6 ms·

Quantum Bayesianism Explained by Its Founder

77 points by guerrilla 6y ago

usgroup 6y ago
Yes ... you add Bayesian to the thing and it becomes new, principled and superior. It’s been a trend for about 3 decades now.
- faaabio1618 6y ago
  Read the article, you can learn something :)
jbay808 6y ago
> Eventually my colleague Rüdiger Schack and I felt that to be consistent we had to break the ties with Jaynes and move more in the direction of de Finetti. For those who are curious, here's Jaynes' view on the subject: https://bayes.wustl.edu/etj/articles/prob.in.qm.pdf https://bayes.wustl.edu/etj/articles/prob.in.qm.pdf
- kgwgk 6y ago
  The entropic dynamics approach from Caticha is closer to Jaynes’ ideas (and more interesting than qbism in my opinion, as it’s quite different from standard QM instead of just giving a Bayesian interpretation to it): https://arxiv.org/abs/1908.04693 https://arxiv.org/abs/1908.04693
MindGods 6y ago
See the discussion from 2015: https://news.ycombinator.com/item?id=9714618 https://news.ycombinator.com/item?id=9714618 Same article but published by Wired.
gsliepen 6y ago
Too many people, including physicists, confuse theories with reality. Quantum mechanics is a very powerful theory that correctly predicts a lot of observed phenomena. But while QM talks about a wavefunction, it doesn't mean the wavefunction actually exists. I myself particularly like the Everett interpretation, which some believe implies a multiverse, but I don't think the actual existence of a multiverse is necessary.
- moonchild 6y ago
  When you say 'theory', I think you mean 'model'.
- lmm 6y ago
  What other definition is there for saying that something exists, than that it correctly predicts observed phenomena? If you say that the table in front of me exists, surely that's nothing more or less than saying that the concept of a table correctly predicts the table-like sensations you see and feel.
  - guerrilla 6y ago
    There's an entire field of philosophy called ontology which includes metaontology and it answers your question as "many definitions." I recommend this book [1] by Berto and Plebani. SEP [2] also has about a dozen articles on the ontology of quantum mechanics and quantum physics more generally. [1]. https://www.bloomsbury.com/us/ontology-and-metaontology-9781472573308/ https://www.bloomsbury.com/us/ontology-and-metaontology-9781... [2]. https://plato.stanford.edu/contents.html#q https://plato.stanford.edu/contents.html#q
  - someguyorother 6y ago
    To me, "exists" is stronger than "predicts observation", although I can't entirely describe how, except by example. Let's say you're in a game. You can create a physics of the game world based on how that game behaves. However, the game world doesn't exist, as such. It's the result of a pattern produced by a computer, interpreted by our minds, which fills in the blanks and makes the game world feel more real than it is. It makes sense that an account of existence should either include the substructure (in this case, the computer) or the observer (in this case, the mind doing the filling-in), or possibly both. On the other hand, a description of the behavior of the system is much simpler. Another example: simulation hypothesis people sometimes talk about the possibility of "breaking out" of the simulation, as if the simulation is less somehow less true than whatever is behind it. But from a predicting-observed-phenomenon perspective, what you describe by physics exists. So the distinction between the rules of physics that apply in a certain domain because you're in a simulation, and the rules of physics that apply in another domain once you find a way to break out, is entirely artificial. That people don't see it that way seems to indicate that they mean something else by existence.
shellac 6y ago
I'm struggling to see how this anything more than Bohm's theory with a dubious interpretation of the guiding wave (which, to be honest, Bohm himself was guilty of). Like Bell without the 'Beables'.
wcoenen 6y ago
If the wavefunction is assumed to only encode epistemic uncertainty of the observer, then how are phenomena like tunneling explained?
- nonbel 6y ago
  From my reading, they would say some particles are just much more energetic than usual (for some reason we are ignorant of). See the post above about flipping a coin. According to the statistical model we use for coin flips, it is really unlikely to flip 100 heads in a row but not impossible.
  - wcoenen 6y ago
    Wouldn't it be possible to see this experimentally? You'd find particles jumping out of a "potential energy well" which they shouldn't be able to escape via tunneling.
RobertoG 6y ago
>>>"At the other end of the spectrum is Bruno de Finetti. He says there’s no reason whatsoever for my probabilities and yours to match, because mine are based on my experience and yours are based on your experience. " That doesn't deny an objective reality out there, it's just saying that we have different information about what it's out there and, therefore, we arrive to different conclusions. I don't understand how that perspective is different from just "objective Bayesianism" with different priors.
- lilgreenland 6y ago
  I agree. It feels like he is just combining normal Bayesianism with normal quantum mechanics. Which is seems fine, but I'm annoyed he dodged the question about nonconscious things also having a personalized set of priors. I'd like to hear him explain the single particle double slit experiment from this QBism perspective.
  - nonbel 6y ago
    Sounds like the wave model describes the statistical properties of a population of photons. Eg, a coin flip is deterministic if you know all the forces involved (airflow, force of flip, exact distribution of mass of the coin, etc). But since we are usually ignorant of all that, instead we model it as a bernoulli trial.
    - kgwgk 6y ago
      But that’s not what qbism is about: a wave function (pure state) doesn’t represent ignorance about a true underlying physical state, it’s a maximally sharp state of belief.
      - nonbel 6y ago
        > Regarding quantum states as degrees of belief implies that the event of a quantum state changing when a measurement occurs—the "collapse of the wave function"—is simply the agent updating her beliefs in response to a new experience. https://en.m.wikipedia.org/wiki/Quantum_Bayesianism https://en.m.wikipedia.org/wiki/Quantum_Bayesianism You could be right, That is what this sounds like to me though. According to the model there is a 50% chance the coin will land on heads, until you flip it.
mellosouls 6y ago
(2015)
deleted 6y ago
[deleted]
GoblinSlayer 6y ago
>As QBism understands a quantum measurement outcome, it’s personal. No one else can see it. I see it or you see it. There’s no transformation that takes the one personal experience to the other personal experience. William James was just wrong when he tried to argue that “two minds can know one thing.” EPR paradox demonstrates that observers can know each other experience.
brummm 6y ago
From the post 5 years ago, this blog post summarizes the article well: https://motls.blogspot.com/2015/06/is-quantum-reality-personal.html https://motls.blogspot.com/2015/06/is-quantum-reality-person... Edit: Going through recent posts of this guy, I would also like to state that anything non physics related on his blog is crazy right-wing babble.
hexxiiiz 6y ago
Am I missing something here? A wave function is NOT a probability distribution! Wave functions have phase! The double slit experiment and bells paradox both clearly show that quantum effects can be created that cannot be explained in terms of classical trajectories that are simply unknown. Phase can cause wave functions to interfere with themselves, and so forth ... I can only imagine that Fuchs must deal with this in his thousands of pages, but the article makes it seem like his interpretation was one dismissed at the beginning because quantum mechanics demonstrably involves effects that cannot just be a due to a lack of classical state information.
Koshkin 6y ago
> PROBABILITY DOES NOT EXIST That's what Bayesianists think, but not frequentists. (As a frequency, probability is very much real. And, what would be the point of talking about something that "does not exist," anyway?)

