String Theory Skeptics and Multiverse Mania

My endless rants here about the hot field of multiverse studies are mainly motivated by concern about the effect this is having on particle theory. Multiverse scenarios all too often function as an excuse for not admitting that string theory/extra-dimensional ideas about unification have failed. Such an admission would encourage people to move on to more promising ideas, but instead hep-th is stuck in an endless doldrums with the high profile public face of the subject dominated by excited claims about what a wonderful discovery this region is.

Independently of the string theory problem, I’m personally a skeptic that multiverse studies have any promise, simply due to the fact that the subject lacks a viable theory, any experimental evidence, and any plausible prospects for getting either. Others feel differently though, and very recently two of my fellow string theory skeptics have written about the subject much more positively.

The first is Lee Smolin, who has written an essay for the Foundations of Physics “Forty Years of String Theory” volume with the title A perspective on the landscape problem. Smolin’s interest in multiverse models goes way back, to long before the current string-theory-based mania. He’s got a good argument that he was the originator of the term “landscape” itself, which he wrote about back in his 1997 book The Life of the Cosmos. If you’re interested in the multiverse at all, Smolin’s article is well-worth reading. I very much agree with his emphasis on the principle that one has to be careful to stick to ideas that can legitimately count as science, by conventional standards of testability. He is pursuing “cosmological natural selection” scenarios which he argues do have testable consequences. I’m not convinced there’s enough there to ever lead to solid evidence for such a scenario, although there may be enough structure there to sooner or later make it clear if the idea is simply falsified by one fact or other about the universe.

Today’s New York Times has an article by Dennis Overbye about Lawrence Krauss and his new book A Universe From Nothing. Much of the book is an excellent discussion of cosmology and the physics of the vacuum, but it also devotes a lot of effort to discussing the meaningless question of “Why is there something rather than nothing?” and arguing against the invocation of a deity in order to answer it. Krauss is no fan of string theory, which he regards as overhyped, but he seems to have developed an attraction to multiverse studies recently, perhaps motivated by their use in arguments with those who see the Big Bang as a place for God to hang out.

Personally I’ve no interest in arguments about the existence of God, which epitomize to me an empty waste of time. Given the real dangers of religious fundamentalism in the US though, I’m glad that others like Krauss make the effort to answer some of these arguments. I’m less happy to see him and others adopting the multiverse as their weapon of choice in this battle, since it’s a lousy one and not going to convince anyone. In the New York Times piece we’re told:

“Maybe in the true eternal multiverse there are truly no laws,” Dr. Krauss said in an e-mail. “Maybe indeed randomness is all there is and everything that can happen happens somewhere.”

Given the choice between this vision of fundamental science and “God did it” as explanations for the nature of the universe, one can’t be surprised if people go for the man in the white robes…

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41 Responses to String Theory Skeptics and Multiverse Mania

  1. Low Math, Meekly Interacting says:

    This one also troubles me. There appears to be an urge among skeptics to fill the gap of universal origins, where the theists God resides, with something else, rather than admitting it must remain empty. I seems somehow unacceptable to have no answer but an admission of ignorance when confronted with claims that the ultimate hows and whys of existence are the purview of religion and not science. For me it’s perfectly acceptable to reject mythology whilst having no clue myself what the “truth” of the matter is. When engaging in such debates, it’s clearly better to be ignorant than wrong, because the theist’s argument cannot be disproven, while the scientist’s can. The theist holds the scientist to such rigorous standards, while needing none for himself. All the worse when the scientist proposes ideas that are not even wrong. If God is untestable and the multiverse is untestable, then claiming superiority as part of the scientific enterprise and using abstruse equations to make the case for untestable hypotheses cannot exonerate one from accusations of hypocrisy.

  2. Nige says:

    “There appears to be an urge among skeptics to fill the gap of universal origins, where the theists God resides, with something else, rather than admitting it must remain empty.”

