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
This morning the 2013 Nobel Prize in Physics was announced, and it was given to Francois Englert and Peter Higgs for the 1964 theory of what’s now often called the Higgs mechanism, recently directly confirmed experimentally by the Large Hadron Collider at CERN (as you might recall) by the finding of the Higgs particle. You might recall that the mechanism, also associated with the term “symmetry breaking”, is responsible for the masses of the elementary particles, as has been discussed here and elsewhere a lot. (And recall, that it has little to do with the mass of everyday objects, as people sometimes say. That’s a different matter… everyday objects’ mass is dominated by their binding energy… coming from the forces that hold them together… not the Higgs mechanism.)
The first thing to say is “Congratulations!” to the winners. It is sad that Robert Brout (Englert’s co-author) passed away before he could get the prize as well. A nice thing you can do is take a look at the actual papers that are central to the citation in Physical Review Letters right here, as the APS have made them specially available. It’s good to take a look at what the actual papers look like, to get a sense for how our field works, so go ahead. I also recommend the lovely book of Frank Close, “The Infinity Puzzle” for a very good presentation of much of the ideas and history of this and related chapters in the field of particle physics.
My own thoughts on all of this are mostly of delight, but there’s something else there as well. Without a doubt, it is great to see particle physics and the pursuit of [...] 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
Yeah! It feels great when I get the workhorse computer really chugging along. 85% is unusual to see on a normal run, since this beast (a 2010 3.32 Ghz Mac pro quad core) has a lot of computational capacity that you don’t need for most tasks. I’m getting up to 85% because all four cores are crunching away independently on the same problem (written in MatLab) but different parts of it. Each point on the resulting graph will be the result of having computed 2000 points. Each of those 2000 points comes from computing a boundary value problem discretized into a million points. See an earlier post for more about that.
(Update: Now running even more tasks associated with this problem: Up to 96% now:
…with nothing idle at all. This is probably not as efficient any more, but it is for a few hours and then back to 85%. In the meantime, it is amusing how it makes me feel I’m doing more work somehow…)
I assigned different parts of the graph to different processes by hand, not using a [...] 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
I just learned* that Ken Wilson died a few days ago (Just 15th). Wilson is another of the giants that you don’t hear much about in the popular media coverage of the great ideas in Physics that form the bedrock of so much of what we do. You still get people saying utter nonsense about “hiding infinities” in physics and so forth (often in discussions on blogs and various similar forums (fora?)) because what he taught us all about effective field theory and the renormalization group still is only taught in some advanced classes on quantum field theory (and still not as well or frequently as it should be in such classes … it has only relatively recently begun to be put at the forefront in textbooks on the subject, such as Tony Zee’s). In the cut and thrust of the mainstream of research though, I’m happy to see that so much of Wilson’s legacy is in the most basic fabric of the language we use to discuss results and ideas in particle physics, condensed matter physics, quantum gravity, string theory, and so forth.
I had the distinct privilege of having Joe Polchinski as a mentor for some of my postdoc years, who is known as being one of the current giants on the scene who [...] 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
Well, the day is here. The Planck collaboration has announced a huge amount of results for the consumption of the scientific community and the media today. The Planck satellite looks with unprecedented precision at the very earliest radiation (“cosmic microwave background radiation”, CMB) from the universe when it was very young (a wee, cute 380,000 years old) and helps us deduce many things about what the universe was like then, and what it is like now. Here’s one of the representations of the universe using the new sky mapping Planck did (image courtesy ESA/Planck):
There’s a ton of data, and a raft of papers with analysis and conclusions. And there’s a very nice press release. I recommend looking at it. It is here, and the papers are here. The title of the press release is “Planck reveals an almost perfect Universe”, and some of the excitement is in the “almost” part. A number of anomalies that were hinted at by the previous explorer of the CMB, WMAP, seem to have been confirmed by Planck, and so there are some important things to be understood in order to figure out the origin of the anomalies (if they ultimately turn out to be real physics and not data artefacts). [Update: Andrew Jaffe has two nice posts I recommend. One on the science, and the other on the PR. Jester also has a nice post on the science from a particle physicist's perspective.]
