So I’ve been a bit quiet as I’ve had a lot going on. This includes preparing ten interesting slides to use as props for a talk I gave this evening to the USC Philosophy Club. It was entitled “Ten Things YOU Should Know About Black Holes”. It started with the original idea by Michell in 1783 (yes, really, that early!) and ended with topics of current research (what is the fate of the singularity? What really happens at a horizon? Etc., etc…) I spoke for a while and then fielded tons of questions, and am now (I am writing a draft of this on the subway train home – uploading later) suffering from a rather broken voice due to too much talking and projection…. Gosh. But it was fun. A really […] Click to continue reading this post
I just spotted (a bit late) that Steven Weinberg (one of the giants of my field) has written a piece in the New York Review ofBooks entitled “Physics: What We Do and Don’t Know”. I recommend it. He talks about astronomy, cosmology, particle physics, and by casting his eye over the arc of their recent (intertwined) histories of ideas, experiments and discoveries, tries to put the Standard Models of particle physics and of cosmology into perspective.
The article is […] Click to continue reading this post
Friday’s meeting was rather nice. There was a really good turnout (especially from UCLA) and so in the end we had the perfect combination of an attentive and receptive audience and four really good speakers. As per design of the whole thing, plenty of time was allowed for discussion and pedagogy, and so I got the feeling that people felt really comfortable raising points during the talks and also chatting further during the breaks and lunch and dinner. It was really good to catch up with friends and colleagues from groups in the area, [...] Click to continue reading this post
Oh! I forgot to mention that the next Southern California Strings Seminar is today! It is being hosted for the first time by the group at UC San Diego. (Thanks Ken!) There’s a webpage with the talk schedule here.
Now, better head there….
Click to continue reading this post
Meanwhile, poor Matt Strassler, who means well, is re-discovering the frustratingly convenient (for some) fact that blogs (or is it blog readers?) have no memory for stuff that has scrolled off the page, so attention-seekers get to make the same deliberately wrong claims and misrepresentations they did before, and that were thoroughly addressed before, and a whole new bunch of people who want to learn a bit of science will be drawn in to a non-debate, not knowing that none of this is new. Attention-seekers get the attention they desire, and since attention is the main point for them (not actual progress in science, oh no, not at all!), they succeed.
Matt is discovering this now… By trying to discuss a little nuance about what recent discoveries at the LHC may or may not mean for string theory, he has wandered into the same old tired shouting match about string theory with attention seekers who have nothing better to do but put their hands over their ears and yell misleading slogans from the sidelines to generate fake controversy, and/or split the world into pro-string vs anti-string which is so simplistic and, frankly, juvenile. An interesting game, if you’re up for it, would be to look at the noise in the long comment stream there, and then look at almost any of my Scenes from a Storm in a Teacup posts (from 2006!!!) and the long comment streams accompanying them (look at, for example IV, V, and VI), and see if you can see the same sorts of patterns. I deliberately collected those posts together to form a partial* record of some of that time’s discussion for precisely this purpose, for those who care to read and see that all attention-seekers (who have no real interest in letting science research run its course) have to do is wait for a while and then start yelling the same faux claims all over again to get attention, sell books, enlarge their mutual admiration society membership, etc.
You know, all this behaviour is hardly different from that of the annoying squirrels I have to deal with at my fruit trees from time to time. Not being so good at cultivating [..] Click to continue reading this post
For those who have a thirst for something physics-y to follow the tomato chutney post, here’s a decorated physics diagram I made in Matlab this morning. Click for a larger view. It’s the phase diagram of interesting black hole transitions* (that I co-discovered 14 years ago) associated with part of the story I mentioned last month. On the right of the line you have small black holes favoured (of a given charge, so move horizontally), and on the left side of the line the system favours large black holes and so when you cross the line you have a sudden jump from one type to the other. That second order critical point I talked about there is the end of the line of first order points. The blue dot. Above there, you cross over smoothly from small to large holes. The blue dot is the border between the two cases.
