The Multiverse, Evidence and Theology

Yes, this multiverse business is tedious, but since it is becoming mainstream physics, with colloquium talks here at Columbia devoted to it, and the Columbia University Press publishing books about it, seems to me that someone at Columbia should be commenting on these, and I don’t see anyone else doing it. Will try to make this short.

Yesterday Matthew Kleban’s talk here was entitled Testing the Multiverse. The only part that actually really was about testing the multiverse was the part describing work on bubble collisions with other universes. This has been heavily advertised in the press, see here, here, here, here, here and many others. Kleban described some of these ideas, but when it came to the experimental testing part, he just briefly acknowledged that all searches for these things have come up empty. The only prospect for the future mentioned was the polarization data to be released later this year by Planck, which would give some new things to look at, but he seemed unenthusiastic that this would realistically lead anywhere. So, as far as the “testing” goes, it has been done and the tests failed.
The rest of the talk was about various inflationary models, including Kleban’s work on “unwinding inflation” (see here, here and here). Some of these models do have testable consequences, and many do lead to “eternal inflation”, so in such models you expect to continually produce new inflated universes, although with exactly the same physics. This is being sold as “testing the multiverse”, and string theory is brought in to justify lots of possible different physics in different universes, but this is not a testable part of these scenarios. What’s being advertised is a grandiose picture of the string landscape, laws of physics determined environmentally, etc., etc., but if you actually look at the product that you’re actually buying as “testable”, you don’t get any of the cool stuff. For slides of a somewhat similar recent talk by Kleban, see here.

A while back I acquired a copy of the new book Worlds Without End: the many lives of the Multiverse, started reading it and was planning on writing a detailed review. I soon got bogged down in the first half of the book, which is a detailed intellectual history of speculation about multiple universes (so lots about relevant parts of Plato, Aristotle, Lucretius, the Stoics, Augustine, Nicholas of Cusa, Giordano Bruno, Kant and others). Finally I realized I just didn’t have the energy to serious read this material. People with other interests and/or more time on their hands may find this quite worthwhile.
The second half of the book is devoted to the question of current speculation about physics, so more up my alley, but again I found it hard to focus on this. I fear it is only mildly interesting to see what a theologian/philosopher of religion makes of the current multiverse mania, not enough so though to do more than skim the text. From this skimming, what’s in the book is a lot of retelling (sometimes introducing misunderstandings) of the hype-laden tales of the multiverse told in dozens of books and magazine articles over the past decade or so.

Rubenstein ends the section about what physicists have to say with Tegmark, seen as having reached the final endpoint of the “Ultimate Multiverse”:

So some worlds will be linear, and some will be cyclical; some will be singular, and some will be plural; some will be infinite, and some will be finite; some will branch forward, and some will branch back. Some worlds will be manufactured, and some will be simulated; some designers will be kind and some will be cruel, some capable and some all but incompetent.
And, presumably, some of the set of all possible world will have a creator-god who breathes over primordial waters, who separates the sea from dry land.
How on earth did we get back here?

I take Tegmark’s vision as empty, so a good thing to ignore, but Rubenstein sees this as an opening for theologians to get back into the mainstream cosmology business, and the rest of the book focuses on this. With the boundaries between science and religion now gone, all sorts of possibilities open up for theologians. The final part of the book begins by invoking (just like Henrich Päs, who comes at it from the mind-altering drug rather than theological angle) Nietzsche:

Nietzsche concludes the Genealogy by expanding this vision, promising “all great things bring about their own destruction through an act of self-overcoming” (3.27, emphasis added). This promise then, has me wondering. If science can be regarded as the self-overcoming of a particular form of religion, might multiverse cosmologies be something like the self-overcoming of science? Might they mark the end of the fantasy that “science” has wrested itself free from “religion”, “objectivity” free from subjectivity, and matter free from meaning? After all, we have seen each of these multiverse cosmologies open onto metaphysics and mythology not in moments of lapse or weakness, but precisely where they are scientifically most compelling.

It seems that, unlike most authors, Rubenstein actually has got the story of multiverse mania right: it’s left conventional notions of science behind and entered into the realm of theology. We do, however, disagree about whether or not this is a good thing…

Update: Bogus claims about Multiverse “predictions” are now all the rage. For the latest, see the Caltech Quantum Frontiers blog, which has Yasunri Nomura writing about Making Predictions in the Multiverse. There of course are no predictions there, just mainly a discussion of the idea that many-worlds and the eternal inflation multiverse are somehow the same, an idea I continue to find unfathomable. Nomura doesn’t mention that he actually did have a prediction from the Multiverse (and someone made a movie about it…). The prediction was for a Higgs mass of 140 GeV, but of course when you’re in the multiverse business, wrong predictions are not a problem, they’re always true somewhere.

