New Year’s Multiverse

I see little to be hopeful about the new year, but had a glimmer of a hope that we’ll see a reduction in Multiverse Mania. Surely people will sooner or later get tired of stale pseudo-science. Just got back to work from vacation and it seems that so far this is not working out at all, quite the opposite.

At the yearly Edge question site, Martin Rees’s answer to the question “What scientific term or concept ought to be more widely known?” is The Multiverse, and he starts out with the usual sort of breathless hype:

An astonishing concept has entered mainstream cosmological thought…

Critics of the multiverse are described as having two arguments:

  • “Some claim that unobservable entities aren’t part of science.”
  • “Some physicists don’t like the multiverse: they’d be disappointed if some of the key numbers they are trying to explain turn out to be mere environmental contingencies governing our local space-time patch—no more truly “fundamental” than the parameters of the Earth’s orbit round the Sun.”

The first of these is the usual straw man argument, painting multiverse critics as too ignorant to realize that much of science is based upon indirect evidence, not direct observation. The actual argument of this sort against the multiverse is not that we can’t get direct evidence for it, but that there is no evidence of any kind for it, direct or indirect, and no plausible prospects of getting any. This case has been made ad nauseam here on this blog.

The second of these arguments is treated in much more detail in a new article at Nautilus by string theorist Tasneem Zehra Husain with the title Even Physicists Find the Multiverse Faintly Disturbing. Husain treats in detail the question of how physicists “feel” about the multiverse, and like Rees, makes the point that what physicists don’t “like” about the multiverse is that it removes hopes of being able to do things like understand the nature and strengths of fundamental forces, or calculate the masses of elementary particles.

Rees tells us that physicists are wrong to feel this way, that instead they should be awed by “the revelation that physical reality was grander and richer than hitherto envisioned” and that “If we’re in a multiverse, it would imply a fourth and grandest Copernican revolution.” Husain in the end seems to agree, quoting Gian Giudice:

Perhaps we need to let go of something we’re holding onto too tightly. Maybe we need to think bigger, refocus, regroup, reframe our questions to nature. The multiverse, he says, could open up “extremely satisfying, gratifying, and mind-opening possibilities.”

Of all the pro-multiverse arguments I heard, this is the one that appeals to me the most. In every scenario, for every physical system, we can pose infinitely many questions. We try to strip a problem back to the essentials and ask the most basic questions, but our intuition is built upon what came before, and it is entirely possible that we are drawing upon paradigms that are no longer relevant for the new realms we are trying to probe.

The multiverse is less like a closed door and more like a key. To me, the word is now tinged with promise and fraught with possibility. It seems no more wasteful than a bower full of roses.

Rees and Husain do a good job of showing that if science is about feelings, then Multiverse fans have a fine argument against critics arguing based on their negative feelings. The problem of course is that science is not about feelings but about evidence. The argument by critics that needs to be addressed is that there is no evidence at all for current multiverse scenarios, and no plausible way of getting any by scientific methods.

Nautilus has another multiverse-related piece just out, We Have Pushed Physics Too Far, by Marcelo Gleiser. My reading of the piece is that Gleiser agrees that the Multiverse is not successful science (“Parallel universes are a non-answer”), and I believe most physicists also agree. Unfortunately the lessons he draws from this (as I’m afraid many others are doing) is that the problem not a particular research program that failed (string theory, by ending up with the string landscape and the multiverse), but the whole idea of pursuing mathematical ideas about further unification:

We can call this the ultimate Platonic dream, the quest for a single simple and broad-ranging theory of physics. Indeed, during the past four decades, the search for such a theory has inspired many of the brightest physicists in the world. But today we are seeing the limits of this Platonic thrust to mathematize nature, due to a lack of experimental validation and several theoretical obstacles—including the possibility of multiple universes and the troubling questions they pose.

Gleiser sees successful physics as “an expression of intellectual humility”, with our current problem that of Icarus, trying to fly too close to the sun. I strongly disagree with him about this, seeing some of the best of physics as an expression of intellectual arrogance, not humility. It is intellectual arrogance that has gotten our understanding of nature as far as it has gone, and it will require intellectual arrogance to go farther. The current problem of theoretical physics is due not the sin of arrogance, but to a somewhat different one, that of refusing to admit error. Multiverse mania is largely about the refusal to admit that string theory unification is a failed idea. Yes, arrogance is one reason for this refusal, and admitting failure takes some humility. But then moving on to find different, more successful ideas will require a lot of both mathematics and intellectual arrogance.