It is a bit like having steam (or water vapour) on the left and liquid water on the right, and crossing the line is what you call boiling. The second order point is the place [...] Click to continue reading this post
Yesterday I submitted a new paper to the arxiv. This is is my favourite curve from it. Some of you who follow the blog will recognize the blue circle-dots and guess that this is the output of the dot-generation I’ve been tinkering away at (and reporting on somewhat cryptically) since April (see e.g. here, here, and here). Correct. There are many reasons why that is the case. One of them might well be because it looks like a very comfy chair, and by time I’d submitted the paper, I was rather tired. I’d pulled an all-nighter to finish the paper because I wanted to submit it by noon yesterday, and the night before I had to spend several hours at a social event.
So once it was an appropriate time to leave the place I was at, I said my goodbyes, jumped on my bike, pedalled home, put on some coffee, some Ana Tijoux (through headphones, so as not to wake anyone. Why her? Kinetic energy was what I needed at that moment – her vocal style is full of that. Try “La Bala” or “1977″. It is in Spanish, but that’s just fine.), and from 10:30pm to about 12 hours later, ground out the paper. I had to do this since I took some time away from the research project for a week, and then on Tuesday evening noticed the title and abstract of a new paper on the arxiv that suggested some overlap with what I was doing. So I had no choice but to gather all the results I’d been gathering the last several weeks and write them up and get them out, putting off reading the other paper until afterwards, so as to remain independent. Hence the all-nighter to finish it all. It was a pretty easy paper to write since I’ve had the results for a while, knew what I wanted to say, and it was just a matter of pulling everything together and writing a lot of background to set the scene for the results. A fair amount of the time was spent fiddling with things like how to generate figures from Matlab that embed nicely into the text, and so forth. Technical tedium.
The physics? Another reason I like the above curve is because it examines physics from an old favourite phase transition I co-discovered almost 14 – gosh yes, cvj, fourteen! – years ago. To my knowledge it is perhaps the earliest example of a [...] Click to continue reading this post
Friday’s Southern California Strings Seminar was a success! Thanks to all who came, who spoke, and the UCLA organizers. I enjoyed all four talks that were put on, and learned a lot from each. (Sera Cremonini is giving her nice talk about duals of hyperscaling violating theories in the photo.)
I was particularly pleased about the talk by Daniel Harlow about the Firewall issue, [...] Click to continue reading this post
The group at UCLA is hosting the next SCSS, and it is on Friday. More details here. The schedule looks good:
9:30-11:00 Sera Cremonini (Texas A&M): “Probing the IR of hyperscaling violating geometries.”
11:15-12:45 Ken Intriligator (UCSD): “Aspects of 3d N=2 Chern-Simons-Matter Theories.”
2:15-3:45: Daniel Harlow (Princeton): “On the Computational Complexity of Hawking Radiation”
4:00- 5:30: Eric D’Hoker (UCLA): “Supermoduli and supersymmery breaking”
-cvj Click to continue reading this post
Yeah. Scary, right? I woke up one morning to this result (see earlier posts here, here, and here) from a night of an intensive computer run. It was not meant to be a straight line, but pretty close to it, so I knew that something was wrong with my code. Took me a good long while to trace the problem, but I did in the end. My signal was being swamped by both [...] Click to continue reading this post
So I’ve moved on to curved lines now, in case you’re wondering. (See previous posts.) The last several days (the research parts) have been taken up with more computations. A lot of the time has been spent calibrating the programs, and trying to assess and understand and characterize the inevitable errors that show up, by running the programs and checking the resulting plots of data points against expectations shaped by hand calculations. Calculating on the train to and from work, I’ve filled several pages of my small notebook with computations, alongside sketches of some of my surroundings as usual (people mostly). As a result (fingers crossed) I think I’ve now understood all the key aspects of the results I’ve been getting, and have good numerical control of things. To get such control, I’ve had to push the error tolerance and the size of the grid of points I’m computing on to regimes where I’m back again to waiting for the better part of an hour for each data point. (One sets up the problem on the computer by making continuous variables, such as space and time, into discrete ones, forming a grid. The problem is then to use various [...] Click to continue reading this post
How is the line coming along? It is very kind of you to ask (if indeed you were). Well, there it is to the left. (See the previous post for background.) In the end, I abandoned Maple since it was taking way too long to do each point, and just for the simple example. (When I tried to do one sample point of the complicated example it took 24 hours and I stopped it before it was done!) The point is that Maple does not easily [...] Click to continue reading this post
I’ve been multitasking in an interesting way. Sort of. I’ve reached a certain point with some computations I am doing that I cannot go beyond by analytic means. This means that I can’t extract the physics I need by doing algebra and other exact manipulations on paper any more. Progress can continue however by using numerical means, employing a computer to solve the highly non-linear equations and extract the juice. There are several steps involved, and ultimately, I want to determine how a certain physical quantity depends on another physical quantity. (I’m sparing you the trouble of knowing what the details of the physical quantities are, since it does not matter for the thing I am trying to tell you. It relates to quantum field theory, gravity, and string theory, which connects the two.)
