Talbert indicated the rationale for the intensified interest in gravity control propulsion research had stemmed from the works of three physicists. They were Bryce DeWitt 's prize-winning Gravity Research Foundation essay; the book Gravity and the Universe by Pascual Jordan ; and presentations to the International Astronautical Federation by Dr. Burkhard Heim. DeWitt's essay discouraged the pursuit of materials that shield, reflect, and/or insulate gravity and emphasized the need to encourage young physicists to pursue gravitational research. He opened his essay with the following paragraph: