|Sep27-03, 09:09 AM||#1|
Interesting argument among string-thinkers
recent post at spr by Jeffery Winkler contributed to the debate between the anthropic and mis-anthropic camps within Stringery
Jeffery cites an earlier exchange between Thomas Larsson and Lubos Motl.
Larsson wrote, 22 Sept:
[[Now I am starting to worry seriously, since I agree with you for the third time. But your comment puzzles me, provided that it means that you are dismissing the anthropic principle (this is how I read the lines above). Leonard Susskind, of whom you have spoken highly before, seems to be deeply rooted in the anthropic camp, see
Is Susskind wrong? ]]
Motl replied, 22 Sept:
[[Yes, I think so. ;-) If you read the New York Times from September 2nd (?) or directly e.g.
you will see that our mis-anthropic camp is not weaker, and Gross and Witten, among others, are reliable members of our camp! ;-) ]]
[[The anthropic principle is gaining popularity. In the abstract of
Banks, Dine and Gorbatov write "We conclude that one must invoke a strong version of the anthropic principle. "
This seems to be quite a turnaround. A few months ago, Banks wrote in
http://www.arxiv.org/abs/hep-th/0306074 , p 48:
"We must ask ourselves whether we are really doing science. So must anyone who indulges in anthropic speculation."
It is also quite different from ref 21, where Motl and two of the authors critized the use of the strong selection principle (the insistence on carbon based life) as overly parochial, see p 21.]]
At this point, having cited these portions of the 22 Sept exchange, Jeffery Winkler chimed in as follows:
[[ I think Lenny Susskind's descriprion of the antropic principle is
basically true. Let's say the entire Universe is infinite but our
observable universe is finite, you could imagine that distant parts of the Universe would correspond to different points within the string vacua, and all points would be realized somewhere, but the section of the Universe that contains our observable universe would correspond to one of the few areas in which life is possible, which explains why we're here. You can use this to explain why our observable universe has the properties it does. You can explain things that can't be otherwise explained. There's other ways of using the anthropic principle, such in the brane world, our universe is a 3-brane, and there would be other 3-branes, or other D-branes with dimension differen than 3, and with different toplogy, they different laws of physics, and ours is one of the few in which life is possible.
So, I don't think there's anything wrong with the anthropic principle. If you take M-theory + inflationary cosmology + anthropic principle, you get the majority view among physicists.
|Sep27-03, 09:43 AM||#2|
Larsson says the paper by Banks, Dine, Gorbatov (BDG) which he cites"seems" to be quite a turnaround. but this is going by the abstract and looking into the main text will correct that misapprehension----BDG have not switched over to the anthropic side. This tends to confirm Motl's claim that the mis-anthropic camp has not grown weaker (as it still contains prominent figures such as Witten, Banks, Dine.....Motl himself [;)] and so on)
"The second possibility, which at first sight might seem appealing in this [Susskind] context, is to implement a version of the anthropic principle.
It is clear that in the context of the [Susskind] landscape, this is the only way in which to explain the value of the cosmological constant, and probably several other quantities of low energy physics.
But we will see that in the flux discretuum, such a viewpoint will almost inevitably lead to predictions which are false."
|Sep27-03, 10:04 AM||#3|
Banks and Dine (and Gorbatov) have certainly not defected to the anthropic camp! They are using his dependence on Anthropism as a talking point against Susskind. Here's a brief exerpt from their recent 39 page paper
"Is There a String Theory Landscape?"
[[...We have previously presented  a variety of arguments against the utility of the anthropic principle in models of this type. In asking about anthropic vacuum selection, we distinguished
two possibilities, which we will refer to as the “Strong Selection” and the “Weak Selection” principles. The weak selection principle asserts that any states which meet some very minimal criteria for the existence of life – the formation of structure in the universe, perhaps of stars, and the like, are acceptable. The strong selection principle postulates the necessity for our own type of carbon based life. The weak selection principle is a very reasonable constraint on mathematical theories of the universe, but is not very powerful. Given a collection of low energy gauge groups and representations, we simply do not understand enough about complex phenomena in (the various possible analogs of) low energy nuclear physics, much less (exo)biology, to assert that life is or is not possible.
In , we presented a variety of arguments against the utility of even the strong selection principle in models of the class exemplified by the flux discretuum. In this paper we modify and extend those arguments, explaining why the predictions of the strong selection principle within the framework of these models , are likely to differ widely from experimental values of many parameters.