Update: One more article at Nautilus about the multiverse. At least this one is explicitly theology, it explains:

a section of liturgy recited whenever we take the Torah out of the ark, and it’s related to a prayer that many Jews know, “Adon Olam.” The phrase is usually translated as “Sovereign of the Universe,” where the word olam can mean both “the universe” and “eternity,” expressing tremendous expanses of both space and time. But in this particular section of the Torah service, God is called “Adon Olamim,” where the suffix -im makes the word plural. This means that God is “Sovereign of the Universes,” as in, “more than one universe.” God doesn’t need to be a designer who had a specific plan in mind that led to the creation of humanity. God is, in fact, the Sovereign over all the universes, including the ones that don’t have life in them.

Update: Yet more explicit theological coverage of the Multiverse at science magazine Nautilus, with an article from Mary-Jane Rubinstein, a professor of religion, who is interested in multiverse versions of pantheism and explains:

As a professor of religious studies, I am particularly drawn to the places where religion and science seem antagonistic, but turn out to be entwined. The multiverse, I would argue, is one of those places.

My only disagreement here would be whether being a place where science and religion are intertwined is a good or bad thing…

Update: Yet more in the Nautilus series on the Multiverse: more theology, and now teleology.

Update
: In case you were worried that Multiverse pseudo-science was incompatible with the Quran, have no fear.

Update: 2017 is well on its way to a bumper crop of Multiverse Mania. Today it’s New Scientist’s turn.

Update: This crap is just endless, more every day. Today it’s at Astronomy Magazine, about this nonsense, debunked long ago by Jennifer Ouellette.

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73 Responses to New Year’s Multiverse

  1. reader says:

    This is a tired topic, but I find your point of view quite odd. The global structure of the universe is either essentially homogeneous or it is of the multiverse type. We don’t know which version is true, so it seems quite reasonable to consider both options. What exactly is your stance: that the multiverse picture is ruled out in some way, or that the whole question is pointless? To me, the homogeneous versus the multiverse structure are roughly equally likely a priori. It doesn’t seem so far fetched that the two options will leave different observable imprints of some sort. Whether this is indeed the case is a difficult question that requires serious thought and analysis, yet you call this pseudo-science. Speaking for myself, there are few questions more grand than that of the global structure of the universe, and we should do everything we can to look for experimental signature before declaring that the search is futile. Your negativity on this matter is puzzling.

  2. S. P. Nova says:

    Perhaps confidence would be a better term for what you mean, rather than arrogance, which has never served anybody well. Quite the contrary. Confidence and humility can co-exist. Arrogance and humility cannot.

  3. Jeff M says:

    I don’t see why unification is mathematization. All physics is mathematization. The four forces are mathematized if they have nothing to do with each other. The fact that a mathematical structure exists which seems to show some relation between three of them is no more mathematical than their individual structures, it’s just different math. And I would agree with SP Nova about confidence, though I have known plenty of arrogant physicists….

  4. neil says:

    “Multiverse mania is largely about the refusal to admit that string theory unification is a failed idea. ”

    I agree that the string theory multiverse is a failed idea for the reasons you state, but what about the eternal inflation multiverse, or for that matter the MWI? In these cases the appeal seems more about the anthropic principle or interpreting QFT than the multiple compactifications of string theory. Do you find these ideas any more appealing than string theory unification?

  5. There is an article by Steven Weinberg in the most recent New York Review of Books where he says he is looking for a modification to quantum mechanics in order to avoid the multiverse issues. See http://www.nybooks.com/articles/2017/01/19/trouble-with-quantum-mechanics/#fn-3

  6. Peter Woit says:

    S.P. Nova,
    I was specifying “intellectual” arrogance as opposed to other kinds, and by that I meant just the opposite of Gleiser’s “intellectual humility”, which to me means having a low opinion of one’s ability to solve difficult problems. Having an unreasonably high (and thus “arrogant”) opinion of one’s ability to solve an intellectual problem is generally a prerequisite for making a serious attempt at solving the most difficult unsolved problems.

    As for the more general sort of arrogance, there’s a lot of that too among successful theoretical physicists, and the part of that characteristic that leads one to refuse to admit something doesn’t work is generally very much not helpful.

    “Intellectual humility” says that the puny human brain is incapable of understanding how the world works at the deepest level. Unlike Gleiser, I see the practice of fundamental theoretical physics as a rejection of this idea and the pursuit of its opposite.

