I hope that believing that MWI clearly wins based on our current knowledge and testing it further are not mutually exclusive. (At least not any more than believing in collapse and testing it further.) For example, it inspired the quantum bomb test.
This argument feels to me a bit strawmanish, as if a creationist would accuse evolutionists of saying: “Evolution clearly wins! No need to test it further.” Well, this specific question seems settled, but it never meant that the whole biology research is over.
Just because something clearly wins today, that does not prevent people from exploring the details… and possibly come to an opposite conclusion later. At some moment scientists believed that Newtonian physics was correct, and it did not prevent them to discover relativity later.
In exactly the same way it is possible to believe in MWI and start constructing e.g. a quantum supercomputer. If MWI is wrong, it’s likely that during the construction of the supercomputer we will find the counter-evidence (e.g. encounter a situation where the hypothetical collapse really happens and the parallel branches stop interfering, which would make constructing quantum supercomputers with more than 42 bits impossible, or something like this). On the other hand, if we invent quantum supercomputer, quantum teleporter and quantum dishwasher without disproving MWI, I guess that would just make MWI more likely.
I agree that saying “I can make a Bayesian estimate based on little data” should not stop us from finding more data. On the other hand, there is always more data possible, but that should not prevent us from making temporary conclusions from the data we already have. I mean, why should we expect that the new data will move our estimate in a specific direction?
I agree that the two are not mutually exclusive. But strongly believing something makes you less likely to want to test it.After all, what’s the point if it’s “clearly true”? The expected surprise value is low, since the prior probability of encountering contrary evidence is low. This is fine for experimentally preferred models, like, say, energy conservation, so there is really no point to test it further by trying to construct various perpetual motion machines. However, if preference of one model over another is based solely on inference and not on experiment, believing this preference tends to act as a curiosity stopper, which is a bad thing, since it’s Nature that is the ultimate arbiter between competing models, not faulty and biased human reasoning.
Re quantum computers/quantum bomb: both collapse and MWI lead to exactly the same predictions. I am yet to see anyone constructing an experiment unambiguously discriminating between the interpretations. (There was this handwaving by Deutsch about conscious reversible quantum computing based on some unspecified future technology, but few unbiased physicists take it seriously.)
strongly believing something makes you less likely to want to test it.
Strongly believing in Catholic Trinity may make people less likely to test it. But strongly believing in electricity didn’t stop people from making thousands of electrical gadgets, each of them implicitly testing the correctness of the underlying theory.
The expected surprise value is low, since the prior probability of encountering contrary evidence is low.
The value of the electric gadgets is not in testing our knowledge of electricity, but they do it anyway. The value of GPS is not in testing the theory of relativity, but it confirms it anyway. Maybe one day quantum computers will be built for commercial reasons...
both collapse and MWI lead to exactly the same predictions. I am yet to see anyone constructing an experiment unambiguously discriminating between the interpretations.
If the collapse interpretation is correct, it should be possible to prove it by designing an experiment which demonstrates the collapse, so the proponents of collapse theory should be interested in doing so. If the MWI interpretation is correct, then… well, the collapse theory is unfalsifiable—you can make a million experiments where the collapse didn’t happen, but that does not prove that it doesn’t happen when you are not looking.
So the main difference is that the proponents of MWI can do their experiments and predict the outcome according to their model of the world, while the proponents of collapse must always think “I believe there is a dragon in my garage, but it will have no influence on the specific outcome of this experiment”. Or less metaphorically: “I believe that the collapse exists, but I also believe it will never influence the outcome of any of my experiments”. It is still possible to do a high-quality research using this belief, just like it is possible to do a high-quality research while being religious.
EDIT: The critical thing is that if someone believes there is absolutely no difference between collapse and no collapse, then what the hell do they actually mean when they say “collapse”? (In real life, did you ever go to a shop to buy a bread which was absolutely experimentally indistinguishable from no bread?) The only way I could interpret it meaningfully is that “collapse” means “the interference between branches becomes too small to measure by our instruments”. But that doesn’t feel like a fact about the territory.
If the collapse interpretation is correct, it should be possible to prove it by designing an experiment which demonstrates the collapse, so the proponents of collapse theory should be interested in doing so. If the MWI interpretation is correct, then… well, the collapse theory is unfalsifiable—you can make a million experiments where the collapse didn’t happen, but that does not prove that it doesn’t happen when you are not looking.