Update: For more on the multiverse front, Edward Frenkel has a review of the Tegmark book in this Sunday’s New York Times. He does a great job of explaining the problems with the way Tegmark is trying to use mathematics. John Preskill tweets in agreement (positive and negative).

Update: Nomura, when asked about experimental evidence for the multiverse, responded that the experimental situation is

not much different from some other situations—e.g. in the big-bang theory, inflationary cosmology, and Darwinism in biology

So, the scientific evidence for the multiverse is “not much different” than the evidence for evolution? And Tegmark thinks I’m the one in league with creationists…

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62 Responses to The Multiverse, Evidence and Theology

  1. Manyoso says:

    I take Tegmark’s vision as empty, so a good thing to ignore, but Rubenstein see this as an opening for theologians to get back into the mainstream cosmology business, and the rest of the book focuses on this.

    Massimo Pigluicci’s blog has a new podcast with Tegmark discussing his ideas. A lot of the answers are not very responsive as you might expect.

    One interesting thing is that Tegmark is now requesting to divorce his critique of the use of infinity in physics with his multiverse of mathematical universes hypothesis. He thinks the two should be treated as unrelated.

    It is very hard to understand his critique of infinity in mathematical physics now. He seems to be saying that because we can’t find any physical process or thing that is infinite that we shouldn’t use infinities in our math describing physics. I’m still trying to figure out what he means by this. Are we allowed to use pi for instance…

  2. Chris W. says:

    I soon got bogged down in the first half of the book, which is a detailed intellectual history of speculation about multiple universes (so lots about relevant parts of Plato, Aristotle, Lucretius, the Stoics, Augustine, Nicholas of Cusa, Giordano Bruno, Kant and others).

    It’s amusing that the supposed thoughts of such thinkers on the “multiverse” would be considered relevant, when the extent most of what we know as the observable universe was completely unknown to them. I can see why you got bogged down.

    Even the notion that we are part of one galaxy among many was only beginning to be understood (mostly as speculation with hints from observational astronomy) in the 18th century, and was a subject of active research and disagreement in the 1920s.

  3. CPV says:

    Throughout history humans have bundled up things they couldn’t explain or understand and called that bundle ‘religion’. While that bundle has gotten smaller, it still contains a fairly large payload of questions. Scientists should feel unashamed of admitting that there are questions that they can’t answer, or maybe even properly formulate, at least for the time being. At some point the answers to these questions may become part of the scientific domain, but until then they can remain labeled as part of religion or pure speculation. The multiverse stuff is almost entirely like that. What will falsify the mulitverse? Nothing. What should people be working on? Better explanations for the specific form and character of physical law. That’s the job.

  4. thecrud says:

    Well we dont have all the answers. I know back to invisible sky beings that grant wishes.

  5. Peter Woit:

    I’m very sorry to hear you’re not going to give more attention to Rubenstein’s book. I think that going further into this would be well worth while for everybody concerned. I am, I confess, a bit afraid of what is happening here. I have fears both for the integrity of science, and for the integrity of religion.

    Rubenstein is plenty smart and pretty engaging, and if she goes astray, she may take some people with her. I think you are prescient in your concern for the empirical integrity of science.

    Manyoso:

    It is possible to consider that the value of pi is NOT infinite because it IS recursively enumerable. You can make as many correct digits as you like using finite means. I think some scientists are thinking this means that pi doesn’t “actually” have an infinite number of digits, because there are simple rules for getting as many as you need, without limit.

    However, there is another arena well known to physicists where an “actual infinity” is much harder to exorcise, and that is the randomness that seems to be built in at a basic level in quantum mechanics. It is now known, thanks to recent results, that it is possible to certify that a sequence of bits produced by quantum processes are truly, irreducibly random. It is also known that it is not possible to compute an irreducibly random sequence of indefinite length using a program of finite size. So as far as I can see, this means that the universe is not any sort of computer, because if it were it would not be possible to physically certify that a random sequence is random.

    The only way that I can even begin to imagine a way out of this quandary is to suppose that the randomness of quantum events is produced by a completely deterministic process that also completely determines how and when we will measure it, so that it is statistically random to us though it is completely pre-determined. This would provide a loophole in the strong free will theorem by removing the freedom that is assumed to exist for experimenters to set up experiments any old way. There are, after all, two senses of “random” at work here, random as uncaused and random as statistically random.

