Polchinski on the Landscape

At the recent Solvay conference there was extensive discussion of the Landscape, and I’ve already discussed here Michael Douglas’s write-up of his talk on the subject, entitled Understanding the Landscape. Now Joe Polchinksi’s rapporteur talk on the subject has appeared; it’s entitled The Cosmological Constant and the String Landscape. Polchinski is essentially making the same argument as Susskind makes in his recent book, and his argument has pretty much the same problems that Susskind’s has, which I discussed in detail in an earlier posting. However, his article is written for physicists, not for the general public, so he is making a much more technical version of the argument. It’s probably the best version of the case for the string theory anthropic landscape available, so worth reading carefully.

Polchinski begins by explaining why the cosmological constant problem is difficult. He divides possible solutions to it into ones where the CC is fixed, and ones where it is adjustable. The problem with the idea that the CC is fixed and calculable is essentially that all the contributions to the vacuum energy that we know about give values of the CC that are far too large. These include things like fermion loops and the Higgs potential in the standard model, supersymmetry breaking in supersymmetric extensions of the SM, and Planck scale effects in theories of quantum gravity. He goes on to explain why it is difficult to try and modify the theory of gravity so that it won’t couple to these sources of vacuum energy.

There is a wide range of ideas about how to select a small CC in theories where the CC is adjustable, and Polchinski describes several of them and what problems they have. Some of these ideas naturally explain a small CC in an empty universe, but not in our matter-filled universe. Finally he ends up with the anthropic explanation: the CC is small because if it wasn’t we wouldn’t be here. He does note that:

Of course, the anthropic principle is in some sense a tautology: we must live where we can live.

this carries a footnote comparing the anthropic principle to Darwin’s theory of natural selection:

Natural selection is a tautology in much the same sense: survivors survive. But in combination with a mechanism of populating a spectrum of universes or genotypes, these ‘tautologies’ acquire great power.

Susskind makes the same sort of claim that the anthropic landscape is much like the theory of evolution, and I think this is extremely dangerous and unwise. There is a mountain of scientific evidence for the theory of evolution and none for the anthropic landscape. It is very important that this distinction be made, and trying to blur the difference between these two very different situations is not something a scientist should be doing at a time when science in general and the theory of evolution in particular is under attack by the forces of the religious right. When I was in Niger one of my travel-mates was a creationist who was generally annoyed at what he saw as the arrogant way scientists dismiss his view of the world. We discussed cosmology, and I tried to tell him a bit about inflation and what aspects of the universe it was supposed to explain. In response he asked me why he shouldn’t just go with his preferred explanation: it was all the doing of the “Big Kahuna”, as he called the deity. I tried to explain about the scientific method: your theory is supposed to make distinctive predictions that you can go out and check by making observations. I think I had some success in getting this idea across, but I don’t see any way I could have defended to him something like the anthropic landscape. It’s not legitimate science since it makes no real predictions that you can use to see if the idea is right or not. What’s at issue here is the credibility of science itself, and physicists who care about this credibility should not be claiming that an idea like the anthropic landscape has the same status as heavily tested and verified theories like that of evolution.

Polchinski goes on to repeat the analogy with evolution a bit later, and I actually don’t understand at all what point he is making here, when he argues that maybe only the anthropic principle determines the CC:

Thus we should seriously consider the possibility that there is no other selection mechanism significantly constraining the cosmological constant. Equally we should not stop searching for such a further principle, but I think one must admit that the strongest reason for expecting to find it is not a scientific argument but a psychological one (footnote): we wish fundamental theory to be as we have long assumed it would be.

and the footnote is:

Again, the Darwinian analogy is notable.

Personally I’m agnostic about whether the CC is computable from first principles or not. As a scientist, one’s job is to come up with theories and extract predictions from them to see if they are right. If you have a theory that says the CC is not computable, that’s fine, but then you have to just forget about the CC and find something that your theory does predict so you can test it. You can’t go around claiming that the fact that your theory is compatible with any value of the CC is somehow some sort of scientific success and evidence for the theory. The problem with a theory where all values of the CC are a priori equally likely is that it’s vacuous (as far as the CC is concerned). Its implications are exactly the same as throwing up your hands and saying “I have absolutely no idea what determines the CC, it could be anything”.