77 points by guerrilla 6y ago

Yes ... you add Bayesian to the thing and it becomes new, principled and superior. It’s been a trend for about 3 decades now.

faaabio1618 6y ago
Read the article, you can learn something :)

jbay808 6y ago

> Eventually my colleague Rüdiger Schack and I felt that to be consistent we had to break the ties with Jaynes and move more in the direction of de Finetti. For those who are curious, here's Jaynes' view on the subject: https://bayes.wustl.edu/etj/articles/prob.in.qm.pdf https://bayes.wustl.edu/etj/articles/prob.in.qm.pdf

kgwgk 6y ago
The entropic dynamics approach from Caticha is closer to Jaynes’ ideas (and more interesting than qbism in my opinion, as it’s quite different from standard QM instead of just giving a Bayesian interpretation to it): https://arxiv.org/abs/1908.04693 https://arxiv.org/abs/1908.04693

MindGods 6y ago

See the discussion from 2015: https://news.ycombinator.com/item?id=9714618 https://news.ycombinator.com/item?id=9714618 Same article but published by Wired.

gsliepen 6y ago

Too many people, including physicists, confuse theories with reality. Quantum mechanics is a very powerful theory that correctly predicts a lot of observed phenomena. But while QM talks about a wavefunction, it doesn't mean the wavefunction actually exists. I myself particularly like the Everett interpretation, which some believe implies a multiverse, but I don't think the actual existence of a multiverse is necessary.

