# Not Even Wrong? I Thought String Theory Was Dead?

1. Aug 16, 2006

### Dr. RMC

http://www.math.columbia.edu/~woit/wordpress/

This week’s Time magazine has as article by Michael Lemonick about the controversy over string theory entitled The Unraveling of String Theory. It mentions my book and Lee Smolin’s, and there’s a quote from Sean Caroll. There’s the usual hysterical reaction from Lubos Motl: Time Magazine: Physics is a Sin.

Lemonick more or less gets the story right, describing the reaction of string theory critics to the landscape as:

It was bad enough, they say, when string theorists treated nonbelievers as though they were a little slow-witted. Now, it seems, at least some superstring advocates are ready to abandon the essential definition of science itself on the basis that string theory is too important to be hampered by old-fashioned notions of experimental proof.

http://www.math.columbia.edu/~woit/wordpress/

Are we allowed to criticize string theory here, or is free thought forbidden? [Don't be a smart ass, because I can be one too and ask you if you know how to read and comprehend the PF Guidelines that you have explicitly agreed to - Zz]

Last edited by a moderator: Aug 27, 2006
2. Aug 16, 2006

### Hans de Vries

Are you Peter Woit ???

I think you are Elliot McGucken..... It's his Video for sure.

(Or are you just quoting his webside without using quotes ?)

Regards, Hans

Last edited: Aug 16, 2006
3. Aug 16, 2006

### Kalimaa23

Poor horse. Even though it's dead, it shouldn't be flogged like that.

Not all string theorists are arrogant twats
The landscape is nonsense.
The let's critic string theory fad is just as tedious as the string theory is the ultimate theory fad. It's a nice theory, and a serious contender for QG. Let's leave it at that for the moment.

Just my 2 eurocents.

"Are we allowed to criticize string theory here, or is free thought forbidden?"

No, it's compulsary. You should give it a try.

4. Aug 17, 2006

### R.X.

> Thought String Theory Was Dead?

What gives you this impression?

5. Aug 22, 2006

### Chronos

String theory is a zombie - an undead creature that retreats to hidden dimensions when threatened.

6. Aug 22, 2006

### R.X.

String theory requires for consistency extra degrees of freedom beyond gravity. In 4d string models, this is what leads to elementary particles such as the electron. Often these extra degrees of freedom can be given a geometric interpretation, namely in terms of extra "hidden" dimensions. This viewpoint is however valid only at weak string coupling, in a particular corner of the parameter space. Generically, such an extra dimensional interpretation does not exist (because quantum corrections blur the classical geometrical picture), and therefore debates whether one likes or does not like extra dimensions are moot - the matter fields must come from somehwere, and whether one uses the language of extra dimensions or rather avoids it, does not matter; the point being that consistency forces one to have certain extra matter degrees of freedom.

In "alternative" theories of gravity, I don't see anything that would account for matter fields that even remotely would make sense. The recent discussions at other places about matter couplings in LQG just show how poorly understood this point is even to the experts in that field. In particular, they don't see anything wrong even when coupling inconsistent matter theories, and this tells me and my collegues that they are far far away of any understanding of what consistency means in their theories to begin with.

So, to come back to the title of the thread: why would you believe that string theory would be dead? Simply because a handful of clueless wannabees and naysayers claims this? If you have a real interest in science and like to get an insight that is worth speaking of, there is no way other than sitting down yourself and study hard for may years, rather than reading misinforming blogs or books.

7. Aug 22, 2006

### Careful

I think the better question is : why would any MODEL which cannot make the link to experiment, neither to established physics in a consistent and predictive way be considered - apart from reasons which have to do with how human nature operates - as being alive and as a candidate THEORY ? Neither should such model be considered dead (as long as its proponents do not start denying the practice of science anyway), it is just hanging in the atmosphere of speculative ideas which I guess is what this particular subforum is about.

Careful

8. Aug 22, 2006

### R.X.

The whole matter is very complicated. There is simply no
free lunch when dealing with quantum gravity and unification. It may well be that with the correct model, string theory or not, things will never be predictive and experimentally checkable. This remains to be seen. It is primarily a matter of the involved energy scales - not a matter of principle.

