Saturday, January 31, 2009

## Visit to Cambridge

I made a quick visit to Cambridge this week to visit the famous Cavendish lab and give this seminar. I saw quite a number of old friends and was introduced to some new people too, and managed to discuss a whole lot of interesting physics in a very short time.

The trip from Oxford to Cambridge is not that far as the crow flies (about 80 miles), but there is no convenient way to get from one to the other. By car, it is a very complicated route and takes two and a half hours. By bus, more than three, and more than one person warned me that it is a bus ride that is sure to make anyone nauseated, because the bus goes around about a hundred roundabouts (known as a traffic circle, or rotary in the united state). By train, which is probably the best way to get from one to the other, you have to go into London Paddington Station, then take the tube to London Kings Cross (*see footnote below), then train to Cambridge. It makes the journey rather a schlep.

While I could wax poetic about some of the physics that is going on at the Cavendish, I think I may have used my quota of physics talk allowed on this blog last week, so instead I will mention something else I learned while I was there:

After a long day of physics, I was invited to High Table dinner at Cambridge’s Pembroke College. Unlike Somerville at Oxford, Pembroke, founded in 1300-something, has a proper High Table where even the students wear gowns to dinner. During this dinner, the old scholar sitting across from me was extremely excited about having recently discovered the first usage of a particular common phrase. He had been reading a text called “The true history and chronicle of King Leir” which was more or less the source for much of the great Bard’s play, and had come across a common expression and was wise enough to realize that this was probably its earliest recorded usage. Being that the scholar sitting across from me was probably about 90 years old, it is rather appropriate that the expression in questions was “One foot in the grave. ” He did admit that it was a bit of an autobiographical discovery.

*Footnote: Last time I was at King’s Cross, I found that there really is a platform nine and three quarters, but I did not manage to find it this time. I hope it is still there.

## Oxbridge Education

The British college education system is quite different from that in the United States. First of all, you go to college to study only one topic (or “Read” the topic, as they say here). So, upon leaving high school, a student will apply to Oxford to Read Physics, and then when they get here, it is all Physics all the time for the length of their college career. Liberal Arts does not really exist over here (or in most of Europe for that matter). On the one hand, it risks developing people who are very one-sided. On the other hand, students coming out of this system can be extremely well prepared in their chosen subject.

The second difference is in how students are examined. As far as I can tell there are only two examinations in the entire student’s career. One exam, the “prelim”, at the end of the first year. This is basically a chance to fail out if you are really doing badly (very very few fail). It also stratifies the class a bit into those who are doing well and those who are not. In the case of physics, there is a three year degree and a four year degree, and if you do badly on the prelim, you can’t get the four year degree. The only other exam you have is the final exam at the end of your career. And that’s all. Of course, having only two exams means that some students can procrastinate learning for years – but most actually do try very hard to keep up – or at least the physics students do. These exams are not written by the people who taught the courses, but rather are put together by an exam committee to test what is supposed to be on the curriculum (which is decided by a curriculum committee). Apparently being on either of these committees is something to be avoided, as they inevitably result in fights.

The third difference is in how the classes are actually taught. There is one person who gives lectures to the entire class of 180 first year physics students. However much of the teaching is actually done by the tutor. Homeworks are assigned and graded by tutors, as well as mock exams (known as “collections”) – and the tutors may or may not be in sync with what the lecturer is doing. Both the tutors and the lecturers are both trying to teach the curriculum (and prepare the student for the real exam) but they are free to do so in different ways. In physics students typically meet with their tutors in a two-on-one setting roughly for an hour every other week per course. This adds up to a whole lot of individual contact with faculty.

Fourth, the terms here are extremely short (two eight week terms and one ~six week term per year), and then there are very long breaks between terms (during which the students are supposed to be studying too). As a result of the very short terms, things get very intense while the terms are in session, and then everyone recovers in the break and prepares for the next term.

We can have a debate about whether the Oxbridge system is better or worse than the American system, but the truth is that I suspect it really depends on the particular student.