The fact that we are here and observe galaxies does put constraints on the CC, and Polchinski would like to make much of this. He’d like to claim that the anthropic landscape predicts that the CC is a random variable, and then, given the fact we see galaxies, it would have an expectation value about an order of magnitude higher than its observed value. He defends the theory against this mismatch by quoting Galileo’s defense that his theory might be inaccurate but was a lot better than Aristotle’s, then writes:

This order of magnitude may simply be a 1.5 sigma fluctuation, or it may reflect our current ignorance of the measure of the space of vacua

One problem with all this that Polchinski doesn’t mention at this point is that the anthropic constraint is not on the CC but on a combination of the CC and Q, the normalization of the primordial temperature fluctuations. Assuming both are random variables, the observed CC is way off what one expects. One can deal with this by just assuming that the CC is a random variable, but Q isn’t for some reason. This gets into the fundamental problem with the string theory anthropic landscape: it doesn’t just not predict the CC, it doesn’t predict anything at all. As far as one can tell, it’s consistent with just about anything. It doesn’t make any predictions, so it’s really not a legitimate scientific theory at all. One can try and claim that it really is a scientific theory, and that it does predict something: we are at some randomly chosen (according to a not yet understood measure) point in the landscape compatible with our existence. The problem with this (as Polchinski notes) is that there is a long list of properties of the world that appear to be rather special and statistically highly disfavored by any likely measure: the theta-angle is very small, proton lifetime is very long, number of generations is small, etc., etc. If one actually took the string theory anthropic landscape seriously as a theory, one would have to abandon it in face of these falsifying observations.

The crucial question for whether the anthropic landscape is science or not is whether it makes any testable predictions. Polchinski doesn’t at all address the question of whether further study of the landscape will lead to any prediction of anything, presumably because like everyone else he has no plausible idea for how this could come about. He does claim that Weinberg’s 1987 arguement makes 5 successful predictions or postdictions:

The anthropic argument is not without predictive power. We can identify a list of post- or pre-dictions, circa 1987:

1. The cosmological constant is not large.

2. The cosmological constant is not zero.

3. The cosmological constant is similar in order of magnitude to the matter density.

4. As the theory of quantum gravity is better understood, it will provide a microphysics in which the cosmological constant is not fixed but environmental; if this takes discrete values these must be extremely dense in Planck units.

5. Other constants of nature may show evidence of anthropic constraints.

Calling these successful predictions seems to me a huge stretch. 1. follows from a tautology, 2. and 3. are the same “predictions” I get by saying I have no idea what is going on here (including having no good reason to believe the CC is zero). 4. isn’t an experimental prediction at all, and 5. is so vague as to be completely meaningless.

Polchinski ends up his defense of the landscape by quoting Dirac:

One must be prepared to follow up the consequences of theory, and feel that one just has to accept the consequences no matter where they lead.

The problem with this is that Dirac undoubtedly didn’t have in mind the idea that if your theory has no experimental consequences, you should accept the idea that you can’t ever predict anything. Obviously, you should give up on your theory at that point, and this is what Polchinski and others show no signs of being willing to even consider. Back in 1998, in lectures at the SLAC Summer Institute, he wrote:

On Lance Dixon’s tentative outline for my lectures, one of the items was ‘Alternatives to String Theory.’ My first reaction was that this was silly, there are no alternatives…

and his attitude doesn’t seem to have changed since. He and others never discuss the possibility that string theory is simply a wrong idea, a possibility for which the landscape provides overwhelming evidence. This seems to be something he is unwilling to seriously consider.

There’s one peculiar reference in his paper. When he refers to the problem that the landscape can’t even predict the one thing people originally hoped it would be able to, the scale of supersymmetry breaking, he writes:

An obvious question is whether we can understand the supersymmetry-breaking scale (see [68] and references therein). Is low energy supersymmetry, or some alternative [69, 70], favored?

