First some links to interesting things:
- There’s a fascinating interview with Deligne in the latest AMS Notices.
- Alexandre Grothendieck: A Mathematical Portrait includes some great expository pieces about the mathematics developed by Grothendieck. There’s also available Grothendieck’s own Esquisse Thématique, giving his description of his major mathematical achievements.
In the category of things that have gotten tedious, first there’s the ongoing hullabaloo about “firewalls” and Hawking (with the bottom line as far as I can tell just that, yes, there is an information paradox, might have something to do with the fact that we don’t understand quantum gravity…). If this interests you, you can take a look at
- Matt Strassler, here, here and here, with creative writing here.
- New Scientist has Fiery black hole debate creates cosmological Wild West.
- Michael Lemonick here sensibly asks whether people really should be paying this kind of attention to Hawking at this point.
In the multiverse-mania category, I’m forcing myself to read the Rubenstein book I’ve mentioned, will report on this when done, in the meantime there’s
It is therefore fair to say, that much of the standard model, and certainly the peculiar values of many of the parameters in the standard model, cannot have an anthropic explanation. In string theory, extra generations of matter correspond to more tuning of moduli, small parameters do not appear to arise without a symmetry explanation, and symmetries are rare on moduli space.
One cannot escape the implication that, on the basis of current theoretical knowledge, the String Landscape is ruled out by experiment.
Besides being experimentally ruled out, the whole Landscape thing doesn’t work anyway
My personal conclusion from all of this analysis, is that the theory of CDL tunneling provides no positive support for, and lots of negative evidence against, the proposal of a String Landscape…
When combined with the phenomenological challenges I presented in Section 2, I conclude that the String Landscape is an hypothesis of dubious validity.
This is a subject in which solid predictions are hard to come by, but I’ll make one here: string theory partisans will just ignore this, with the “String Landscape” now an hypothesis which has achieved some sort of new extra-scientific status. It’s an ideology you sign up for to justify not giving up on string theory (or as a foundation for your multiverse-mania), and as such, arguments like those from Banks are irrelevant.
I was interested to see that his perception of what has been going on for the past decade as endless popular books promoting the multiverse have appeared is that
whenever a physicist writes a book about them [multiverse ideas], the Web erupts with claims that they are unscientific nonsense.
Curious to know what part of “the Web” he is referring to other than my blog…
Max Tegmark has jumped the shark.
There, I said it…
(It’s hardly worth saying anything more on the subject.)
1-
Actually, he does no such thing. The article is about the media hype that has surrounded Hawking for much of his career, and it includes a mention of how Hawking himself has opposed it. The article at some points was a bit too hostile and unfair, but the relevant point is that it admits the fact that Hawking was and still is “one of the world’s leading physicists”.
2-
You quoted from the 1st paragraph. If you look at paragraph immediately after it you’ll find that Tegmark says:
The black hole information paradox and firewall paradox have jumped the shark. I think I’m going to try to stop paying attention to this until somebody comes up with a theory that makes an actual prediction.
Ahab,
1, Actually, he calls him a “pretty-great” physicist…
2. I did read that. And actually I linked to the New Scientist Buchanan review in my blog posting here
http://www.math.columbia.edu/~woit/wordpress/?p=6551
The parts Tegmark quotes are questions, not statements, with Buchanan only saying about them “some scientists wonder”. As close as Buchanan gets to criticism is
““there does seem to be something a little questionable with this vast multiplication of multiverses”. As far as I can tell, of the dozen or so reviews out there, only Buchanan’s and mine contain any criticism of the sort Tegmark is claiming “erupt all over the web”. Of the other many multiverse books, I can’t at the moment think of any reviews (certainly not in New Scientist) or a significant other number of blog postings (besides mine) criticizing these books. Tegmark seems awfully thin-skinned about criticism for someone who poses as “Mad Max” the revolutionary with controversial ideas…
There are parts of the Web (a multiweb, really) that you cannot possibly access, now or in the future.
Thanks for the link to the Schneps’ page on “Alexandre Grothendieck: A Mathematical Portrait”, Peter. Do you by any chance know if this will get published in a book/ebook format?
I wish you had more links like that than depressing ones to articles/books/blogposts tirelessly rehashing the same thing about multiverses :-\
” … for someone who poses as “Mad Max” ”
Some kids will just never accept they will never become Einstein when they grow up…
I have attacked the level II, III, and IV multiverses on my blog also. Tegmark admits that many of the multiverse ideas are untestable, but says that we should take them seriously anyway because they can be formulated as parts of theories that have testable implications for our universe.
