News of the Multiverse

When I was reading Susskind’s book The Cosmic Landscape, I was paying close attention to the main problem with the whole multiverse/anthropic string landscape idea: is there any sort of experimental prediction that emerges from this that would justify calling it science? One thing that kind of mystified me was Susskind’s claim, in the Introduction and Chapter 12, that the “cosmic horizon” beyond which other parts of the multiverse live is like a black hole horizon and in principle information about what is beyond the horizon is accessible in the analog of Hawking radiation. This seemed to be a rather vague idea, which Susskind goes on to drop, never mentioning it in the chapter he devoted to possible experimental tests of the landscape. Since I’d never heard of anyone claiming this anywhere else, and Susskind didn’t seem himself to take it very seriously, I just ignored it.

Cosmologist G. F. R. Ellis, in a new preprint entitled On horizons and the cosmic landscape has decided to take it seriously, and show that it is wrong. Ellis’s paper is rather peculiar; I’ve never before seen an arXiv paper that argues against not another scientific paper, but some vague statements in a popular book. I haven’t tried to follow Ellis’s argument, partly because it seems rather vague itself, with not a single equation in it. Perhaps this is unavoidable, given the vagueness of Susskind’s argument that he is challenging. Anyway, at the present time, the situation seems to be that neither Susskind nor anyone else has come up with a calculation that would show how to detect information about other parts of the multiverse hidden in some sort of Hawking radiation from a cosmic horizon, and now we have an argument from Ellis that this is in principle impossible.

Some people have been giving me grief about writing blog entries with no equations, but here no one seems to have any.

If you want to hear more from Susskind about the multiverse, he’s giving the colloquium next week at MIT with title The Landscape and the Megaverse, and the abstract of this talk is:

A new paradigm for the origin of the laws of physics may (or may not) be emerging out of observational cosmology and theorists efforts to understand string theory. The ordinary 15 billion light-year universe is being replaced by a vastly bigger “megaverse” consisting of a huge number of what Guth calls “pocket universes.” If this is true then many of the Laws of Physics that we normally think of as “written in stone” will be local environmenal facts. I will explain the evidence for this controversial view, its implications, and the various views of leading physicists and cosmologists.

Susskind is also giving a talk here in New York on April 10 at the New York Academy of Sciences. The description of the talk tells us that

Several decades ago, Susskind introduced the revolutionary concept of string theory to the world of physical science. In doing so, he inspired a generation of physicists who believed that the theory would uniquely predict the properties of our universe. Now Susskind argues that the very idea of such an “elegant theory” no longer suits our understanding of the universe….

… Susskind believes that string theory, rather than reaching a dead end, has led to a vastly expanded concept of the universe, which he calls “the lanscape,” where the anthropic principle makes perfect sense.

Attending the talk would cost $20, so I think I’ll skip this one.

The last issue of the NYAS publication Update Magazine has an article by Lee Smolin on all of this entitled A Crisis in Fundamental Physics. Later this year Smolin will have a new book out, entitled “The Trouble With Physics”.

There is something I would very much like to attend, but will be out of town so will have to miss. The American Museum of Natural History each year organizes a debate in honor of Isaac Asimov. This year the topic will be Universe: One or Many?, and the blurb goes:

Join a panel of cosmologists to argue and debate the possibility that our Universe is just one of many universes that comprise the “multiverse.” This notion invokes dimensions beyond our everyday experience and draws from the leading edge of our conception of the cosmos. The presence or absence of data in support of these ideas forms a central theme for the evening.

I’m not sure who is going to argue for the presence of data in support of these ideas since I’ve never heard of any. The panelists are Michio Kaku and Andrei Linde, presumably pro-megaverse, Lawrence Krauss, who I’m guessing is on the anti-side, and Lisa Randall and Virginia Trimble, about whose views on the subject I know nothing.

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42 Responses to News of the Multiverse

  1. Aaron Bergman says:

    Ugh. Kaku again.

  2. Tung says:

    In that article, Smolin is saying that the pragmatic style (the American style) of doing physics is posing great harm to the current progress of physics.
    In Einstein’s words, our generation is one that filled with mere artisans rather than real seekers of the truth.

  3. Chris Oakley says:

    It seems that the anthropic evangelists would rather destroy the subject altogether than forego the opportunity to preach their foolish philosophy.
    Let us be clear on this: the public may not understand Calabi-Yau manifolds or heterotic strings, but they certainly understand the basics of scientific reasoning, and are perfectly capable of identifying situations where certain people choose to abandon such principles. If Susskind et al manage to convince people that fundamental physics has now ground to a halt, how can this be good for funding?
    A lot of string theorists seem to want to silence Peter, but it seems to me that the anthropists are the ones who are desperately in need of censorship.

