In 1940 physical chemist Philip Abelson and physicist Edwin McMillan discovered neptunium, the first transuranic (heavier than uranium) element.

During the 1940s physicist Arthur Compton, winner of the 1927 Nobel Prize for physics for his discovery of the dual nature of electromagnetic radiation, directed research for the Manhattan Project, setting up the Metallurgical Laboratory at the University of Chicago in 1942.

Molecular biologists Max Delbruck and Salvador Luria collaborated in 1940 to show the dynamics of bacterial mutations. In 1945 Delbruck demonstrated that the bacteriophage (a virus that infects and sometimes destroys bacteria) can reproduce sexually.

In 1949 biologists John Enders, Thomas Weller, and Frederick Robbins cultivated poliovirus in vitro (that is, outside the human body) on human embryonic tissue.

In 1940 physicists Richard Feyman, Julian Schwinger, and Sin-Itiro Tomonaga began development of the modern theory of quantum electrodynamics; their work continued until 1950.

In 1947 physiologists Ralph Gerard, Judith Graham...