Adam Riess of Johns Hopkins University is one of three researchers just awarded the Nobel Prize for Physics for their part in the discovery that the expansion of the universe is accelerating. In 2009, Gregg Easterbrook of The Atlantic interviewed Riess about his work on galactic expansion. Here Easterbrook looks back on that meeting.
In the 1920s, Edwin Hubble showed that the universe, thought since the Greeks to be changeless, instead is expanding. But at what rate? Some theoreticians predicted the expansion, driven by the momentum of the Big Bang, should be slowing. Eventually the galaxies would either stop their outward travel and the cosmos become static, or gravity would pull everything back together for a Big Crunch. Other theoreticians felt cosmic expansion would continue at a steady pace essentially forever. Since the galaxies must long ago have overcome the gravity of the Big Bang in order to be rushing outward, this reasoning went, they'll simply keep going.
Numerous attempts were made to measure the movements of distant galaxies, in order to estimate whether the expansion is steady or slowing. In the mid-1990s, a team led by Adam Riess of Johns Hopkins employed images of very distant supernovae to derive what was considered the most accurate measurement to date of cosmic speed. The researchers reviewed their data many times, always coming to the same vexing conclusion: the expansion of the universe is speeding up.
Riess and his associates found that for the last 7 billion years or so -- roughly the halfway point of the apparent lifetime of the cosmos - galactic expansion has been gaining speed. This would be possible only if something is pushing the galaxies, adding energy to them. So Riess posited "dark energy," a force that is real but eludes detection.
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