    Premature uncheckable speculations which harden into an orthodoxy have founded some of the world’s greatest religions. The replacement of a single God with a multiverse of them goes against Occam’s Razor, and it isn’t new either.

  3. JE says:

    Interesting post, right to the meat of the matter… in this pseudo-obscurantist era? All in all the multiverse and the man in the white robes provide similar circular answers to the same old question. Ironically, most scientists wear white aprons, as opposed to black soutanes, and some seem to be taking the analogy too far. Either the LHC sheds light on the landscape of particle physics, with the God particle explaining EWSB and reinforcing the SM as the framework into which to try to accomodate deviations (or from which to build a larger framework that can accomodate escapologist deviations and unsolved issues), with SUSY being largely ruled out and black robes and circular thinkers being gradually ousted from the scientific arena, or this neverending multiverstring idea may end up synergizing with God to last another 2,000 years. Unless, please, someone comes out with a better idea.

  4. emile says:

    I like the multiverse idea. It may well be true. A priori, I don’t see why there should be only one universe. In general, I would be careful about just bashing this idea: it’s not as if it does not make any sense at all. Granted, it is clear that, at this point, this type of speculation is not science and may never will be. And of course, scientists should be careful if/when they discuss this idea. They should make it very clear that this is not science until we know how to test it. The public is already on to scientists who make claims without evidence: they turn around and say they can also make similar claims about the supernatural world.

  5. Peter Lynds says:

    Hi Peter,

    Good post. One thing puzzled me though. Why do you think the question “why is there something rather than nothing” is meaningless?

    Also, I think I should note that, unless one believes that a universe can be magic’ed from truly nothing a finite time in the past (whether by a non-physically existing, timeless, eternal God, or by non-physically existing, timeless, eternal laws of physics, with both being to said to somehow magically bridge to the physical to create a universe out of nothing), eternal physical existence is the only other option, whether it be in the form of an eternal multiverse, eternal cyclic universe, or a finite universe in which time is cyclic. That is, and although it is very difficult to see how any of these models could realistically be confirmed empirically, they are still on a much firmer footing than any theory that posits physical existence had a beginning a finite time in the past. Also, multiverse obviously need not mean string theory.

    Best wishes


  6. Anonyrat says:

    Why “Why is there something rather than nothing” is meaningless:- how do you formulate it as a scientific question which can have an experimental or observational test?

  7. David Metzler says:

    @Peter Lynds: I think you may be confused about what a universe with a finite past means. It doesn’t mean that there was nothing, then there was suddenly something, in some dynamical process—that would involve a notion of time that went back before the big bang. I think the error is the common one of assuming that any space or spacetime must be embedded in something larger (and usually more familiar)—what mathematicians call the extrinsic point of view. But from the intrinsic point of view, a universe “starting with a big bang” is completely self-consistent, and need refer to no notion of “how it got started”.

    (To use a pure-mathematical example, a finite open interval is just as natural a Riemannian manifold as the real line is, and neither needs to be embedded in something larger to be made sense of.)

    Pardon me if that misrepresents what you were saying, but I know that it is a major point of confusion with the lay public.

    Now, the likely quantum-gravitational nature of the initial few Planck times is still a huge source of uncertainty, so quite possibly the pure classical relativistic notion of a singularity is not realistic. But I feel that that is a different issue from the resistance many people have to the very notion of a finite (in time) universe.

  8. Peter Woit says:


    Please avoid the temptation to turn this into an opportunity to discuss your favorite ideas about the big bang and pre-big bang physics. I’m in a bad enough mood already. If it’s not about what Krauss or Smolin have to say, it’s probably off topic…

  9. Peter Lynds says:

    Hi Anonyrat,

    Yes, I agree that it cannot be formulated as a scientific question that can be experimentally or observationally tested, but as long as nothing rather than something is a possibility, it is still a meaningful question and in need of an answer. If one perhaps disagrees with this, one would need to show why nothing isn’t a valid possibility (and in doing so, they would also actually provide an answer to the question). I’ve got my own ideas on this, but I’ll keep them to myself here.

