Asymptotia

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 Continue reading ‘Has the Fat Lady Sung?’

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 Continue reading ‘Scribbling about Quantum Gravity’

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”) Continue reading ‘Tune In!’

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 Continue reading ‘Almost at an End’

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 Continue reading ‘Infinity Coincidence’

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 Continue reading ‘QFT Rocks!’

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 hoping to hear about this sooner. Continue reading ‘Southern California Strings Seminar’

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 Continue reading ‘Landmarks’

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 Continue reading ‘AdS Vs CMT’

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 Continue reading ‘Looking Back and Forth’

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, Continue reading ‘Quasicrystals!’

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 Continue reading ‘Breakfast Guy’

We had a really interesting discussion of the quantum physics of de Sitter spacetime yesterday here in Aspen, starting with a review of the behaviour of scalar fields in such a background, led by Don Marolf, and then, after lunch, an open-ended discussion led by Steve Shenker. This is all quite difficult, and is of course quite relevant, since a piece of de Sitter is relevant to discussions of inflation, which seems (from cosmological observations) to have been a dominant phase of the very early universe. As the most symmetric space with positive cosmological constant, de Sitter may also be relevant to the universe today, since dark energy (first recognized after 1998′s observations of the universe’s accelerating expansion) may well accounted for by a positive cosmological constant.

So we need to understand this type of spacetime really well… and it seems that we don’t. Now there’ve been a lot of people looking at all this and doing really excellent work, and they understand various issues really well – I am not one of them, as I’ve not worked on this in any detail as yet. Do look at the papers of Marolf, and of Shenker, and collaborators, and references therein, and catch up with what’s been going on in your own way. For what it is worth, the sense that I get is that we’re trying to solve very difficult issues of how to interpret various quantum features of the spacetime and getting a lot of puzzles by trying to make it look a lot like things we’ve done before.

Now, we may solve all these puzzles…. but my current take on this all is that we’re Continue reading ‘Heretic…?’

As far as particle physics and big questions about how the universe works, we are living in very interesting times, I’m happy to say. We’ve all been waiting for the Large Hadron Collider (LHC) for over two decades, and now it turns out (I’ve been hearing from a number of people in various conversations here at the center) that the machine is running really well – impressively so. That alone is great, but an interesting thing is that we are almost certainly going to know something significant before the end of the current scientific run next year, maybe even by the end of 2011!

Recall (see posts like this one) that the primary goal is to understand the physics responsible for the Higgs mechanism – the physics that gave mass to those elementary particles that have mass. The particle that does this is called the Higgs particle, and exactly how Nature implements the Higgs mechanism is what we hope to learn. There’s sort of a vanilla version of the story, that fits into the Standard Model of particle physics without any further adornment than just doing the basic job. Then there are more complicated versions of the story, where, in some cases, the Higgs comes as part of a bigger physics story that leads the way to what’s generally called Beyond the Standard Model Physics. As the machine searches toward higher and higher energy that probes higher and higher mass, the simplest possibilities will begin to fall by the wayside pretty soon if nothing is seen. An exciting thing is that it seems that whether or not we have the Standard Model Higgs might be known soon.

Now that’s exciting enough, but there’s more. Actually, a lot of people, for various Continue reading ‘Living in Interesting Times’

It was a quiet and good day today on the work front, here in Aspen. I started at the Center relatively early (having risen at about 7:00am today – a bit later than I have been) and the plan was definitely a vastly-mostly-physics day, digging into some of the things I’ve been puzzling over, and having some conversations with one or two people about their projects. The first order of the day, once arriving, was to turn off my phone and go dark on IM, and turn off my email… The plan for such days is to only check messages and so forth at lunchtime, and then much later in the afternoon, which is rather helpful, I find. (In fact, I ignore the phone for the entire day until the evening…)

I won’t give you a tedious blow by blow of my day, since it was mostly a mixture of sitting and reading or staring into space (along with some scribbling here and there), and so forth. I also went for some walks, down by the Aspen Institute (where there’s currently the interesting “Brainstorm Tech” conference sponsored by Fortune magazine going on) and of course over to the Music tent, where there were lots of people in the morning, since the Music Festival orchestra (and a lot of very young pianists – maybe from the piano competition? – taking turns) were rehearsing for tonight’s concert. I sent an email or two, I’ll admit, but they were specifically concerning a project I’m working on with a colleague back in LA, and so they count as ok.

