I don’t think that the QM example is like the others. Explaining this requires a bit of detail.
From section V.:
My understanding of the multiverse debate is that it works the same way. Scientists observe the behavior of particles, and find that a multiverse explains that behavior more simply and elegantly than not-a-multiverse.
That’s not an accurate description of the state of affairs.
In order to calculate correct predictions for experiments, you have to use the probabilistic Born rule (and the collapse postulate for sequential measurements). That these can be derived from the Many Worlds interpretation (MWI) is a conjecture which hasn’t been proved an a universally accepted way.
So we have an interpretation which works but is considered unelegent by many and we have an interpretation which is simple and elegant but is only conjectured to work. Considering the nature of the problems with the proofs, it is questionable whether the MWI can retain its elegant simplicity if it is made to work (see below).
One (doubtless exaggerated) way I’ve heard multiverse proponents explain their position is like this: in certain situations the math declares two contradictory answers – in the classic example, Schrodinger’s cat will be both alive and dead. But when we open the box, we see only a dead cat or an alive cat, not both. Multiverse opponents say “Some unknown force steps in at the last second and destroys one of the possibility branches”. Multiverse proponents say “No it doesn’t, both possibility branches happen exactly the way the math says, and we end up in one of them.”
What I find interesting is that Copenhagen-style interpretations looked ugly to me at first but got more sensible the more I learned about them. With most other interpretations it is the reverse: initially, the looked very compelling but the intuitive pictures are often hard to make rigorous. For example, if you try to describe the branching process mathematically, it isn’t possible to say when exactly the branches are splitting or even that they are splitting in an unambiguous way at all. Without introducing something like the observer who sets a natural scale for when it is okay to approximate certain values by zero, it is very difficlt to way to speak of different worlds consistently. But then the simplicity of the MWI is greatly reduced and the difference to a Copenhagenish point of view is much more subtle.
Generally, regarding the interpretation of QM, there are two camps: realists who take the wave function as a real physical object (Schrödinger, Bohm, Everett) and people who take the wavefunction as an object of knowledge (Bohr, Einstein, Heisenberg, Fuchs).
If the multiverse opponent describes the situation involving “some unknown force” he is also in the realist camp and not a proponent of a Copenhagenish position. The most modern Copenhagenish position would be QBism which asserts “whenever I learn something new by means of a measurement, I update”. From this point of view, QM is a generalization of probability theory, the wavefunction (or probability amplitude) is the object of knowledge which replaces ordinary probabilities, and the collapse rule is a generalized form of Bayesian updating. That doesn’t seem less sensible to me than your description of the multiverse proponent. Of course, there’s also a bullet to bite here: the abandonment of a mathematical layer below the level of (generalized) probabilities.
The important point is that this is not about which position is simpler than the other but about a deep divide in the philosophical underpinnings of science.
Taking this exaggerated dumbed-down account as exactly right, this sounds about as hard as the dinosaurs-vs-Satan example, in terms of figuring out which is more Occam’s Razor compliant. I’m sure the reality is more nuanced, but I think it can be judged by the same process. Perhaps this is the kind of reasoning that only gets us to a 90% probability there is a multiverse, rather than a 99.999999% one. But I think determining that theories have 90% probability is a reasonable scientific thing to do.
As per what I have written above I think that there’s a crucial difference between the examples of the fossils and the sphinx on the one hand and the interpretation of QM on the other hand. Which interpretation of QM one prefers is connected to one’s position on deep philosophical questions like “Is reductionism true?”, “Is Nature fundamentally mathematical?”, “What’s consiousness?”, etc. So the statement “[there’s a] 90% probability there is a multiverse” is connected to statements of the form “there’s a 90% probability that reductionism is true”. Whether such statements are meaningful seems much more questionable to me than in the case of your other examples.
Generally, regarding the interpretation of QM, there are two camps: realists who take the wave function as a real physical object (Schrödinger, Bohm, Everett) and people who take the wavefunction as an object of knowledge (Bohr, Einstein, Heisenberg, Fuchs).
Einstein was a realist who was upset that the only interpretation available to him was anti-realist. Saying that he took the wavefunction as object of knowledge is technically true, ie, false.
a Copenhagenish position
Thanks for conceding that the Copenhagen interpretation has meant many things. Do you notice how many people deny that? It worries me.
Einstein was a realist who was upset that the only interpretation available to him was anti-realist. Saying that he took the wavefunction as object of knowledge is technically true, ie, false.
I agree that my phrasing was a bit misleading here. Reading it again, it sounds like Einstein wasn’t a realist, which of course is false. For him, QM was a purely statistical theory which needed to be supplemented by a more fundamental realistic theory (a view which has been proven to be untenable only in 2012 by Pusey, Barrett and Rudolph).
Thanks for conceding that the Copenhagen interpretation has meant many things. Do you notice how many people deny that? It worries me.
