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B Quantum Mechanics, What is it exactly?

  1. Aug 6, 2018 #1
    I recently watched a video where Sean Carroll talked about QM and multiverses

    1/ Could you please explain:

    Where does all the energy come from to drive all these universes.
    Surely this must take an enormous amount of energy to drive a multiverse
    system (infinite).

    Does each universe have it's own energy supply system? or do they
    share one massive (infinite power supply?)

    Is it energy or power? Power implies work doesn't it? And energy is
    what? particle things working?..bouncing around appearing and reappearing?

    If we are in one multiverse ..why can't we tap the energy of
    another universe. From this ..if the multiverse system exists then there
    must be a universe where this is already happening..at least one anyway
    if it needs to satisfy a multiverse system with an infinite number of
    possibilities universes.

    Have I got this right?.. is it an infinite number of universes?..or
    just copies of one universe?...which origin universe gets copied over
    and over or are there only certain number of universe types (what is
    criteria determination?) that get copied and over. And if a universe
    gets copied over and over does it degrade with each copy?


    A multiverse system containing infinite universes where each universe
    contains one (maybe more? ..again what is criteria determination?)
    possibilities of a universe?

    Why would nature?..natural laws need so many copies of universes anyway?
    I can kind of see this as we have an incredible number of life systems
    on earth..the question is why?..I believe Evolution takes care of this
    ...but maybe this explains why there could be lots of universes?..could
    there be an evolution of universes ..where certain criteria/mutations
    create different types of universes.
    Surely not every universe contains exactly the same balance of energy
    and all that ...like every human is different due to slight differences
    in DNA...(even in twins) and there are now approximately 7 billion of us
    on earth..all slightly different.

    2/ Being a Senior Electronic Technical Officer by training..I find this
    observe/measure thing hard to fathom ...dead cat..live cat thing!

    When you measure a voltage in a circuit using a mutimeter...what am I
    actually doing?...aren't I observing.. then measuring?...but I guarantee
    in a correctly operating, stable electronic circuit....if I make a
    measurement and get a reading of 5.00 Vdc..I will get a reading of 5.00
    Vdc 10 seconds later, 20 seconds later, 30 seconds later, etc

    Aren't I disturbing the state of the circuit by observing and
    measuring?..so how/why can I get repeatable value measurements?

    I guess it's a good thing that we are not in a copy? of the universe
    that contains nothing (empty - has to be a possibility if multiverse
    system of universes reflect infinite possibilities or I would not be
    writing this right now!

    Anyway ..find it all fascinating...still can't get my head round the
    double slit experiment either.
    Does it really happen like that or only because we observe it?...
    I know you can see the physical outcome of this, when you drop separate,
    close stones into a pond (generating peaks and troughs) and I guess you
    don't need to observe it to know it is happening..it is a default
    physical effect of the stones on the water....but only in our version of
    our universe?!..........

  2. jcsd
  3. Aug 6, 2018 #2


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    Hi Doogiewonder,

    1. There are different multiverse ideas, and none of them are yet supported by any observations nor experiments.

    2. The question about measurements (and the so called measurement problem) in quantum mechanics is in the domain of comparatively very, very small systems down to single particles. So it is not about what we see or measure on macroscopic scales, like your example with a multimeter.

    I may also have some links to post, and if so I'll get back to this thread.
  4. Aug 6, 2018 #3


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    Which video? If we don't know what you've been studying, we can't help you understand it. But be aware that very few online videos, even ones done by respected physicists, are a good way of learning physics.
  5. Aug 6, 2018 #4
    It was on You tube and was by Sean Caroll explaining his support for the school of thought of a 'multiverse'.
    I found it interesting and emailed him with my queries, but he could not reply and suggested this site as a way to have questions answered, learn about physics, etc
  6. Aug 6, 2018 #5


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    Can you post a link? This way we'll know which kind of a multiverse he was talking about, so that we don't talk past each other.
  7. Aug 6, 2018 #6