I went for a walk to think and eventually returned to the tent after one or two Continue reading ‘Workin’’

I’ve a big meeting in the morning at 9:00am and have not the slightest bit of sleepiness in me at all, and it is 11:30pm. This may have something to do with me making a pot of coffee at about 9:00pm after deciding that it was way too early to go to sleep and I should do some work. I’ve done some, and now im in bed. Let’s see if a little blogging off the cuff about some internal stuff helps…

Well, sort of internal. Pretty sure you would not want full-on internal stuff. Even I don’t know what’s in there all the way down…

….hmmm, and now it is 13 minutes after midnight. The intervening time was spent prepping a draft of what I expect will be the next post, involving generating a video and uploading it to YouTube and so forth. Do have a look. [Update: here.]

One of the more interesting things from today was getting excited about a paper I was asked to referee. It turned out that I really liked it a lot. I’d somehow missed it in the regular scheme of things, and so this time around I get to say that refereeing was really useful for me. I cannot tell you which paper it s, unfortunatley. It was actually about something that I’d planned to try to do myself, before I got distracted by another set of projects and never returned to the issue… So it was nice, a bit of the way through, to suddenly realize what was going on and sit up and take note. I’ve a few minor comments to the authors to encourage a bit of clarity in the presentation, but other than that my report will be “nicely done, chaps”. It has all served the purpose of reminding me to get back to some of those projects I had in mind three years ago. (Three years already! Geez…)

Was chatting with a bunch of different sorts of physicists today. It was enjoyable. Continue reading ‘Bed Post’

So, apparently, electrons are round. Very very round. So when drawing those terribly wrong but evocative pictures of atoms as a lump in the middle (the nucleus) with a collection of round balls in orbit around them (the electrons), go ahead and make them nice and round. Very round. How “very” are we talking about here? According to this report on the recent experimental measurements in the Guardian:

Were the electron scaled up to the size of the solar system, any deviation from its roundness would be smaller than the width of a human hair [...]

So you’d have to be using a pretty impressively sharpened pencil to draw it that accurately round. But give it a try.

Ok, what’s the story here? Well, oddly, this seemed to be on a lot of news sources yesterday, and I’m not sure exactly why. Maybe because it mostly seemed to be pitched as a “back to the drawing board for the theorists” story (two major sources I heard had it spun this way), which editors seem to like running with. And the roundness? What’s that about? Well, what they’re taking about is the result of a long careful set of measurements done by Hudson et. al. at Imperial College (my Continue reading ‘Stick with the round balls, for now’

Last night I graded the exam for my advanced string theory course, computed the final grades, and will enter them into the System today. Hurrah! It was a fun class to teach, maybe even to learn (you’ll have to ask them). The final exam took me most of Sunday to write and LaTeX carefully, checking for typos since there were a few “show this” type questions where I gave a complicated expression that they had to derive. In Continue reading ‘Done. Sort Of.’

I had an early rise this morning, to make it down to campus early enough to set up (with the help of my co-conspirator Tameem) the room for the all day meeting I mentioned earlier, in order to start at 9:00am. All worked well… And things are progressing nicely (see photo of some of us in the lovely room we’re using) with local participants from USC, UCLA, UCSB, and even Stanford! It is excellent to see such support and enthusiasm for this semi-annual event!

-cvj

We’re hosting the next Southern California Strings Seminar here at USC. It will be on Friday 6th May. I’ve been working on it a lot over the last several days* and put the finishing touches on the arrangements just this morning.

