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.
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!)