Ok, so how long did it take you to spot that NPR’s 3D story today (“Advances In 3-D May Mean No Ridiculous Glasses”) was an April Fool joke? I thought it was rather excellent, and was in unbelieving mode from the moment that they began to talk about the surgery, which is utterly ridiculous, and made no physics sense to me at all. But the funniest give away was the line:
[…] Click to continue reading this post
The exo-planet hunting craft Kepler has found 1235 candidate planets orbiting other suns so far. The APOD site has a lovely composition by Jason Rowe showing representations of all of those suns with the spots on them that represent the planet transiting in front of them (that’s how they are found by Kepler). They are all nicely […] Click to continue reading this post
Tomorrow’s full moon is going to be the closest to us in 18 years, apparently. It’s called a supermoon by some, and no doubt some will try to link it to many major events here on earth, both natural and man-made (if you’ll forgive the distinction). I won’t do a long post about this issue, but instead refer you to Phil, who is excellent on the science of this and related subjects.
What I will say instead is that all commentators seem to have missed that this is the best opportunity in years to gather moon-milk! Get out your ladders and buckets and go for it!
What am I talking about? At my last birthday I was given* a lovely collection of stories by Italo Calvino, and the first one is entitled “The Distance of the Moon”. It begins with a description of the fact that a long time ago the moon orbited much closer to the earth, as you may know, and then weaves a delightful story from there. The story involves reminiscences, by the narrator Qfwfq, about those good old days when the moon came so close that once a month (yes, I know) the earth’s inhabitants would take boats out onto the sea to the where the moon came close and climb up a ladder to its surface to gather the much-desired substance known as moon-milk. A lovely extract follows: […] 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 [tex] {\cal A }[/tex] 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 [tex]{\cal A}=0[/tex]. It is zero because all the infinite modes of oscillation of the string gather themselves up nicely to give a factor:
[tex]
q^{-\frac{1}{6}}\prod_{n=1}^{\infty}(1+q^{n-\frac{1}{2}})^8-q^{-\frac{1}{6}}\prod_{n=1}^{\infty}(1-q^{n-\frac{1}{2}})^8-16q^{\frac{1}{3}}\prod_{n=1}^{\infty}(1+q^{n})^8=0\ .
[/tex]
Think of [tex]q[/tex] 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
Before jumping on to a plane last week, I went to meet some filmmakers to do a quick shoot we’d arranged. They are making a series of shorts for TV and myself and one of my co-contributors/presenters from The Universe, Laura Danly (from the Griffith Observatory) are doing some on-camera bits for them. (There may be others involved too, I don’t know.)
I mention this since there are two bits of novelty, I think. The first is that it is interesting that the company that commissioned these pieces are looking for shorts (4 minutes or so, apparently), and will be interspersing them with their programming in some way that will be somewhat unusual for current TV formats in the USA. I always welcome opportunities to help put some fun bits of science out there for the public, and in short bites mixed up with other things is just great!
The second novelty is that they are in 3D. You’ll recall, perhaps, that last year I contributed to a special show that was commissioned in 3D as part of the drive […] Click to continue reading this post
Ok, so it is last week’s Sunday bread, but you get the idea. This week’s is actually in the oven this very minute. I feel that all is more or less ticking away alright in my life’s day to day scheduling if I am getting bread made each week. I … Click to continue reading this post
Struggling for a post title, I went for a slight critique of the work I did on the character you’ve seen earlier*. She’s been grabbed from a panel showing her looking for a seat in a cafe where a conversation (about a physics issue) is to continue.
It is a large panel showing the layout of the cafe with all the people sitting and reading and talking and so forth, and she’s one of several small figures in it, so it is probably not that big a deal that she has somewhat heroic proportions here as compared to her more ordinary proportions in other panels.
Heroic here refers to the various choices of proportions you can give to figures, usually based on how many heads tall they are. You might have heard of people talking about how many heads tall a figure should be.