  4. anon says:

    Peter, the relationship between black hole information loss, assuming the universe is a black hole, and Hawking/Susskind/t’Hooft was discussed in a here on this blog last July, although the link from Google doesn’t work.

    My recollection is that Hawking first showed in say c1976 that information gets lost in black holes. He gave a lecture in San Francisco a couple of years later, that Susskind and ‘t Hooft attended. They bought Hawking’s idea and applied it to the universe, on the assumption the universe is a black hole. Recently, say c2004, Hawking found an error in his original argument.

    It is sweet that Susskind is under attack now from G. F. R. Ellis, who is co-author of Hawking’s major treatise, “The Large Scale Structure of Spacetime”.

  5. Anon. says:

    Peter, I find it strange that you are harshly critical of string theorists but allow others to make sweeping and ridiculous claims without comment. I found Smolin’s article to be highly disingenuous. For instance, he says “Theories of quantum gravity include twistor theory, causal set models, dynamical triangulation models, and loop quantum gravity. One reason string theory is popular is that there is some evidence that it points to a quantum theory of gravity.”

    On the other hand I think it is clear to most theorists that, despite its (many) problems, string theory is a quantum theory of gravity. Smolin’s “there is some evidence” is vastly understating the case. However, it is not at all clear that loop quantum gravity is a theory in the technical sense in which physicists use the word “theory.” Naively quantizing gravity, one runs into the problem of nonrenormalizability, i.e. of infinitely many undetermined couplings, so we say that this is not a theory. It is not at all clear that LQG avoids this problem, and in fact it appears quite likely that it does not. Even Lee admits that he does not know whether there are infinitely many undetermined couplings or not!

    Here is a thread from your blog in which this is spelled out pretty explicitly.

    So, given that it is not clear that LQG is a theory at all, whereas string theory is at least that, I find Lee’s article troubling. If LQG eventually proves to contain some new principle that restricts possible interactions and creates a sensible theory, that would be exciting, and the community would not ignore it. But until then it is justifiably ignored by most of the community. Appealing to non-experts and claiming to be part of a grand philosophical tradition are moves that I find distatesful.

    (I find the landscape equally distasteful, but clearly that receives plenty of attention already. I just fail to see why you appear to encourage one sort of non-scientific hype while frowning on others.)

  6. woit says:

    The LQG/string theory war is off-topic here, it has nothing to do with this posting. I mentioned Lee Smolin’s article in passing because it is mainly about the multiverse and was published in a NYAS publication, thus relevant to the topic at hand.

    I strongly disagree with your characterization that string theory is a theory, LQG not, and don’t see anything wrong with what you quote from Smolin. There are serious questions still up in the air about both of them. In the case of string theory, no, it is not a consistent quantum theory of gravity in 4d, since all we have is a divergent perturbation expansion.

    The current situation is that no one has anything that I would call a really satisfactory theory of quantum gravity, one that is completely consistent and well understood, and either makes testable predictions or explains in a convincing way how the standard model is related to quantum gravity. As long as this is the case, my point of view is that people should be trying as many different kinds of ideas as possible. The problem with string theory is not that some people are doing it, but with the way it is being fanatically pursued, despite its by now obvious failures, driving out people who try and work on other ideas. If you think ideas about quantum gravity should be “justifiably ignored” because they have problems, you need to ignore everything.

    Personally I see some of the ideas the LQG people are investigating to be much more promising than the ones used in string theory, others will differ. Until either side comes up with a completely consistent theory that makes testable predictions that are then checked, reasonable people can differ about this.

    Please, take the polemical string theory/LQG arguments somewhere else. They don’t belong in the comment section to this posting.

  7. I do not know about Trimble’s views on this issue, but I have
    found an interesting passage that she quotes:

    We understand the concern of cosmologists that unbridled speculation should not take over the field, that it is better to persist with the standard model, warts and all, than for opinions to become splintered, with the decline of professional standards which would then almost inevitably ensue.

    Our response to this point of view, with which we have some sympathy, is that undesirable fragmentation has been permitted already, through the invasion of cosmology by Particle physicists. If the invasion had the precision and the certainty of earlier invasions of astrophysics by atomic theory and nuclear physics, the consequences would obviously be positive. However, one can have reservations about the advantages of becoming caught up in speculations from a different field, especially when those speculations are announced with an air of authority that will probably turn out to have been taken too seriously.

    [Attributed Sir Fred Hoyle, Geoffrey R. Burbidge, and Jayant Narlikar, according to Trimble´s article “Can’t You Keep Einstein’s Equations out of my Observatory?”, BeamLine 29, No. 1, p 21-25 (1999).]

    Interesting enough, as she points out, these researchers are well-known for their relatively non-mainstream contributions to cosmology.

