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> “ The universe supposedly splits, or branches, whenever one quantum particle jostles against another, making their wave functions collapse.” I’m very tired o

by mlthoughts2018 7y ago

> “ The universe supposedly splits, or branches, whenever one quantum particle jostles against another, making their wave functions collapse.” I’m very tired of seeing pop science articles describe this so incorrectly. It’s a similar mistake as describing quantum computing as simultaneously trying a bunch of solution states “in parallel.” The multiverse theory doesn’t imply any “splitting” action and certainly no such thing as special measurement or collapse. If you make a measurement that distinguishes one universe from another, then “you” just discover which Everett branch you happened to have belonged to all along. It’s no different from observing outcomes of a random variable. Your mind is ignorant of a certain state of affairs, you measure something, now you’re slightly less ignorant of the state of affairs. I am so sick of these articles. Multiverse QM is a settled debate. Move on.

pchiusano 7y ago
The thing missing is an explanation for why we find ourselves in a particular branch. Insisting that this doesn’t require an explanation is never going to be satisfying for some people. I’ll try to explain why, using your random variable sampling analogy, which is telling. In the case of say, sampling from a coin toss random variable, there is indeed a more primitive explanation for why the coin comes up heads or tails, it’s just that it would be a much more complicated explanation involving knowledge of huge amounts of detail about the exact force applied to the coin, maybe air currents in the area where coin is being flipped, etc. But in principle that is all explainable. With quantum measurement, there is no such explanation available, even in principle. We are told only that we will find ourselves in one of the possibilities admitted by the distribution predicted by QM. We have no further explanation for which one it will be. The QM multiverse folks then expect us to be okay with this as the end of the explanation. But notice this is a choice to adopt something as axiomatic. We could have done that at other points in the history of physics but didn’t.
- zajio1am 7y ago
  > The thing missing is an explanation for why we find ourselves in a particular branch. That question does not really make sense. In every branch, there is 'you' asking about why is being in that particular branch.
  - pchiusano 7y ago
    I think you are making a hidden assumption. Here is a good question to tease it out: why does it make sense to ask why a coin flip came up heads but not make sense to ask why we observe one QM outcome? With the coin flip, it’s understood that the probability distribution is not reality. It’s just a way of approximating reality without having to model all the things that would explain our observations. With QM we have equations that predict probability distributions, and there is debate about whether reality is literally a distribution of possible states, or if it’s more like the coin flip random variable.
    - zajio1am 7y ago
      Yes, i was assuming MWI, so my point was it is not a problem itself (it does not need an explanation) in context of MWI.
    - MockObject 7y ago
      > why does it make sense to ask why a coin flip came up heads but not make sense to ask why we observe one QM outcome? But you had just explained why: > With quantum measurement, there is no such explanation available, even in principle.
teilo 7y ago
> Multiverse QM is a settled debate. Move on. That's ridiculous. The Copenhagen Interpretation is still the prevailing view, among MANY others: https://en.wikipedia.org/wiki/Interpretations_of_quantum_mechanics https://en.wikipedia.org/wiki/Interpretations_of_quantum_mec... Further, the science is settled, so anyone who disagrees is a denier? Is that you, Mr. Carroll?
- mlthoughts2018 7y ago
  Why do you think a poll among certain people adds credulity to one or the other? Many Worlds allows purely unitary wave function evolution while explaining all known experimental and observational results with no less fidelity than any alternative. It’s solely a matter of Occam’s Razor that, until there is experimental evidence to the contrary, MWI is the solely most parsimonious available explanation. Wave function collapse is a purely unjustified extraneous detail that violates the scientific method to believe it without additional evidence. MWI is by its own definition the choice of belief not requiring attaching vestigial extra details onto the theory, as far as any currently known experimental results go.
  - teilo 7y ago
    That's just, like, your opinion, man. It's also a red herring. You stated that the science is settled. It is not. Not even close. "Settled" means that that there is a scientific consensus by all but a fringe, that MWI is the correct interpretation of QM. Of course, that is not the case, as should be blatantly obvious to you. Besides which, nothing in science is ever "settled." It is always open to new interpretations when new data presents itself, or when a more persuasive theory is formulated. So on both counts your "settled" argument fails. Furthermore, this statement is pretty bold, but let me re-write it, because it applies better to MWI than to the wave collapse function: "The Many Worlds conjecture is a purely unjustified extraneous detail that violates the scientific method to believe it without additional evidence." The inability of the MWI to distinguish itself from the CI by any experiment, real or imagined, is the very reason why it has not gained traction.
    - 7y ago
gnaritas 7y ago
> Multiverse QM is a settled debate. Move on. Uh, no it isn't; we have zero evidence of a multi-verse. Math is not evidence, it can only help point to evidence.
CuriouslyC 7y ago
The fact that we observe decoherence is the reason that people talk about "splitting". If things were consistent (either behaving in a classical or "quantum" mannner), the idea that the universal wavefunction was in constant superposition would be much more intuitive. Also, your assumption that there is no "collapse" is predicated on the notion that whatever wavefunction amplitude is modeling is a continuous variable, but IMO it is much more likely that it is discrete. If that thing is discrete, as the universe evolves, some states will cease to exist simply due to the fact that their measure will fall below the unit value. When the measure of all states but one fell below that unit, that would essentially be a collapse.
- mlthoughts2018 7y ago
  I disagree about your claim re: decoherence. Decoherence is just when any informational aspect of a system leaks such that the mind of an observer can update it’s state of knowledge to know which Everett branch it had been on all along. Nothing “splits” .. you just discover which version of “you” that you are.. which of the continuum of possible outcomes your personal measurement happened to see. Likewise I think you are incorrect about your discreteness claim. I agree with you that QM suggests the nature of reality is fundamentally discrete, but that reality also places the Born rule as a continuous mixture model across discrete states, and this is specifically what allows there to be a continuum of universes of every measurement regardless of whether the outcome is continuous or discrete.. like reality’s own Lesbesgue-Stieltjes measure.

