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"The Many-Worlds Interpretation has it that each time we make a measurement, reality splits into several alternative versions, identical except for the measurem

"The Many-Worlds Interpretation has it that each time we make a measurement, reality splits into several alternative versions, identical except for the measurement outcome." That's not right, the Many-Worlds Interpretation is just that the wavefunction in the Schrödinger equation (or its generalizations) is real, and it rejects that there's a separate process that somehow collapses the wavefunction to the single "branch" we perceive ourselves to be in. At the metaphysical level, there's no splitting involved, and no ontological measurements either (much less a "we" to do the measuring).

millstone 6y ago
No offense intended, but the "lost contact with empirical reality" critique really lands for the above description of MWI. A mathematical construct (the wavefunction) is taken as more real than basic empirical experiences like "measurements" and "we."
- Konohamaru 6y ago
  How do we know that opponents of MWI aren't succumbing to antibrunoist prejudice? > [Giordano Bruno] is known for his cosmological theories, which conceptually extended the then-novel Copernican model. He proposed that the stars were distant suns surrounded by their own planets, and he raised the possibility that these planets might foster life of their own, a philosophical position known as cosmic pluralism. I need to point out that he was burned at the stake for advocating cosmic pluralism.
  - canjobear 6y ago
    Later observations proved Bruno's speculations to be correct. But MWI does not make different predictions from other quantum interpretations. No observations can confirm or falsify it.
    - Konohamaru 6y ago
      Maybe in the greater context of our universe cosmic pluralism is a design pattern, which would make MWI a more preferred interpretation.
    - baddox 6y ago
      Modern cosmology by definition doesn’t make different predictions than saying “cosmological models mention things like stars and galaxies, and those models fit our observations, but those stars and galaxies aren’t technically real.”
  - phaemon 6y ago
    > I need to point out that he was burned at the stake for advocating cosmic pluralism I need to point out that he wasn't. His heresy trial had nothing to do with his cosmic beliefs. He was convicted for teaching religious beliefs, as a Catholic, that were contrary to Catholic dogma. The church punishment for this was excommunication but the secular punishment was execution, so he got burned.
- baddox 6y ago
  The mathematical construct was developed/discovered to explain observations. Normally when we do that we consider the mathematical explanation to be “real” in that it is describing reality.
- adeledeweylopez 6y ago
  One of the major aims of physics is to try to describe reality with mathematical constructs. If you start with what can be directly observed or experienced, then that's phenomenology. Those are both valid and interesting ways of trying to understand reality, and I believe they are ultimately fully compatible with each other. But I think you are trying to hold physics to phenomenology standards in a way that doesn't make sense. No one thinks that Newton's theory of gravity "lost contact with empirical reality" because it doesn't have measurements or people as ontological components. Anyway, that's all beside the point I was trying to make, which was just that the description of the MWI in the article was plain wrong.
  - Ma8ee 6y ago
    But Newtonian physics is compatible with our experience of reality. The Many Worlds Interpretation as described above isn’t.
    - DiogenesKynikos 6y ago
      How is MWI incompatible with our experience of reality?
      - TheOtherHobbes 6y ago
        We experience one reality, not many realities. MWI handwaves that problem away without really explaining it. "It's random but subject to the Born Rule" is a description of what's already observed, not an explanation with predictive power for new and distinct observations. There are much more complex criticisms that use words like "ontic" and "epistemic", but that's the fundamental problem that MWI claims to solve but doesn't.
        DiogenesKynikos 6y ago
        > We experience one reality, not many realities. How does MWI imply that we should simultaneously experience multiple realities? If two different states of you experience two different realities, each state of you is only aware of one reality. MWI largely reduces to something like the Copenhagen interpretation for large systems. It's just that MWI explains the transition between the quantum and classical regime, doesn't require any ad hoc rules about observers, and doesn't need Schrödinger's equation to be violated.
- feanaro 6y ago
  I think there is some misunderstanding here based on the wording used. OPs point is simply that there is no separate, explicit branching process. Instead, there is only the normal, continuous evolution of the wavefunction. Our experience is recovered from this by positing that subjective/phenomenological experience is somehow tied to the individual components of the wavefunction. Since the individual components don't interact with each other, it gives the appearance of branching. This is compatible with our observations.
  - ithkuil 6y ago
    Furthermore it firmly places ourselves and our own experiences within the very same fabric of reality it's describing. This is a rather inevitable problem of a fundamental theory of reality, since we ourselves are part of it and our inner working (whatever that is) must be layered on top of that fundamental machinery.
  - kgwgk 6y ago
    So we get from the “the wave function somehow collapses” to “the phenomelogical experience is somehow tied to the individual components wave function” which are somehow connected go the measurements.
    - feanaro 6y ago
      You're right regarding the first part, we don't have a clear explanation of how the wave function might be related to subjective experience, but that's mostly because we don't have a good account of subjective experience at all. For the second part, there's nothing mysterious going on at all: measurement is simply physical interaction.
      - kgwgk 6y ago
        What are "the individual components of the wave function"? They are a mathematical construction. The wave function can be decomposed in many (and infinity of) ways. Why is one decomposition chosen and not another? Or are all the decompositions equally "(un)real"? The issue is not so simple and it's related to the "mysteriousness" of the first part.