I can see that dependence quite clearly if I simply plot a graph of one versus the other, and in this case I need the computer to work out what the points on that graph are. I actually don’t know the answer for the cases I really am interested in, nobody does (that’s why it is research!), and so that’s what I want to find. I want lots of points to get a nice smooth graph, so the computer has to compute a lot of points, and I need to run it for a long time since I want it to compute the points very accurately. So I wrote a program (in Maple) to work on the problem, studying just one [...] Click to continue reading this post
You might recall that last year I gave a talk at TED Youth, in their second year of short TED talks aimed at younger audiences. You’ll recall (see e.g. here and here) I made a special set of slides for it, composed from hundreds of my drawings to make it all in graphic novel style, and somehow trying to do (in 7 minutes!!) what the TED people wanted.
They wanted an explanation of string theory, but when I learned that I was the only person in the event talking about physics, I kind of insisted that (in a year when we’d discovered the Higgs boson especially!) I talk more broadly about the broader quest to understand what the world is made of, leaving a brief mention of string theory at the end as one of the possible next steps being worked on. Well, they’ve now edited it all together and made it into one of the lessons on the TED Ed site, and so you can look at it. Show it to friends, young and old, and remember that it is ok if you don’t get everything that is said… it is meant to invite you to find out more on your own. Also, as you see fit, use the pause button, scroll back, etc… to get the most out of the narrative.
I’m reasonably pleased with the outcome, except for one thing. WHY am I rocking [...] Click to continue reading this post
In other interesting announcements today, the great physicist Alexander Polyakov has been given the Fundamental Physics Prize. (See the announcement here.) There was a remarkable award ceremony in Geneva yesterday, hosted by Morgan Freeman, and with lots of Physicists and others celebrating great work in various areas of physics. Polyakov has been a key and brilliant leader in many areas of theoretical physics, and influenced so many ideas and techniques that have fed into the whole field, and so this is a well deserved recognition.
I must note that it is a bit sad (to say the least) to do a google search on the news about this prize and see so many articles with a lot of just plain stupid focussing on a big prize going to a “string theorist”, as though this is somehow negative or ironic, and also missing the fact that Polyakov’s contributions are so broad and far-reaching [...] Click to continue reading this post
A while ago I got an email out of the blue from an enthusiastic young fellow who wanted to do an interview with me on camera for his YouTube channel. After we bounced emails back and forth a bit and I got a sense that this was both legitimate, worth supporting, and that I had time to do it, we agreed that we’d meet to do it. So we met at the excellent Mystery and Imagination bookshop in Glendale, and he set the camera running and threw a bunch of questions at me. We talked about all sorts of things from dark matter, the LHC, supersymmetry and string theory to trumpets, jazz clubs, and noir films.
It was fun, and you can find the results on his YouTube channel (here), that he hopes to populate with more interviews with people working in science and other topics. He’s got an interview with mathematical physicist John Baez up there already, so go and look.
Below, I’ve embedded the interviews with me, for your convenience.
