Physics and cosmology
1923 Edwin Hubble confirms the true nature of galaxies as independent star systems millions of light years beyond the Milky Way.
1929 Hubble establishes that the universe is expanding, and that galaxies move away from us more rapidly the farther away they are (the so-called “Hubble Flow.”)
1950s American astronomer George Abell compiles the first detailed catalogue of galaxy clusters. Subsequent studies of galaxy clusters have repeatedly confirmed the existence of dark matter.
1950s –present Various models of the Big Bang predict that it should have generated much more matter than that which is currently ...