I was born in December 1969 in Washington DC, the youngest of three children with two older sisters. Growing up I was a lover of all sports (especially soccer) and curious about everything. Besides pestering my family with questions, I conducted my own “experiments” to learn about the world around me including sticking wires into electrical outlets, tasting everything in the spice rack and cutting earthworms in half – all to see what would happen.
After high school I attended the Massachusetts Institute of Technology where I majored in physics. The work was very hard but very satisfying. I especially enjoyed the experimental labs where we reproduced many of the famous experiments of the early 20th Century. I decided to make science and perhaps astrophysics a career. That summer I worked at the Lawrence Livermore National Laboratory as an intern on the search for Massive Compact Halo Objects, where I met a young and clever researcher, Saul Perlmutter, a Co-winner of the Shaw Prize!
In 1992 I went to Harvard University to earn a doctorate in astrophysics. After a first course I knew I wanted to help measure the expansion rate of the Universe. Professor Robert Kirshner suggested I proceed by measuring distances to type Ia supernovae in collaboration with Professor William Press. I was extremely fortunate to work with Bob who had great commonsense, and Bill who had incredible talents in data analysis. Bob’s senior graduate student, Brian Schmidt (the other co-winner of the Shaw Prize!) patiently taught me the techniques of making precise measurements with telescopes. This work culminated in my thesis, the Multicolor Light Curve Shape Method, a technique which could distinguish between the effects of distance, dust and dimness in type Ia supernovae and the collection of one of the largest datasets of type Ia supernovae, 22 in all, for measuring the recent expansion rate of the Universe. (My thesis later received the 1999 PASP Trumpler Award for the doctoral thesis with the greatest impact in astrophysics.)
I went to UC Berkeley in 1996 as a Miller Fellow, having recently become a founding member of the competing High-z Supernova Team. At Berkeley I was again fortunate to work with the best, Professor Alex Filippenko, an enthusiastic and nurturing figure. By 1997 the High-z Team had managed to find and observe a significant sample of very distant supernovae. Working down the hill from Saul’s talented and competing team, I collected the raw data and led the process of analyzing it, transforming large pixelated images into a record of the light history of a dozen distant supernovae. Armed with a similar product from local supernovae from my thesis (as well as the Calan-Tololo Survey) I measured the recent and past expansion rate of the Universe and transformed these measurements into an expectation of the forces at work in the Universe. The initial results indicated the dominating presence of negative mass accelerating the Universe! Since there is no such thing as negative mass I introduced the next best thing, Einstein’s famous cosmological constant to the fit in desperation and immediately found that its dominating presence (i.e., a non-zero vacuum energy with negative pressure causing repulsive gravity) could explain the apparent acceleration I was seeing. This was remarkable and experience told me that such “discoveries” are usually the result of simple errors. Being young and insecure about my capabilities, I spent a long time double checking my results but could find no errors. With growing confidence in the results, I told Brian who spot-checked the final calculations and came to the same conclusions.
Coincidentally, another, even more exciting event was occurring in my life as Nancy Joy Schondorf and I were married on January 10th in 1998, the best day of my life.
In the end the High-z Team published our paper entitled, “Observational Evidence From Supernovae for an Accelerating Universe and a Cosmological Constant”. Saul’s competing team reached the same conclusion and together the two teams’ conclusion became the “Breakthrough of the Year” of Science Magazine in 1998.
Our lingering worries about the correctness of the results remained. What if we somehow were being fooled and the supernovae appeared dim for some non-cosmological reason (i.e., an astrophysical contaminant like some kind of exotic dust or evolution) making us only think the Universe was accelerating? A powerful test of competing paradigms was suggested: measure supernovae even farther and see if they begin to look relatively brighter. If so, we would be witnessing the expected but never seen effect of the matter-dominated Universe, decelerating the expansion when cosmic structures first formed, before acceleration began. If instead more distant supernovae looked relatively fainter we would have been fooled in 1998 by some unexpected and still unexplained astrophysical source of dimming. The only problem was that such SNe were too faint to be discovered with any telescopes except the Hubble Space Telescope. This was not inconvenient for me because in 1999 I had moved to its headquarters at Space Telescope Science Institute in Baltimore.
Trolling through the archives in 2001 I found evidence of the preceding deceleration—a very good sign. In 2002 when a new, more powerful camera was put on Hubble, I formed a new team, the Hubble Higher-z Team, to make a definitive measurement of this confirming or refuting effect. My teammates were very skilled and knowledgeable and we worked hard to use Hubble to find and measure the dozen most distant supernovae known. In 2004 we reached the conclusion that the supernova story told in 1998 was correct—the Universe had indeed only recently begun accelerating and that the dark energy-like force causing this phenomenon did look just like Einstein’s cosmological constant was expected to. That year I was honored to receive the Warner Prize of the American Astronomical Society and the Sackler Prize from Tel Aviv University for my work on the accelerating Universe.
That same year my favorite “supernova” was born, my daughter, Gabrielle. Her own light curve has continued to rise and I observe it closely. In 2006 I moved to Johns Hopkins University. The big question has now changed for me to, “What is the nature of this Dark Energy?” The quest for the answers fills my research time as it stirs my mind and tweaks my curiosity.
12 September 2006, Hong Kong