Enjoy! [...] Click to continue reading this post
What? The final exam I set on Friday. I spent a lot of time trying to get this final exam right. The problem is that I tend to decide at some point that I want to set an “interesting” exam, and then this usually ends up being more work for me than for the students, since you not only have to think of the questions and make them the right level of difficulty (made harder by being open book and, in this case, a take home -well, take to where ever for 4 hours), but then endlessly debug to see that it has no mistakes (since I won’t be present to answer questions). This time, I spent a lot of time on units, since I wanted to set an exam that kept all the factors of c and mu and epsilon present in all the relativistic notation and right down to the final unpacked Maxwell equations and all the quantities they computed in various examples. I decided to have them explore a little non-linear electrodynamics, since everything they’d seen was mostly linear. You start with the familiar (Maxwell) form of the equations:
[...] Click to continue reading this post
Well, Thursday’s meeting was a blast! I had decided not to try to get people to RSVP for the meeting this time, and so when it came down to the day before, I had no idea how many were going to show up. This meant that I had to make some guesses about how much coffee and tea and cookies to organize, which was a little bit of a challenge. But just before 9:00am people began to show up, and kept showing up, and by time I was ready to start off the day’s meeting, there was a really good crowd!
In the end it was a great day, with five really good talks and lots of excellent discussion. [...] Click to continue reading this post
The next Southern California Strings Seminar is on Thursday 13th December! I’ve now made the website for this one and it is here. Come back to it from time to time to see the updates of talk titles as speakers let me know what they are. It is a one-day event filled with five talks and plenty of time for discussion. I’ve snagged a lovely room in the Doheny library again. (Photo left has a shot of the room we used last time it was at USC in May 2011. The most recent one was over at UCLA.)
You are welcome to come and do physics with us! Also, if you’re part of a group in [...] Click to continue reading this post
…Again. I’ll be on the road again this morning. Heading to California State University Long Beach. They invited me to give a colloquium a while back and I agreed, and when I returned from New York last week I realized I needed to urgently spend a chunk of time thinking about what I was going to talk about, and designing a set of slides for it. The last couple of days saw me devoting a lot of time to it. Eventually I decided to dig back into ancient times (the 1990s) surveying some of the interesting things we’ve learned about strong coupling phenomena (involving unexpected reorganization of degrees of freedom and the number of spacetime dimensions at times), and then discuss what it all might be good for in view of work going on in the last decade or so.
Come to think of it just this moment, this is a chance to do a tribute to David Olive, who passed away earlier this month. (He was one of my professors when I was at Imperial College in the ’80s.) Ideas of strong/weak coupling dualities and their utility were given a huge boost by his work in this area from decades ago, perhaps the most famous being Montonen-Olive duality… I must remember to mention that in the talk. (See here for an archive of 2004 talks in celebration of his work. I borrowed the image to the right from there. I do not know who took it.)
Here’s the title and abstract: [...] Click to continue reading this post
Ack! As you know, it has been an incredibly busy semester for me, but I still try to find time to tell you a bit of what is going on. Not long ago I got an email from the TED people asking me if I’d like to talk at one of their events. This event is for young people, called TEDYouth. It’ll be on November 17th. Well, this is such a good cause – how can I not do this?
You can see the announcement of the “incredible lineup” of speakers on TED’s site here. (I linked the photomontage they used there.) I’m looking forward to being in the audience to hear some of these guys talk!
So of course, I now find myself a week behind where I should be in terms of preparation, and in the middle of a whole bunch of other deadines… [...] Click to continue reading this post
I did not make it to the annual “Strings xxxx” conference this year (where xxxx = current year), but I heard that it was good. It was held in Munich. See the lovely poster on the right. (I wonder who did the splendid painting?)