  7. Peter Woit says:

    neil/Laurence B. Lurio,

    The multiple worlds interpretation of quantum mechanics has nothing to do with the multiverse discussed in these articles, one where laws of physics are different in different universes. Bringing completely unrelated things together, making it impossible to know what one is actually talking about, is part of multiverse mania. I don’t want to discuss MWI here.

    I read the Weinberg piece, didn’t see anything at all new there, and it’s off-topic here.

  8. Peter Woit says:

    reader,
    My claim is that the question is pointless in the sense that it’s not now science. Maybe someday someone will come up with a multiverse theory that explains something and can be (indirectly) tested. At the moment the “theories” being put forth that have different physics in different universes don’t explain anything, all they are is elaborate excuses for failure.

  9. S. P. Nova says:

    Perhaps “reader” confuses the general concept of inhomogeneous cosmological models, of which there are many, with the specific concept of a string theory multiverse of 10^500 universes with different constants and physics in each.

  10. Peter Woit says:

    S.P. Nova,

    Yes, that’s the essential point. That the Big Bang was just one of many such events, with lots of other universes out there with the same physics as ours is a plausible idea, and you can even claim it follows from your favorite inflationary model. Personally I’m not very interested since it explains nothing about unanswered questions of fundamental theory, and I doubt it has testable implications. A claim that there are lots more universes out there like ours, but disconnected from us, may be thrilling to some but it tells us nothing about ours.

    Unless you have a model you can calculate things in (unlike the string theory landscape) a multiverse with different physics in different universes also tells us nothing about our universe, all it adds is an excuse for why we can never calculate certain things (they depend on which universe one is in). Maybe this excuse is true, maybe not, but lacking any way to calculate things and make testable predictions, all it is is an excuse, and pseudo-science rather than science.

  11. reader says:

    I would like to stress that whether or not you like the multiverse or find it interesting has no bearing on whether or not is a true fact of our world. Everyone agrees that it would be lovely if, for example, SU(3)xSU(2)xU(1) was the unique outcome of some deep new principle yet to be discovered. But the world might not be like that — it might just be a more or less random fact about our local vacuum. It’s a challenging situation, since it’s hard to think of ways to distinguish the two possibilities. What is pseudoscience is to pretend that this issue does not exist.

  12. Thomas says:

    reader,

    it might be that SU(3)xSU(2)xU(1) is due to the sequence octonions, quaternions, complex, real; it might be that SU(3)xSU(2)xU(1) is due to the three Reidemeister moves; it might be that SU(3)xSU(2)xU(1) is due to some other principle. But SU(3)xSU(2)xU(1) cannot be due to the multiverse, because that term makes no sense: multi-everything is a contradiction.

  13. a1 says:

    Re arrogance vs. humility I would say that humility is to admit that we still do not know everything knowable. But pushing humility too far would destroy science, it would amount to say that we will never know. Saying ‘never’ is of course arrogance. Multiverse theory is arrogant as it assumes that we already know everything relevant: obviously this is not enough to explain some features of physics, so a multiverse has to be hypothesized. But the real point is that it obliterates our lack of relevant knowledge.

  14. Bee says:

    “In every scenario, for every physical system, we can pose infinitely many questions.”

    The multiverse is great because it means they can write papers about fictional universes until eternity.

  15. Peter Woit says:

    reader,
    Yes, the string landscape explanation may be true, it also may be true that SU(3)xSU(2)xU(1) was chosen by the Jolly Green Giant for reasons we can never understand. The problem is that neither explanation is a scientific one.

  16. reader says:

    Thomas,

    You left out the possibility that SU(3)xSU(2)xU(1) might not be “due” to anything. Of course the danger lies in jumping to that conclusion prematurely, which is why it seems best not to “believe” in the multi-verse, but rather to accept it as a possibility and remain vigilant for signs of its (non)existence.

    Here is the kind of questionable logic one reads on this blog and elsewhere: string theory predicts the multiverse, the multiverse in inherently unpredictive, therefore “string theory unification doesn’t work”. This logic would only make sense if there were some alternative theory that had a monoverse and that made some successful prediction beyond what string theory can do. But in the absence of that, if you assign a priori 50-50 odds for multiverse or monoverse, you can’t possibly use the “string theory predicts multiverse” line to argue that string theory is “wrong” or “doesn’t work” — that makes no logical sense.