[69] is a reference to split supersymmetry, and [70] is a reference to a paper by Fox et. al called Supersplit Supersymmetry. The strange thing about the apparently serious reference to [70] is that the paper in question is actually an April Fool’s joke (check the date on it…). The authors were making fun of how supersymmetric phenomenology is being pursued, and specifically of the idea of split supersymmetry. In “supersplit supersymmetry”, all superpartners are pushed up to unobservability at the Planck scale, solving all the problems caused by the lack of observation of effects of supersymmetry. For any conceivable purpose, the supersplit supersymmetry model is precisely the standard model. The joke is that particle physicists have become so enamored of supersymmetry that they would happily study a supersymmetric model inherently indistinguishable from the much, much simpler standard model. Part of being unwilling to consider the idea that superstring theory might be wrong is being unwilling to consider the idea that supersymmetry might be wrong, and thus, instead of referring to the standard model, one adopts the supersplit supersymmetry model.

The funny thing about this April Fool’s joke paper is that, according to SPIRES, Polchinski’s is the sixth paper to cite it. Looking through these six papers, only one of them seems to be aware of the joke, with a footnote to the reference pointing out that the paper appeared on April Fool’s day and that the model was equivalent to the standard model. Some of the particle theory community now seems to think that the idea of a vastly more complicated model that is inherently indistinguishable from the standard model but is in some sense “supersymmetric” is a model worth taking seriously and making reference to. Yet another weird thing about this paper is that there is one trackback to it, and this trackback was generated by a comment from LambchopofGod on a Cosmic Variance posting. Presumably it’s a bug, not a feature, that any commenter on an approved blog can generate trackbacks at the arXiv, but seeing the way the arXiv handles trackbacks, who knows. In any case we’ll see at some point if trackbacks to the Polchinski paper and the Fox et. al. paper get generated from this posting. Hopefully at least a trackback to the Fox et. al. paper will appear, since many readers of that paper don’t seem to realize that


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63 Responses to Polchinski on the Landscape

  1. JC says:

    Besides Witten defecting from string theory, what else could possibly make Susskind, Polchinski, and others give up string theory? It seems like all this anthropic silliness over the last few years isn’t enough.

  2. woit says:


    I’m sure Susskind and Polchinski will give up on string theory if and when someone comes up with a much better idea and the physics bandwagon changes direction to follow it. The weird thing is that it seems that deciding that the theory can’t predict anything doesn’t seem to be enough to make them give up on it. If you had told me a few years ago that this would happen, I would have refused to believe it. I’m still having trouble…

  3. JC says:

    I’ve always wondered what would be going through the mind of a retired theorist who had spent his/her entire working life on a theory which turned out to be either wrong and/or vacuous in the end.

    I get the impression that for some folks, the anthropic stuff is almost like a last ditch attempt to salvage their life’s work into something meaningful and/or at least to slow down the decline to oblivion and/or meaninglessness.

    I would guess that knowing that one’s entire life’s work was a huge boondoggle, isn’t exactly something to be proud about in retirement.

  4. Chris Oakley says:

    “A new scientific truth does not triumph by convincing opponents and making them see the light, but rather because its opponents eventually die, and a new generation grows up that is familiar with it.”

    — Max Planck, A Scientific Autobiography and Other Papers, 1949

    This may also be true about adherents of a non-predictive methodology admitting that they were backing the wrong horse.

  5. JC says:

    Allegedly Lorentz was a true believer in the ether to the very day he died. (I don’t have a reference handly offhand).

    I wouldn’t be surprised to see that other physicists of Lorentz’s generation (ie. mid-late 19th century) were all true believers in the ether, all the way to their graves.

  6. Tony Smith says:

    Peter says “… Susskind makes the same sort of claim that the anthropic landscape is much like the theory of evolution …”.

    I would hope that everyone (even Joe and Lenny) could agree that the “theory of evolution” includes at least the following structures:
    1 – a fairly detailed fossil record showing an understandable progession of organisms from early blue-green algae to oxygen production … etc … to dolphins in the sea and humans on land; and
    2 – a crude understanding of genetics at the molecular level and that mutations can cause genetic change.

    Maybe people can argue about the punctuations in puntuated equlibrium speciation, etc, but there IS a progressive fossil record and there IS a molecular mechanism for genetic change.

    My question to Joe and Lenny would be:
    Can you show me where the “anthropic landscape” contains ANY comparable structures ?

    Where is a string-theory-model of a progressive fossil record,
    i.e, a series of states leading from the Big Bang to our present Earth arranged in an understandable progression like the series of fossils in our fossil record ?