    CPV:

    Religion has in the past provided mythological explanations for things that now are explained scientifically, but without such explanations, there is still religion.

    Let’s say you love your wife, and she is working on a novel. She asks you to promise that if she dies before she finishes the book, you will not publish it. And because you love her, you do promise that. And then, unfortunately, she dies before the book can be finished.

    Your wife is dead and gone, but your obligation not to publish her book lives on. Physically she is dead, scientifically she is dead, but existentially she is alive, because your promise was not to any publishers and not to yourself, but to her.

    Spiritually, she is eternal.

    There’s a lot more to say about this, but this is not the place. I’m just trying to point out that there are ways of demarcating human discourse between science and religion that do not reduce the one to the other, or the other to the one.

  6. David says:

    Absolutely. Theology and multiverse cosmologies are remarkably simpatico. It does require setting aside some things – “fine tuning” arguments and “first cause” arguments being among them. But the potential for interplay between classical theology and this speculative cosmology is nontrivial.

  7. Manyoso says:

    It is possible to consider that the value of pi is NOT infinite because it IS recursively enumerable.

    Huh? Just because pi is computable doesn’t mean it is not irrational. There are an infinite number of digits to pi and this has been proven for centuries. I still don’t know if this means Tegmark wishes us to develop a mathematics without the reals for calculating physical processes or what…

  8. Koray says:

    Manyoso: there are non-standard analyses in mathematics, e.g. computable analysis. If certain concepts like infinity or transcendental reals don’t make sense (or are not required) in physics, it may make sense to restrict the math used in physics to exclude them.

  9. Peter Woit says:

    Enough about infinity, please. Besides not being very interesting, that argument of Tegmark’s doesn’t appear in the book, or in Kleban’s talk for that matter.

  10. vmarko says:

    “It seems that, unlike most authors, Rubenstein actually has got the story of multiverse mania right: it’s left conventional notions of science behind and entered into the realm of theology.”

    Belief in untestable conjectures is a natural realm of religion. IMO, it was just a matter of time before people picked up on the multiverse (level II) as a piece of that realm.

    In the next period, various folks will spend some time playing with the “multiverse religion”. Once they get to know enough of it, they’ll figure out that multiverse is a very lousy example of a religion, providing almost no answers that any respectable religion does. Once that happens, they’ll throw multiverse out the window, and return to more serious religions, and serious science.

    I am only eagerly waiting to see how multiverse-loving atheists are going to handle this… ;-)

    Best, :-)
    Marko

  11. Peter Woit says:

    Marko,
    The thought did occur to me that I didn’t really want to review this book, but I did want to read a review by Sean Carroll of the book…

    Also, perhaps theologians could try marketing religion as the “Level V” multiverse.

  12. I’m not sure which audiences Rubenstein is addressing. But you are right it is following the multiverse mania. There is much attention to the work of Mersini-Houghton. I’m not sure what is purpose of this book. A review of multivariate literature?

  13. Peter Woit says:

    Jerry Lisantti,
    It’s an academic monograph, aimed mostly at an academic audience interested in the universe/multiverse debate throughout intellectual history, but also aimed at an audience with interests in philosophy of religion. It’s definitely not a mass-market book, like the typical multiverse-promoting book of recent years.

    Anm,
    Thanks, but I know next to nothing about that kind of math, so comments should go to Tao’s blog. I did notice this, but also noted that he says “There is a real (but remote) possibility that this sort of construction can be adapted to the true Navier-Stokes equations.” and ” The paper reflects my current thinking on the subject, which is that (a) proving global regularity for Navier-Stokes is a hopeless task for the foreseeable future, but (b) proving blowup for Navier-Stokes is not… But there is still quite a long way to go to actually reach a proof of blowup for Navier-Stokes.”

  14. paddy says:

    Sometimes I wonder why I come here to read these comments once or more a day. As PW says some of them are tedious. Especially since I must expend some considerable effort in resisting the temptation for snarky posts (e.g., “Bless me father of Tegmark V for I have sinned…oh not you father of Tegmark X”). On the other hand one does finds jewels like Anm’s Navier-Stokes/Tao reference. Thank You

  15. Patrice Ayme says:

    “Nietzsche concludes… promising “all great things bring about their own destruction through an act of self-overcoming” … This promise then, has me wondering. If science can be regarded as the self-overcoming of a particular form of religion, might multiverse cosmologies be something like the self-overcoming of science? Might they mark the end of the fantasy that “science” has wrested itself free from “religion”, “objectivity” free from subjectivity, and matter free from meaning?”