  17. Jeff M says:

    I think Bee hit the nail on the head 🙂

  18. Peter Morgan says:

    “Multiverse mania is largely about the refusal to admit that string theory unification is a failed idea.” I’ll pick up on this for a different reason than that given by neil.

    I find string theory/Multiverse ideas too unsupported by evidence, but to say that it’s all a “failed idea” seems too much. Someone could come up with a big new idea tomorrow that changes all that. I can expend a lot of hot air on how unlikely I think that is, but that’s just feelings. Nonetheless, it’s always too soon to declare an idea “failed”. I think far too many resources are being given to string theory, but the alternatives seem in about the same shape, of needing a new idea to make it really attractive enough as a possibility for many people to move to it. Note that I don’t think of this as the common “we should all work on string theory because there’s no alternative” argument, because there are plenty of slight possibilities that might deserve a decade of someone’s time, or even mine, but research most always gives the desperate feeling of having made bad choices, except for the occasional, fleeting moments when everything feels kinda right.

  19. Peter Woit says:

    reader,
    The logic is: the string theory unification hypothesis leads to a scenario that predicts nothing (or, anything, the same thing…) and thus cannot ever be tested. This means the hypothesis is scientifically empty, on a par with the Jolly Green Giant theory and many others. You can decide to believe it if you want, and devote your life to arguing that your untestable explanation is the best one around, but you’re not doing science.

    Peter Morgan,

    I think it best to call a spade a spade.

  20. tt says:

    “you assign a priori 50-50 odds for multiverse or monoverse,”

    Occams razor would not agree with that prior

  21. reader says:

    Peter,

    If we knew for certain that the multiverse hypothesis cannot ever be tested then I would basically agree. But this conclusion seems rather premature, although I admittedly can’t provide you with a clear path towards testing the theory.

    What odds do you assign to the multiverse being a true description of nature? I start with something like a 50% prior belief. Weinberg’s argument for the cosmological constant, combined with the complete failure over several decades to uncover any deeper structure behind the Standard Model, pushes the probability to perhaps 60% for the multiverse. I think that anyone whose ultimate goal is to understand the laws of nature should do this exercise, and I encourage all readers of this blog to think about this in a serious way.

  22. RandomAnonymous says:

    reader:
    What “exercise” – you simply pull numbers out of the air. You cannot possibly expect anyone to take a starting point of 50/50 seriously.

    “this conclusion seems rather premature, although I admittedly can’t provide you with a clear path towards testing the theory.”
    If someone comes up with a testable theory then we can discuss it. Until then, the multiverse is empty metaphysics. Predict something or go home.

  23. Peter Woit says:

    reader,

    I expressed an opinion about this question here:
    http://www.math.columbia.edu/~woit/wordpress/?p=8587

  24. Roofus McLoofus says:

    “[…]is due not the sin of arrogance, but to a somewhat different one, that of refusing to admit error. […] Yes, arrogance is one reason for this refusal, and admitting failure takes some humility. But then moving on to find different, more successful ideas will require a lot of both mathematics and intellectual arrogance.”

    I will align these statements with that of Dr. Richard Hamming: “…the difference between being ‘strong-willed’ and ‘stubborn’…I’ve seen people abandon a good idea too soon, and I’ve seen people cling to a bad idea too long. They’re both difficult problems.”

  25. reader says:

    Random anonymous writes: “What “exercise” – you simply pull numbers out of the air. You cannot possibly expect anyone to take a starting point of 50/50 seriously.” Yes, to you this probably seems like it’s pulled out of thin air. But some of us have spent a lot of time thinking about the early universe and the kinds of behavior that can occur. A Lagrangian with lots of different fields and a complicated potential doesn’t seem terribly unlikely given what we know, and this sort of theory seems to lead to a multiverse. Sorry if you find that uncomfortable.

    Peter: thanks for the link, although it seems that you are avoiding the question. It’s incredibly important to separate which observed facts about our world have a deeper explanation and which are just essentially random variables. The decades long search for deeper mathematical structure underlying the SM has so far had zero success in terms of contact with experiment. This doesn’t mean we should stop trying, but intellectual honesty requires that we consider the possibility that the task is misguided.

  26. RandomAnonymous says:

    You spent a lot of time thinking and postulating Lagrangians, and what you got in return was a guess of exactly 50/50? I’m truly sorry.
    I don’t find the idea uncomfortable, I find it unscientific, there is a difference. What exactly is it that we know which points to a Lagrangian with a huge number of fields and a complicated potential?