This year, I’m doing tutorials for three courses, and I’m not lecturing at all. I have six students I tutor in first year electricity and magnetism, eight in second year statistical physics, and five in third year solid state physics. Truth be told, this is pretty hard work for me right now. ( I had this panic before I got here that the E+M course looked pretty hard – but in fact, it turned out I was looking at the wrong course – and the E+M course is pretty similar to what first or second year physics students get in the US.). I’m sure once I’ve gone through the curriculum once, I’ll find this much easier. Right now, trying to figure out what problems to assign my students is pretty time consuming. Then of course, I have to actually solve the problems myself to make sure they are all actually solvable. Plus of course grading homework, figuring out what students are having trouble with, and preparing for, and doing the tutorials. I’m sure next year, it will be much easier (I’ll already know which problems are good to assign, and I’ll know what students are going to have trouble with.) But for now, it is a lot of work. And it is kind of emotionally draining. The students are counting on the tutors to prepare them for the exams – and (at least most of them) are trying very hard to do well – so I feel I should try equally hard to help them.

I have the distinct feeling I am going to be completely exhausted before the end of my first term.

This is my excuse for not having posted anything all week.

Update: I was corrected by some of my students, they do take a final exam at the end of the second year as well, and it counts something like 20% of their final grade at the end of the degree.
Sunday, January 25, 2009

## Nonlinear Electron Waves for Pedestrians:

Besides Nuntiya's posted "Huh?", I've gotten a few (unposted) comments by email that it might be a good idea not to completely snow all my readers at the first opportunity. So this posting is meant to kind-of sort-of explain what was in the previous post. (Doug and Ilya and any other condensed matter physics people reading this, please don't shoot me for oversimplifying, I just started teaching this month so that's my excuse why I'm not so good at simple explanations).

Imagine a large tub of Jell-O. If you punch it, waves will jiggle outward from where you punched it. (See the cute animation on this page). This is a typical response of most materials. Although it is not so easy to see, the same thing happens when you hit a rock, or a steel girder. Electrons do the same thing. If you think of the electrons in a material as forming a jell-o like fluid (and ignore all the nuclei of atoms that are sitting still while the electrons are doing there thing), when you hit the electrons, electronic waves will emanate out from where you hit them.

If you think about waves moving in the ocean, you know that their structure slowly changes. Some waves get bigger, others smaller, sometimes they merge, sometimes they split. The claim made in the previous posting is that the electron waves (in fractional quantum Hall systems of electrons -- never mind what this means) evolve in such a way that they end up looking like individual sharp pulses, each carrying a particular amount of electronic charge. Of course it would be really nice if each pulse carried one single electron worth of electronic charge. But in fact, the claim is that each pulse carries a third of an electron, each electron having "fractionalized" into three pieces. There are other odd and interesting things about the electron waves in questions that I'm sweeping under the rug too, but that is the general idea.

Unfortunately, this proposal disagrees with the accepted dogma of the scientific community. However, it only disagrees a bit and it seems within the realm of those things that might actually be right. If I had to bet right now, I'd give it about a 1 in 5 shot of being right. But 1 in 5 is pretty good when you are talking about overturning 20 years of study.
Friday, January 23, 2009

## Nonlinear electron waves

The audience of my blog is mainly nonphysicists. The only physicists who are reading this blog (that I am aware of) are my father, and Doug the propreitor of this blog. (Added: and Ilya. Added: and Austen. Wow, I'm actually getting a couple of real physicists reading me!). At the risk of scaring everyone else off, I am going to actually write about physics here. Maybe my blog will start to attract other physicists too. Perhaps this attempt to discuss physics will be an abject failure, but why not try? (Added: Yes, I am also showing off that I can typeset pretty equations in my blog. Those interested in doing the same can find out how here).

Yesteday I heard an extremely interesting talk by Paul Weigmann about work with Sasha Abanov. (Full disclosure: I've spoken to them both about this work several times in the last year). The general idea is to study the (nonlinear) hydrodynamics of electronic motion along the edge of drops of electron fluids (in particular quantum Hall edges). They find, after some long and detailed arguments that I don't completely follow, that the motion of the electrons is very similar to the motion of certain waves in deep water (and in particular to the so called Benjamin-Ono equation). One of the results of this work is that when a large wave is introduced it will eventually break up into individual pulses of quantized charge. If this is true, it overturns about 20 years of dogma about "edge" physics.