    Science was never the self-overcoming of a religion. It was the triumph of common sense. Buridan made that very clear, when he discovered the Principle of Inertia and used it to propose the heliocentric system around 1320. (For 140 years after that, the Church approved of Buridan, his “impetus”, and heliocentric system. His works were put on the “Index” later!)

    Nietzsche’s proposal is more akin to Gödel First Incompleteness Theorem (at some point a choice appears, on esthetic grounds)

    What may simply be going on with the Will To Multiverse is much simpler. What was the first multiverse theory? Everett’s Many World Interpretation of Quantum Mechanics.

    So, on the face of it, the Multiverse arose first as a self-overcoming of Quantum Mechanics. Not a self-overcoming of science, just an “overcoming” of the “collapse”, “measurement”, “observer” and “EPR/Elements of Reality” problem in QM. Behind the whole thing may be an anxiety about Quantum Mechanics, and, or “Cosmic Inflation”.
    Unfortunately, the proffered solution, the Multiverse, has indeed jumped far out of science.

  16. Lisantti:

    Rubenstein’s audience would be, for the most part, her colleagues in academic theology and the philosophy and history of religion, but also the educated public.

    The purpose of the book, as nearly as I can make it out (I haven’t read it [yet?]), is to take the “multiverse” as a contemporary myth of creation, a contemporary cosmogony, that can be related to ancient myths of chaos that predate the patriarchal, “create everything out of nothing” God of Christian (until the late 20th century anyway) theology.

  17. Georg Mayer says:

    Hi Peter,

    thank you for your patience in pointing out “what comes from” certain kinds of theories, even if (some of) their creators did not intend to open the door to the dark alleys of theology, which I thought our species has roamed long enough in the past. Reading your blog (and other materials) during the last weeks, have changed my mind mainly about the intend of the multiversers and I still puzzled that this was necessary.

    I was not aware how quick people are capable to jump from “new theoretical physics theory” to “mathematical platonism” to “every religious believe is just a wonderful reality in our happy infinite possibilities muliverse duckburg”. But I find it even more frustrating that scientists who come up with these initial theories (which is in general a great thing) do not clearly and strictly speak up against e.g. the movie “The Principle” (thanks for linking to the trailer) or the Rubinstein book you just reviewed. This gives the whole approach of many of these theories a very bad taste – it leaves me with an impression as if people are looking for such esoteric cross-references, maybe to just get more popular (bad) or because they believe it themselves (baaad).

    This not only discredits natural sciences, but also those people who try hard to understand the nature of abstract principles in e.g. mathematics or philosophy. Anything that goes into the direction of metaphysics has to be handled carefully in order to not fall into the abyss of mysticism and people coming up with wild explanations should not fort that sometimes oneself is not aware of the fact that she or he is already in the process of accelerated downfall into fairies country.

    We don’t know why math works so well, most of the people who see it working are startled by this fact. There are tons of philosophical books and articles about this and many of them are a better read than multiversology. Just because we do not understand something doesn’t mean we should push it as the explanation itself. And just saying “as long as math works it proves that math is the thing itself” is at best strange – tomorrow linguists stand up (as they did before) and proclaim that “as long as words can describe everything, everything is language” and immediately afterwards we see the well-known folks coming up and arguing that Pegasus and unicorns are part of reality (as they are part of language).

    Therefore, after looking into the mathematical universe I return to the tools of refutability, Occam’s razor and at most the Quine-Putnam Indispensability argument. We have to respect the limitations of our perception and have to be very serious about them, else we are lost in speculations that do not bring us forward, but cause tragic (esoteric) deviations from the scientific strive for truth and understanding.

    Thanks again – you gave my brain a good shake, now my feet stand on solid ground again.

  18. Peter Woit says:

    Michael Gogins,

    I think you’re making some unjustified assumptions, based on the idea that Rubenstein is a “feminist theologian”. Her book isn’t really concerned with myth, or with feminist theology and the issue of a “patriarchal” deity. It’s very much about the standard Western philosophical tradition, from Plato on, together with the standard physics story about cosmology. As I mentioned, it ends up with Nietzsche as inspiration for “overcoming” science, and he’s not exactly a feminist role model. The book ends by invoking the possibility of a theology
    “that asks more interesting and pressing questions than whether the universe has been “designed” by an anthropomorphic, extracosmic deity” and, to the extent that she has a voiced agenda, that’s it.