Note that swapping the terms collapse and MWI (“world splitting”, to make it more concrete) in the above does not affect the [in]validity of this statement. This might give you a hint. Nah, who am I kidding.
So, what exactly does the word “collapse” mean to you?
Do you believe there is a specific moment when the collapse happens? Could you describe an experimental difference between the collapse happening at the time t or ten minutes later?
Or does the collapse happen gradually, like at some moment we have 10% of the collapse and at some later moment we have 90% of the collapse? What experimental observation would mean that the collapse is at 50%?
(My assumption was that the collapse happens in some completely unspecified moment after the interference between different branches becomes too small to measure by our instruments. Which pattern-matches to “when we can’t observe X, it suddenly changes to Y, because we believe in Y and not in X. But if my definition of the collapse is wrong, please tell me the correct one so I can stop making strawman arguments.)
I have outlined by views on this several times on this forum. I do not favor one interpretation over another based solely on logic. I am very skeptical of any kind of “objective collapse” for the same reasons Eliezer is, because in the EPR setup (singlet decay) it would require some sort of correlation between spacelike-separated processes. But stranger things have happened to physics, so who knows. For the same reason I am also skeptical of the naive MWI, since the two pairs of split worlds would have to “recombine” in just the right way to produce only two worlds when the measurements are compared. I am slightly partial to Rovelli’s Relational QM (Eliezer hates it), because it provides an explicit ontology matching the shut-up-and-calculate non-interpretation (unitary evolution + Born rule), without postulating any invisible processes, like collapse or world-splitting. I think that Bohmian mechanics is extremely unlikely to reflect the “reality” (i.e. the potential future model one level deeper than the present-day QM), if only because it’s so clunky.
As I said before, we have no good model of how a single observed eigenstate emerges during an irreversible multi-state interaction (known as the measurement), and this biggest mystery in all of quantum physics deserves more research. The magic incantation “MWI” is a curiosity-stopping spell, which might be interesting in the HPMoR universe, but has no value in the one we live in.
Thanks for the answer! I wish someone would explain to me RQM in simple terms, then I could make an opinion about it.
I know this probably doesn’t sound good, but I remember reading in Feynman’s book how when he was talking to mathematicians about complex mathematical things, he tried to imagine a specific object, like a ball, and then apply what they said to that specific object; and if didn’t make sense, he objected. I am essentially trying to do something similar, but with the concepts of physics. So I’d like to hear a story about what happens with the ball in the MWI multiverse, and what happens in the RQM multiverse. (I am not asking you specifically do to that, I just express my wish.)
I hope that believing that MWI clearly wins based on our current knowledge and testing it further are not mutually exclusive. (At least not any more than believing in collapse and testing it further.) For example, it inspired the quantum bomb test.
This argument feels to me a bit strawmanish, as if a creationist would accuse evolutionists of saying: “Evolution clearly wins! No need to test it further.” Well, this specific question seems settled, but it never meant that the whole biology research is over.
Just because something clearly wins today, that does not prevent people from exploring the details… and possibly come to an opposite conclusion later. At some moment scientists believed that Newtonian physics was correct, and it did not prevent them to discover relativity later.
In exactly the same way it is possible to believe in MWI and start constructing e.g. a quantum supercomputer. If MWI is wrong, it’s likely that during the construction of the supercomputer we will find the counter-evidence (e.g. encounter a situation where the hypothetical collapse really happens and the parallel branches stop interfering, which would make constructing quantum supercomputers with more than 42 bits impossible, or something like this). On the other hand, if we invent quantum supercomputer, quantum teleporter and quantum dishwasher without disproving MWI, I guess that would just make MWI more likely.
I agree that saying “I can make a Bayesian estimate based on little data” should not stop us from finding more data. On the other hand, there is always more data possible, but that should not prevent us from making temporary conclusions from the data we already have. I mean, why should we expect that the new data will move our estimate in a specific direction?
I agree that the two are not mutually exclusive. But strongly believing something makes you less likely to want to test it.After all, what’s the point if it’s “clearly true”? The expected surprise value is low, since the prior probability of encountering contrary evidence is low. This is fine for experimentally preferred models, like, say, energy conservation, so there is really no point to test it further by trying to construct various perpetual motion machines. However, if preference of one model over another is based solely on inference and not on experiment, believing this preference tends to act as a curiosity stopper, which is a bad thing, since it’s Nature that is the ultimate arbiter between competing models, not faulty and biased human reasoning.
