Einstein's theory of general relativity was proposed over 100 years ago and has successfully passed a large number of observational tests in the weak field regime. However, the strong field regime is largely unexplored, and there are many modified and alternative theories that have the same predictions as Einstein's gravity for weak fields and present deviations when gravity becomes strong. X-ray reflection spectroscopy is becoming a powerful tool for testing the strong gravity region around astrophysical black holes with electromagnetic radiation.

BIO：Cosimo Bambi is currently Xie Xide Junior Chair Professor at the Department of Physics at Fudan University (Shanghai, China) and a Humboldt Fellow at Eberhard Karls Universität Tübingen (Tübingen, Germany). He received the Laurea Degree from Florence University in 2003 and the Doctoral Degree from Ferrara University in 2007. He was appointed as a postdoctoral research fellow at Wayne State University (Michigan) in 2007-2008, at IPMU at The University of Tokyo (Japan) in 2008-2011, and at Ludwig-Maximilians-Universität München (Germany) in 2011-2012. At the end of 2012, he moved to Fudan University as a faculty member under the Thousand Young Talents Program. He has published over 100 papers as first or corresponding author in high impact factor journals and has over 3,000 citations. His h-index is 34 (INSPIRE). He is authors/editors of a few books with Springer, including "Black Holes: A Laboratory for Testing Strong Gravity" (Springer Singapore 2017), "Introduction to Particle Cosmology" (Springer-Verlag 2016), "Astrophysics of Black Holes: From Fundamental Aspects to Latest Developments" (Springer-Verlag 2016).