Hi Peter,
Thanks for linking to my discussions with Sesh.
Whereas I agree with Sesh that the anthropic prediction for Lambda is off by 10^3, that was still a *prediction* that got closer to the correct value than any other prediction of its time. That alone makes it compelling enough to me that, whereas I’m glad that I don’t have to work on it myself, I have no qualms if other people do want to explore it. I certainly don’t view a multiverse as even close to established fact, but as a speculative idea it *does* have its *scientific* merits.
On this side of the Atlantic I rarely encounter anything I would label multiverse mania. And even string theory in general, although certainly part of the mainstream in Europe, is far from dominant (arguably it is on decline). My perception of the U.S. is that things are a little different (at least from theory postdoc job advertisements over the last five years, which *typically* are either dealing with data/the lattice, or string-inspired-something-or-other – with some notable exceptions, e.g. in/near Chicago).
I think both sides (the hypers and the naysayers) need to take a longer term view of things. No, the multiverse is not established fact, and the hypers shouldn’t be saying it is just to score media points, but neither is it unfalsifiable, in the long term.
Sorry, I can’t edit the above post, but I should stress, that whenever I mention “multiverse” (here, or elsewhere) I am referring solely to the eternal inflation with multiple possible vacua one (Tegmark Type II, I guess), and definitely not Tegmark’s III and IV.
But all in all is the Tegmark’s level IV multiverse very different from what Lawrence Krauss is continuously repeating about a supposed origin of the laws of physics from nothing (whatever that means)? I think he went on that direction several times.
Anyway I currently think that the main problem is that physicists are starting to feel authorized to try to answer questions that would have been considered outside physics just few years ago.
I pretty much agree with the Platonist philosophy of Penrose (much less with his view about physics) but I think he never confused philosophy with physics. It seems to me that the main attitude is becoming “any sensible question is a physical question”. Of course I strongly disagree.
Anyway I currently think that the main problem is that physicists are starting to feel authorized to try to answer questions that would have been considered outside physics just few years ago.
I pretty much agree with the Platonist philosophy of Penrose (much less with his view about physics) but I think he never confused philosophy with physics. It seems to me that the main attitude is becoming “any sensible question is a physical question”. Of course I strongly disagree.
This in triplicate. What’s worse is that we are learning that very bright scientists nonetheless can produce very naive/shoddy philosophical thinking.
Yes Manyoso, “What’s worse is that we are learning that very bright scientists nonetheless can produce very naive/shoddy philosophical thinking.”
And also that not very bright scientists nonetheless can produce very naive/shoddy philosophical thinking.
OK, as a mathematician I’m really curious how Tegmark thinks you might go about proving that “some physical phenomenon has no mathematical description.” I guess it depends on what you mean by “mathematical description,” I mean naively everything has a mathematical description in that one can take a description (e.g. the visual description, but it could be anything) and use math to encode that. I assume Tegmark is talking about a predictive description of some sort, though perhaps not given the current state of theoretical physics. Even with a limited meaning for mathematical description I can’t see how one would go about proving it didn’t exist for some phenomenon.
Jeff McGowan,
Indeed, I remember in freshman calculus the “Spherical Cow” and wonder if Tegmark believes that because one can – crudely – mathematically model a cow as a sphere, if he believes there is some universe of spherical cows 🙂
Cheers,
Adam
Shaun,
Thanks for your comments. I think though that the multiverse (specifically the anthropic string theory multiverse) is unfalsifiable, in the long term. I know of no current or planned, or even conceivable experiment that could falsify this picture, since it makes virtually nothing in the way of significant predictions. For the one it is claimed to make (Weinberg’s), failure of the prediction (off by a factor of a thousand is pretty bad…) is explained away, either by an unknown measure factor, or by the “at least it’s not off by 10^120” argument.
In the paper I linked to, Banks gives good arguments that if you look at other things than the CC, and apply the anthropic string landscape argument logic, you get massive failures, so the whole thing should be experimentally ruled out. Arguments like his are just ignored, what is going on here is not the usual sort of science.
