Category Archives: science

Goldilocks Final

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So it is the final exam for my quantum field theory class tomorrow, and today I need to write it and typeset it. I’d given them a choice of exam. They seemed to want a take-home exam, but I warned them that a take-home is probably going to be way more challenging. I’d be thinking up newer, harder material that you can’t just google the results for. An in-class exam has a time limit, which seems to freak people out, but on the other hand (assuming the examiner (me) is a reasonable person – and I think I’ve given them every reason to believe that) it is likely to be written to be solvable in the assigned couple of hours. So there is a much stricter limit to the length or depth of what they’re going to be asked to do. If they’ve really been following along in the class and doing the homework, they should be able to get most of the exam done without breaking a sweat in 3/4 of the time allowed… maybe the last 1/4 of it might need a bit of furrowing of the brow, squinting the right way, scribbling hurriedly here and there, but in the spirit of a challenge, not torture. Even if they don’t get every last part solved, a well-designed exam will give them several opportunities to show off what they’ve learned.

I like setting take-home exams too, but I’ve a soft spot for in-class exams, I’ll admit. As you may have guessed, I loved in-class exams when I was a student. Yeah, I’m weird. This does not mean that I always scored super-well on them, but I enjoyed the […] Click to continue reading this post →

Whale Song – Your Help Needed

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I heard on NPR this morning that there’s a shout out to everyone to help with an interesting scientific project. It is crowd-sourcing in order to achieve certain objectives in science, which is an excellent idea. I wish I could do certain research projects I’m working on in this way – would be fun and quite novel indeed… Crowd-sourcing crowds of processors is maybe the closest I’d get to that. Anyway, it is all about identifying different types of whale song, and as a citizen scientist you’ll […] Click to continue reading this post →

Almost at an End

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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 →

Tales from the Industry XXXVIII – Improvising

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For the second half of today I was involved in film-making again, but this time not the usual science documentary material, but something else. What, exactly, I am not at liberty to tell you since I don’t really know, if the truth be told. It is going to be a rather beautiful-looking piece of work, with an interesting narrative arc, and… well that’s all I know. I was cast in it a while back following an interesting story in and of itself. I’d made friends with a really engagingly interesting bartender at a bar downtown that specializes in rum, a while back…(a year? more?) We had a great time chatting about ideas in science, the arts, and beyond, and did that “let’s stay in touch” thing that people do a lot, which may or may not really happen…

Some months later, the same fellow came to see me in my office to tell me about this film he was making, and that he’d like me to come and be in it. At the end of the conversation, somehow I still knew nothing about the film and what I was to be doing in it. I was just going to be in a splendid house somewhere, talking to people, and… […] Click to continue reading this post →

Rough Pages

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Well, it’s a time-consuming process (continuing the new work on The Project mentioned in a recent post), especially when you put in more detail than really needed on what is supposed to be a rough layout. Sigh… Anyway, I’m several pages along in layouts for a story I wrote a while back, and I’m flipping ahead from time to time and wondering how long this beast is going to end up being! In any case, it’s a fun topic (or topics) being explored in this one. I’m wondering if I should try to find a way of splitting it into two stories or perhaps […] Click to continue reading this post →

Infinity Coincidence

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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 →

A Mighty Pen

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Wow, Friday already! It has been a busy week, but with some good stuff here and there, I’d say. “Good Busy”, as I sometimes say. I’d like to dig into some work this early morning before the day gets into my head (although I’ve already been emailing with the East Coast) and so I’ll be brief.

One of the things I’ve been doing is experimenting with Pencasts, for PBS. What are those? Well, after I agreed to do one, the main instrument needed arrived in the post. An Echo smartpen, by Livescribe. It is a pen that records (when you write on the right paper) every penstroke you make digitally and you can play back that page elsewhere…It also has a microphone built in, and so what you can do is play back the writings/scribblings/drawings, along with the sounds that were playing at the time you were drawing. You can play them back right from the pen’s little speaker, or upload the whole thing to your computer or to the web and have the whole thing playback there. It is an excellent and powerful tool. The people who make this are heavily advertising it to students as a tool for studying, which I don’t have a problem with, but a lot of the sense of the marketing (and discussions I’ve seen on the web) seem to hint that it is somehow a magical substitute for actually learning how to take notes, since you are recording the lecturer’s voice… That I do have a problem with. Making good notes is an important skill and the act of paraphrasing and distilling what is being said is vital to learning… it is arguably the most important stage now, given that students seem to have less and less time to re-work and supplement the lecture’s material in their own non-class time… These pens should supplement that process, not substitute it… Like all tools, they need to be used properly for best results.

