6 ms·

Interpretations of quantum theory: A map of madness

46 points by mathgenius 11y ago

madaxe_again 11y ago
"We must consolidate into single school of thought"? Scientific method, much. This is the thinking that lead to pilot wave qm being disregarded for a few generations. If anything, pilot wave gives the easiest explanation of locality - there is none, and it's a deterministic universe.
- amelius 11y ago
  Any books that teach (introductory) QM from the pilot wave perspective?
- mathgenius 11y ago
  Yeah, the whole discussion of entanglement (specifically Bell's inequality) was sidelined for decades. But maybe the single school of thought should be this: we have none, and that's good.
- darkmighty 11y ago
  That's not exactly the point of this paper (and the quote above is not in it?) > these two types [of interpretations] are so radically different that there must be experiments that, when analyzed outside the framework of quantum theory, lead to different empirically testable predictions
pygy_ 11y ago
This paper gives the context in which this other one has been written: http://arxiv.org/abs/1509.03641 http://arxiv.org/abs/1509.03641 Discussed 13 hours ago: https://news.ycombinator.com/item?id=10228435 https://news.ycombinator.com/item?id=10228435
buffoon 11y ago
Well that was more abstract and citations than body. Slightly disappointed.
- mathgenius 11y ago
  I was too but then, well that's the point maybe: There's not much to be said about all of these interpretations.
nabla9 11y ago
Locality in in quantum theory confuses the proverbial journalist because meaning of locality is different from the intuitive understanding of the word. Two entangled particles light years apart share state. Physicists can still say that principle of locality is not violated because definition of locality in physics is does not include quantum state. Quantum states have no location. Quantum correlations are non-local. As long as this is excluded from definition of locality everything is fine. Information transfer and energy transfer follows principle of locality strictly.
- darkmighty 11y ago
  I don't think that's correct? Bell's theorem implies you can't have a theory of local hidden variables that reproduces entanglement (and the rest of QM), no?
  - nabla9 11y ago
    Quantum state is not local hidden variable. It's non-local.
zamalek 11y ago
> As Mermin points out, “quantum theory is the most useful and powerful theory physicists have ever devised. Yet today, nearly 90 years after its formulation, disagreement about the meaning of the theory is stronger than ever. New interpretations appear every day. None ever disappear” Isn't this the essence of science (excluding the last sentence)? The widespread conflicting interpretations of QT is something to be proud of, every time a new interpretation is dreamed up it's yet another opportunity to draw closer to the truth. Science is a field where being wrong should be seen as a good thing and that certainly used to be the case.
- azernik 11y ago
  The problem is that nothing is being proven wrong. Science doesn't advance by the proliferation of theories, but by their narrowing into a smaller set of theories that agree on more and more points.
  - effie 11y ago
    Well said. All the various opinions aren't going to matter much if "professionally unsafe" decisive experiments will not be suggested or if those suggested are not performed.
ThePhysicist 11y ago
The main problem with interpretations of quantum phenomena is that even today many physicists receive very little information about modern concepts in quantum mechanics (QM) during their University training. The standard QM course usually starts off by explaining the two "postulates" of quantum mechanics, i.e. that a state is described by a wave function which evolves in a totally predictable fashion, but which suddenly "collapses" to a classical state in a random and non-predictable way when we perform a measurement on the quantum system. Unfortunately, this picture is almost completely wrong. In fact, there is no randomness and non-predictability in quantum mechanics. The fact that we observe wave function collapse in a quantum system is the consequence of coupling the system to a larger, external one that becomes entangled with the "small" quantum system and -through so-called decoherence- produces what we call the collapse of the wave function to a "classical" state. This process is entirely deterministic. The theory of such "open quantum systems" is well established today and explains many of the seeming paradoxes that have plagued quantum mechanics, and it also provides clear answers to many of the questions posed in the article. Some questions, in particular what happens to the parts of the wave function that do not become part of our reality after a collapse cannot be answered by any known theoretical framework, hence different people will have different opinions concerning those. The problem here is that we ourselves are described by a quantum wave function and therefore "live" inside the quantum world, we can therefore not "step back" and look at a wave function from the outside, which is why we can't answer what happens with the parts of a wave function that correspond to measurement results that we have not obtained when measuring an observable of a quantum system. Different interpretations of quantum mechanics like the "Many Worlds" or the "Copenhague" varieties are basically just arguing about what happens with a wave function after it "collapses". To my knowledge there is no way to discriminate between different alternatives here, the preferences that individual physicists have in this matter are therefore based more on personal belief or concepts like simplicity or "beauty", hence we should not waste time trying to find out which is the right one.
- n4r9 11y ago
  I don't like to sound glib, but... > In fact, there is no randomness and non-predictability in quantum mechanics. Depends on the interpretation. > wave function collapse in a quantum system is the consequence of coupling the system to a larger, external one that becomes entangled with the "small" quantum system Depends on the interpretation. > we ourselves are described by a quantum wave function Depends on the interpretation. > Different interpretations of quantum mechanics like the "Many Worlds" or the "Copenhague" varieties are basically just arguing about what happens with a wave function after it "collapses". You only really need to worry about "what happens with a wave function" if you have a decidedly psi-ontic view of it. Otherwise, collapse is not itself a physical process. > To my knowledge there is no way to discriminate between different alternatives here The same author recently uploaded a paper which argues that there is a way to discriminate between interpretations based on physical principles. See http://arxiv.org/pdf/1509.03641v1.pdf http://arxiv.org/pdf/1509.03641v1.pdf .
deleted 11y ago
[deleted]
misnome 11y ago
> At the end of the day, the journalist asks: "How do you plan to make progress if, after 90 years of quantum theory, you still don't know what it means? Maybe not asking for lay-person descriptions would gain more consistency. Also, it says "A Group of Physicists" which is remarkably vague - physics is a vast field, and picking random scientists doesn't guarantee actually finding someone who has more than a basic grasp (not a criticism of the individual scientists).
- mathgenius 11y ago
  I think this is a well observed phenomenon [1],[2]. At least in the theoretical quantum group I am in: there is very little agreement about the interpretation of quantum theory. (Maybe the experimentalists don't care as much.) [1] http://www.preposterousuniverse.com/blog/2013/01/17/the-most-embarrassing-graph-in-modern-physics/ http://www.preposterousuniverse.com/blog/2013/01/17/the-most... [2] http://arxiv.org/abs/1301.1069 http://arxiv.org/abs/1301.1069
- TheOtherHobbes 11y ago
  Perhaps quantum theory is itself a manifestation of quantum theory - random, observer dependent, and subject to an unavoidable minimal level of ontological indeterminacy.
themgt 11y ago
Mermin put it perhaps most succinctly, that reality is "correlations without correlata", or as Ron Garret coined, the "zero-worlds interpretation"[1] It also makes sense to me on a sociological level, that the way in which this interpretation seems to undermine the very foundation of western, scientific thought is the reason it has been so desperately avoided for so long, with many preferring to believe in an infinite forking (but somehow still "real) multiverse, than the idea that reality itself is intersubjective. [1] https://www.youtube.com/watch?v=dEaecUuEqfc https://www.youtube.com/watch?v=dEaecUuEqfc
- lisper 11y ago
  Or if you don't want to sit through the video: http://www.flownet.com/ron/QM.pdf http://www.flownet.com/ron/QM.pdf
- westoncb 11y ago
  Regarding "correlations without correlata": this feels to me like we are starting to hit on properties on our mechanism for describing/representing and confusing it with what we're trying to describe/represent. Rather than saying there's "nothing really there," couldn't it just be a property of human conceptual structure that it expresses abstract relations about abstract symbols, but there are never any 'things' that are related?
dghf 11y ago
"Shut up and calculate." -- Richard Feynman (attrib.)
NickHaflinger 11y ago
What the fuc~ ..
stared 11y ago
Still (and I am a quantum physics PhD) I don't get what is wrong with having many _interpretations_. Especially, as in physics there are many other phenomena that can be _interpreted_ in different ways. For the simplest: movement as forces vs as a teleological least action principle. While for some phenomena one is easier that the other, considering that there should be only one "true" interpretation, is, at best, narrow-mindness (and at worst: dogmatism, a very enemy of science).
- iofj 11y ago
  Well the reason that it is "wrong" is that for many people (generally the ones outside of scientific endeavours) the interpretations are physics. Let's face facts : most people are never going to learn even basic physics beyond high school level, and oversimplified "philsophy" is all they'll ever know. (As my philosophy professor said: history seems to indicate that science is the way to be right, and philosophy is the science of being wrong) And the opinion that interpretation doesn't matter, there's equations, and what they say takes precedence over whatever a human mind produces. That they don't fit well in any of these "interpretations" merely amplifies that belief (as it should). It's a matter of perspective.
  - stared 11y ago
    Some interpretation may matter, as e.g. they can be more fruitful in generating new predictions, or extending a theory. And some may turn out to be wrong (e.g. the hidden variable interpretation, which before Bell was considered just a different interpretation). So my impression is that the lay audience like hearing big words, even if they cannot understand it at all (but it is easier to delude oneself that one understands "many words" than a particular set of equations).
ThomPete 11y ago
The issues with explaining QM today seems to be that the math and experimental parts are all as tested and proven as they possible can be just as much as classical physics. Whats putting sand in the machine is that it just doesn't make sense philosophically. So if you will allow a complete novice some wild speculation here to provide a different perspective. Maybe they are just two different fields with a different base premise and maybe thats ok. Perhaps what is really shown here, is the limits of western thought process. I have always wondered if zen buddhisms way to deal with reality, is much better capable at explaining whats going on because it's comfortable dealing with paradoxes ("If it's not paradoxical it's not true" as Zen Master Suzuki Roshi wrote). I am not a zen buddhist and there is a big risk that I as a westerner don't understand zen buddhism (I know i don't understand QM) but it seems to me that western semantics and rhetorics are actually getting in the way of providing us with a way to be at ease with what seems to be a fact; that we can't explain QM through language.
- Raster42 11y ago
  It sounds like you might enjoy "The Tao of Physics" by Fritjof Capra. There's a free PDF version online.
- anentropic 11y ago
  so you're saying they should give up?
  - ThomPete 11y ago
    I am saying they should change the question.
- marcosdumay 11y ago
  It looks like the "shut-up and calculate" school is the one with most adepts. It's also very zen-like to me (or I completely don't understand what zen is, not an unlikely alternative). The problem is that the imaginary journalist has an agenda and will completely ignore any "shut-up and calculate" answer. The author really needs to make a better case about the interpretations having different empirical outcomes, because it's not obvious at all.

