21st-century American physicists

Donald Delbert Clayton (March 18, 1935 – January 3, 2024) was an American astrophysicist whose most visible achievement was the prediction from nucleosynthesis theory that supernovae are intensely radioactive. That earned Clayton the NASA Exceptional Scientific Achievement Medal (1992) for “theoretical astrophysics related to the formation of (chemical) elements in the explosions of stars and to the observable products of these explosions”. Supernovae thereafter became the most important stellar events in astronomy owing to their profoundly radioactive nature. Not only did Clayton discover radioactive nucleosynthesis during explosive silicon burning in stars but he also predicted a new type of astronomy based on it, namely the associated gamma-ray line radiation emitted by matter ejected from supernovae. That paper was selected as one of the fifty most influential papers in astronomy during the twentieth century for the Centennial Volume of the American Astronomical Society. He gathered support from influential astronomers and physicists for a new NASA budget item for a gamma-ray-observatory satellite, achieving successful funding for Compton Gamma Ray Observatory. With his focus on radioactive supernova gas Clayton discovered a new chemical pathway causing carbon dust to condense there by a process that is activated by the radioactivity.Clayton also authored a novel, The Joshua Factor (1985), a parable of the origin of mankind utilizing the mystery of solar neutrinos; a science autobiography and a memoir; and a history of the origin of each isotope, Handbook of Isotopes in the Cosmos (Cambridge Univ. Press, 2003).
Clayton died on January 3, 2024, at the age of 88.

Antony Garrett Lisi (born January 24, 1968), known as Garrett Lisi, is an American theoretical physicist. Lisi works as an independent researcher without an academic position.
Lisi is known for "An Exceptionally Simple Theory of Everything," an unpublished preprint paper proposing a unified field theory based on the E8 Lie group, combining particle physics with Einstein's theory of gravitation. The theory is incomplete and has unresolved problems. The theory has been extensively criticized in the scientific community.

Alvin Virgil Tollestrup (March 22, 1924 – February 9, 2020) was an American high-energy particle physicist best known for his key roles in the development of the superconducting magnets for Fermilab's Tevatron and the formation of CDF.

George Edward Alcorn Jr. (born March 22, 1940) is an American physicist, engineer, inventor, and professor. He taught at Howard University and the University of the District of Columbia, and worked primarily for IBM and NASA. He has over 30 inventions and 8 patents resulting in his induction into the National Inventors Hall of Fame in 2015.

Carl Henry Brans (; born December 13, 1935) is an American mathematical physicist best known for his research into the theoretical underpinnings of gravitation elucidated in his most widely publicized work, the Brans–Dicke theory.

John Gleason Cramer Jr. (born October 24, 1934) is a professor emeritus of physics at the University of Washington in Seattle, Washington, known for his development of the transactional interpretation of quantum mechanics. He has been an active participant with the STAR experiment at the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory, and the particle accelerator at CERN in Geneva, Switzerland.

Stanley Albert Schmidt (born March 7, 1944) is an American science fiction author and editor. Between 1978 and 2012 he served as editor of Analog Science Fiction and Fact magazine.

Richard Lawrence Garwin (born April 19, 1928) is an American physicist, best known as the author of the first hydrogen bomb design.In 1978, Garwin was elected a member of the National Academy of Engineering for contributing to the application of the latest scientific discoveries to innovative practical engineering applications contributing to national security and economic growth.

Leonard Emanuel Parker (born Leonard Pearlman; in 1938) is a distinguished professor emeritus of physics and a former director of the Center for Gravitation and Cosmology at the University of Wisconsin–Milwaukee. During the late 1960s, Parker established a new area of physics—quantum field theory in curved spacetime. Specifically, by applying the technique of Bogoliubov transformations to quantum field theory with a changing gravitational field, he discovered the physical mechanism now known as cosmological particle production. His breakthrough discovery has a surprising consequence: the expansion of the universe can create particles out of the vacuum.
His work inspired research by hundreds of physicists and has been cited in more than 2,000 research papers; it was credited in the memoirs of Soviet physicist Andrei Sakharov and helped Stephen Hawking discover the creation of particles by black holes.Along with David Toms of Newcastle University, Parker co-wrote a latest addition to graduate-level textbooks on quantum field theory in curved spacetime, entitled Quantum Field Theory in Curved Spacetime: Quantized Fields and Gravity (Cambridge University Press, 2009, ISBN 978-0-521-87787-9).
He received his PhD from Harvard University in 1967. His advisor was Sidney Coleman.