Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

I MWI and Lev

  1. Dec 12, 2016 #1
    There's no question that MWI is an important part of QM, whether we agree with it or not. And consciousness is essential for MWI, it can't be defined without it. For instance, Stanford Encyclopedia https://plato.stanford.edu/entries/qm-manyworlds/#2.2 says:

    The MWI consists of two parts:

    i.A mathematical theory which yields the time evolution of the quantum state of the (single) Universe.
    ii.A prescription which sets up a correspondence between the quantum state of the Universe and our experiences.

    2.2 Who am "I"?

    “I” am an object, such as the Earth, a cat, etc. “I” is defined at a particular time by a complete (classical) description of the state of my body and of my brain. “I” and "Lev" do not refer to the same things (even though my name is Lev). At the present moment there are many different “Lev”s in different worlds (not more than one in each world), but it is meaningless to say that now there is another “I”. I have a particular, well defined past: I correspond to a particular “Lev” in 2012, but not to a particular “Lev” in the future: I correspond to a multitude of “Lev”s in 2022. In the framework of the MWI it is meaningless to ask: Which Lev in 2022 will I be? I will correspond to them all. Every time I perform a quantum experiment (with several possible results) it only seems to me that I obtain a single definite result. Indeed, Lev who obtains this particular result thinks this way. However, this Lev cannot be identified as the only Lev after the experiment. Lev before the experiment corresponds to all “Lev”s obtaining all possible results.

    Although this approach to the concept of personal identity seems somewhat unusual, it is plausible in the light of the critique of personal identity by ... {lots more similar comprehensible twaddle}

    Probability Postulate ...

    An observer should set his subjective probability of the outcome of a quantum experiment in proportion to the total measure of existence of all worlds with that outcome. ...

    The basic concept in this approach is a conscious experience. He assigns weights to different experiences depending on the quantum state of the universe, ...

    Every bold word or phrase refers, one way or another, to human consciousness. Clearly MWI, at least, "thinks there's something special about consciousness".
  2. jcsd
  3. Dec 12, 2016 #1


    Staff: Mentor

    I would want a mainstream physics reference to back up this statement. There are quite a few in the bibliography of the philosophy article you linked to, but note carefully that none of them are referenced in the particular passages you quote. Also, note that the article says it will present "a particular approach to the MWI", but it gives no maintream physics reference for this approach--it just says it isn't the one in DeWitt 1970. So I am not very confident that this philosophy article is correctly interpreting the actual physics.
  4. jcsd
  5. Dec 13, 2016 #2


    User Avatar

    Sounds like metaphysics to me. If some experiment can be devised proving decoherence on the conscious level, then I would appreciate any links on the matter. But, this is getting to the level of asking a physicist what are the stuff dreams are made out of?
  6. Dec 13, 2016 #3
    There's a lecture by Scott Aaronson where he quotes some insightful comments made by Peter Byrne, a biographer of Hugh Everett:

    "One thing that crystallized my thinking about this was a remark made in a lecture by Peter Byrne, who wrote a https://www.amazon.com/The-Many-Worlds-Hugh-Everett/dp/0199552274. Byrne was discussing the question, why did it take so many decades for Everett’s Many-Worlds Interpretation to become popular? Of course, there are people who deny quantum mechanics itself, or who have basic misunderstandings about it, but let’s leave those people aside. Why did people like Bohr and Heisenberg dismiss Everett? More broadly: why wasn’t it just obvious to physicists from the beginning that “branching worlds” is a picture that the math militates toward, probably the simplest, easiest story one can tell around the Schrödinger equation? Even if early quantum physicists rejected the Many-Worlds picture, why didn’t they at least discuss and debate it?

    Here was Byrne’s answer: he said, before you can really be on board with Everett, you first need to be on board with Daniel Dennett (the philosopher). He meant: you first need to accept that a “mind” is just some particular computational process. At the bottom of everything is the physical state of the universe, evolving via the equations of physics, and if you want to know where consciousness is, you need to go into that state, and look for where computations are taking place that are sufficiently complicated, or globally-integrated, or self-referential, or … something, and that’s where the consciousness resides. And crucially, if following the equations tells you that after a decoherence event, one computation splits up into two computations, in different branches of the wavefunction, that thereafter don’t interact—congratulations! You’ve now got two consciousnesses."
    Last edited by a moderator: May 8, 2017
  7. Dec 13, 2016 #4


    User Avatar
    Gold Member

    @secur, thanks for posting this. I have to agree with @n01 that the quotes are metaphysical arguments.
  8. Dec 13, 2016 #5


    User Avatar
    Staff Emeritus
    Science Advisor

    Okay, I think this is slightly different from the usual claim that "consciousness collapses the wave function". In MWI, there is no physical effect on the evolution of the universe that depends on whether an observation is made by a conscious observer or a machine. Rather, the issue in your part #ii is: Can we explain how things seem to a conscious observer, given that the physics is described by part #i? This is an important question, since ultimately in science we're trying to explain our own observations, but I don't think that it implies that there is a special role for consciousness, other than the fact that we, as conscious beings, have a special interest in it.