There’ll be no Saturday morning component this time, since there’s yet another huge event down at USC this weekend, and things will be rather disrupted, I understand, as there’ll be lots of people, street closures, and so forth**. (It is the Revlon Run/Walk event in exposition park, across the street from us, an excellent event!)

So I’ve packed five exciting talks into Friday, and I think it is going to be fun! Here’s the schedule:

Continue reading ‘Southern California Strings Seminar’

I’m lounging around. In Cincinnatti Ohio. Why? Well, it has been a long day, and I’m tired. I spent the whole day yesterday traveling to get here, changing planed in Chicago, eventually getting to my hotel at 10:00 pm, having arisen at 6:00am. I spent the flying time thinking about physics and writing the talk I was invited to give here as part of the regional SPOCK meeting at the University of Cincinnatti. The letters stand for something, but I can’t recall what it is right now. It does not mean, as the title might suggest, that several emotionally-challenged and otherwise tv-cliche-handicapped individuals were meeting to discuss arcane matters in a room somewhere. It was a meeting of several people from the region’s string theory community to discuss…. Ok, ok, Ok…stop giggling!

I got up at 7:00am -really 4:00am my time- transferred all my pages of notes to the iPad, and got ready, leaving to do the short (I assumed) walk to the physics department in the wind and rain. I enjoyed that bit… I had however mis-estimated how long it would take me to get to the Physics department building, largely due to Continue reading ‘Lounging’

It was a fun week in the string theory class this week, as we got to some major landmarks that are always fun to teach. We’ve uncovered the extended objects called D-branes (see numerous previous posts for how useful and important these objects are in string theory research) in all their glory in the lectures before, and deduced lots of their properties, such as the form of the action that determines how a D-brane moving in spacetime responds to the various fields (including the geometry) created by the string theory. That’s all fun, but then the key thing to do next is to compute the mass of these dynamical objects, or the mass per unit volume – the tension. Computing it fully, with no hand-wavy factors. Your mass measures how strongly you interact with gravity. So you can measure it by studying the gravitational interaction between masses. (You do that when you step on a scale to measure your weight… well the scale does it by showing how much force it takes to stop you from falling through the floor toward the center of the earth…)

So in class this is when we go all Polchinski and unpack the tension computation, stopping to admire the various features of string theory you learn along the way, and seeing how simply beautifully the various basic features of the superstring theories that we’ve met in the last few lectures encode themselves in one nice object – the vacuum amplitude from the cylinder diagram representing either exchange of closed strings (including quanta like the graviton – this is what you focus on to learn what the mass is) between a pair of D-branes, or an open string with its ends tethered to a pair of D-branes going in a closed loop. That there are two ways of looking at the diagram, an open string way (running time around the cylinder) and a closed string way (running time along the cylinder) is a hugely powerful thing, and is at the heart of so very much of what we do in string theory these days especially – including a lot of what I’ve told you in previous posts (see e.g. here and here) about applications to things of interest in current experiments.

One of the fun things about all this is that the answer is actually . It is zero because all the infinite modes of oscillation of the string gather themselves up nicely to give a factor:

Think of as a book-keeping device that lets one track energy contributions (in the power of it that appears in a term if one expanded this expression), and how many Continue reading ‘Tension’

A student asked a question in the string theory class today to which my answer was a suggestion of how to think about the issue raised in order to go about answering the question themselves. There’d be a few minutes of diagram drawing, and all would (hopefully) be clear. I thought that might not be an unreasonable thing to ask of a student, particularly in a graduate class, where they are ultimately trying to develop skills to do research. Well, it all went a bit pear-shaped as the student seemed to get quite strongly annoyed by this suggestion. I’ve still no idea why.

Anyway, on the bus home I thought I’d do some idle doodling, and ended up doing the exercise I’d suggested… and sure enough what I suggested doing works nicely and does (I think) make it clear.

I’m sure it was all a misunderstanding… Probably my fault.

