37 ms·

Physicists want to rebuild quantum theory from scratch

90 points by cgmg 9y ago

noobermin 9y ago
All I ask is the headline not be "Physicists want..." but rather "Some physicists want..." A couple of people I've never heard of don't speak of all physicists, in fact most >[...] just shrug and say we have to live with the fact that quantum mechanics is weird. In fact, I don't think it's weird, I think it's reality.
- xelxebar 9y ago
  > In fact, I don't think it's weird, I think it's reality. At the risk of sounding snarky, I think it's useful to point out that we call it the Standard Model and not the Standard Reality. Model ≠ Reality, yadda yadda. We have an immensely useful model of fundamental physics as long as the energies are low enough. However, I feel that we lose a lot by letting that utility stop us from asking epistemic questions of the model itself. Historically, math has gained a lot by taking such questions seriously, especially in the areas of logic and computation.
  - astrodust 9y ago
    Sure, but string theory shows what happens if you can't come up with a testable theory in a reasonable timeframe. It is the ultimate "version 2.0" product. Missing features in the original, vastly over-engineered, and never ready to ship.
    - xelxebar 9y ago
      I wouldn't be so quick to judge. It's pure research, and String Theory has pioneered a lot of new ideas that have successfully cross-pollinated into other fields. Even the LHC employs String Theorists with good reason. Seems a mistake to write it off as "not delivering" simply because it hasn't given us exactly what we originally expected. On a more social level, a focus on "delivering" and "impact" in pure science seems like it can be taken to the point of shooting ourselves in the foot. Think of all the discoveries from pure exploratory research that we recognized as useful only after the fact.
      - nikofeyn 9y ago
        so quick? it's not as if string theory is just getting started.
    - empath75 9y ago
      That string theory is already compatible with everything we know about reality is a titanic achievement. If you think it's not, go ahead and list all of the other alternatives that also have a hope of unifying gravity?
      - red75prime 9y ago
        String theory is in fact compatible with a large number of possible realities. That's the problem.
      - jcranmer 9y ago
        Except that string theory requires supersymmetry, and the latest LHC results are not happy for supersymmetry. As for other unifying theories, loop quantum gravity is somewhat popular. And Wikipedia has a nice list of alternative theories: https://en.wikipedia.org/wiki/Quantum_gravity#Other_approaches https://en.wikipedia.org/wiki/Quantum_gravity#Other_approach.... String theory is far from the only game in town, despite what string theorists would have you believe.
  - platz 9y ago
    > Model ≠ Reality, yadda yadda. I think im a fan of what is described as quantum bayesianism in the article, that quantum mechanics is basically a probabiltiy theory, and this probability theory is required to express our expectations from measurements (quantum mechanics encodes our beliefs about what will be observed given some knowledge about a system) and this is fundamentally a "retreat" because we dont know how to describe the underlying reality. even though calculating the probabilitoes may be very precise. but i am havig trouble distinguising quantum bayesianism from the standard "model vs reality" fare as the motovation seems very similar
    - ianai 9y ago
      "model vs reality" implies a very clear delineation between theory and data. Bayesian models muddle that up - particularly with (based on my understanding of) the standard model. (Insert the classic statistical decision theory debate about classic/Bayesian models here.) What I really wonder about is how, if ever, we will refine our abilities to observe the finer grains - and to what extent that's possible. I remember physicists discussing the observations possible given particle accelerator size from lectures in undergrad. The future was not very bright.
    - noobermin 9y ago
      The thing I say is "what underlying reality?" If you can't measure it, how can you make a theory out of it or research it (or publish papers on it unless you're a string theorist)? If something is not measurable, then how can you claim it exists or not? Whenever people ask me these "deep questions" after I tell them I'm a physicist, I tell them that. Science is all about the reality you can measure, not about meaning and what lies "deeper".
      - platz 9y ago