    Where are the string-theory-model laws (NOT vague hand-waving) that govern how string-theory states can mutate from one to another a la molecular genetics with mutation ?

    Unless and until Joe and Lenny can put up such examples, they should shut up about the Landscape being “much like the theory of evolution”.
    Of course, as long as their audience (present-day superstringers = 90% of USA theoretical particle physicists) is sufficiently sheep-like to buy their stuff, they are not likely to “shut up”. Rather, they are more likely to shout louder and attempt to drown out any voices of reason.

    Tony Smith

    PS – I am particularly disappointed in Joe. Years ago he did calculations that could be compared with experiment, and if he had stuck to his guns, he could have claimed predictions against then-conventional wisdom, which predictions were later validated. For example, in Nuclear Physics B221 (1983) 495-523, entitled “Minimal Low-Energy Supergravity”, Joe Polchinski (with Alvarez-Gaume and Wise) said:
    “… Weak-interaction breakdown occurs for top-quark masses between 100 and 195 GeV. If we take A to have its value in the Polonyi model … the top-quark mass lies in the smaller range 140-195 GeV. … The renormalization group equation … tends to attract the top quark mas towards a fixed point of about 125 GeV. …”.

    However, Joe et al lost their nerve and caved when in 1984 CERN claimed to find the T-quark around 45 GeV.
    Instead of saying that the CERN 45-GeV “discovery” was wrong (as indeed it was, with CERN embarrassingly “undiscovering” it over the next several years), they seem to have followed the sheepish herd of consensus exemplified by this quote from Mohapatra’s book Unification and Supersymmetry:
    “… An ingenious … method has been proposed by Alvarez-Gaume, Polchinski, and Wise … It is interesting that m_t lies in the range [between] 100 GeV …[and]… 190 GeV.
    The recent discovery of the t-quark in the mass range of 40 to 60 GeV therefore rules out the simple-minded analysis …”.

    If Joe et al had stuck to their guns from 1983 to 1994, Fermilab data would have vindicated their predictions, and they could have claimed a great success for theory vindication by experiment.

  7. Folks that think they know and understand Evolution Theory would really do good in reading Ernst Mayr: Ernst Mayr (EDGE) and Ernst Mayr (Amazon).

    At least according to what i’ve read and heard, there’s a huge gap between what is being called “evolution theory” and what contemporary neo-Darwinism actually is (the tantalizing evidence goes from fossils to virus and bacteria drug resistence, i.e., from ancient to modern times).


  8. Arun says:

    Most probably it is because of my shortcomings, but I do not see how any of the proposals of Polchinki’s talk solve the problem posed at the beginning – namely, the gravitation of the Lamb’s shift energy.

  9. woit says:


    The idea of anthropic landscape solution to the CC problem is that for some particular points on the landscape all the large contributions to the CC like the ones from electron loops just about exactly cancel, leaving a CC close enough to zero for galaxies (and us) to be able to develop.

  10. As you know, I was of course aware that Fox et al is a joke. Furthermore, at the time of the posting I believed, and I still do believe, that Sean thought it was a joke too, and that his reference to it was an extension of the joke. But I have no experimental evidence for this belief of mine……

  11. Sean Carroll says:

    I think that more people got the April Fool’s joke than Peter is giving them credit for.

  12. boreds says:

    Yep, citing the paper hardly indicates that he doesn’t get the joke.

  13. Arun says:

    So there a near-continuum of landscape states, all with our standard model as the low-energy limit, but differing in contribution to the CC by stringy fields, so that in one of them, the CC comes out right? Or is it more that landscape vacua with the wrong CCs also have the wrong low energy physics?

    I’d feel a lot less unhappy if it were the latter.


  14. Arun says:

    We can think of Fig. 2 to good approximation as representing the shift of the electron zero point energy in the environment of the atom or the nucleus. Thus we must understand why the zero point energy gravitates in these environments and not in vacuum, again given that our vacuum is a rather complicated state in terms of the underlying fields. Further, if one thinks one has an answer to this, there is another challenge: why does this cancellation occur in our particular vacuum state, and not, say, in the more symmetric SU(2) × U(1) invariant state of the weak interaction? It cannot vanish in both because the electron mass is zero in the symmetric state and not in ours, and the subleading terms in the vacuum energy (1.1) — which are still much larger than the observed V — depend on this mass.