    But I must restate: I do not know her present opinions on the multiverse issue.

  8. Another Anon says:

    I agree with the other Anon that Smolin’s article is a bit distasteful and self-serving. He seems to be seizing on the multiverse/landscape situation as an opportunity to knock string theory off the throne and replace it with LQG and related approaches, exchanging one brand of hype for another. Not much in this for peasants like me working on such mundane topics as ordinary gauge theory (boring things like trying to construct nonperturbative chiral gauge theories, so as to have a chance of determining whether that tedious hypothesis about sponaneous gauge symmetry breaking in electroweak theory is true or not.) Doesn’t sound like there would be any more crumbs for us if King Witten were to be replaced by King Smolin.

  9. woit says:

    Another Anon,

    Undoubtedly Smolin would like to see less resources and attention flowing to string theory and more to LQG. Given the current huge imbalance on this issue in favor of string theory, this is not at all unreasonable. I don’t see the slightest danger any time soon of a “King Smolin” controlling the bulk of resources in the field and suppressing alternative points of view.

    I think I share your point of view that the problems I care most about are being addressed neither by string theory nor LQG. But, again, this really is not the place for more battles about string theory vs. LQG.

  10. Aaron Bergman says:

    This is pretty off-topic and Peter’s welcome to delete it if he wants, but….

    You know, I’m trying to be polite to Lee over on another blog, but my god. That article is so unbelievably tendentious, self-aggrandizing and condescending that it passes into the realm of dishonesty. You want to know why you get such a bad reaction from other physicists, Lee? It’s not because string theorists hate LQG. It’s because of supercilious articles like that.

  11. woit says:


    You’re right that this is both off-topic, uncivil, as well as stupid to boot, and I should delete it. Instead I’ll leave it up as yet another indication of the kind of ugly behavior that string theorists insist on engaging in these days.

    Look, Lee is someone who has always been completely civil to everyone, in his comments on blogs and in everything he writes and does elsewhere. He has maintained this civility in the face of absolutely appalling behavior towards him by Lubos Motl (behavior that no one in the string community sees fit to publicly denounce or take any action against), as well as a less than civil tone from you, Jacques and others. For you to be complaining about Lee’s behavior as “so unbelievably tendentious, self-aggrandizing and condescending that it passes into the realm of dishonesty” and “supercilious”, given the tone and content of the way string theory has been promoted and the behavior of your string theory colleagues, both close ones and not so close ones, is completely ridiculous.

    Just knock it off with the personal attacks, I’m sick to death both of being the target of this kind of shit from people like Lubos, Jacques (and many others), and of seeing you throwing it at people like Lee, and anyone who dares to point out the problems with string theory. If you think something someone writes is inaccurate or you have a scientific criticism to make, go ahead and make it in a civil fashion. If you can’t do that, shut up. In any case, stop polluting this field with this kind of nastiness.

  12. Aaron Bergman says:

    Lee’s “civility” has begun to feel to me to be tremendously superficial and political. He keeps a tone of civility while being substantively dishonest. It’s getting to be offensive. At least Lubos doesn’t hide his disrespect for others behind a false guise of comity.

    You accuse me of “throwing [personal attacks] at … anyone who dares point out the problems with string theory.” Please give me an example. I’m quite googleable. If you can’t, don’t foist on me the actions of others. Perhaps you’ve forgotten the various times when I’ve agreed with various criticisms of string theory?

    As for the scientific criticism of Lee’s tired points, that’s been done a zillion times both here and on Cosmic Variance. That Lee seems to not have listened to any of it at all is part of the problem.

    And WTF am I supposed to do about Lubos? I lost the code to the orbital mind-control satellites a few years ago, and I think it would be clear by now that Lubos isn’t going to listen to anyone. I’m open to suggestions.

  13. Who says:

    Aaron, I was surprised by your latest comment, in reference to Smolin’s NYAS article A Crisis in Fundamental Physics. I re-read the article and could find nothing that I could imagine calling “unbelievably tendentious, self-aggrandizing and condescending” or “supercilious ” or smacking of “dishonesty”.

    The article has very little to say about LQG and the imbalance in theory research funding. It really is about what it says in the title: a crisis in fundamental physics.

    I urge anyone who can to take an objective unemotional look at the article. It is clearly targeted at a passage by Steven Weinberg which Smolin quotes. Weinberg depicts a major foundations crisis situation–a “turning point” in the “history of science” (not merely the history of physics, he would have it, but science as a whole)—and suggests that humanity may have to relax the standards by which science is done and the criteria of what is science. In particular, Weinberg refers to the current tendency to “legitimate anthropic reasoning as a new basis for physical theory”.