    I’d characterize her position as much like that of the Templeton Foundation. They’re very excited to support multiverse research, for much the same reason she likes the topic: it promises to erase conventional boundaries of what is science and what isn’t, bringing science and religion together and giving legitimacy to people who want to mix the two. In both cases, their interest in theology is not at all in fundamentalist religion, so they are just as much interested in invoking science against that as they are in bringing science and their conception of religion together.

  19. Peter Woit says:

    Georg Mayer,
    There are some big differences between these various topics. The world is full of people like the geocentrists promoting their outlandish alternative science ideas, and it’s both wise and conventional to just ignore them (I wrote about the “Principle” here mainly because I thought it was hilarious to see physicists taken in by this, not because anyone is going to take this seriously). As for academic monographs claiming some support for their philosophical positions from speculative science, they’re also normally best ignored (do you have any idea how many people read a typical book of this kind? I’m guessing they’d all fit in one room, and not a very big one…). So, the fact that physicists are ignoring geocentrism and Rubenstein isn’t either surprising or a bad thing.

    Tegmark is quite a different issue. He’s a prominent physicist at a leading institution, a talented expositor, academic fund-raiser and politician, working very hard for his agenda, getting a lot of top-level media attention. In this case I do think it is a big mistake for influential physicists to ignore this, hoping it will just go away, which I think it what most of them are doing.

  20. John Urbanik says:

    Sometimes the simplest explanation is this best. Theology is about the universe being created and with that a purpose for the universe to be created. The Multiverse is the attempted explanation that there was no “creation” or purpose but instead the universe was just one out of all possibilities. It all comes down to design vs. random chance.

    Both should be part of philosophical discussion and neither should be part of any scientific debate.

  21. Martin says:

    This multiverse business will continue as long as it is funded. In addition, theoretical physics has in common with theology that it does not cost that much. Experimental work is much more expensive. And if the public likes to read about this sort of esoteric stuff then politicians think that some tax money should go toward this subject. Panem et cercensis, it is an old practice.

  22. Jim Given says:

    As a devout Catholic and professional physicist, I tell you that string theory is located at the similtaneous limit of no physics and no theology.

  23. Peter Woit says:

    Martin,
    I don’t think people do multiverse stuff because they think that’s what the NSF wants (I suspect that NSF panels are not very enthusiastic about multiverse research proposals). Tegmark in his book explicitly explains how he was careful to only do this as a sideline, not so much that it would hurt his career. This is mostly not being funded by taxpayer money, but often by private money (e.g. Templeton). Don’t blame politicians for everything, they’re mostly leaving physicists alone to make their own funding decisions.

    The appeal of the multiverse physics is that it’s a way to do research work which seems to engage with the deepest problems in physics, but isn’t very demanding. This is appealing for reasons of personal motivation (see Arkani-Hamed’s comments about what it takes to get up in the morning and go to work on a physics problem), also if you like media attention, this will get it for you, unlike more serious work. If you look at most multiverse papers, they’re using minimal mathematics, and nothing very difficult in the way of calculations. Then of course, nothing you do is testable, so there’s no danger of it being wrong. John Baez describes this sort of activity as “playing tennis with the net down”. Some people enjoy this, others don’t…

  24. Kavanna says:

    There are questions that science cannot answer, and it’s best to admit these are not science. For a philosopher or theologian to be interested in them as forms of speculative metaphysics is fine. Just don’t call it science.

  25. Eric Habegger says:

    I think this interest in the multiverse is fascinating as a social phenomenon. What is the attraction to science for an idea, which by most lights, cannot ever be tested and which allows for almost any solution. It is hard to see, yet the attraction is obvious in the ever increasing attention paid to it.

    Maybe it’s time to quit analyzing that attraction if there really is no substance to the main tenets of the idea. Maybe we should look instead for a nexus of ideas that people are uncomfortable with and dislike. Sort of like a black hole nexus of ideas that people sense peripherally that is pulling them in and from which they want to be distracted.

    Throughout the dark ages something similar happened. Religion and belief in a God that attended every fallen sparrow provided comfort to individuals in an often harsh physical environment. People wanted to feel cared for when times were tough. That seems like the primary motivation for a geocentric universe that predominated then. Maybe there is something similar going on today. Of course nobody, especially a physicist, would willingly admit that they are prey to such feelings and that it influences their thinking about science. What better way to refute it than to invent a whole panoply of universes. It’s the little kid in them saying to everybody “See, I’m not afraid of nothing!”

  26. SUSY says:

    do other BSM theories like LQG and AS predict a multiverse?