    Answering issue #ii is very hard, and I think that it goes beyond physics, in that it requires identifying what aspects of the history of the world correspond to the experiences of a conscious being. My opinion is that, to whatever extent we can make sense of this, we could make sense of a broader class of objects with experience, including robots that make observations and act on their observations. So I would reject the claim that MWI somehow gives a special role for consciousness. There is a certain sense in which MWI is simply that program of asking "How can we make sense of QM if the smooth evolution of the wave function is the only dynamics that exists?"
  9. Dec 13, 2016 #6


    User Avatar
    Science Advisor

    Consciousness is not more essential for MWI in physics than for identical twins in biology.

    "I have a twin brother, but he is not "I". There are two persons with my genes, me and my twin brother." So what? Completely irrelevant from biological point of view. The same with MWI and physics.
  10. Dec 13, 2016 #7
    @stevendaryl's response is right on the money. "Answering issue #ii is very hard, and I think that it goes beyond physics, in that it requires identifying what aspects of the history of the world correspond to the experiences of a conscious being." That's the issue alright. @MrRobotoToo is also somewhere in the ballpark. I'll briefly address others, and intend to respond carefully to @stevendaryl later (assuming I get to it).

    The author, Lev Vaidman, is a noted physicist working in the field. He knows what he's talking about. His key claim is that MWI requires "A prescription which sets up a correspondence between the quantum state of the Universe and our experiences". I don't know if there's a "mainstream physics reference to back up this statement". But, no offense, it's not really relevant. This is not science per se, but meta-science. We're talking about MWI, not doing MWI. No experiment can prove Lev Vaidman's MWI definition; no math can demonstrate it. It's simply a question of logical reasoning, for which no Authority is needed.

    Nevertheless I did read some papers, looking for support for this MWI-consciousness link, including:

    "Relative State" Formulation of Quantum Mechanics, by Hugh Everett III http://www.univer.omsk.su/omsk/Sci/Everett/paper1957.html [Broken]

    Quantum mechanics and reality, by Bryce S. DeWitt http://physicstoday.scitation.org/doi/pdf/10.1063/1.3022331

    Quantum Theory of Probability and Decisions, by David Deutsch http://lanl.arxiv.org/ftp/quant-ph/papers/9906/9906015.pdf

    On the Interpretation of Measurement in Quantum Theory, by H. D. Zeh http://www.rzuser.uni-heidelberg.de/~as3/FP70.pdf

    Interpreting the many-worlds interpretation, by Albert & Loewer https://philpapers.org/rec/ALBITM

    I found support for Vaidman but nothing really specific. Why don't you read them also, see what you think. I had prepared some excerpts earlier (complete with bolded words and phrases) but since it turns out @stevendaryl is already on the right page, I think I'll skip it. My response to him (assuming I get to it) should make Vaidman's point quite clear.

    Of course they are, it's a metaphysical issue. Not science, but about science. You can't experimentally or mathematically prove that MWI requires "A prescription which sets up a correspondence between the quantum state of the Universe and our experiences". Indeed, the entire topic of QM interpretations is basically metaphysics.

    No offense but you're not responding to Vaidman's point. You're merely denying it. You've probably read "The Hunting of the Snark" by Lewis Carroll? According to the Bellman, "What I tell you three times is true". Going on that theory, if you repeat your denial twice more, it should convince me. Worth a try :-)
    Last edited by a moderator: May 8, 2017
  11. Dec 13, 2016 #8


    Staff: Mentor

    It's false - the following reference explains MWI:

    Conciousness has nothing to do with MW. There is a variant called the Many Minds interpretation where its essential:

    But that is NOT MWI.

    Very briefly the modern MWI is basically the same as decoherent histories (DH). In DH QM is the stochastic theory of histories. The twist of MW is all histories occur simultaneously in different worlds but other than that are remarkably similar. David Wallace explains all this in full mathematical detail in his book.

    Note: David Wallice has a Phd is both particle physics and philosophy so his physics can be trusted. I have the book, and while I believe MWI is a pile of the proverbial the math and reasoning is tight - the math is very beautiful actually. Also note my opinion that it's a pile of you know what means nothing - its a personal opinion. All interpretations are equally valid - none is better than the other. Science is based on correspondence with experiment - all equally correspond thus all are equally valid - at least until someone figures out how to experimentally tell them apart.