What is the title of my post referring to? Well, the refined measurements have allowed us to update some of the vital statistics of the universe. First, it is a bit older than previous measurements have indicated. The age is now measured as 13.82 billion years. (I’m already updating pages in the draft of my book…) Second, the proportion of ingredients [...] Click to continue reading this post
Got a 30 second elevator pitch about your research? Several of my colleagues over at the USC Keck School of Medicine have. Here are 9 in a playlist:
[...] Click to continue reading this post
So it’s very much worth noting that there are some new announcements from earlier this week concerning last years’ landmark discovery at the Large Hadron Collider. The news is that a Higgs particle was discovered. There were several news stories about it in the last few days. This might be a bit confusing, and many of you are thinking that this is recycling news from last year concerning the discovery of the Higgs. It is not recycling. If you go back and look at the results that were announced last year, there was an important note of caution, notable in the fact that the particle discovered was referred to as “Higgs-like”. More analysis was needed to be sure that it was indeed a particle that fits the name Higgs. Well, that analysis has been done, with more data included and so forth, and both experiments (CMS and ATLAS) are now sure that they are seeing a Higgs particle, and indeed it is one that is very close to what you’d expect for the Standard Model of particle physics.
The latter is is important and interesting to note, since many people expect that there [...] 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
On Saturday we had another series of celebration events for the 50th Anniversary of the Aspen Center for Physics. It began at 2:00pm with a discussion in Paepke auditorium entitled “The Future of Physics”, and it was introduced by Michael Turner, and moderated by Lisa Randall, with three Nobel Prize winners forming the panel: David Gross, Bob Laughlin, and Adam Riess. (I decided to do a short sketch during some of it, and then quickly splashed on some colour later in the evening*. The result is above. The sketches are meant to give a sense of the stage and people on it, not be representative likenesses, so I refer you to pictures of them for actual portraits…)
There was an excellent turnout, and audience members were treated to a good and wide-ranging discussion. It was a difficult subject to grapple with, and Lisa started out in a good place, by getting each panelist to take turns to describe their way into physics, then around again to talk about the areas they got their Nobel Prizes in. She supplemented their contributions with some of her reflections on her own experiences and points of view, and tried to unpack some of the concepts brought up here and there when she thought it might help the audience.
From there, things became a bit tricky, since there were several directions in which to go and it was not clear what the best structure to follow was, given the time allotted and that they needed to stop and get members of the audience involved. Like I said, it was a difficult assignment for all of them. What emerged was a loosely structured series of interesting reflections from each of them at various points, some healthy disagreements there and here (I think it was good for the public to see that we’re not all cut of the same cloth) – for example between David and Lisa on the meaning of [...] 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
Dont forget that today there will be big announcements of the latest results from the LHC about the search for the Higgs…(and some of us are hoping for news about what might be the beginning of the search for what lies beyond…)
There are so many live blogs, so follow a few… Like Resonances… for an expert view, Matt Strassler, for another expert view, or Quantum Diaries, for a non-expert view.
(update… Looks like it is a strong enough set of results, statistically, to call the Higgs discovered… Hurrah!
And with possible hints of new physics too? Excellent….)
Further update… A CERN press release is to be found here. Also, looks like any deviation from the standard model Higgs, at least for the decay channels examined so far, is very small… So there’s a lot left to do and understand…
-cvj Click to continue reading this post
Amsterdam! I’m here for a workshop for a while. It is on string theory – many aspects – and so the mix of people is a good one overall, with conversations ranging from high energy physics, the LHC (including the Higgs announcement at CERN expected tomorrow) and black holes all the way over to condensed matter and various kinds of exotic physics one can do in the laboratory in that context. It should be an excellent time here… It is good to be back in the city after over a decade, and to catch up with a number of friends and colleagues in the field. I also want to properly explore the city this time, not having done that much exploration last time. (Photo above is a snap taken of the lovely moon that came out last night, with the Amstel and accompanying reflections and so forth… Was pretty to see.)
