February 28, 2004

On the internet, nobody knows you’re a dog.

In one way, that’s great. If you want to be anonymous, there’s plenty of scope for it on the internet. Even when you post comments on this blog and I ask you for an email address and/or a URL of your website, nothing prevents you from entering totally bogus ones.

On the other hand, say you’ve already established something of an online identity, perhaps through your own web site, or as a frequent commenter at this or some other blog(s). What prevents someone else from coming along and posting a comment here, leaving your name and your website’s URL to identify himself? Put another way, how can readers determine the authenticity of comments left here?

Let me pause to say what I mean by ‘authenticity.’ Most readers of this blog have never met you, personally. They know you through your comments, and perhaps through your own web site. What they would like to know is that the person who authored the comment in question is the same person who authored those other comments and who runs that web site1.

Well, now there’s a way to reassure them. If you have a PGP public key (if you don’t, create one for yourself), put a link to it in the <head> section of your web page:

<link rel="pgpkey" type="application/pgp-keys" href="http://yoursite.com/path/to/yourkey.asc" />

Then you can

1. Compose and preview your comment as before.
2. Edit it, as needed, and preview again.
3. When you’re satisfied with the final form of the comment, use GPGDropThing (for MacOSX) or GPGShell (for Windows) or your favourite PGP tool to clear-sign the text in the comment-entry box. Paste the clear-signed comment into the comment-entry box, replacing the unsigned version.
4. Click PREVIEW once again, and then click on POST.

To outward appearances, your comment will look no different than before. The only difference will be a clickable link to “verify” the comment.

If you, or another reader, clicks on it, your key is fetched from the URL specified in the link on your web site, and is used to verify that you — and you alone — composed the comment. The key is cached locally, so subsequent verifications of the signature will be nearly instantaneous. The raw, clear-signed comment is available, so paranoid readers can check the signature themselves — provided they have your public key.

I’d been thinking about implementing this for a while, and even went through the hideously-complicated process of installing Crypt::OpenPGP on MacOSX. Fortunately, Krishnan Srijith did the rest of the heavy lifting and wrote a MovableType plugin. I added a few of my own tweaks and … there we are.

Update (3/3/2004): Automatic fetching of PGP keys, as described above is enabled now. In my and Srijith’s limited testing, it seems to work well. But please let me know if you encounter problems.

Update (3/5/2004): I’ve posted some more thoughts on PGP-signed comments.

1 This is a little different from the exigencies of verifying the identity of the author of an email, which is the traditional use of PGP signatures. There, the PGP “Web-of-Trust” model works fairly well. Here, it doesn’t necessarily work so well, a point elaborated on in greater detail by Phil Ringnalda.

Posted by distler at 2:40 PM | Permalink | Followups (29)

February 27, 2004

itex2MML 0.7

Yet another release of itex2MML. Many thanks to Bob McElrath for a boatload of improvements.