    Vanadium 50

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    Note that the only new information you provided was "It was on Youtube". That's like responding to "which book" with "it was in a library".
  8. Aug 6, 2018 #7
    Thanks DennisN
    1. So the multiverse is more of a hypothesis or still an idea, not a theory?
    2. Ok. I get that . But if we are looking at particle size systems..surely it must be very difficult to sus this out. Is multiverse an attempt to explain gaps in knowledge? to explain what set of circumstances of particle activity.?....
  9. Aug 6, 2018 #8
    Pretty cool he recommended PF as a resource, just not sure how he could suggest PF without replying. Do you mean he did not have the time to explain and recommended PF? There some "Closer to the truth" interviews on YT where he talks about the multiverse was the video one of those?
  10. Aug 6, 2018 #9
    Thanks Bandersnatch..
    Here is Link:
  11. Aug 6, 2018 #10


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    Ah, now I think I understand :smile:. I have seen that clip before, and I am pretty certain that he talks about an interpretation of quantum mechanics in that clip that is called the Many Worlds Interpretation (MWI). That is not the same as the multiverse idea. Also, there are several other interpretations of quantum mechanics.
  12. Aug 6, 2018 #11


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    QM is not my area of (flimsy) expertise, but I'll give you my two cents anyway. This is how I compartmentalised this issue, so it doesn't bother me at night.

    In the video, he's talking about an interpretation of quantum mechanics. It's neither theory, nor a hypothesis, since these interpretations don't by themselves make any testable predictions. The key word being testable - e.g. the many-worlds interpretation just posits that there are many worlds, without giving one any hint as to how to check if there really are any. There are no new equations that come with choosing it over any other interpretation.
    As such, these are pretty much just how somebody wants to think about certain, arguably more philosophical implications of QM.

    Interpretations are of some interest to theoretical physicists, since thinking about a problem in some particular way may lead one to gain an insight that could lead to developing an actual theory, that could perhaps not be stumbled upon if it was thought about differently. But so far it's all about personal preference, and deciding which interpretation is one's favourite is hardly a scientific process.

    Being what it is, there's little point in trying to apply scientific reasoning to the consequences of an interpretation, in terms of energy, location of other universes, or anything really. There are just no grounds on which one could answer.
    In general, though, it is already known that many laws of physics are a consequence of certain local conditions - specifically, conservation laws are not universal, and depend on symmetries. So questions like 'where does the energy for the universe(s) come from' may simply not apply.

    In the video Sean Caroll is bemoaning that after all these years this seemingly important and far reaching question is still outside the realm of scientific inquiry, and describes his favourite way to look at it. He's not saying that science tells us whether the quantum-mechanical multiverse exists or not.
  13. Aug 6, 2018 #12


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    Hi again Doogiewonder, and please note I made a distinction between the Many Worlds Interpretation (MWI) and multiverse in post #10...
    1. I think different people call the multiverse ideas different things. But one thing is certain, it is not any established theory. Regarding MWI, it is an interpretation which is experimentally equivalent to the other interpretations.

    2. "Is multiverse an attempt to explain gaps in knowledge?". Again multiverse is not MWI :smile:. But you could say that MWI, as the other interpretations, are attempts to explain gaps in knowledge. Basically, quantum mechanics is pretty counterintuitive and often even considered weird and unsatisfying, and that is one reason there have arisen a number of different interpretations.
  14. Aug 6, 2018 #13


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    Much of what you'll find in the popular press about quantum mechanics will be some combination of flat-out wrong, oversimplified to the point of being misleading, or presented out of context. What you've been hearing about Schrödinger's cat is likely just plain wrong (you'll find some good explanations in threads here though). Your Sean Carroll video is about as good as any math-free explanation can be - but it's only covering one small piece of the overall subject, so it's likely to confuse more than it helps with the question that started this thread: "Quantum mechanics: What is it exactly?".

    (Digression: It's an interesting question for another thread why popular presentations of QM so often do more harm than good - no other branch of science attracts so many bad explanations).

    So the way to answer the "What is it?" question is to learn what it is from a reliable source that begins with the basics. Ideally that would be a proper first-year QM textbook, something you'd encounter in the second year of an undergraduate physics degree program; there are some good recommendations in our "Science and math textbooks" section. However, the mathematical price of admission is steep: multivariable calculus and partial differential equations, linear algebra, a nodding acquaintance with complex analysis. If that's more than you want to take on, Giancarlo Ghirardi's "Sneaking a look at god's cards" isn't a substitute for the real thing but is a good start for building a layman level understanding.
  15. Aug 6, 2018 #14
    Thank you..and yes he said he had no time to explain...
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