    So, either the landscape vacuum does the appropriate CC cancellation at one scale, and we still have the puzzle of which scale, or the landscape vacuum manages the magic of CC cancellation at all scales?

  15. woit says:

    Sean and boreds,

    Looking at the six papers that referenced Fox et. al., my guess was that some knew it was a joke, but it is pretty clear that some didn’t. I still find Polchinski’s reference to it strange. Undoubtedly he knew about the joke, and maybe his reference to it was some sort of self-deprecating humor. But when there’s a huge question about the predictivity of your research program, and you’re writing an article defending it, ignoring the predictivity problem and putting in a reference to a joke paper where the lack of predictivity is the joke, seems to me exceedingly weird.

  16. woit says:


    It’s the former. There’s no known reason why having the right small value of the CC would imply getting anything else right about low energy physics.

    In the landscape, the CC is the same at all scales. There is one section of Polchinski’s article where he discusses the possibility of a version of gravity that doesn’t couple to the CC at all scales, but this has lots of problems that he explains.

  17. Arun says:

    In the landscape, the CC is the same at all scales.

    How is that magic accomplished?

  18. woit says:


    All I mean is it behaves like a standard CC in Einstein’s equations. This is just a constant. Probes of any wavelength see the same CC. This is standard gravity. Polchinski is discussing the idea of modifying gravity.

  19. Who says:

    Going back to your 23 August 2005 post
    which is closed so I cannot add a comment,

    the book is available for order from amazon.uk for $21

    or more precisely 12 pound ster. (hardcover)


    the availability date they give there is 16 march 2006

    ordinary US amazon gives a date of 25 april 2006 and has one review, but lists no price

    so it seems that amazon.uk is already shipping

  20. woit says:

    About the book,

    The information on Amazon isn’t correct. Last I heard, publication date in England is June 1. A few weeks ago I went over the final proofs, so they should start being able to print books soon, but I haven’t seen any yet. Publication in the US should be sometime in September. I’m just starting dealing with the production people here for that version. It will probably have a different preface.

  21. anon says:

    “It will probably have a different preface.” Oh, I see. The British version is different to the American one; it has a topless girly on page 3.

  22. Lubos Motl says:

    Peter, you are kind of crazy if you think that Polchinski does not realize that supersplit SUSY is a joke.

  23. Not a Nobel Laureate says:

    To put this anthropomorphic principle in perspective imagine the reaction in the condensed matter community if someone invoked the same principle to “explain” high Tc superconductivity.

    Nothing more pathetic than a group of relatively smart people believing their own bullsh*t.

    Henry Kissinger sum it up best after his retirement to academia.

    “Why are academic battles so fierce?”

    “Because the stakes are so low.”

    So it is with strings and their proponents.

  24. Hech Baan says:

    Dear Not a Nobel Laureate,

    Anyone should understand that anthropic principle isn’t part of the string/M-theory. It’s a temporary way of making sense of some results. When we know more we’ll be able to make predictions without relying on the anthropic principle.

    Rest assure that if something is obvious to almost everyone then it’s obvious to the scientists too.

  25. Peter, there’s another difference between natural selection and the anthropic principle, one that to my mind is even more basic than testability. This is that natural selection is an “algorithmic workhorse” — a mechanism for amplifying low-probability events to higher probability. Start it up, and it takes you the rest of the way. It’s a tautology with oomph, something any mathematician should recognize. Whereas the anthropic principle is an oomphless tautology.

  26. Not a Nobel Laureate says:

    Hech Baan wrote

    “Anyone should understand that anthropic principle isn’t part of the string/M-theory.”

    No, but a number of string/M-theory proponents invoke it to avoid question the merit of having so many in the field pursue this line of research.

    “It’s a temporary way of making sense of some results.”

    It’s a way of avoiding physical reality.

    “When we know more we’ll be able to make predictions without relying on the anthropic principle.”

    That doesn’t sound very promising given that you can’t make any testable predictions by relying on the anthropic principle.

    “Rest assure that if something is obvious to almost everyone then it’s obvious to the scientists too.”

    Not in my experience.

