Ars Mathematica

In a blow to the physics weblog community, Christine Dantas has closed her weblog, and deleted all of the posts but one. She outlines her reasons on Physics Forum. She had gotten embroiled in the fight over string theory (even in the Brazilian media), and as she put it:

You see, I do not have the right temperament for “living in the blogosphere”…

and

I am a quiet person, and wish to go back to my quiet life, to my quiet readings and studies.

It’s a fairly tragic development: Christine had been teaching herself various alternate approaches to quantum gravity, and would summarize her readings. It was evolving into a handy guide to the literature. She was also unfailingly polite, an obvious rarity on the internet.

Via the comments at Not Even Wrong.

Bee of Backreaction has an excellent summary of the evidence for the existence of dark matter.

Backreaction has a long post on applications of the AdS/CFT correspondence in heavy ion physics. The topic is interesting because it is a potential experimental prediction derived from string theory. Interestingly, it doesn’t involve string theory as a theory of everything; instead it uses string theory ideas to make calculations about quark-gluon plasma.

Penny Smith has posted a preprint to arXiv, Immortal Smooth Solution of the Three Space Dimensional Navier-Stokes System that, if correct, would solve one of the Clay Institute’s Millenium Problems. Christina Sormani has created detailed summary of Smith’s work on PDEs and Navier-Stokes.

The Navier-Stokes equation is a set of equations that describe fluid flow in Newtonian mechanics. The equations are notoriously difficult to analyze. The existence of smooth solutions for all time (the meaning of “immortal” in the paper title) has long been an open question. One now perhaps closed.

Via Peter Woit.

Update. The paper has been withdrawn. (Via John Baez in the comments.)

I’d like to point out that the 2006 Nobel Prize in Physics was awarded for this diagram:

No word on whether the original diagram included the same caption. More information available from Backreaction. Graphic via XKCD.

I’m back from vacation. With any luck, I’ll even think of something to say. Until that happens, I wanted to link to Peter Woit’s post, Open Access Publishing, which links to this CERN task force report on the subject. I haven’t read the report, but Peter’s description makes it sound pathetically timid. As he characterizes it:

The CERN task force doesn’t seem to me to be providing a viable long-term plan for moving to the kind of open access model they are supporting. It doesn’t address the fundamental problem of keeping a system where physicists hand over the scientific literature to Elsevier, then have to figure out how to buy it back.

The enterprising citizen-journalists affiliated with the Huffington Post have discovered the truth about me: I am a Pluto-hating fiend. First we remove it from the list of planets, next we remove it from the sky altogether…

I know it doesn’t really matter, but I felt very strongly that Pluto should be demoted from being a planet. Now that it’s actually happened I feel sad that it’s happened. That means I’ve had two more emotions about Pluto than I ever expected to have.

Well, John Baez was right, the mysterious NASA press release about a dark matter discovery was about the Bullet Cluster.

The discovery provides clear evidence in favor of dark matter, and against MOND. In the Bullet Cluster, when two clusters of galaxies collided, the regular matter in each cluster interacted, causing it to slow down, while the dark matter just kept going on its merry way. So while in a normal galaxy the gravitational forces pull towards the center of the visible galaxy, in the Bullet Cluster, the pull is now towards the bulge of dark matter to the side. It would be difficult to explain the discovery in the context of MOND — you would have to explain why in these particular galaxies the gravitational pull is asymmetric, while in most galaxies it’s symmetric.

So years of internet pundits are apparently wrong. Dark matter is not the new Ptolemaic epicycle. NASA’s article is here. Some animations of the collision can be found here.

John Baez of This Week’s Finds in Mathematical Physics fame, David Corfield of Philosophy of Real Mathematics fame, and Urs Schreiber of The String Coffee Table fame have banded together to form a new weblog, The n-Category Café, dedicated to n-category theory, and their potential applications to physics.