  27. Peter Woit says:

    SUSY,
    String theory doesn’t “predict” a multiverse, since it doesn’t actually predict anything. You can have string theories with a single universe, or ones with a populated landscape, lots of universes. The function of the multiverse in string theory is not as a prediction, but as an excuse for not making being able to make predictions. Theories like LQG don’t have anything to say about non-gravitational forces, they explicitly are not designed to make predictions about such things, so they don’t need an excuse. If you wanted to make an LQG multiverse, you probably could, but there’s no reason for it.

  28. Max Tegmark says:

    I’m amused that Peter keeps finding novel ways to criticize me on this blog. If some theologian misunderstands the multiverse predictions of inflation etc., this doesn’t constitute a scientifically valid critique of inflation. I very much doubt that all theologians imagine a deity that strictly obeys mathematical equations, and can therefore equivalently be described as a purely physical entity.
    I’ve summarized the top-8 criticisms of my book here: http://mathematicaluniverse.org

  29. Peter Woit says:

    Max,
    The part I quoted is Rubenstein’s reaction to your Level IV multiverse, which Brian Greene calls the “Ultimate Multiverse”. This really has nothing at all to do with inflation.

    As for whether a deity can be consistently described by a mathematical structure, I’d guess that depends on your deity. From my little knowledge of theology I’d suppose theologians have more definite ideas about what they don’t know about a deity than about what exactly its properties are and whether or not they can be expressed as a mathematical structure. Maybe you’ve opened up a whole new area of debate in theology about this kind of question.

    As for your “top 8 criticisms”, the only one that is one of mine is number 6. I don’t think “our cosmos has no non-mathematical properties” is a testable prediction of a conventional scientific sort.

  30. Thomas Larsson says:

    “Also, perhaps theologians could try marketing religion as the “Level V” multiverse.”

    The Level VII multiverse would be better. The seventh heaven.

  31. Georg Mayer says:

    To Kavanna, John Urbanik, others:

    It strikes me that people say “there are questions, which science cannot answer, so leave those to theology/religion/believe”.

    First of all – we don’t know which questions science can answer and which not. So if there is something were we cannot get further today then in my eyes (if we are really interested in the question), we should look for scientific ways to get at least close to an answer.

    500 years ago some might have asked how man exactly got created. Science at that time gave no answer. So some left the question to the local preacher. After we got the answer from Darwin we saw (in the light of evolution) that our question was put a bit self-important in the first place and that the answer was not really what we expected. But now we know. It was wise to not give up and to explore further, without relying on the holy scriptures.

    Furthermore, if we leave open questions to religion, mysticism and unscientific teachings, these “explanations” do not answer anything, but mutually contradict each other (Jesus says the Gluon is blue, but Buddha had a more greenish vision of it, whilst the Tao guarantees you it is black and white). So what good are these answers (if you are interested in *answers*)?

    And even more, this makes it so hard to think seriously about anything that scratches the metaphysical discussion – e.g. like the nature of numbers/sets/mathematical laws. There are a lot of questions in this area, but once somebody asks such a questions you can find a whole lot of deep thought guys jump up and down and sing the “Pegasus exists, because we have a word for it” song.

    Approaching questions is a difficult business and for sure not solved by just giving up on them, i.e. leaving them to non-scientific realms. The hardest thing most likely is to admit that wedon’t know most of the things at the moment. But that should make us eager to to equip ourselves better (scientifically) to approach the lack of knowledge somehow.

    I am also a bit shocked how easily people put theology/religion and philosophy into one pot. “Don’t call it science, leave it to philosophy and theology” – but guys, philosophy IS science and many parts of it strive to find the best ways on how to do (natural) science and how we can expand our knowledge in reliable ways. (Yah, theology is also science, but based on axioms from certain books who a supposedly metaphysical being offered as the ultimate truth in the language of the neolithic age). Bacon, Leibniz, Kant, Russel, Popper are just a few who made the scientific method how we use it today possible.

  32. Jesper says:

    When Georg Mayer writes “We have to respect the limitations of our perception and have to be very serious about them…” then I think he’s completely right.

    To me, physics is about making sensible statements, and about recognizing insensible ones. For instance: the question “where is the electron, when we don’t measure it” doesn’t make much sense and is best left out. To me, physics is not so much about “what is” but about “what can be said (described)” – and therefore I find this whole debate about philosophy and multiverse stuff quite a bit in the wrong direction. Sure – it can be very useful to digress into pseudo-philosophical thinking, perhaps in order to find some useful metaphors and mental images – but I think one must be very careful not to take it too serious.

    Without knowing the subject very well at all, I also think this is the “tone” of modern philosophy: more about limitations of perception and language, and less about “what is”.

