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.
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.