# Why is string theory on the verge of collapse?

1. Jul 19, 2010

### zewpals

The question I want to ask is pretty much in the title: Why is string theory becoming less of an excitement amongst the scientific community?

I don't want to sound picky, but my background in physics is pretty inferior. I understand that the explanation is mainly in the mathematics, so, just to give a quick background, I've taken first year physics in college and have a pretty minor background in cosmology. In mathematics I've gotten no further than multivariable calculus so far. Please answer accordingly =D. Thanks!

EDIT:

For the rest of you: When I posted my minor background in science and math I did not intend for you guys to treat me like a half-brained nitwit. Some of you directly criticized me for asking a question and some of you provided responses that were nothing more than "do some research". Inducting that I am (and I quote) "brainwashed" and that I asked this as if I was "stating fact" is absurd logic. I am not here to be flamed at, I am here to learn. Simply stating "only dumb people think this" is naive and uncalled for. Modern application of string theory is substantially smaller than Newtonian physics and Einstein's Relativity, so it is very viable to question the theory.

I really am looking for input that is at the very least honorable, not to mention insightful, which is what I was originally going for.

I refuse to address each insufficient response (and sorry for the few of you that were helpful) out of sheer laziness.

Instead, I will rephrase the question:

Why have I observed many respectable scientists with PhD's in physics or astronomy personally telling me that they see string theory as an improbable theory? Why does a portion of the scientific community not invest their beliefs in string theory?

What is the science behind this rebuttal? I am not looking for a history lecture. If you cannot think of a scientific answer, then I ask that you do not contribute. Any posts that scientifically explain why string theory is valid or invalid is fine by me. The topic is, though, why are strings seen as an scientific improbability by some scientists?

Last edited: Jul 19, 2010
2. Jul 19, 2010

### atyy

It is not. Anyone interested in quantum gravity must study string theory.

3. Jul 19, 2010

### Demystifier

Because it failed to make a mayor breakthrough around 2005.

Let me explain:
- Around 1975, it was realized that string theory has o potential of unifying all interactins, including gravity. It was really a breakthrough.
- Around 1985, the first string-theory revolution happened by realizing that certain superstring theories are anomaly free.
- Around 1995, the second string-theory revolution happened by realizing that all these anomaly free superstring theories seem to be special cases of a single theory (M-theory).
- By induction, it was naturally expected that a new breakthrough should happen around 2005. Unfortunately (or fortunately, for those who do not like string theory) this has not happened.

4. Jul 19, 2010

### bapowell

I agree with atyy that string theory is an integral part of modern attempts to quantize gravity, and should be studied accordingly. The most common criticisms of string theory stem from its lack of falsifiable predictions, and the related lack of a unique solution to the string theory equations of motion. The lack of a unique solution stems from the fact that string theory predicts a 10-dimensional universe, but has not yet yielded much insight into the form of these extra dimensions (notably their geometry). Different geometries give different physics -- different particle species with different properties -- with our universe just one of the many possible realizations. Just how our universe is 'selected' out of this (very very large) set is currently unknown, and has been the target of much criticism in recent times.

5. Jul 19, 2010

### Demystifier

Tell it to the LQG people. :tongue2:

6. Jul 19, 2010

### bapowell

By induction? I didn't realize that scientific breakthroughs in the field of string theory followed a 10 year cycle.

7. Jul 19, 2010

### Finbar

why?

I don't see why I must study string theory.

Part of the problem is that not enough young string theorists are studying quantum field theory. Studying established physics is far more useful to understand quantum gravity than studying strings.

8. Jul 19, 2010

### atyy

9. Jul 19, 2010

### Demystifier

It was a joke, of course. But like for any good joke, there is some truth in it.

10. Jul 19, 2010

### Demystifier

Maybe some guys (such as Rovelli) would not agree that Baez is the best, but I think it is safe to say that Baez has the best sense for scientific humor.

11. Jul 19, 2010

### MTd2

John Baez doesn't work on LQG anymore or any quantum gravity. After week 300 (the actual is 299) he will shift his interests to environmental issues. He will have a blog for that.

But he still assists people interested on QG. His student John Huerta has been publishing nice things on this.

12. Jul 19, 2010

### George Jones

Staff Emeritus
13. Jul 19, 2010

### suprised

How come you state this as a fact? Perhaps because you are brainwashed by the ideological climate here, a truly amazing case of group think and wishful/hateful thinking? Where sense and nonsense is mixed up beyond any recognition? It represents amateurs and few, if at all, serious professional scientists.

Just have a look at hep-th where the current research keeps to be focused on for very good reasons; there is no collapse in sight (I remember that already years ago people counted here papers in order to fabricate evidence for such a decline... nope. Now they count talks at conferences to painstakingly identify some decline...they want it sooo bad... it is nothing but silly. It just won't happen).

