Edge Dinner Talk: Greene Surrenders on String Theory Claims

[arivero]

Some blogs are discussing Edge dinner talk, but it is interesting to read it yourself:
http://www.edge.org/3rd_culture/einstein07/einstein07_index.html

particularly

STEINHARDT: Well I think there is a key difference, which is that no one believes the standard model is the ultimate theory, and string theory is claiming to be the ultimate theory.

GREENE: Oh, I think we should put claims of that sort…

STEINHARDT: But the question was raised, why are people upset about it? And the answer is, because whether you personally believe it or not, string theory has been advertised as being the ultimate theory from which we should be able to understand…

GREENE: I guess I would say it is unfortunate that people get worked up over that kind of advertising. If you look at the history of string theory, I agree with you; there was a time when people thought this could be it—the final theory that would describe everything. In fact, it still may be it.

But I think there was a certain kind of youthful exuberance that took hold when the theory was in its early infancy in the 1980s and early ‘90s and so forth, which perhaps was a little bit unfounded because it was such an immature theory that you really couldn't make pronouncements about it that you could have any real faith in. I personally, as do I think many string theorists, view string theory as a possible next step towards a deeper understanding of the laws of physics. It could be the final step, we can't judge yet.

But I think the most sober way of looking at it is that we have quantum mechanics, we have general relativity, we have to put them together in some consistent way, string theory is a possible way of doing that, and therefore we should explore it and see where it goes. I think it would be unfortunate if simply by virtue of it's being advertised within a certain framework of it being the final theory, one then judges it differently from any other scientific theory, which is on its merits.

STEINHARDT: That's a stupendous retreat from what many people have claimed.

GREENE: You really think so?

STEINHARDT: Yes, sure.

 

[mathman]

Most scientists would take the position that Greene is stating and I don't think it is a retreat, as Steinhardt asserts. Throughout history scientists will try to improve on existing theory or even replace it with a better one, but claiming a final theory is best described as youthful exuberence or possibly old-fogyism. Toward the end of the nineteenth century, before Planck and Einstein, the old-fogys thought that physics was almost complete - just a few loose ends.

 

[arivero]

Where, it seems a retreat if you consider the six or seven first articles of Greene "in its early infancy in the 1980s", about some models for E8xE8 with three generations of the Standard Model.

Moreover, a selling point of string theory was uniqueness, in a physical sense, not in the mathematical sense of consistency (in this sense, every consistent mathematical theory is unique). They were not claiming sort of, "hey, I have developed a theory of non associative normed algebras, and it only has a solution". It was more of "hey, I have developed a theory of quantum gauge dynamics, and it singles out a model".

 

[rewebster]

Greene must be writing a 'new' book


(TITLE: 'THE TROUBLE WITH' GREENE)

 

[BenTheMan]

arivero---

Why is it a retreat? It's more or less a statement of the obvious---we thought the problem would be a lot easier than it turned out to be.

Didn't you do any Jackson problems in grad school?

Proponents of other approaches to quantum gravity claim that they don't want to detract from string theory, yet they call it ``the trouble with physics'', and use words like ``retreat'' and ``surrender''. A bit subversive, maybe?

 

[josh1]

And the jihad against string theory continues.

 

[pelastration]

And the jihad against string theory continues.

Josh,

your bring string theory in a religious perspective. Is that intentional? ;-)

 

[Chronos]

That will be an oft quoted remark, josh1. No dissent, discussion, or even a 'sigh'. If you have a point, the time is ripe.

 

[eendavid]

Why is it a retreat?

String theory has gained a lot of interest (and money), partly because of this claim. Seen in this context the analogy with end-of-19th-century physics fails. One should not be surprised that proponents of other approaches have a mixed feeling about this, and see it as a retreat.

I don't see any problem in claiming the string community has 'cheated' (as in the sense of the above), while holding that string theory might be an interesting approach.

 

[rewebster]

I bet there has been other hypotheses that have gained some favor at different points (and interest and financial support) in history that have been eventually been proven wrong, and I'm not saying with 100% certainty that string theory or everything in string theory is not right------At the 'present' time, it seems to me, that it is a mystical, magical, mathematical idea for a particle/ (whatever a string is) that is more like a genie in a bottle granting wishes (IF you CAN 'arrange' the math 'just right') to do (just about) anything you want it to do--- (talk about other people calling some questions 'philosophical'!).