The organizers did a great job of rapidly updating the website with slides and video of the talks so that a wider audience can benefit from them. The video page is [...] Click to continue reading this post
It wasn’t all lecture halls, discussion rooms, and cafeterias for the workshop. The organizers arranged for a boat tour last week, and we all sat on one of those splendid long, wide and low tour boats that you often see on the canals in Amsterdam. It was nicely equipped with a bottle of wine at each table, and the crew members handed us each a glass of sparkling wine as we embarked. Very nice. There was a lot of fun chatter from each table for the whole trip around the canals (so much so that they stopped the attempts to inform us over the PA system about some of the sights we were seeing, since the sound was drowned out by the conversations), covering (from what I could hear) a wide range of topics from well beyond physics to matters concerning topics presented in the workshop.
Sometimes pads of paper and pens appeared. Above is a group (David Tong, [...] Click to continue reading this post
The workshop has been fantastic, overall. In between discussions, the talks, and some thinking about my own projects, I’ve had some time to wander a bit, and look around. Yesterday after lunch I wandered a bit and then found myself settling down and doing a sketch of a bridge at a junction with lots to see. The Amstel is joined by Prinsengracht canal here, and it was fun to sit a while and put down some pencil lines, followed by firmer ink lines. I pulled the result into the iPad and splashed on some colour for good measure.
Having finished the paper last week, it has been fun to field questions about it from various people, as well as think at a more leisurely pace about the next [...] Click to continue reading this post
Well, the workshop is going well. I had to miss a talk this morning in order to carry on with this writing of a paper I was doing. Basically, we’re over due in producing our submission to a special volume of some publication or other that is going to be all about magnetic fields and models of strongly coupled matter… As you may have gathered by now, I’ve dabbled in magnetic fields for some several years by now, so it was natural to be asked. My collaborator in a lot of these dabblings, Tameem Albash, and a student, Scott MacDonald, and I have been working on a suitable project for a while, and due to my travels and entanglements with a previous project, I’ve made us all a bit late.
The last few days have been difficult for writing. I’d forgotten [...] Click to continue reading this post
Speaking of film projects involving science, I’m involved in two new ones I’ve been meaning to tell you about. I’m working on producing a short film about the Aspen Center for Physics, to be used in the upcoming 50th Anniversary celebrations. My partner in crime on this is Bob Melisso, who I’ve worked with before a number of times, and it’s already been interesting, and fun. I think that the final piece ought to be interesting at the very least. I’ve been trying to work in a very particular look and feel for the film that reflects something about the nature of the work that goes on at the center (both its content and how it is done), and so there’ll be lots of chalk, scribbling on boards, reflections on the creative process and how a place like the Aspen Center helps, and so on and so forth.
We’ll be shooting from time to time over the early and middle Spring, and doing the [...] Click to continue reading this post
Gosh, I got a bit swamped there over the last week. Several things took me away from sitting down and doing a blog post, including teaching my class (more on that shortly), working on a film project (more on that longly) and doing my taxes (late this year – bah!) and the usual raft of committee meetings and so forth. But one of them was locking myself away for two days with my computer and a web connection and writing a paper from start to finish with Tameem Albash. We’d more or less completed the bulk of the project over two months ago, with some very interesting results that we’d talk about from time to time to try to understand what was going on, but I held things up, being distracted by several other things (some of which you know about from this blog). We decided two weeks ago that we’d just finish the thing once and for all, and then somehow ten days went by with me not getting to it. Then I decided to close the door and just do it. So from lunchtime on Friday through lunchtime on Sunday I became a recluse (kind of) and I wrote, in turn with Tameem, as we emailed and IMed back and forth, until we had a nice paper entitled “Holographic Studies of Entanglement Entropy in Superconductors”.
It is a project I’ve been hoping to do for a long time, but not all the pieces were on the market until late last year. The entanglement entropy has been a quantity of interest among physicists in various fields for years, especially in the condensed matter and quantum information community, and is regarded [...] Click to continue reading this post
So I mentioned that I was doing some more material for the Nova people, via their website. (See here for some earlier material about Multiverses.) They’ve a blog called The Nature of Reality with contributions from many interesting people. Well, now they’re featuring those pencasts I think I told you about in an earlier post.
