3 ms·

Disproving some form of measurable wave function does not provide evidence for MWI, which is unmeasurable and untestable nearly by definition.

by lupire 4y ago

fallingfrog 4y ago
Well, the thing is that the MWI is actually simpler than all the other interpretations, because it simply removes the idea of wave function collapse entirely. Any theory involving wave function collapse is adding something extra to quantum physics that can't be demonstrated experimentally. Because we live in the macro world, it feels like a single unitary reality is simpler, but actually, the MWI makes fewer assumptions. So I would turn that around and put the burden on the other theories to show that collapse is real, the default position should be MWI.
- TheOtherHobbes 4y ago
  You don't think postulating an unknown number of extra universes with a very poorly defined relationship with each other qualifies as an extra assumption?
  - pdonis 4y ago
    The MWI does not postulate extra universes, although that pop science description is unfortunately common even though it is wrong. The MWI just says that the one universe that exists is actually very, very different from what we perceive. (To be clear, I'm not saying this correct description makes the MWI any more palatable. I am just clarifying exactly what kind of unpalatableness the MWI requires.)
    - ryeights 4y ago
      Can you elaborate on this? The Wikipedia page for MWI says >The many-worlds interpretation implies that there are most likely an uncountably infinite number of universes. https://en.wikipedia.org/wiki/Many-worlds_interpretation https://en.wikipedia.org/wiki/Many-worlds_interpretation
      - GoblinSlayer 4y ago
        Those worlds are states in superposition, the term "world" is an allegory to help people understand that those states don't interact due to linearity of the Schrodinger equation, because not all properties of linearity are obvious.
      - pdonis 4y ago
        One should not be trying to learn physics from Wikipedia, particularly not for something as complicated as QM, even more particularly not for an aspect of QM as contentious as the MWI. The MWI says that there is one single universal wave function, which evolves in time by unitary evolution forever, and that that universal wave function is all that exists. That is one universe, not an infinity of them. It is just one universe that is nothing like what we think we perceive.
        jamiek88 4y ago
        Your last paragraph is verbatim gonna be the ‘Lord’s Prayer’ of my space cult. Wanna join? You can be number 2 thus have second dibs at the buffet.
      - d_tr 4y ago
        Not the parent, but I 'd say this amounts to how you define a "universe". There is a single wavefunction which says that one "copy" of you observes result A and another "copy" observes result B. Using the phrase "many universes" implies that these two scenarios are considered as "different universes". I personally do not like this phrase and find it misleading.
        TEP_Kim_Il_Sung 4y ago
        You are all the "copies", and, under certain conditions, can experience all their observations. Think of yourself more as an aspect of a multifaceted being experiencing the universe through you.
        pdonis 4y ago
    - GoblinSlayer 4y ago
      We perceived flat earth and geocentrism, so not the first time. I can recommend quantum electrodynamics to people who are too attached to corpuscular paradigm.
    - kgwgk 4y ago
      "The MWI" is not one thing. There are many-people saying many-things about those many-worls.
  - d_tr 4y ago
    It is the other way around. The "universes" are there when you solve the equations, and you can either let them be or keep only one by invoking the collapse. The collapse amounts to just setting some terms to zero.
- tsimionescu 4y ago
  It is not simpler, since MWI still needs the Born postulate to actually predict the results of quantum experiments. It replaces this idea of the wave function collapsing with a redefinition of what a measurement apparatus / observer is (in MWI, a measurement apparatus exists in a single "branch" of the wave function). This is especially problematic because QM doesn't predict any particular decomposition of a quantum state into particular classical states. That is, the Schrodinger equation doesn't actually predict that a particle has some amplitude here and some other amplitude there, as is often presented; instead, it predicts that it is described by some vector which can be decomposed in many different ways. You can say it has some amplitude X here and some amplitude Y there, but with any 2 points in space-time (adjusting the amplitudes). Or, it can have some combination of position and spin with amplitude X, and some other combination of position and spin with amplitude Y. You can choose any basis you like for the measurement, and you will get the corresponding answer. But, for MWI to actually predict experimental results (and the classical world we live in) you not only have to choose to look at a single element of that basis, but you also have to believe that the classical basis is somehow preferred.
  - GoblinSlayer 4y ago