Over late night dinner just now, since I can’t put down this lovely brush pen I’ve been drawing with recently, I scribbled the figures out from the notebook for you to look over my shoulder, as it were, and see what we’re up to in the class. Don’t worry so much about what it all means. It is sometimes nice to just look at the shapes*. (Actually, one of the students brought his mother to visit the class today. She sat through the whole hour and fifty minutes of the lecture. That was nice. I hope she enjoyed it all!)

I find these diagrams and the computations they represent rather pretty.

Wednesday will be the big climactic lecture of a sequence I’ve been leading them Continue reading ‘Ribbons’

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 Continue reading ‘Summer Reminder’

Well, today was the first lecture of the string theory course (part 2) that I mentioned in the previous post. And I applied the “when they think you’re going to zig, you zag” principle. They have been expecting me to dive into the whole business of open strings and D-branes and so forth (the subject of the book), and I did not. Sure, that will come, and sure, we’ll explore what they mean and what they can tell us about string theory beyond perturbation theory and so on and so forth. But I want first to spend a couple of weeks on getting to the heart of the matter. They made several standard choices along the way in doing their first semester of study of string theory. What did they mean? Why did they work? Were those the only choices? What is underlying a lot of it all, and what, when stripped down to the essence, is at the core of string perturbation theory and beyond? In other words, let’s look more closely at the path integral definition (such as it is) of a string theory (slightly schematically):

and make sense of all the bits. (Er, for the two of you still reading, is an Continue reading ‘Back to Basics’

I’m feeling strangely cold, although the heating is on and I’ve got a jumper (“sweater” to readers in the States) on. It has been this way all day, so I suspect it is something to do with my frame of mind. I’m feeling a bit reflective with it too, so I’ll think out loud (as it were) a bit before going to bed early.

Well, it is almost time to start another round of teaching. This semester, starting Monday, it is a graduate course that I’ll be teaching, the second part of a year’s sequence of string theory that we teach from time to time. My focus will be non-perturbative issues, focusing on much of what has been forming the foundation of research in various areas of string theory since the 1990s. Should be fun. Some of the material will come from my book, D-branes, that was published back in 2002. It seems so long ago now. I actually looked in it today, as I was discussing a research issue with a colleague, and could not recall some details. Happily there was a chapter with it all in there. That’s rather nice. The book serves me well as a personal reminder of things I used to have at my fingertips all the time back then, and as a bonus, lots of people around the world still use it as a handbook/guide/intro/etc, I hear.

I joke, of course. The cart and the horse are the other way around.

Speaking of books, I’ll be doing my best to continue working on the current book project, with all the excitement and adventure in developing it. (And the occasional Continue reading ‘New Semester Approaching’

Ah. This is just perfect. I actually looked into my Institute For Advanced Study news magazine this time around and noticed a gem I’d like to share. Edward Witten gave a lovely talk entitled Knots and Quantum Theory for a (sort of) general audience, and there is video of it available. Ever wondered why mathematicians study knots? Why do physicists care? What do they bring to the table? Well, this could be a talk for you to take out a bit of time to watch.

Not long ago I wrote a post about Ed, his huge influence on the field of theoretical physics, and some of his role in my own development as a physicist during my time Continue reading ‘Knots from a Master’

It is midnight and I really should get to sleep in order to wake up and work some more on editing the final exam for my class so that it can go to the printer by noon. But I’ve got several pokes from people clamouring to find out what The Project actually is, and I promised yesterday I’d start to spill the beans. Thanks for the interest! I think I’d better get at least some of it out there or I’ll have an angry mob by morning! So here goes. I will drag out the draft I sketched yesterday and beat it into shape:

So, as you may have guessed, The Project, which I’ve been mentioning here since a post way back in February, is a writing project, but it is somewhat different from what you might expect. The bottom line is that I hope that at some point into future you will be able to purchase a copy of your own, and that you will find it instructive, exciting, and enjoyable. At least.

Yes, it is a book about science. However… Well, here’s the thing. Over many years, people (friends, colleagues, potential agents and publishers, blog readers, etc) have been asking me when I am going to write my book. You know, the popular-level book that every academic who is interested in the public understanding of their field (as you know I am from reading this blog) is expected will write at some point. To be honest, I have given it some thought over the years, and it has been something I figured I might do at some point. In fact, several different ideas have occurred to me over the years, and I may well implement some of them at some point.