I’ve been trying to read some notes in preparation for working on a draft of a [...] Click to continue reading this post
The OPERA experiment has reported that they may have found the source of the timing discrepancy that produced the result that neutrinos moved apparently faster than light. It seems that there was a faulty connection that affected the timing measurements. Here’s a physics world article on the matter, along with a link to a CERN press release. (Note that there are some doubts related more directly to the GPS timing signals they used, which on their own would make for even faster neutrinos, but clearly there’s cause to really doubt their strong claim from back in the Fall and take a step back.)
You’ll recall the huge press storm about it last Fall, accompanied by all the usual hysteria about the establishment (this time, Einstein) being overturned. I blogged about it here, with the noncommittal title “No, Uh-uh, Nope, Nuh-uh”. They’ll be doing more experiments later in the year, as will a number of other groups, in order to solidify the results one way or another. It’s clear that most people have decided the whole business is over, and will turn away from it to other things. Some will be pleased, some annoyed, some confused, and so forth.
My hope is (as I discussed in the article I wrote back then) that this gets as much [...] 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
Later today, there’ll be a joint seminar by physicists from ATLAS and CMS, the two experimental halls at the Large Hadron Collider (LHC) looking for evidence of the Higgs boson. This will be the first official announcement of the physics seen (or not seen) by the combined results from both independent searches. Neither search has enough data to announce a discovery of anything (as far as I’ve heard) and the combined results would not constitute one either, but people are hoping for at least some nice hints of something suggestive that support each other. We shall see! this is an exciting time, as you’ve read me say before, and so I recommend looking out for what will be announced. Even a negative result (e.g., “we’ve found nothing yet”) [...] Click to continue reading this post
I’ve had a fun time over the last few lectures with some more mature topics, pointing the students to things that they will see more (I hope) in the advanced class next semester. We covered the large N Gross-Neveu model in some detail, giving me the opportunity to give a glimpse of several important topics and techniques… at large N the 2 dimensional model’s solution is exact, and it shows important phenomena such as spontaneous chiral symmetry breaking, dynamical mass generation for the fermions and dimensional transmutation. These are all important phenomena shared by (the more difficult to study) quantum chromodynamics, the theory of the strong nuclear interactions. (See an earlier post about some of these properties and what they are… there’s also a mention of a new general level book that goes into some detail on the physics and the history.)
The other thing I took some time to explore was the diagrammatics of the model, and the interesting patterns that emerge [...] Click to continue reading this post
So here’s an interesting sequence of events. On Tuesday in the QFT class I finished the lecture on Renormalization Group Flow, and the idea of a “beta function”, unpacking the results we’d accumulated from QED and quartic scalar field theory to use as illustration. The key result, for those of you about to scroll away (or the few of you who have not, but are hovering over the scroll bar), is as follows. Never mind what a beta function is right now. The issue at hand concerns whether it is positive or negative for a force of interaction being studied. A positive beta function tells you that the strength of the interaction between constituent things (particles, etc) gets weaker as you work at lower energies… This is an important result in understanding how Nature behaves in a variety of situations… one way of seeing variety is to look at different energy scales, and sometimes what seems familiar takes on different character. The converse is true… that positive beta function tells you that the interaction gets stronger at higher energies… Energy is also rather like the inverse of distance scale too, so high energy is akin to shorter distance scales (higher resolution), and low energy like longer distance scales (grainier resolution). In other words, looking at stuff in really tiny detail means using higher energy… and the nature of that stuff can change when you look at that sort of resolution since the way things interact changes… For electromagnetism, for example, we see that it gets stronger the closer we look, digging more deeply into the structure of the atom, say, probing the charged constituents of the nucleus once we’ve understood electrons. The result is that you see the electromagnetic interaction changes, ultimately turning into something else… (it merges with one of the nuclear forces, in fact…but that’s a story for another day)