        I take it you are a fan of the copenhagen interpretation of quantum mechanics. its the right answer for making calculations. but how do come up with a new theory? you have to tell a story or envision an underlying reason to justify it. new theories dont come out of nowhere. this is also like saying the universe in the time of newton consisted of only newtons laws, which is untrue. if the universe is science, then you have to say the universe is changing as science changes. unless the universe really is just made of published journal papers.
  - noobermin 9y ago
    When I say "reality" as a scientist, I mean experiment, and the standard model does a pretty decent job of fitting experiment/observation. I just had this conversation last week actually, where a group mate and I were discussing "determinism" and basically, we agreed scientists have weaker definitions for words like "reality" and "determined" and such that essentially mean "within the error bars of repeatable experiment."
- al452 9y ago
  Well the original article headline doesn't talk about anyone "wanting" anything at all -- I don't know, why would Wired repost articles from Quanta, changing only the headline? https://www.quantamagazine.org/quantum-theory-rebuilt-from-simple-physical-principles-20170830/ https://www.quantamagazine.org/quantum-theory-rebuilt-from-s...
  - bazzargh 9y ago
    From Quanta Magazine's 'about' page: To reach an even wider audience, we have syndication partnerships with several publications, which reprint our articles. https://www.quantamagazine.org/about/ https://www.quantamagazine.org/about/ And I presume what's in it for Wired is that it was well written - thanks for pointing out it came from Quanta, I was surprised reading something this detailed from Wired (with links to all the original papers, no less). Sadly the headline became their Battlechess Duck (https://blog.codinghorror.com/new-programming-jargon/ https://blog.codinghorror.com/new-programming-jargon/)
- WhitneyLand 9y ago
  But they are right, it is totally weird. When people say that they usually mean counterintuitive with respect to everyday experience. It makes it progressively harder for lay people to grasp bits of it, from classical mechanics, to general relativity, to QM. Maybe it’s even a factor for theoreticians, but that’s just speculation.
  - noobermin 9y ago
    I guess my perspective is that a lot of physics is weird. When I learned Newton's First Law in undergrad, it was counterintuitive, because I based my knowledge on experience. The idea that throwing a ball out of the window of a moving car would have a velocity component in the direction of the car contradicted naive experience of putting your hand outside the window and feeling the wind. Not just GR, but even Newtonian gravity is weird, how is the force making me fall the same as the force that makes planets move in circles[0]? May be "weird" isn't the word but "confusing/unexpected" is. I feel like a lot of the "weirdness" of QM is really due to physicists who were wedded to classical ways of thinking are confounded when x and p don't commute, and what that means. That plus not knowing about the delayed choice quantum eraser (not their fault).
    - tbabb 9y ago
      There is a "sermon" that is given at the beginning of almost every QM intro lecture, and as it was given by Feynman more than a half century ago, it went something like: > "Quantum mechanics is weird. Particles are not like baseballs; leave your classical intuitions behind." Which is all well and good. But it has subtly shifted to: > "Quantum mechanics is weird. Our human brains are not wired to understand it intuitively, so don't try, because you will fail and get the wrong answer. Just turn the math crank and get results." And IMHO that attitude is both (a) flatly wrong and (b) mind poison. With regards to (a), the human brain is a turning machine-- it can simulate any rules. Learn the rules and work with them enough, and they will become intuitive. If you can learn DiffEQ or Fourier transforms, you can learn QM. Actually, the rules for the "spooky bits" are probably simpler than both of those two things. For (b), all these undergraduates grow up into research physicists and still believe the creed they were solemnly lectured on Day One about how to think about quantum mechanics (which is to NOT think about it). As such, they are all very bad scientists because they have stopped wondering about what makes it all tick. Case in point: A good fraction of scientists still believe in "wavefunction collapse", which blows my mind, because it's so self-evidently rejectable[1]. Science went from a Plum Pudding atom to quantum field theory in about 30 years. It's been nearly a century since then, and we don't really understand things much more deeply, and I think this is because we are too busy banging particles together and not asking "why" enough. I (boldly) posit that if undergrads didn't get the "don't ask" lecture, quantum physics would be decades ahead of where it is today. We can understand, and we should try, and I would love it if undergrads were told that instead. The kind of thing in this article is what more serious physicists should be doing. [1] This is a controversial statement, but that's kind of my point. Explaining Why Not Copenhagen is probably a topic for a separate diatribe.