  27. reader says:

    RandomAnonymous: answering your question here would take up too much space and get off topic. But I will say this: it’s not “unscientific”, quite the opposite. If you are a scientist thinking about fundamental theory this sort of judgement call about what might be calculable literally affects how you spend your time every single day. You have to decide: “should I attempt to come up with an explanation as to why the dark energy density / CC is what it is, or should I just view it as a random number with no explanation.”. Actual scientists, as opposed to blog readers, can’t avoid confronting this issue.

  28. Peter Woit says:

    reader,
    I should note that RandomAnonymous seems no more unlikely to me to be a serious scientist than you are. You’d be surprised who comments here anonymously. The ad hominem argument isn’t a good one.

    The problem with your argument about how scientists work is that
    1. attempting to calculate X
    2. deciding that X is a random number with no explanation
    are not the only two possibilities. If you don’t have an idea for how to attack 1, a much more sensible attitude than 2. would be
    3. I don’t know what explains X, will keep this open question in the back of my mind, maybe someday I or someone else will get an idea about this.

    This is the serious problem here: instead of just admitting that string theory unification doesn’t work, and we don’t understand where some things come from, multiverse maniacs claim that string theory shows that no testable explanation is possible. There’s a big difference between telling people “I don’t know how to solve this problem” and “This problem can’t be solved”. Here I guess I’m with Gleiser that some humility is in order. Just because you have failed to solve a problem doesn’t imply that the problem is insoluble.

  29. reader says:

    Peter,

    option (3) is of course what most people do in practice. But when you get a glimmer of an idea, you have to decide: am I going to pursue this with full vigor, pushing my other projects aside, or am I just going to let this thought flow in and out of my brain. Taking the example of the cosmological constant, which option you choose is heavily influenced by your belief as to whether a deeper explanation exists. This sounds abstract, but it is in fact how people operate. My comment about “blog readers” was not meant as an ad hominem attack, it was to emphasize that when you are at home sitting on your couch reading a blog you can dismiss these issues, but you can’t when sit in your office and get to work.
    .
    Saying “string theory unification doesn’t work,” is a gross simplification of a complex issue, and does little to advance understanding. But I agree that more humility is in order.

  30. RandomAnonymous says:

    Here we are both readers, in real life we are both scientists. It is clear that you are a hep-th theorist, so for fairness I’ll state that I’m a hep-ex experimentalist.
    I stand by my “unscientific” claim. A scientific idea may yet arise by pursuing this direction, but until then the multiverse is empty. At times we all have to decide which speculative direction to pursue, and this by necessity must be done without proper evidence, and based only on half-formed ideas / priors / guesses / etc. For this purpose the kind of reasoning you present above is ok – but absolutely not as a serious explanatory statement about nature. This is currently a big problem with your community – that the speculative ideas currently regarded as most promising get presented far too much as accepted fact.
    “Saying “string theory unification doesn’t work,” is a gross simplification of a complex issue, and does little to advance understanding.”
    As things stand, it is impossible to argue that string theory unification has worked. Wasn’t it originally meant to be a theory of QCD before that? A breakthrough could change all of this and the program could turn into a spectacular success of course. Until then, I repeat the statement from my first post – predict something, or go home.

  31. vmarko says:

    reader:

    “But the world might not be like that — it might just be a more or less random fact about our local vacuum. It’s a challenging situation, since it’s hard to think of ways to distinguish the two possibilities.”

    The way to distinguish between universal laws of nature and random contingencies is well-known: given a statement about the physical system, if all instances of the physical system obey the statement, it’s a law. If only a few instances obey it, it’s a contingency.

    Maybe the most vivid example of this at work was the Titius-Bode law, which was considered to be a true law of nature, even used (successfully!) to make predictions, until people discovered Neptune, and later on other solar systems different from our own. At that point the “law” was demoted to the contingency of the initial conditions for the formation of the Solar system.

    The problem with interpreting physical constants as a contingency of the multiverse is therefore obvious — until you find experimental evidence that in some part of spacetime the constants are different, I have no reason to say that they are a contingency. In contrast, there is overwhelming evidence that the constants are the same throughout observable spacetime, making a 50/50 prior very unrealistic.

