The Platonic Imperative: Reality and the Many Worlds of Quantum Mechanics

By Adam Frank | April 6, 2008 12:44 pm

Adam FrankFoundational studies of quantum physics hold a deep fascination for anyone interested in questions about the ultimate structure of the world. Quantum mechanics (QM) is now hovering around its 100th anniversary (depending on whether or not you take the work of Planck, Einstein, or Bohr to mark its true birth). Unlike other theories, quantum mechanics has proven to be remarkably elusive in terms of pinning down what truly, absolutely, no-kidding-anymore, really exists.

With classical physics, things were easy—it was all just billiard balls. Not so with quantum physics. As Feynman famously quipped, “I think I can safely say that nobody understands quantum mechanics.” Interpretations abound, but agreement does not. Given the central role QM plays in understanding what the world is made of, this situation causes a lot of consternation for physicists. The problem boils down to reality, what’s in it, and what access we have to it.

Here at the University of Rochester, we’ve been running seminars on physics and philosophy. Last Friday, Peter Lewis, a philosopher from the University of Miami, visited and gave a great talk on the now famous “Many-Worlds Interpretation” of QM. His argument turned on probabilities in the Many-Worlds Interpretation. Rather than run through his reasoning on that topic, I thought it would be worth a note on the interpretation itself because it speaks so loudly to the central issue of what scientists think we are, ultimately, aiming for.

The problem with quantum mechanics is that the basic entity of its mathematical machinery—the so-called wave function—does not give a single prediction for the outcome of experiments. Instead it provides a description of many outcomes with associated probabilities which all seem to exist simultaneously. It is not until a measurement is made that the wave function gets suspended (collapsed is the term) to yield a single answer. Or, at least, that is the way the standard interpretation of QM tells the story.

This bothers lot physicists who like to take their mathematical descriptions of reality seriously. Why should a perfectly good equation that describes the evolution of the world (the wave function) go away just because someone made a measurement? To deal with this strange state of affairs, Hugh Everett proposed what would become the Many-Worlds Interpretation in the late 1950s (Bryce Dewitt did a lot of development on the idea, too). The Many-Worlds solution is, in a sense, a platonic one. The mathematical physics stays put, but our notion of what constitutes reality changes. Well, that is an understatement—it really, really changes.

According to the Many-Worlds Interpretation, the wave function is never suspended. Every time a measurement is made, the world splits off into as many copies as there are pieces (terms) in the wave functions. If you are the lab technician making the measurement, you split off into multiple copies, as does the entire universe with you. In each copy, a different value of the measurement is recorded. After the measurement, each copy world goes on evolving and splitting as more quantum events occur.

Sounds wacky, don’t it? Why would anyone believe in a universe that is endlessly splitting into (as far as we know) unobservable slightly-different versions of itself? Here is the point at which, as a physicist or philosopher, your biases will likely show themselves.

People will line up behind the Many-Worlds Interpretation because of its consistency. Its advantage is that it keeps the math whole. There is no special pleading about consciousness intruding on the measurement. There is no sense that our access to the world is limited. You have a beautiful equation. It describes the evolution of physical reality, and that is that. People who favor the Many-Worlds Interpretation tend to be Platonists somewhere in their scientific souls. Recall that Plato argued that behind the world we see lies an ideal world made of purely mathematical forms. This idea dovetails with the worldview of many theoretical physicists. Timeless, immutable, mathematical laws govern the world. That is what makes physics so indescribably beautiful. Some people, like Max Tegmark, take their Platonism further—the world is not just governed by that math; it is that math (you can read more about Max’s views in an interview I did with him in the July 2008 issue of DISCOVER).

The Many-Worlds Interpretation seems crazy to a lot of people, physicists and non-physicists alike. Personally, as a theorist of the astrophysical sort, I see its allure but remain suspicious of the enormous commitment it asks. What may be most interesting about it, however, is how, by taking things to an extreme, it raises two of the oldest and deepest questions we can ask:

What truly exists, and what kind of access do we have to it?

Adam Frank is a professor of astrophysics at the University of Rochester who studies star formation and stellar death using supercomputers. His new book, “The Constant Fire, Beyond the Science vs. Religion Debate,” has just been published. He will be joining Reality Base to post an ongoing discussion of science and religion—you can read his previous posts here, and find more of his thoughts on science and the human prospect at the Constant Fire blog.

CATEGORIZED UNDER: Evolution, Science & Religion
MORE ABOUT: Adam frank, creationism

Comments (54)

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  1. Steve F.

    Hi Adam:

    Good stuff, even if one’s only conclusion is that science in its pursuit of the best and most accurate explanation leads up some very interesting alleyways.

    It seems to me that quantum mechanics – the most accurate science we have – leads to some of the most illogical-seeming conundrums we can imagine. One of those conundrums, of course, is how modern theoretical physicists – many-world interpreters and string theorists especially – have become the modern equivalent of crazed medieval mystics trying to determine how many angels are on the head of pin.

    My favorite conundrum is entanglement, which has the advantage over the many-world’s interpretation of being accesible to experiment (where is Karl Popper when we need him?), but I must admit to being fascinated by other such conundrums as dark matter and dark energy – areas of your expertise which are computationally and experimentally accessible as well.

    But where I would like to go is the correspondence with religion.

    What we have here is an extraordinarily powerful and successful science – quantum mechanics – which reveals aspects of the world that in principle are unknowable.

    A similar case exists for religion, although those without experience easily misconstrue it. This is that God – the ultimate reality – Bhudda-nature – whatever you want to call it, is unknowable.