    The main things Smolin does in the article are simple to state: he describes Weinberg’s position, and he opposes it. He describes the circumstances which have brought matters to a head. He takes Weinberg’s statement as a confirmation that there is a (philosophical) crisis in physics—a crisis having to do with foundations—and he gives an historical account of how he thinks this crisis came about.

    Then he states his main thesis in this key paragraph

    I believe we should not modify the basic methodological principles…Science works because it is based on methods that allow well-trained people of good faith, who initially disagree, to come to consensus about what can be rationally deduced from publicly available evidence. One of the most fundamental principles of science has been that we only consider as possibly true those theories that are vulnerable to being shown false by doable experiments.

    Smolin says we should NOT change the basic methodological principles. Theorists, in his view, should continue the practice of proposing theories that are “vulnerable to being shown false by doable experiments.” This is what allows the scientific community to function, by making differences empirically resolvable.

    I think that to sustain this precept is not self-serving on Smolin’s or anyone’s part. I rather think it is a service to physics and the scientific community in general.

    It seems to me that you can disagree with Weinberg and Smolin about the magnitude of the unresolved foundation issues and the seriousness of the present situation in physics. You can argue that there is no crisis, and there is no major “turning point”. Or, you can concede the gravity of the situation and come down on Weinberg’s side, against Smolin.

    But I don’t think you gain respect by simply bad-mouthing Smolin’s article—calling it “supercilious” and “condescending” etc.

    Nor do I suspect that you speak for very many string researchers when you say such things.

  14. Anon. says:

    Who says:

    The main things Smolin does in the article are simple to state: he describes Weinberg’s position, and he opposes it.

    You seem to have read a different article than Aaron and I did! There was a bit about that, yes — a few short paragraphs in the middle. But I see this as sort of a diversion from the main thrust of Lee’s article, which is stressing the need for thinking about “conceptual puzzles” and “foundational issues.” I don’t mean to be off-topic and polemical, I’m just trying to respond to what I see as the central focus of Lee’s article: namely, his assertion that most physicists don’t care about conceptual or foundational issues, whereas he does. This is what I see as condescending, and I think it’s what Aaron was referring to as well. The implication that no one else is willing to think deeply is made pretty bluntly, and it is offensive. Lee explicitly links his own work — and that of his collaborators — with that of “Einstein, Bohr, Mach, Boltzmann, Poincare, Schrodinger, Heisenberg.” Is this not self-aggrandizing?

    Peter, if this is off-topic, feel free to delete, but I think I’m clearly replying to the text of one of your links…. Just because (some) string theorists often make overhyped and arrogant statements, it doesn’t excuse similar statements from those opposed to string theory.

  15. woit says:

    I’m not going to tolerate a stupid off-topic flame war here, so will delete any more comments on this thread (after exercising my prerogative as blog owner to have the last word). If someone has an intelligible scientific point to make, make it, but I won’t tolerate either personal attacks or repetitive and tendentious LQG vs. string theory arguments.

    You’re perhaps right Aaron that I have unjustly accused you, however “tendentious”, “supercilious”, and “condescending” are words that seem to me to apply to some of your postings, most recent example the ones over at the blog belonging to Christine Dantas. But you’re right that you don’t ever behave like Lubos, and most of the time avoid behaving like Jacques.

    I reread Lee’s article, and found it perfectly reasonable (although I disagree with him at some points: I’m much less optimistic than him that work on the foundations of QM will get him what he wants, and less convinced that LQG now leads to solid, testable predictions). The main point he is making is both very true, exceedingly important, and rarely said in public by a theorist: if one believes that string theory leads to a landscape such that there is no plausible way of testing it, it is one’s duty as a scientist to abandon work on it, not to start promoting some new paradigm of how to do untestable science.

    I see not the slightest evidence the Lee is being dishonest at any point, whereas the vast promotional string theory literature at this point just reeks of dishonesty. As you might guess I also happen to feel that I’ve been personally treated in an exceptionally dishonest and unethical way recently due to my opposition to string theory.

    What can you do about Lubos or others who behave badly? Come on, when he posts something offensive, write in a comment saying so. If you and all the other string theorists reading these blogs did this regularly, he might actually change his behavior, or at least you would make it clear that the string theory community doesn’t support him. Instead, his idiotic nastiness goes unchallenged, with string theorists doing things like writing comments supporting what he has to say, except perhaps noting that he is a bit “undiplomatic”. And he’s not the only string theorist whose behavior people should challenge, just the craziest.

  16. Aaron Bergman says:

    Feel free to delete this one, too, Peter. If it does get you can leave that “Who” is welcome to e-mail me or tell me of another forum in which I can respond.

