretations generally are empirically distinguishable from non-collapse interpretations. So even though non-collapse interpretations are generally thought to be ‘untestable’ relative to each other, they are testable relative to collapse interpretations. (And collapse interpretations as a rule are falsifiable relative to each other.)
To date, attempts to test collapse interpretations have falsified the relevant interpretations. It is not technologically possible yet to test the most popular present-day ones, but it is possible for collapse theorists to argue ‘our views should get more attention because they’re easier to empirically distinguish’, and it’s also possible for anti-collapse theorists to try to make inductive arguments from past failures to the likelihood of future failures, with varying amounts of success.
I don’t have an argument against MWI specifically, no.
No, that is not how it works: I don’t need to either accept or reject MWI. I can also treat it as a causal story lacking empirical content. Nothing wrong with such stories, they are quite helpful for understanding systems. But not a part of science.
By that logic, if I invent any crazy hypothesis in addition to an empirically testable theory, then it inherits testability just on those grounds. You can do that with the word “testabiity” if you want, but that seems to be not how people use words.
If some smart catholic says that evolution is how God unfolds creation when it comes to living systems, then any specific claims we can empirically check pertaining to evolution (including those that did not pan out, and required repairs of evolutionary theory) also somehow are relevant to the catholic’s larger hypothesis? I suppose that is literally true, but silly. There is no empirical content to what this hypothetical catholic is saying, over and above the actual empirical stuff he is latching his baggage onto. I am not super interested in having catholic theologians read about minimum descriptive complexity, and then weaving a yarn about their favorite hypotheses based on that.
I like money! I am happy to discuss bet terms on this.
Yes if you have an interpretation that gives different predictions than QM, then yes that will render that interpretation falsifiable of course (and indeed some were). That is super boring, though, and not what this argument is about. But also, I don’t see what falsifiability of X has to do with falsifiabiliity of Y, if X and Y are different. Newtonian mechanics is both falsifiable and falsified, but that has little to do with falsifiability of any story fully consistent with QM predictions.
My personal take on MWI is I want to waste as little energy as possible on it and arguments about it, and actually go read Feynman instead. (This is not a dig at you, I am just explaining where I am coming from when it comes to physics).
To say that MWI lacks empirical content is also to say that the negation of MWI lacks empirical content. So this doesn’t tell us, for example, whether to assign higher probability to MWI or to the disjunction of all non-MWI interpretations.
Suppose your ancestors sent out a spaceship eons ago, and by your calculations it recently traveled so far away that no physical process could ever cause you and the spaceship to interact again. If you then want to say that ‘the claim the spaceship still exists lacks empirical content,’ then OK. But you will also have to say ‘the claim the spaceship blipped out of existence when it traveled far enough away lacks empirical content’.
And there will still be some probability, given the evidence, that the spaceship did vs. didn’t blip out of existence; and just saying ‘it lacks empirical content!’ will not tell you whether to design future spaceships so that their life support systems keep operating past the point of no return.
There’s no ambiguity if you clarify whether you’re talking about the additional crazy hypothesis, vs. talking about the conjunction ‘additional crazy hypothesis + empirically testable theory’. Presumably you’re imagining a scenario where the conjunction taken as a whole is testable, though one of the conjuncts is not. So just say that.
Sean Carroll summarizes collapse-flavored QM as the conjunction of these five claims:
Many-worlds-flavored QM, on the other hand, is the conjunction of 1 and 2, plus the negation of 5 -- i.e., it’s an affirmation of wave functions and their dynamics (which effectively all physicists agree about), plus a rejection of the ‘collapses’ some theorists add to keep the world small and probabilistic. (If you’d like, you could supplement ‘not 5’ with ‘not Bohmian mechanics’; but for present purposes we can mostly lump Bohm in with multiverse interpretations, because Eliezer’s blog series is mostly about rejecting collapse rather than about affirming a particular non-collapse view.)
If we want ‘QM’ to be the neutral content shared by all these interpretations, then we can say that QM is simply the conjunction of 1 and 2. You are then free to say that we should assign 50% probability to claim 5, and maintain agnosticism between collapse and non-collapse views. But realize that, logically, either collapse or its negation does have to be true. You can frame denying collapse as ‘positing invisible extra worlds’, but you can equally frame denying collapse as ‘skepticism about positing invisible extra causal laws’.
Since every possible way the universe could be adds something ‘extra’ on top of what we observe—either an extra law (e.g., collapse) or extra ontology (because there are no collapses occurring to periodically annihilate the ontology entailed by the Schrodinger equation) -- it’s somewhat missing the point to attack any given interpretation for the crime of positing something extra. The more relevant question is just whether simplicity considerations or indirect evidence helps us decide which ‘something extra’ (a physical law, or more ‘stuff’, or both) is the right one. If not, then we stick with a relatively flat prior.
