Is String Theory Really a Scientific Theory?

vk38 writes, "The New Yorker is running a story on whether String Theory is really a scientific theory or just an abstract exercise in math designed to churn out papers and Ph.Ds for the established academics. The article reviews two current books, by Lee Smolin and Peter Woit, laying out the case against string theory." From the article: "Dozens of string-theory conferences have been held, hundreds of new Ph.D.s have been minted, and thousands of papers have been written. Yet... not a single new testable prediction has been made, not a single theoretical puzzle has been solved. In fact, there is no theory so far — just a set of hunches and calculations suggesting that a theory might exist. And, even if it does, this theory will come in such a bewildering number of versions that it will be of no practical use: a Theory of Nothing... String theory has always had a few vocal skeptics... Sheldon Glashow, who won a Nobel Prize for making one of the last great advances in physics before the beginning of the string-theory era, has likened string theory to a 'new version of medieval theology,' and campaigned to keep string theorists out of his own department at Harvard. (He failed.)"

Comments

Rolled up dimensions don't require extra dims

[benhocking]

Having a "rolled up" dimension doesn't require an extra dimension, because they're not _actually_ rolled up. The metric used to describe them is just easy to picture that way. Just like curved 4-dimensional space time doesn't need a 5th dimension to be curved into. I tried looking for a good web-site that explains this, but didn't find one in the time I'm willing to spend looking for one. I'm sure someone else knows of one, though.

Re:Uh no

[808140]

Here's the problem though. GR and QM are both, relative to ST, extremely simple. And while ST may make the same predictions that GR and QM make, it does so in a far more complex way, without adding any extra information -- QM and GR are incompatible, but ST fails to resolve those incompatibilities in a testable way.

GR was more complex than Classical Newtonian Mechanics, but it was, essentially, a value-added theory: it explained a bunch of things that Classical Mechanics couldn't, all while remaining compatible with Classical Mechanics in places where Classical Mechanics made accurate predictions. Therefore, GR was taken to replace classical mechanics, despite the added complexity of the theory, because it was broader in scope, falsifiable, and provably more correct than the theory it replaced.

ST does not fit this mold. It is far, far, far, far more complex than either GR or QM, and makes no extra falsifiable predictions. It doesn't resolve the inconsistencies between the two. In other words, from a purely scientific perspective, it's just a hypothesis and not a particularly useful one at that.

Of course, I'm a mathematician by training and lots of interesting math has come out of ST, so for that I'm happy.

Re:Uh no

[backdoorstudent]

Of course String Theory makes testable predictions. Just like General Relativity and Quantum Mechanics make testable predictions. The bad news is that they are the same predictions that General Relativity and Quantum Mechanics make, many of which we've already tested, and is thus indistinguishable from them. The good news is that String theory makes the same predictions as GR and QM while still being only one theory.

This is completely wrong.

First of all it is no surprise that it resembles QM because it is QM. It assumes QM and applies it to a vibrating string, brane, etc.. But there is no new theory because there's at least a handful of different ways to do this and they're all called string theory. GR on the other hand is not as obvious. They are able to get equations that resemble Einstein's equations, but GR does NOT just pop out of it.

problems

[bcrowell]

I read Smolen's book recently, and learned a lot of new and interesting things about string theory from it. Some problems with string theory:

1. There are lots and lots of possible string theories, describing different ways for the extra dimensions to curl up. Some string theorists have been reduced to using the anthropic principle to explain why one version would exist and not the others; this is a major admission of defeat, since the anthropic principle is really not an accepted way of doing science.
2. String theory was always thought to require a zero or negative cosomological constant, which was fine when the cosmological constant was believed to be zero. When observations showed it was nonzero and positive, it should have been taken a disproof of string theory. Instead, string theorists came up with a massive kludge to try to get a positive value from string theory. It's not clear whether the kludge is really a reasonable, viable mechanism.
3. String theory is done on a background of spacetime, but we know that spacetime is dynamic. String theory, in its present versions, appears to be incompatible with a time-varying background spacetime.
4. Many important results in string theory are merely conjectures that everybody believes to be true. In particular, string theory's finiteness has never been proved in general. All that's been proved is that a certain type of term in perturbation theory is always finite. According to Smolen, very few string theorists are even careful enough about this kind of thing to realize that finiteness hasn't been proved in general.
5. There are strong, model-independent arguments that spacetime must be discrete at the Planck scale. (There's a good, nontechnical discussion of the argument in Smolen's Three Roads to Quantum Gravity.) String theory assumes it's continuous.