    Hi David,

    Yes, of course, but almost every modern cosmologist would agree that the big bang needs an explanation. What caused it? If the universe arose from truly nothing, we have 2 options (laws of physics or God). As I explained earlier, both require magic.

    Best wishes


  10. Giorgio says:


    a simple question about the multiverse shows how nonsensical the idea is (I got it from a physics book for free download somewhere):

    Why do you believe in only ONE multiverse?

    Real men believe in many.

  11. Marcus says:

    Peter L, anonyrat, David, I don’t think inflation has been mentioned in the current discussion. Part of the impetus towards multiverse thinking comes from the inflation mechanisms people dream up.
    As Peter L said cosmologists confronted with visible features of the early universe generally agree there should be an explanation for the big bang. That’s not an impossible job there are a bunch of models—but the catch is that to get results that look right a lot of cosmologists think a period of exponentially rapid expansion has to be included. Once you think up and include a mechanism it becomes a headache, it keeps happening, or you need to fine tune it so it lasts long enough but then stops etc etc. So far most of the imagined inflation mechanisms tend to drag multiverse in on their coat-tails. Try to think of an explanation not just for the start of expansion but for the usually assumed amount of inflation, and try to make it not give you a multiverse.

  12. Marcus says:

    I think too often people confuse the job of explaining the big bang with deep/ultimate questions like why do we have these physical laws and why does existence exist.

    Explaining the big bang is just an obvious next step in gradual growth of understanding. Get rid of the singularity, go back in time from there, fit the available data. It’s physics business as usual, no need to get philosophical and confuse it with ultimate questions.

  13. What Krauss holds is similar to the reason why I have always expected the multiverse. Simply, a modest agnostic will. Apart from that, multiple world models are anyway tautologically true. This I have explained both here and in links:
    The multiverse/MWI cannot excuse everything and string theory must not be beyond the reach of criticism, but it is time that those who poo poo the multiverse at every opportunity also address fundamental arguments that were never based on their pet peeve.

  14. Bane says:

    Is Krauss still a physicist of the first rank? Christopher Hitchens (his friend) used to say Krauss was the greatest living physicist. Not sure if he was right…

  15. Anon says:

    Krauss: “Maybe […] everything that can happen happens somewhere.”

    This is the kind of statement that makes my blood boil. Seriously, nobody calling himself a physicist should be allowed to poison the minds of the public with this nonsense. I have started hiding the fact that I am a physicist from new acquaintances from sheer exasperation at the futility of having to try to unteach them these kinds of ideas that they pick up from the media and believe to be mainstream.

  16. hdz says:

    Peter, I share your reservations regarding the many-worlds-hype (as far as it is a hype), but you have to differentiate:
    Max Tegmark’s level 1 appears trivial, since any possible state must exist within any given approximation at sufficient distance in a presumed infinite universe. However, proposed numbers for distances are usually quite unrealistic, since they are based on mere chance configurations (such as “Boltzmann brains”) and do not consider an evolutionary universe of given age. (I have never seen realistic estimates for the rate of evolution of specific life forms per volume, for example, but I don’t actually care for such trivial doppelgängers.)
    If you give up homogeneity (as you do in inhomogeneous inflationary models, usually presented at level 2), you may speculate about all kinds of “landscapes” and ages, but any estimates must depend on your specific speculation – so here is the true hype.
    The original many worlds concept is given by level 3 (Everett). They do not exist somewhere in space and time, but somewhere else in what we classically call configuration space. In contrast to all other levels, these many worlds are NOT science fiction, since they are solely based on the empirically well founded Schrödinger equation. (I would instead regard collapse theories or hidden variables, when used to avoid Everett’s conclusion, as science fiction.) Unfortunately, David Deutsch introduced considerable confusion, when he turned Everett’s proposal into science fiction by considering time travel between different “worlds” (in conflict with Schrödinger and decoherence, for example), or when he regarded quantum computers as calculating in parallel worlds. This parallelism would be no more than the superposition principle. If quasi-classical “worlds” split according to decoherence, quantum computers have to remain in one and the same world in order to be able to produce results that may be used in our world.
    Tegmark’s level 4, finally, seems to be based on a confusion between the concepts of physical existence (to be based on observations and experience) and mathematical existence (which means no more than consistency of a definition – usually within a given axiomatic system). This level does not seem to be relevant for physics at all (except that inconsistent formal concepts cannot be used in physics either).