 

[arivero]

One should not be surprised that proponents of other approaches have a mixed feeling about this, and see it as a retreat.

Well, I am not sure if there were proponents of other approaches. GUT was subsumed into string theory, and other models, as my beloved Non Commutative Geometry, had not traveled differently even without string theory.

 

[arivero]

Why is it a retreat? It's more or less a statement of the obvious---we thought the problem would be a lot easier than it turned out to be.

Actually I have some doubt about if the problem was thought. We had some string students in Les Houches (actually we got Greene as one of the teachers that year) and at that time (1995?) it was not easy for them to explain how particles and forces were supposed to emerge, except as I said above, by claiming contact with GUT.

Perhaps at some time it was hoped that a second uniqueness theorem could be proved about the compactification manifold. Still, it was unclear how it could drive to predictions about the CKM and masses.

THinking about, perhaps there was some hope that the compactification manifold, if unique, could predict some unique new particles and there its finding at the LHC would confirm string theory.

Didn't you do any Jackson problems in grad school?

Hey, this is Europe. For classical fields, we proceed with handwritten lecture notes; it was conjectured that they were coming directly down from Maxwell and Onnes.

Proponents of other approaches to quantum gravity

Note I started this thread in "High Energy, Nuclear, Particle Physics" subforum, and the moderator moved it here. I have not argument (others could have some) about the use of string theory to calculate quantum gravity.

 

[nrqed]

Maybe there should be two "Beyond the Standard Model" subforums on PhysicsForums.

One would be about the sociology of the field (about opinions, about the people in the field - including who did his PhD with whom, who is working on what etc etc etc) and one subforum which would be about the actual physics and maths and where loop quantum gravity, string theory, noncommutative geometry and everything else would all be treated with interest (I can't help notice how threads about actual physics are few in between and often fairly short, with string theory questions being ofetn left unanswered which is unfortunate) and the only goal would be to learn the topics and discuss them.

It seems to me that a huge fraction of the posts here are of the "sociology" type which, from the point of view of someone interested in the physics and maths of the field is quite disappointing.

I guess I have to run for cover now...the flak will be intense.


patrick

 

[eendavid]

Well, I am not sure if there were proponents of other approaches. GUT was subsumed into string theory, and other models, as my beloved Non Commutative Geometry, had not traveled differently even without string theory.

I too was referring to quantum gravity.
Of course it is difficult to forecast how theories would have evolved without string theory. To me it seems reasonable that LQG would've had a faster grow. At the moment string booms (mid-90's) LQG did have some results (which were negligible compared to a theory claiming to become the ultimate theory (GUT+quantum gravity)).

 

[josh1]

Maybe there should be two "Beyond the Standard Model" subforums on PhysicsForums.

One would be about the sociology of the field (about opinions, about the people in the field - including who did his PhD with whom, who is working on what etc etc etc) and one subforum which would be about the actual physics and maths and where loop quantum gravity, string theory, noncommutative geometry and everything else would all be treated with interest (I can't help notice how threads about actual physics are few in between and often fairly short, with string theory questions being ofetn left unanswered which is unfortunate) and the only goal would be to learn the topics and discuss them.

It seems to me that a huge fraction of the posts here are of the "sociology" type which, from the point of view of someone interested in the physics and maths of the field is quite disappointing.

I guess I have to run for cover now...the flak will be intense.


patrick

I agree with every word of this.

 

[f-h]

I'm with josh1 here. The hype for String theory is over and the statement of Greene is a welcome realistic summary of the state of the field, something that was not present in the public image of String Theory for a while, but to call it a surrender is disingenuous and mis informative.

Everybody working in QG from whatever background, agrees that ST deserves mayor investigation and funds and positions. The problem was it's claim for exclusivity, that this claim is no longer propagated or tolerated is to be welcomed but it is just as bad to now go on a ST witchhunt. And it has as little basis in physics as the original hype had.

 

[arivero]

Perhaps the two forums should be "Beyond Standard Model" and "Beyond General Relativity".

