Question: When was the American theoretical physicist and cosmologist which Alexander Vilenkin worked with in 2013 born
Context: Chris Quigg (born December 15, 1944) is an American theoretical physicist at the Fermi National Accelerator Laboratory (Fermilab).  He graduated from Yale University in 1966 and received his Ph.D. in 1970 under the tutelage of J. D. Jackson at the University of California, Berkeley.  He has been an associate professor at the Institute for Theoretical Physics, State University of New York, Stony Brook, and was head of the Theoretical Physics Department at Fermilab from 1977 to 1987. Stephen William Hawking, {'1': ", '2': ", '3': ", '4': "} ( born 8 January 1942) is an English theoretical physicist, cosmologist, author and Director of Research at the Centre for Theoretical Cosmology within the University of Cambridge.  His scientific works include a collaboration with Roger Penrose on gravitational singularity theorems in the framework of general relativity and the theoretical prediction that black holes emit radiation, often called Hawking radiation.  Hawking was the first to set out a theory of cosmology explained by a union of the general theory of relativity and quantum mechanics.  He is a vigorous supporter of the many-worlds interpretation of quantum mechanics. David Jonathan Gross ( ; born February 19, 1941) is an American theoretical physicist and string theorist.  Along with Frank Wilczek and David Politzer, he was awarded the 2004 Nobel Prize in Physics for their discovery of asymptotic freedom.  David Gross is the Chancellor’s Chair Professor of Theoretical Physics at the Kavli Institute for Theoretical Physics of the University of California, Santa Barbara, and was formerly the KITP director and holder of their Frederick W. Gluck Chair in Theoretical Physics .  He is also a faculty member in the UC Santa Barbara Physics Department and is currently affiliated with the Institute for Quantum Studies at Chapman University in California.  He is a foreign member of the Chinese Academy of Sciences. Stephon Alexander is a theoretical physicist, cosmologist, musician and author known for blending the worlds of theoretical physics and jazz music. Paul Joseph Steinhardt (born December 25, 1952) is an American theoretical physicist and cosmologist who is currently the Albert Einstein Professor in Science at Princeton University. Alan Harvey Guth ( ; born February 27, 1947) is an American theoretical physicist and cosmologist.  Guth has researched elementary particle theory (and how particle theory is applicable to the early universe).  He is currently serving as Victor Weisskopf Professor of Physics at the Massachusetts Institute of Technology.  Along with Alexei Starobinsky and Andrei Linde, he won the 2014 Kavli Prize “for pioneering the theory of cosmic inflation.” Alexander Vilenkin (Russian: Алекса́ндр Виле́нкин ,Ukrainian: Олександр Віленкін ; 13 May 1949, Kharkiv, Ukraine, Soviet Union) is Professor of Physics and Director of the Institute of Cosmology at Tufts University.  A theoretical physicist who has been working in the field of cosmology for 25 years, Vilenkin has written over 150 papers.  Soon after Paul Steinhardt presented the first example of eternal inflation, Vilenkin showed that eternal inflation is generic.  Working with Arvin Borde and Alan Guth, In 2003, he showed that a period of inflation has to have a beginning and there has to be a period that precedes it.  This is a problem because, without a theory to explain the conditions before inflation, it is not possible to determine how likely it is for inflation ever to occur.  Some considerations suggest that the probability is very small, resulting the "initial conditions problem.” Gerald Edward "Gerry" Brown (born July 22, 1926 in Brookings, South Dakota; † May 31, 2013 in New York City) was an American theoretical physicist who worked on nuclear physics and astrophysics.  Since 1968 he had been a professor at the Stony Brook University.  He was a distinguished professor emeritus of the C. N. Yang Institute for Theoretical Physics at Stony Brook University. George Gamow (March 4 [O.S. February 20] 1904 August 19, 1968), born Georgiy Antonovich Gamov (Russian: Гео́ргий Анто́нович Га́мов ; ] ), was a theoretical physicist and cosmologist.  He was an early advocate and developer of Lemaître's Big Bang theory.  He discovered a theoretical explanation of alpha decay via quantum tunneling, and worked on radioactive decay of the atomic nucleus, star formation, stellar nucleosynthesis and Big Bang nucleosynthesis (which he collectively called nucleocosmogenesis), and molecular genetics. Mikhail "Misha" Voloshin (born 1953) is a Russian and American theoretical physicist.  Voloshin started working at ITEP in 1976 and accordingly earned his Ph.D. in 1977.  In 1983 he received a Soviet medal and an award in physics.  Since 1990 he started at the William I Fine Theoretical Physics Institute, University of Minnesota, a division of the University of Minnesota College of Science and Engineering where he teaches quantum physics.  In 1997 elected a fellow of the American Physical Society.  In 2001 he was awarded J.J. Sakurai Prize for Theoretical Particle Physics and in 2004 he was awarded the Alexander-von-Humboldt Award.
Answer: February 27, 1947