    And if you try to claim that the patches of spacetime where constants are different are necessarily beyond the observable horizon, then you are leaving the realm of science, and talking metaphysics. I can equally claim that there are unicorns beyond our observable horizon, and assign to it a 50/50 prior. That just isn’t science anymore.

    Best, 🙂
    Marko

  32. Dan Winslow says:

    Well, science has to end somewhere, right? The idea that we can find every explanation for everything seems like it would have to result in a circularity or infinitely receding stack at some point.
    I guess the question ultimately is : can Science contain itself? Since we are using chains of causality in our thinking, don’t we ultimately have to wind up at a first cause, an outermost explanation? If we get to any explanation, isn’t there then by definition the need for an explanation for that?
    I am not talking about anything to do with a diety at all.I just mean that I don’t think we can arrive at an explanation for everything. It’s got to end somewhere, even if it’s just our own ability to understand. Have we reached that spot? I have no idea, but we might be getting close. The way that current thought about physics seems to be fracturing and wandering off into theology and wishful thinking may be an indication of that.

  33. Peter Woit says:

    Dan Winslow,

    Yes, there’s a real danger that we’re getting to the limits of what we can understand. What concerns me is that instead of having a situation where the open problems we don’t understand are clear and people can keep trying if they wish to make progress, we’ll end up instead with an entrenched influential ideology saying that the string landscape is our best understanding, and that shows that no progress is possible, no point in trying. This would be convenient for a generation of theorists who invested heavily in string theory: they can avoid admitting failure, and might figure that there’s little hope of progress anyway during the rest of their careers. It would not be a good thing for physics, or for science and its public perception in general.

  34. Anonyrat says:

    Gravity was an elaboration on Newton for centuries, until Einstein. Particle physics might have a similar centuries-long detailing of the Standard Model before the next step. There is no reason yet to succumb to the multiverse because one or two generations of physicists haven’t made the next breakthrough.

  35. Arnaud says:

    reader :
    I think the multiverse hype is the failure of string as a theory for
    the following reason where I use in parallel the example of gauge
    theory.
    A postulate of string theory is a 4+D dimensions space where the D
    dimensions as to be compactified to describe our universe. A postulate
    in gauge theory is that it exists a gauge group G describing
    fundamental interactions.
    In string theory nobody knows how to compactify the D dimensions to
    get our observed physics and there is 10^(…) possibilities. In gauge
    theory we have a priori an infinite number of group but we know G =
    SU(3)xSU(2)xU(1) works very well (may be it has to be extended somehow
    but at least now, it does the job).
    Last step, some string theorists unable to find the correct compactification
    for our universe postulate a multiverse. This is where the science
    fails. It would be like postulating that since gauge theory works here
    then there is another type of “gauge multiverse” where all different
    gauge group are realized. It is useless to understand physics in our
    universe to postulate that it exists other universe with other gauge
    groups. It is bad science to hide the fact that no known
    compactification describes our universe (at the precision of current
    experiments) by postulating a multiverse.

  36. DoZen says:

    Peter,

    (Sorry for my ignorance, I’m not a physicist).
    If string theory is not intrinsically incompatible with other approaches (representation theory, QFT, quantum gravity, twistors,….???) then all the other approaches also allow for nearly infinite mathematical possibilities. If, on the other hand, they are incompatible, that is Big News. Or does the question even make sense?

    As to string theory per se: if you are stuck, why can’t it be left on the back burner while other approaches are tried?

    As a mathematician, it’s hard to understand the struggle physicists are having. We work on things we think are interesting, and the main (only, for many of us) guide is interest and beauty. There’s fairly wide acceptance of what fits these criteria. If I do something good, colleagues will be interested. So I never need have the feeling I am wasting my time, that it was all for naught! So there is no need to be defensive, or to write self-congratulatory expository articles. The reward is in the struggle, in the insight, in the doing.

    I think some people confuse mathematical possibilities with physical possibilities.
    Somebody could study gravitational orbits with a law different from inverse-square,
    but that doesn’t mean it “exists” someplace else, and it certainly doesn’t mean it’s
    worth spending time on. If some grad student wants to do that as an exercise, well and good, but I wouldn’t wake up in the morning excited to think about it- at least not
    yet. If I do some day, good for me; that would make me happy! But I hope I won’t run around claiming this is an alternate “reality”.