    In addition to Lee repeating various incorrect claims about string theory and ‘background independence’ (something pretty much guaranteed to make me irate), this paragraph was particularly bad:

    Meanwhile, many of those who continue to reject Einstein’s legacy and work with background-dependent theories are particle physicists who are carrying on the pragmatic, “shut-up-and calculate” legacy in which they were trained. If they hesitate to embrace the lesson of general relativity that space and time are dynamical, it may be because this is a shift that requires some amount of critical reflection in a more philosophical mode.

    I don’t appreciate being told that I’m “reject[ing] Einstein’s legacy”, and hesitant to “embrace the lesson of general relativity” because this “requires some amount of critical reflection”. This isn’t an attack on string theory; it’s an attack on the people who research string theory.

    Rereading the essay, it’s true that the majority of it probably does not justify my reaction (as I said, repeating the same incorrect claims about background independence got me angry), but that paragraph is particularly offensive. The self-serving aspect of this essay is how Lee continually sets himself as the defender of Einstein, background independence and deep physics as if no one in string theory ever thinks of such things. Plenty of such discussion occurs, although it usually doesn’t end up in papers. One person who does publish papers with discussions along those lines is Tom Banks.

    I think it’s interesting that, Lubos excepted, most of the critiques about LQG by string theorists have to do with how the theory could match up with the real world, ie, anomalies, the semi-classical limit and, somewhat more loosely, black hole entropy. On the other hand, the critiques of string theory seem to be more philosophical, complaining that it’s not background independent or that it has too many vacua to be predictive.

    The latter critique is certainly legitimate (although still somewhat permature in my opinion contra both the anthropists and the anti-anthropists). But it is still a metaphysical complaint.

    So, I think that Lee’s dichotomy between the deep thinkers doing “background independent” quantum gravity and the “shut up and calculate” stringers leaves a lot to be desired.

  17. Eric Dennis says:

    By the same token, Smolin is “linking” the shut-up-calculate crowd’s work with that of Feynman, Dyson, Gell-Mann, and Oppenheimer. His point is not to play “my guys are smarter than your guys”. It’s to note an interesting ideological division among physicists and ponder its relevance to the future progress of the field.

  18. woit says:

    Other comments came in while I was writing the last one, so I’ll leave them.

    No, Aaron, complaining that string theory can’t predict anything and thus is not legitimate science is not “metaphysical”, it’s scientific method 101. What is “metaphysical” are the arguments used to justify continuing work on the landscape and string theory unification.

    But I really don’t want any more of this nonsense here. Just stop it. At this point I’ll delete anything at all about this that anyone tries to put here.

  19. ObsessiveMathsFreak says:

    Ellis’s paper is rather peculiar; I’ve never before seen an arXiv paper that argues against not another scientific paper, but some vague statements in a popular book.

    Interesting. This sounds like the kind of paper you would find in the humanities, where views on books are regularly discussed. Might this be the start of a new trend in physics publishing? The phrase “natural philosophy” comes to mind.

  20. Dumb Biologist says:

    I really don’t understand Dr. Smolin’s assertion that the “shut up and calculate” approach has somehow led science to the Lanscape. I rather thought the oringinal sentiment was to avoid wooly philosophizing about an approach that, while defying human comprehension, nevertheless made perfectly accurate and testable predictions. As Landscapology apparently addresses problems that are neither calcuable (i.e. NP-hard and intractable) nor testable, I’m not sure how “shut up and calculate” is even relevent. It’s not at all clear to me how more wooly philosophizing is supposed to help when experimental verification of its fruits are no closer than what can be attained with any other approach. I’d say if the experiment isn’t doable (which apppears to be true of any current approach to unification physics or quantum gravity), “shut up and do something else” might be good advice.

    I’m not even a physicist, and I simply can’t wait for some humongous collider to come along and give scientists something else to argue about besides philosophy. Like data.

  21. Chris W. says:

    This one is meant for deletion, and is inoffensive and helpful (I hope):

    Typo alert: …which he calls “the lanscape,”

  22. Chris W. says:

    One more typo: …local environmenal facts

    (Sorry for not including it the previous comment.)

  23. Another Anon says:

    Thanks for your reply above, Peter. The stuff I wrote about “King Smolin” was of course exaggerated for theatrical effect. But as someone who doesn’t have anything at stake in the outcome of any strings vs LQG fight I still found parts of the article a bit objectionable. In particular toward the end where Smolin writes:

    “So, while the new foundational approaches are still pursued by a minority of theorists, the promise is quite substantial. We have in front of us two competing styles of research. One, which 30 years ago was the way to succeed, now finds itself in a crisis because it makes no experimental predictions, while another is developing healthily, and is producing experimentally testable hypotheses.”