 

[marcus]

Arivero thanks for calling attention to this very interesting conversation! In a way it can serve as a landmark signaling a change in how the issues are thought of and discussed in future. IMHO Greene does articulate a NEW position, which may be a very usual position in Europe where nonstring approaches have been given a place at the table and live in peace with string approaches (if I can judge from some things f-h has said at various times) without claims to exclusivity on either side.

So perhaps it is only new on the US scene, where string philosophy has been hyped as the "only this" and "only that" even in recent memory. Or perhaps a non-exclusionary attitude is not really new even in the US.

In any case, the Edge conversation seems to be tending more towards a EUROPEAN mentality where each bunch of theorists realizes that theirs is not the only car on the road. This still needs to be implemented in policy in the US, where there is at present only one university with a nonstring quantum gravity group: PhDs from there normally have to emigrate to Canada, UK, the Netherlands, France (to places where nonstring is more developed).

Maybe all that is obvious and not even controversial. So I want to look at what I would call the MAIN IDEA OF THE EDGE DISCOURSE----something that was set out by Steinhardt and is deeply insightful and constructive.

If we just wanted to talk about one thing from that trialog, surely it should be this!

PAUL STEINHARDT: The question that I have about Einstein relates to the one that Brian raised, but with a twist, because I see what has been happening in theoretical physics in the last 30 years, and especially in the last few years, maybe from a slightly different point of view.

Over the last 30 years, there have been grand ideas that have emerged in theoretical physics that were meant to simplify our understanding of the universe. One is the idea of inflation; the idea that there was a period of very rapid expansion that smoothed and flattened the universe and which explains why when we look out anywhere in space it looks almost the same everywhere. And it is of course based on Einstein's theory of general relativity, and relates directly to his introduction of the cosmological constant back in 1917, but elaborated in a way that this rapid expansion would only occur in the early universe, and not in the later universe. Just to explain why the universe is the same, or looks the same, almost everywhere.

The other grand idea that has been developing is the one that Brian has written so elegantly about, which is the idea of string theory, that everything in nature is made of quantum vibrating strings, and that we can derive a simple unified theory to explain all the physical laws that we see.

The hope was that string theory would explain the microphysical world, and inflation would explain the macrophysical world.

What have we learned from these two grand theories, inflation and string theory? Well, in the last few years, especially in the last decade, we've learned that—at least to my way of reckoning things—neither of them is really delivering on their promise. It turns out inflation doesn't do what we originally thought it did back when it was introduced in the 1980s. It doesn't take an original initially complicated inhomogeneous, non-uniform, curved and warped universe and flatten it out everywhere—and leave it with a universe which is full of matter that we see, which is then smoothed and flat.Instead, what inflation does, once it takes hold, is continue to make a more and more inflating universe, only occasionally leaving behind a few pockets of universe that have matter that we would recognize and that might be inhabitable.

And in fact, among those pockets, it seems that the pockets that would look like the ones we observe would be exceedingly rare. So whereas inflation was designed to explain why the universe is as uniform as it is, and why that's a likely occurrence, it seems that the theory is actually leading us to a point of view where with inflation we are actually unlikely to find pockets of the universe that look as smooth and flat as we observe.

Similarly, the hope for string theory was that it would uniquely explain why the laws of physics are what they are. But developments over the last few years suggest that actually string theory doesn't make a unique prediction for the physical laws—there might be a google, or many googles, of possibilities. And the ones that we happen to observe are not particularly likely—at least there is no reason why they should be likely.

So a key conclusion according to the current view of string theory and inflationary theory is the fundamental nature of the universe is random. Although the universe seems to be remarkably the uniform everywhere as far as we can see, our leading theories currently suggest that the conditions we observe are actually very rare and unlikely phenomena in the universe entire. And I wonder what Einstein would have thought about that. I wonder if he would have found that idea that is, a theory of this type, to be acceptable. My own point of view is that we have to change one or both of these two key components of our understanding of the universe. We either have to dramatically revise them, or we have to overhaul them entirely, replace them with something that combines to make a powerful theory that really does explain, in a powerful way, why the universe is the way that it is.

The flaw in inflationary theory he is highlighting only applies to scenarios which resort to exotic matter---some kind of "inflaton" field. I think the key thing in this passage is Steinhardt's critique of the prevailing notions of inflation.