Following up on an earlier entry on a similar topic, I note Qcircuit, a LaTeX package by Steve Flammia and Brian Eastin that makes drawing quantum circuits extremely easy. Should be pretty useful!

Doron Zeilberger gives the best reasons I’ve seen for eschewing Powerpoint in favour of whiteboard talks. His reasons are pretty pertinent for detailed technical seminars where you want to understand ideas in detail. I still think Powerpoint has a place when you’re just trying to communicate the gist of your results, as is often the case in conference talks, and a higher baud rate is appropriate.

Lots of people (including yours truly) love to brag about their Erdos numbers. My colleague Steve Flammia wrote to the people at the
Erdos number project asking them if they had computed the Erdos numbers for infamous people. Steve asked specifically about Ahmed Chalabi, who has a PhD in mathematics.

Turns out Chalabi has an Erdos number of at most six!

Which means my Chalabi number is at most eight…

The Princeton Math Department’s Graduate Students’ Guide to Generals is pretty interesting. They don’t exactly give them an easy time, and the list of examiners is pretty scary (Conway, Wiles and Fefferman in one case!)

Leiden, 50 kilometers soutwhest of Amsterdam, is like a combination of UC Santa Barbara (bikes everywhere), Caltech (the piece of the Ariane 5 rocket engine being exhibited as a sculpture is a particularly nice geek touch), and some of the nicest towns I’ve visited in Europe.

Everything is beautiful and cared for in the nicest possible way – not that sterile way you find in some places, but rather, the way that tells you a place is well-used and much loved; it is neat because people care.

Between talk preparations and sleeping, I haven’t yet explored as much as I’d like, but it sure looks a great place for a workshop.

Posting will continue to be light-to-non-existent over the next week and a half, as I finish up several big projects. In particular, I’m heading to Amsterdam on Saturday, and expect to be largely out of touch for a week.

What are the different possible phases of matter?

One of the big advances of twentieth century physics was the development of a very general set of ideas – the renormalization group – that let you analyse and understand the properties of different phases of matter, and the phase transitions between them. This development was done by a whole bunch of people, including Landau, Ginzburg, Kadanoff, Michael Fisher, Wilson, and others.

In a recent issue of Science there’s an article by Senthil, Balents, Sachdev, Vishwanath and Matthew Fisher claiming to have found a significant class of phase transitions that can’t be understood within this framework. (Here’s the long (and possibly more comprehensible) version of the paper at a publicly accessible site.)

This would seem to be extremely significant if true, which is why I’m reading the paper. I’m reminded, as I read, however, of the many basic items of background material I don’t understand all that well.

One thing that always bugs me when I read about phase transitions is the question “What is an order parameter?” Landau introduced this concept as the unifying idea behind his theory of phase transitions. Examples include the magnetisation of a ferromagnet, and the phase in a superconductor.

So far as I can tell, the order parameter is usually divined, as opposed to defined. How are we supposed to deduce the order parameter? Is there a freedom in our choice of order parameter? What makes one choice of order parameter a good one? I’d love to fully understand the answers to any of these questions.

In the comments to the previous post, Pyracantha points to a post at Electron Blue. It’s all interesting, but I thought this deserved wider propagation:

In gratitude for his Web curriculum efforts, I dared to write Dr. ‘t Hooft an e-mail explaining what I was doing and inviting him to look at my own Website. To my astonishment, he promptly sent me a reply! He commented positively on my site, and reminded me that his curriculum section was only at the beginning stages. Yes, this busy elite scientist took the time to send a reply back to a beginning student. This is a class act. I would call it nobelprize oblige.

This reminded me of a nice story I heard years ago: Stanford Nobelist Doug Osheroff excused himself from the party Stanford threw in his honour when his Nobel was announced, saying that he had to go and teach his class of first year engineers. That’s class.