Reality Conditions

Monday, May 15, 2006

Landscape chat

A couple of days ago I met in MSN an old friend from the University of Buenos Aires who is doing his PhD in America, in an area of physics unrelated to string theory or quantum gravity. He asked me for my opinions on the anthropic landscape controversy, and we got into a lively discussion about that. I thought of writing my opinions as a serious post, but finally I decided it would be of interest to quote the relevant part of the raw conversation we had, only translated into English and with a few personal things and jokes edited out. So what follows is NOT a summary of my considered, carefully thought and argued opinions on string theory and the anthropic principle, but rather a verbatim record of an informal chat conversation full of vague, spontaneous, half-baked and imprecise ideas… which will probably be more fun to read.

Friend: what is your position with respect to the concept of “landscape” in string theory?

Alejandro: well, it is clearly a blow to the ambitions some had in ST of attaining a unique possible theory to recover the standard model, but I don’t see it as something that necessarily transforms it into a pseudoscience unconnected with reality, as some extremists say

A: it is more like transforming string theory into something more similar to quantum field theory… a general language in which many “theories” can be written and relations between them be found

F: hmmmm

A: there is still no proof that it has anything to do with the real world, but all theories of quantum gravity are alike in that… and though I have more instinctive simpathy for loop quantum gravity, I must admit that sting theory gives a more solid impression.

F: so?

A: so, I dunno

F: hahahahaha

A: what are people saying in your university?

F: there are people that are betting on the concept of landscape

F: others are completely against
F: there’s quite a fight over that

A: what I think creates more polemic is not the landscape itself but applying to it the anthopic principle

A: that does seem a bit phony to me

A: it may be true that the vacuum in which we live is selected anthropically, but it is not a scientific approach to argue in that way. The anthropic principle requires the assumption that there exist other universes with other vacuum states (that is, that the landscape is a real landscape of existing universes, not only of mathematical solutions to the theory)

F: but why do you think it’s phony?

A: and as the existence of other universes is as unknowable as God’s, to say “the universe is at it is because of anthropic selection” is like saying it is so because of divine creation… both may be true, but they are untestable

F: and so?

A: it may be true, but it is not a part of science, or at least I don’t see how it can be made into one at the moment

A: that doesn’t imply that no testable predictions may come out of string theory… only not by that kind of reasoning

F: I dunno… What it seems to me is that if one accepts the anthropic principle then it ceases to make sense to look for a fundamental explanation of why the universe is as it is and I think that has a huge impact on science

F: I agree that it is not something testable, but that is not important

A: you mean, at a philosophical level, what would it imply if it was true

A: but I don’t know if it is such a big deal

A: it would imply that very basic features of the universe, like the particle spectrum of the standard model, or perhaps the number of dimensions, don’t have anything deep justifying them, allright

A: but from the point of view of sting theory, assuming it to be correct, it could be said that those features precisely cesase to be the really “fundamental” ones that we must understand. The really fundamental features could be those included in string theory itself, beyond its low energy solutions

A: analogy: perhaps a pre-Darwinist biologist tried to find a fundamental explanation to why we have 5 fingers… And now perhaps we say that there is no fundamental explanation, simply the first creature that developed fingers millions of years ago happened to develop 5 instead of 4 or 6, just by chance…

A: but that does not prevent us from having a fundamental explanation of life in terms of genetics and DNA

A: I don’t know if it’s a good analogy, but do you get my idea?

F: yes I do, and I think precisely that is the important thing, that it makes no sense to try to understand why we have five fingers!

F: it says that there are things that it makes no sense to try to understand why they are as they are

F: one could regroup considerably the scientific effort!

A: but precisely, it changes the focus so now that no longer seems to be a fundamental thing… but there are other things that are indeed fundamental and understandable… isn’t that enough for you?

A: did you want to understand eveything everything everything?