46 points by mathgenius 11y ago

"We must consolidate into single school of thought"? Scientific method, much. This is the thinking that lead to pilot wave qm being disregarded for a few generations. If anything, pilot wave gives the easiest explanation of locality - there is none, and it's a deterministic universe.

amelius 11y ago
Any books that teach (introductory) QM from the pilot wave perspective?
mathgenius 11y ago
Yeah, the whole discussion of entanglement (specifically Bell's inequality) was sidelined for decades. But maybe the single school of thought should be this: we have none, and that's good.
darkmighty 11y ago
That's not exactly the point of this paper (and the quote above is not in it?) > these two types [of interpretations] are so radically different that there must be experiments that, when analyzed outside the framework of quantum theory, lead to different empirically testable predictions

pygy_ 11y ago

This paper gives the context in which this other one has been written: http://arxiv.org/abs/1509.03641 http://arxiv.org/abs/1509.03641 Discussed 13 hours ago: https://news.ycombinator.com/item?id=10228435 https://news.ycombinator.com/item?id=10228435

buffoon 11y ago

Well that was more abstract and citations than body. Slightly disappointed.

mathgenius 11y ago
I was too but then, well that's the point maybe: There's not much to be said about all of these interpretations.

nabla9 11y ago

Locality in in quantum theory confuses the proverbial journalist because meaning of locality is different from the intuitive understanding of the word. Two entangled particles light years apart share state. Physicists can still say that principle of locality is not violated because definition of locality in physics is does not include quantum state. Quantum states have no location. Quantum correlations are non-local. As long as this is excluded from definition of locality everything is fine. Information transfer and energy transfer follows principle of locality strictly.

darkmighty 11y ago
I don't think that's correct? Bell's theorem implies you can't have a theory of local hidden variables that reproduces entanglement (and the rest of QM), no?
- nabla9 11y ago
  Quantum state is not local hidden variable. It's non-local.

