Category Archives: string theory

Whither String Theory? – Too Soon To Tell

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stringscape image from physics worldGosh, a thoughtfully-written general level (more or less) article on some of the general outcomes of string theory research! It’s written by Matthew Chalmers, and is in the Sept. ’07 edition of Physics World*. The article can be read online here, and downloadable pdf is here. The graphic on the right came with the article. I don’t fully understand what it is, but the title, like that of the article, is “stringscape”… Look, let’s not over-think this cvj – it’s a pretty decoration.

I’ve done a quick read of it (should re-read more carefully later on – it will no doubt have some emphases with which I disagree somewhat**) and I’d say it is very much worth reading. While not a perfect summary (what is?), compared to a lot that’s been out there, you’ll find it rather more informed, less sensational, (refreshingly unpoisoned by various prejudices, such as the presentations of Smolin and Woit – see numerous earlier discussions in the “More Scenes from the Storm in a Teacup” series of posts, and others), and unafraid to go to some length to unpack the issues somewhat carefully.

Very importantly, it contains numerous quotes from various respected researchers in […] Click to continue reading this post →

The 9/11 Flip

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Dijkgraaf Verlinde Verlinde 9 -11 flip figureOk, so here goes. A bit of physics linked to this all so significant date. There’s this term that people in string theory were using a lot in the middle to late 90’s, called the “9/11 flip”. I think maybe the Verlinde brothers, Erik and Herman, possibly in conjunction with Robbert Dijkgraaf, made the term popular but I am not sure about that and I welcome a correction. [Update, since there is some confusion: I’m talking about the term here, not the technique itself, which is older.]

(On right (click for larger) is a snapshot of one of the figures from their influential 1997 “Matrix String Theory” paper. You can see the use the term there, and it is in the paper’s text too, and soon everyone was using it in seminars and other papers to follow.)

The flip became particularly useful when people were discovering the wonders of “M-theory”, which is the catch-all term for whatever is the parent theory of string theory, something we are still trying to formulate. There are a number of narrower uses of the term, however – some more justified than others. For a while, everyone was thinking about the five ten-dimensional supersymmetric string theories (“type IIA”, “type IIB”, “type I”, and two types of “heterotic” theory) which, prior to the middle of 1995 (actually as early as late 1994 or early 1995) all seemed like totally distinct theories, and in the post middle-1995 era (after Witten’s remarkable talk at strings 1995 here at USC: paper here) were recognized to be all part of the same theory. The universe (at least the continually expanding string theory one) changed radically overnight.

m-theory puzzle
(One of my preferred ways of presenting the puzzle that is M-theory, and how the ten dimensional string theories fit in the puzzle. This is a slide from one of my general talks on the subject.)

The 9/11 flip is really simple, although when a setting is complicated enough, it can […] Click to continue reading this post →

Lookin’ For Some Hot Stuff

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___________________________________________________________________________________
Hot, hot, hot, hot stuff
hot, hot, hot
hot, hot, hot, hot stuff
hot, hot, hot

– from “Hot Stuff”, by Donna Summer (1979). I refer to not only the physics but the c. 100 oF temperatures we’ve been having here every day recently.
___________________________________________________________________________________

On my way back from the conference, I spotted this book (left) last Saturday in Foyles (the booksellers) in London 1. Quark Gluon Plasma book It is a collection of reprints of a lot of the papers forming the foundations of the physics of the quark-gluon plasma (QGP) idea, going back the early to mid 1970s with such papers as Collins and Perry (Gosh, I had no idea Malcolm was one of the early workers on this idea. He’s much more thought of as associated with black holes, gravity, strings and so forth, ideas which – ironically – have recently turned out to be relevant to the discussions of the physics too. See my recent post, and there are also various popular articles to be found2).

Putting aside the usual ridiculous price that Springer Elsevier charges for books, I found myself in two minds about this book, in view of the surprises being uncovered about the properties of this remarkable state of matter at the RHIC experiment. Is this collection of early papers a useful working tool, or is it now just of historical interest, since many of the basic expectations about the properties of the plasma seem now to be incorrect?

rhic collision of gold ionsWell, after a bit of thought, I decided that the latter view would be way too hasty. First and foremost, on a general level, even if some of the computations in some papers were done in the “wrong” light (it’s a strongly coupled liquid that flows, not a weakly coupled gas of quarks and gluons), much of their content will still be useful in many ways – good and correct calculations last for all time, it is the sense of the words decorating them that may crumble over time. More specifically, one can worry about whether there were assumptions (and approximations based on those) that went into the computations that will render […] Click to continue reading this post →

News From The Front, VI: Simultaneity

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aspen from gondolaI stopped the previous post rather abruptly (I had to do another task and then run some errands) without getting to tell you a little twist at the end of the story. Here it is.