The pencasts are all about Quantum Gravity, a major research topic in physics. I talk about what it is and why we care about it. I speak and write, scribble and draw and [...] Click to continue reading this post
I’m having a blast teaching the introductory quantum field theory class, as you may have gathered from several previous posts. It has been taking a lot of time, but I’ve been doing detailed computations with the students (and hence taking up a lot of preparation time) to make sure they really get how to compute in a quantum field theory (such as Quantum Electrodynamics (QED)) and see how it connects to the real world. Having spent time on the electron anomalous magnetic moment computation (I told you about that spectacular feature of QED earlier) we went back to basics to discuss in more detail the nature of the physics that is to be extracted from what are called one-loop diagrams – diagrams of the sort I drew before that have a closed loop in them.
This is where I get to try to clear up a huge conceptual issue that still afflicts most people’s popular-level knowledge of quantum field theory due to poor writing – the nonsense often spouted about there being “hidden infinities” and so on and so forth. Covering the poorly-named “renormalization” procedure and treating it in a more physical way to see that the whole “infinity” business is dreck can be fun, since it allows for an emphasis on a lot of the key issues I care about in the science that we do, such as the idea of effective field theory, the importance of separation of scales in your physics, and most importantly the reminder: Let’s not confuse the tools we use to describe Nature with Nature itself.
I like to use that phrase, and it comes back again and again, whether it is to do with [...] Click to continue reading this post
The next Southern California Strings Seminar is on Friday 21st October! The website is here. It is going to be held over at UCLA this time, and I expect it’ll be fun and informative, as these regional meetings have proven to be. This time it is a one-day event again. You may recall that the last one, on May 6th, was over at USC. See here. There’s a random picture from it above left.
Apologies to anyone who was [...] Click to continue reading this post
I’ve no idea who he was, but he made for an interesting subject for several minutes*, sitting eating his breakfast with his (I think) wife. I was staying at a hotel and having breakfast, just North of Santa Barbara. The person I set out wanting to draw (very interesting face) was sitting right opposite me, at the same table as me, looking over regularly, and so it seemed a bad idea to try to sketch him. Also, he turned out to be a physicist also visiting at the KITP for a workshop, and so it could have ended up quite awkward.
It was a pretty good week at the workshop. I had a number of interesting conversations with young people trying out ideas and calculations, who’ve actually read (!) various papers of mine, and so had questions and [...] Click to continue reading this post
It is 8:20am, and only now is the sun appearing from behind the mist that seemed to cover the world since I got up this morning at 6:00am and since I boarded the Amtrak train at 7:30am, bound for Santa Barbara. We’ve arrived at beautiful downtown Northridge, and have another two hours and a half to go. I’ve got my bike folded neatly in the luggage rack above me (I tried not to look too smug when passing two cyclists struggling a bit to find room for their giant bikes in the space remaining to them), have had my second slice of multigrain bread smeared with whipped cream cheese and homemade fig jam (I made a batch a few weeks ago) and an sipping coffee while catching up on various things, such as telling you what I am doing. I think I’ll stop writing for the blog now, getting back to thinking about some physics I want to put into a new paper, looking out the window at the landscape as it opens up more (we’ll be running through farmland, and then along the seaside soon!), and letting my mind drift and be open to those expansive kinds of thoughts that typically come in when I am sitting on a train watching the world go by. I don’t get that with driving up here, since so much it put into driving safely and so forth, one’s mind is never fully free. I love train travel, and I love this journey, even though I know there’s no good reason why in the 21st Century in the USA it should take three hours. (Three and a half on the return – I mean, really).
Ok… back to stuff.
Oh, wait – Why am I going to Santa Barbara, you ask? Is it another “jump on the train and see where I end up” sort of day? (See an earlier post.) No, I’m going up there (actually my stop is Goleta) to spend a bit of the week at[...] Click to continue reading this post
As you may know already there’ll be a new NOVA series on PBS in the Fall, based on one of Brian Greene’s books, The Fabric of the Cosmos. Last Fall I did some a shoot with them for my role in it (I’ve no idea how much they will use), and I learned a short while ago that they’ll be using some of it on the NOVA website too. They extracted some parts of the on-camera interview segments I did concerning the idea of multiple universes and transcribed them into something you can read online. Have a look here. I touch on the idea in a fragmented way, mostly being led by the questions I was asked, but it’s a fun topic to chat about, and may lead you in interesting directions should you wish to learn more, so have a look.