    There are very real limits to what we can know and understand. Zen Buddhists have
    understood this for a long time; their explanations are completely compatible with science. The experience of zen “knowing” by not knowing (perhaps called “just this”) is quite useful and refreshing for scientists, as a lesson in humility and wonder. If you don’t have to know it all, and yet “can” in a different way, you can relax a bit and have fun. The stress is less, and the delight remains. It all fits together, and it is all remarkable and amazing. The only part that causes a misfit is due to
    our own egos, arrogance and jealousy. Anyone who gets to spend some time thinking about math, physics and all this is supremely lucky, can make real contributions, and
    could brag a little less while feeling a little more of gratitude. At least in this part of the multiverse!

  37. EThomas says:

    Peter,

    Is it reasonable to expect all of reality to be accessible via empirical scientific methods? Is it even reasonable to expect all of reality to be conducive to mathematical modeling?

    If not, where do we go from there?

    (Disclaimer: I am not a fan of String Theory, or the Multiverse theories, mostly for some of the same reasons you state)

  38. Peter Woit says:

    Ethomas,
    We have no way of knowing in advance how much further we can go, with experiment or mathematics. The only thing that’s clear though is that if we convince ourselves it’s not worth trying, we definitely won’t go any further. So, for that I’d like to see a solid argument, not the bogus ones that prop up the string theory landscape.

    As to where to go from here, personally it seems to me that there is still a huge amount we don’t understand about quantum field theory, which has been our best tool for understanding fundamental physics. I don’t see any serious argument for why we can’t understand quantum field theory better, and hope to make progress that way.

  39. Chris Kennedy says:

    To put the Jolly Green Giant in the same category as the Multiverse is an insult to the Jolly Green Giant. At least there is a 55 foot statue of the JGG in Blue Earth Minnesota. There is no statue of the Multiverse (at least not in this Universe).
    Personally, I think there are a lot of branches of science who are missing out on a wonderful opportunity currently monopolized by the theoretical physics community. For example: Multiverse Meteorologists could forecast for planets in the multiverse and predict the high/low temps, precipitation, etc. without fear of ever being incorrect. They might even be able to convince viewers that their forecast accuracy rate for worlds in the multiverse is 90%. Of course, once you multiply that 0.90 by “reader’s” 50/50 chances of the planets being there to begin with, the more realistic figure drops to around 45%.

  40. Peter Woit says:

    Chris Kennedy,
    I don’t know about a sculpture, but there is this
    http://www.crawickmultiverse.co.uk/

  41. Petite Kabylie says:

    Peter,

    What if in 20 or 30 years a new theory, completely different from string theory, and based on sound and strong first principles, comes along and reveals the same landscape of the laws of physics as well as universes for ever disconnected from ours. Would you endorse the multiverse concept?
    Thank you!

  42. Petite Kabylie says:

    N.B: Assume this theory has made tested predictions for phenomena in our universe.
    Thank you!

  43. chris says:

    reader,

    I am genuinely curious how you come up with a 50/50 prior for the existence of a multiverse. The arguments you gave (brooding over Lagrangeans etc.) seem purely sociological to me and i at least try to disregard such items as background noise when thinking about laws of nature.

    Subtracting all the jargon, the statement “i give a 50/50 prior to the multiverse” for me is just the plain statement:
    “The existence of things we can never detect is equally likely than not.”
    I guess this is something i would expect from an agnostic or maybe a philosopher – but what is the scientific content of such a statement?

  44. martibal says:

    Thanks Anonymat for your comment 🙂 I find quite arrogant the idea that “we may be at the end of what physics can explain”. Why on Earth should the fact that the so-called “best minds” of the last (or two last) generations did not reach a breakthrough mean that we are reaching a limit of what could be explained ? It sounds as meaningless as “the end of history” of Fukuyama (after the end of communism, the world will leave in a the war-free happiness of free market).

    Also, regarding the repetitive argument that multiverse deserves all the hype it gets because there is northing more convincing on the market, it is a bit tiring to repeat that there are others approaches which try to understand – with quite success – the structure of the standard model (e.g. noncommutative geometry). Not that these other approaches should be much more hyped, but at least they could make the the multiversemaniacs understand that it would be very, very, nice for everybody if they calm down a little bit.

  45. Peter Woit says:

    Petite Kabylie,
    If there were a convincing fundamental theory that made confirmed testable predictions, and also predicted a multiverse with different parameters for particle masses etc, making them environmentally determined, I would be a believer in this multiverse (in the sense of assigning it a high probability and acting accordingly).