    Last edited by a moderator: May 8, 2017
  12. Dec 13, 2016 #9
    Quantum Mechanics does not require observers or consciousness.

    https://www.math.rutgers.edu/~oldstein/papers/qts/qts.html [Broken]

    Last edited by a moderator: May 8, 2017
  13. Dec 13, 2016 #10
    Ok, you repeated it three times, so that means I have to believe you ... but it doesn't seem to be working.

    Here we have a question which probably won't be answered definitely for 100 or 1000 years. No one knows whether consciousness has anything to do with wavefunctions collapsing, or related phenomena. We need to examine the issue carefully. So, your brilliant debating technique is:

    1. Answer, with absolute certainty, a question which can't be answered at this stage of technological and scientific progress.
    2. Throw in a link to some reference I read and understood long ago, and doesn't address a word of my post.
    3. Keep doing that until the opposition is convinced (Bellman's theorem).

  14. Dec 13, 2016 #11


    Staff: Mentor

    That's not the question.

    Its if its got anything to do with MWI. It doesn't. With a few other interpretations - yes - but not MWI.

    Don't take my word for it it - read Davids book - there you will find the full mathematical detail. I don't believe in MWI but I am glad I studied the book - its good. It also provides a lot of the detail and key theorems of the dcoherent history approach of Gell-Mann and others that Feynman was converted to towards the end - at least according to Gell-Mann anyway.

  15. Dec 13, 2016 #12


    Staff: Mentor

    A very few do - but they are generally well out of favor these days. The history behind the idea is interesting but needs another thread.

    MWI is not one of those very few.

  16. Dec 14, 2016 #13


    Staff: Mentor

    Plenty of noted physicists working in the field (any physics field, but quantum physics seems to be a particularly fertile one in this regard) say all kinds of things in non-physics sources that they would never get away with in a physics paper. The Stanford Encyclopedia of Philosophy is a non-physics source. Look up this author's physics papers and see (a) whether he tries to make these claims in them, and (b) if so, what other physicists say about such claims in their own physics papers.
  17. Dec 14, 2016 #14


    Staff: Mentor

    "Support" in the sense of "nothing they say absolutely contradicts Vaidman", yes. But that's pretty lukewarm "support". In physics papers authors are more careful about what they claim.
  18. Dec 14, 2016 #15


    User Avatar


    Lol... awesome! [COLOR=#black]. [/COLOR] Absolutely awesome!! ... really.

    Oh, and, by the way, here is...
    Ya think...?
    Last edited: Dec 14, 2016
  19. Dec 14, 2016 #16
    True, they say things in non-physics sources that they wouldn't say in a physics paper.

    Right, it's not a physics source. It is, however, a philosophy source.

    I looked through a number of his papers, and as far as I know he doesn't. I didn't expect him to. "These claims" are not physics claims, they're meta-physics claims. That's why Vaidman says them in a respected philosophy source, but not when he's writing a physics paper.

    There's only one part of the Stanford article that I care about, let's ignore all the rest. It is:

    This is a claim about science, it's not science per se. A scientific claim, by definition, must be justifiable on experimental, observational, and/or mathematical grounds. Whereas meta-science claims, like this one, are based on reasoning and demonstration. AFAIK, such claims don't - at least, shouldn't - appear in physics papers by Lev Vaidman or anyone else.
  20. Dec 14, 2016 #17


    User Avatar
    Staff Emeritus
    Science Advisor

    That paper isn't actually arguing that quantum mechanics does not require observers, it's a survey of three different approaches to formulations of QM that don't use observers: decoherent histories, spontaneous localization and Bohmian mechanics. The author doesn't actually conclude that any of the approaches is unambiguously successful, although he seems to favor Bohmian mechanics as the most promising.

    If I understood that paper correctly, what they're really arguing is that consciousness is not needed to destroy interference patterns. They are using the destruction of the interference pattern as a proxy for the collapse of the wave function. But those aren't really exactly the same thing. Decoherence explains the lack of interference patterns.
    Last edited by a moderator: May 8, 2017
  21. Dec 14, 2016 #18


    Staff: Mentor

    In which case they are off topic here. Remember, this is a physics forum, not a metaphysics or philosophy forum.
  22. Dec 14, 2016 #19


    Staff: Mentor

    And with that, this thread is closed.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Similar Discussions: MWI and Lev
  1. Proof of MWI? (Replies: 29)

  2. Splitting in MWI (Replies: 6)

  3. The Assumptions of MWI (Replies: 27)

  4. MWI understanding (Replies: 5)