• ”|” and “\mid” now both use the same glyph, U+2223 (∣) with hopefully better (i.e., more LaTeX-like) horizontal spacing.
• \quad is now a 1em horizontal space, (again, as in LaTeX).
• Added \&, \%, \$and \qquad (a 2em horizontal space). • Added a whole mess of single-word identifiers (\sin, \log, \ker, etc.) from LaTeX. • Some memory bugs fixed. As always, a MacOSX binary is included in my source distribution. A Windows binary and a Linux binary are also available. Posted by distler at 12:42 AM | Permalink | Followups (4) February 25, 2004 Ketchup isn’t a Vegetable It’s a Durable Good. For the most part, I’ve avoided posting about the sorry excuse for “Economic Policy” that is this Administration’s. Brad DeLong does such an excellent of covering the “Clown Show,” that there seems little that I could add. But their desperate attempt to disguise the fact the GWB is the first president since Herbert Hoover to preside over a net loss of jobs1 during his term has engendered instances of true humour. It takes real wit to contemplate reclassifying food-service work as manufacturing jobs2. Fortunately, Representative John Dingel was right there to congratulate Gregory Mankiw on his cleverness. 1 I discount the logical possibility — which not even the Administration actually believes — that their latest forecast might actually come true, and non-farm payroll employment for 2004 might be ever-so slightly higher than the 132.5 million when Bush took office. 2“See! We’re not losing manufacturing jobs, we’re gaining …” Posted by distler at 1:23 AM | Permalink | Followups (5) February 24, 2004 Book List Ed Felten asks his readers for a “top-five” list of books in Science and Technology — books one might might hope every university student would read. Here’s my stab at one. Posted by distler at 9:59 AM | Permalink | Followups (3) February 21, 2004 Don’t GET it! Quite by accident, I discovered that one can post comments to MovableType blogs using HTTP GET requests (instead of the normal POST requests). The implications of this are, to say the least, a little worrisome. Trackback Pings can also be sent using GET, even though that behaviour was supposed to have been removed from MovableType over a year ago. Note: in older versions of the TrackBack specification, pings are sent using HTTP GET requests. This behavior is deprecrated; support for GET requests will be removed from the Movable Type implementation in January of 2003. Here’s a patch to fix both problems. As usual, if you’re using MT-Blacklist, you need to apply the patches to MTBlPost.pm and MTBlPing.pm instead. Posted by distler at 1:42 AM | Permalink | Post a Comment February 17, 2004 Free Texts [Via Bitácora de matemáticas] an amazing collection of Mathematics texts available free over the Web. To that, maybe I should add a couple of Warren Siegel’s books: Fields and the long out-of-print, but now free Superspace (Gates, Grisaru, Roček and Siegel). Any others? Posted by distler at 12:14 PM | Permalink | Followups (5) February 16, 2004 Headrick We had Matt Headrick visting last week. He gave a really nice talk about his work on on the Adams, Polchinski & Silverstein conjecture for the fate of the $\mathbb{C}/\mathbb{Z}_n$ orbifold. APS noted that this nonsupersymmetric orbifold has a closed string tachyon in the twisted sector, and conjectured that it would decay, via condensation of this tachyon, into a supersymmetric ground state (usually, the unorbifolded $\mathbb{C}$). They were able to find evidence for this conjecture by studying a D-brane probe in this background, and noting that the closed-string perturbation would tend to drive the nonsupersymmetric quiver gauge theory of the D-brane in a $\mathbb{C}/\mathbb{Z}_n$ background to flow, via the renormalization group, towards a supersymmetric one. Matt (and also Gregory and Harvey) studied the late-time behaviour, where the probe analysis is untrustworthy, but where supergravity should be a good approximation. The 2+1 dimensional dilaton gravity problem turns out to be soluble, leading to a beautiful picture of the final state of the decay of this orbifold. Is there any hope to connect the early- and late time behaviours? It’s not clear that there’s a sensible stringy formalism for doing so. But there’s an old paper by Vafa, which proposes a worldsheet renormalization group flow which interpolates between the early and late-time behaviours: consider a gauged linear $\sigma$-model, with two charged fields, with charges $(n,-1)$. The D-term constraint, $n|\phi_1|^2-|\phi_2|^2=r(\mu)$ means that, for $r\gg 0$, the theory corresponds to the $\mathbb{C}/\mathbb{Z}_n$ orbifold, whereas for $r\ll 0$, it corresponds to $\mathbb{C}$. And $r(\mu)$ decreases under renormalization group flow… Posted by distler at 12:05 AM | Permalink | Post a Comment February 15, 2004 Cursing One’s Tools I’m trying to write a talk in Keynote. As I noted when the program first came out, it is ridiculously easy to do all sorts of whizbang animated effects. But the stuff that I actually care about, like mathematical equations, is an incredible annoyance. TexShop has a nifty feature. You can select a rectangular region from the PDF preview, and copy and paste it into Keynote. The resulting PDF object in the Keynote Presentation can be dragged around and resized. But you can’t, say, reflow the text in it. It’s not too hard to keep a TeX file, containing the equations, in parallel with the Keynote Presentation. It’s a little kludgy, but works OK for display equations. But it’s useless for inline equations. The only thing I’ve been able to do that works worth a damn is to import whole paragraphs containing inline equations as PDF objects. That’s very kludgy: • You can’t reflow the text, so you have to typeset the TeX paragraph at the width you need. • The fonts don’t match the surrounding text. (The Computer Modern fonts aren’t ATSUI-compatible, so I’m using Baskerville for the Keynote Presentation. If I only use Computer Modern for display equations, they’re close enough that it looks OK, but a paragraph of inline text sticks out like a sore thumb.) • Not being able to edit much the text of the talk in-place gets very frustrating. Surely, on a system whose native display format is PDF, and where there already exist Text Services to convert snippets of TeX code into PDF, one could do better. How about an equation object? Double-click on it, and you open up a text palette, where you can edit the underlying TeX code. Close the palette, and the equation gets rendered into PDF — in-place, at the right point-size, with the surrounding text reflowed as-necessary. Would that be too much to ask? I’d even be willing to forgo the spinning pie-charts. Posted by distler at 10:31 PM | Permalink | Followups (3) February 10, 2004 MathPlayer 2.0 The latest beta of Design Science’s MathPlayer plugin for IE/Win is out. This free plugin brings MathML support to Internet Explorer. Unlike the previous version, no custom-coding is necessary; it works with ordinary Standards-based XHTML+MathML pages. Thanks to the great work of Paul Topping, Robert Miner, and the other folks at Design Science, MathPlayer 2.0beta 5 and later work the MathML-enabled blogs hosted here. So, if you’re an IE/Win user, and a regular reader of Musings or of the String Coffee Table, send them an email and say you’d like to get on the beta-testing list for MathPlayer 2.0. They’re eager for beta-testers, as this is hoped to be the last beta release before MathPlayer 2.0 goes final. For the technically-inclined, my changes to support MathPlayer 2.0 consisted entirely of the following tweak (in red) to my mod_rewrite rules: RewriteRule ^$ index.shtml
RewriteCond  %{HTTP_USER_AGENT} Gecko|W3C.*Validator|MSIE.*MathPlayer
RewriteRule \.html$|\.shtml$   - [T=application/xhtml+xml]
RewriteCond  %{HTTP_USER_AGENT} Chimera|Camino|KHTML
RewriteRule \.html$|\.shtml$   - [T=text/html]
RewriteCond  %{HTTP_USER_AGENT} Camino.*MathML-Enabled
RewriteRule \.html$|\.shtml$   - [T=application/xhtml+xml]