Having chipped away at the thoughts that Strominger’s talk stirred in my head for several days last week, scribbling equations to check that all I was thinking was on the right track (and chatting a couple of times with Nick Halmagyi), I decided that it was all fitting together so nicely that the framework and my extensions of it just had to be true. There was that feeling that it was too nice to be wrong, and it passed all the obvious checks I could think of. There were two independent consistency checks everything had to pass (using my way of formulating things) and they gave exactly the right results as required by the general setup, with no room for maneuver.

When that happens so nicely, usually at that point in thinking about a physics problem, a thought occurs to me. If I’m playing with a good idea and everything is working so well, then there’s at least 200 other people in the field who probably are also playing with it, and 199 of them have way more time than I do to think it through and write it up before I can. One should not really worry about these things in an ideal world, but I’d be lying to you if I said it did not come up as a concern from time to time. I’ve a history of having my thunder stolen out from under me several times in the field (and not always accidentally), so I’m a bit gun shy.

Anyway, I started writing a draft of the paper on Thursday the way I usually do: I write […] Click to continue reading this post →

News From The Front, V: Microscopic Weekend Diversions

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I’ve been spending the day so far as an administrator, and not a researcher, since I have to present the results of two committees’ deliberations at one of the big annual organizational meetings tomorrow here at the Aspen Center for Physics. So I’ve been gathering and arranging data in a presentable form. Enough. I will take a break and blog a tiny bit before turning to a truly riveting task – reviewing an introductory physics textbook for a publisher… (Sigh…it is not so easy to escape these things out of semester time.)

I had big plans to do a hike each day on the weekend, but physics intervened. I should explain a bit more. Earlier last week I eventually got around to following Nick’s suggestion from an earlier post to take a look at Andy Strominger’s Strings 2007 talk entitled “Search for the Holographic Dual of N Heterotic Strings”. It was the usual nice Strominger talk, where he motivates the physics very well, and presents interesting and clear D-branesthoughts on the problem in hand. I shall try to say a bit more about what it is about later on, but the general gist of it is that it is to do with understanding certain types of four dimensional black hole in string theory. As you may know, one of the extraordinarily successful results in string theory in the last decade (and slightly more) has been that we can understand one of the most central results of semi-classical quantum gravity -that they have an entropy and behave like thermodynamical objects (the work of Bekenstein and of Hawking from the early 70s)- in precise terms in the full theory of quantum gravity that string theory appears to present us with. This started with the work of Strominger and Vafa in 1996, that showed how to describe a large class of black holes as essentially made of extended objects called D-branes (about which I’ve spoken at length earlier1).

Just to fill in the gaps roughly: Hawking’s result that black holes can radiate as thermodynamical objects comes from taking Einstein’s theory of General Relativity and combining it with Quantum Mechanics in a partial way. He could not really do much better since there was no proper quantum theory of gravity at the time, but even in […] Click to continue reading this post →

Strings 2007: Share the Memories

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trees near the aspen center for physicsA big chunk of yesterday (recall, I’m visiting at the Aspen Center for Physics) was spent chatting with old friends in the field I have not seen in a while, including going for a walk or two in the local surrounds with colleagues, discussing some of the physics issues of the day.

One of the things that comes up a lot with everyone I spoke to (and met at lunch, and in corridors and so forth) was Strings 2007, the big annual meeting that was held in Madrid last month (blog post here). It comes up in the form of people asking each other things like: “were you at Strings?”, “what did you think of Strings?”, “what were your favourite talks?”, “is there any interesting gossip about…?” (where the latter is not necessarily directly about physics).

So it occurred to me that some of those conversations and responses might be useful to workers in the field. Of course, you can just sit and work your way through the entire collection of online talks, a good thing to do. But it’s interesting to hear from others what talks they liked, and why, just as we do (and maybe have done) over tea and coffee in lounges all over the world after someone returns from a meeting. Often, this is where we hear of some excellent work by the less famous speakers (or even by someone who did not talk at all), etc.