  17. Peter Woit says:


    Thanks for the clear outline of the various “multiverses”, which seems quite sensible to me.

    One of the more annoying aspects of multiverse mania is the tendency to throw some very different things all together. In particular, there’s

    1. The “multiple worlds” of decohered quantum phenomena, which are an interesting and very real topic we know a lot about theoretically and experimentally.

    2. The cosmological “multiverse” of causally separated parts of what used to be called the universe. These may exist, but require a serious theory, since we have no direct experimental evidence. These are the ones that get exploited by string theorists, giving them whatever properties (different values for anything string theory should be able to explain but can’t) they find convenient.

    3. Different laws of physics. Once we understand what the fundamental consistent mathematical structure is behind the laws of physics, we may very well find out that it contains pieces disconnected from ours (with different values of some constant, different numbers of dimensions, different gauge groups, etc.). Then if one wants to think of these pieces as “existing”, I suppose one can. But we’re a long way away from this…

  18. hdz says:

    Peter: so we seem to agree!
    I guess when you talk about the “laws of physics and the consistent mathematical structure behind them”, you mean the empirically founded laws (that we hypothetically and consistently extrapolate beyond what we have observed). We should also be aware that some parameters in what we regard as laws may have come into existence by some “symmetry breaking”. They would then not form fundamental laws, but characterize either specific Everett worlds or, if locally different, just regions of a “landscape” (without necessarily requiring string theory). Yes – we are very far from understanding it!

  19. Peter Woit says:


    I agree. We have no idea now what determines the parameters of the Standard Model. Most of them just appear as mass/mixing matrices in the Yukawa terms coupling the Higgs to fermions. These may be calculable from first principles in a better version of the theory, or they may be characteristics of one particular state of the fundamental theory that we happen to locally be in. In either case though, you need a better theory than anything we have now.

  20. Kent Traverson says:

    According to this piece, one may be able to detect neutrons from another universe, thus a testable hypothesis. Is there any validity to it?

  21. Vince says:

    Sorry, this is off topic, but I think you should know that the supposed faster-than-light neutrinos are no more:

    Many pet theories have now been ruled out!

  22. Peter Woit says:

    Thanks for posting the news!


    If one feels like it, one can certainly devote one’s life to carefully watching particles, and if one suddenly disappears, you can then announce that it jumped into another universe. The problem of course is that you need to have some plausible consistent theory that would predict that this would happen. I don’t think there is such a thing here.

    You can easily come up with absurd theories that are completely implausible and explain nothing, then make a big deal that they’re testable because they predict something bizarre will happen someday (even though such a thing has never happened before). I don’t think this can really be called doing science though.

  23. Kasuha says:

    Personally I don’t need God or Multiverse to explain our origin. Anthropic principle in the form “we see our universe because we are here to see it” makes me perfectly happy. And regarding arguments about fine tuning of fundamental constants – imagine a Julia set, the classic one. It is driven by just two constants. Change them just a little and you get a very different picture – may be similar overall for tiny changes but the better look you take at it the more fundamental differences you find. If fundamental constants were different, the universe would probably be very different as well but that does not mean it would not support its “fractal edge” on which we are all living. The edge would just be very different from what we are used to and there would be some totally different life forms contemplating how comes their universe’s fundamental constants are just so exactly fine tuned.

  24. Having read Krauss’s book, I do have to stick up for him a bit and say that he’s neither convinced of, nor happy about, the possibility that all is randomness and there are no fundamental laws. He’s simply resigned to the possibility.

