stanford university PPHYSICSHYSICS Newsletter DEPARTMENT FEBRUARY 2007 February, 2007 ment of Physics and SLAC. Prof. tions relevant to interpreting observa- Letter from the Chair Wechsler was a Hubble Fellow and tional data, especially large surveys Enrico Fermi Fellow at the Kavli Insti- and multi-wavelength studies of galaxy Dear Physics alumni and friends, tute for Cosmological Physics at the properties. Her work with the Sloan University of Chicago. Her research Digital Sky Survey and as a member of interests are primarily in the areas of the Dark Energy Survey collaboration reetings and Happy New Year! theoretical cosmology and galaxy for- has provided essential theoretical input This past year marked the comple- mation. Risa’s work has involved mak- to the survey planning. We are very G tion of our new Physics and Astro- ing detailed predictions for the evolu- continued on page 8 physics building next door to Varian tion of structure in R Physics. We invite those of you who cold dark matter E T L E have not seen our new building, or the models, studying the F D A new Physics Main Office adjacent to assembly history L G it, to stop by campus for a visit. The and clustering of E V E Physics and Astrophysics building hous- T dark matter halos S : es both Kavli and HEPL activities, as O and galaxies, galaxy T O well as the teaching laboratories. We formation modeling, H P are very pleased with the new construc- and the use of galax- tion, which will allow for much needed ies and clusters as expansion and increased productivity probes of cosmology for the future. and fundamental physics. A primary This past fall, we were happy to welcome focus of her work new faculty member Risa Wechsler as a has been to make joint Assistant Professor in the Depart- theoretical predic- New faculty appointee, Risa Wechsler Professor David Griffiths Visits Stanford Professor John W. Harris: avid Griffiths of Reed College gave a lecture for the Society of Physics Students this past Decem- the 2007 Robert Hofstadter ber. Thirty undergraduate physics majors and a D smattering of graduate students and faculty Memorial Lecturer attended, eager to meet the author of their favorite textbooks. Professor Griffiths discussed the charge e are pleased to announce that distribution on two-dimensional and one-dimension- the annual Robert Hofstadter al conductors, and results for force laws other than Memorial Lectures will be giv- the inverse-square law. Emboldened by the genial David Griffiths W en this year by John W. Harris, speaker, students asked questions on a variety of top- Professor of Physics and Group Leader ics: How does one become a good teacher? What makes some physicists of the Relativistic Heavy Ion Group at famous? And how will the future discoveries in physics compare to those Yale University. Professor Harris is a of the past? Many students took the opportunity to have their textbooks Fellow of the American Physical Society, autographed by the award-winning educator. David Griffiths will return to was voted one of the top 40 Distin- Stanford this spring to work on the second edition of his particle physics continued on page 2 textbook and co-teach Physics 121 (Intermediate Electricity & Magnetism). stanford university PHYSICS NEWSLETTER Hofstadter Lecture – from page 1 Committee of the Institute of guished Alumni of Stony Brook Uni- Nuclear Theory at the University of versity, and is the recipient of the Washington. Alexander von Humboldt Senior Research Award. Prof. Harris has The Hofstadter lectures are sched- been both a collaborator and uled for Monday, April 30, 2007 spokesperson for the STAR exper- (an evening public lecture at 8:00 iment at Brookhaven National Lab- PM) and Tuesday, May 1 (an after- oratory and a National Coordina- noon colloquium at 4:15 PM). tor of ALICE-USA, at the CERN Both lectures will be held at Stan- Large Hadron Collider. He has also ford University, and we hope that served on the National Advisory you will plan to attend. h John W. Harris EVENING PUBLIC LECTURE AFTERNOON COLLOQUIUM 8:00 pm – Monday, April 30, 2007 4:15 pm – Tuesday, May 1, 2007 Hewlett Building, Room 200 Hewlett Building, Room 201 “What is that Black Hole “Evidence for a Quark-Gluon Plasma Doing in My Quark Soup?” in the Laboratory” It’s hot – at an absolute temperature of 1012 K – one hun- Ultra-relativistic collisions of heavy nuclei are being investigated for dred thousand (105) times hotter than the center of the the first time at the Relativistic Heavy Ion Collider (RHIC) at Brook- sun. It’s runny – runnier than anything known to man – haven National Laboratory and will soon be investigated at the even superfluids. What is it made from – its ingredients? Large Hadron Collider at CERN. These collisions