Posts with this logo use 
Low-functioning pinhead...
April 29, 2005
Too Polite
Surely, subscribers to the comment feeds here at Musings or at the String Coffee Table must have noticed that the <PubDate>s of the comments in the feed coincided with the date the corresponding entry was posted, rather than with the date the comment was posted.
Turns out that it was a subtle incompatibility between SimpleComments and (recent versions of) MovableType. Easily fixed, once I figured out what was going on.
In other news, as reported at Talking Points Memo, Preposterous Universe and elsewhere, Edward Witten and Chiara Nappi joined the Frist Filibuster at Princeton University’s Frist Campus Center.
It appears that they both read from Griffiths, Introduction to Elementary Particles. My, how that must have thrilled and inspired the crowd. Alas, I missed their appearance on the live video feed. Perhaps some other Princeton Faculty will take a turn at the bullhorn. I’d be happy to suggest some suitably uplifting readings …
Update (4/29/2005):
Looks like the Frist Filibuster is turning into a veritable Who’s Who of Theoretical Physics. Frank Wilczek is scheduled to pick up the bullhorn at 8:30 pm, tonight. [Hat tip: Aaron Bergman]April 28, 2005
Google Blows Me Away (Again)
First it was Google Scholar. Now it’s Google Print.
Search for “todd class”, and find hits like this.
April 24, 2005
Weird
Last night, I had a dream.
The plot doesn’t matter much. But, at some point, one of the characters drew a knife, grabbed my arm, and thrust the knife into my side. I awoke with a start, and then lay, half-awake, in bed, replaying the scene over and over in my mind. Eventually, I remembered my bagua and, puzzle solved, drifted back to sleep.
It’s been seven years since I quit doing Kung Fu. Could this be a sign?
April 18, 2005
WebDAV
I’ve recently started using WebDAV to share files with a colleague at another University, for a joint project. Not a big deal, really. There are lots of ways to share files, including emailing them back and forth.
But the integration of WebDAV support in the MacOSX Finder is particularly nice. With a couple of mouseclicks, he can mount the shared DAV directory on his Desktop, double-click on files to open them, drag&drop files to/from his own hard drive. The Finder takes care to warn him if he attempts to overwrite a newer version of a file in the DAV directory. And the WebDAV protocol takes care of file-locking etc.
To set up a shared DAV directory, I needed to
- Create a directory, owned by
www. - Configure the webserver to use that directory as a DAV share
<Directory /Users/distler/Sites/[sS][oO][mM][eE][dD][iI][rR]> DAV On AuthType Digest AuthDigestFile /usr/local/apache2/var/davusers AuthDigestGroupFile /usr/local/apache2/var/davgroups AuthDigestDomain /~distler/somedir/ AuthName "dav" AllowOverride None Options FollowSymLinks Indexes require group youcantoo </Directory> - Create a digest password for my colleague, using
htdigest. - Add him to the appropriate group in
/usr/local/apache2/var/davgroups.
Connecting to the server is as simple as hitting ⌘ -K in the Finder, typing in the URL (the Finder remembers recently-accessed URLs), and entering a password (which can be stored in the Keychain).
Sweet!
April 17, 2005
itex2MML 0.13
Thanks to feedback from users, another release of itex2MML, the commandline filter for turning a dialect of TeX into MathML.
This release brings the following new features:
\mathfrak{}is now implemented as a synonym of\mathfr{}.\lbraceand\rbraceare synonyms of\{and\}respectively.\:and\;are synonyms for\medspaceand\thickspacerespectively (joining\,and\!which are synonyms for\smallspaceand\negspace).$$...$$can now be used as a delimiter for display equations (synonymous with\[...\]).{ A \over B }is synonymous with\frac{ A }{ B }.
Thanks to Urs Schreiber for suggesting 1,2,3 and to W.K. Park for providing a patch to implement 4,5.
As usual, my distribution come bundled with the MovableType plugin, an itex2MML binary for MacOSX and the source code to compile the binary on other platforms.
April 12, 2005
Supercritical
Luboš, on his blog, seems to have gotten into a bit of an argument with Eva Silverstein about the status of “supercritical strings.”
I hesitate to wade into the middle. But, while it’s clearly true that these supercritical strings have some nice properties, it’s also obscure whether one can really make them into sensible interacting theories.
Two types of backgrounds have been proposed:
- A flat background, with a linearly varying dilaton (varying along a timelike direction).
- An AdS background.
In flat space, on general grounds, the observables should be an S-matrix.
- In critical string theory in flat space, the dilaton is a constant, and an S-matrix is defined (for sufficiently small dilaton VEV) for the scattering of perturbative string states into perturbative string states.
- In 1+1 dimensional noncritical string theory, there is also a linear dilaton background (varying in a spacelike direction). And there’s a “Tachyon wall,” preventing strings from penetrating the region of strong coupling. So one has an S-matrix, of sorts, for string coming in from the weakly-coupled region, bouncing off the wall, and returning to the weakly-coupled region.
However, for supercritical strings, the theory is strongly-coupled either in the far future or in the far past. It’s not clear how one defines an S-matrix. It certainly isn’t for perturbative string states.
In AdSd backgrounds, the observables are correlation functions of a conformal field theory on the dimensional conformal boundary. However, there are n