Christopher Isham  Christopher Isham (; born 28 April 1944), usually cited as Chris J. Isham, is a theoretical physicist at Imperial College London. Isham's main research interests are quantum gravity and foundational studies in quantum theory. He was the inventor of an approach to temporal quantum logic called the HPO formalism, and has worked on loop quantum gravity and quantum geometrodynamics. Together with other physicists, such as John Baez, Isham is known as a proponent of the utility of category theory in theoretical physics. In recent years, since at least 1997, he has been working on a new approach to quantum theory based on topos theory. Isham has appeared in several "NOVA" television programmes as well as a film about Stephen Hawking. Physicist Paul Davies has described Isham as "Britain's greatest quantum gravity expert." As a practising Christian, Isham has also written about the relationships among philosophy, theology, and physics.