    >This is especially problematic because QM doesn't predict any particular decomposition of a quantum state into particular classical states. It does predict it, this decomposition is called decoherence, where a classical state splits into a superposition of several different classical states.
    - pdonis 4y ago
      > this decomposition is called decoherence, where a classical state splits into a superposition of several different classical states. No, that's not what decoherence is. Decoherence is the spread of entanglement over a very large number of untrackable degrees of freedom (usually referred to as the "environment"). This makes interference effects unobservable. But decoherence itself does not involve any "splitting"; the entanglement that decoherence spreads over a very large number of untrackable degrees of freedom has to already be there before decoherence can act on it.
- lamontcg 4y ago
  > Any theory involving wave function collapse is adding something extra to quantum physics that can't be demonstrated experimentally. Title article is literally about trying to test those theories experimentally.
  - fallingfrog 4y ago
    ..And failing to find any evidence of collapse. Hence "can't be demonstrated". I didn't mean "can't be looked for" I meant that attempts to find it have not been successful.
- sfink 4y ago
  Only to the extent that MWI is actually a position. My understanding of MWI is: shit happens, and there's no need to understand why specific shit happens because all shit "happens" (by a definition of "happens" that carries basically no meaning) and you should be happy just to prove that the shit that happens is among the full set of shit that could happen. It's the "don't worry your pretty little head over it" theory of reality. Here's the best poem ever written, or that will ever be written: Roses are red Violets are blue MWI stinks And so do you. Don't think it's that great? Well, that's because there exist other versions of me that wrote different words up there, and you just happened to read a version that wasn't that great. I hereby accept my position as God Poet of the Universe.
  - GoblinSlayer 4y ago
    Shit happens because that's how the state of matter changes over time, the wave function is the description of the state and the Schrodinger equation is the description of the state's change. That's as complete and happy understanding as it goes.
c1ccccc1 4y ago
Wait, I'm pretty sure that if these measurements had shown a collapse, that would have to be taken as disproving many worlds. You can't very well have many worlds when your wavefunction is physically collapsing all the time before those worlds can diverge. So it is actually kind of testable, since a test was just performed that could have ruled it out. Maybe you're saying that it's untestable relative to unmeasurable collapses of the wavefunction. But if those collapses are contrived to be unmeasurable, doesn't that make them kind of, well, pointless?
Diggsey 4y ago
Only if you assert that the other worlds are in some way "real". See https://en.wikipedia.org/wiki/Many-worlds_interpretation#Debate_whether_the_other_worlds_are_real https://en.wikipedia.org/wiki/Many-worlds_interpretation#Deb... The MWI is a simpler theory than other interpretations because it does not require "collapse" to be a physical process. The "realness" of the other worlds is untestable, but also not part of the theory. "unreal" MWI should be the null hypothesis given what we know to be true about quantum mechanics. If we find evidence that collapse is a physical process then we can reject it, but otherwise it makes the fewest leaps. At the moment the Copenhagen intepretation is taught instead, which is a problem. To quote wikipedia: > There is no uniquely definitive statement of the Copenhagen interpretation And > the device used to observe a system must be described in classical language, while the system under observation is treated in quantum terms In other words, it does allow you to predict the result of an experiment, but we know it can't be right because it's impossible to formalize without building this "classical observer" into the model. Attempting to build on this inevitably leads to metaphysical nonsense about consciousness. In "unreal" MWI there is a universal wave function, and something is "real" to us if it is entangled with us. The "many worlds" terminology makes it easier to visualize but doesn't mean those other worlds are real because whether something is real is subjective in this interpretation. Subjective reality may be a problem for some people, but if you look at the evolution of physical theories, we consistently find that everything is more subjective than we thought it was (see also: relativity).
- platz 4y ago
  Believers in Everett may not end up being right. But believers in Copenhagen aren't more right than believers in Everett. In fact, they "aren't even wrong" either, because they refuse to even engage with the question. So I think it's like the situation with democracy. You have to go with Everett until you find something better, providing you want to be scientific at all.
eterevsky 4y ago
MWI in a sense it a null theory regarding the collapse, so it should be assumed true by default if collapse is not observed.