- vorotato 9y ago
  Okay but it's not reality, it's a mathematical model and if you don't look for other mathematical models you could be missing a much cleaner simpler model that is just as accurate in predicting outcomes.
siglesias 9y ago
It will be interesting to see if theoretical physics and computer science converge at all over the next century. Intuitively there’s much to suggest that our understanding of computational limits on things (not to mention the idea that the world itself is a simulation of some kind) has analogs in fundamental physical limits (speed of light, quantum noise).
- f00_ 9y ago
  I would be interested if anyone knows about the connection between information theoretic entropy and physical entropy. I think thermodynamics and statistical physics are really interesting. In Parallel Distributed Processing they discuss an extension of the entropy metaphor to learning and neural networks https://mitpress.mit.edu/books/parallel-distributed-processing https://mitpress.mit.edu/books/parallel-distributed-processi...
  - grondilu 9y ago
    > I would be interested if anyone knows about the connection between information theoretic entropy and physical entropy. I'm pretty sure they're the same, with minor differences in notation and units, unless of course I misunderstand what you mean by "physical entropy". Entropy in physics only got a precise definition once physicists understood that the concept really comes from information theory.
    - f00_ 9y ago
      erm, I think boltzman figured out entropy for thermo like 100 years before shannon's theory of communication could be totally wrong though entropy, complexity, and evolution are words that come to mind
      - vitus 9y ago
        Yes, Shannon explicitly stated in Mathematical Theory of Communication that the general form was the same as that in statistical mechanics: "The form of H will be recognized as that of entropy as defined in certain formulations of statistical mechanics where p_i is the probability of a system being in cell i of its phase space. H is then, for example, the H in Boltzmann’s famous H theorem." where the general form was H = -K\sum p_i * log(p_i) IIRC, this form is the only kind with the following two properties: - chain rule -- H(X,Y) = H(X) + H(Y|X) - maximized for the uniform distribution.
girzel 9y ago
I found this article's explanation of the basic state of physics to be one of the best I've read. I know squat about the field, and so can't say if it was accurate or not, but the layman's explanation of the core problems of quantum theory, the probability and whatnot, was easy to grasp, and made sense.
erik_landerholm 9y ago
Information theory will hopefully give us deeper insight into the why. If we derive QM from information theory it might come at it from another angle and provide different insights. I had read about people trying this in the past, but not for a while...maybe it proved fruitless or uninteresting.
Koshkin 9y ago
Problem is, all these redefinitions of quantum mechanics via "quantum logic" or "quantum probability theory", while looking more fundamental and formal than the usual theory based on Schrödinger's equation and Born's rule, do not make it any more intuitive and do not allow anyone to say, "aha! now I get it!". This is because these new foundations themselves are just as unintuitive as quantum mechanics... [Edit] On the other hand, I find the famous derivation of Schrödinger's equation by Feynman illuminating: http://fermatslibrary.com/s/feynmans-derivation-of-the-schrodinger-equation http://fermatslibrary.com/s/feynmans-derivation-of-the-schro....
kodfodrasz 9y ago
So this is a project to create the "Maxwell equations of Quantum Physics"?
taw55 9y ago
What if quantum mechanics are the causal basis for spacetime. Then to the observer it might appear as random, because spacetime is a prerequisite for observation. Also for causation, this must imply time moves sideways in the quantum domain. Clearly! I clearly had one to many to drink. My head hurts.
rocqua 9y ago
I'm surprised time and time again by the removal of causal ordering from quantum mechanics. It seems to be throwing away so much.

