Wednesday, November 16, 2005

Just noticed this:

China reports first three human bird flu cases. I'm not saying this to alarm or because I'm terribly worried at the moment but because I think we've known about this for several days now. It's interesting to see the flow of news from here. I'm not worried about saying this because nobody would have minded had I mentioned it last week. It wasn't hushed here by any means.

Anyway, that's not why I'm writing this. I wanted to comment on the strange reaction to the sudden weather change here. In England as the temperatures plummet most of us are content to sit inside wrapped up warm with a nice cup of tea and some toasted crumpets, feet in front of the fire etc. At the very most we might think it good for the soul to go for a brisk stroll on a frosty day but this is because we know that back home there is the tea, crumpets, fire, tv...etc waiting for us and really it's so that we can appreciate the niceties even more that we do these things. It appears that here, things are different. As the temperature dropped below zero tonight and the fog descends, the Chinese have come out in force. On the road outside my window there is currently a tug-of-war underway. Not in a metaphorical sense. Fifty students and a long rope chanting rythmically and screaming at intervals. People are setting up rollerblade slallom courses and generally everyone seems happy to be outdoors warming themselves up.

I was feeling rather proud of myself, before I saw all these selfless activities, that I've just played pingpong for the first time in years. Frankly the Chinese idea of pingpong just isn't cricket. My tabletennis sabbatical has lasted ten years and they gave me not an inch. I've been smashed at, spun at and generally dizzied for the last hour and a half. It would be a lie to say I gave them a run for their money, perhaps a nice-sit-down-and-a-cup-of-tea for their money would be more apt. Anyway, they seemed relatively amused that the funny English chap knew which end of the bat to hold and I shall return next week at the same time for more punishment.

The last couple of days have been frustrating from a beaurocratic point of view. They didn't mention to me when I arrived that to claim for my travel expenses I would need to retain my boarding pass. This is so that I can claim that I really came here!I have exactly the same information on my baggage tag and my passport that they would need and I'm surprised that I am not sufficient proof that I am here. I think Descartes would have something to say about this. Anyway, after faxes from England were sent, seals of honour stamped and various hood-winks to higher authorities, they agreed that I was really here and paid me half the airfare. They can't pay the return part yet because I haven't used it! Anyway, all sorted eventually but I guess this is the sort of thing I will face regularly. Some people are telling me a bank account is being sorted for me, some people tell me otherwise. I've no idea and I'm too tired to find out right now.

A bit of technical physics now so look away those who may be offended or bored by the following.

I've finally got hold of a copy of Conformal Field Theory by Di Francesco et al. It's a superb book that looks in detail at two-dimensional CFTs with everything from the original formulation of minimal models through many examples from statistical mechanics up to WZW models. This is something I should know a lot more about as it is the building block of string theory. As a one-dimensional piece of string travels through space-time, its path maps out a two-dimensional surface called the world sheet. String theory is formulated in terms of a field theory (I'll explain this some other time) on the world sheet. As I mentioned before, symmetries are part of the tool-kit of the theoretical physicist. They allow complex problems to be simplified greatly and the properties of the system can often be understood from their symmetries alone. It turns out that the symmetries of the theory living on the string worldsheet are vast. In fact the symmetry 'algebra' is said to be infinite-dimensional (for those wanting to know, there are an infinite number of conserved charges) and is known as a two-dimensional conformal field theory. Anyway, when you're trying to understand the fundamentals of string theory, conformal field theory is the cornerstone and is something that I would like to understand in more detail. Because I use a certain limit of string theory in my work, I have never needed to know a lot about these two-dimensional models but it seems that now is a reasonable time to try and learn.

One of the important symmetries of a CFT is scaling invariance. Scaling invariance pops up in many physical systems. There are certain conditions of pressure and temperature under which water will be in a liquid state and gas state simultaneously. This is known as the critical point and at this point the system is said to be scale invariant. This means that you can zoom in and out of the liquid with a microscope and it will appear to look the same whatever scale you're looking at it on. When zoomed right out you will see a liquid full of bubbles of gas. If you were to look inside one of those bubbles of gas you would find many tiny drops of liquid. If you were to look inside one of the drops, you would find bubbles which looked very much like those you saw the first time round, each containing drops of liquid, containing bubbles of gas and on and on and...well not forever because there is a scale in the system given by the size of the water molecules. As you neared this length scale, the system would stop looking the same and indeed as you zoom out, you'll get to a scale where the size of the vessel is important. In between these scales however the system is scale invariant. You find this phenomenon in many systems of interacting objects under just the right conditions.

Sorry about just seemed necessary to speak some physics for once.


Anonymous said...

Do you bruise as easily when hit by a pingpong ball as you do when hit by a slowly-moving, hit-by-a-girl squashball??!!! kate x

Jonathan Shock said...

I managed to avoid it this time though I'm sure I won't be given such small mercies next week. Will tell you then.