zamalek 11y ago

> As Mermin points out, “quantum theory is the most useful and powerful theory physicists have ever devised. Yet today, nearly 90 years after its formulation, disagreement about the meaning of the theory is stronger than ever. New interpretations appear every day. None ever disappear” Isn't this the essence of science (excluding the last sentence)? The widespread conflicting interpretations of QT is something to be proud of, every time a new interpretation is dreamed up it's yet another opportunity to draw closer to the truth. Science is a field where being wrong should be seen as a good thing and that certainly used to be the case.

azernik 11y ago
The problem is that nothing is being proven wrong. Science doesn't advance by the proliferation of theories, but by their narrowing into a smaller set of theories that agree on more and more points.
- effie 11y ago
  Well said. All the various opinions aren't going to matter much if "professionally unsafe" decisive experiments will not be suggested or if those suggested are not performed.

ThePhysicist 11y ago

The main problem with interpretations of quantum phenomena is that even today many physicists receive very little information about modern concepts in quantum mechanics (QM) during their University training. The standard QM course usually starts off by explaining the two "postulates" of quantum mechanics, i.e. that a state is described by a wave function which evolves in a totally predictable fashion, but which suddenly "collapses" to a classical state in a random and non-predictable way when we perform a measurement on the quantum system. Unfortunately, this picture is almost completely wrong. In fact, there is no randomness and non-predictability in quantum mechanics. The fact that we observe wave function collapse in a quantum system is the consequence of coupling the system to a larger, external one that becomes entangled with the "small" quantum system and -through so-called decoherence- produces what we call the collapse of the wave function to a "classical" state. This process is entirely deterministic. The theory of such "open quantum systems" is well established today and explains many of the seeming paradoxes that have plagued quantum mechanics, and it also provides clear answers to many of the questions posed in the article. Some questions, in particular what happens to the parts of the wave function that do not become part of our reality after a collapse cannot be answered by any known theoretical framework, hence different people will have different opinions concerning those. The problem here is that we ourselves are described by a quantum wave function and therefore "live" inside the quantum world, we can therefore not "step back" and look at a wave function from the outside, which is why we can't answer what happens with the parts of a wave function that correspond to measurement results that we have not obtained when measuring an observable of a quantum system. Different interpretations of quantum mechanics like the "Many Worlds" or the "Copenhague" varieties are basically just arguing about what happens with a wave function after it "collapses". To my knowledge there is no way to discriminate between different alternatives here, the preferences that individual physicists have in this matter are therefore based more on personal belief or concepts like simplicity or "beauty", hence we should not waste time trying to find out which is the right one.

n4r9 11y ago
I don't like to sound glib, but... > In fact, there is no randomness and non-predictability in quantum mechanics. Depends on the interpretation. > wave function collapse in a quantum system is the consequence of coupling the system to a larger, external one that becomes entangled with the "small" quantum system Depends on the interpretation. > we ourselves are described by a quantum wave function Depends on the interpretation. > Different interpretations of quantum mechanics like the "Many Worlds" or the "Copenhague" varieties are basically just arguing about what happens with a wave function after it "collapses". You only really need to worry about "what happens with a wave function" if you have a decidedly psi-ontic view of it. Otherwise, collapse is not itself a physical process. > To my knowledge there is no way to discriminate between different alternatives here The same author recently uploaded a paper which argues that there is a way to discriminate between interpretations based on physical principles. See http://arxiv.org/pdf/1509.03641v1.pdf http://arxiv.org/pdf/1509.03641v1.pdf .

deleted 11y ago

[deleted]

misnome 11y ago

> At the end of the day, the journalist asks: "How do you plan to make progress if, after 90 years of quantum theory, you still don't know what it means? Maybe not asking for lay-person descriptions would gain more consistency. Also, it says "A Group of Physicists" which is remarkably vague - physics is a vast field, and picking random scientists doesn't guarantee actually finding someone who has more than a basic grasp (not a criticism of the individual scientists).

mathgenius 11y ago
I think this is a well observed phenomenon [1],[2]. At least in the theoretical quantum group I am in: there is very little agreement about the interpretation of quantum theory. (Maybe the experimentalists don't care as much.) [1] http://www.preposterousuniverse.com/blog/2013/01/17/the-most-embarrassing-graph-in-modern-physics/ http://www.preposterousuniverse.com/blog/2013/01/17/the-most... [2] http://arxiv.org/abs/1301.1069 http://arxiv.org/abs/1301.1069
TheOtherHobbes 11y ago
Perhaps quantum theory is itself a manifestation of quantum theory - random, observer dependent, and subject to an unavoidable minimal level of ontological indeterminacy.