90 points by cgmg 9y ago

All I ask is the headline not be "Physicists want..." but rather "Some physicists want..." A couple of people I've never heard of don't speak of all physicists, in fact most >[...] just shrug and say we have to live with the fact that quantum mechanics is weird. In fact, I don't think it's weird, I think it's reality.

xelxebar 9y ago
> In fact, I don't think it's weird, I think it's reality. At the risk of sounding snarky, I think it's useful to point out that we call it the Standard Model and not the Standard Reality. Model ≠ Reality, yadda yadda. We have an immensely useful model of fundamental physics as long as the energies are low enough. However, I feel that we lose a lot by letting that utility stop us from asking epistemic questions of the model itself. Historically, math has gained a lot by taking such questions seriously, especially in the areas of logic and computation.
- astrodust 9y ago
  Sure, but string theory shows what happens if you can't come up with a testable theory in a reasonable timeframe. It is the ultimate "version 2.0" product. Missing features in the original, vastly over-engineered, and never ready to ship.
  - xelxebar 9y ago
    I wouldn't be so quick to judge. It's pure research, and String Theory has pioneered a lot of new ideas that have successfully cross-pollinated into other fields. Even the LHC employs String Theorists with good reason. Seems a mistake to write it off as "not delivering" simply because it hasn't given us exactly what we originally expected. On a more social level, a focus on "delivering" and "impact" in pure science seems like it can be taken to the point of shooting ourselves in the foot. Think of all the discoveries from pure exploratory research that we recognized as useful only after the fact.
    - nikofeyn 9y ago
      so quick? it's not as if string theory is just getting started.
  - empath75 9y ago
    That string theory is already compatible with everything we know about reality is a titanic achievement. If you think it's not, go ahead and list all of the other alternatives that also have a hope of unifying gravity?
    - red75prime 9y ago
      String theory is in fact compatible with a large number of possible realities. That's the problem.
    - jcranmer 9y ago
      Except that string theory requires supersymmetry, and the latest LHC results are not happy for supersymmetry. As for other unifying theories, loop quantum gravity is somewhat popular. And Wikipedia has a nice list of alternative theories: https://en.wikipedia.org/wiki/Quantum_gravity#Other_approaches https://en.wikipedia.org/wiki/Quantum_gravity#Other_approach.... String theory is far from the only game in town, despite what string theorists would have you believe.
- platz 9y ago
  > Model ≠ Reality, yadda yadda. I think im a fan of what is described as quantum bayesianism in the article, that quantum mechanics is basically a probabiltiy theory, and this probability theory is required to express our expectations from measurements (quantum mechanics encodes our beliefs about what will be observed given some knowledge about a system) and this is fundamentally a "retreat" because we dont know how to describe the underlying reality. even though calculating the probabilitoes may be very precise. but i am havig trouble distinguising quantum bayesianism from the standard "model vs reality" fare as the motovation seems very similar
  - ianai 9y ago
    "model vs reality" implies a very clear delineation between theory and data. Bayesian models muddle that up - particularly with (based on my understanding of) the standard model. (Insert the classic statistical decision theory debate about classic/Bayesian models here.) What I really wonder about is how, if ever, we will refine our abilities to observe the finer grains - and to what extent that's possible. I remember physicists discussing the observations possible given particle accelerator size from lectures in undergrad. The future was not very bright.
  - noobermin 9y ago
    The thing I say is "what underlying reality?" If you can't measure it, how can you make a theory out of it or research it (or publish papers on it unless you're a string theorist)? If something is not measurable, then how can you claim it exists or not? Whenever people ask me these "deep questions" after I tell them I'm a physicist, I tell them that. Science is all about the reality you can measure, not about meaning and what lies "deeper".
    - platz 9y ago
      I take it you are a fan of the copenhagen interpretation of quantum mechanics. its the right answer for making calculations. but how do come up with a new theory? you have to tell a story or envision an underlying reason to justify it. new theories dont come out of nowhere. this is also like saying the universe in the time of newton consisted of only newtons laws, which is untrue. if the universe is science, then you have to say the universe is changing as science changes. unless the universe really is just made of published journal papers.
