AGILE launch

AGILE successfully launched today! Congratulations to the whole AGILE team. AGILE is a space based Gamma-Ray observatory, which has sensitivity in the 30Mev - 50Gev range. It also has a very large field of view, 3 steradians. This is the European entry into the Gamma-Ray observation game. I worked on the US competitor at Stanford called GLAST, which is set to launch this fall. GLAST has a much larger range of energy sensitivity, 20Mev - >300Gev and the same field of view. They both have great resolution due to the silicon strip detector technology on both satellites, and will be able to pin point the sources of high energy gamma-rays to 30 arcseconds. This is orders of magnitude more accuracy then we currently have with ground based observatories and with previous space based observatories (EGRET).
These satellites will both be scanning the sky for AGN (Active Galactic Nuclei), Gamma-Ray bursts, and many other gamma-ray sources. Gamma ray sources are the most energetic phenomena in the Universe and it will be interesting to see the science that comes out of both AGILE and GLAST.

The Hollywood Cell Story

The Inner Life of the Cell is one of the greatest visualization/animations I have ever seen. This beats the best astronomy visualizations I have ever seen. There are some inaccuracies in the movie (e.g. the assembly and disassembly of objects is too ordered to represent the real Brownian motion processes, which would realistically take too long), but it is all done in the name of slick animation and for the glamorization of cellular biology. This is just plain cool!

Nicotine and other cognitive enhancers

I just read a great blog entry on nicotine and it's effects on the brain written by Madam Fathom. She give a great review of how the nerves in the prefrontal cortex behave and how they are effected by nicotine in both a person that smokes and a nonsmoker. I would love for her to do a similar story on modafinil. The maker, Cephalon, claims there is no negative side effects and information from a resent ongoing study seems to indicate what college kids and silicon valley body hackers already know. It improves memory and seems to have a similar effect to nicotine, in that it "may enhance the signal-to-noise ratio" allowing people to concentrate better.

Teaching Company

A couple of my simulations appear in a new course put out by the Teaching Company. Prof. Alex Filippenko, UC Berkeley, asked to include the visualizations of two dark matter simulations I did as a graduate student in a course he recorded for the Teaching Company. The course is called Understanding the Universe: An Introduction to Astronomy.

Strange Loops (Part 1)

I just read a review of the new book from Douglas R. Hofstadter entitled "I am a Strange Loop". This may seem like a bizarre title for a book, but if you have read his other tome, the famous "Goedel, Escher, Bach" (GEB), you will understand the title. I ordered this new book today and will most likely write about it after I have read it. The reason I bring it up today is because I have been meaning to write a review, synopsis, and my thoughts on GEB. This is going to be the first installment of a few short articles I plan to write on this book and subjects contained within. Given the fact that GEB is over 750 pages long and that Hofstadter's rambling narrative covers so many topics all at once it deserves many write ups. One last note before I begin: I must admit it has been about a year since I read GEB, so many of the things I am writing about come from my notoriously bad memory and I, unfortunately, also did not follow my normal practice and mark the book up with a red pencil. So here goes.

In GEB Hofstadter, who actually has a PhD in solid state physics, tries to tie number theory, intelligence, and philosophy together for an admittedly vague purpose through the concept of what he calls the "strange loop". A strange loop is simply a self referential cycle. More on that later. He uses a variety of didactic instruments to communicate his thoughts. One instrument which is employed throughout the book is the use of dialog. Before every chapter Hofstadter presents a dialog between the Homeric hero Achilles, the comical figure of the Tortoise, and other fictional and non-fictional characters in a style mimicking Carroll's remake of the Zeno paradox. The dialogs are meant to illustrate the main focus of the proceeding chapters through the use of humor and situation. Hofstadter's use of such dialogs is difficult to get used to and often breaks the flow of the book up in a very unnatural way. Not to mention, he is only marginally successful at illustrating his points in these dialogs. A number of times I found myself getting bored by the dialogs and skipping them to get to the real chapters. Depending on how one learns, the mileage one gets from these dialogs will vary.

Another instrument Hofstadter uses relates directly to the title of the book. He uses the work of Goedel, Escher, and Bach to illustrate his ideas although all not in the same manner. Goedel's work is used directly as the basis for many of Hofstadter's arguments, where the mentions of Escher and Bach's works have more of an art historian feel. He presents interpretations of their work viewed "through the looking glass" of the arguments he is building. The Escher examples come across easier due to their visual nature, but for one to understand the Bach examples one must familiar with the canon's of his writing. Hofstadter does a good job of explaining and exposing some of the more hard to recognize mathematical aspects to both artist's works. There always seemed to be a mathematical quality to Escher's work which ran deeper than just geometry and Hofstadter exposes some of that in GEB. Besides these two examples Hofstadter successfully uses literary tools such as Zen koans and language translations combined with biological and mathematical ideas to make his points.