    For example, if like a good physicist, we think of God as intelligence (in the abstract, of course), then our own personal intelligence is simply an instantiation of that intelligence and is understandably diminished in capacity with respect to God as intelligence writ large.

    And, of course, our very attempt to attribute intelligence to God is simply a feeble attempt to understand something unknowable by extrapolation from what we have experience of.

    The unknowability of God explains many things, including why religion is a user and source of science and rational thinking. This unknowability means that all of religious truth is understood through the thinking facility. The teachings of Christ, for example, are often in the form of parables that demand thought and experience if their meaning is to be made clear.

    It is also explains the commonality of science and religion much more powerfully than does awe. Awe, a product of the mind, is but one spoke of the wheel of understanding, whereas the search for understanding is the wheel itself. And, it is necessitated by science and religion in face of the mysteries – including those shown to us by quantum mechanics.

    Warmly,

    Steve F.

  2. Eric the Leaf

    I suspect that you may be a Halikaarnian. Does Hylaean Theoric Worlds ring a bell?

  3. jayne

    Well, I am most definitely a non-physicist. I therefore have very little to contribute here in terms of theoretical knowledge. However, I just gotta say I simply love the sheer mystery of this topic. For me, it’s rather exciting to be reminded that as human beings, we who often think we are so very certain of so very many things, really just don’t know for sure. And I love it when physicists – the ones we (I?) so often turn to for explanations – speak of the wacky and the wonky. Not sure what that makes me… a Wonkarian perhaps? : )

  4. Perhaps you are a latitudinarian. All this stuff reminds me of thinking about how the universe seems infinite both inward and outward, that is, no matter how big a telescope or microscope we build there is more to see. I once imagined that the universe out ward looked a lot like the universe inward and that our entire universe, that we see, may be part of a molecule of a blade of grass that was just cut by some giant much further out.

  5. Eric the Leaf

    see “Anathem”

  6. Just a couple of notes. I think the most interesting thing about the conflicting interpretations of QM is that it means some very fundemental aspect of our understanding, of our “picture” of reality has yet to be resolved. Note its possible that it WILL be resolved in some very classical manner (I think this is what Popper wanted) but that has not happened yet (100 years and counting).

    It may be that physicists and philosophers and all of us will be left with the world that can not be fully determined (or pictured) in the classical sense. Either direction will have consequences for how we understand both the Universe and our place in it. I am not sure how or if this should have consequences for the science and religion debate just becuase I think results and specific theories are a slippery ground to build connections between what people experience as “sacred” and the general worldview of science. Metaphors are important though and are often traded between art and science and culture as part of a broad zietgiest. They can guide thinking and act as a means interpretation for experience.

  7. I love Neal Stephenson and have Anathem on my list of to reads…

  8. PeterS

    The MWI has some interesting implications. But imagine I had constructed a theology on the basis of the MWI merely adjusting the terminology. Then imagine the snide, scornful, dismissive reaction of our Fundamentalist Atheist friends. I would have been banished to the outer cosmos as a religious nutter. Weird and wacky in cosmology is ‘in’ and religion is weird and wacky but that is definitely ‘out’. That is just not cricket!

  9. Mike Gottschalk

    My hope is that some day, the phenomenon of subjective experience, is given the credibility of whackiness accorded to QM. How do we let our familiarity breed such contempt?

  10. I am amazed at how modern cosmology has gotten into ideas that would have seemed like the most wacked out of possibilities a few decades ago. The crucial difference between it and theological metaphysics will be if theories of multi-verse can be falsified (Karl Popper again). If not then one has to ask what their status as “knowledge” should be. Many astronomers roll their eyes at mention of the multiverse (the still do for inflation but less so now that there is some evidence pointing in that direction).

    @Mike – I agree about subjectivity. I have always imagined that eventually science would have develop a real account for it rather than brush it away. Developing that account would pose both great challenges and opportunities.

  11. edendane

    The concept that gets to me is one of connecting the function of uncertanty and the theory that ( i know that i am getting the name wrong) the universe holds fixed context, information. the two seem to be diametrically opposed, how can potential be actually “uncertain” when the context for it is prexisting. This does not even get into the horrizon problems and exactly where, in the quantum mean are these dimensions “housed”.
    how does this relate to Bells theory, and entanglement, ect.ect.

  12. patrick

    Are many-worlds and multiple universes separate ideas?
    Does the graviton play into the many-worlds theory?
    Can any of these worlds be somehow connected to a surrounding observable universe in which the deviations of our reality actually exist in their own reality?
    Are these worlds governed by the same time?
    If the scientist making the measurements splits into other worlds, doesn’t his world go with him?
    If so, doesn’t that mean we already existed in other worlds before then, or does each new world’s time line begin in a laboratory?
    Yes, no, undetermined?

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  14. Christopher M

    I am a little confused by this description of the MWI: “Every time a measurement is made, the world splits off into as many copies…” I thought — and you seem to say elsewhere in this post — that the MWI doesn’t need to give any special status to “measurements.” There’s just the wavefunction and its evolution over time, right? Does the so-called “splitting” involve discrete events, or just a continuous, infinitely-finely-grained branching?

  15. Siddharta

    Do physicists consider the works of philosophers like, say, David Lewis?

  16. Josef-PeterRoemer

    As to MW, one needs only to look into the past history of mainstream scientists who surmised that the earth is flat, and the sun revolves around the earth. Argument to that today is: well we are much more advanced then they where in their day!! chuckle!. Well that is exactly I’m sure their response was to their not so mainstream contemporaries in their day. Astronomers that roll their eyes when they hear about MW, well for people who look at the cosmos past, don’t really have any room to Chuckle. I would consider them just mere narrow minded lookers without a clue.

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