Is String Theory a scientific theory or a hypothesis?
In scientific usage it is a hypothesis. A Theory is reserved for bodies of knowledge that are assumed to be so true that they form the underpinnings of other sciences. The Theory of Relativity, The Theory of Gravity, the Theory of Evolution.
However, popular usage doesn’t truly differentiate between theory and hypothesis, and in fact uses theory in usages that scientists would reserve for hypothesis.
So there is no one general answer for the OP. It depends on context and circumstance and audience and how precise you need to be to convey your point.
Does it even really count as a hypothesis? A hypothesis needs to be testable, and so far, String Theory has proposed nothing testable.
It’s a pan-dimensional Rubik’s Cube for gods, cranks, and physicists that don’t have anything better to do with their time.
I assume, of course, that you’re generally talking about the framework of various supersymmetric string theories that fall under the aegis of M-Theory, and not about the theories that cats have regarding the evil and conspiratorial nature of strings which must be vigorously attacked and suppressed before they take over the world. (The same is also true of milk jug rings and the little plastic bits on the ends of shoelaces. Subversion knows no bounds when it comes to the mundane.)
Stranger
One of my normally very intelligent friends has just come out to me as a young Earther. One of his first arguments about “the theory of evolution” is that it’s just a theory. 
Just like number theory, game theory, probability theory, and set theory, where our knowledge is nothing better than wild-ass conjecture, of course.
[To be fair, the use of “theory” in the mathematical context isn’t quite the same as in the scientific context either, but, yeah, “It’s just a theory” is just such a ridiculously silly thing to believe forms an argument]
Was string theory name by scientists? M-theory was named by Witten, why would he call it M-theory if it not a scientific theory?
I am certainly no physicist but I love reading about it. My take is that string theory is much less of a theory in pure scientific terms than young earth theory. String theory can’t be tested and it tends to be all over the place even if it could. From the way I read it, string theory has also taken some massively destructive hits in the past few years and there isn’t much left even if it could be tested.
Like I said, I am an arm-chair physicist at best and I cheer for whoever gets the right answers but the meta-commentary I have read suggests strongly that string theory is just made up crap and always has been. I welcome commentary from others.
Yes, string theory was given that name by scientists. When not being formal, they talk in everyday language just like other people. Except they know the technical differences, unlike Creationists.
And M-theory was named after string theory was. Witten just showed that five supposedly different versions of string theory were in fact mathematically equivalent.
No, this suggested definition misses the nub of what scientists mean by “theory”. The meaning is more like “a systematic and coherent non-trivial model” or “an interrelated set of propositions or explanations”. There’s no implication about whether it is true or not. Nor about the confidence or tentativeness with which it is put forward.
To take an example I happen to have easily to hand, Gell-Mann’s first preprint on SU(3) symmetry in hadrons was called “The Eightfold Way: A Theory of Strong Interaction Symmetry”. No physicist reading these two pages in 1961 would have taken Gell-Mann to be suggesting with this title that his scheme was “so true [as to] form the underpinnings of other sciences”. It was a (testable) proposal whose theory-ness derived from the fact that he was using a mathematical structure to model part of the available data.[sup]*[/sup] As events panned out, it turned out he’d identified a useful (but not exact) approximation that did indeed make sense out of much of the experimental evidence. That success make physicists regard the theory as truer and less hypothetical, but it didn’t make it more theory-like. His proposal was already a theory from the start. Nor would it ceased to have been a theory had its predications been falsified.
Working physicists amongst themselves thus use the word to apply to a much wider range of ideas than the well-confirmed examples like relativity or quantum theory that tend to be mentioned in popular media. And this is not because they are using the word in the sloppy everyday sense when they do so.
Note that number theory, relativity, gravity and evolution are very much still theories. The usual creationist objection to the name “theory of evolution” fails, not because Darwin’s hypothesis has been sufficiently well tested that it has become a theory, but because the name was never implying anything about tentativeness in the first place.
String theory fits this definition as well and that’s why particle physicists/quantum field theorists referred to it as such amongst themselves in the first place.[sup]**[/sup]
[sub]* In this instance, it’s the mathematical structure that defined Gell-Mann’s theory. But theories can be theories without being formal mathematics. They will however have some sort of logical structure to them. They’re not simply a bunch of unrelated, disconnected assertions.[/sub]
[sub]** With the caveat that it’s often now regarded as a research programme in search of a specific theory - any theory - rather than that theory itself.[/sub]
Witten may also have been influenced by the various ways “theory” is used in mathematics. Most often it means the body of results having to do with a particular kind of structure, e.g., group theory. But, in algebraic topology (which is part of the math behind string theory), “theory” is also used for a particular kind of object, a “homology theory” or “cohomology theory.” One example is called K-theory. I very much suspect that Witten came up with the name M-theory based on this usage.
Those are called aglets, fact fans.
The only answer is, yes, evolution is a theory. Creationism, however is not.
Tris
I just want to say that I don’t know diddly about string theory, but *this *is now permanently filed in my factlet collection. Thanks!
Like Copernicus’ proposal of the sun as the center of the solar system, it’s not really intended as “this is the way things ARE” but as “this is something that simplifies calculations, leading to predictions that match our observations.”
But the same applies to many other “theories” or “definitions” in science, for example to all the different versions of the atom.
The OP may be interested in Woit’s book (and associated blog) Not Even Wrong: The Failure of String Theory And the Search for Unity in Physical Law.
This post goes in my permanent file of all-time great posts on this board. 
I’m with you there. I know only one guy who is interested in string theory, and he has very, very severe mental problems despite being extremely intelligent. He talks about it as if it’s a religion. Listening to his ramblings about it have turned me off, big time.
I was all set to point out how that article shot itself in the foot by misspelling “Zermelo” as “Zurmelo”, but it looks like they’ve fixed that now.