An associate professor of physics and astronomy at the Massachusetts Institute of Technology and the University of Pennsylvania, Max Tegmark focuses his research primarily on cosmological theory and connecting theory to observation. He uses data from analyses of galaxy clustering and the cosmic microwave background radiation to place sharp constraints on cosmological models, that is, to try to ground them in what can be measured in experiments. A native of Sweden with baccalaureate degree both from the Stockholm School of Economics and the Swedish Royal Institute of Technology, he studied theoretical cosmology with astronomer Joseph Silk at the University of California, Berkeley, and received his Ph.D. in physics in 1994. After two years as a research associate at the Max-Planck Institute for Physics in Munich, he spent more than three years doing post-doctoral research at the Institute for Advanced Study in Princeton before joining the Penn faculty in 1999 and the MIT faculty in 2004. Dr. Tegmark has held a Hubble Fellowship awarded by the Space Telescope Institute and currently holds a David and Lucille Packard Foundation Fellowship, a Cottrell Scholar Award given by the Research Corporation, and a National Science Foundation Career Grant. He shared the top honors awarded by Science Magazine for the “Number 1 Breakthrough of the Year” in 2003 for his work with the Sloan Digital Sky Survey (SDSS). Involving an analysis of a quarter-million galaxies, it resulted in the most accurate measurements to date of how the density of the universe fluctuates from place to place on scales of millions of light years. Dr. Tegmark’s first work involved predicting the size of the earliest galaxies based on molecular physics. He has developed widely-used statistical techniques for analyzing cosmic microwave background and galaxy maps to measure cosmological parameters such as the amounts of ordinary matter and dark matter in the universe, the curvature of space, and the amplitudes of various types of density fluctuations that emerged in the first split second after the Big Bang. Many of his more than 150 scientific papers present ideas and data relevant to parallel universes, including evidence for infinite space and cosmological inflation, as well as for the possibility that the microwave background fluctuation level, the dimensionality of spacetime, and fundamental laws of physics can vary throughout a multiverse.