    At the risk of being paranoid, this sounds a lot like “The previous bandwagon has ended in a ditch, so now it’s time to build a new bandwagon”. (I’m no expert on the current state of LQG etc, but that last bit smacks of propaganda hype a la string theory.) I would have preferred a conclusion more along the lines of “Since the previous bandwagon ended in a ditch, perhaps bandwagons themselves are not such a great idea”. Instead of trying to predetermine which philosophy or research program will turn out to be the best, how about encouraging people to follow their own ideas, and rewarding them purely according to the progress they make without preferential weighting for any particular research program. For many years the rewards for making progress in string theory have been way out of proportion with other areas. My worry after reading this article is that, if Smolin had his way, that would simply be changed to preferential weighting for progress on the “new foundational approaches” he advocates.

  24. woit says:

    Chris W.,

    The typos are in the original, so I’ll leave them. This whole subject is characterized by incredible sloppiness, why not sloppy spelling too?

    Dumb Biologist,

    My interpretation is that Smolin is arguing “shut up and do something else”, the something else being thinking about foundational issues, ones that are neglected in string theory. The hope would be that if you do this you’ll get some insight into a different, more promising direction than string theory, at which point you can shut up and calculate again. I have a somewhat similar view, but replacing studying foundational issues in QM, by looking for a deeper mathematical interpretation, and I prefer to start with the standard model rather than gravity.

    Another Anon,

    I think Smolin would agree with you that this is all about “encouraging people to follow their own ideas, and rewarding them purely according to the progress they make without preferential weighting for any particular research program” and your opposition to bandwagons. The problem with the way research is currently structured is that it is very hard to get attention for any formal research if it’s not string theory. He’s just making the argument that this is not good and pointing to one kind of research that he sees as having suffered because of the way string theory has driven everything else out. If miraculously he manages to get people to listen, becomes power-mad and constructs a new bandwagon designed to drive other ideas out of business, that would be a bad thing. I just don’t see the slightest danger of that happening in the forseeable future.

  25. Zelah says:

    Reading this Blog has discouraged me about how High energy physics is conducted.I mean, crying foul at a webarticle? By String Theorists?

    It seems to me that Lee is just politely speaking his mind. A totally legitimate thing to do! Most probably there is some sort of hidden insult that Lee is giving out to his fellow high energy physicist theorist?! Cannot take the heat Stringers? I say if you want to dish it out like say Lubos, then you have to take it on the chin!

    My final thoughts. As an amateur, it seems to me that there is a whole lot of data waiting to be explained! Like Dark Matter / Energy.Surely, it is a serious indictment of String theory if it has NOTHING TO SAY on these matters? Worst in my book is to ask higher standards of ones competitors!

  26. Who says:

    The typos are in the original, so I’ll leave them. This whole subject is characterized by incredible sloppiness, why not sloppy spelling too?

    IIRC Susskind once posted something on arxiv about “Sting Theory”,
    You had a thread relating to it here, I believe. It was funny (not only the Freudian spelling, the whole thing).

    A propos. Baez just gave a talk at Rovelli’s CPT—he posted a link in yesterday’s TWF #227—and at the end of the talk Rovelli asked him “doesn’t this mean that the physics of the last 25 years is junk?”

    and Baez agreed. this is from someone who was there and just posted it on PF. Baez talk and Smolin’s essay are parallel in some respects, both illuminate embarrassing problems in fundamental physics

  27. Another Anon says:

    Thanks Peter, although it seems your reading of the article is quite different from mine. I guess we’ll just have to agree to disagree.

  28. vb says:

    You’ve got an excellent blog, which I regularly read (via Google Reader, so I skip the replies most of the time, but anyway) and share similar sceptical views, but similarity between the Darwin theory of natural selection and the landscape idea is appealing. In your own opinion, what web site or blog would be the most antagonist to your blog? Thanks, vb.

  29. Lee Smolin says:

    Dear Aaron and others,

    I apologize if you found what I said to be “condescending” and “offensive”. My point is not to insult anyone and it is certainly not to support one trendy fashion against another. I meant what I wrote in the Physics Today article, which is that intellectually independent individuals with something original and important to contribute always deserve priority, even over people pursuing my own research program. This is what I do in practice, as I think those who know me will attest to.

    The point of this article was not to make a polemic for LQG, which is mentioned just once (and then just in a list of theories) but to offer a new hypothesis as to why physics is in a crisis. To the people I inadvertently offended, I would ask you to look beyond labels to the facts I describe. It is just true that there is a small community of people whose scientific work is centered on “foundational issues.” By this I mean those questions usually labeled such, for example the measurement problem in quantum mechanics, the problems of time or what is observable in quantum cosmology, or the relational/absolute debate about the nature of spacetime.