- cjfd 6y ago
  From a physics point of view this is a very strange thing to say. Why are 'we' or 'measurements' things of special status? Because we have a soul or something? Now, that would be a theory where an abstract concept is taken to be more real than observable things. The measurement apparatus is also a physical thing that should be described by the physical theory in use as would the humans be. The very painful point about the copenhagen interpretation is this distinction between 'normal' time evolution and the special procedure when a 'measurement' is carried out. Actually, there exist mathematical proofs that the normal time evolution when applied in cases where information is transferred from microscopic stats to macroscopic ones leads to something that looks like a collapse of the wave function but is actually a split of it. This is as a physical theory much more attractive than giving a 'measurement' a special status. The question what this all means is a bit more mind-boggling though including multiple worlds and that kind of stuff. Taking 'a mathematical construct as more real than basic empirical experiences' is basically the history of physics and it has in the past been highly successful.
  - chongli 6y ago
    Why are 'we' or 'measurements' things of special status? Because we experience the world through our senses. Everything else is one mathematical model or another that we’ve created. And our models aren’t even consistent! very painful point about the copenhagen interpretation is this distinction between 'normal' time evolution and the special procedure when a 'measurement' is carried out This is not a special procedure. Measurement occurs whenever physical interactions take place. To measure a particle, we bounce another particle off of it and then try to detect the result. The measurement is the particle collision, not the detection. It’s like playing billiards in the dark. We don’t know where the balls are. Taking 'a mathematical construct as more real than basic empirical experiences' is basically the history of physics and it has in the past been highly successful. Except for all of the times when it broke down. When one model was found to contradict our experiments and we had to replace it with another, which later turned out to be wrong as well. Perhaps the most embarrassing example of this, in human history, is all of our attempts to make geocentric models work [1]. The most well-known critique of science’s institutional habit of inventing new models whenever old ones broke down is probably Kuhn’s paradigms [2]. If you’re interested, you’re better off reading Kuhn than anything I have to write here. I think the best evidence for Kuhn’s thesis is the abject disappointment we witness every time particle physicists fail to overturn the standard model. If that’s not supremacy of measurement, then I don’t what is. [1] https://en.wikipedia.org/wiki/Geocentric_model https://en.wikipedia.org/wiki/Geocentric_model [2] https://en.wikipedia.org/wiki/The_Structure_of_Scientific_Revolutions https://en.wikipedia.org/wiki/The_Structure_of_Scientific_Re...
- sullyj3 6y ago
  I mean, it seems strange to reject implications of a successful model if those implications aren't observable. Eg, I believe that stuff exists outside our light cone, because it would be unparsimonious for there to be an extra rule saying that stuff that I can't access doesn't exists.
- Viliam1234 6y ago
  > A mathematical construct (the wavefunction) is taken as more real than basic empirical experiences like "measurements" and "we." In chemistry, atoms are also taken as more real than "measurements" and "we". Some chemists would probably insist that "we" are actually composed of atoms.
vixen99 6y ago
A first rate presentation on this topic is 'The emergent multiverse' by David Wallace. There's a detailed review in http://philsci-archive.pitt.edu/10940/1/Wallace_review_final_single-spaced.pdf http://philsci-archive.pitt.edu/10940/1/Wallace_review_final... In the book, Wallace quotes an interchange between Paul Davies and David Deutsch. <Davies> "So the parallel universes are cheap on assumptions but expensive on universes?" <Deutsch> "Exactly right. In physics we always try to make things cheap on assumptions." & Wallace re-quotes 'I do not know how to refute an incredulous stare'.
- im3w1l 6y ago
  Multiverse and many-worlds are two different things.
throwawayhacka 6y ago
uh... didnt early proponents of many worlds interpretation actually say that it did? Say Hugh Evrett? If it is reinterpreted to say otherwise, is it really the same QM model anymore?
pontus 6y ago
The MWI is literally obtained by taking traditional Copenhagen QM and removing the postulate of measurement. In other words, it is by the most genuine way of measuring complexity of a theory, demonstrably simpler than copenhagen! We just don't like it because it doesn't jive with our experience... it feels weird. When you have two theories that make the same predictions, but one is strictly simpler than the other, Occam's razor tells us to prefer the simpler one. In my mind, MWI or something akin to it, is the way to go, and is generally the way I conceptually think about QM.
- hackinthebochs 6y ago
  I don't think you get to claim simplicity for the theory that results in an exponential explosion of entities. Simplicity isn't just about descriptive simplicity.
  - pontus 6y ago
    That's not the right way to frame MWI, there's no explosion of entities at all, just a single wave function that evolves. The wave function starts out being a function of n variables, evolves according to a differential equation and remains a function of n variables.
    - pontus 6y ago
      Put another way, suppose you have some linear dynamical differential equation in n variables that you solve somehow. Then, take that solution and expand it in some set of basis functions (e.g. a Fourier series). You wouldn't throw your hands up in the air and say "wow that's so complex, look at all those infinite terms in the solution!". The complexity isn't really there, it just appears to be there because you've chosen to expand your solution in a basis that makes it appears really complex. Similarly in the MWI we see something that looks complex simply because we've chosen to expand the solution in a set of states that makes sense to us (state1 = particle at location 1, state2 = particle at location 2, ...)
      - 6y ago