themgt 11y ago

Mermin put it perhaps most succinctly, that reality is "correlations without correlata", or as Ron Garret coined, the "zero-worlds interpretation"[1] It also makes sense to me on a sociological level, that the way in which this interpretation seems to undermine the very foundation of western, scientific thought is the reason it has been so desperately avoided for so long, with many preferring to believe in an infinite forking (but somehow still "real) multiverse, than the idea that reality itself is intersubjective. [1] https://www.youtube.com/watch?v=dEaecUuEqfc https://www.youtube.com/watch?v=dEaecUuEqfc

lisper 11y ago
Or if you don't want to sit through the video: http://www.flownet.com/ron/QM.pdf http://www.flownet.com/ron/QM.pdf
westoncb 11y ago
Regarding "correlations without correlata": this feels to me like we are starting to hit on properties on our mechanism for describing/representing and confusing it with what we're trying to describe/represent. Rather than saying there's "nothing really there," couldn't it just be a property of human conceptual structure that it expresses abstract relations about abstract symbols, but there are never any 'things' that are related?

dghf 11y ago

"Shut up and calculate." -- Richard Feynman (attrib.)

NickHaflinger 11y ago

What the fuc~ ..

stared 11y ago

Still (and I am a quantum physics PhD) I don't get what is wrong with having many _interpretations_. Especially, as in physics there are many other phenomena that can be _interpreted_ in different ways. For the simplest: movement as forces vs as a teleological least action principle. While for some phenomena one is easier that the other, considering that there should be only one "true" interpretation, is, at best, narrow-mindness (and at worst: dogmatism, a very enemy of science).

iofj 11y ago
Well the reason that it is "wrong" is that for many people (generally the ones outside of scientific endeavours) the interpretations are physics. Let's face facts : most people are never going to learn even basic physics beyond high school level, and oversimplified "philsophy" is all they'll ever know. (As my philosophy professor said: history seems to indicate that science is the way to be right, and philosophy is the science of being wrong) And the opinion that interpretation doesn't matter, there's equations, and what they say takes precedence over whatever a human mind produces. That they don't fit well in any of these "interpretations" merely amplifies that belief (as it should). It's a matter of perspective.
- stared 11y ago
  Some interpretation may matter, as e.g. they can be more fruitful in generating new predictions, or extending a theory. And some may turn out to be wrong (e.g. the hidden variable interpretation, which before Bell was considered just a different interpretation). So my impression is that the lay audience like hearing big words, even if they cannot understand it at all (but it is easier to delude oneself that one understands "many words" than a particular set of equations).

ThomPete 11y ago

The issues with explaining QM today seems to be that the math and experimental parts are all as tested and proven as they possible can be just as much as classical physics. Whats putting sand in the machine is that it just doesn't make sense philosophically. So if you will allow a complete novice some wild speculation here to provide a different perspective. Maybe they are just two different fields with a different base premise and maybe thats ok. Perhaps what is really shown here, is the limits of western thought process. I have always wondered if zen buddhisms way to deal with reality, is much better capable at explaining whats going on because it's comfortable dealing with paradoxes ("If it's not paradoxical it's not true" as Zen Master Suzuki Roshi wrote). I am not a zen buddhist and there is a big risk that I as a westerner don't understand zen buddhism (I know i don't understand QM) but it seems to me that western semantics and rhetorics are actually getting in the way of providing us with a way to be at ease with what seems to be a fact; that we can't explain QM through language.

Raster42 11y ago
It sounds like you might enjoy "The Tao of Physics" by Fritjof Capra. There's a free PDF version online.
anentropic 11y ago
so you're saying they should give up?
- ThomPete 11y ago
  I am saying they should change the question.
marcosdumay 11y ago
It looks like the "shut-up and calculate" school is the one with most adepts. It's also very zen-like to me (or I completely don't understand what zen is, not an unlikely alternative). The problem is that the imaginary journalist has an agenda and will completely ignore any "shut-up and calculate" answer. The author really needs to make a better case about the interpretations having different empirical outcomes, because it's not obvious at all.