So What Is String Theory, Anyway?

The usual answer you’ll get from the person on the street (as it were) includes lots of nice words about wiggling strings that look like particles, and so forth, and that’s fine. However, the [informed] next level answer, when you’ve worked enough in the field, is that we don’t know. I’ve told you why (at least in part) in previous posts and so I’ll let you read them. We’re still working on it.

While we work, we’ve learned that it is a quite marvellous thing (from the bits of it we’ve come to grips with) that is teaching us a lot about all kinds of physics, and mathematics too. Some of this may be good for describing things about Nature, and we’re still working out lots of that (although see some of the exciting things I’ve been talking about in my previous post and the links therein).

So what do we put on the T-shirt? (You know, the analogue of Maxwell’s equations for electromagnetism – light, etc – that every physics undergrad likes to have on their T-shirt). Well, we don’t know yet.

polchinski what is string theory

But that’s all my opinion. Every now and again it is good to hear from one of the masters about what they think of string theory*, and what it is and so forth. Happily, Joe Polchinski has been known to agree to stand up and give an exposition on this topic from time to time, and the good news is that he’s been at it again, just yesterday!

Joe tries to answer the T-shirt question.

So go along to the (K)ITP website to stream his (moderately technical) talk and listen to the discussion (as I am now as I blog)**. There are a lot of healthy exchanges with good humour and some great (in)jokes too.


[Update: The last ten minutes of his presentation illustrates quite a bit of what I mean in my second sentence…]


(*As opposed to people who don’t know what they’re talking about, and sometimes with an axe to grind, shouting loudly (and sometimes deliberately misleadingly) about it. See lots of discussion, sometimes useful and sometimes otherwise, in here.)

(**Thanks KB and JP!)

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22 Responses to So What Is String Theory, Anyway?

  1. senderista says:

    I prefer the version of Maxwell’s equations that fits on a thong 😉

    dF = 0
    d*F = J

  2. Adam Benkato says:

    Hi Professor,

    An off-topic comment: I stopped in at Bacaro the other day, and found it extremely delightful! It is an excellent atmosphere for reading or playing chess (which I did with a friend). I mentioned that I had been one of your students and Santos (I think his name was) said to say hi. Maybe I’ll run into you there sometime..


  3. Clifford says:

    senderista: – Thanks much for the top notch thong idea! There have been times when I’ve wondered what I might write on one, and then for one reason or another never finished the thought…

    Adam – Great! Happy to hear this…It is an excellent place. Great to hear from you!



  4. Christine says:

    Hi Clifford,

    Thanks for this post. If possible, in a few words, what would you say “string theory is *not*”?

    Best regards,

  5. Blake Stacey says:

    If possible, in a few words, what would you say “string theory is *not*”?


  6. Christine says:


    Well, perhaps I should have added (the obvious) — what string theory is not, in the context of what some have nevertheless claimed(claims) it to be. What is the consensus of the community today — in the sense that string theory was(is) claimed to be something, but turned out not to be what was claimed or expected. *If* that is the case.

    If the question is too easy, then disregard it.

  7. Clifford says:

    Hi Christine, other than the words “fully understood”, (as in not), I can’t offer anything very useful to say at this juncture (especially before my morning oatmeal). History warns me against saying such things, generally, since there can always be surprises.

    Oh… I guess I can quote the title of one of my own papers on the matter, from 1995:

    It is not a theory of strings.


  8. graduate student says:

    It was indeed a great talk and the room was jam-packed!

  9. Blake Stacey says:

    OK, cheap jokes aside, that was a great talk — thanks for pointing it out!

  10. Christine says:

    Hi Clifford,

    Well, it evolved from strings to further generalizations/abstractions, but the name “string theory” remained, perhaps for being a popular name? Something perhaps akin to (although less problematic than) “big bang theory”, which actually never meant to be an explosion located in space but a theory for the very hot initial phase of the universe…?

    What would you call string theory, if it were to give a more representative name? A “generalized” or “extended” quantum field theory?