A word on the picture they are using (er…see above left). It seems to be one that the [...] Click to continue reading this post
We had a really interesting discussion of the quantum physics of de Sitter spacetime yesterday here in Aspen, starting with a review of the behaviour of scalar fields in such a background, led by Don Marolf, and then, after lunch, an open-ended discussion led by Steve Shenker. This is all quite difficult, and is of course quite relevant, since a piece of de Sitter is relevant to discussions of inflation, which seems (from cosmological observations) to have been a dominant phase of the very early universe. As the most symmetric space with positive cosmological constant, de Sitter may also be relevant to the universe today, since dark energy (first recognized after 1998′s observations of the universe’s accelerating expansion) may well accounted for by a positive cosmological constant.
So we need to understand this type of spacetime really well… and it seems that we don’t. Now there’ve been a lot of people looking at all this and doing really excellent work, and they understand various issues really well – I am not one of them, as I’ve not worked on this in any detail as yet. Do look at the papers of Marolf, and of Shenker, and collaborators, and references therein, and catch up with what’s been going on in your own way. For what it is worth, the sense that I get is that we’re trying to solve very difficult issues of how to interpret various quantum features of the spacetime and getting a lot of puzzles by trying to make it look a lot like things we’ve done before.
Now, we may solve all these puzzles…. but my current take on this all is that we’re [...] Click to continue reading this post
I’m sad to say that Ken J. Barnes died recently. My sympathies and wishes of comfort go to Jacky and the family.
There are many theoretical high energy physicists who will tell you of their wonderful time as students in the theory group in Southampton, England. I’m one of them. I think a huge component of that is due to Ken. He founded the group, nurtured it, and led it for many years. As a nearly completing undergraduate who was somewhat certain about what I wanted, after a lot of fastidious researching of various options, I picked the Southampton group very carefully back then. I had it set in my mind that I wanted to do research in string theory, and was looking for a group that felt dynamic and energetic, and while I got offers from some good places (including the excellent group at Durham which I was later to join as a faculty member 11 years later), there was a spark that I felt when I visited Southampton’s group, the group Ken founded way back in the early ’70′s.
The group was more than just Ken, of course, but the fact that such great faculwho and staff were there, and doing great work, was part of his building process. Tim Morris, who was to be my advisor, and who was doing interesting things in string theory, was one such person who impressed me greatly. I was so glad I went there, from the moment I first arrived, and I loved those days so dearly.
It all began (as many will tell you) with Ken’s “pep talk” where he would tell the prospective students who were visiting the group about the possibly crazy decision they were making (to go into a highly technical field with few employment prospects in academia)… essentially reminding us that we’d better be doing it for the love of the subject. I think that we all were in awe of him, and perhaps a little afraid early on, but later [...] Click to continue reading this post
I had an early rise this morning, to make it down to campus early enough to set up (with the help of my co-conspirator Tameem) the room for the all day meeting I mentioned earlier, in order to start at 9:00am. All worked well… And things are progressing nicely (see photo of some of us in the lovely room we’re using) with local participants from USC, UCLA, UCSB, and even Stanford! It is excellent to see such support and enthusiasm for this semi-annual event!
Click to continue reading this post
We’re hosting the next Southern California Strings Seminar here at USC. It will be on Friday 6th May. I’ve been working on it a lot over the last several days* and put the finishing touches on the arrangements just this morning.
There’ll be no Saturday morning component this time, since there’s yet another huge event down at USC this weekend, and things will be rather disrupted, I understand, as there’ll be lots of people, street closures, and so forth**. (It is the Revlon Run/Walk event in exposition park, across the street from us, an excellent event!)
