Musings

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 …

First it was Google Scholar. Now it’s Google Print.

Search for “todd class”, and find hits like this.

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?

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

1. Create a directory, owned by www.
2. 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> 

3. Create a digest password for my colleague, using htdigest.
4. 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!

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:

1. \mathfrak{} is now implemented as a synonym of \mathfr{}.
2. \lbrace and \rbrace are synonyms of \{ and \} respectively.
3. \: and \; are synonyms for \medspace and \thickspace respectively (joining \, and \! which are synonyms for \smallspace and \negspace).
4. $$...$$ can now be used as a delimiter for display equations (synonymous with \[...\] ).
5. { 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.

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:

1. A flat background, with a linearly varying dilaton (varying along a timelike direction).
2. 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 AdS_d backgrounds, the observables are correlation functions of a conformal field theory on the $d-1$ dimensional conformal boundary. However, there are no nontrivial field theories for dimensions greater than 6. So, for AdS_d, $d\gt 7$, the observables are, in some sense, all “trivial.”¹

Those are the two paradigms that we know about for the observables of quantum gravity. Neither seems to lead to a satisfactory answer for supercritical strings. Perhaps there’s a third prescription for what the observables of quantum gravity are, which would yield a satisfactory answer in the case of supercritical strings.

But I’d like to hear what that is.

We had the great pleasure of having Lenny Susskind visiting last week. He gave a regular seminar on whether one might be able to see the imprint of Coleman-de Luccia tunnelling (from some false vacuum into the initial state of the inflaton) in the CMBR. I think the upshot was, “not too likely.” At best, it is yet another explanation for the dearth of power in low ($l=2,3$) multipoles seen by WMAP.

Thursday, he gave a brown bag talk on his paper about wormholes. It was a rather illuminating discussion, in which various flaws in his argument were revealed. The next day, he put out a rebuttal paper. Which was kinda amusing, though I liked Aaron Bergman’s more quantitative argument better.

The fruitbats at IDtheFuture seem to be on a Physics kick. So I guess I’m on a fruitbat kick (I think I need a new Category).

First it was J. Richards on Einstein. Today it’s W. Dembski on Laughlin. Bob Laughlin is a brilliant Condensed Matter theorist. But, when he talks about subjects outside of his area of expertise, he can sometimes say some very stupid things. Evolutionary Biology is very far from Laughlin’s area of expertise … and it shows.

That’s Laughlin’s excuse. What’s Dembski’s?

Update: Dembski Solves the Cosmological Constant Problem

I’ve spent many post discussing various aspects of the Cosmological Constant Problem (most recently these two). Evidently, I shouldn’t have wasted my time. Jumping off from an out-of-context quote from Arno Penzias explaining how the discovery of the CMBR leads inexorably to a hot Big Bang cosmology, through some typical Paul Davies quotes (probably accurate — who cares?), Dembski arrives at his own solution to the Cosmological Constant Problem.

It’s not the Anthropic Principle, or superhorizon fluctuations, or a gravitational Peccei-Quinn mechanism. It’s … Intelligent Design!

Intelligent design, by contrast, places no such requirement on any designing intelligence responsible for cosmological fine-tuning or biological complexity. It simply argues that certain finite material objects exhibit patterns that convincingly point to an intelligent cause.

And he’s convinced that everyone’s jumping on board:

[M]ainstream physics is now quite comfortable with design in cosmology. … Why should inferring design from the evidence of cosmology be scientifically respectable, but inferring design from the evidence of biology be scientifically disreputable, issuing in the charge of creationism?

I literally fell off my chair laughing. Lucky that’s solved and we can all go home now.

I have a suggestion for Dembski’s next humour piece, Use this quote from Steve Weinberg,

Life as we know it would be impossible if any one of several physical quantities had slightly different values.

to argue that Weinberg, too, is an enthusiast of Intelligent Design.

Once upon a time, not so many years ago, a contingent left-leaning Historians, Sociologists and Philosophers of Science were engaged in a vigorous critique of Science and its presumption of a privileged place in our epistemology.

Their not-so-subtle science-bashing¹ was ripe for parody and the “Science Wars” dragged on for a while in academic circles, reaching their height, perhaps, in a conference at the New York Academy of Science, from which the title of this post was borrowed.

Back then, conservatives could be found siding with Science against its “postmodernist,” “relativist,” “social constructionist” (but, one presumes, most importantly, leftist) critics.

Those days are long gone. Now we have the Heritage Foundation (for my non-American readers, perhaps the most prominent conservative think tank in Washington, with vast intellectual influence on our Republican Overlords) sponsoring symposia on “Intelligent Design”. There’s a broad push to bowdlerize the teaching of evolution in schools and IMAX Theaters across the South no longer feel they can show movies mentioning Evolution, Big Bang Cosmology or modern Geology. (I could post a longer list of depressing links, but I think you get the idea.)

Of course, the trouble with picking away at bits of Science that you don’t like is that it’s a bit like a sweater: pull on a thread, and soon the whole thing starts to unravel. If Evolution is “just a theory,” and Big Bang Cosmology is “just a theory,” and …, then pretty soon, everything else needs to be called into question, too.

Thus we find the Vice-President of the Discovery Institute telling us that Einsteinian Relativity must be wrong, too.

Sean Carrol takes time out for a little smackdown. But I have a meta question: where did American Conservativism go off the intellectual rails? And is there any hope for getting it back on?

I erred in not clearly distinguishing Jim Holt’s summary of Einstein’s argument, from Einstein’s argument itself.

Sounds pretty diagnostic of the whole crowd over at IDthe Future, dunnit? He goes on to reasure us skittish physicists that

I am not a skeptic of special or general relativity.

Whew! That’s a relief. Any other branches of Physics that I should be worried about?

I really have to marvel at the intellectual audacity of Science’s new right wing assailants: being a *-skeptic (Global Warming-skeptic, Evolution-skeptic, Big Bang Cosmology-skeptic, …) doesn’t require any actual knowledge of “*”. But it does (particularly if Horowitz and Baxley and their allies get their way) guarantee you a place at the intellectual table. Can I sign up as an official ID-skeptic?

Time for another release of itex2MML, the commandline utility that converts a dialect of TeX to MathML. It’s the brains behind plugins for various blogging platforms (MovableType, WordPress, ecto, b2Evolution, …) which allow you to enter TeX formulæ and have them automatically rendered to MathML.

itex2MML acts as a stream filter, converting TeX equations delimited by $...$ (for inline equations) or \[...\] (for display equations) to MathML. This version adds support for a boatload more LaTeX/AMSLaTeX symbols. I was motivated by a recent post in which I needed \gtrsim ( ≳ ). Please let me know if you encounter any bugs, misfeatures or, for that matter, features that ought to be there but aren’t.

As always, my distribution comes with a precompiled binary for MacOSX, the plugin for MovableType, and the source code to compile itex2MML for other platforms (just type “make”).