millstone 6y ago

No offense intended, but the "lost contact with empirical reality" critique really lands for the above description of MWI. A mathematical construct (the wavefunction) is taken as more real than basic empirical experiences like "measurements" and "we."

Konohamaru 6y ago
How do we know that opponents of MWI aren't succumbing to antibrunoist prejudice? > [Giordano Bruno] is known for his cosmological theories, which conceptually extended the then-novel Copernican model. He proposed that the stars were distant suns surrounded by their own planets, and he raised the possibility that these planets might foster life of their own, a philosophical position known as cosmic pluralism. I need to point out that he was burned at the stake for advocating cosmic pluralism.
- canjobear 6y ago
  Later observations proved Bruno's speculations to be correct. But MWI does not make different predictions from other quantum interpretations. No observations can confirm or falsify it.
  - Konohamaru 6y ago
    Maybe in the greater context of our universe cosmic pluralism is a design pattern, which would make MWI a more preferred interpretation.
  - baddox 6y ago
    Modern cosmology by definition doesn’t make different predictions than saying “cosmological models mention things like stars and galaxies, and those models fit our observations, but those stars and galaxies aren’t technically real.”
- phaemon 6y ago
  > I need to point out that he was burned at the stake for advocating cosmic pluralism I need to point out that he wasn't. His heresy trial had nothing to do with his cosmic beliefs. He was convicted for teaching religious beliefs, as a Catholic, that were contrary to Catholic dogma. The church punishment for this was excommunication but the secular punishment was execution, so he got burned.
baddox 6y ago
The mathematical construct was developed/discovered to explain observations. Normally when we do that we consider the mathematical explanation to be “real” in that it is describing reality.
adeledeweylopez 6y ago
One of the major aims of physics is to try to describe reality with mathematical constructs. If you start with what can be directly observed or experienced, then that's phenomenology. Those are both valid and interesting ways of trying to understand reality, and I believe they are ultimately fully compatible with each other. But I think you are trying to hold physics to phenomenology standards in a way that doesn't make sense. No one thinks that Newton's theory of gravity "lost contact with empirical reality" because it doesn't have measurements or people as ontological components. Anyway, that's all beside the point I was trying to make, which was just that the description of the MWI in the article was plain wrong.
- Ma8ee 6y ago
  But Newtonian physics is compatible with our experience of reality. The Many Worlds Interpretation as described above isn’t.
  - DiogenesKynikos 6y ago
    How is MWI incompatible with our experience of reality?
    - TheOtherHobbes 6y ago
      We experience one reality, not many realities. MWI handwaves that problem away without really explaining it. "It's random but subject to the Born Rule" is a description of what's already observed, not an explanation with predictive power for new and distinct observations. There are much more complex criticisms that use words like "ontic" and "epistemic", but that's the fundamental problem that MWI claims to solve but doesn't.
      - DiogenesKynikos 6y ago
        > We experience one reality, not many realities. How does MWI imply that we should simultaneously experience multiple realities? If two different states of you experience two different realities, each state of you is only aware of one reality. MWI largely reduces to something like the Copenhagen interpretation for large systems. It's just that MWI explains the transition between the quantum and classical regime, doesn't require any ad hoc rules about observers, and doesn't need Schrödinger's equation to be violated.
feanaro 6y ago
I think there is some misunderstanding here based on the wording used. OPs point is simply that there is no separate, explicit branching process. Instead, there is only the normal, continuous evolution of the wavefunction. Our experience is recovered from this by positing that subjective/phenomenological experience is somehow tied to the individual components of the wavefunction. Since the individual components don't interact with each other, it gives the appearance of branching. This is compatible with our observations.
- ithkuil 6y ago
  Furthermore it firmly places ourselves and our own experiences within the very same fabric of reality it's describing. This is a rather inevitable problem of a fundamental theory of reality, since we ourselves are part of it and our inner working (whatever that is) must be layered on top of that fundamental machinery.