heat nuclear mat- Tiny quarks and gluons. Where did it come from? It’s ter to energy densities previously reached only within the first few nothing ever made by man, it existed ten millionths microseconds after the Big Bang. Temperatures of 2 x 1012 K are (10-5) of a second after the beginning of the Universe or reached, melting the vacuum into a plasma of quarks and gluons. about thirteen billion years ago. Can we figure out how The goal of physicists in this field is to re-create and uniquely iden- to make it – is there a recipe? Yes, we have and we are tify properties the primordial quark-gluon plasma in order to under- cooking it up right now. It’s a Quark Soup. stand Quantum Chromodynamics at high energy densities. After six years of operation, RHIC and its experiments have established the I will address these and other questions about the recent presence of such extreme energy densities, temperatures and pres- creation of a primordial quark soup in the laboratory. Why sures. The system that is created behaves somewhat unexpect- would we even want to cook it up? What does this soup edly as a strongly-interacting, low viscosity liquid of quarks and taste like? It seems to have a unique flavor – has any- gluons and is opaque to energetic quark and gluon probes. I will one ever really sampled a soup of quarks and gluons? present an overview of the results establishing the creation and Perhaps there is a secret ingredient? And by the way – behavior of a hot (T = 2 x 1012 K) quark-gluon liquid at RHIC and its what is that tiny Black Hole doing in my Quark Soup? quenching of energetic probes. The quark-gluon liquid has behav- ior and properties similar to those of strongly-interacting classical fluids that are studied in atomic physics. Remarkably, a theoretical approach to black holes involving strings in five dimensions can describe the unique properties observed in this quark-gluon liquid. 2 stanford university PHYSICS NEWSLETTER RNA – the “Dark Matter” of the Genome by Jan Lipfert and Sebastian Doniach he “central dogma” of molecu- lar biology was formulated in the 1950s, soon after the dis- T covery of DNA structure by Watson and Crick. It states that the information flow in the cell is from DNA (which stores the genetic infor- mation) to RNA (which acts as a “messenger”) to proteins (which car- ry out the bulk of cellular func- tions). DNA is copied to RNA in a process called transcription. The base sequence of RNA is then trans- lated (using the genetic code as a “dictionary”) into the amino acid sequence of proteins. In this picture, still largely present in textbooks, Physics graduate student Jan Lipfert with the SAXS measurement set-up at RNA is the -somewhat boring- beamline 12 of the Advanced Photon Source. “middle man” between DNA and proteins. whom were awarded Nobel Prizes in While traditionally in the realm of 2006. Roger D. Kornberg received biochemistry and molecular biology, This picture started to change in the the Nobel Prize in chemistry for his RNA science offers interesting ques- early 1980s, when Tom Cech, Sidney contributions to the understanding tions to physicists. The RNA back- Altman and others discovered that of the intricate machinery that car- bone is highly negatively charged and certain RNA molecules, much like ries out transcription and Andrew in order to fold into a distinct 3- proteins, can fold into distinct 3- Z. Fire (shared with Craig C. Mello dimensional shape, RNA must over- dimensional shapes and catalyze of the University of Massachusetts) come an enormous Coulombic repul- chemical reactions, a discovery for was awarded the Nobel Prize in sion. Overcoming this free energy bar- which they shared the Nobel Prize Medicine for their discovery of rier is facilitated by the presence of in Chemistry in 1989. Even more “RNA interference,” one of the positively charge counter ions, such as recently, it has become increasingly mechanisms by which RNA can Mg2+. The resulting problem of com- clear that RNA molecules control regulate genes. puting the arrangement and interac- transcription and translation tion energies of negatively charged through a variety of mechanisms RNA surrounded by a cloud of and play a key role in regulating the Unfolded mobile ions is a classical analogy to metabolic state of the cell. Only 2% the quantum mechanical problem of of the human genome codes for pro- computing the electron density around teins, but as much as 50% is tran- Glycine Bound Buffer only + 10 mM Glycine charged nuclei. The energy scale of scribed to RNA, a sizable fraction the classical problem is set by kT, as of which is presumably involved in 2+ Partially Folded opposed to h-bar in the quantum gene regulation and other cellular + 10 mM Mg mechanical case.