Important Discoveries in Cosmology
Six Who Probed the Cosmos

 ALBERT  EINSTEIN -  when: 1916
what he did: Introduced the "cosmological constant," a form of antigravity, 
                   to make general relativity agree with a cosmos that  seemed not to be expanding 

Person of the Century: Albert Einstein

 EDWIN  HUBBLE - when: 1927
what he did: Discovered that faraway galaxies all seem to be flying away from Earth, which suggested that the universe was in fact expanding. In doing so, Hubble gave Einstein scientific license to abandon the cosmological constant, whose creation the brilliant physicist dubbed the greatest blunder of his career. In retrospect, it was an inspired guess that could have won him another Nobel Prize

TIME 100: Astronomer Edwin Hubble

 FRITZ   ZWICKY  - when: 1936
what he did: Noted that the orbits of distant galaxies were impossible without the gravitational tug of some sort of "dark matter." The idea was ridiculed; now it is mainstream

Unofficial Zwicky Site: "Supernovae, an alpine climb and space travel."

what they did: Accidentally detected the leftover glow from the Big Bang — which astronomers 
                       are now deciphering to learn the composition and ultimate fate of the cosmos

Winning the Nobel Prize: 1978 Nobel Laureates in Physics

 ADAM  RIESS  - when: 1998-2001
what he did: Helped prove that Einstein was right in the first place: a mysterious antigravity force 
                     that acts like Einstein's cosmological constant is evidently quite real

Innovators — Science on the Edge: Adventures in Antigravity

Photos: Einstein by AP; Hubble photo courtesy of Palomar Observatory; Zwicky by BETTMAN—CORBIS; Penzias and Wilson by TED THAI FOR TIME; Riess by JONATHAN SAUNDERS FOR TIME