Of the things we’re likely to experimentally learn in the future, the most obvious case is the Planck polarization data, I hear due this summer. I’m no expert, but it seems there are “predictions” of a measureable effect, as well as “predictions” of no measureable effect. No matter what Planck reports, I see no possibility that it can count as evidence against the string landscape picture, and I’m pretty sure that it will reported as “new scientific evidence about the multiverse”, with scientists X, Y, and Z explaining how it agrees exactly with their multiverse model.
As for the sociology, ten years ago when I was writing my book, the whole anthropic landscape thing seemed so unserious and with such little support that it barely seemed worth mentioning (I did write about it, without much detail). I was pretty sure, like I think most people, that this was something that would just disappear of its own accord. I was very wrong then, and this has made me much less sanguine about the future, for instance about what will happen with obvious absurdities like Tegmark’s. Multiverse mania in the US dominates the popular coverage of the subject, and in physics departments from what I can tell the problem is one of “the best lack all conviction, the worst are full of passionate intensity”.
Jeff,
The same though occurred to me. A problem with the idea of a physical phenomenon that can’t be described mathematically, is that you can embed the English language in a mathematical structure, then any description you make in words is a mathematical description. What Tegmark needs for his falsification is some physics that can’t be described, something like “the peace of God, which surpasses all understanding”…
I wish people would stop referring to “Tegmark Type II” etc. It makes him sound as though he raised some profound questions.
Which he didn’t.
Jeff: Yes, our theories are mathematical, and they predict experiments well, but Tegmark wants to make an ontological argument that the physics is the math. If two distant electrons are entangled, then it is impossible to give a mathematical description of one electron independent of the other one. The usual way out of this paradox is to day that there is a mathematical action-at-a-distance, but not a physical one. To me, that says that the physics is not the math.
There are alternative explanations, such as saying that there is a physical nonlocality that is not directly observable. To me, this is unsatisfactory as it is like believing in psychic powers that can never be demonstrated in a controlled way, or believing in one of the unobservable multiverses.
Peter,
Regarding prospects for testing the multiverse (it looks like the multiverse of eternal inflation, not the string landscape, although the comment about extra spacial dimensions muddies that a bit), here’s something close to home this Monday:
http://physics.columbia.edu/colloquium-matt-kleban
CU Phil,
Probably will try and make that, although it’s just likely to lead to more tedious material appearing here…
A lot of Hawking-envy out there in physics-land… Which is strange: hands up, those who want to trade places. The point is well taken that, like the elderly Einstein, the media pay un-justified attention to his recent work. But I don’t think you can change that behavior; the human-interest story is just too compelling. What you can do is to exploit that attention to educate and re-direct the curious. I suppose that’s what Wilczek was attempting, like you said, but it still strikes me as a particularly clumsy attempt.
Thanks much for the Deligne interview link. Imagine a lecturer postponing a session because an auditor was absent!
Sorry for that Russ, I completely agree. He made the classification of course, but given that he only invented one of the classes in his classification and it is the “either he’s a genius who has seen deeper than everyone else, or he’s just talking nonsense” class, that doesn’t really count.
Thanks for the reply, Peter. I do think that people take heed of all the issues you’ve pointed out, just perhaps not the vocal people, at least not publicly. The reason why those issues aren’t enough to kill off the idea is that (and this does depend on priors, I suppose) the anthropic explanation of the cosmological constant, even if that far off, is still one of the best on the table (though I guess you’d disagree). If the cosmological constant problem were to be compellingly solved with some other mechanism people would give up on an anthropic multiverse pretty quickly (though maybe that is youthful naivety).
Also when I write “long term” I mean *long term* (i.e. potentially 100s of years) and I’m implicitly considering the possibility that the correct inflationary potential gets determined (if inflation is correct), and/or the standard model is found within the landscape and/or early collisions of inflating bubbles can get witnessed, and/or more catastrophic boundaries are discovered. The point is, any elapsed period of time during which any of the above is not achieved does “falsify” the multiverse a little, but substantial “falsification” will take this continuing to happen for many years and/or the more compelling alternative arriving.
Or, at least, that’s how I currently view things.
