Geraint Francis Lewis (born 14 March 1969) is a Welsh astrophysicist, who is best known for his work on dark energy, gravitational lensing and galactic cannibalism. Lewis is a Professor of Astrophysics (Teaching and Research) at the Sydney Institute for Astronomy, part of the University of Sydney's School of Physics. He is head of the Gravitational Astrophysics Group. He was previously the Associate Head for Research at the School of Physics, and held an Australian Research Council Future Fellowship between 2011 and 2015. Lewis won the 2016 Walter Boas Medal in recognition of excellence in research in Physics. In 2021, he was awarded the David Allen Prize of the Astronomical Society of Australia for exceptional achievement in astronomy communication. In April 2020, Geraint was elected as a Fellow of the Learned Society of Wales. He is also an elected fellow of the Royal Society of New South Wales. Until the end of 2020, he held the position of Deputy Director of the Sydney Informatics Hub, a Core Research Facility of the University of Sydney. Education Originally from Wales, Lewis was born in Neath and raised in Seven Sisters and Crynant, completing schooling at Llangatwg Comprehensive and Neath Tertiary College. He completed his first degree at the University of London and PhD at the University of Cambridge's Institute of Astronomy. He has worked in the State University of New York, the University of Victoria in Canada, and the University of Washington in Seattle. After research positions in the US and Canada, he then became a Research Astronomer at the Anglo-Australian Observatory in 2000. In 2002, Lewis joined the University of Sydney where he is currently the head of the Gravitational Astrophysics Group. Research fields Lewis undertakes a broad spectrum of research in astronomy and cosmology. On the largest scales, his program involves looking at the influence of dark energy and dark matter on the evolution and ultimate fate of the universe. Another aspect of Lewis's research uses the phenomenon of gravitational lensing to probe the nature and distribution of the pervasive dark matter, and employing individual stars to magnify the hearts of quasars, the most luminous objects in the universe. Closer to home, Lewis's research focuses upon galactic cannibalism, where small dwarf galaxies are torn apart by the much more massive Milky Way and Andromeda Galaxy. Using telescopes from around the world, including the 10-m Keck telescope in Hawaii, he has