- noobermin 9y ago
  When I say "reality" as a scientist, I mean experiment, and the standard model does a pretty decent job of fitting experiment/observation. I just had this conversation last week actually, where a group mate and I were discussing "determinism" and basically, we agreed scientists have weaker definitions for words like "reality" and "determined" and such that essentially mean "within the error bars of repeatable experiment."
al452 9y ago
Well the original article headline doesn't talk about anyone "wanting" anything at all -- I don't know, why would Wired repost articles from Quanta, changing only the headline? https://www.quantamagazine.org/quantum-theory-rebuilt-from-simple-physical-principles-20170830/ https://www.quantamagazine.org/quantum-theory-rebuilt-from-s...
- bazzargh 9y ago
  From Quanta Magazine's 'about' page: To reach an even wider audience, we have syndication partnerships with several publications, which reprint our articles. https://www.quantamagazine.org/about/ https://www.quantamagazine.org/about/ And I presume what's in it for Wired is that it was well written - thanks for pointing out it came from Quanta, I was surprised reading something this detailed from Wired (with links to all the original papers, no less). Sadly the headline became their Battlechess Duck (https://blog.codinghorror.com/new-programming-jargon/ https://blog.codinghorror.com/new-programming-jargon/)
WhitneyLand 9y ago
But they are right, it is totally weird. When people say that they usually mean counterintuitive with respect to everyday experience. It makes it progressively harder for lay people to grasp bits of it, from classical mechanics, to general relativity, to QM. Maybe it’s even a factor for theoreticians, but that’s just speculation.
- noobermin 9y ago
  I guess my perspective is that a lot of physics is weird. When I learned Newton's First Law in undergrad, it was counterintuitive, because I based my knowledge on experience. The idea that throwing a ball out of the window of a moving car would have a velocity component in the direction of the car contradicted naive experience of putting your hand outside the window and feeling the wind. Not just GR, but even Newtonian gravity is weird, how is the force making me fall the same as the force that makes planets move in circles[0]? May be "weird" isn't the word but "confusing/unexpected" is. I feel like a lot of the "weirdness" of QM is really due to physicists who were wedded to classical ways of thinking are confounded when x and p don't commute, and what that means. That plus not knowing about the delayed choice quantum eraser (not their fault).
  - tbabb 9y ago
    There is a "sermon" that is given at the beginning of almost every QM intro lecture, and as it was given by Feynman more than a half century ago, it went something like: > "Quantum mechanics is weird. Particles are not like baseballs; leave your classical intuitions behind." Which is all well and good. But it has subtly shifted to: > "Quantum mechanics is weird. Our human brains are not wired to understand it intuitively, so don't try, because you will fail and get the wrong answer. Just turn the math crank and get results." And IMHO that attitude is both (a) flatly wrong and (b) mind poison. With regards to (a), the human brain is a turning machine-- it can simulate any rules. Learn the rules and work with them enough, and they will become intuitive. If you can learn DiffEQ or Fourier transforms, you can learn QM. Actually, the rules for the "spooky bits" are probably simpler than both of those two things. For (b), all these undergraduates grow up into research physicists and still believe the creed they were solemnly lectured on Day One about how to think about quantum mechanics (which is to NOT think about it). As such, they are all very bad scientists because they have stopped wondering about what makes it all tick. Case in point: A good fraction of scientists still believe in "wavefunction collapse", which blows my mind, because it's so self-evidently rejectable[1]. Science went from a Plum Pudding atom to quantum field theory in about 30 years. It's been nearly a century since then, and we don't really understand things much more deeply, and I think this is because we are too busy banging particles together and not asking "why" enough. I (boldly) posit that if undergrads didn't get the "don't ask" lecture, quantum physics would be decades ahead of where it is today. We can understand, and we should try, and I would love it if undergrads were told that instead. The kind of thing in this article is what more serious physicists should be doing. [1] This is a controversial statement, but that's kind of my point. Explaining Why Not Copenhagen is probably a topic for a separate diatribe.
vorotato 9y ago
Okay but it's not reality, it's a mathematical model and if you don't look for other mathematical models you could be missing a much cleaner simpler model that is just as accurate in predicting outcomes.

