MATTERS OF GRAVITY The newsletter of the Topical Group on Gravitation of the American Physical Society Number 32 Fall 2008 Contents GGR News: Rembembering Wheeler, by Jim Isenberg ................... 4 Research Briefs: A Brief Summary of the WMAP5 Results, by Lyman Page ......... 6 Science with LIGO, by Maria Alessandra Papa ............... 11 Conference reports: 7th LISA Symposium, by Edward K. Porter ................. 16 The Fourth Gulf Coast Gravity Conference 4(GC)2, by Lior Burko ..... 18 1 Editor David Garfinkle Department of Physics Oakland University Rochester, MI 48309 Phone: (248) 370-3411 Internet: garfinkl-at-oakland.edu WWW: http://www.oakland.edu/physics/physics people/faculty/Garfinkle.htm Associate Editor Greg Comer Department of Physics and Center for Fluids at All Scales, St. Louis University, St. Louis, MO 63103 Phone: (314) 977-8432 Internet: comergl-at-slu.edu WWW: http://www.slu.edu/colleges/AS/physics/profs/comer.html ISSN: 1527-3431 2 Editorial The next newsletter is due February 1st. This and all subsequent issues will be available on the web at http://www.oakland.edu/physics/Gravity.htm All issues before number 28 are available at http://www.phys.lsu.edu/mog Any ideas for topics that should be covered by the newsletter, should be emailed to me, or Greg Comer, or the relevant correspondent. Any comments/questions/complaints about the newsletter should be emailed to me. A hardcopy of the newsletter is distributed free of charge to the members of the APS Topical Group on Gravitation upon request (the default distribution form is via the web) to the secretary of the Topical Group. It is considered a lack of etiquette to ask me to mail you hard copies of the newsletter unless you have exhausted all your resources to get your copy otherwise. David Garfinkle Correspondents of Matters of Gravity • John Friedman and Kip Thorne: Relativistic Astrophysics, • Bei-Lok Hu: Quantum Cosmology and Related Topics • Gary Horowitz: Interface with Mathematical High Energy Physics and String Theory • Beverly Berger: News from NSF • Richard Matzner: Numerical Relativity • Abhay Ashtekar and Ted Newman: Mathematical Relativity • Bernie Schutz: News From Europe • Lee Smolin: Quantum Gravity • Cliff Will: Confrontation of Theory with Experiment • Peter Bender: Space Experiments • Jens Gundlach: Laboratory Experiments • Warren Johnson: Resonant Mass Gravitational Wave Detectors • David Shoemaker: LIGO Project • Stan Whitcomb: Gravitational Wave detection • Peter Saulson and Jorge Pullin: former editors, correspondents at large. Topical Group in Gravitation (GGR) Authorities Chair: David Garfinkle; Chair-Elect: Stan Whitcomb; Vice-Chair: Steve Detweiler. Secretary-Treasurer: Gabriela Gonzalez; Past Chair: Dieter Brill; Delegates: Alessandra Buonanno, Bob Wagoner, Lee Lindblom, Eric Poisson, Frans Pretorius, Larry Ford. 3 Remembering Wheeler Jim Isenberg, University of Oregon isenberg-at-uoregon.edu John Wheeler died a few months ago, at the age of 96. His life spanned a revolutionary era in physics which saw all of our ideas on space, time, and the universe completely reworked. Wheeler’s ideas played a major role in all of this. Much more important, however, is the effect Wheeler had through his students. The students he inspired and cajoled and loved have been leaders of the physics revolution from the 1940’s to this day. The first time I really talked to John Wheeler was during the student strike of the late spring of 1970. I was a freshman at Princeton, going door to door for something called the Movement for a New Congress. I hated it. Usually, no one came to the door; when they did, they usually weren’t interested in my spiel: ‘Are you willing to support our efforts to elect congressmen who want to stop the invasion of Cambodia and end the war in Vietnam?’ One day, when I was close to quitting, I saw that the next house was John Wheeler’s. I knew Wheeler was famous for having done important work on the hydrogen bomb; he was also known as a strong opponent of the strike. I didn’t expect much. I hit the jackpot: not for the Movement, but for me. Wheeler listened politely, and then said, ‘Let me tell you about how photons can orbit around a black hole.’ I wasn’t sure what a black hole was, nor was I sure if he knew I was a physics student. It didn’t matter. After two hours, I was convinced that black holes were the best things to be found in the universe, and I was ready to dive into one just to see what those orbiting photons would look like from the inside. General relativity was proposed by Einstein in 1915, and became very popular with the public in 1919, but for decades it was viewed by most physicists as a scientific dead end. The ideas of curved space and time were very appealing, but it was not at all clear that the theory’s predictions were testable by experiment. It was primarily Wheeler (together with Dennis Sciama in Britain, and Peter Bergmann in New York) who during the 1960’s revived general relativity as a vital science, with important things to tell us about cosmology and astrophysics. Wheeler was well known for his work on nuclear fission and fusion and the brilliant discoveries made by his student Richard Feynman, so when Wheeler and his students began to talk seriously about general relativity again, physicists paid attention. They found that not only do such fascinating ideas as black holes, wormholes and gravitational waves arise from the theory, but that these ideas might lead to an understanding of real, observable, and testable physical effects that profoundly shape the universe. Despite its reputation for innovation, in many ways physics is a conservative enterprise. To convince people to take general relativity seriously, Wheeler first needed to train a cadre of brilliant students and postdocs who could make important discoveries using relativity. He did this: Some, like Kip Thorne and Jacob Bekenstein, focused on black holes and astrophysics; others, like Charlie Misner, Dieter Brill, Bob Geroch, Demetrios Christodoulou and Jimmy York, worked on the mathematics of general relativity; still others, like Bob Wald, Bill Unruh and Hugh Everett, thought hard about the relation between quantum theory and general relativity. Together they produced a sea change in how we think about the universe. I didn’t work with Wheeler directly until almost two years after that first encounter. But I did learn a huge amount from him the next year, by wandering around Jadwin Hall (home of Princeton’s physics department) at night. Often, peeking into darkened lecture halls, you could still see the physics lecture masterwork of Wheeler on multi-storied blackboards covered 4 with beautifully colorful representations of black holes, wormholes and expanding universes, together with the equations which modeled these things. Even before I knew much general relativity, I loved trying to work through those lectures, all from the blackboard drawings. When I started working with Wheeler in my junior year, I learned a huge amount and not just physics. Wheeler understood that scientific discovery is not enough. You need to be able to tell people about it effectively and convincingly. So, a key feature of every Wheeler lecture was that you remembered something interesting, something he wanted you to remember. It was no accident that Wheeler coined the term ‘black hole’ for those strange collapsed stars which he and others were just beginning to understand during the 1960s. These theoretical objects had earlier been called ‘frozen stars,’ but Wheeler knew that a frozen star is chilling and forgettable while a black hole is awesome and fascinating. Wheeler’s writing was just as memorable as his lectures. Some have found his writing, sprinkled as it is with phrases like ‘it from bit’ and ‘mass without mass,’ a bit strange. This point was brought home to me when I submitted my first scientific article to a leading physics journal. Wheeler had gone over the article with me many times, and had suggested a multitude of changes, which I dutifully made. The referee report was short. It said that the science seemed fine, but ‘Wheeler can write like this; you can’t!’ I still don’t write like Wheeler. However, as I and other physicists await the word from the Laser Interferometer Gravitational-Wave Observatory that we can detect gravitational radiation, and as we discuss how we can use these observations to probe the physics of black holes (without having to dive into them ourselves), I think it a worthy goal to strive to do science like Wheeler. —————————————————- This article, with a few small changes, was published last May in The Register Guard, which is the Eugene, Oregon daily newspaper. 5 A Brief Summary of the WMAP5 Results Lyman Page, Princeton University page-at-princeton.edu In March 2008 the Wilkinson Microwave Anisotropy Probe (WMAP ) science team pre- sented results on the analysis of five years of WMAP data. WMAP is a NASA Medium-Class Explorer that yields full-sky maps of the temperature and polarization anisotropy in the cos- mic microwave background (CMB) of unprecedented fidelity. Simultaneous measurements in five frequency bands between 23 and 94 GHz facilitate the separation of the CMB signal from foreground emission arising both from our Galaxy and from extragalactic sources. The CMB angular power spectrum derived from these maps exhibits a coherent acoustic peak structure which makes it possible to extract a wealth of information about the composition and history of the universe, as well as the processes that seeded the fluctuations. Readers of “Matters of Gravity” will appreciate that the superb agreement between CMB theory and measurement is a significant test of the General Theory of Relativity. The “WMAP5” release comprised seven papers.