moonchild 6y ago
When you say 'theory', I think you mean 'model'.
lmm 6y ago
What other definition is there for saying that something exists, than that it correctly predicts observed phenomena? If you say that the table in front of me exists, surely that's nothing more or less than saying that the concept of a table correctly predicts the table-like sensations you see and feel.
- guerrilla 6y ago
  There's an entire field of philosophy called ontology which includes metaontology and it answers your question as "many definitions." I recommend this book [1] by Berto and Plebani. SEP [2] also has about a dozen articles on the ontology of quantum mechanics and quantum physics more generally. [1]. https://www.bloomsbury.com/us/ontology-and-metaontology-9781472573308/ https://www.bloomsbury.com/us/ontology-and-metaontology-9781... [2]. https://plato.stanford.edu/contents.html#q https://plato.stanford.edu/contents.html#q
- someguyorother 6y ago
  To me, "exists" is stronger than "predicts observation", although I can't entirely describe how, except by example. Let's say you're in a game. You can create a physics of the game world based on how that game behaves. However, the game world doesn't exist, as such. It's the result of a pattern produced by a computer, interpreted by our minds, which fills in the blanks and makes the game world feel more real than it is. It makes sense that an account of existence should either include the substructure (in this case, the computer) or the observer (in this case, the mind doing the filling-in), or possibly both. On the other hand, a description of the behavior of the system is much simpler. Another example: simulation hypothesis people sometimes talk about the possibility of "breaking out" of the simulation, as if the simulation is less somehow less true than whatever is behind it. But from a predicting-observed-phenomenon perspective, what you describe by physics exists. So the distinction between the rules of physics that apply in a certain domain because you're in a simulation, and the rules of physics that apply in another domain once you find a way to break out, is entirely artificial. That people don't see it that way seems to indicate that they mean something else by existence.

shellac 6y ago

I'm struggling to see how this anything more than Bohm's theory with a dubious interpretation of the guiding wave (which, to be honest, Bohm himself was guilty of). Like Bell without the 'Beables'.

wcoenen 6y ago

If the wavefunction is assumed to only encode epistemic uncertainty of the observer, then how are phenomena like tunneling explained?

nonbel 6y ago
From my reading, they would say some particles are just much more energetic than usual (for some reason we are ignorant of). See the post above about flipping a coin. According to the statistical model we use for coin flips, it is really unlikely to flip 100 heads in a row but not impossible.
- wcoenen 6y ago
  Wouldn't it be possible to see this experimentally? You'd find particles jumping out of a "potential energy well" which they shouldn't be able to escape via tunneling.

RobertoG 6y ago

>>>"At the other end of the spectrum is Bruno de Finetti. He says there’s no reason whatsoever for my probabilities and yours to match, because mine are based on my experience and yours are based on your experience. " That doesn't deny an objective reality out there, it's just saying that we have different information about what it's out there and, therefore, we arrive to different conclusions. I don't understand how that perspective is different from just "objective Bayesianism" with different priors.

lilgreenland 6y ago
I agree. It feels like he is just combining normal Bayesianism with normal quantum mechanics. Which is seems fine, but I'm annoyed he dodged the question about nonconscious things also having a personalized set of priors. I'd like to hear him explain the single particle double slit experiment from this QBism perspective.
- nonbel 6y ago
  Sounds like the wave model describes the statistical properties of a population of photons. Eg, a coin flip is deterministic if you know all the forces involved (airflow, force of flip, exact distribution of mass of the coin, etc). But since we are usually ignorant of all that, instead we model it as a bernoulli trial.
  - kgwgk 6y ago
    But that’s not what qbism is about: a wave function (pure state) doesn’t represent ignorance about a true underlying physical state, it’s a maximally sharp state of belief.
    - nonbel 6y ago
      > Regarding quantum states as degrees of belief implies that the event of a quantum state changing when a measurement occurs—the "collapse of the wave function"—is simply the agent updating her beliefs in response to a new experience. https://en.m.wikipedia.org/wiki/Quantum_Bayesianism https://en.m.wikipedia.org/wiki/Quantum_Bayesianism You could be right, That is what this sounds like to me though. According to the model there is a 50% chance the coin will land on heads, until you flip it.

mellosouls 6y ago

(2015)

deleted 6y ago

[deleted]

GoblinSlayer 6y ago

>As QBism understands a quantum measurement outcome, it’s personal. No one else can see it. I see it or you see it. There’s no transformation that takes the one personal experience to the other personal experience. William James was just wrong when he tried to argue that “two minds can know one thing.” EPR paradox demonstrates that observers can know each other experience.

brummm 6y ago

From the post 5 years ago, this blog post summarizes the article well: https://motls.blogspot.com/2015/06/is-quantum-reality-personal.html https://motls.blogspot.com/2015/06/is-quantum-reality-person... Edit: Going through recent posts of this guy, I would also like to state that anything non physics related on his blog is crazy right-wing babble.

hexxiiiz 6y ago

Am I missing something here? A wave function is NOT a probability distribution! Wave functions have phase! The double slit experiment and bells paradox both clearly show that quantum effects can be created that cannot be explained in terms of classical trajectories that are simply unknown. Phase can cause wave functions to interfere with themselves, and so forth ... I can only imagine that Fuchs must deal with this in his thousands of pages, but the article makes it seem like his interpretation was one dismissed at the beginning because quantum mechanics demonstrably involves effects that cannot just be a due to a lack of classical state information.

Koshkin 6y ago

> PROBABILITY DOES NOT EXIST That's what Bayesianists think, but not frequentists. (As a frequency, probability is very much real. And, what would be the point of talking about something that "does not exist," anyway?)