The idea is quite pretty, but I still am not sure if I believe it. For the experts in the audience, here is the argument that gives me concern.

Let us start by considering the following special case

(1) Take the special inter-electron interaction  V_1  for which the Laughlin wavefunction is exact

(2) Take the Harmonically confinement  U=\alpha r^2

The reason I choose (1) and (2) is because for this combination, the Laughlin wavefunction remains the exact ground state.

Assuming (1) and (2) it turns out that the edge state spectrum is trivial. In the conventional language of bosonic edge modes, we have
 H = \sum_{m \geq 1} \epsilon_m b^\dagger_m b_m + \mbox{higher order terms}
where in the usual Luttinger liquid story, one neglects the higher order terms. Keeping assumptions (1) and (2), it is an exact result that higher order terms all vanish and
 \epsilon_m = \tilde \alpha \, m
where \tilde \alpha  is the coefficient of the harmonic confinement  \alpha times some constants. This structure differs markedly from that of Weigmann and Abanov. Lets call this "Issue 1"

Further let us relax condition (1) and consider more general inter-particle interactions. The following remains an exact statement only assuming the quadratic confinement. Given an eigenstate of the system  \Psi_a  with energy E_a then you can generate another descendant eigenstate
|\Psi_{a,j} \rangle = (b^\dagger_1)^j |\Psi_a \rangle
where
 E_{a,j} = E_a + j \tilde \alpha
This is simply the statement thatb^\dagger_1  excites the center of mass degree of freedom of the disk.

As far as I can tell, the Weigmann Abanov theory does not have this structure built into it. Lets call this "Issue 2". However, I do not think this is necessarily cause to throw one's hands up in the air in disgust. It may, in fact, be easy to "mod-out" the center of mass degrees of freedom and then more or less avoid Issue 2. (Mind you, this step has not been done yet, but I can imagine it being done).

So suppose we remove issue 2, we are left with issue 1 to cause us to lose sleep. But in fact, this may not be so bad either. The special Hamiltonian we have chosen may be a particularly singular point. Even perturbing slightly away from this point will introduce nonlinearities in the spectrum. It is possible (again, not yet proven in my mind) that these nonlinearities, though small, will result in precisly the nonlinear wave equation that they have predicted --- with only a length scale that is nonuniversal. This length scale may become infinite precisely in the above limit, thus not causing any contradiction.

So to summarize, the story in my mind is quite interesting enough to be studied. Right now I see problems with it but if one is optimistic it is possible that these problems can be overcome. I hope to work with Weigmann and Abanov over the next few months to see if it is possible.
Thursday, January 22, 2009

## Rantus Latinus

Latin was once the language of scholars, and remains the language of certain religions, some of medicine, and various other people who are trying to be completely obscure.

This week, as mentioned in my previous blog, I was admitted into the society of fellows of Somerville College with a latin vow to uphold the laws of the college. This is the tradition of the college and was dutifully carried out by the Principal of the college -- roughly she reads a long latin passage stating my duties and I answer with just a few latin words that I will uphold them. Fortunately a translation was provided so that I knew what it was that I was promising. As for the performance of the principal, I was warned in advance that, although she is a very good principal of the college, latin is not her strong point and to try to keep a straight face as she struggles through her part. (In retrospect, I thought she did a very respectable job, slipping up less than Judge Roberts did in his administering of Obama’s oath of office).

At any rate, this confusing little ritual made me start wondering whether there might be some other latin around here that I would be wise to have translated in advance. Because as a kid I had an Oxford t-shirt (brought home to me by someone who visited there on vacation), I have long since known the latin motto of the school “Dominus illuminateo mea”. Although I probably could have guessed this in retrospect, I admit that I did have to look up the translation which is “The Lord is my light” (As an devout agnostic, I certainly prefer “Veritas” , but being that this was mainly a religious institution of learning for most of the last thousand years, I’ll give them a pass).