    Put differently, I simply don’t know what Tegmarks statement (I didn’t read the book) “all mathematical structures exist” means and I suspect it means nothing.

  33. vmarko says:

    Georg Mayer,

    “It strikes me that people say “there are questions, which science cannot answer, so leave those to theology/religion/believe”.”

    There are questions about facts, and there are questions about choices. The former are answerable by science, the latter are answerable by religion. And the two don’t mix.

    Unless you think that humans are automatons without any form of freedom of choice (a stance which can be called “cognitively unstable” as Sean Carroll likes to say), there are always these two types of questions. Sometimes (like in the case of the multiverse) it isn’t very clear into which of these two categories a given question belongs, but eventually such things get cleared up.

    But no serious scientist claims that science can answer *all* questions. Just like no serious theologian claims that religion can answer *all* questions. At best, they can both answer all questions from their respective domains, nothing more.

    HTH, :-)
    Marko

  34. Bernhard says:

    Nomura did get a direct question about predictions from Jerry Lisantti (http://quantumfrontiers.com/2014/02/13/making-predictions-in-the-multiverse/comment-page-1/#comment-7636).

    Would be interesting if he would answer to it at length (although Lisantti should have said “present or future data”).

  35. Peter Woit says:

    All,
    Please, enough general discussion of science and religion, this has little to do with the topic of the posting, and I doubt anyone has anything new to say about this in general.

    Bernhard,
    Yes, it would be interesting to try and get a response to the predictions question. From all I can tell, at this point Nomura has a prediction that failed, and a story about why predictions aren’t really possible (the measure problem). Given this, why pursue the subject?

  36. George Ellis says:

    Yasunri Nomura states “In cosmology our space is surrounded by a cosmological horizon”, and then develops ideas related to the horizons that occur in black holes. However the horizon that limits what we can see in cosmology is an *event horizon*, not a particle horizon (see Rindler’s classic paper: http://adsabs.harvard.edu/full/1956MNRAS.116..662R). His further discussion then uses results that refer to black hole event horizons: but they do not apply to the particle horizons that occur in cosmology (in the actual paper, he refers to “apparent horizons”, which again occur in black holes but are not the same as the visual horizon that occurs in cosmology, see http://scitation.aip.org/content/aapt/journal/ajp/61/10/10.1119/1.17400).
    So not only does he have no testable predictions but his theory is based on a case of mistaken identity. The properties of event horizon and particle horizons are not the same, and are both distinct from the properties of apparent horizons, which are locally defined (event horizons are globally defined).

  37. Will Nelson says:

    I like your blog although I also like strings and susy quite a bit, and the multiverse too, which I feel is just a logical development of the copernican insight. It certainly could exist, logically and mathematically, so whatever consequences that has for the nature of science are kind of tough luck. The universe wasn’t made to match the preconceptions of some philosopher of science.

    But anyway, not to be tedious. I wish you would highlight more of whatever interesting things you think researchers *ought* to be doing, instead of bashing what various people are doing. That seems kind of tired and a better way to “win” the battle would be to help people see different and better directions to go in. For example the fact that the LHC hasn’t found susy isn’t great, but it hasn’t found anything else either aside from the Higgs, so who’s doing something interesting based on that? I don’t know, maybe you do…

  38. Shantanu says:

    Peter, did anyone in the question ask the obvious question about prediction?

  39. Peter Woit says:

    Shantanu,
    Kleban did in the talk explicitly make clear what actual predictions there are. For bubble collisions, certain signals are predicted, they’ve been looked for, they’re not there. For the various inflationary models, there are some very general predictions, e.g. about the spatial curvature, that he did mention.

    To me, the problem was the high level of hype, that the discussion of models for the inflaton potential, instead of seriously examining exactly what current data implies, and what prospects for future data are (this was basically not discussed) was all about eternal inflation and the multiverse. While the models and data have nothing to say about bubble universes with different physics and string theory, that was a lot of what was being sold.

    At all of the many hype-filled physics talks I’ve been to, I’ve never seen anyone in the audience object to this or point out the problem, and that didn’t happen here. To all appearances, the audience ate up the hype, considers this normal physics these days.

  40. CPV says:

    I think a topic that is relevant here is the “cult of personality”. It seems that many of the physicists involved in the Multiverse type of ideas are people who clearly enjoy hearing themselves talk, and also enjoy media attention (at least, much more than most people enjoy it!). Since the conventional approach to progress has proven difficult, here’s a new road with very little effort required that produces great amounts of publicity. Some of these people are complete charlatans, but some are not. The unifying similarity seems to be the idea that it’s much more important to get attention of any type than to have integrity. It’s really all about them at the end. They will not be ignored.