Well, there really is no “should be”, and different practitioners use different […] Click to continue reading this post
I’m guessing that a lot of you (especially those doing graduate work in Biology Labs) will just love this video, because you can relate to it. It’s about that frustrating feeling that (for one reason or another, or several) you’re stuck doing the endless project from hell… We’ve all been there. Oh, and it is done in the style of a Lady Gaga video I am told (not having ever seen or heard a Lady Gaga video, as far as I am aware, I can’t attest to this). Video after the fold:
[…] Click to continue reading this post
So you’ve probably heard the news, but just in case I thought I’d mention it here. The Kepler observatory, up there in orbit keeping an eye on things for us, has found a bumper crop of planets orbiting a sun-like star a mere 2000 or so light years away. It is amazing what you can see if you look closely. Every now and again the star’s brightness dips ever so slightly, and that tells you something has passed in front of it – another planet. Or in this case, once you’ve analyzed the pattern of dips, as the team of astronomers did, six planets!
These are not earths, although the headlines all over the news sure try to grab you in […] 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.
A
nyway, 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
So, a huge number of decisions went into getting the work to where I wanted it to be, and I’ve shown you samples in various previous posts, some collected here. But where does it all begin? It starts with the idea or concept that I am thinking about, and conversations which will form the dialogue for the piece in question. I start fleshing it out more, perhaps with a setting beginning to form in my mind. Maybe pencil drawings begin to take shape, and I start laying out pages, capturing the beats of the conversation, and the visuals that might get used. Characters (the people who will be in dialogue) begin to assert themselves by this point as well.
Incidentally, this is a place where sometimes the iPad comes into its own, and it is a great tool at several stages of all this. This project is one of the reasons I got the iPad, although I could not tell you at the time I got it back in the early Summer since I was not revealing what I was working on then. (Much of the other stuff I happily discovered about the iPad that I blogged about a while back (here, here, and here) are actually nice bonuses. I got it primarily to help me with development aspects on this project that had little to do with those other features.) I draw rough layouts on the iPad sometimes, and I can store all my rough ideas and print them out, modify them, call them up for later viewing, and so forth. I can carry work in progress with me, reference photos from location scouting, etc. It is also good for practice sketching, and sometimes, using it, I’ve grabbed some nice quick drawings of people in a meeting or in a bar or on a bus. Drawing from life is an important skill to keep up. The iPad is not used in final production on the graphic novel though. I work at a level of detail and complexity that the iPad would not be able to […] Click to continue reading this post
I just saw on the USC news site that DJ Strouse, one of our excellent current physics majors, has been selected as one of 14 students in the USA to get a Churchill Scholarship this year! He is the first USC student to get one, actually. DJ is one of those students who reminds you why teaching is such a delight. He engages with the material in class and beyond, exploring it extensively on his own, and […] Click to continue reading this post
This always catches people off guard (myself included), so I thought I’d post a little reminder. The deadline for applications to the Summer workshops at the Aspen Center for Physics is January 31st. That’s coming up soon, so to physicists interested in doing a research stay, start thinking about the dates you want to attend, finding funds for support, planning for things like childcare or summer programs for children if you have any, and so on and so forth. There’s a wide variety of excellent […] Click to continue reading this post
Although the planning of a panel on a page is entirely freehand pencil or pen work, it is indeed the case that sooner or later I start detailed placing of subjects, and I often use perspective to do the layouts. Not just for skyscrapers and so forth, but for down to earth things too. I do it the old-fashioned way, which is repetitive and time-consuming, but I must admit – It is fun! Take some time to look at everything around you – real or represented in drawings, photos, etc – and you’ll likely see perspective cues that help give sense of depth and placing. It is all about geometry, which our universe seems to like a lot, and which we use to navigate in it. Learning a bit of this geometry, and how to build it in projection in two dimensions on the page (and it is much easier than this sentence makes it sound!) allows one to make reasonably convincing recreations of the universe (or simulacra of your choosing) and how we perceive it. Real artists (not hacks like yours truly) use geometry a lot, in one way or another, to interpret, represent, or distill aspects of the world, and so in a sense, they are companions on the same road as those of us in (especially) the physical sciences.
Babble aside, here you can see parts of the interior of a cafe taking shape. I did it using three-point perspective*:
This will be the skeleton upon which I build the flesh of the rest of the piece. It is based on my knowledge of a real cafe that I location-scouted (well, I happen to drink coffee there from time to time), but you’d never get this view without (a) perhaps being able to fly, and (b) removing the ceiling. Trying to be somewhat discreet in this […] 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):
[tex] Z=\int [{\cal D}g {\cal D}X] e^{-S(X,g)}\ ,[/tex]
and make sense of all the bits. (Er, for the two of you still reading, [tex]S(X,g)[/tex] is an […] Click to continue reading this post