    I don’t think there is anything arrogant about pointing out that there are different communities, or that these communities have different styles and evaluate research according to different values. The foundations community, in my experience, values intellectual independence and depth of thought more than many people in more mainstream fields. This is partly because one needs acquaintance with the philosophical tradition to make a contribution here, and also because there being almost no professional opportunities in research universities for such people, they tend to be intellectually independent people who value their independence more than they do the usual sorts of professional success.

    Nor is it “self-aggrandizing” to mention that this foundational tradition owes a great deal to and feels itself to be connected to Einstein, Bohr and other foundational thinkers of the first half of the 20th Century. Again this is just a fact. You are much more likely to find someone who has actually read the original writings of Einstein, Bohr, Boltzmann etc among the foundations community than you are among more mainstream communities.

    There is nothing wrong with a theoretical physicist not having an interest in foundational problems. Most don’t, it’s a choice about where you think the answers to the questions you want to solve are going to come from. I choose to go to meetings in foundations of quantum mechanics, because I think they are relevant. I’ve seen very few people at these meetings who also contribute to string theory-I only recall Brian Greene and Gerard ‘t Hooft. So it’s just a statement of fact to say that most string theorists don’t think the foundational issues are relevant for their field. Another piece of evidence for this is that there are few if any papers by someone considered a leading string theorist proposing a new solution to one of the foundational problems I listed above. But many of the leaders of the non-string approaches to quantum gravity have written such papers, such as Crane, Dowker, Finkelstein, Hartle, Isham, Markopoulou, Penrose, Rovelli, Sorkin.

    The point of my essay is to propose that it is an intellectual mistake to separate the problem of quantum gravity from the foundational issues. This implies that more attention and scope needs to be given to those who understand and care about the foundational issues and have ideas of how they relate to the problem of quantum gravity. This could be right or wrong. If you don’t agree with it, that’s fine, but please don’t be insulted just because your style of research is labeled “non-foundational,” when in fact you have not focused on the problems that are called “foundational”.

    As for rejecting Einstein’s legacy, this is again just a fact. If you study the work of historians such as Stachel and Barbour, who are intimately familiar with Einstein’s work and its historical context, you learn that background independence is the core of what they consider Einstein’s legacy to be. I don’t understand why this bothers anyone. If you have thought about the issue and decided to reject background independence then you are in disagreement with Einstein. But this should hardly bother most contemporary theorists as very few of us agree with Einstein’s views on quantum theory, which puts almost all of us outside of his legacy.

    Is it arrogant to say that shifting one’s view on these issues requires a certain amount of critical reflective thinking? Perhaps, but all I can say is that this is what it took for me to make the switch, having been trained originally as a quantum field theorist and having done all my early work on perturbative quantum gravity. It took sustained interactions with Barbour and Stachel, as well as close study of their and Einsein’s work, over several years, to come to their point of view.

    Finally, thanks to WHO, who made several points better than I could have.



  30. woit says:

    I gave Lee the last word here since there was a significant amount of criticism here and he deserved the right to respond to it. But, please restrict comments to the topic of the posting (the multiverse, remember?). There’s a lot of interesting things to debate about foundational issues, but I’d rather people not do it here and now. For one thing, such a debate is exceedingly hard to properly moderate, and I’m way too busy for that right now.

  31. woit says:


    Depends what you mean by antagonist. There’s Lubos Motl, who goes nuts when my views are mentioned, except that he and I kind of agree on the landscape. I don’t know of any blog that actively promotes the landscape point of view regularly from the point of view of someone doing research in that field.

  32. vb says:

    Thanks for the answers. Yes, youve guessed right in your second part, “antagonist” in this sense, as you’ve said, who: “…actively promotes the landscape point of view regularly from the point of view of someone doing research in that field.” — not aware of any site, which, btw, tells a bit of story: perhaps it’s easier to be sceptical; “poking around” controversial hypothesis [landscape] publicly by an established scientist [e.g. Susskind] can make him vulnerable to “not even wrong” kind of opinions (on the other hand, for a non-well-known scientist, it may be an opportunity). Science has no other way but to advance though; and someone has to make first steps, even if they fall…

  33. woit says:


    One interesting aspect of the landscape idea is that it is significantly less popular among younger researchers without much of a reputation, which is also the same population that is most likely to start a blog. My interpretation is that this is because adopting the landscape point of view is a kind of giving up which is much more likely to appeal to older people who have spent more than 20 years struggling to get a prediction out of string theory. Younger people who haven’t been at this as long are more likely to believe that giving up is not necessary, that some nice vacuum state of the right kind can still be found.

    I do wish Susskind would start a blog though, that would be interesting.

  34. Jimbo says:

    I think everyone should read Smolin’s paper, ref’d by Peter. It is an outstanding delineation of the crisis impending in theoretical physics. The reason that Ellis’ comment is devoid of math is that all the calculations supporting his claim that Lenny is wrong about horizon distinctions, are done in the paper he ref’s by Davis & Lineweaver.
    Sounds to me like Susskind was trying to slip the public a `mickey’, vis a vis, particle v. event horizons, in order to bump sales.