  41. Jess Riedel says:

    Hi Peter,

    Like you, I’m baffled by this claimed equivalence between many worlds and inflating patches, and I’m likewise skeptical that any of this will lead to testable predictions. But I do want to point out that it’s unfair to say that Nomura is falsely claiming to derive an observable prediction from a multiverse theory in this blog post. (Your words: “bogus claim”.) Rather, he’s trying to solve the measure problem, which means finding a method for extracting predictions–even mundane ones that will agree with non-multiverse theories–from a theory of eternal inflation. Like you I think he’ll fail (and moreover that repeated failures of this type are evidence that this school of thought is diseased), but the effort to extract predictions and to describe his reasoning is defensible in principle so long as he does not prematurely claim success.

  42. Peter Woit says:

    Jess,
    What struck me as bogus about Nomura’s piece was his using the title “Making predictions”, when the piece was really mostly about this “Multiverse= quantum many worlds” business, which as far as I can tell has nothing at all to say about how to make a prediction. Nomura says “the picture presented here does not solve all the problems in eternally inflating cosmology”, but I can’t see how it solves any problems at all.

    Yes, he does explain the obvious measure problem, so in that sense addresses “Making predictions”, but purely negatively. Entitling the piece this way when the only relevant content is about why you can’t make any predictions is maybe best described as misleading, if not a “bogus claim”. I could for instance write a blog entry and title it “Calculating the electron mass”, then use it to tell you that my idea was just that the electron mass could be anything at all, so, not surprisingly I have a “measure problem” and can’t calculate anything. That’s about what he is doing here.

  43. Peter Woit says:

    I’ve deleted an exchange with “Caltech graduate student”, who I’m pretty sure is not one, but someone else with a particular agenda.

  44. Chris W. says:

    I like your blog although I also like strings and susy quite a bit, and the multiverse too, which I feel is just a logical development of the copernican insight. It certainly could exist, logically and mathematically, so whatever consequences that has for the nature of science are kind of tough luck. The universe wasn’t made to match the preconceptions of some philosopher of science. [from Will Nelson]

    That the multiverse could exist, logically and mathematically, is not a reason to assert that it does exist, and especially to do so without regard for “whatever consequences [it] has for the nature of science”.

    Theories are not epistemologically neutral. Theorizing of any kind runs a risk of undercutting the basis for any critical examination of the theory that is being proposed. The worst of such theories are nonsensical “word salad”, but they can be much more insidious than that.

    The Copernican insight led to a whole line of investigation with rich empirical ramifications. The multiverse ideas now being discussed have no empirical ramifications, essentially by construction, and that very fact is being used to argue that they could be true. This mendacious game could have been played at any time in the history of science. If it had been, and its legitimacy had been widely accepted, then the “science” at issue would have devolved into a shallow, self-justifying fraud.

    I suppose the main protection against that happening now is that the results will in the end be mind-numbingly boring and vacuous, and later generations will lose interest in them. We’re already pretty far down that road.

  45. Neil says:

    Does any multiversarian, if that is what they are called, actually assert that the multiverse exists? I thought their position is that it *could* exist and that this perspective, if that is what it is, allows us to interpret some puzzling observations, such as fine tuning, in a useful way. It can be argued, as it is in this forum, that unless we are given more reason than logical possibility for the multiverse to exist, it really provides no interpretation. The multiversarians think that the landscape or eternal inflation provides such a reason, but of course there is no evidence for either. They too are simply logical possibilities.

  46. vmarko says:

    Neil,

    “I thought their position is that it *could* exist and that this perspective, if that is what it is, allows us to interpret some puzzling observations, such as fine tuning, in a useful way.”

    There is nothing useful about the multiverse “explanation” of fine tuning. It’s actually completely useless in every possible sense, since it basically says that all fine-tuned parameters are such as a result of a pure accident. Saying that the SM parameters have been chosen randomly is an absence of explanation.

    HTH, :-)
    Marko

  47. Peter Woit says:

    Please all, if it’s not about the topics of the posting (the Kleban talk and the Rubenstein book) it’s off-topic.

  48. Simple biologist says:

    “not much different from some other situations—e.g. in the big-bang theory, inflationary cosmology, and Darwinism in biology”

    The last bit could actually be the first evidence for multiverse. Nomura clearly lives in a different universe than I do.

    In my universe, I work with evidence of evolution on (almost) daily basis.

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