Claims 1 and 2 are testable, which is why we were able to acquire evidence for QM in the first place. Claim 5 is testable for pretty much any particular ‘collapse’ interpretation you have in mind; which means the negation of claim 5 is also testable. So all parts of bare-bones MWI are testable (though it may be impractical to run many of the tests), as long as we’re comparing MWI to collapse and not to Bohmian Mechanics.
(You can, of course, object that affirming 3-5 as fundamental laws has the advantage of getting us empirical adequacy. But ‘MWI (and therefore also ‘bare’ QM) isn’t empirically adequate’ is a completely different objection from ‘MWI asserts too many unobserved things’, and in fact the two arguments are in tension: it’s precisely because Eliezer isn’t willing to commit himself to a mechanism for the Born probabilities in the absence of definitive evidence that he’s sticking to ‘bare’ MWI and leaving almost entirely open how these relate to the Born rule. In the one case you’d be criticizing MWI theorists for refusing to stick their neck out and make some guesses about which untested physical laws and ontologies are the real ones; in the other case you’d be criticizing MWI theorists for making guesses about which untested physical laws and ontologies are the real ones.)
Are you kidding? I would love it if theologians stopped hand-waving about how their God is ‘ineffably simple no really we promise’ and started trying to construct arguments that God (and, more importantly, the package deal ‘God + universe’) is information-theoretically simple, e.g., by trying to write a simple program that outputs Biblical morality plus the laws of physics. At best, that sort of precision would make it much clearer where the reasoning errors are; at worst, it would be entertainingly novel.
Yes.
Right. But I think it’s a waste of energy to assign probabilities to assertions lacking empirical content, because you will not be updating anyways, and a prior without possibility of data is just a slightly mathier way to formulate “your taste.” I don’t argue about taste.
One can assume a reasonable model here (e.g. leave a copy of the spaceship in earth orbit, or have it travel in a circle in the solar system, and assume similar degradation of modules). Yes, you will have indirect evidence only applicable due to your model. But I think the model here would have teeth.
Or we are thinking about the problem incorrectly and those are not exhaustive/mutually exclusive. Compare: “logically the electron must either be a particle or must not be a particle.”
I am not explicitly attacking MWI, as I think I said multiple times. I am not even attacking having interpretations or preferring one over another for reasons such as “taste” or “having an easier time thinking about QM.” I am attacking the notion that there is anything more to the preference for MWI than this.
To summarize my view: “testability” is about “empirical claims,” not about “narratives.” MWI is, by its very nature, a narrative about empirical claims. The list of empirical claims it is a narrative about can certainly differ from another list of empirical claims with another narrative. For example, we can imagine some sort of “billiard ball Universe” narrative around Newtonian physics.
But I would not say “MWI is testable relative to the Newtonian narrative”, I would say “the list of empirical claims ‘QM’ is testable relative to the list of empirical claims ’Newtonian physics.”
The problem with the former statement is first it is a “type error,” and second, there are infinitely many narratives around any list of empirical claims. You may prefer MWI for [reasons] over [infinitely long list of other narratives], but it seems like “argument about taste.” What’s even the point of the argument?
Let’s say I prefer some other interpretation of ‘QM’ than MWI. What does that say about me? Does it say anything bad? Am I a ‘bad rationalist?’ Do I have ‘bad taste?’ Does it matter what my favorite interpretation is? I think this lesswrongian MWI thing is belief-as-attire.
Full disclaimer: I am not a professional philosopher, and do not think about testability for a living. I reviewed a paper about testability once.
Could you restate your response to the spaceship example? This seems to me to be an entirely adequate response to
Favoring simpler hypotheses matters, because if you’re indifferent to added complexity when it makes no difference to your observations (e.g., ‘nothing outside the observable universe exists’) you may make bad decisions that impact agents that you could never observe, but that might still live better or worse lives based on what you do.
This matters when you’re making predictions about agents far from you in space and/or time. MWI is a special case of the same general principle, so it’s a useful illustrative example even if it isn’t as important as those other belief-in-the-implied-invisible scenarios.
Collapse and non-collapse interpretations are empirically distinguishable from each other. I’ve been defining ‘QM’ in a way that leaves it indifferent between collapse and non-collapse—in which case you can’t say that the distinction between bare QM and MWI is just a matter of taste, because MWI adds the testable claim that collapse doesn’t occur. If you prefer to define ‘QM’ so that it explicitly rejects collapse, then yes, MWI (or some versions of MWI) is just a particular way of talking about QM, not a distinct theory. But in that case collapse interpretations of QM are incompatible with QM itself, which seems like a less fair-minded way of framing a foundations-of-physics discussion.
You are not engaging with my claim that testability is a property of empirical claims, not narratives. Not sure there is a point to continue until we resolve the disagreement about the possible category error here.
There is another weird thing where you think we test claims against other claims, but actually we test against Nature. If Nature says your claim is wrong, it’s falsified. If there is a possibility of Nature saying that, it’s falsifiable. You don’t need a pair of claims here. Testability is not a binary relation between claims. But that’s not central to the disagreement.