So anyway one of the things I ended the class with was the idea that if you had a negative beta [...] 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
We reached certain key landmarks in the quantum field theory class last week. Not only did we uncover how the Dirac equation predicts that the electron’s spin couples to a background magnetic field, but that it is (to a first approximation) twice the coupling that its angular momentum couples with. This is a remarkable output (once again) from that wonderful equation, the result of putting together Quantum Mechanics and Special Relativity. (I’ve discussed other properties of it before, here.) Makes you wonder, doesn’t it? If finding an equation that puts together QM and SR results in so many marvellous things about Nature just falling out so nicely (recall that spin, and also antimatter are also inevitable predictions of the Dirac equation), doesn’t it make you just thirst to know what we’ll learn (predict, explain, discover) when we find how Quantum Mechanics and General Relativity fit together? This is one of the great motivations for the work my research community does, in case you sometimes find yourself wondering – the quest for finding how Nature combines the two things together to make what we call Quantum Gravity. We’ve found one way, on the page, that you can put together QM and GR for sure (you’ve heard of it, it is called string theory) but it’s not yet clear if this form of quantum gravity is the one Nature chooses to work with, and in any case we need to work on it a lot more to understand what we’ve got, as it surely isn’t complete yet. There are huge pieces of the puzzle missing.
Anyway, the next thing we did was the classic computation of the first quantum correction to the “twice” I mentioned above. This is the computation of the famous [...] Click to continue reading this post
So there are two workshops going on here at the KITP in Santa Barbara that pertain to issues in condensed matter physics. (You may recall that I am here for some of the week, and in LA at USC for the rest of the week – adds up to a full week each week.) One is Holographic Duality and Condensed Matter Physics (often referred to as AdS/CMT), concerning applications (I’ve told you about this here before) of techniques from string theory to issues in condensed matter theory and experiment, and the other is Topological Insulators and Superconductors. there are people from both communities on both workshops, and so it is an exciting and interesting time.
The KITP Fall picnic was yesterday, and this means that there’s the traditional football (i.e. soccer) contest between workshops. Not to resolve physics issues, you understand, but to blow off some steam before getting down to the business of eating all the food… Well, at the top of this post and in the following, you can see some pictures of the process of the string theory crowd getting slaughtered for a change:
The score was 5-0.
The KITP Director, David Gross, who has presided over very many matches where the [...] Click to continue reading this post
Somehow after Wednesday I lost track of time, in a sense, in the natural course of having another very busy week. There were several things competing for time, and some of them may be of interest to you. (Left: Some lovely pink gladiolus flowers that have sprung up in my garden.) The Nobel Prizes kept coming, of course, with some very interesting winners announced. In addition to the ones I mentioned already in two earlier posts, I’ve got to find some people among our faculty who’ll be willing to spend 10 to 15 minutes making some informal remarks about the Who/What/Why aspects of the prize at one of two lunches I’ll be hosting in the coming weeks about the Nobel Prize. I’ve mentioned this before. It is an annual event I’ve tried to get going as part of the Dornsife Commons (formerly known as College Commons) series. I’ve locked in Physics and Peace, and want to get people for all the others. This year I know that if I have problems with Chemistry, I can step in if need be, although I’d rather not have to do that – I want to broaden participation, not do everything myself. Look out for those lunches (see here) and come along!
Speaking of doing everything myself, I’ve been continuing the weeks long struggle to get support, interest, and participation for the Science Film Competition I told you about earlier. Having spent a lot of time meeting with many faculty and other parties to build support and understanding, getting lots of faculty to make announcements (one time even coming down from Santa Barbara to campus to give a ten minute announcement in a class at the film school and going up again after!) and so forth – and thanks everyone who has helped! – I decided to amplify my focus on tackling [...] Click to continue reading this post