  27. Who says:

    Obviously what gives natural selection oomph is reproduction.
    Polchinski’s “survivors survive” misrepresents the tautology, which is more like “the prolific proliferate”—-reproductively successful (genotypes) succeed in reproducing.

    Of course, the anthropic principle is in some sense a tautology: we must live where we can live.

    Natural selection is a tautology in much the same sense: survivors survive. But in combination with a mechanism of populating a spectrum of universes or genotypes, these ‘tautologies’ acquire great power.

    My comment:

    One can imagine a centralized “mechanism of populating” a range of possible genotypes which operates randomly—where individuals do not reproduce individually but are produced by a central machine. Each is the expression of a random sequence: almost no individuals are viable—most come out of the machine dead or as unorganized mess.

    If I understand Scott Aaronson’s remark, such a scheme has no oomph. It does not amplify low-probability instances of organization.
    If his point is valid, then Landscape philosophers won’t get anywhere until they think of a way for nice universes to reproduce and thereby proliferate.

  28. Hech Baan says:

    Dear Not a Nobel Laureate,

    Let’s face it string/M-theory isn’t perfect, but it’s the best theory we have today. It’s a pity that the theory is so complex that not everyone can appreciate the beauty and predictive power of it.

    Sooner or later we will make a testable prediction without relying on the anthropic or any other questionable principle. At the same time we shouldn’t overestimate the anthropic principle’s role.

    My advice to you is: be patient. There are much simpler things we don’t know answers yet (e.g. twin prime conjecture). Understanding physical reality is the most complex problem. Nobody expects quick or short answers. If the anthropic principle will get us there then so be it.

  29. knotted string says:

    Dear Hech,

    Your belief that eventually a testable prediction will arise seems to have absolutely no scientific validity. It is just a belief, like the beliefs of religion.

    The world has been patient for 20 odd years with various forms of string theory, and you advise us to be patient?

  30. anonymous says:

    Excellent post, “Who”. Nicely expresses the fundamental difference between the two.

  31. Arun says:

    I’m still scratching my head as to how the landscape produces a cosmological constant that is the same at all scales, when the physics accessible to us is not doing so. How does the landscape vacuum arrange for the appropriate cancellations at all scales?

  32. woit says:

    “Peter, you are kind of crazy if you think that Polchinski does not realize that supersplit SUSY is a joke.”


    You don’t even bother reading what I write. You seem to have missed my comment about Polchinski:

    “Undoubtedly he knew about the joke”

  33. Thomas Larsson says:

    Both Polchinski’s paper and the supersplit paper (v1) were uploaded on March 31. If Polchinski’s paper was also intended as an April’s fool joke, he surely fooled me.

  34. island says:

    Hech Baan Says:

    Let’s face it string/M-theory isn’t perfect, but it’s the best theory we have today.

    Didya hear the one about the string-tailed cat in a room full of rocking chairs?

    … or the one about the stringy-haired hippie who wondered into barber camp?


    This strongest implication of the anthropic connection to the forces of our universe is through evolutionary theory since the anthropic constraint on the forces indicates that there is very possibly a mechanism that enables the universe to (((convolve))) it’s characteristics inherently forward to higher orders of entropic efficiency, just like we humans did when we evolved from apes to harness fire… and beyond.

    This obvious extension can’t be ignored because the TOE becomes the ToE when the anthropic principle explains “why” the forces cannot be unified.

    Which has absolutely nothing to do with string theory, but you’d have to a real air-head to think that there is no connection between evolutionary theory and the anthropic principle.

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  36. Tony Smith says:

    Who said “… Landscape philosophers won’t get anywhere until they think of a way for nice universes to reproduce and thereby proliferate …”.

    Polchinski, in hep-th/0603249, said “… while it is difficult to select for a single vacuum of small cosmological constant, it is extremely easy to identify mechanisms that will populate all possible vacua –
    either sequentially in time, as branches of the wavefunction of the universe, or as different patches in an enormous spatial volume.
    … if the many vacua are metastable: inflation and tunneling, two robust physical processes, will inevitably populate them all …
    But this is all that is needed! … Thus we meet the anthropic principle….”.

