Einstein's General Relativity says gravity is a manifestation of dynamic spacetime. There are, however, hints—particularly from string theory—that spacetime may be an emergent concept, analogous to fluids arising from large collections of molecules at macroscopic scales.
Entanglement, which describes intrinsic quantum correlations without classical counterparts, was recognized early by Einstein, Podolsky, Rosen, and Schrödinger in the 1930s, but its significance in quantum many-body systems only gained prominence since the 2000s. Concurrently, von Neumann's work in the late 1920s and early 1930s on the mathematical foundations of quantum mechanics led to the development of operator algebras (now called von Neumann algebras), which have found wide applications in mathematics, but not so much in physics.
These three seemingly disparate subjects—emergence of spacetime, entanglement, and von Neumann algebras—are now understood to be intricately connected, providing new languages and powerful tools for characterizing the emergence of spacetime.
Hong Liu is a theoretical physicist at Massachusetts Institute of Technology. His research areas include string theory, quantum gravity, nuclear physics and condensed matter physics.
His research has helped establish and foster surprising interconnections among gravity, nuclear physics, and condensed matter physics. He was among the first to use string theory methods to study properties of the quark-gluon plasma created at Brookhaven National Laboratory (his papers on this subject were rated top achievements in 2007 by the APS News), and was among the first to point out possible deep connections between black hole physics and the strange metal phase of high temperature superconductors. He also uncovered new understanding of superfluid turbulence, and developed new approaches for studying quantum chaos. In 2015, he presented a complete formulation of fluctuating hydrodynamics, solving this long-standing problem. Recently, he introduced a new approach to understanding the emergence of spacetime in quantum gravity using operator algebras.
Hong Liu received his B.S. in 1993 from the University of Science and Technology of China and his Ph.D. in 1997 from Case Western Reserve University. He was a postdoctoral fellow at Imperial College and New High Energy Theory Center of Rutgers University, before joining the faculty of MIT in 2003. He was an Alfred Sloan Fellow, an Outstanding Junior Investigator of the Department of Energy, a Simons Fellow, a Guggenheim Fellow, and is a Fellow of the American Physical Society.