pchiusano 7y ago

The thing missing is an explanation for why we find ourselves in a particular branch. Insisting that this doesn’t require an explanation is never going to be satisfying for some people. I’ll try to explain why, using your random variable sampling analogy, which is telling. In the case of say, sampling from a coin toss random variable, there is indeed a more primitive explanation for why the coin comes up heads or tails, it’s just that it would be a much more complicated explanation involving knowledge of huge amounts of detail about the exact force applied to the coin, maybe air currents in the area where coin is being flipped, etc. But in principle that is all explainable. With quantum measurement, there is no such explanation available, even in principle. We are told only that we will find ourselves in one of the possibilities admitted by the distribution predicted by QM. We have no further explanation for which one it will be. The QM multiverse folks then expect us to be okay with this as the end of the explanation. But notice this is a choice to adopt something as axiomatic. We could have done that at other points in the history of physics but didn’t.

zajio1am 7y ago
> The thing missing is an explanation for why we find ourselves in a particular branch. That question does not really make sense. In every branch, there is 'you' asking about why is being in that particular branch.
- pchiusano 7y ago
  I think you are making a hidden assumption. Here is a good question to tease it out: why does it make sense to ask why a coin flip came up heads but not make sense to ask why we observe one QM outcome? With the coin flip, it’s understood that the probability distribution is not reality. It’s just a way of approximating reality without having to model all the things that would explain our observations. With QM we have equations that predict probability distributions, and there is debate about whether reality is literally a distribution of possible states, or if it’s more like the coin flip random variable.
  - zajio1am 7y ago
    Yes, i was assuming MWI, so my point was it is not a problem itself (it does not need an explanation) in context of MWI.
  - MockObject 7y ago
    > why does it make sense to ask why a coin flip came up heads but not make sense to ask why we observe one QM outcome? But you had just explained why: > With quantum measurement, there is no such explanation available, even in principle.

teilo 7y ago

> Multiverse QM is a settled debate. Move on. That's ridiculous. The Copenhagen Interpretation is still the prevailing view, among MANY others: https://en.wikipedia.org/wiki/Interpretations_of_quantum_mechanics https://en.wikipedia.org/wiki/Interpretations_of_quantum_mec... Further, the science is settled, so anyone who disagrees is a denier? Is that you, Mr. Carroll?

mlthoughts2018 7y ago
Why do you think a poll among certain people adds credulity to one or the other? Many Worlds allows purely unitary wave function evolution while explaining all known experimental and observational results with no less fidelity than any alternative. It’s solely a matter of Occam’s Razor that, until there is experimental evidence to the contrary, MWI is the solely most parsimonious available explanation. Wave function collapse is a purely unjustified extraneous detail that violates the scientific method to believe it without additional evidence. MWI is by its own definition the choice of belief not requiring attaching vestigial extra details onto the theory, as far as any currently known experimental results go.
- teilo 7y ago
  That's just, like, your opinion, man. It's also a red herring. You stated that the science is settled. It is not. Not even close. "Settled" means that that there is a scientific consensus by all but a fringe, that MWI is the correct interpretation of QM. Of course, that is not the case, as should be blatantly obvious to you. Besides which, nothing in science is ever "settled." It is always open to new interpretations when new data presents itself, or when a more persuasive theory is formulated. So on both counts your "settled" argument fails. Furthermore, this statement is pretty bold, but let me re-write it, because it applies better to MWI than to the wave collapse function: "The Many Worlds conjecture is a purely unjustified extraneous detail that violates the scientific method to believe it without additional evidence." The inability of the MWI to distinguish itself from the CI by any experiment, real or imagined, is the very reason why it has not gained traction.
  - 7y ago

gnaritas 7y ago

> Multiverse QM is a settled debate. Move on. Uh, no it isn't; we have zero evidence of a multi-verse. Math is not evidence, it can only help point to evidence.

CuriouslyC 7y ago

The fact that we observe decoherence is the reason that people talk about "splitting". If things were consistent (either behaving in a classical or "quantum" mannner), the idea that the universal wavefunction was in constant superposition would be much more intuitive. Also, your assumption that there is no "collapse" is predicated on the notion that whatever wavefunction amplitude is modeling is a continuous variable, but IMO it is much more likely that it is discrete. If that thing is discrete, as the universe evolves, some states will cease to exist simply due to the fact that their measure will fall below the unit value. When the measure of all states but one fell below that unit, that would essentially be a collapse.

mlthoughts2018 7y ago
I disagree about your claim re: decoherence. Decoherence is just when any informational aspect of a system leaks such that the mind of an observer can update it’s state of knowledge to know which Everett branch it had been on all along. Nothing “splits” .. you just discover which version of “you” that you are.. which of the continuum of possible outcomes your personal measurement happened to see. Likewise I think you are incorrect about your discreteness claim. I agree with you that QM suggests the nature of reality is fundamentally discrete, but that reality also places the Born rule as a continuous mixture model across discrete states, and this is specifically what allows there to be a continuum of universes of every measurement regardless of whether the outcome is continuous or discrete.. like reality’s own Lesbesgue-Stieltjes measure.