Next I went to find the translation of the motto of Somerville college which reads “Donec rursus impleat orbem”. Well, here, even after some head scratching, I really didn’t know what any of the words might mean. Fortunately I had been presented with a book history of Somerville college upon my arrival here, and I figured that it must have the translation in there somewhere. In fact, the only discussion of the motto is on page 47 where it states that “in 1892 ... Somervillians made their first attempt to interpret the baffling Somerville motto”. This left me scratching my head a bit more. But living in the modern age, I figured Google would come to my rescue. Well, alas, on the Somerville college web pages, it describes the college motto as “notoriously untranslatable”. Huh? It seems that this motto was cooked up either by someone who did not speak latin very well who simply wrote gibberish, or by someone who was deliberately trying to be obscure. Somerville was started in 1879 as a women’s college and was not accepted as part of the university until many years later. I have to wonder if all the (male) Latin scholars were snickering behind their back “Those women don’t even know that their college motto is meaningless!”.

The obscurity of this expression only made me more curious as to what the words might even sort-of mean. Fortunately, Google once again came to the rescue. On this page of hundreds of Latin phrases (in convenient alphabetical order), the Somerville motto “Donec rursus impleat orbem” is translated as “Until it again fill the world” –- whatever that means. Baffling indeed. The rest of the page of latin expressions is kind of interesting though. Right below the Somerville motto, the next expression on the list is “Donna nobis pacem” (Give us peace) certainly well known to all singers. The expression following that, though, is probably my favorite: "Draco dormiens nunquam titillandus" (Never tickle a sleeping dragon). This, of course, is the official motto of Hogwarts School of Witchcraft and Wizardry.

Added: Apparently from the beginning it was known that this latin expression is nonsense. However, it was already established on the Somerville family crest and motto, and therefore was adopted by the college even despite it not making any sense. Mary Somerville for whom the college is named, was quite a spectacular woman but unfortunately came from a family that did not speak latin very well.
Wednesday, January 21, 2009

## The Gown and other Matters.

It was once the tradition that scholars would wear their academic gowns at all times when they were at the university. I think here at Oxford the professors stopped teaching in robes sometime in the 1970s (probably because they were all wearing bell bottoms and love beads). Nonetheless, the academic gown is still used very heavily here. At many of the colleges, it is still required that the fellows of the college (faculty etc) wear their gowns at high table (I.e., at dinner – where the faculty sits at the “high” table and the lowly students sit in the rest of the Hall: think Hogwarts). Somerville, where I am a fellow, is somewhat more progressive, probably due to its history as a women’s college until the early 1990s. We only wear robes for a few rather formal occasions, such as important meetings, graduations, examinations, and the like. I’m just as happy not to have to wear a gown at high table, as I’m certain the sleeves would end up in my soup.

The first meeting of the governing body of Somerville (of which, as a fellow, I am a part), occurred this week, which was the first time I had to wear a gown. Although Somerville offered to provide one, a number of the other fellows recommended that I probably wanted to get my own. Taking a walk down the old cobblestone streets, I stopped into the robe-shop. The old man behind the counter muttered “Size 50.. Hmmm interesting”. He then showed me to a rack of black gowns that all looked pretty similar to me and he asked me to choose one. Then he said, curiously, “you know, the robe chooses the scholar”.

At this meeting of the governing body, I was officially Admitted to the Society of Fellows of Somerville – which entailed Dame Fiona Caldicott reading some Latin – and required me to respond in Latin. (No references to that scene in the movie top secret where the monks all speak pig latin). The rest of the meeting of the governing body was mostly a discussion of fiscal matters and the discovery that our college is certainly not infinitely wealthy, although some of the other colleges appear to be. (The endowments of the different colleges at Oxford differ by up to a factor of ten).

After the meeting there was champagne and tea for my official welcome, which was certainly a very nice touch. By this time, I’ve met many of the other fellows of the college, but this was an opportunity to meet the few remaining ones who have managed to avoid me so far. On the whole they seem to be extremely nice and they all seem to get along with each other too. I'm told this is not necessarily usual for an Oxford college. I like to think of us as Hufflepuffs (yes, I am a geek for twice quoting Harry Potter in this Blog entry). So far I've met three engineers, a biochemist, two chemists, two classicists, two psychologists, two biologists, two mathematicians, two historians, two other physicists, two italian scholars, and a german scholar. I think I can remember one or two of their names.
Tuesday, January 20, 2009

