5 ms·

> Physicists tend to like the many worlds interpretations. According to Sean Carroll, this is because if you 'buy' the mathematics of the wavefunction, even be

by platz 9y ago

> Physicists tend to like the many worlds interpretations. According to Sean Carroll, this is because if you 'buy' the mathematics of the wavefunction, even before collapse you already have to accept "many worlds" at the quantum level. "many worlds" for them simply means superposition/linear combinations. After all, if you already accept "superposition" at the level of quantum states, you don't have to invoke anything new to deal with so-called "collapse", if everything simply stays as superpositions i.e. linear combinations. Or, in other words, if you assume classical behavior first, and you need to get that out of superpositions at the quantum level, you need wavefunction collapse. but if you start with superpositions at the quantum level, you already have superpositions, and then classical behavior can simply be derived from locating yourself in one of those superpositions. Explained this way, "many worlds" doesn't seem so shocking, if you have already resigned yourself to quantum level superpositions. I think of many worlds as kind of a literal interpretation that quantum superpositions are fundamentally real, as opposed to quantum superpositions merely being a very accurate mathematical model. (Most scientists think QM represents something real instead of some lucky equations.)

westoncb 9y ago
This sounds a lot like someone has fallen for a subtle confusion of map and territory...
- platz 9y ago
  well you might want disagree with the most senior research prof at Caltech, but I woudln't. That's what they really think of many worlds. And, really, is it any worse than any of the alternatives?
  - westoncb 9y ago
    I'm just responding to this: > I think of many worlds as kind of a literal interpretation that quantum superpositions are fundamentally real, as opposed to quantum superpositions merely being a very accurate mathematical model. If the stance is predicated on that assumption, as you suggest (and I'm inclined to agree, having read other of Carroll's writings), then I have to continue disagreeing. If the rest of the world of physicist luminaries were unanimously aligned with Carroll it would be more difficult (but still tempting...)—but luckily that's not the case.
- DavidSJ 9y ago
  At some level, if we take scientific theories seriously as descriptions of the world out there, and not merely tools for prediction, then we have to assume some sort of isomorphism between the map (our theory) and the territory (the world), even if they're not the same thing. This isn't only for quantum theory.
  - westoncb 9y ago
    Isomorphism, yes, exactly—that's the basic principle of a map: it's a description that enables us to make predictions about the territory, because it's possible to put the two into systematic correspondence. However once you start considering the 'representational' features of the map, which aren't an essential part of the isomorphism, as equally real (because you've made the simplification: dealing with the map is the same as dealing with the territory—our minds are predisposed to do this in many cases)—then you're in trouble.
  - jackson1372 9y ago
    > we have to assume some sort of isomorphism between the map (our theory) and the territory (the world) But a mathematical model != a theoretical model. The very same mathematical model will be compatible with uncountably many theoretical models. (By 'theoretical model' I mean something like 'an interpretation of what the math is representing'.)So you can't read off theoretical structure from mathematical structure. And so you can't read off the structure of the world from mathematical structure.
    - lmm 9y ago
      > (By 'theoretical model' I mean something like 'an interpretation of what the math is representing'.)So you can't read off theoretical structure from mathematical structure. And so you can't read off the structure of the world from mathematical structure. Occam's razor favours a theoretical model that corresponds more closely to the mathematics, rather than one that adds a bunch of epicycles to arrive at a different interpretation. If you follow your logic then you can never reject geocentrism, because it's possible to create a geocentric model that generates the same predictions as a heliocentric one; nevertheless we would generally say that heliocentrism is "more true" and "more physically real" than geocentrism.
