1609, Galileo
Improving on earlier telescope designs, Galileo discovers Jupiter's four largest moons and sunspots, helping overturn the Earthcentric view of the universe.
1687, Gravity
Sir Isaac Newton publishes his theory of universal gravitation and the laws of motion in his seminal book, "Philosophiae Naturalis Principia Mathematica."
1921, E=mc2
Albert Einstein receives the Nobel Prize for his general theory of relativity, which explained the notion of a space-time continuum.
1927, Bang
Georges Lemaître proposes a model of the universe's birth, which later attracts the derogatory nickname "big-bang theory."
1929, Hubble
Astronomer Edwin Hubble observes that galaxies beyond our own Milky Way are actually moving away from each other at terrific speed.
1929, Cyclotron
Ernest Lawrence builds the first particle accelerator, which is only 10cm in diameter.
1931, Radio Waves
Working for Bell Labs, Karl Guthe Jansky discovers that there are cosmic radio waves emanating from beyond our solar system, after constructing a radio telescope to identify the static interfering with radiotelephone service.
1945, the Atomic Bomb
The first nuclear weapons, created by a team of physicists working for the United States, are detonated over Hiroshima and Nagasaki.
1981, The Big Expansion
Alan Guth proposes that the expansion of the universe after the big bang was due to a repulsive gravitational force.
1988, Best Seller
Having discovered Hawking radiation in black holes, among other scientific works, Stephen Hawking publishes "A Brief History of Time," his first book for a mainstream audience.
1993, Tunnel to Nowhere
After spending $2 billion, the U.S. Congress pulls the plug on the Superconducting Supercollider in Waxahachie, Texas.