Re quantum computers/quantum bomb: both collapse and MWI lead to exactly the same predictions. I am yet to see anyone constructing an experiment unambiguously discriminating between the interpretations. (There was this handwaving by Deutsch about conscious reversible quantum computing based on some unspecified future technology, but few unbiased physicists take it seriously.)
Strongly believing in Catholic Trinity may make people less likely to test it. But strongly believing in electricity didn’t stop people from making thousands of electrical gadgets, each of them implicitly testing the correctness of the underlying theory.
The value of the electric gadgets is not in testing our knowledge of electricity, but they do it anyway. The value of GPS is not in testing the theory of relativity, but it confirms it anyway. Maybe one day quantum computers will be built for commercial reasons...
If the collapse interpretation is correct, it should be possible to prove it by designing an experiment which demonstrates the collapse, so the proponents of collapse theory should be interested in doing so. If the MWI interpretation is correct, then… well, the collapse theory is unfalsifiable—you can make a million experiments where the collapse didn’t happen, but that does not prove that it doesn’t happen when you are not looking.
So the main difference is that the proponents of MWI can do their experiments and predict the outcome according to their model of the world, while the proponents of collapse must always think “I believe there is a dragon in my garage, but it will have no influence on the specific outcome of this experiment”. Or less metaphorically: “I believe that the collapse exists, but I also believe it will never influence the outcome of any of my experiments”. It is still possible to do a high-quality research using this belief, just like it is possible to do a high-quality research while being religious.
EDIT: The critical thing is that if someone believes there is absolutely no difference between collapse and no collapse, then what the hell do they actually mean when they say “collapse”? (In real life, did you ever go to a shop to buy a bread which was absolutely experimentally indistinguishable from no bread?) The only way I could interpret it meaningfully is that “collapse” means “the interference between branches becomes too small to measure by our instruments”. But that doesn’t feel like a fact about the territory.
Note that swapping the terms collapse and MWI (“world splitting”, to make it more concrete) in the above does not affect the [in]validity of this statement. This might give you a hint. Nah, who am I kidding.
So, what exactly does the word “collapse” mean to you?
Do you believe there is a specific moment when the collapse happens? Could you describe an experimental difference between the collapse happening at the time t or ten minutes later?
Or does the collapse happen gradually, like at some moment we have 10% of the collapse and at some later moment we have 90% of the collapse? What experimental observation would mean that the collapse is at 50%?
(My assumption was that the collapse happens in some completely unspecified moment after the interference between different branches becomes too small to measure by our instruments. Which pattern-matches to “when we can’t observe X, it suddenly changes to Y, because we believe in Y and not in X. But if my definition of the collapse is wrong, please tell me the correct one so I can stop making strawman arguments.)
I have outlined by views on this several times on this forum. I do not favor one interpretation over another based solely on logic. I am very skeptical of any kind of “objective collapse” for the same reasons Eliezer is, because in the EPR setup (singlet decay) it would require some sort of correlation between spacelike-separated processes. But stranger things have happened to physics, so who knows. For the same reason I am also skeptical of the naive MWI, since the two pairs of split worlds would have to “recombine” in just the right way to produce only two worlds when the measurements are compared. I am slightly partial to Rovelli’s Relational QM (Eliezer hates it), because it provides an explicit ontology matching the shut-up-and-calculate non-interpretation (unitary evolution + Born rule), without postulating any invisible processes, like collapse or world-splitting. I think that Bohmian mechanics is extremely unlikely to reflect the “reality” (i.e. the potential future model one level deeper than the present-day QM), if only because it’s so clunky.
As I said before, we have no good model of how a single observed eigenstate emerges during an irreversible multi-state interaction (known as the measurement), and this biggest mystery in all of quantum physics deserves more research. The magic incantation “MWI” is a curiosity-stopping spell, which might be interesting in the HPMoR universe, but has no value in the one we live in.
Thanks for the answer! I wish someone would explain to me RQM in simple terms, then I could make an opinion about it.
I know this probably doesn’t sound good, but I remember reading in Feynman’s book how when he was talking to mathematicians about complex mathematical things, he tried to imagine a specific object, like a ball, and then apply what they said to that specific object; and if didn’t make sense, he objected. I am essentially trying to do something similar, but with the concepts of physics. So I’d like to hear a story about what happens with the ball in the MWI multiverse, and what happens in the RQM multiverse. (I am not asking you specifically do to that, I just express my wish.)