But a major thought began to enter my mind well over ten years ago. In my field, there is a rather narrow range of models for the shape of such books, usually involving about 80% of it being a series of chapters covering all the standard introductory material (some relativity, some quantum mechanics, and so forth) for the lay reader, before culminating in a chapter or two of what the researcher really wants to tell them about: some aspect of their research. This is a fine model, and it is great that people continue to write such books, and I will no doubt use that model one day, but to be honest, I don’t think there is any urgency for me to add to the canon yet another one of those books. Moreover, if you line examples of that type of book up against each other, you see that the Continue reading ‘The Project – 1′

Jacques Distler pointed out that ALICE has just published their first paper, only a little over a week after the beginning of the heavy ion phase of the LHC at CERN! Moreover, they are way ahead in energy of the previous heavy ion collision experiment (RHIC) and have verified “elliptic flow” (the main sign that the quark-gluon plasma behaves like a strongly coupled fluid, the big experimental surprise of some years back, with properties of a type that can be nicely captured using string theory models). Have a look at Jacques’ post here, and go directly to the paper of ALICE here.

Hurrah!

Please see my post from last week (“Experimental Excitement” was the apt title) about why I’m excited about all this!

-cvj

Well, this week is a big week, in some ways. The Large Hadron Collider has gone into a new phase! For a while, the experiment has turned aside from the task of searching for the origin of mass (the Higgs Particle, or whatever it is that mediates the generation of the masses of elementary particles – see earlier posts, and features like this, etc) and is turning to heavy ion collisions. Rather than studying processes in which only a few particles at a time are interacting at super-duper-uber-high energies, the experiment will instead collide together the nuclei of lead atoms, so that you get lots of particles colliding together and creating a messy “soup” of high energy stuff all together. The goal is to understand the constituent nuclear particles (quarks and gluons) working collectively at high temperature (and low to moderate density), instead of focusing on issues concerning individual fundamental particles. Today (starting late yesterday, actually) is an exciting day because it marks the first step on the journey to probe deeper into this physics. The ALICE experiment has started looking at these collisions. See top right for some screen-shots of the mess of particle tracks that are left after the soup flies apart. The trick is to analyze all these tracks from millions of such collisions to work out the properties of the soup.

As you perhaps know from reading this blog, while of course I’m interested in the behaviour of fundamental particles and the origin of mass, and so on and so forth, I’m very interested in this nuclear issue too. Some of the most interesting work that Continue reading ‘Experimental Excitement!’

Oh! I almost forgot to remind local readers that the next Southern California Strings Seminar is happening this week. Friday and Saturday.

It will be held at UCLA, and there’s a great line up of speakers. As I’ve said here before, graduate students are especially encouraged to come…

…since special effort is made to make sure that each talk begins with a pedagogical portion to help non-experts in that subfield navigate and see the motivation.

The speakers and talks are:
Continue reading ‘Southern California Strings Seminar’

Charles Day on the Physics Today blog asks an interesting question: Why has physics today’s news coverage of string theory been so sparse? I must admit that I had not noticed what the level of coverage is, and so the matter had not sprung to mind, but it is an interesting one. He looks back at the number of major articles written about the subject in recent years (he was a feature editor, and so shepherded some of them through), and concludes that the numbers are low, and he may well be right, but I am not sure I know what the best measure is.

How do we measure the appropriate coverage level? Is it by the number of people working in a sub-field as a percentage of the overall field of physics? If it were possible to break things down that way (I’m happy to see that we have come to a point in the field where I’ve no idea how to define what a “string theorist” is, per se, any more than I know what a “field theorist” is. There are simply people working in various fields who use both as tools to make progress) I wonder what fields would end up appearing under or over covered?