  46. reader says:

    Chris,

    50/50 is really meant as shorthand for the middle third of three options: very unlikely, somewhat likely, very likely. I don’t think that “brooding over Lagrangians” is “purely sociological”, as the space of Lagrangians is our best way of thinking about the space of physical laws. And once you start thinking about this you realize how incredibly easy it is to get a multiverse picture: you basically just need a large number of fields and this is generically what you will find. The Standard Model seems to me to be intermediate between being very simple and very complicated. It’s clearly a bit of a mess, but not nearly as messy as it could be. Extrapolating this lesson to higher energies where eternal inflation would take place, it seems to me fairly plausible that the Lagrangian at this scale is of the needed complexity to support a landscape and eternal inflation.

    Anti-multiversalists hold on to the hope that the Standard Model is actually much simpler because there is some deep structure there that we haven’t yet uncovered. Could be, but decades of effort devoted to finding this deep structure have so far yielded zilch.

  47. BR says:

    Reading some of the posts one could arrive at the conclusion that the multiverse is a dominant theme in hep-th, which is far from true in my opinion.
    My impression is that outside the community it is discussed much more than inside. Perhaps that a few but influential scientists push for the idea,
    either because for some reason they got convinced or because they simply started running out of steam and have a hard time to swallow the fact
    may have some truth in it, however whatever they have to say I think has most of its impact on the general public and I suspect in fact that they are fine with that.
    Historians of physics could perhaps look for some other situation in the past where a concrete subgroup of legitimate physicists declared the problems that
    could not solve as (essentially) unsolvable or pointless. I would bet that this is not the first time, but I do not know.
    And if those problems where eventually understood and solved or they indeed turned out to be unsolvable.
    Also, more generally, I have the feeling that this is not the first period in time where the boundary region between fundamental science and philosophy is
    a bit more fuzzy than usual.
    On the other hand I would not be so sure that string theory and the multiverse are in one to one correspondence, at least not until
    we understand its dynamics more deeply, including supersymmetry breaking and (related) non-perturbative effects.
    Now wether the scientific relevance of string theory has been connected by its development too tightly to sociological and personal arrogance issues I think
    is an unpleasant but fair discussion because these things are then connected to positions, grants, future research directions, education etc.
    But the system can and does eventually regulate itself, one needs some patience and accept the fact that the time scale of such processes may be larger than O(30) years…

  48. vmarko says:

    EThomas,

    “Is it reasonable to expect all of reality to be accessible via empirical scientific methods? Is it even reasonable to expect all of reality to be conducive to mathematical modeling?”

    I just noticed that nobody addressed these two questions of yours. 🙂 Regarding the first question, the answer is — it depends. Regarding the second, the answer is — no.

    The idea that all of reality can be understood by empirical scientific methods is a metaphysical position one may or may not endorse. People who believe in reductionism of everything that exists to (ultimately) elementary particles (“more is not different”) tend to endorse that idea, and believe that everything can be reduced to (ultimately) fundamental physics. On the other hand, people who do not believe in reductionism (“more is different”) are usually more open-minded to the possibility of non-scientific access to knowledge about reality, complementing the scientific one. So the answer to your first question depends on who you are talking to, and their prejudices and opinions about reality.

    Regarding the second question — already in physics there are systems which resist being properly mathematically modeled. Examples include high-Tc superconductivity, mass gap in Yang-Mills theories, etc. Beyond physics (your question was about the whole reality), I think that systems which are complicated enough (things studied by biology, psychology, sociology, ecology, meteorology, etc.) will always be out-of-reach of mathematical models, despite our best efforts. This is basically a property of all strongly interacting physical systems, which cannot be studied by cutting the system into pieces and analyzing it piece by piece. The latter, so-called “analytic” technique is effective only if the interaction between the pieces is reasonably low and reasonably local, which is not the case for a huge class of systems (say, a human brain). The highly-interacting systems need to be studied using “synthetic” (also called “holistic”) techniques, which study the system as an undivided whole — and most such systems are utterly awfully hard to describe mathematically. So no, it is not reasonable to expect that all of reality can be described using mathematical models.

    Best, 🙂
    Marko

  49. Peter Shor says:

    Chris: you say

    decades of effort devoted to finding this deep structure have so far yielded zilch.

    These decades of effort were nearly all devoted to finding this deep structure using string theory. How do you know that the reason for the failure isn’t due to string theory rather than a multiverse?

  50. Peter Shor says:

    Oops: that last comment should have been directed to “reader” rather than “Chris”.

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