So I’ll kick off. Although I was not there, and have yet to start a serious assault on […] Click to continue reading this post →

Strings 2007

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goya strings The main annual conference in my main field of interest starts today. Strings 2007 is in Madrid, and runs all week. The website is here (while there, have a play with the front page image of the Goya painting – quite entertaining). They promise to update the schedule/speakers page with scans of slides, and video, so you’ll be able to keep track of some of the new developments online. There’s no system for doing this live, or asking questions remotely, so if you want to quiz Ed Witten about his new 83-page monster paper on three dimensional gravity that came out yesterday (just in time for the conference!), or feel the buzz of event-anticipation whenever Witten talks about huge new sets of results, you’ll still have to show up in person.

Why am I not there? Well, it would be nice, but there are lots of reasons I’m not going […] Click to continue reading this post →

Nuts and Bolts

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notebook workingYes, part of my job is to sit and think about how the universe works. People hear this, and they wonder exactly what that entails. Well, it entails a lot of things – sometimes there’s the grand thoughts and the thought experiments and the like that you hear of from documentaries and books about Einstein and other famous scientists – but more often that not it is grungy nuts and bolts.

Take yesterday for example. After a week of working on various calculations and chipping away at improving my understanding of how to approach a certain problem, I decided to take Saturday and be outdoors a bit more…see what it was like outside. You know…. Have an actual Saturday Saturday. (I did not end up being booked to do that TV shoot, by the way, so I had a nice clear day ahead of me.)

What actually transpired was this: […] Click to continue reading this post →

TASI@Home

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This year’s month-long Theoretical Advanced Study Institute -TASI- looks especially good, from my point of view, with a great combination of topics and lecturers. As usual, it is held in Boulder, Colorado. It’s all about current ideas and experiments and observations in particle physics and cosmology. Three USC students are there and I’ve heard from them that things have been great so far.

raphael bousso at TASIWell, the great news is that the TASI people are making the lectures available online a fairly short time after their delivery. The link is here. So even though not there, you can schedule some time to take these lecture courses if you like. I glanced for a while at Raphael Bousso’s first lecture in the series “Cosmology and the Landscape”, and it was clear and very well presented. (This is not entirely surprising – Raph is always an excellent lecturer.) […] Click to continue reading this post →

That Ain’t Workin’

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Remember the Tune “Money for Nothing”, by Dire Straits? It was a big hit in the 80s. (Remember those?) Well, Warren of the new blog A Strange Universe wrote a rather brilliant physics version of it, to be sung to the same tune. The “stringer” is the object of the ridicule of the song’s character. The original post is here, where he’ll tell you his thoughts on the song. I can’t resist (I hope he forgives me) posting the entire thing here, rather than an extract, which would break up its impact. (Original song’s lyrics are here, by the way, for comparison.)

So here it is: […] Click to continue reading this post →

Masterclass, II

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Don’t forget to catch the latest installment of Joe Polchinski’s rather thorough deconstruction of the nonsense, obfuscation, selective memory, and other confusions that constitute the bulk of Lee Smolin’s attack on string theory.

All the points I’ve had the energy to raise have been made here on Asymptotia […] Click to continue reading this post →

Quark Soup Al Dente

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Here’s Rob Myers in action, giving Monday’s excellent departmental colloquium, entitled “Quark Soup Al Dente: Applied String Theory”:

robert c myers quark soup al dente

Here was his abstract:

In recent years, experiments at the Relativistic Heavy Ion Collider have discovered an exotic new state of matter known as the quark-gluon plasma. Simple theoretical considerations suggested that this plasma would behave like an ideal gas, however, the experiments show that it actually behaves very much like an ideal liquid. Thus the standard theoretical tools, such as perturbation theory and lattice gauge theory, are poorly suited to understand this new phase. However, recent progress in superstring theory has provided us with a theoretical laboratory for studying very similar systems of strongly interacting hot non-abelian plasmas. This surprising new perspective extracts the fluid properties of the plasma from physical processes in a black hole spacetime. At present, this approach seems to provide some of the best tools which theoretical physicists have to understand the heavy ion collisions at RHIC.

For a very good blog post on this issue, see Bee and Stefan’s post at Backreaction.

It was really excellent to see Rob and spend some time with him at dinner afterwards and at lunch the next day with my students. We got to chat over a nice Tapas-style meal and catch up a bit on what each other has been up to (both in and out of physics – Rob is one of my most long standing friends and collaborators in the field), and he even gave us a seminar on Tuesday before leaving.

Now, here’s a physics question for you: […] Click to continue reading this post →