Why do you think collapse interpretations are ‘narratives’, and why do you think they aren’t empirical claims?
Regarding testability: if you treat testability as an intrinsic feature of hypotheses, you risk making the mistake of thinking that if there is no test that would distinguish hypothesis A from hypothesis B, then there must be no test that could distinguish hypothesis A from hypothesis C. It’s true that you can just speak of a test that’s better predicted by hypothesis ‘not-A’ than by hypothesis A, but the general lesson that testability can vary based on which possibilities you’re comparing is an important one, and directly relevant to the case we’re considering.
There are two issues, what I view as non-standard language use, and what I view as a category error.
You can use the word ‘testability’ to signify a binary relation, but that’s not what people typically mean when they use that word. They typically mean “possibility Nature can tell you that you are wrong.”
So when you responded many posts back with a claim “MWI is hard to test” you are using the word “test” in a way probably no one else in the thread is using. You are not wrong, but you will probably miscommunicate.
An empirical claim has this form: “if we do experiment A, we will get result B.” Nature will sometimes agree, and sometimes not, and give you result C instead. If you have a list of such claims, you can construct a “story” about them, like MWI, or something else. But adding the “story” is an extra step, and what Nature is responding to is not the story but the experiment.
The mapping from stories to lists of claims is always always always many to one. If you have [story1] about [list1] and [story2] about [list2], and Nature agrees with [list1], and disagrees with [list2], then you will say:
“story1 was falsified, story2 was falsifiable but not falsified.”
I will say:
“list1 was falsified, list2 was falsifiable but not falsified.”
What’s relevant here isn’t the details of story1 or story2, but what’s in the lists.
When I say “MWI is untestable” what I mean is:
“There is a list of empirical claims called ‘quantum mechanics.’ There is a set of stories about this list, one of which is MWI. There is no way to tell these stories apart empirically, so you pick the one you like best for non-empirical reasons.”
When you say “MWI is testable” what I think you mean is:
“There are two lists of empirical claims, called ‘quantum mechanics’ and ‘quantum mechanics prime,’ a story ‘story 1’ about the former, and a story ‘story 2’ about the latter. Nature will agree with the list ‘quantum mechanics’ and disagree with the list ‘quantum mechanics prime.’ Therefore, ‘story 1’ is testable relative to ‘story 2.’”
That’s fine, I understand what you mean, and I think you are right, up to the last sentence. But I think the last sentence is a category error.
Because you are equating lists of claims with stories, you are carrying over the testability property of the list ‘quantum mechanics’ to your favorite story about this list, ‘MWI.’ But there is an infinite list of stories consistent with ‘quantum mechanics’. I can replace ‘MWI’ in your argument with any other consistent story, including those involving the flying spaghetti monster, etc.
Then you get unintuitive statements like ‘the flying spaghetti interpretation of quantum mechanics is testable relative to X.’ This is a sufficiently weird use of the word “testable” that I think we should not use the word “testable” in this way. And indeed, I believe the standard usage of the word “testable” is not this.
At one point I started developing a religious RPG character who applied theoretical computer science to his faith.
I forget details, but among other details he believed that although the Bible prescribed the best way to live, the world is far too complex for any finite set of written rules to cover every situation. The same limitation applies to human reason: cognitive science and computational complexity theory have shown all the ways in which we are bounded reasoners, and can only ever hope to comprehend a small part of the whole world. Reason works best when it can be applied to constrained problems where clear objective answer can be found, but it easily fails once the number of variables grows.
Thus, because science has shown that both the written word of the Bible and human reason are fallible and easily lead us astray (though the word of the Bible is less likely to do so), the rational course of action for one who believes in science is to pray to God for guidance and trust the Holy Spirit to lead us to the right choices.
Plus 6: There is a preferred basis.
In so far as I understand what the “preferred basis problem” is actually supposed to be, the existence of a preferred basis seems to me to be not an assumption necessary for Everettian QM to work but an empirical fact about the world; if it were false then the world would not, as it does, appear broadly classical when one doesn’t look too closely. Without a preferred basis, you could still say “the wavefunction just evolves smoothly and there is no collapse”; it would no longer be a useful approximation to describe what happens in terms of “worlds”, but for the same reason you could not e.g. adopt a “collapse” interpretation in which everything looks kinda-classical on a human scale apart from random jumps when “observations” or “measurements” happen. The world would look different in the absence of a preferred basis.
But I am not very expert on this stuff. Do you think the above is wrong, and if so how?
I think it’s being used as an argument against beliefs paying rent.
Since there is more than one interpretation of QM, empirically testing QM does not prove any one interpretation over the others. Whatever extra arguments are used to support a particular interpretation over the others are not going to be, and have not been, empirical.
No they are not, because of the meaning of the word “interpretation” but collapse theories, such as GRW, might be.