I don’t know how many people really deny this. Sure, people often talk about “the” Copenhagen interpretation but most physicists use it only as a vague label because they don’t care much about interpretations. Who do you have in mind denying this and what exactly worries you?
I think so, too, but I don’t know it (Eliezer’s Sequence on QM is still on my reading list). Given the importance people around here put on Bayes theorem, I find it quite surprising that the idea of a quantum generalization -which is what QBism is about- isn’t discussed here apart from a handful of isolated comments. Two notable papers in this direction are
I don’t think the QM sequence would tell you anything you don’t know.
The story is that EY became super convinced by Deutch’s Fabric or Reality, and never really looked into any approaches other than the ones DD mentioned.
I don’t think that the QM example is like the others. Explaining this requires a bit of detail.
From section V.:
That’s not an accurate description of the state of affairs.
In order to calculate correct predictions for experiments, you have to use the probabilistic Born rule (and the collapse postulate for sequential measurements). That these can be derived from the Many Worlds interpretation (MWI) is a conjecture which hasn’t been proved an a universally accepted way.
So we have an interpretation which works but is considered unelegent by many and we have an interpretation which is simple and elegant but is only conjectured to work. Considering the nature of the problems with the proofs, it is questionable whether the MWI can retain its elegant simplicity if it is made to work (see below).
What I find interesting is that Copenhagen-style interpretations looked ugly to me at first but got more sensible the more I learned about them. With most other interpretations it is the reverse: initially, the looked very compelling but the intuitive pictures are often hard to make rigorous. For example, if you try to describe the branching process mathematically, it isn’t possible to say when exactly the branches are splitting or even that they are splitting in an unambiguous way at all. Without introducing something like the observer who sets a natural scale for when it is okay to approximate certain values by zero, it is very difficlt to way to speak of different worlds consistently. But then the simplicity of the MWI is greatly reduced and the difference to a Copenhagenish point of view is much more subtle.
Generally, regarding the interpretation of QM, there are two camps: realists who take the wave function as a real physical object (Schrödinger, Bohm, Everett) and people who take the wavefunction as an object of knowledge (Bohr, Einstein, Heisenberg, Fuchs).
If the multiverse opponent describes the situation involving “some unknown force” he is also in the realist camp and not a proponent of a Copenhagenish position. The most modern Copenhagenish position would be QBism which asserts “whenever I learn something new by means of a measurement, I update”. From this point of view, QM is a generalization of probability theory, the wavefunction (or probability amplitude) is the object of knowledge which replaces ordinary probabilities, and the collapse rule is a generalized form of Bayesian updating. That doesn’t seem less sensible to me than your description of the multiverse proponent. Of course, there’s also a bullet to bite here: the abandonment of a mathematical layer below the level of (generalized) probabilities.
The important point is that this is not about which position is simpler than the other but about a deep divide in the philosophical underpinnings of science.
As per what I have written above I think that there’s a crucial difference between the examples of the fossils and the sphinx on the one hand and the interpretation of QM on the other hand. Which interpretation of QM one prefers is connected to one’s position on deep philosophical questions like “Is reductionism true?”, “Is Nature fundamentally mathematical?”, “What’s consiousness?”, etc. So the statement “[there’s a] 90% probability there is a multiverse” is connected to statements of the form “there’s a 90% probability that reductionism is true”. Whether such statements are meaningful seems much more questionable to me than in the case of your other examples.
Einstein was a realist who was upset that the only interpretation available to him was anti-realist. Saying that he took the wavefunction as object of knowledge is technically true, ie, false.
Thanks for conceding that the Copenhagen interpretation has meant many things. Do you notice how many people deny that? It worries me.
I agree that my phrasing was a bit misleading here. Reading it again, it sounds like Einstein wasn’t a realist, which of course is false. For him, QM was a purely statistical theory which needed to be supplemented by a more fundamental realistic theory (a view which has been proven to be untenable only in 2012 by Pusey, Barrett and Rudolph).
I don’t know how many people really deny this. Sure, people often talk about “the” Copenhagen interpretation but most physicists use it only as a vague label because they don’t care much about interpretations. Who do you have in mind denying this and what exactly worries you?
There’s no doubt a story as to why QBism didn’t become the official LessWrong position.
I think so, too, but I don’t know it (Eliezer’s Sequence on QM is still on my reading list). Given the importance people around here put on Bayes theorem, I find it quite surprising that the idea of a quantum generalization -which is what QBism is about- isn’t discussed here apart from a handful of isolated comments. Two notable papers in this direction are
https://arxiv.org/abs/quant-ph/0106133
https://arxiv.org/abs/0906.2187
I don’t think the QM sequence would tell you anything you don’t know.
The story is that EY became super convinced by Deutch’s Fabric or Reality, and never really looked into any approaches other than the ones DD mentioned.