    In other words, Polchinski and the anthropic / landscape people are happy with reproduction and proliferation by “dumb” processes like inflation and tunneling that don’t act to select “nice universes” – Who described such processes as “… a centralized ‘mechanism of populating’ a range of possible genotypes which operates randomly – where individuals do not reproduce individually but are produced by a central machine. Each is the expression of a random sequence: almost no individuals are viable – most come out of the machine dead or as unorganized mess …”.
    people like Who (and me) think that the processes of reproduction and proliferation should act to select “nice universes”,
    in the sense that evolution by genetic mutation and environmental requirements acts to select “fit” organisms.

    In other words, my view is that nature is built upon processes that, in Who’s words, “… amplify low-probability instances of organization …”,
    any landscape, anthropic principle, or whatever that just sort of randomly produces stuff will never produce any physics other than, in Who’s words, an “unorganized mess”.

    Tony Smith

    PS – As to how to build a process that will “… amplify low-probability instances of organization …”, maybe it might be productive to generalize the quantum computer / spin network viewpoint of Paola Zizzi expressed in gr-qc/0304032.
    It also might be nice to look closely at exceptional algebraic structures, because, since they are “special” mathematically, they might be good at selecting/amplifying “special” physics structures.
    In my view, it would be nice if such work received funding on the order of the current level of superstring funding. After all, as knotted string said to Hech Baan: “… Your belief that eventually a testable prediction will arise [from conventional string theory] seems to have absolutely no scientific validity. It is just a belief, like the beliefs of religion. The world has been patient for 20 odd years with various forms of string theory, and you advise us to [continue to] be patient? …”.

  37. Hech Baan says:

    Dear knotted string and Tony Smith,

    I wouldn’t call it a belief. I would call it an educated guess. It has the same scientific validity as our confidence that one day we will prove the Riemann Hypothesis. The world was patient for almost 150 years with various approaches to prove the Riemann Hypothesis. And in that case I ask you to be patient too.

    Alternatively, join the group of scientists addressing the current problems to appreciate the beauty and complexity of the nature (be it distribution of primes or Quantum Gravity).

  38. woit says:

    Hech Baan,

    No, belief in string theory does not have ths same scientific validity as belief in the Riemann Hypothesis. There is overwhelming numerical evidence that the Riemann Hypothesis is true, zero experimental evidence for string theory. In the case of function fields (which are closely analogous to number fields), the Riemann hypothesis has been proven, which is one of several reasons to believe that a proof for the standard Riemann Hypothesis will be found. I’ve heard this analogy repeated elsewhere, but sorry, it really is complete nonsense.

    And please, everyone, if you have something to say about the Polchinski paper, please do so, if you want to rant in an empty way about the anthropic principle in general, do this elsewhere.

  39. I think Polchinski’s paper raises a lot of interesting issues. I wonder if anyone can comment on what he means by “post-selection” of the cosmological constant [the last paragraph before his conclusion]?
    Meanwhile, see the final sentence of
    for an interesting new suggestion as to how the CC problem might ultimately be solved……

  40. Tony Smith says:

    Hech Baan said: “… Dear knotted string and Tony Smith … I ask you to be patient … Alternatively, join the group of scientists addressing the current problems to appreciate the beauty and complexity of the nature …”
    and went on to say, further:
    “… CC paradox: ‘Landscape is huge. The probability that I live in a universe with a small CC is almost zero. In spite of this, I live in one of them. Now how is that?’
    A possible solution – Antropic principle …
    … If you find a better solution … then you can apply it to the CC paradox. Good luck. …”.

    To Hech Baan. Please don’t assume that only conventional string theorists can deal with the CC paradox. For example (and here I am NOT mentioning my work to get into a discussion of its merits because Peter does not want his blog to get into such things, but am only mentioning it as one concrete example of an alternative to conventional string/M theory ),
    based on a generalization of Irving Segal’s conformal structures related to gravity, I can and have calculated the present value of the ratio
    Dark Energy : Dark Matter : Ordinary Matter
    with the result 0.73 : 0.23 : 0.04
    which is pretty close to the WMAP results.
    Calculations are on the web as a pdf file at CERN CDS preprint EXT-2004-013
    but they are not on the Cornell arXiv because I am blacklisted there.
    They can also be found, with more details, in html format at

    Maybe my work is right, maybe it is wrong, or maybe it at least contains some seeds from which a useful theory that can be used to calculate (not relying on anthropic stuff) the CC / Dark Energy : Dark Matter : Ordinary Matter ratios that we see experimentally.