Re:why does the new yorker care?

[jefu]

Should the New Yorker not cover things that may be beyond the reach of the average reader?

Even if they were publishing the mathematical theory itself, they should be free to do so (though it would probably not appeal to the average reader), but they're not doing that, they're publishing about a controversy in the field - just as they might about any other field. Is physics somehow different than (to take an example from one article I remember) considering the effectiveness of different kinds of therapy on people who've experienced stressful events and who might then be subject to PTSD?

Writers and journalists should be encouraged to write about whatever interests them and their audience, even if the people they're writing about don't always find it flattering or helpful.

As someone who frequently reads the New Yorker, I must say I've learned a lot from it over the years - and in many areas that I'm not familiar with such readings have sometimes taught me something (perhaps only a little, but something), sometimes aroused my curiousity, and sometimes introduced me to whole new ideas that I might not have otherwise run into. I say "More power to 'em".

Re:Thanks for the troll submission

[k98sven]

It's not "FUD" in the least. Have you forgotten entirely what that term's origin and use is? Just because you disagree with a critical view doesn't make it a baseless propaganda effort. If it had been that, they wouldn't have bothered writing an entire book to presesnt their arguments. They wouldn't be presenting arguments to begin with!

There are reasons why string theory has failed to come up with any NEW predictions. For one thing, it's being constantly tweaked so that it is consistent with EXISTING experimentation. After all, why would you build a theory that you hope will become a GUT if it's not consistent with other proven theories?

This is why you don't get it: That is behaviour which is generally considered unscientific. If you need to keep modifying your theory to explain stuff, then it's not a scientific theory. It's an ad-hoc mess of empiricism of zero real value. The rules of the game are:
1) It must be testable (falsifiable)
2) You must provide new predictions
3) You must explain previous observations, observations not used in formulating the theory., and ideally, none at all.
4) You must do so using fewer postulates (assumptions) than the previous theory.

The other thing is that this is a theory... the fact that it (mathematically) treats particles as being a 1D string vibrating in n-dimensions doesn't actually mean that if you could see items smaller than the planck length, that you would actually see a vibrating string!! It's a mathematical representation... the math doesn't have to represent exactly what's happening as long as it can be used to describe what is happening.

The word you're looking for is "model". But how is this another thing? Our current understanding is a model as well. The question is whether it's a better model or not is still there and unanswered.

After all, modern chemistry is incredibly useful for predicting how atoms interact with eachother to form compounds... even though it's based off the idea that electrons orbit a nucleus like a tiny little planet orbitting a sun... that is precisely NOT what an electron does, but who cares, the math allows you to make determinations. It's the same with string theory.

You have no clue. Modern chemistry is not based on any such model. It's based entirely on the standard model of physics. There is not one, not one! molecular property that can be described in anything less than a fully quantum-mechanical treatment. All of chemistry is purely due to quantum-mechanical effects.

And string theory is not the same at all, even if you'd been right. String theory is an attempt at a more basic and general theory of quantum mechanics, in the same way as classical mechanics is a limiting case of quantum theory. It is not an approximation of quantum theory, and not intended to be one.

They're starting with a very simple, and very elegant premise (that all particles are periodic vibrations with different frequencies corresponding to different particles) and then building from there. Hell... start with that and just try and figure out how to represent the periodic table... that alone would be mind-boggling.

You don't get it. The periodic table is already entirely explained from QM, and has been for some time. There's no more reason to describe it in terms of string theory than to describe the motion of billiard balls in terms of quantum mechanics: It's unnecessary because it's already explained by classical mech, and we know classical mech is a subset of quantum mech.

In the case of string theory, all they need to do is show that QM is a subset of that theory. That's not hard and it is. It forms the basic premise of their work as well as the goal. The idea is that they're going to work from part of quantum theory and relativity and somehow arrive at the whole thing. Which parts the