Apart from these negative comments, we note that there is one prediction that the flux vacuum might make: low energy supersymmetry. In particular, we explain why the vast majority
of vacua with suitable cosmological constant, and suitable weak gauge hierarchy, are likely to exhibit some form of low energy supersymmetry. This is not necessarily a success; again, withinthe framework of the strong anthropic selection principle, our arguments suggest that the flux discretuum is not likely to agree with experiment. Some, though not all, of these observational problems are linked to the prediction of low energy SUSY...]]
|Sep27-03, 10:13 AM||#4|
Interesting argument among string-thinkers
The clearest brief comment on the clash over Anthropism between Banks (anti) and Susskind (pro) that I have seen was by someone outside the immediate arena, a mathematician at Columbia who teaches math-physics: Peter Woit. Woit the outsider knows people on both sides of the debate. Here is his Tuesday post on usenet spr:
[[From: Peter Woit <firstname.lastname@example.org>
Organization: Columbia University
Subject: [spr] The string theory crackup, continued
Date: Tue, 23 Sep 2003 04:51:29 +0000 (UTC)
Anyone interested in what is happening in string theory
might want to take a look at a new preprint whose
co-authors include two prominent senior string theorists:
Their title is "Is there a string theory landscape?" and
they begin with the statement "String Theory has always been
plagued by a plethora of solutions which do not describe
the real world" and go on to note that in recent years
new such solutions have appeared ("flux compactifications").
Some estimate that there are at least 10^1000 families of
The authors go on to note that some string theorists are now claiming that string theory might somehow still be salvaged as a theory with predictive value by invoking an anthropic principle.
Whatever mysterious process magically picks out the solution we find ourselves in, it must be capable of supporting life, and maybe solutions of this kind actually predict something. The authors conclude that this is not the case, that: "many features of anthropically selected flux compactifications are likely to disagree with experiment".
The string theory community seems to be cracking up into
1. Those who argue that string theory basically
can't be used to ever predict anything, but since you
thus can't show it is wrong, you should believe
it anyway, invoking some deus ex machina that determines
everything that isn't explained by the standard model.
2. Those who argue "Never, never, never, never give up!"
(see David Gross's summary talk at Strings 2003), which
seems to mean "our colleagues in camp 1 aren't doing science
anymore, but even though we don't have a glimmer
of an idea about how to ever get a prediction out of string
theory, we have far too much invested in it to admit
By the way, in case one has heard that string theory
is an incredibly sophisticated mathematical formalism
that requires years of mathematical training to follow,
this new preprint has few equations and high school math
is all that is needed to understand most of them, except
perhaps for an ODE or two that you might need a first-year
calculus class to understand. As with the rest of this
kind of literature, while the math is straightforward, the
physics is obscure beyond belief.]]
End quote. Woit teaches Quantum Field Theory and the graduate level group representation course at Columbia. Interesting viewpoint. What Susskind calls a "landscape"----the selection problem presented by a proliferation of predictively insufficient theories----is what Banks et al call a "discretuum"
(by analogy with continuum, the word suggests a discontinuous infinity of choices)
And Woit, using more ordinary english terminology, calls it a "plethora".
Well, "landscape", "discretuum", or "plethora"----whatever: a kettle of fish
|Oct3-03, 01:17 AM||#5|
I just noticed a fascinating exchange between two of our fellow PFers. It really deserves study since it bears on string/brane thought.
As you know there was a huge outpouring of string/brane research papers during the 1990s, which has slacked off considerably. It appears to me (but certain others deny this!!!) that research interest is shifting to actually quantizing General Relativity, so far the loop, spin network, spin foam etc is the only active program doing that. So my personal opinion is the heyday of string is past and one's time is better spent trying to follow what is currently going on in loop quantum gravity and loop quantum cosmology.
But everyone is welcome to follow whatever! Intellectual freedom is basic here! So I wish all string/braners well and good luck!