    I am NOT saying, as Hech Baan is saying about conventional string/M theory, that my work is “the best theory we have today”.

    I am only saying that it seems to give a more concrete result than conventional string/M theory, and is therefore a possible counterexample to Hech Baan’s assertion that conventional string/M theory is “the best theory we have today”.

    There may be many other models that may turn out to be more useful than either my model or conventional string/M theory (for example, some forms of loop quantum gravity, spin foams, etc).

    My point is NOT to try to sell my model.
    My point is that ALL possible approaches should be funded and explored,
    that it is quite likely (given 20+ years of work by hundreds of very smart well-funded people on conventional string/M theory, resulting in failure to produce concrete results that can be compared with experiments)
    that being “patient” and “join[ing] the group of [conventional string/M theory] scientists …” in such things as the anthropic landscape may well only lead theoretical physics into a Dark Age.

    Tony Smith

  41. woit says:


    That paper doesn’t offer any way to solve the CC problem. Right now the anthropic “prediction” of the CC is too high by at least one order of magnitude, more if you let Q vary. The argument of this paper seems to be that if you observe planets in certain dwarf galaxies, then you could claim that the CC is too high by as much as three orders of magnitude, even keeping Q fixed.

    This doesn’t offer any positive prediction about the CC, it just holds out hope for one more piece of evidence against the anthropic explanation of the CC. There already is lots of evidence against the anthropic landscape, even if this particular new piece of evidence turns out to be possible, I don’t think it will have much effect.

  42. Errr….actually I was mainly referring you to the *last sentence*, where the author suggests that the CC problem will ultimately be solved when we receive an instructional broadcast from a more advanced civilization….. 🙂

  43. woit says:


    Oops, seems that I sometimes don’t read things carefully, and don’t get the joke….

  44. a philosophy student says:

    the anthropic principle is in some sense a tautology:
    we must live where we can live.

    Natural selection is a tautology in much the same sense:
    survivors survive.

    Since terms are important in this context, this note:
    These two terms or principles stand for different things:

    When saying: ‘we live where we must live’ (AP), then on equal terms, concerning evolution, would be: ‘we survive where we must survive’. Let’s call it, for ease, the ‘natural principle’ (NP).

    Going a bit further, we could modify NP, while keeping it on equal footage qua scope of meaning to AP, to: ‘survivors survive because they càn survive’.

    If we take this as a pricinple after the example of AP, then now we should try find the reason behind what the principle states, or we are stuck with our tautology.

    But the difference between the two is of course that for NP the reason has been found, namely natural selection (NS), while for AP it hasn’t, despite the two being put on equal footage here (in the quote), mixing the principle NP with it’s reason NS, while for AP there’s only the principle.

  45. a philosophy student says:

    I mean ‘can’ where I say ‘must’, twice, in:

    “When saying: ‘we live where we must live’ (AP), then on equal terms, concerning evolution, would be: ‘we survive where we must survive’. Let’s call it, for ease, the ‘natural principle’ (NP).”

  46. boreds says:


    I guess lubos is referring to what you say in the posting above:

    “the apparently serious reference to [70]”

    rather than what you said in the comments, which is clearer.

    In any case, I don’t think it’s that weird that Polchinski made a joke about the paper.

    I don’t know about the other five citations, but it would be hard to imagine they didn’t realise it was an April fools if they’d read the paper.

  47. Who says:

    philos. student,
    you might be interested in Scott Aaronson’s comment in this thread

    I think it has something to do with what you are discussing. Perhaps you saw it and simply didn’t think it germane to your points. But I think it does have some bearing. I expanded on Scott’s a couple of comments later. See if you can make anything of the earlier discussion and if it fits with what you are saying.

  48. Shantanu says:

    Peter have you seen astro-ph/0604242 ? It talks about an observational
    test of antrophic origin of cosmological constant. your thoughts on it?

  49. woit says:


    I just wrote about that in a comment above, responding to Lambchopofgod, who was actually pointing to the kind of absurd end of the paper. But now, my comment is relevant, as an answer to your question.

  50. Shantanu says:

    Thanks Peter,. Sorry I missed your comment above. anyhow I am not sure how serious about the last sentence.

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