- kgwgk 6y ago
  So we get from the “the wave function somehow collapses” to “the phenomelogical experience is somehow tied to the individual components wave function” which are somehow connected go the measurements.
  - feanaro 6y ago
    You're right regarding the first part, we don't have a clear explanation of how the wave function might be related to subjective experience, but that's mostly because we don't have a good account of subjective experience at all. For the second part, there's nothing mysterious going on at all: measurement is simply physical interaction.
    - kgwgk 6y ago
      What are "the individual components of the wave function"? They are a mathematical construction. The wave function can be decomposed in many (and infinity of) ways. Why is one decomposition chosen and not another? Or are all the decompositions equally "(un)real"? The issue is not so simple and it's related to the "mysteriousness" of the first part.
cjfd 6y ago
From a physics point of view this is a very strange thing to say. Why are 'we' or 'measurements' things of special status? Because we have a soul or something? Now, that would be a theory where an abstract concept is taken to be more real than observable things. The measurement apparatus is also a physical thing that should be described by the physical theory in use as would the humans be. The very painful point about the copenhagen interpretation is this distinction between 'normal' time evolution and the special procedure when a 'measurement' is carried out. Actually, there exist mathematical proofs that the normal time evolution when applied in cases where information is transferred from microscopic stats to macroscopic ones leads to something that looks like a collapse of the wave function but is actually a split of it. This is as a physical theory much more attractive than giving a 'measurement' a special status. The question what this all means is a bit more mind-boggling though including multiple worlds and that kind of stuff. Taking 'a mathematical construct as more real than basic empirical experiences' is basically the history of physics and it has in the past been highly successful.
- chongli 6y ago
  Why are 'we' or 'measurements' things of special status? Because we experience the world through our senses. Everything else is one mathematical model or another that we’ve created. And our models aren’t even consistent! very painful point about the copenhagen interpretation is this distinction between 'normal' time evolution and the special procedure when a 'measurement' is carried out This is not a special procedure. Measurement occurs whenever physical interactions take place. To measure a particle, we bounce another particle off of it and then try to detect the result. The measurement is the particle collision, not the detection. It’s like playing billiards in the dark. We don’t know where the balls are. Taking 'a mathematical construct as more real than basic empirical experiences' is basically the history of physics and it has in the past been highly successful. Except for all of the times when it broke down. When one model was found to contradict our experiments and we had to replace it with another, which later turned out to be wrong as well. Perhaps the most embarrassing example of this, in human history, is all of our attempts to make geocentric models work [1]. The most well-known critique of science’s institutional habit of inventing new models whenever old ones broke down is probably Kuhn’s paradigms [2]. If you’re interested, you’re better off reading Kuhn than anything I have to write here. I think the best evidence for Kuhn’s thesis is the abject disappointment we witness every time particle physicists fail to overturn the standard model. If that’s not supremacy of measurement, then I don’t what is. [1] https://en.wikipedia.org/wiki/Geocentric_model https://en.wikipedia.org/wiki/Geocentric_model [2] https://en.wikipedia.org/wiki/The_Structure_of_Scientific_Revolutions https://en.wikipedia.org/wiki/The_Structure_of_Scientific_Re...
sullyj3 6y ago
I mean, it seems strange to reject implications of a successful model if those implications aren't observable. Eg, I believe that stuff exists outside our light cone, because it would be unparsimonious for there to be an extra rule saying that stuff that I can't access doesn't exists.
Viliam1234 6y ago
> A mathematical construct (the wavefunction) is taken as more real than basic empirical experiences like "measurements" and "we." In chemistry, atoms are also taken as more real than "measurements" and "we". Some chemists would probably insist that "we" are actually composed of atoms.