Today my country inaugurated its 44th president, Barak Obama.I really wanted to watch it live with other Americans, so I looked on the web to see where this might be happening. There was one gathering of expat democrats at an upscale club where you needed tickets months in advance. (Scratch that). Then there was another gathering at a local Hawaiian bar that wanted to celebrate the first Hawaiian president. But alas I fear the tropical drink. So I settled on a gathering at Rhodes House (check out the interactive map of the complex). First lesson of the day, Cecil Rhodes had a $^!&*-load of money. Quite a house it is (as compared to the rest of Oxford which is so modest. NOT). They had a huge projection TV set up in one of the large public rooms.Most of the people there were students, and many were American. It was a fun crowd to watch with.Everyone dutifully booed when Cheney came wheeling in looking oh so much like Mr. Potter from “It’s a wonderful life”. Everyone cheered when Michelle Obama showed up in her bright yellow dress. There was a rather strange moment when everyone laughed at the Queen of Soul singing “My Country 'tis of thee” which is sung to the tune of the British national anthem “God Save the Queen”. She is still wonderful, although she don’t quite sound like she used to.Some people looked like they were crying a bit when Obama took the oath of office. I loved his speech – but then again, I love everything he says. The Americans stood for the National Anthem at the end.Even though I am 3000 miles away, I still felt that I was part of a very important event in the history of my country. Monday, January 12, 2009 ## Welcome to England - Avoid the Germs I’m not sure if it is completely fair to blame Air India for this, but being that they charged me 243$ extra for four small suitcases, I think they probably could afford to install some better disinfectant system. I had the feeling that I was travelling on a giant petri dish, and one week later I discover I was right.

So I step off the air india flight to the UK last Monday morning at 6am and by 5 pm Thursday I have strep throat. I don’t think I’ve had strep since I was in high school, so I thought it was the flu at first. In particular, I failed to remember the other main symptom besides the high fever and the wicked sore throat: the rash. Woo boy. I look like I got massively sunburned 360 degrees around from knees to shoulders, like a lobster. And it itches like the bejesus. So this delightful little welcome wagon will give me my first experience with the British health care system. Unfortunately, to complicate my life it turns out that I do not yet have a national insurance number (there was some snafu and the paperwork was delayed). Nonetheless, I now need to convince someone to give me some damn penicillin. Although right now I think I would settle for some hydrocortisone to get rid of this nasty rash. I’ll keep you updated.

First update: Walked into the local health clinic with no identification whatsoever, explained my story and they happily gave me an appointment for later this afternoon.

Second update: The doctor apologized for being 10 minutes late at the end of the day and then spent over half an hour examining me. Not that I was unhappy with my doctor in NY but to get his full attention for half an hour would probably have required four visits. He concluded that it looked like a strep infection of some sort - but not the typical strep throat. More likely scarlet fever. Prescribed penicillin to kill the strep, and zantac zirtek and a large bottle of calamine for the rash. Doctor's visit was free. Drugs totaled something like 15 GBP. So far I'm thrilled with the british health care system.

Third update: After 36 hours on the drugs, the fever is certainly gone and even the persistent painful rash seems to be fading a bit. I can even stand up and sit down without wincing (Note to self: never get a sunburn on rear). Thank god for penicillin. Thank Alexander Fleming.
Thursday, January 8, 2009

## The second necessity upon arriving in the UK

In addition to food, the most important other basic human need is shelter. This is particularly important being that it has been quite cold out here recently -- dipping below zero in the last few days (zero Celsius that is. Well, the Brits think this is cold at any rate). I can't remember if I already blogged about the place I am renting. Oxford is a bit like NY or the bay area -- everyone wants to live there so real-estate is insanely expensive. The university understands this and has various systems in place to help faculty find appropriate accommodations. In my case, I am renting a place owned by the college for a very reduced rate. Unfortunately, the college owns only a few places and most of them are filled, so I only had the choice of one possible building which I then accepted.

The apartment (or house, or flat, I'm still not sure what to call it... terraced house (in American terms it is a 2FL 2BR 1BA attached row house with garden) is actually quite big by Oxford standards in terms of total floor space - but it is rather strangely set up so I'm not actually sure how I am going to make practical use of this space. The downstairs would be a terrific living/dining area if they removed the wall between the living and dining room. As it is, the living room and dining room are both much too small. Unfortunately, the wall is there and I have to figure out a way to live with it. To make up for the tiny living room, the bathroom is huge. You could play football in there (the American kind, not soccer. I don’t think there would be room for that).