This point is confused and deliberately misrepresented all the time. Namely whether something is unpredictive in principle, or just in practice. Mother nature does not care whether we human beings of today are able to measure up to the Planck scale or not. Similarly to ants, who have no possibility to detect radio waves... if they would be able to write down and contemplate upon the Maxwell equations, would this be science or not?

Certainly string theory makes an (essentially infinity) multitude of predictions, simple because it is a highly constrained theory (it makes predictions about infinitely many massive excitations, for example. I am not saying here that any one could do such kind of computations today, rather that these interactions are highly constrained and fixed, and in principle computable and testable). It is just the opposite of an arbitrary random fluffy structureless theory, despite it is claimed like that everywhere on the web, nowadays. The point is that it is only in the zero mode sector where things are quite arbitrary, and unfortunately this is the only sector that is accessible to us today. Were we able to measure up to the Planck scale and above, there wouldn't be any problem with testing and potentially falsifying the theory.

Moreover, as for lack of a model: things simply _are_ very complicated. Even ordinary QCD has not been solved analytically in the infrared. Any theory involving gravity is a trillion times more complicated, and it is questionable whether there will ever be a concise numerically correct result from first principles, that includes the relevant quantum corrections. But as far as the generic structure goes, string theory is in good shape - all the ingredients of the standard model (chiral fermions, gauge interactions, family replication) are naturally there, and it may well be that one won't ever be able to go beyond that. This however applies to any "alternative" contender as well; and as far as LQG goes, this theory is by far not in a similar shape. None of these generic features are there, and there is no sign that this will change anytime soon. The LQG guys struggle to even get flat space right, and matter coupling seems a very shaky issue, to say the least.

As a toy model, string theory does pretty well for many kinds of phenomena. This is perhaps similar to the solution of N=2 Susy gauge theory of Seiberg and Witten: while unrealistic, part of the theory is exactly solvable and teaches a lot about the structure of the theory, like instanton corrections and confinement. I would view most of what has been done in string theory so far as an analogous toy model, which allows to learn a lot about certain phenomena like black holes, effective field theories, non-perturbative dualities, etc. That all of this makes sense and is perfectly self-consistent is extremely non-trivial; unfortunatly only experts can gauge how non-trivial this really is. That we have today such a good toy model is a great achievement and a good reason to be happy and optimistic.

9. Aug 22, 2006

### Careful

Hi, I will be brief since I have not much time now.

**
The whole matter is very complicated. There is simply no
free lunch when dealing with quantum gravity and unification. It may well be that with the correct model, string theory or not, things will never be predictive and experimentally checkable. This remains to be seen. It is primarily a matter of the involved energy scales - not a matter of principle. **

I partially agree in the sense that indeed, you may have the correct model but it is impossible to calculate in (but then it is not much good for you anyway huh ). On the other hand, one could argue that it would be better to postpone the question what matter is for some time, make some reasonable effective ansatze about what it could be and do for you and develop a model which consistently unifies gravity and quantum mechanics given these assumptions. One such thing which comes to my mind is the measurement postulate in QM : the latter is clearly an incorrect oversimplification but with the right grains of salt, we still apply it after 80 years.

** This point is confused and deliberately misrepresented all the time. Namely whether something is unpredictive in principle, or just in practice. Mother nature does not care whether we human beings of today are able to measure up to the Planck scale or not. Similarly to ants, who have no possibility to detect radio waves... if they would be able to write down and contemplate upon the Maxwell equations, would this be science or not? **

Like I said, that would be mathematical speculation. Personally, I think deeper insight will come from looking at what we know to be true in a different, new way. Speculative theories have the nasty tendency to end up in religion when results remain absent. For now, there are only could-be'' results and no real exciting physics to speak about yet, nothing of the magnitude of the discoveries in the seventies anyway.
I can support the rest of what you say ... although I do not think in the way you do. Personally, I think that string theory and LQG both contain some good ingredients which might lead to fundamentally new exciting discoveries...

Careful