siglesias 9y ago

It will be interesting to see if theoretical physics and computer science converge at all over the next century. Intuitively there’s much to suggest that our understanding of computational limits on things (not to mention the idea that the world itself is a simulation of some kind) has analogs in fundamental physical limits (speed of light, quantum noise).

f00_ 9y ago
I would be interested if anyone knows about the connection between information theoretic entropy and physical entropy. I think thermodynamics and statistical physics are really interesting. In Parallel Distributed Processing they discuss an extension of the entropy metaphor to learning and neural networks https://mitpress.mit.edu/books/parallel-distributed-processing https://mitpress.mit.edu/books/parallel-distributed-processi...
- grondilu 9y ago
  > I would be interested if anyone knows about the connection between information theoretic entropy and physical entropy. I'm pretty sure they're the same, with minor differences in notation and units, unless of course I misunderstand what you mean by "physical entropy". Entropy in physics only got a precise definition once physicists understood that the concept really comes from information theory.
  - f00_ 9y ago
    erm, I think boltzman figured out entropy for thermo like 100 years before shannon's theory of communication could be totally wrong though entropy, complexity, and evolution are words that come to mind
    - vitus 9y ago
      Yes, Shannon explicitly stated in Mathematical Theory of Communication that the general form was the same as that in statistical mechanics: "The form of H will be recognized as that of entropy as defined in certain formulations of statistical mechanics where p_i is the probability of a system being in cell i of its phase space. H is then, for example, the H in Boltzmann’s famous H theorem." where the general form was H = -K\sum p_i * log(p_i) IIRC, this form is the only kind with the following two properties: - chain rule -- H(X,Y) = H(X) + H(Y|X) - maximized for the uniform distribution.

girzel 9y ago

I found this article's explanation of the basic state of physics to be one of the best I've read. I know squat about the field, and so can't say if it was accurate or not, but the layman's explanation of the core problems of quantum theory, the probability and whatnot, was easy to grasp, and made sense.

erik_landerholm 9y ago

Information theory will hopefully give us deeper insight into the why. If we derive QM from information theory it might come at it from another angle and provide different insights. I had read about people trying this in the past, but not for a while...maybe it proved fruitless or uninteresting.

Koshkin 9y ago

Problem is, all these redefinitions of quantum mechanics via "quantum logic" or "quantum probability theory", while looking more fundamental and formal than the usual theory based on Schrödinger's equation and Born's rule, do not make it any more intuitive and do not allow anyone to say, "aha! now I get it!". This is because these new foundations themselves are just as unintuitive as quantum mechanics... [Edit] On the other hand, I find the famous derivation of Schrödinger's equation by Feynman illuminating: http://fermatslibrary.com/s/feynmans-derivation-of-the-schrodinger-equation http://fermatslibrary.com/s/feynmans-derivation-of-the-schro....

kodfodrasz 9y ago

So this is a project to create the "Maxwell equations of Quantum Physics"?

taw55 9y ago

What if quantum mechanics are the causal basis for spacetime. Then to the observer it might appear as random, because spacetime is a prerequisite for observation. Also for causation, this must imply time moves sideways in the quantum domain. Clearly! I clearly had one to many to drink. My head hurts.

rocqua 9y ago

I'm surprised time and time again by the removal of causal ordering from quantum mechanics. It seems to be throwing away so much.