- coldtea 9y ago
  In physics the map IS the territory. Or, if you prefer, we're not merely constructing a map, but a model, that is, we try to feel out and understand the territory, what it's made of, and how it works.
  - westoncb 9y ago
    So you think an electron IS a mathematical expression, not that a mathematical expression describes its behavior? > ...we're not merely constructing a map, but a model, that is, we try to feel out and understand the territory, what it's made of, and how it works. 'map' is a metaphor there. You're description of what physics is doing still fits within the metaphor. It doesn't change the fact that there is something 'out there' and then there's our description of it, via physics, and our description is not the thing that's out there. Suppose we develop a unified theory in physics which supersedes current formulations of quantum theory. Then would the old quantum theory still BE the territory at that point? Or would it be just a less accurate description than the new one we came up with?
    - coldtea 9y ago
      >So you think an electron IS a mathematical expression, not that a mathematical expression describes its behavior? No, I think that a mathematical expression describes the behavior of something real as close as possible to our knowledge -- it's not just a picture of how it looks. In other words, in contrast with the map analogy, the equations for electrons etc can be used for a simulation. >Suppose we develop a unified theory in physics which supersedes current formulations of quantum theory. Then would the old quantum theory still BE the territory at that point? Or would it be just a less accurate description than the new one we came up with? Why assume one can describe the territory in just a single (perfect) level of representation? For some things not even the full precision we can muster today is even needed (e.g. I don't need Relativity to know where a baseball will land).
      - beobab 9y ago
        Are you saying that after a certain level of accuracy, it is impossible to be sure, but you CAN say for certain within an error radius?
- akvadrako 9y ago
  There is lots of mathematical evidence that every quantum state maps 1-to-1 on a physical state¹, or at least be uniquely determined by the physical state². The main assumption both make is that there is some physical state. So it doesn't really matter if it's a map or not - it tells you something about the territory. [1] The completeness of quantum theory for predicting measurement outcomes, https://arxiv.org/abs/1208.4123 https://arxiv.org/abs/1208.4123 [2] On the reality of the quantum state, https://arxiv.org/abs/1111.3328v3 https://arxiv.org/abs/1111.3328v3
  - n4r9 9y ago
    > The main assumption both make is that there is some physical state. I'd phrase this as: the main assumption is that reality is literally encoded by some sort of objective hidden variables theory.
    - akvadrako 9y ago
      I'm not sure what your point is, but it doesn't have to be hidden and in this case, objective just means two parties agree on the outcomes of experiments.
jackson1372 9y ago
> if you already accept "superposition" at the level of quantum states, you don't have to invoke anything new to deal with so-called "collapse" All three interpretations of QM 'accept' superposition, construed as a mathematical construct. What's at issue is how this mathematical construct maps onto reality. If you mean something more by 'accepting superposition', you have to spell out what that is. And doing that just leads you right back to the three different interpretations.
EGreg 9y ago
Well you may as well just accept nonlocality. After all, the other interpretations do nothing to rule it out!
- platz 9y ago
  There are lots of signs that locality is not tenable
- lmm 9y ago
  I want to keep locality. Being able to derive it would be a happy bonus, but I'm perfectly willing to adopt it as its own axiom.