Or do you seriously believe that amateurs and armchair scientists would have any better insight into things that need many years of hard work to learn? There is no way that you can form a qualified opinion by reading those opinions expressed here. It is a pure waste of time.

14. Jul 19, 2010

### BenTheMan

15. Jul 19, 2010

### BenTheMan

I think you should stop getting all of your physics news from Marcus and pop science magazines.

Science forums cranks (i.e. he-who-will-not-be-named) and pop science magazine editors who realize that underdog'' stories sell more are the only people that think string theory is on the verge of collapse''.

16. Jul 19, 2010

### humanino

Demystifier, there was at least one major breakthrough in 2003 with the twistor string. In case you missed it, Witten provided momentum which ranged all the way to QCD background calculation for LHC.

17. Jul 19, 2010

### Demystifier

Actually, maybe it is AdS/CFT that destroyed string theory (from the inside), because it turned out that AdS/CFT makes sense even without string theory, so many string theorists suddenly started to do AdS/CFT without doing string theory.

But then again, some say that whatever they do, they call it string theory. For example, strings do not play a fundamental role in M-theory, but they still call it string theory. In this way, string theory cannot collapse; it can only change its form.

18. Jul 19, 2010

### marcus

Re:

Well, you asked two quite different questions:

a) Why is string theory on the verge of collapse?
b) Why is string theory becoming less of an excitement?

There still are lots of stringy papers being written, although they tend now to be by the less prominent people and they tend to be less cited. Current papers don't get as much notice by fellow string researchers, and don't get cited as references as much as, say, pre-2005 papers.

In terms of raw numbers, to gauge the research output and get an idea of the string workforce actively writing papers, here is a link:
Part of that post discusses the changed rate of peer-reviewed research publication. Another part of the post tracks popular book sales over several years.

So in raw numbers there may be some decline but it is not a "collapse". So Atyy is right about that.

I'm not sure that someone who wants to be an expert in Quantum Gravity and get a faculty job actually needs to learn string though. I've noticed lots of hires in LQG recently, compared with the (small) size of the existing loop research community. There may be some math ideas which are not the sole property of string theorists which it is good to pick up---techniques which string folks might think of as stringy but which aren't especially.

But I agree with Atyy in not seeing an imminent "collapse". For one thing there are too many people with careers invested in the field for it to collapse.

================================
I think the real question you are asking is b).
Why is string theory becoming less of an excitement?

I think that question is quite interesting. There are several factors. I cant say what the single most important factor is. Maybe some are not causes but symptoms. I will mention a few.

1. Leaders like Witten, Horava, Verlinde, Arkani-Hamed, Steinhardt... getting interested in other stuff, or wavering about whether string is the right way to go.
2. The "landscape"---huge number of string vacua. Unsuccessful search since 2003 for selection principle. Exclusion of "anthropic landscape" people from giving talks at String 2008. Rejection of landscape-ology by important sectors of string community.
3. Tendency of talks at annual String conference to be about application of string-inspired math tools to other physics---like modeling nuclear/condensed matter physics---not fundamental/unification. Less enthusiasm for the Grail and more straying around looking for something to do with the techniques.
4. New astro instruments put the focus on cosmology---which is a Loop strength. Loop quantum cosmology (Lqc) has models of the big bang from which predictions can be derived and tested with instruments either planned or already in orbit. Cosmology has drawn attention to Lqc, where one can calculate stuff, run computer models of the universe with various simple sorts of matter etc, and there has been rapid growth in the number of Lqc papers.
5. Judgement by prominent string theorists such as Hermann Nicolai that "string phenomenology has become increasingly Baroque, if you follow the literature." Said with some distaste at the XXV Max Born conference in 2009.

These are just ideas, often involving a subjective element, and people will no doubt disagree---or give different reasons.
You asked a rather subjective, but significant, questions: "why has excitement diminished?"
It has diminished. The excitement, conviction, dedication, energy is very different now from what it was in 2000 or even as recently as 2005. I can only offer some guesses. Maybe others can say something more definite.

Last edited: Jul 19, 2010
19. Jul 19, 2010

### MTd2

I don't know about a decline of a string theory. But if anyone take a look at the non QG papers, at least the ones listed on this thread https://www.physicsforums.com/showthread.php?t=7245&page=62

will see that the number of papers is increasingly fast. We usually cannot follow the number of papers posted daily and miss many.

20. Jul 19, 2010

### Demystifier

I must admit, I never heard about that. But isn't it an indication that this is not SUCH a big breakthrough, as compared with those I mentioned?

Anyway, I would appreciate a link to the mayor publication on this stuff. (Not only to see what is this about, but also to see the number of citations it received, which can be taken as a measure of breakthroughness.)