    As someone who is haunted by the question “Why is there something rather than nothing?” I’m curious why you think it a meaningless one, Peter. I also think the multiverse answer that Krauss and others give not terribly convincing. That one universe somewhere might be “nothing” seems rather besides the point.

  25. Shantanu says:

    Vince, thanks for the link.
    Someone should ask all those who claimed that this is evidence for string theory,
    whether now they think string theory is ruled out.

  26. Thomas Larsson says:

    The anthropic explanation of the Michelson-Morley experiment: a non-zero ether wind is incompatible with human life.

  27. harryb says:


    Back to topic.

    I read Smolin’s article and I’d agree its is much more balanced than most in this arena. Krauss’s book, which I mentioned a few weeks ago on this blog, is also good stuff, but I also agree when he gets to the multiverse issue, its all arm-waving fluff, which is disappointing given the solidity he shows when discussing more standard physics.

    Smolin appears to hinge his arguments on a philosophical maxim that he describes as “Laws must evolve to be explained”. This allows him the space to therefore discuss landscape theories such as Linear Cyclic Cosmology, Eternal Inflation etc on the basis that our (current?) laws may merely be the latest manifestation of previous ones that were in existence in “deep time”.

    He finishes the piece with:

    ” The main lesson which can be drawn from the successes and failures of at-
    tempts to resolve the landscape problem surveyed here is that theories which embrace the evolution of laws have a better chance to make falsifiable predictions than do theories which try to hold onto to the notion that law is eternal. ”

    I must admit I felt after this in a bid of a bad mood too. The obvious question of – well, what was the original law / theory? in deep time seems to be given over to String or M theory (or something else) by Smolin. At least he only discusses this and posits no others in detail.

    True , Smolin points out that S/M theory is still unproven and not really going anywhere, and true he demands testability (eg he seems to rule out cosmological natural selection on observed data).

    But although much more rigorous than Krauss, it still seems to be, in summary, something along the lines of – only a multiverse argument will provide the answers to deep principles, and those deep principles may well have something to do with string theory followed by evolution of its laws to create us.

    I am sure Smolin would say that is too simplistic, but it sort of comes through no matter how many subtle caveats are used.

    I can buy the argument we need to be more thoughtful re how we look at the early universe and what may have changed since then, or at that point. The current answers posed seem a long way from being a graspable deep truth however: Unless we embrace the multiverse, string vacua and symmetry breaking, and evolution via endless cycles.

    Some may find this uplifting. For whatever reason, not sure why, I do not. There must be better answers than this. On a day when many grand, fluffy theories attached to faster than light-speed neutrinos have been brushed aside by faulty wiring, I remain in the camp of hoping for more straight-forward solutions.

  28. Paolo says:

    Thanks for recommending Lee Smolin’ paper. I found it very clear and useful, in particular I liked the comparison between the various cosmological scenarios and the observations about AdS/CFT (By the way, I noticed a few trivial typos, nothing worth mentioning)

  29. Joel Rice says:

    That profusion of speculative hypotheses would be more convincing if they had a theory that dealt with what we observe. One can complain about the Anthropic Principle, but at least we are pretty certain that we exist, and it does point to curious properties of Carbon, but going on about possible different regions or epochs having different laws sounds like giving up on the idea that Nature knows more math than we do. GR explains the redshift of the CBR but not the spectrum, and QM explains the Planck spectrum but not expansion. That one gets from this predicament some need for different laws sounds like one is desperate to save the bacon. Are they willing to throw out Arithmetic ?

  30. Dan Winslow says:

    Doesn’t what we think of as ‘knowledge’ have to run out at some point? Since no matter what explanations we derive, it’s always possible to then say ‘Yes, but what explains that?

    It seems to me that we must inevitably arrive at the end of what is possible for us to know. That point might look somewhat like what we are seeing now. I personally don’t like the idea, and I’m not suggesting we’ve reached it, but I think it needs to be acknowledged that we might at some point.