Perhaps a large part of it it is the issue of how many articles on the topic can be written that are of general enough interest, and finding the people who are both able and willing to write. This is a tricky issue, and depends on a combination of the topic in hand and the knowledge and writing skill of the author. There are two extremes that would be a factor here. On the one hand, you have the obvious difficulty of a non-expert journalist either not being able to see the general relevance or value of new results in such a specialist field, or if having seen it, not being able to explain it Continue reading ‘Too Little, Too Much, or Just Right?’

That was the unmentioned title of yesterday’s group meeting. We try to do this every year, and so one of the first meetings of the year is us sitting together, eating our lunches, chatting about ideas. We basically catch up, and chat about things we learned about from Summer travels, perhaps from conferences, schools or workshops. We also mention what we’ve been up to in terms of projects worked on, work in progress, etc. I find the latter especially useful from the standpoint of student development, since it is often the first time that a student gets to tell a wider audience (but in a safe environment) a little about what they are doing, often their first projects. Even a few minutes summarizing what you have been doing can be daunting at the early stages of your research career, so this is a good place to start.

Talking about things that we’ve learned are going on in the larger community (or Continue reading ‘I Know What You Did Last Summer’

I just noticed that last week’s episode of The Universe on Time Travel, which I told you about here and here, is available online on their website. Click here to learn more about the ins and outs of it, and I show you how to make one too! Kind of.

It is a difficult subject to explain, and one that must be tempting to Continue reading ‘Time Travel a Click Away’

I just noticed, via this article at the Guardian, that not only has Edward Witten been awarded the Institute for Physics’ Isaac Newton medal, but his lecture at the ceremony has been posted online for all to see! See the link below. It is not often that you get an opportunity to see Witten, one of today’s giants in theoretical physics, on the public stage, to the extent that most people outside the field have not heard of him at all. The public view of who is driving forward and massively contributing to the field is rather skewed as a result of the number of appearances and grand pronouncements (often on subjects they’d be better shutting the hell up about!) from certain other renown theoretical physicists. So here’s an opportunity to hear from one of the true masters of the field.

When you speak to sensible people in the subject, whatever their own work is about and whether they like some of the things he works on or not (such as string theory), they will quite readily concur that he has done a huge amount for the field, driving forth many powerful ideas, sharpening the way we think about certain kinds of problems, conceiving of new ideas, and overall strongly influencing much of the basic manner in which practitioners think about the physics they are doing. Often, even if he is not the originator of a particular Continue reading ‘Witten at Your Fingertips’

In case you were wondering, things are moving steadily along in the search for the Higgs boson, and in the general ramping up to study entirely new frontiers of particle physics. I noticed a couple of interesting articles today that give you a nice sample. The first, by Dick Ahlstrom in the Irish Times, and is about the announced “rediscovery” of the W and Z bosons at the Large Hadron Collider, by a team working at the LHCb experiment. (I personally think that the term “rediscovery” is somewhat misleading since it makes it seem like the community forgot where they (the key signatures of the unity of the electromagnetic and weak nuclear forces at high energy) were since their discovery in the early 80s, but let me not quibble too much.) The point is that experimental teams are refining their searching techniques while sifting through all the new data being produced in the collisions at the LHC, and one thing you need to do before you begin to look for new things (like the Higgs) is to make sure you can find and recognize old things. Especially very important old things. Continue reading ‘Happy Higgs Hunting’

In the New York Times this week there’s an article* by Dennis Overbye on Erik Verlinde and his paper on the idea that gravity is not a force at all, but a consequence of thermodynamics. You can think of it as an extreme take on one of the directions a lot of the research (that I’ve mentioned a number of times has been going on in string theory) has been pointing, although I think it is safe to say that there’s a lot to be done on making the statement a concrete one that you can do physics with. I think it contains the germs of the right thing we’re all reaching for, but does not quite get there yet. We’re now quite routinely formulating some of the key physics of gravity entirely as physics of a completely non-gravitational dual theory – this is the content of what we call holography – and in particular the quantum physics of black holes in those settings get holographically mapped to the thermodynamics of the non-gravitational physics. This is the basis of the tools that we’ve been applying to studying aspects of phenomena showing up in various experimental systems in nuclear physics and cold atomic physics (and studies of phenomena relevant to various condensed matter systems are also being done). I’ve told you about a lot of this in various posts. (Some of them are listed below.) Running this the other way, the model non-gravitational systems (certain gauge theories at strong coupling and with large rank gauge groups) can be thought of as examples of how gravity (and space-time itself) is really an emergent phenomenon, appearing simply as Continue reading ‘Emerging Gravity’