Also we get good notices for our LQG threads----Rutwig dropped in twice and commended me on some explanation---another time Lubos Motl cited the LQG thread I started on Stone-vonNeumann and gave a link in SPR to it. And some people drop in and participate constructively.
but others may feel threatened by LQG threads and wish to divert them into disagreeable personal bickering, here an EXCUSE is given for doing that. Apparently it is based on this person's view of the typical PF poster as naive---unable to think for him or her self and thus liable to be DECEIVED by reading a post about LQG. (my guess is that anybody who reads a LQG thread can think for themselves just fine---propaganda begins with a failure to respect the reader and its not how I operate)
Anyway this is a really enlightening post from the "What's with string theory?" thread:
I'm not worried about people who like me can evaluate theories on their own. I'm worried about the 99.9 % of the people here who've decided to invest time (and as you know this sort of physics is difficult and demands much energy) in learning about what drives current research in QQ - which of course is SMT (String/M-theory, or as I like to call it these days, S&MT) and not LQG or any of the other small scale research programs - but are easily mislead, intentionally or not, into believing that because it's not "background-independent", they should forget about SMT, and thus virtually everything that's going on in theoretical physics these days. For example, I don't think you appreciate how monumentally important SMT has and continues to be in moving forward ideas in connection with QFT, cosmology, and mathematics. As well, the people in LQG are constantly on the lookout for a way to connect LQG to SMT. Do you think they'd be doing that if they felt the same way about SMT as some of the people here do?
Also, we're not talking about politics in which opinion and fact are closely mixed. We're talking about an exact science in which there is a an extremely strong relation between what is currently the most popular idea and what is in fact currently our best idea. I don't think the right place for neophytes to start is with polemical papers or the jaundiced and ill-informed personal opinions of others. Consider the thread begun by marcus entitled "String irrelevant to quantizing General Relativity (quantum spacetime geometry)". Now, technically, he was talking about quantizing GR directly which is not what SMT does (this is in fact why LQG was so unlikely to ever work), but I'm pretty sure he knew that the people here would not pick up on that subtlety.
Now, technically, he was talking about quantizing GR directly which is not what SMT does (this is in fact why LQG was so unlikely to ever work), but I'm pretty sure he knew that the people here would not pick up on that subtlety.
But I was confident that PF posters who were savy enought to read the thread would pick up on the fact that I was talking about directly quantizing GR--which I've emphasized repeatedly until I'm blue in the face. It is not such a subtle point: String/Brane does not quantize General Relativity (as this poster notes)
and String/Brane theory does not try to quantize GR because back 18 or 19 years ago when the second string wave got rolling it was thought to be a deadend or impossible or not the thing to do---particle physicists circa 1990 thought that trying to quantize GR would lead to failure! So they took another tack and there was the boom in string research of the 1990s leading to a proliferation of theories with little in the way of testable results.
Im basically just paraphrasing Rovelli's sketch of the history.
This HEP belief from earlier times is reflected in saying---right, string/brane theory does not quantize GR and LQG does and this is "in fact the reason that LQG was so unlikely ever to work".
Ah hah! We see that even today there are people still clinging to the idea that it is a bad idea (a research deadend) to try to directly quantize GR in the way that classical theories are normally quantized.
Logical consequence (?): marcus is bad because he might mislead innocent juveniles into supposing that it wasnt a bad idea to try to quantize GR---and wasnt necessarily doomed to failure! Wow!
So the innocent juveniles of PF should be protected from this harmful influence. It might cause them to waste their time.
Well, you know IMHO for a young person nowadays it is a waste of time for them to start trying to learn string. It is a waste of time because GR is becoming more important (dark energy, BB, BH, observational cosmology, removal of BB singularity etc and much more) and the more interesting GR gets the more important and interesting it is to quantize it------Tom Banks a prominent string guy was making a related point in his critique of string.
(the internal critics are the best)
But I am happy for people to learn whatever they want!!!! I dont have any urge to defend people from being bamboozled into learning string theory or believing outdated claptrap. I would not stand in those defender-of-the-innocent shoes for anything. Smart people, young or old, can make up there own minds and what they do is their business.
And there always are some who drop into LQG threads, presumably with their eyes open---"mature individuals" like selfAdjoint [;)] who really helped out before the format change, on several.
That reminds me, selfAdjoint said something interesting just before that. I will get it
|Oct3-03, 01:58 AM||#6|
Yeah, the thread was supposed to be "What is it with String theory?" Which is interesting---there has been growing criticism
from within and without (I dont mean from LQG people who are busy with their own thing) because of not being science in a conventional sense, not falsifiable. So what is it, a belief system?