and a similar one for my cgi-bin directory.

Posted by distler at 3:59 PM | Permalink | Followups (8)

February 9, 2004

Not So Hot

This PhysicsWeb article reports on the buzz being generated by a recent paper on astro-ph. According to the authors, the Sunyaev-Zeldovich effect (inverse Compton scattering of CMB photons off energetic electrons in the inter-galactic medium of a cluster of galaxies) may be important at angular scales as large as 1° (due to supercluster ‘haloes’ of hot gas) — much larger than previously thought.

Their method was to cross-correlated galactic surveys with decrements in the CMB temperature in the WMAP data.

We have found evidence for anti-correlation between WMAP data and the positions on the sky of galaxy clusters derived from the ACO, APM and 2MASS surveys. We interpret the signal as caused by the SZ effect, inverse Compton scattering of the CMB photons by hot gas in groups and clusters of galaxies. The signal may extend to ≈ 1deg scales around ACO clusters, implying they have extended gaseous haloes which may also constitute a diffuse gas component in superclusters.

The galactic surveys they analyze are not “deep” enough to significantly affect the first acoustic peak in the CMB power spectrum (though they may affect higher peaks). But, if the effect persists for more distant clusters of galaxies, it could potentially affect even the first acoustic peak in the CMB power spectrum, and hence the fit of WMAP data to the cosmological parameters.

We have briefly investigated how SZ contamination might affect the location and shape of the acoustic peaks in the WMAP temperature and find that although there is little effect from the temperature decrements found so far, if they persist out to z≈0.5 with the amplitude and extent seen at z<0.2, then even the first acoustic peak at the 1 deg scale could be significantly affected. Further crosscorrelation analysis of deeper catalogues of groups and clusters will be needed to judge the seriousness of this potential SZ ‘contamination’.

February 7, 2004

Three Card Monte

I’ve been pondering why I find the discussion of Thomas Thiemann’s recent paper over at the String Coffee Table so disturbing.