It is enjoyable and often useful to interpret science and math concepts from a humanistic point of view and I feel that that is what this book does well. With in mind, this book should then be divided into two books; one teaching number theory and one on the humanistic view of intelligence and number theory. Hofstadter has done himself an injustice by combining the two subjects which in turn has limited his audience to a narrow group of individuals both willing to read a 750 plus page book and explore both the rigorous development of a number theory and it's philosophical consequences. There are many people, I know, that I feel would love to read what Hofstadter has to say about certain subjects, but who would be unwilling to read this book. Overall, I liked this book, but mainly because I felt a personal connection with Hofstadter and what he has to say. I am not so sure many other readers will have or have had same experience, but I may be wrong considering Hofstadter won the Pulitzer prize for GEB in 1980.

In part 2 I will give an overview of the construction of the number theory Hofstadter uses to present the strange loop concept and then in part 3 I will give an overview of the philosophical side of GEB.

Nearly Naked Dark Matter Halo

In two important papers (paper 1 and 2) put on astro-ph two days ago, a group of astronomers describe the observations and analysis of two colliding galaxy clusters which have temporarily stripped each other of their hot X-ray emitting gaseous cores respectively, leave nearly naked dark matter halos. The most important aspect of this set of papers is their confirmation of a major prediction of Cold Dark Matter theory which is not explainable by alternatively proposed solutions to the missing mass problem.

The holy grail for proving that cold dark matter halos exist, thereby also proving that dark matter exists, is being able to "observe" a naked halo. When baryons are present, there is always a way to modify gravitational theory, albeit rarely self consistently, or propose the existence of more cold (unobservable) baryons around a galaxy or cluster to explain observations of gravitational lensing and other phenomena, which are naturally explained by the presence of a dark matter halo. Because dark matter halos are so massive and most began forming very early in the universe, all of them have had a long enough time and have a large enough gravitational potential to pull in the intergalactic gas around them. Only some small halos are theorized to be truly "empty". And even if large naked halos existed, where would we look to find them? The next best observation would therefore be of a dark matter halo where the baryonic matter and the dark matter are clearly separated by a process that would leave no significant amount of cold baryons at the center of the halo. This is what this observation show.

Using the phenomenon of weak gravitational lensing, an effect well know to observers (easily seen by the Hubble telescope through the presence of the arced galaxies), one can determine the mass along the line of sight needed for such distortions in background galaxies. This method was used to determine the mass and center position of the two colliding dark matter halos. Because both of the galaxies clusters are at the same redshift and are traveling perpendicular to the plane of the sky away from each other they must have just made a pass through one another. The significance of this is that dark matter only interacts gravitationally allowing the halos to pass through each other. Baryons on the other hand collide, shock, and heat up which slows them down relative to the dark matter. The heated gas can be seen in the X-rays and is observed to have formed a bow shock behind the gravitational centers of the halos. It is impossible for much gas (baryonic matter) to have remained at the center of the halos and at the same time remained cold (no X-rays). Therefore, a modification of gravity exerted by baryons can not be used to explain this observation, nor can the presence of a large amount of cold unobservable baryons.

This is a great step in proving the existence of dark matter, but there is a long way to go to truly understanding the nature of dark matter and dark matter halos. It is, however, exactly this combination of weak and strong gravitational lensing observations combined with multi-wavelength observations that will lead the way. I will soon post an explanation of what these kinds of observations can tell us about the nature of dark matter.

BPS - Body Positioning System

Stanford biologist have just published a paper on the study and discovery of three genes in fibroblasts, which are contained in the deepest epidural layer and in the surface of most organs. They find that the expression of the genes is correlated with location on the body. It is well known that fibroblasts are responsible for embryonic development of limbs and other body parts, but it was thought that they become dormant after the body is fully formed. The working hypothesis of the Stanford scientist is that these and other genes in the fibroblasts are still active and communicate position information to other cells. This allows skin cells to know how much to regenerate in order to heal wounds. It is still unclear as to whether the gene expression is a remnant of the embryonic development stage or if they are continually active and influencing cellular development. If right, the scientist are hopeful that this may lead to the development of organ and limb regeneration by adult cells instead of embryonic stem cells. There is a NYT article on the study here.