Hey Peter,
Here’s a link I’d like to get your view on:
http://iainews.iai.tv/articles/beyond-the-universe-auid-309
(sorry for going off topic)
Cheers
Asnant,
Never got around to mentioning that particular piece of multiverse mania, there just are too many… But I did write here recently about Mersini-Houghton’s claims, basically the same ones she is making in that piece, see
http://www.math.columbia.edu/~woit/wordpress/?p=5907
Peter,
The speakers for ICM 2014 are announced. Any rumors for yet?
mathematician,
Haven’t heard any, just speculation about the obvious candidates (for the Fields). If I do hear any interesting rumors, will blog about it (or, if I don’t, may do this anyway to try and generate some…). But, so far, I got nuthin.
Meanwhile, ideas for the next european circular hadron collider at 100 TeV are being collected.
In his SciAm article, Tegmark writes:
” … all their arguments involve what logicians know as “modus ponens”: that if X implies Y and X is true, then Y must also be true. Specifically, they argue that if some scientific theory X has enough experimental support for us to take it seriously, then we must take seriously also all its predictions Y, even if these predictions are themselves untestable (involving parallel universes, for example). ”
Well, I dont see why we have to take seriously _ALL_ its predictions. Most theories are only applicable in a limited domain of energies, scales, or other simplifying assumptions. Eg, Newton’s gravity theory. And who hasn’t heard of the “spherical cow” simplifying assumption?
re Tegmark’s comment:
” … falsify the mathematical universe hypothesis by demonstrating that there’s some physical phenomenon that has no mathematical description … ”
Seems to me most complex systems _don’t_ have a tractable mathematical description.
Try creating a mathematical description of human consciousness & self-awareness.
Too hard?
Try to create mathematical description of the c.elegans’ (a nematode worm) behaviour. It has only 109 neurons.
Still can’t do it?
QED, I have falsified Level IV multiverses.
@TomH
“Try creating a mathematical description of human consciousness & self-awareness.
Too hard? ”
Not for Max. You must’ve missed his new consiousness paper.
http://arxiv.org/abs/1401.1219
Tom H,
I don’t have a problem with Tegmark’s claim that if some parts of a theory are well-tested and we have lots of reasons to trust them, then it’s reasonable to believe that other implications of these parts of the theory will work out, even if we can’t test them. Of course this all assumes you are talking about a theory you understand well, so you know what its implications are, and you have serious and compelling tests of the relevant parts of the theory. The situation with Level II multiverses, which are supposed to be predictions of theories like the string theory landscape, is that we don’t understand the theory at all, and to the extent we understand it have zero evidence for it (or, as Banks argues, good arguments against it). I also see no serious argument for how we are supposed to get such evidence in the future.
Tegmark’s tactic here is to argue based on assumptions that are nowhere near where science is or has any hope of getting, but are close to the place he wants to end up. It’s kind of like arguing with someone about the existence of God, and you start by saying “assume that an Angel with gold tablets appears in front of you….”
As for falsifying Level IV, Tegmark is certainly not discussing “tractable” mathematical descriptions. As he states his argument, to falsify his hypothesis you need to show there is no possible mathematical description of some phenomenon, not just be unable to find a tractable such description. It has been pointed out here that “no possible mathematical description” seems to be equivalent to “no possible description”, since one can embed a natural language like English in a mathematical structure. Tegmark does claim “consciousness can’t be described using mathematics” as a possible falsifying example, but I’m not sure what that means, unless you are a non-materialist, believing consciousness is not a physical phenomenon, in which case this has nothing to do with his hypothesis.
Tegmark’s comment:
” … falsify the mathematical universe hypothesis by demonstrating that there’s some physical phenomenon that has no mathematical description … ”
I think Tegmark’s statement itself is problematic. From what I can get from his work, he makes a claim of ontology not the less radical claim of description. Here he gives a falsifying example for the “uncontroversial” claim as proof that his “ontology” theory is scientific. Doesn’t work. If he is only claiming description, so what? Description does not beget ontology.
Off topic,
Peter, I see your first post for NEW was 3-17-04. Do you have anything planned for the ten year anniversary of NEW?
One cannot escape the implication that, on the basis of current theoretical knowledge, the String Landscape is ruled out by experiment.
Besides being experimentally ruled out, the whole Landscape thing doesn’t work anyway
My personal conclusion from all of this analysis, is that the theory of CDL tunneling provides no positive support for, and lots of negative evidence against, the proposal of a String Landscape…
When combined with the phenomenological challenges I presented in Section 2, I conclude that the String Landscape is an hypothesis of dubious validity.
^
if the string landscape is of dubious validity what does this mean for string/M-theory and offshoots like adS-CFT?