Finally, Thiemann’s latest comment made it all fall into place for me (emphasis added):

In any case, whether or not you should have an exact or projective rep. of a symmetry depends on the physical system under study and hence must be decided ultimately by experiment. In case of the string everything is allowed until we have quantum gravity experiments.

For the love of God, no! In the absence of direct experimental tests, we have to be all the more careful to ensure that what we do is mathematically self-consistent. Thiemann’s “anything goes” attitude is exactly the sort of thing that string theory sceptics warned us against.

In case you haven’t been following, here’s the executive summary:

Thiemann: I can quantize the bosonic string with no Virasoro central extension (and hence no restriction on the critical dimension) and no tachyon.

Us: No you can’t. The Virasoro central extension follows directly from the canonical commutation relation and the necessity of regularizing the Virasoro generators.

Thiemann: Your proof doesn’t apply to my quantization because it makes unwarranted assumptions about the Hilbert space, and the Hermiticity properties of the operators.

Us: No such assumptions were made. The proof relies only on the canonical commutation relations and the necessity of regularizing the Virasoro generators.

Thiemann: OK, so maybe the algebra of constraints is centrally-extended. But I wish to work with the exponentiated constraints (with the group, rather than the Lie algebra). I can just copy those over verbatim from the classical theory.

Us: The group elements are even more subtle to regularize, You are only shifting the problem to where we, hopefully, won’t be able to see it. Besides, if you take group elements infinitesimally close to the identity, you will just reproduce the Lie algebra computation. Moreover, if you could blindly copy over the classical symmetries to the quantum theory, you’d reach absurd conclusions.

Thiemann: Umh … Look, a plane!

Posted by distler at 10:05 PM | Permalink | Followups (14)

February 2, 2004

MathML News

In the Sisyphean task of implementing the conversion of LaTeX symbols to MathML Named Entities, here’s another update to the itex2MML executable used by my plugin. Urs Schreiber discovered that variant Greek letters weren’t supported. Now they are…

\varepsilon
&varepsilon; ($\varepsilon$)
\varkappa
&varkappa; ($\varkappa$)
\varphi
&varphi; ($\varphi$)
\varpi
&varpi; ($\varpi$)
\varrho
&varrho; ($\varrho$)
\varsigma
&varsigma; ($\varsigma$)
\vartheta
&vartheta; ($\vartheta$)

As always, my distribution contains a MacOSX binary, as well as the source code to compile the new itex2MML. But, in a new wrinkle, Abiola Lapite and James Graham have made precompiled binaries for Windows and Linux.

In other MathML news, Design Science has MathPlayer 2.0 in beta. The exciting news is that this MathML plugin for IE/Win will finally support XHTML+MathML documents.

Modulo some finessing of MIME-type issues, we, here at Musings, may even be able to support Internet Explorer someday.

Update (2/3/2004): Whoops! Urs found a missing binary operator, \circ. Turns out there were a whole bunch of standard ones missing:

\circ
&SmallCircle; ($\circ$)
\bigcirc
&bigcirc; ($\bigcirc$)
\wr
&wr; ($\wr$)
\odot
&odot; ($\odot$)
\uplus
&uplus; ($\uplus$)
\diamond
&diamond; ($\diamond$)
\sqcup
&sqcup; ($\sqcup$)
\sqcap
&sqcap; ($\sqcap$)
\rhd
&RightTriangle; ($\rhd$)
\lhd
&LeftTriangle; ($\lhd$)
\unrhd
&RightTriangleEqual; ($\unrhd$)
\unlhd
&LeftTriangleEqual; ($\unlhd$)

A new copy of my distribution is up, along with new Windows and Linux binaries.

Update (2/7/2004): Some portability fixes from Bob McElrath. itex2MML should now compile correctly on Alpha and, presumably, other 64-bit processors. No new functionality with this update, so, if the previous one was working for you, there’s no need to download it again. But, if you were having trouble compiling the previous version, you might want to give the latest one a try. Ah, the beauty of Open Source …

Posted by distler at 10:38 PM | Permalink | Followups (6)

February 1, 2004

30 Seconds

Apparently, CBS, in its corporate wisdom, won’t air their ad during the Superbowl.

But that’s no reason for me not to, is it?

Posted by distler at 1:05 AM | Permalink | Followups (5)