by platz 9y ago

westoncb 9y ago

This sounds a lot like someone has fallen for a subtle confusion of map and territory...

platz 9y ago
well you might want disagree with the most senior research prof at Caltech, but I woudln't. That's what they really think of many worlds. And, really, is it any worse than any of the alternatives?
- westoncb 9y ago
  I'm just responding to this: > I think of many worlds as kind of a literal interpretation that quantum superpositions are fundamentally real, as opposed to quantum superpositions merely being a very accurate mathematical model. If the stance is predicated on that assumption, as you suggest (and I'm inclined to agree, having read other of Carroll's writings), then I have to continue disagreeing. If the rest of the world of physicist luminaries were unanimously aligned with Carroll it would be more difficult (but still tempting...)—but luckily that's not the case.
DavidSJ 9y ago
At some level, if we take scientific theories seriously as descriptions of the world out there, and not merely tools for prediction, then we have to assume some sort of isomorphism between the map (our theory) and the territory (the world), even if they're not the same thing. This isn't only for quantum theory.
- westoncb 9y ago
  Isomorphism, yes, exactly—that's the basic principle of a map: it's a description that enables us to make predictions about the territory, because it's possible to put the two into systematic correspondence. However once you start considering the 'representational' features of the map, which aren't an essential part of the isomorphism, as equally real (because you've made the simplification: dealing with the map is the same as dealing with the territory—our minds are predisposed to do this in many cases)—then you're in trouble.
- jackson1372 9y ago
  > we have to assume some sort of isomorphism between the map (our theory) and the territory (the world) But a mathematical model != a theoretical model. The very same mathematical model will be compatible with uncountably many theoretical models. (By 'theoretical model' I mean something like 'an interpretation of what the math is representing'.)So you can't read off theoretical structure from mathematical structure. And so you can't read off the structure of the world from mathematical structure.
  - lmm 9y ago
    > (By 'theoretical model' I mean something like 'an interpretation of what the math is representing'.)So you can't read off theoretical structure from mathematical structure. And so you can't read off the structure of the world from mathematical structure. Occam's razor favours a theoretical model that corresponds more closely to the mathematics, rather than one that adds a bunch of epicycles to arrive at a different interpretation. If you follow your logic then you can never reject geocentrism, because it's possible to create a geocentric model that generates the same predictions as a heliocentric one; nevertheless we would generally say that heliocentrism is "more true" and "more physically real" than geocentrism.
coldtea 9y ago
In physics the map IS the territory. Or, if you prefer, we're not merely constructing a map, but a model, that is, we try to feel out and understand the territory, what it's made of, and how it works.
- westoncb 9y ago
  So you think an electron IS a mathematical expression, not that a mathematical expression describes its behavior? > ...we're not merely constructing a map, but a model, that is, we try to feel out and understand the territory, what it's made of, and how it works. 'map' is a metaphor there. You're description of what physics is doing still fits within the metaphor. It doesn't change the fact that there is something 'out there' and then there's our description of it, via physics, and our description is not the thing that's out there. Suppose we develop a unified theory in physics which supersedes current formulations of quantum theory. Then would the old quantum theory still BE the territory at that point? Or would it be just a less accurate description than the new one we came up with?
  - coldtea 9y ago
    >So you think an electron IS a mathematical expression, not that a mathematical expression describes its behavior? No, I think that a mathematical expression describes the behavior of something real as close as possible to our knowledge -- it's not just a picture of how it looks. In other words, in contrast with the map analogy, the equations for electrons etc can be used for a simulation. >Suppose we develop a unified theory in physics which supersedes current formulations of quantum theory. Then would the old quantum theory still BE the territory at that point? Or would it be just a less accurate description than the new one we came up with? Why assume one can describe the territory in just a single (perfect) level of representation? For some things not even the full precision we can muster today is even needed (e.g. I don't need Relativity to know where a baseball will land).
    - beobab 9y ago
      Are you saying that after a certain level of accuracy, it is impossible to be sure, but you CAN say for certain within an error radius?
akvadrako 9y ago
There is lots of mathematical evidence that every quantum state maps 1-to-1 on a physical state¹, or at least be uniquely determined by the physical state². The main assumption both make is that there is some physical state. So it doesn't really matter if it's a map or not - it tells you something about the territory. [1] The completeness of quantum theory for predicting measurement outcomes, https://arxiv.org/abs/1208.4123 https://arxiv.org/abs/1208.4123 [2] On the reality of the quantum state, https://arxiv.org/abs/1111.3328v3 https://arxiv.org/abs/1111.3328v3
- n4r9 9y ago
  > The main assumption both make is that there is some physical state. I'd phrase this as: the main assumption is that reality is literally encoded by some sort of objective hidden variables theory.
  - akvadrako 9y ago
    I'm not sure what your point is, but it doesn't have to be hidden and in this case, objective just means two parties agree on the outcomes of experiments.

jackson1372 9y ago

> if you already accept "superposition" at the level of quantum states, you don't have to invoke anything new to deal with so-called "collapse" All three interpretations of QM 'accept' superposition, construed as a mathematical construct. What's at issue is how this mathematical construct maps onto reality. If you mean something more by 'accepting superposition', you have to spell out what that is. And doing that just leads you right back to the three different interpretations.

EGreg 9y ago

Well you may as well just accept nonlocality. After all, the other interpretations do nothing to rule it out!

platz 9y ago
There are lots of signs that locality is not tenable
lmm 9y ago
I want to keep locality. Being able to derive it would be a happy bonus, but I'm perfectly willing to adopt it as its own axiom.