Disproving some form of measurable wave function does not provide evidence for MWI, which is unmeasurable and untestable nearly by definition.

by lupire 4y ago

Disproving some form of measurable wave function does not provide evidence for MWI, which is unmeasurable and untestable nearly by definition.

fallingfrog 4y ago

Well, the thing is that the MWI is actually simpler than all the other interpretations, because it simply removes the idea of wave function collapse entirely. Any theory involving wave function collapse is adding something extra to quantum physics that can't be demonstrated experimentally. Because we live in the macro world, it feels like a single unitary reality is simpler, but actually, the MWI makes fewer assumptions. So I would turn that around and put the burden on the other theories to show that collapse is real, the default position should be MWI.

TheOtherHobbes 4y ago
You don't think postulating an unknown number of extra universes with a very poorly defined relationship with each other qualifies as an extra assumption?
- pdonis 4y ago
  The MWI does not postulate extra universes, although that pop science description is unfortunately common even though it is wrong. The MWI just says that the one universe that exists is actually very, very different from what we perceive. (To be clear, I'm not saying this correct description makes the MWI any more palatable. I am just clarifying exactly what kind of unpalatableness the MWI requires.)
  - ryeights 4y ago
    Can you elaborate on this? The Wikipedia page for MWI says >The many-worlds interpretation implies that there are most likely an uncountably infinite number of universes. https://en.wikipedia.org/wiki/Many-worlds_interpretation https://en.wikipedia.org/wiki/Many-worlds_interpretation
    - GoblinSlayer 4y ago
      Those worlds are states in superposition, the term "world" is an allegory to help people understand that those states don't interact due to linearity of the Schrodinger equation, because not all properties of linearity are obvious.
    - pdonis 4y ago
      One should not be trying to learn physics from Wikipedia, particularly not for something as complicated as QM, even more particularly not for an aspect of QM as contentious as the MWI. The MWI says that there is one single universal wave function, which evolves in time by unitary evolution forever, and that that universal wave function is all that exists. That is one universe, not an infinity of them. It is just one universe that is nothing like what we think we perceive.
      - jamiek88 4y ago
        Your last paragraph is verbatim gonna be the ‘Lord’s Prayer’ of my space cult. Wanna join? You can be number 2 thus have second dibs at the buffet.
    - d_tr 4y ago
      Not the parent, but I 'd say this amounts to how you define a "universe". There is a single wavefunction which says that one "copy" of you observes result A and another "copy" observes result B. Using the phrase "many universes" implies that these two scenarios are considered as "different universes". I personally do not like this phrase and find it misleading.
      - TEP_Kim_Il_Sung 4y ago
        You are all the "copies", and, under certain conditions, can experience all their observations. Think of yourself more as an aspect of a multifaceted being experiencing the universe through you.
        pdonis 4y ago
  - GoblinSlayer 4y ago
    We perceived flat earth and geocentrism, so not the first time. I can recommend quantum electrodynamics to people who are too attached to corpuscular paradigm.
  - kgwgk 4y ago
    "The MWI" is not one thing. There are many-people saying many-things about those many-worls.
- d_tr 4y ago
  It is the other way around. The "universes" are there when you solve the equations, and you can either let them be or keep only one by invoking the collapse. The collapse amounts to just setting some terms to zero.
tsimionescu 4y ago
It is not simpler, since MWI still needs the Born postulate to actually predict the results of quantum experiments. It replaces this idea of the wave function collapsing with a redefinition of what a measurement apparatus / observer is (in MWI, a measurement apparatus exists in a single "branch" of the wave function). This is especially problematic because QM doesn't predict any particular decomposition of a quantum state into particular classical states. That is, the Schrodinger equation doesn't actually predict that a particle has some amplitude here and some other amplitude there, as is often presented; instead, it predicts that it is described by some vector which can be decomposed in many different ways. You can say it has some amplitude X here and some amplitude Y there, but with any 2 points in space-time (adjusting the amplitudes). Or, it can have some combination of position and spin with amplitude X, and some other combination of position and spin with amplitude Y. You can choose any basis you like for the measurement, and you will get the corresponding answer. But, for MWI to actually predict experimental results (and the classical world we live in) you not only have to choose to look at a single element of that basis, but you also have to believe that the classical basis is somehow preferred.
- GoblinSlayer 4y ago
  >This is especially problematic because QM doesn't predict any particular decomposition of a quantum state into particular classical states. It does predict it, this decomposition is called decoherence, where a classical state splits into a superposition of several different classical states.
  - pdonis 4y ago
    > this decomposition is called decoherence, where a classical state splits into a superposition of several different classical states. No, that's not what decoherence is. Decoherence is the spread of entanglement over a very large number of untrackable degrees of freedom (usually referred to as the "environment"). This makes interference effects unobservable. But decoherence itself does not involve any "splitting"; the entanglement that decoherence spreads over a very large number of untrackable degrees of freedom has to already be there before decoherence can act on it.
lamontcg 4y ago
> Any theory involving wave function collapse is adding something extra to quantum physics that can't be demonstrated experimentally. Title article is literally about trying to test those theories experimentally.
- fallingfrog 4y ago
  ..And failing to find any evidence of collapse. Hence "can't be demonstrated". I didn't mean "can't be looked for" I meant that attempts to find it have not been successful.
sfink 4y ago
Only to the extent that MWI is actually a position. My understanding of MWI is: shit happens, and there's no need to understand why specific shit happens because all shit "happens" (by a definition of "happens" that carries basically no meaning) and you should be happy just to prove that the shit that happens is among the full set of shit that could happen. It's the "don't worry your pretty little head over it" theory of reality. Here's the best poem ever written, or that will ever be written: Roses are red Violets are blue MWI stinks And so do you. Don't think it's that great? Well, that's because there exist other versions of me that wrote different words up there, and you just happened to read a version that wasn't that great. I hereby accept my position as God Poet of the Universe.
- GoblinSlayer 4y ago
  Shit happens because that's how the state of matter changes over time, the wave function is the description of the state and the Schrodinger equation is the description of the state's change. That's as complete and happy understanding as it goes.

