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There fact the Universe is probabilistic isn't what MWI is needed to explain. There's nothing even especially counterintuitive about the Universe being probabil

There fact the Universe is probabilistic isn't what MWI is needed to explain. There's nothing even especially counterintuitive about the Universe being probabilistic. MWI is a (so-far) unavoidable implication of the laws that predict real, observable QM effects. When people crunched the numbers and saw that it predicted quantum decoherence that resembles so-called "splitting" Universes (in actuality it's not a discrete process) they said, "That can't be right," and circumscribed a mysterious and ill-specified boundary beyond which the empirically validated rules don't apply. MWI requires you believe that physics is governed by the Schroedinger wave equation. Copenhagen requires you to believe that the Universe is governed by the Schroedinger wave equation, but only when we're not looking at it, and when we look at it reverts back to the classical world through some mechanism so far unexplained, and this collapse of the quantum world into the classical world somehow produces no testable predictions that would distinguish it from what we would expect the system to look like if the wave equation just kept on working.

btilly 15y ago
This. In other words, the MWI is what QM predicts if you assert that the observer is described by QM. So either we assert that there is some complex "collapse" mechanism which is somehow tied to observation, or we're stuck with MWI. Thus Occam's Razor says that, unless we have evidence for a complex "collapse" mechanism (hint: we don't), we should accept the MWI. Unfortunately Everett did his work after most physicists had become comfortable with "shut up and calculate". And therefore they did not want to bother thinking about it seriously. Of the people who did think about it, many were wedded to other interpretations, and so were not inclined to accept a weird upstart. However it is worth noting that a survey of cosmologists some years ago found that over 50% accepted the MWI. When you get away from the philosophical fringe, there is simply no other interpretation of QM whose reasoning is half as compelling as the MWI.
- goodside 15y ago
  Also, MWI acceptance is drastically higher among those who entered the field recently enough to not worry about the orthodoxy of Copenhagen. There are two driving forces in science: the skepticism of grad students and the mortality of professors.
  - btilly 15y ago
    The Structure of Scientific Revolutions pointed this out decades ago. New paradigms tend not to win by converting existing practitioners, but instead by converting everyone entering the people and lasting until the skeptics die. I could cite a great many examples of this.
- extension 15y ago
  Doesn't MWI just change the question "who decides how superpositions collapse?" into "who decides which world I see?" I suppose that at least turns it into a psychological rather than physical mystery, but still a vexing one.
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  - bodigital 15y ago
    You see all of the worlds. Each copy of you has a brain state encoding the history of the path he saw. Each of you simultaneously remember being in their own unique history and are unaware of the other histories.

btilly 15y ago

This. In other words, the MWI is what QM predicts if you assert that the observer is described by QM. So either we assert that there is some complex "collapse" mechanism which is somehow tied to observation, or we're stuck with MWI. Thus Occam's Razor says that, unless we have evidence for a complex "collapse" mechanism (hint: we don't), we should accept the MWI. Unfortunately Everett did his work after most physicists had become comfortable with "shut up and calculate". And therefore they did not want to bother thinking about it seriously. Of the people who did think about it, many were wedded to other interpretations, and so were not inclined to accept a weird upstart. However it is worth noting that a survey of cosmologists some years ago found that over 50% accepted the MWI. When you get away from the philosophical fringe, there is simply no other interpretation of QM whose reasoning is half as compelling as the MWI.

goodside 15y ago
Also, MWI acceptance is drastically higher among those who entered the field recently enough to not worry about the orthodoxy of Copenhagen. There are two driving forces in science: the skepticism of grad students and the mortality of professors.
- btilly 15y ago
  The Structure of Scientific Revolutions pointed this out decades ago. New paradigms tend not to win by converting existing practitioners, but instead by converting everyone entering the people and lasting until the skeptics die. I could cite a great many examples of this.
extension 15y ago
Doesn't MWI just change the question "who decides how superpositions collapse?" into "who decides which world I see?" I suppose that at least turns it into a psychological rather than physical mystery, but still a vexing one.
- deleted 15y ago
  [deleted]
- deleted 15y ago
  [deleted]
- bodigital 15y ago
  You see all of the worlds. Each copy of you has a brain state encoding the history of the path he saw. Each of you simultaneously remember being in their own unique history and are unaware of the other histories.