So people like Larsson and Woit are bearing down in SPR and defenders are getting a little hysterical. So it is an interesting topic "What is it with String Theory?" An observer can go to Usenet and find out. One can talk about it. It has a bearing on what science is or has always been.
So Jeff starts to protect Mentat from being influenced and says: remember there are tens of thousands of string papers! String is what the majority believe in! LQG is negligible!
The LQG business is irrelevant, the thread is about criticism that has arisen of stringery---not from LQG people or involving LQG---because the research is not showing signs of producing after 18 or however many years.
But then selfAdjoint says a very interesting thing----the validity of research is not in the numbers that join the parade!!!!!!!!
I'm thrilled. Let me quote the whole post:
Jeff, I can't help but find this post irrelevant. I am sure that in other contexts you would be eager to disavow the idea that correctness in science is to be determined by headcount.
The response of physicists to the various initiatives of stringy physics has been described (perhaps unfairly caricatured) as a feeding frenzy. Certainly an awful lot of the papers on hep-th will not be cited say, five years from now. This could be true of the LQG papers too, of course, but which is which cannot be determined until the physical consequences are worked out.
a bit of genuine understanding of what science is about creeps in.
the fact that tens of thousands of papers were written in the 1990s is irrelevant, what is happening now and in particular what is getting cited. Arxiv has this great feature that gives you a handle on how important a paper has been for other reasearchers---a robot counts the number of other papers citing the given one.
But in the end even those numbers dont matter. What matters is nature's numbers----the test of a theory's predictions (if it makes any) by experimental measurements
What the string-thinkers are arguing about---and raising the sad prospect of the "anthropic principle" and dividing into camps and squabbling about among themselves---is fundamentally this: the failure of string to make testable predictions.
I thought Peter Woit characterized the situation well, with the two camps, or was that Lubos Motl who described it as two camps? Well, to be continued.
|Oct3-03, 09:53 AM||#7|
Marcus I hate this fight. Both the near flame war here on PF and the Woit - Baez - Motl smackdown over at spr.
It's not just the disagreeable posts that get me, but what this may be saying about the state of research. If any of the spr participants had a thought of how to move forward they'd be doing it. Instead they squabble over who's ahead.
Baez seems to be spending his time on other stuff.
Motl should be doing M theory (well he is) but he wastes time doing these BH mode calculations to stick it to LQG. Counterproductive.
My idea is your idea before Jeff abraded you so much. Let everybody work at what they think is best and let nobody waste time and energy attacking others' work.
|Oct3-03, 10:33 AM||#8|
and engaged you in an argument---effectively stopping the threads---but I didnt say a word: just went away.
I think people should leave each other alone and not waste time on acrimony and derogatory comments. I was having a conversation with Mentat and Jeff stepped in and started tearing me down-----believe it or not, I was willing to ignore this (I put up with a lot because I'm basically a pacific animal, a herbivore rather than a carnivore) but Mentat said: "I expected you to reply to Jeff! why didn't you counter his criticism?" So I felt compelled to respond. But usually I either dont read his posts or just let them pass.
I leave Jeff completely alone and would like him to return the courtesy. I have no animosity against him---just find contact with him a waste of time.
Now to something more interesting! I am excited by your comment on the discussion at SPR! So many people have jumped in. Aside from Baez himself (who is actually rather forbearing and not all that active in it, it seems to me) the discussion has no LQG people that I recognize. It is all string people and miscellaneous non-string. There seem to be real issues being raised of what is science and what is non-science or pseudoscience---what the standards should be. I am glad you commented on this especially because I respect both your decency (from what I have seen) and your judgement. will think about this some more and perhaps reply later about the String Fracas at Usenet SPR.
|Oct3-03, 11:14 AM||#9|
But people interested in studying QG have every right to know that SMT does dominate all other QG research and that this fact cannot be attributed to mere differences of opinion, psychology or politics: LQG and SMT are not and have never been by any practical measures equals. The reason why you hear about LQG rather than the other small scale research programs in QG has as much to do with PR as with LQG itself.
Once again and for the record, I believe that background-independence is a necessary ingredient in any successful QGT. But just because a theory is background-independent doesn't mean it's correct. In fact, what LQG shows in hindsight is that it's really quite simple to construct such a theory. The tough part is to find one that is relevant to our universe, and results obtained so far indicate that LQG doesn't.
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