So I’ve packed five exciting talks into Friday, and I think it is going to be fun! Here’s the schedule:
[...] Click to continue reading this post
It was a fun week in the string theory class this week, as we got to some major landmarks that are always fun to teach. We’ve uncovered the extended objects called D-branes (see numerous previous posts for how useful and important these objects are in string theory research) in all their glory in the lectures before, and deduced lots of their properties, such as the form of the action that determines how a D-brane moving in spacetime responds to the various fields (including the geometry) created by the string theory. That’s all fun, but then the key thing to do next is to compute the mass of these dynamical objects, or the mass per unit volume – the tension. Computing it fully, with no hand-wavy factors. Your mass measures how strongly you interact with gravity. So you can measure it by studying the gravitational interaction between masses. (You do that when you step on a scale to measure your weight… well the scale does it by showing how much force it takes to stop you from falling through the floor toward the center of the earth…)
So in class this is when we go all Polchinski and unpack the tension computation, stopping to admire the various features of string theory you learn along the way, and seeing how simply beautifully the various basic features of the superstring theories that we’ve met in the last few lectures encode themselves in one nice object – the vacuum amplitude from the cylinder diagram representing either exchange of closed strings (including quanta like the graviton – this is what you focus on to learn what the mass is) between a pair of D-branes, or an open string with its ends tethered to a pair of D-branes going in a closed loop. That there are two ways of looking at the diagram, an open string way (running time around the cylinder) and a closed string way (running time along the cylinder) is a hugely powerful thing, and is at the heart of so very much of what we do in string theory these days especially – including a lot of what I’ve told you in previous posts (see e.g. here and here) about applications to things of interest in current experiments.
One of the fun things about all this is that the answer is actually . It is zero because all the infinite modes of oscillation of the string gather themselves up nicely to give a factor:
Think of as a book-keeping device that lets one track energy contributions (in the power of it that appears in a term if one expanded this expression), and how many [...] Click to continue reading this post
A student asked a question in the string theory class today to which my answer was a suggestion of how to think about the issue raised in order to go about answering the question themselves. There’d be a few minutes of diagram drawing, and all would (hopefully) be clear. I thought that might not be an unreasonable thing to ask of a student, particularly in a graduate class, where they are ultimately trying to develop skills to do research. Well, it all went a bit pear-shaped as the student seemed to get quite strongly annoyed by this suggestion. I’ve still no idea why.
Anyway, on the bus home I thought I’d do some idle doodling, and ended up doing the exercise I’d suggested… and sure enough what I suggested doing works nicely and does (I think) make it clear.
I’m sure it was all a misunderstanding… Probably my fault.
Over late night dinner just now, since I can’t put down this lovely brush pen I’ve been drawing with recently, I scribbled the figures out from the notebook for you to look over my shoulder, as it were, and see what we’re up to in the class. Don’t worry so much about what it all means. It is sometimes nice to just look at the shapes. (Actually, one of the students brought his mother to visit the class today. She sat through the whole hour and fifty minutes of the lecture. That was nice. I hope she enjoyed it all!)
I find these diagrams and the computations they represent rather pretty.
Wednesday will be the big climactic lecture of a sequence I’ve been leading them [...] Click to continue reading this post
Well, today was the first lecture of the string theory course (part 2) that I mentioned in the previous post. And I applied the “when they think you’re going to zig, you zag” principle. They have been expecting me to dive into the whole business of open strings and D-branes and so forth (the subject of the book), and I did not. Sure, that will come, and sure, we’ll explore what they mean and what they can tell us about string theory beyond perturbation theory and so on and so forth. But I want first to spend a couple of weeks on getting to the heart of the matter. They made several standard choices along the way in doing their first semester of study of string theory. What did they mean? Why did they work? Were those the only choices? What is underlying a lot of it all, and what, when stripped down to the essence, is at the core of string perturbation theory and beyond? In other words, let’s look more closely at the path integral definition (such as it is) of a string theory (slightly schematically):
and make sense of all the bits. (Er, for the two of you still reading, is an [...] Click to continue reading this post