Well, my work at the Quantum Gravity school over (see previous posts here, here and here), I hopped on a plane yesterday, in order to return to Los Angeles. It was an excellent time. I enjoyed being in Mexico again, and seeing a new part of it (see posts to come), and the school was well organized and very enjoyable. The students were very receptive overall, and I spent a huge amount of time chatting with them about physics between sessions, over lunch, and on the bus back and forth between the campus and the city (and on the excursion on Sunday for a while). A number of students seemed very interested in some of the quantum gravity phenomena that are possible to describe using string theory – surprised in most cases (since the background independence issue that keeps being waved about by some as a naive (in my view) and bluntly used principle seems to have served as a block to many) – and it was a pleasure to be able to open them up to new physical ideas. It worked pretty well because I gave them three lectures on the basics of string theory, and so could build on that material in the one to one discussions to explain more detail.

Dynamical changes of spacetime dimension is one thing that captured a lot of interest, as well as string theory’s various ways of showing in model examples how spacetime is an emergent, classical approximation to an underlying quantum description that does not have manifest spacetime geometry. The latter is something that all approaches to quantum gravity hope to realize in one way or another (since those sorts of ideas and fantasies about what quantum gravity should be appeared in the mid 20th Century), and exactly how it emerges in string theory is a beautiful story. Who knows, perhaps they will take these hints from string theory about how quantum gravity can work and develop them Continue reading ‘Scenes from School’

This is a quick update on the school. I’ve been trying to give the students some of the core concepts they need to help them understand what string theory is, how it works, and what you can do with it. Here’s the really odd thing about all this (and an explanation of the post title): While this is a school on Quantum Gravity, after talking with the students for a while one learns that in most cases the little they’ve heard about string theory is often essentially over 20 years out of date and almost always totally skewed to the negative, to the extent that many of them are under the impression that string theory has nothing to do with quantum gravity at all! It is totally bizarre, and I suspect it is largely a result of things that are said and passed around within their research community.. So there are a few students here and there who have some familiarity with strings, huddling together at times for warmth in a sea of miscommunication, misinformation, and strange preconceptions. Let me be the first to point out that the string community also tends to pass on its prejudices about other Quantum Gravity approaches to its students. But my goodness it does seems extreme to me that an approach that has so many clear benchmarks of success (at achieving goals that at least used to be key objectives) in quantum gravity is treated as an irrelevant backwater by the community that thinks of itself as the main practitioners of quantum gravity. Odd. Anyway, my main message is to try to clearly show that the basics are quite easy to grasp if a student has a decent education in Continue reading ‘Minority Report’

(Anyone remember Mike Oldfield? I recall a lovely piece of music of his with the same title as this post and it has now been playing distantly in my head as I type…very pleasant.)

Well, I’m sitting at an outside table across from the main square with the cathedral and having a simple lunch. It is hot, and so I have a glass of cold pale beer in front of me, and everyone around me is speaking Spanish. This feels like it could be that I am back in Madrid, but in fact I am in Morelia, Mexico. (I can tell because, among other things, I’ve never been offered a shoe shine quite so many times in the space of 15 minutes…) It is quite a lovely place, as far as I’ve seen so far (I’ve not explored much yet). I’m resting after a very early morning travel schedule which saw a slight panic (er…long story) at LAX to catch my flight which left just before 1:00am. The seats were fixed to the bolt upright position the whole flight and so the two and a half hours I’d planned to snooze were not so Continue reading ‘Arrival’