But anyway… Where was I? Yes, so the pen arrived, and I experimented with it a bit […] Click to continue reading this post →

Boxes

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Some more Feynman diagrams from quantum electrodynamics (QED), with squiggly lines representing photons and straight lines representing electrons or positrons (their anti-particle), depending upon which way you read the arrows. The process represents an entirely quantum process, with no classical counterpart, of light scattering off light. You can read the diagrams any way you like, running time in your chosen direction, and you’ll get a sensible story. For example two photons approach […] Click to continue reading this post →

Premiering…

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Well, it is a week full of premieres, it seems, all with a little personal flavour for me, but possibly of wider interest. I’m talking about two TV shows and a movie.

The movie is going to be out in theatres at the end of the week, and it is called “Being Elmo”, co-directed by Phillip Shane and co-written by Phillip Shane and Justin Weinstein, two friends of mine who are flying into LA for the premiere. It is about Kevin Clash, the guy who operates the Elmo muppet. In short, it is a film that people seem to be really enjoying (it won the special jury prize at Sundance, and was a finalist for the Humanitas prize), and I can’t wait to see it! I worked with Phil on a two hour Einstein special that aired on the History Channel a while back (see Equation Wrangler), and so I know his working style a bit, and the results are great – so I think this’ll be really good!

The new Nova mini-series based on Brian Greene’s second book “The Fabric of the Cosmos” begins this week. They do a very good job, working closely with Brian to produce a show of rather high quality. I hope they do a good job (as you can see from the picture, they’ve got Brian to reveal his superpowers on screen – we’re not supposed to do that Brian!). It should be interesting to see, I think. I can’t recall if I mentioned, but I filmed some contributions for it last year, and some of that will be in the first episode (and I think the fourth). (You may recall that they extracted some of my interview […] Click to continue reading this post →

Scary Science?

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The mask I wore to two Halloween parties last night. (Click for larger view.) I got the raw mask at a costume shop and then built some interior support into it to have it sit over my glasses without pressing on them uncomfortably… Then I inked and painted some symbols on it. The idea? People often get scared when I mention science or […] Click to continue reading this post →

QFT Rocks!

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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 →

Southern California Strings Seminar

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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 →

Landmarks

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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 →

Back to the Routine

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I’ve finished my four weeks of back and forth between Los Angeles and Santa Barbara. It was very rewarding, although it (of course) meant that I had to make several adjustments to my usual routine, putting aside a number of things (including and consistent work toward moving The Project forward). This is fine, as it was part of the plan to put things aside somewhat and focus on the visit. It meant an interesting process of trying to put most of my Los Angeles business (including teaching and any meetings, etc) into Monday and Friday as much as I could, and catching up with reading and lecture writing in the in-betweens, often on the three to three and a half hour journey on the train. (People universally assumed that I’d driven up, and were mostly surprised when I mention I took the train. One person even inquired as to whether I don’t have a car. I politely explained that I do, but I don’t feel compelled to drive it everywhere. One person could not understand how I would get to the train station in LA without a car. I explained there was a subway system… Others talked about how they never visit LA from Santa Barbara because they can’t get around without a car and the traffic is terrible… They prefer (in one or two examples related to me) to go all the way up to San Francisco where they can just leave the car and explore without it. I smiled politely and mentioned that you can do this in Los Angeles too. This had no effect on their belief system, as far as I can tell. I am constantly amazed at the incredibly limited images of Los Angeles that people hold in their heads. In all cases, we agreed that getting to work on the train was in fact a good thing. I explained, as a bonus, that I get over the business that the train takes twice as long as it should be simply pretending it is twice as great a distance than the 95 miles it actually is. This is true.)

So anyway, sad as it was to leave the KITP behind, with all the stimulating conversations, great talks to attend, friends old and new, and so forth, it is time to […] Click to continue reading this post →

AdS Vs CMT

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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 →