  31. JC says:

    The problem with all these BS from so-called high-energy/cosmology experts is the lack of any experimental guidance. I’m so happy that I work in a different area of physics where fascinating emergent phenomena can be studied both theoretically and experimentally.

    I totally agree with the suggestion that we should put multiverse, landscape, … in the same category of the ideas of God(s), or the world is supported by infinite elephants, turtles, etc.

    And I also think really smart math-oriented people should just do mathematics.

  32. Pingback: Uncommon Descent | Peter Woit on the multiverse as a weapon against religion: “a lousy one and not going to convince anyone”

  33. Peter Woit says:


    I’ll just repeat my usual comment that you can’t blame the multiverse on mathematical physics. I don’t think there are any equations in Smolin or Krauss, and that’s par for the course in multiverse studies. The people who find the multiverse idea appealing tend not to be those fond of using sophisticated mathematics in physics, but those looking for “physical” ideas they can easily explain to their grandmothers. While I share skepticism about string theory with Smolin and Krauss, I suspect their attitude towards the relationship of math and physics is quite different than mine.

    By the way, I don’t completely disagree with the idea that if you really understand something you should be able to explain it to your grandmother. It’s just that the explanation of some ideas would require said grandmother to sit still and pay close attention for quite a while. Others, like the multiverse, can be explained in minutes, with perhaps a few hits from a bong to help the understanding along.

  34. IT says:

    “Its much too a wild a night to travel in.”
    “Wild nights are my glory,” Mrs. Whatsit said, “I shall just sit down for a moment and pop on my boots and then I’ll be on my way. Speaking of ways, pet, by the way, there is such a thing as a tesseract.”

    But then Peter Woit appeared in the Murrys’ kitchen, proclaimed “No there isn’t” and shot Mrs. Whatsit dead.

  35. harryb says:


    How the web works…

    Here is a cut and paste of your comments above already showing up in pro-Christian faith websites. It really is depressing to see Multiverse speculation undermining science in this way. Playing into the theologists hands it seems. No wonder you felt in a bad mood.

    For interest here is the Dawkins / Krauss talk on the “something from nothing” debate from a few weeks ago. More nuanced.

    Maybe you are right. Multiverse / string etc now urgently need data and equations. Otherwise its tennis with the net down, and priests and mullahs hitting it back easily from the other side.

  36. Anon says:

    hdz says: “Max Tegmark’s level 1 appears trivial, since any possible state must exist within any given approximation at sufficient distance in a presumed infinite universe. ”

    This is not so trivial as it is often made out to be, since it depends on speculative assumptions regarding ergodicity, mixed in with speculative assumptions of infinite volume and even more speculative assumptions regarding QM and quantum gravity as applied to the cosmos as a whole.

  37. Allan Rosenberg says:

    Vince, all we can say with confidence is that the FTL neutrinos haven’t been discovered in THIS universe.

  38. Nancy Reagan says:

    Thanks Peter,
    I have been trying to get kids to: “Just say no to the Multiverse” for years. Maybe your message will help.

  39. pierre says:

    I too like the poster above am haunted by the question ‘why is there something rather than nothing’ and don’t find it a meaningless question to ask. It seems to show the limitation of what we’re capable of, in the sense that not only do we not know, but we can’t even imagine an answer. I suspect if we were ever told the answer by some higher intelligence , we would look at them like a dog being shown a card trick, to quote the late Bill Hicks.

    The problem I suspect is that the answer must be ‘logical’ for us to accept it, and we’re confined to just one system of logic. We’re trapped in logic flatland.

  40. Hansl says:

    Why is there something rather than nothing?
    – Because the Man In The White Robe had a higgup
    (sorry Peter, I had to get this out)

  41. Marcus says:

    Most apt, Hansl. The hiccup analogy underlies multiversal reasoning: once Andrei has imagined one hiccup he cannot think how the hiccups will stop. So the hiccups must go on forever—producing a multiverse.

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