Amorphous Silicon


Paul J. Steinhardt is the Albert Einstein Professor in Science and Director of the Princeton Center for Theoretical Science at Princeton University, where he is also on the faculty of both the Department of Physics and the Department of Astrophysical Sciences.

P.J. Steinhardt
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Prof. Paul J. Steinhardt
Department of Physics
Department of Astrophysical Sciences
Director, Princeton Center for Theoretical Science

Steinhardt received his B.S. in Physics in 1974 from Caltech, where he worked with Richard Feynman, Barry Barish and Frank Sciulli. He received his M.A. in Physics in 1975 and Ph.D. in Physics in 1978 from Harvard University, where his doctoral advisor was Sidney Coleman. Other mentors included Richard Alben (Yale) and Praveen Chaudhari (IBM). He was a Junior Fellow in the Harvard Society of Fellows from 1978-81. Steinhardt joined the faculty of the Department of Physics and Astronomy at the University of Pennsylvania in 1981, where he was the Mary Amanda Wood Professor from 1989-1998. He joined the faculty in the Department of Physics and the Department of Astrophysical Sciences at Princeton University in 1998, and was named the Albert Einstein Professor in Science in 2001. He co-founded the Princeton Center for Theoretical Science in 2004, and now serves as its Director.

Steinhardt's research spans problems in particle physics, astrophysics, cosmology and condensed matter physics. He is one of the original architects of the inflationary model, an important modification of the standard big bang picture that explains the large-scale homogeneity, geometry and structure of the universe. He was among the first to show that quantum fluctuations combined with inflation can generate a nearly scale-invariant spectrum of density variations; and, then, extending these ideas, he was the first to demonstrate that inflation can be eternal, the result of which is the multiverse. He introduced the concept of ``quintessence,'' a dynamical form of dark energy that may account for the recently discovered cosmic acceleration. He has also introduced novel models for dark matter, including self-interacting dark matter (SIDM).

In 2001, Steinhardt and collaborators proposed that the big bang might instead be a big bounce, and that the key events shaping the large-scale structure of the universe may have occurred before the bounce. The next year, Steinhardt and Neil Turok (Perimeter Institute) proposed the ``cyclic model" of the universe, which has now become the leading rival to big bang/inflationary cosmology. According to the cyclic theory, the bounces occur at regular intervals, perhaps every trillion years or so, and the current epoch of accelerated expansion will eventually halt due to the decay of the vacuum, triggering a phase of contraction and, ultimately, the next big bounce.

In condensed matter physics, Steinhardt and Dov Levine (Technion) first introduced the concept of quasicrystals in 1983, a new phase of solid matter with symmetries that are forbidden for periodic crystals (such as five-fold symmetry in two dimensions or icosahedral symmetry in three dimensions). Throughout the more than three decades following that theoretical breakthrough, Steinhardt has continued to make contributions to understanding quasicrystals' unique mathematical and physical properties.

Motivated by these ideas, he conducted a decade-long international search for a natural quasicrystal that culminated in the discovery of the first example (now called icosahedrite) in a sample found in the mineralogical collection of the Museo di Storia Naturale in Florence, Italy and purported to have come from a remote region of the Kamchatka Peninsula. Steinhardt then organized and led an international geological expedition to Kamchatka in 2011 to prove the origin and find new samples. The expedition succeeded in unearthing new samples of icosahedrite and showing that it traced its origin to a 4.5 billion year old meteorite that was previously unknown. From the evidence provided by Steinhardt's team, the Meteoritical Society acknowledged the meteorite and the proposed name, Khatyrka (derived from the name of a river near the impact site). Steinhardt and his team later discovered a second natural quasicrystal, decagonite, in the Khatyrka samples. Also found was a crystalline phase consisting of an alloy mixture of aluminum, iron and nickel, which the International Mineralogical Association officially named steinhardtite in his honor.

One of the most significant consequences of Steinhardt's work on quasicrystals has been the development of new types of photonics solids for efficiently trapping and manipulating light. Steinhardt worked with Weining Man (SFSU) and Paul Chaikin (NYU) to construct the first three-dimensional icosahedral photonic quasicrystal; and, with Salvatore Torquato (Princeton), and Marian Florescu (University of Surrey) he has invented new types of photonic solids called hyperuniform disordered solids (HUDS), that have a complete photonic band gap despite the fact they are isotropic and disordered.

Steinhardt is a Fellow in the American Physical Society and a member of the National Academy of Sciences. He shared the P.A.M. Dirac Medal from the International Centre for Theoretical Physics in 2002 for his role as one of the three leading architects of the inflationary model of the universe; the Oliver E. Buckley Prize of the American Physical Society in 2010 for his contribution to the theory of quasicrystals; and the John Scott Award in 2012 for his work on quasicrystals, including the discovery of the first natural quasicrystal. He was been a Sloan Fellow (1982-6) and Guggenheim Fellow (1994-5). In 2012, he was named Simons Fellow in Theoretical Physics; Radcliffe Institute Fellow at Harvard; and Moore Fellow at Caltech. In 2014, he was named a Caltech Distinguished Alumnus.

Professor Steinhardt is the author of over 200 refereed articles, 100 reviews and popular articles, ten patents, two patents pending, three technical books, numerous popular articles, and, in 2007, co-authored Endless Universe: The Big Bang and Beyond, a popular book on contemporary theories of cosmology.