Category Archives: science

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 →

Looking Back and Forth

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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 →

Quasicrystals!

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Wow! WOW!

As you can tell, I am very pleased about the 2011 Chemistry Nobel Prize announcement. I’d love to tell you a bit more about why, but I’m supposed to be working on something urgently right mow, and so will try to do so later. The key thing is that I think the discovery of quasicrystals is fantastic and very visual example of how we can dream up a mathematical structure just because it is interesting and beautiful (Penrose tilings, independently discovered by Roger Penrose as the answer to a mathematical puzzle, (see two dimensional version on left) but also showing up in Islamic tiling patterns from much earlier) and then find later that Nature has exploited that same pattern to make something- a new form of matter (the quasicrystals themselves… The subject of today’s prize to Dan Shechtman – image below on right is of a silver and aluminium quasicrystal compound. Both images here are from wikimedia commons.).

I was in love with these things when I was an undergraduate, not long after their discovery, […] Click to continue reading this post →

The 2011 Nobel Prize in Physics

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Ok. So who was surprised by this one? My hand is not up… is yours? (That’s a screen shot from the Nobel Prize site to the left. More here. Cheeky of me, but it’s early in the morning and I’ve got to pack, shower, and cycle like mad to the subway to get to my train to Santa Barbara, so time is of the essence.)

I was pretty sure that this would be the prize sometime very soon, although I’ll not say that I knew it would be this year’s for sure. It is well deserved, since this was a genuinely major change in how everyone in the field thinks about the universe, and we’re still trying to get to grips with it today. The acceleration of the universe that they […] Click to continue reading this post →

Breakfast Guy

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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 →

Science Film Connections

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So journalist Pamela Johnson (no relation!) did a nice article last week about the science+film competition I mentioned to you (see also here). It is entitled “It Could Happen One Night”, and you can take a look at it here.

If you’re a student at USC and thinking that you can’t do this because you don’t know about science, or you don’t know about film… don’t give up! You might just need help to figure out how to get in contact with students who also want to get involved in making a film and want to learn more about one side or another (so you’re in the […] Click to continue reading this post →

No. Uh-uh. Nope. Nuh-Uh.

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I’ve received any number of emails from excited friends pointing me to articles in the news saying that particles have been discovered moving faster than the speed of light. Thanks everyone! My initial gut-response to the whole thing has been as given in the title of this post. My measured, scientist-response has been “this is extremely unlikely”. You see, it doesn’t seem to make much sense to me at all, and I expect that the scientists involved will at some point find an error, or other scientists will fail to reproduce the experiment. But, let’s see what happens. The great thing about science is that it is not about what people believe. It is about demonstrating phenomena with reliable, repeatable experiments. (The experiments were done by the OPERA collaboration, and their preliminary paper is here. I don’t need to point to the news articles since every news outlet has a bit on it.)

It’s funny, I’ve recently been writing about this in a part of the graphic novel. Somehow I think that the speed of light is presented too much as a speed limit in popular discourse, and so people naturally keep thinking that there’s some way of violating the law, like you can on the highway, or that some things are not subject to that law, like motorcycle cops, or people in a hurry to get home to watch Madmen, etc… I don’t expect this to be terribly clear in the short time I have to type this between this and that, but I think things are better thought of not in terms of a speed limit, but rather in terms of the fact that it all has to do with the meaning of what space and […] Click to continue reading this post →

Categorically Not! – Food

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The new season of Categorically Not! gatherings started last Sunday night. It went very well. You may recall that it is held at the Santa Monica Art Studios. It’s a series – started and run by science writer K. C. Cole – of fun and informative conversations deliberately ignoring the traditional boundaries between art, science, humanities, and other subjects. Here is the website that describes past ones, and upcoming ones.

This one was about food, and had musings on food and bringing people together at New York’s Cornelia Street Cafe, by the founder Robin Hirsch. He talked about the history of the place, read some extract from his writings about it, and also described the beginnings of the “Entertaining Science” series that got going when K C Cole, Roald Hoffman, and Oliver Sacks did a performance there many years ago. The Categorically Not! series, now five years or so in age, was a spiritual outgrowth of that series, and so it was great to see Robin speak at it. He was very pleasant and interesting to talk to before and after the event too. (I did a quick, rough, sketch during his 20 minute segment – with some tidying up later – and have included it for you to see. Click for slightly larger view.)

Robin was followed by Amy Rowat, of UCLA. Amy gave us a nice overview of what’s going on in her lab. She’s a physicist, and spends a lot of her time looking at food through that lens. The concerns she described were largely ones of structural, […] Click to continue reading this post →

Journeying

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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 →

That Was the Week that Was

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I might be losing my stamina, or have simply taken on more than I usually do, but it sure seems more tiring and hectic than it usually does this early in the semester.

It was a busy week, but I managed to get a few things done here and there that seem worthwhile, so I count my blessings, as they say. (Or used to say – maybe that’s somehow too loaded a phrase to use now? Not sure.)

To attempt to wind down yesterday after a tightly wound day and found myself walking with large sketchbook in hand in the warm evening sunlight to a studio to […] Click to continue reading this post →

Spin

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This week marks a landmark in the class (Introduction to Quantum Field Theory) since it focuses on the seminal work of one my heroes, Paul Dirac, who quietly went about his business of puzzling over the issue of how to find an equation that describes the properties of electrons (particles of spin one-half), and in finding what is now called the Dirac equation (see snapshot from my notes on right), uncovered a hugely rich and bright cornerstone of fundamental physics. It is famously described as a sort of square root of the relativistic wave equation known at the time – the Klein-Gordon equation – and in that way of thinking you quickly arrive at the idea of anti-particles (as did Dirac), since taking a square root leads to two solutions (both +2 and -2 square to give you 4). One solution turned out to be the electron, and the other leads (by an appropriate path of reasoning) to its anti-particle, the positron*.

Besides leading inevitably to anti-particles, the equation (which Dirac pursued in […] Click to continue reading this post →