  35. Who says:

    The reason that Ellis’ comment is devoid of math is that all the calculations supporting his claim that Lenny is wrong about horizon distinctions, are done in the paper he ref’s by Davis & Lineweaver.

    That was my impression too: Ellis didn’t need to include equations since he is dealing with established concepts familiar to cosmologists, and he gives ample references.

    BTW the paper he cited by Davis and Lineweaver is one of several by those authors about cosmological horizons.

    To amplify Jimbo’s remark, contrary to Susskind’s claim, what cosmologists call the particle horizon is not analogous to a black hole event horizon, except in a verbal or poetic sense. Moreover the cosmic microwave background is not coming to us from the particle horizon (but from the surface of last scattering), and it is not produced in a way analogous to Hawking radiation. Even if one were to grant for the argument’s sake that information about matter eaten by a black hole is encoded in the Hawking radiation, this would not imply that information about other universes (“pocket universes” and the like) is present in the CMB. The exerpts from Susskind’s book which Ellis includes in his article are extraordinary—I recommend reading the Ellis article (all 3 pages of it) just for the quotes.

  36. csrster says:

    Ellis has obviously misunderstood Susskind’s argument, as no-one with a primary school education could have made such an absurd blunder as the one Ellis attributes to Susskind.

  37. Eli Rabett says:

    It may be time to reconsider )after a few centuries of success( the proposition that the universe can be understood at all levels by humans. Perhaps there is some level at which this cannot be done, and attempts to do so only lead to madness and ill tempered posts.

  38. woit says:


    I don’t know about “at all levels”, but at the level string theory is trying to understand, there’s no evidence yet that this can’t be done. String theorists at the moment are trying to promote the idea that since string theory leads to a complicated mess that can’t be understood, the world must be a complicated mess that can’t be understood. That string theory is just a wrong idea is a much simpler explanation.

  39. Who says:

    [csrster: Ellis has obviously misunderstood Susskind’s argument, as no-one with a primary school education could have made such an absurd blunder as the one Ellis attributes to Susskind.]

    Your guess is understandable (because what Susskind claim is so absurd) but unfortunately you would seem to be mistaken. Ellis quotes passages from Susskind’s book which are explicit, and gives a link to longer exerpts providing context.

    The case is quite clear. Please do not rely on my imperfect paraphrase, but read the quotes from Susskind in Ellis original paper. It is only 3 pages and no trouble to read.

    [b]On horizons and the cosmic landscape[/b]

    Abstract: “Susskind claims in his recent book The Cosmic Landscape that evidence for the existence and nature of ‘pocket universes’ in a multiverse would be available via detailed study of the Cosmic Blackbody Background Radiation. I point out that apart from any other queries one might have about the chain of argument involved, this claim is invalid because it rests on a confusion between the nature of a particle horizon and an event horizon in cosmology.”

    Ellis gives this link to exerpts from Susskind’s book containing the questionable claim:

    Some quotes from Susskind are:
    “…The very same arguments that won the Black Hole War can be adapted to cosmological horizons. The existence and details of all the other pocket universes are contained in the subtle features of the cosmic radiation that constantly bathes all parts of our observable universe…”

  40. Very interesting paper by Ellis, with excellent references.

    He writes,

    In reality, the limit is even stronger: no significant cosmological information reaches us at the present time from beyond the visual horizon – defined by the world-lines of the furthest matter from which we receive electromagnetic radiation today.

    As far as I understand, however, another horizon could be set by a primordial gravitational radiation background. The observational aspects of this possibility, in classical and string theory contexts respectively, can be found in astro-ph/0504290 and hep-th/9907185. Another interesting paper is by Craig J. Hogan: astro-ph/9809364. However, I do not know how far these studies could be extended to the multiverse issue in the sense that information coded in the primordial gravitational radiation background (observed from WMAP or LISA) could be used to infer on the existence of these “other universes”.

  41. Anon1 says:

    For pple who r confused about ‘particle’ and ‘event’ horizons..(actually, u can add the hubble radius to this list..these 3 are often mixed up) look at this paper.. Ofcourse, this is much before black hole radiation etc.. but this is one of the first to spell out the differences clearly. Hope it helps..

  42. Eli Rabett says:


    True there is no evidence that we cannot understand the universe at the level of string theory, but equally well there is no guarantee that it can. Moreover it is not even clear that the methods that have been used to characterize nature up to this point can continue to work ad infinitum.

    I offer this thought in the same spirit as the anthropic principle was created. The level of string theory is so far from human experience that the universe may not be explicable to or by us at that level.

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