  11. Clifford says:

    I see no urgency to give it a name, lest we again misname it. It’s not about the PR as much as it’s about the physics. Besides, a name was given in 1995/6 during the Revolution, and it was M-Theory. The press never caught on, and several people in the field misappropriated the name, thinking, for example that it meant 11D supergravity, etc – which it did not.

    Anyway… lots of things are misnamed due to historical accidents, misunderstandings, etc., some in other fields, and lots of them in science…(the uncertainty principle is a good example – it’s not uncertainty so much as indeterminacy – the word used in various translations of the word) and we manage ok.



  12. A.J. says:

    Presumably, once we figure out what the fundamental degrees of M-theory are, we’ll name them “M”s.

  13. Clifford says:


    (Of course, this assumes that there is going to be a single set of such degrees of freedom. A possible – probably likely – outcome is that the answer to that is always context dependent.)


  14. Christine says:

    Sure, “A rose by any other name would smell as sweet”… What is important is the physics, of course.

  15. Blake Stacey says:

    If you push the “precision of language” business too far, you’d have to say that “electromagnetism” is as bad a name as “string theory”, since E&M is not confined to the study of amber and rocks from Magnesia.

  16. metal says:

    there is a place called Magnesia?

    Well I learned something today 🙂

  17. Elliot says:

    So a group of “M”s of order 2 would be “M and M s”?


  18. Nige Cook says:

    ‘So what do we put on the T-shirt? (You know, the analogue of Maxwell’s equations for electromagnetism – light, etc – that every physics undergrad likes to have on their T-shirt). Well, we don’t know yet.’

    The candour is nice. If string theorists were working on an alternative to a mainstream idea (instead of being the mainstream), and they admitted that they couldn’t even define their theory, they might have a tough time being taken seriously. Alternatives are shunned by string theorists: authors are told by peer-reviewers to go away, solve their problems, and come back when they have the theory completed to a more understandable level.

    This double-standard, where mainstream work on string theory is taken seriously and published, but alternative ideas with few people working on them are rejected (simply because they are not fashionably mainstream and haven’t had the same investment of time as string theory has) creates critics with axes to grind.

    The usual defence of string theory is that so many people have worked on it for so long and published so much, and have all these indirect successes like the CFT/AdS equivalence conjecture and lots of other applications from it, but you can get such useful spin-offs from failed theories. E.g., Ptolemy’s epicycles theory of the earth-centred universe was so complicated it was a major motivation that led to the development of trigonometry to simplify the calculations, but this result doesn’t justify the epicycle theory as solid physics.

    It’s quite possible that more spin-offs would have occurred if people had taken the more nearly correct solar system theory of Aristarchus more seriously (in it’s original form it had errors such as circular orbits), and worked on that instead of dismissing it out of hand! Trigonometry would probably still have arisen.

  19. Clifford says:

    No, no, no – the usual defence of string theory is its rather interesting and promising results in several areas that a lot of people are interested in. Plain and simple. And people working on string theory love alternatives. If something better comes along (and you’re free to present it to the community through the usual channels), the community would start working on that overnight.

    See all this laid out plainly in the earlier discussions I’ve pointed to in the post. No point rehashing it all here.


  20. Nige Cook says:

    Hi Clifford,

    Thank you very much for correcting my misunderstanding!

  21. Don says:

    Seems me that bosonic strings were designed to be a theory of nuclear forces, but it was killed during 70´s, when physicists become aware that THE aimed theory was QCD.
    However, by invoking super (non-natural) symmetry strings were reborn, and, just again (after AdS/CFT) showed itself to be unable to describe strong nuclear forces.
    So, this physical theory “of everything”, which can neither describe the physical aspects it was designed for, can be simply printable on a T-shirt as:

    ST = {?} = void set!

  22. Just Learning says:

    I think Stringy Theory is here to stay. What it encompasses is the behavior of certain types of hypersurfaces. The notion that these surfaces themselves can be strongly connected and exhibit tension is remarkable. It is the distortion of spacetime and its connection to particles that is important. Our notion of energy, displacement and ordering are closely linked concepts. Point particles ultimately fail to describe our world because their is no room for there to be a displacement nor do they lead to a natural concept of ordering that can account for their internal energy.