So right now I am staying in this rather large house and I brought only four suitcases, so it is a bit sparse. Of course I shipped all my stuff from New Jersey, but in the meantime, I had to borrow a bed from the university until my stuff gets here next week. On the other hand, when all my stuff was all boxed up in NJ, it ended up being a whole lot of mostly junk (mostly books and clothing-that-was-only-barely-good-enough-to-keep). I was rather hoping that the transporting ship would sink and I could just collect the insurance and start over. Unfortunately, I was just told that the ship did make indeed it to the UK, and through customs and they will deliver it all next week. I didn't send a bed, so I'll have to go buy one this weekend.

The biggest disappointment of this apartment is that there is a washing machine but no dryer. This means either I will have to set up drying racks and lines (which is a pain, particularly since it tends to be humid here so nothing dries quickly) or take my stuff out to be laundered. After living without laundry machines for the last five years or so, i was looking forward to coming into the 20th century. Alas.

The location of my flat is really close to the college and the physics department, in a neighborhood known as Jericho, which looks really nice. There is a very fine pub right across the street. I could be a frequent guest (See above comment about gym).
Wednesday, January 7, 2009

## The first necessity upon arriving in the UK

You might think it is strange that my first blog entry from the UK is going to start with food, which the British are not particularly known for. However, eating is one of the necessities and I think it is generally a good idea to iron these out first.

I arrived in the UK two days ago and since then most of my time has been spent meeting people, running errands, and cutting through red tape. Of course I have learned many many things so far -- mostly things like who is in charge of getting me registered for national health insurance and other necessary but boring facts. However, in addition to these boring things (and a few interesting things about physics) a rather large number of the random things I have learned have to do with food.

(1) There is some automated web-based system that tells you everything you need to know about dining at the college. To have either lunch or dinner you click something and they know to expect you. The same web site apparently lists a bunch of other information and rules about dining. Unfortunately, I don't have a login yet, so I am breaking all the rules and everyone is too polite to correct me (to begin with I am showing up without having clicked on the website)

(2) Daytime feeding time at Somerville College Oxford is roughly 1 pm. Fellows (professors, readers, lectures) and other important personage sit at the high table in the dining hall. The table is filled from right to left as people arrive. But when the Principal of Somerville College, Dame Fiona, arrives, she sits at the middle of table in a larger chair reminiscent of royalty. At this point the rules change and you are supposed to sit with Dame Fiona and seat outwards from there.

(3) The food at the college, so far, is pretty good. I already feel I am at risk of being the oldest person ever to put on the freshman 15. Desserts appear to be particularly dangerous. Fortunately, I had my cholesterol checked recently and it seems to be very good so I can afford a bit of British cooking. Then again, cholesterol or no, I'd like to avoid getting any doughier than I already am (My brother would tell me to go to the gym and lift weights. Got to figure out where the gym is. Then I've got to start going.)

(4) Dinner is not served this week (the term has not started), so I've been fending for myself. Found a decent bagel with salmon and cream cheese for dinner... and tea… speaking of which…

(5) Tea and coffee for fellows of the college (faculty etc) are served in the "senior common room" after lunch. This reminds me a bit of the "staff porch" we had in summer camp years and years ago -- although it is decorated a bit more like you would expect of Oxford: bookshelves of ancient books. Big plush victorian couches, chairs, and rugs. Paintings of long-since dead faculty and donors. And the motto is posted in latin, so I have no idea what it says.

(6) Tea in the theoretical physics building is served at 11 am in the discussion room. A mug of tea is 30 pence and a hobnob cookie is 5 pence. Coffee is more expensive, but appears to be the good kind. I think there is also tea served in the neighboring physics building in the afternoon. And of course there is tea in the senior common room of the college again at 4pm. I suspect I could easily fill an entire day going from one tea to another, then to elevensies, then to lunch, then tea, then..., then... I'll have to try that sometime just to see if it is really possible.