F: no, but it seems to me that some people lose perspective of what it is worthy to try to understand and what not

F: and having a theoretical limit may be helpful to use better the efforts

A: (warning, all what I said is assuming string theory, the landscape and the anthropic principle to be correct, things I don’t accept at all to be certain. I’m playing a bit devil’s advocate here)

F: I agree completely with you there

F: but for now string theory seems the only alternative

F: lqg is in much worse shape it seems to me

F: until recently some people were convinced that it was worth to try to find a theory of everything

F: the anthropic principle would allow those efforts to be better used

A: lqg has some deep problems to be solved yet, but it is making progress… I still have hopes in it

F: ok, but maybe it turns out to have the same problem

A: the point is that it is less ambitious… it never tried to be a theory of everything

A: strings was sold as a theory of everything, and now they are discovering that they almost certainly cannot be one

A: unless it redefines what is understood by a theory of everything, as you say

F: dunno… I think that all this anthropic principle business, whether or not it was necessary, is provoking a pause that seems needed to me

F: the strange thig is that it puts man in the center again, we are back to Copernicus!

F: but in a slightly different way

A: it seems to me that despite its name the anthropic universe is more de-centralizing of man… it implies that there are millions of alternative universes and that we are simply in the only one in which we can be

A: the formulations of it as saying “the universe is as it is because we exist” are tricky, I think

F: sure, but they are not necessarily invalid

F: just like the aesthetic concepts are not necessarily valid within physics

A: my personal suspicion, is that there is a huge amount of physics we still don’t understand (like, what we know is just the tip of the iceberg) and so that to realte the physics we are starting to understand just now (like string theory, if it turns out to be correct) to fundamental conclusions about a Theory of Everything or an anthropic explanation by chance of everything will turn out presumptuous

A: I don’t think we have came to the point in which physics can start giving us answers to those fundamental questions

F: I agree completely!

F: but there are many that think (or thought) differently!

F: and that is why the emergence of the anthropic principle is refreshing

F: that is the only advantage I see to it

A: I dunno… I think it may be falling in the sme mistake in a different way

F: what do you mean?

A: like, replacing an explanation of everything from a unique theory, by an explanation of everything by chance

F: wait, I’m not saying that the anthropic principle is correct, I’m saying that the fact that it is considered and discussed implies that people are revising their ideas and they will not dream on reaching the final theory of whatever…

A: yes, well, maybe in that sense it is ok

F: it is something that seems so irrational and yet came out of something so rational that it must make you think there is something beyond worth looking for

F: so… whatever

A: whatever


  • Hey Alejandro,

    very nice post :-) You won't believe it, I was about to write a post in my blog on the anthropic principle! I sat around on airports yesterday reading Susskind's book, and found I have to get an opinion. Did you read the book? What do you think?

    I agree very much with what you say. The only good thing I see coming out of the landscape discussion is that it has made parts of the string-community rethink their beliefs. Best,


    By Blogger Bee, at 6:33 PM, May 15, 2006  

  • A:
    The anthropic principle requires the assumption that there exist other universes with other vacuum state

    Say what?!

    No, sorry, the anthropic principle requires no such assumption.

    I dunno… What it seems to me is that if one accepts the anthropic principle then it ceases to make sense to look for a fundamental explanation of why the universe is as it is and I think that has a huge impact on science.

    That's false dogma, and it damned sure isn't what Brandon Carter said, nor is it the approach that John Wheeler took:

    it seems to me that despite its name the anthropic universe is more de-centralizing of man… it implies that there are millions of alternative universes...

    No, that's false, and you either need to learn what the AP is really about and where it came from, or you need to learn to differentiate the manner that string theorist's "abuse" it.

    I notice that you both have that "tip-o-the-iceburg" mentality that comes from nowhere theories and assumptions that lead you to erroneously believe that ToE is out of reach...


    I'd read my whole blog very carefully, were I you.

    Now I'm off to cure Bee of her misconceptions and false dogma as well... ;)

    By Blogger island, at 6:44 PM, May 15, 2006  

  • Thanks Bee! No, I have not read Susskind's book yet, though it is on my (very large) list. I look forward to reading your post. I liked a lot the ones on minimal length and 3+1 dimensions, I think you are doing an excellent blogging job!

    By Blogger Alejandro, at 7:03 PM, May 15, 2006  

  • Hey Alejandro,

    thanks so much for the nice words :-) My jet-lag let me outsit my officemate here at PI and I spent some time in writing the post...

    The Principle of Finite Imagination



    By Blogger Bee, at 1:48 AM, May 16, 2006  

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  • Thank you for the great story.

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