A century of an idea

How the idea grew

This type of universe was proposed by Aleksandr Friedmann and Georges Lemaitre in the 1920s. The modern version was developed by George Gamow and colleagues in the 1940s. Britannica

The detection of extragalactic redshift by Vesto Slipher, Britannica says, led to the realization in the 1920s that all galaxies are receding. Britannica Edwin Hubble correlated these observations in mathematical form to provide evidence that the universe is expanding. Britannica

Beginning in 1948, George Gamow, Ralph Alpher and Robert Herman investigated the idea that the chemical elements might have been synthesized in a primeval fireball, and calculated that the leftover radiation temperature would have dropped to about 5 kelvins. Britannica

The actual discovery occurred by accident. Arno Penzias and Robert Wilson, of Bell Telephone Laboratories, Holmdel, New Jersey, measured excess radio noise that seemed to come from the sky in every direction, in experiments connected with the first Telstar communication satellite. Britannica The two groups published simultaneously in 1965 papers detailing the prediction and discovery of a universal thermal radiation field with a temperature of about 3 K. Britannica

This remnant is the cosmic microwave background radiation — the “three degree” (actually 2.728 K) background radiation — discovered in 1965 by Arno A. Penzias and Robert W. Wilson. Britannica

Precise measurements made by the COBE satellite launched in 1989 determined the spectrum to be exactly characteristic of a blackbody at 2.735 K. Britannica In 1992, NASA's COBE satellite discovered these tiny temperature differences on large angular scales. WMAP measured anisotropy with much finer detail and greater sensitivity than COBE did. NASA

Mather shares the 2006 Nobel Prize for Physics with George F. Smoot for their work using the COBE satellite to measure the heat radiation from the Big Bang. NASA

The WMAP mission launched on 30 June 2001. It was renamed after team member David T. Wilkinson. It ended the collection of science data on 19 August 2010. NASA

It was mapped with satellites NASA and ESA built: COBE, WMAP and Planck. The universe at that point was extremely smooth, with only tiny ripples in temperature. NASA