c1ccccc1 4y ago

Wait, I'm pretty sure that if these measurements had shown a collapse, that would have to be taken as disproving many worlds. You can't very well have many worlds when your wavefunction is physically collapsing all the time before those worlds can diverge. So it is actually kind of testable, since a test was just performed that could have ruled it out. Maybe you're saying that it's untestable relative to unmeasurable collapses of the wavefunction. But if those collapses are contrived to be unmeasurable, doesn't that make them kind of, well, pointless?

Diggsey 4y ago

Only if you assert that the other worlds are in some way "real". See https://en.wikipedia.org/wiki/Many-worlds_interpretation#Debate_whether_the_other_worlds_are_real https://en.wikipedia.org/wiki/Many-worlds_interpretation#Deb... The MWI is a simpler theory than other interpretations because it does not require "collapse" to be a physical process. The "realness" of the other worlds is untestable, but also not part of the theory. "unreal" MWI should be the null hypothesis given what we know to be true about quantum mechanics. If we find evidence that collapse is a physical process then we can reject it, but otherwise it makes the fewest leaps. At the moment the Copenhagen intepretation is taught instead, which is a problem. To quote wikipedia: > There is no uniquely definitive statement of the Copenhagen interpretation And > the device used to observe a system must be described in classical language, while the system under observation is treated in quantum terms In other words, it does allow you to predict the result of an experiment, but we know it can't be right because it's impossible to formalize without building this "classical observer" into the model. Attempting to build on this inevitably leads to metaphysical nonsense about consciousness. In "unreal" MWI there is a universal wave function, and something is "real" to us if it is entangled with us. The "many worlds" terminology makes it easier to visualize but doesn't mean those other worlds are real because whether something is real is subjective in this interpretation. Subjective reality may be a problem for some people, but if you look at the evolution of physical theories, we consistently find that everything is more subjective than we thought it was (see also: relativity).

platz 4y ago
Believers in Everett may not end up being right. But believers in Copenhagen aren't more right than believers in Everett. In fact, they "aren't even wrong" either, because they refuse to even engage with the question. So I think it's like the situation with democracy. You have to go with Everett until you find something better, providing you want to be scientific at all.

eterevsky 4y ago

MWI in a sense it a null theory regarding the collapse, so it should be assumed true by default if collapse is not observed.