Jim Akerlund,
Well, I’ll be on a spring break vacation in Northern Italy, nothing planned yet.
SUSY,
For string/M-theory, just that even a pathetic last-ditch, pseudo-scientific effort to salvage unification via string/M-theory doesn’t work. For adS/CFT, nothing at all.
It seems to me that it would be quite easy and simple to empirically refute any version of the multiverse hypothesis, including Tegmark’s approach. The test is that if we ever happen to meet an omniscient and honest being, then the being would affirm the sentence, “Tegmark’s hypothesis is true” if and only if the hypothesis is true and would affirm the negation if and only if false. Now granted, we don’t happen to be able to carry out this decisive experiment given current conditions, but the availability of the future possibility of this decisive test clearly shows that it is falsifiable in principle, and hence fully scientific.
Peter,
Your blog is always an inspiration for me. Today I have one point to ask: isn’t the best prediction of the cosmological constant simply that it is the zero-point energy of the box defined by the universe? This gives a prediction (1/Radius of the universe)^2 for the cosmological constant, very near to the observed value, with an error of the order 50%.
The prediction has the disadvantage that the constant would need to change with time. But the experimental data is not yet good enough to allow checking for such a decay. Is there a reason that this “prediction/postdiction” is not discussed more often?
Peter, do you find Tom Banks reasoning sound on scientific grounds?
How would you respond to a string theorist who would argue that the moduli of the Yau-Calibi space cannot be determined on a priori grounds but only through experiment and observation, and that we do not have the technology to test this. Once this universe moduli could be thus determined string theory becomes completely predictive with only 1 parameter.
Both of these are off-topic, so, please, do not try and turn this into a discussion of the CC or moduli stabilization, about which I don’t think there is anything to say that hasn’t been said hundreds of times here and elsewhere.
SUSY,
There are plenty of problems with string theory models, Banks is pointing out some, I’ve discussed others here and in my book. The standard answer from string theorists is that we don’t understand string theory well enough to know how severe these problems are. If we understood string theory better, maybe they would go away, is the argument, but that seems to me just pure wishful thinking.
There are typically dozens to hundreds of Calabi-Yau moduli parameters, not 1. In addition, you need to add some physical mechanism to fix the parameters (e.g. KKLT moduli stabilization), which introduces yet more physics you don’t understand, ensuring you can calculate nothing.
Susanne,
I’m not sure exactly what argument you have in mind, the distance scale of the CC I would have thought was 10^-3 eV (since it is the 4th power of this). If you do want to relate it to the size of the universe you do have the problem that it is supposed to be changing, which is presuamably testable.
cthomas,
“if we ever happen to meet an omniscient and honest being, then the being would affirm…”
“the availability of the future possibility of this decisive test clearly shows that it is falsifiable in principle”
I don’t think, to ask someone is what is considered a scientific experiment and even the possibility to do so is not falsifiability.
Cspan — my bad. Failed attempt at sarcasm on my part. Not very humorous, in retrospect.
Best regards.
Thanks for the article about Hawking.
IMO, Melnick is being too generous – much of Hawking’s o
overblown reputation is due to his wild self promotion
rather than media hype.
For a great example, read his latest autobiography
where he claims to have created a successful
approach to quantum gravity and
explained the origin of the universe. via his No Boundary proposal
Both claims are completely false, but my dishonestly
presenting mere speculations as established scientific fact in
popular books, Hawking has created an image of having done
far more than he actually has.
For those interested the play about Grothendieck’s life, Grothendieck’s Dream of the Rising Sea, by Adrian Heathcote, is available here:
https://independent.academia.edu/AdrianHeathcote
The link at Leila Schneps site is broken — has been for some time.
Nice article in “New Scientist”. From layperson’s point of view, does not this remind of the ultraviolet catastrophe in the early 1900 physics that started the quantum era, only in reverse? There, classics dictated continuous spectrum where micro structure was discrete…. here, classic theory says discrete wall (event horizon) where on micro level (Planck scale?) there could be still some continuity. Look for a theory with a smudged event horizon? Would be really funny and ironic if this “little spot on the horizon” sparked a new theoretical revolution, wouldn’t it? 🙂
Is the Universe a Simulation? Edward Frenkel in the New York Times:
http://www.nytimes.com/2014/02/16/opinion/sunday/is-the-universe-a-simulation.html