vixen99 6y ago

A first rate presentation on this topic is 'The emergent multiverse' by David Wallace. There's a detailed review in http://philsci-archive.pitt.edu/10940/1/Wallace_review_final_single-spaced.pdf http://philsci-archive.pitt.edu/10940/1/Wallace_review_final... In the book, Wallace quotes an interchange between Paul Davies and David Deutsch. <Davies> "So the parallel universes are cheap on assumptions but expensive on universes?" <Deutsch> "Exactly right. In physics we always try to make things cheap on assumptions." & Wallace re-quotes 'I do not know how to refute an incredulous stare'.

im3w1l 6y ago
Multiverse and many-worlds are two different things.

throwawayhacka 6y ago

uh... didnt early proponents of many worlds interpretation actually say that it did? Say Hugh Evrett? If it is reinterpreted to say otherwise, is it really the same QM model anymore?

pontus 6y ago

The MWI is literally obtained by taking traditional Copenhagen QM and removing the postulate of measurement. In other words, it is by the most genuine way of measuring complexity of a theory, demonstrably simpler than copenhagen! We just don't like it because it doesn't jive with our experience... it feels weird. When you have two theories that make the same predictions, but one is strictly simpler than the other, Occam's razor tells us to prefer the simpler one. In my mind, MWI or something akin to it, is the way to go, and is generally the way I conceptually think about QM.

hackinthebochs 6y ago
I don't think you get to claim simplicity for the theory that results in an exponential explosion of entities. Simplicity isn't just about descriptive simplicity.
- pontus 6y ago
  That's not the right way to frame MWI, there's no explosion of entities at all, just a single wave function that evolves. The wave function starts out being a function of n variables, evolves according to a differential equation and remains a function of n variables.
  - pontus 6y ago
    Put another way, suppose you have some linear dynamical differential equation in n variables that you solve somehow. Then, take that solution and expand it in some set of basis functions (e.g. a Fourier series). You wouldn't throw your hands up in the air and say "wow that's so complex, look at all those infinite terms in the solution!". The complexity isn't really there, it just appears to be there because you've chosen to expand your solution in a basis that makes it appears really complex. Similarly in the MWI we see something that looks complex simply because we've chosen to expand the solution in a set of states that makes sense to us (state1 = particle at location 1, state2 = particle at location 2, ...)
    - 6y ago