Scientific puzzles don’t come much bigger than these. How old is the Universe? How big is it? And what is its ultimate fate?
A single number, Hubble’s constant, is the key that can unlock all of those questions, but it’s a number that has proved notoriously hard to accurately measure. Hubble’s constant is the rate at which the Universe is expanding. The first team to accurately make that measurement was co-led by Jeremy Mould, now a professor at Swinburne University of Technology and professorial fellow at the University of Melbourne.
Instrumental to the team’s success was the launch in 1990 of the Hubble Space Telescope (HST). Mould and his colleagues used the HST to carefully measure the distances to 800 pulsing stars called Cepheids in 18 distant galaxies, and from this to refine models of cosmic distance measurement. They could then gauge how long the Universe has been expanding since the Big Bang. Their answer, 13 to 14 billion years, tallies well with estimates of the age of the oldest stars.
For this trailblazing work, the three team leaders—Jeremy, plus Wendy Freedman from the Carnegie Institution of Washington in Pasadena, US, and Robert Kennicutt from the University of Cambridge, UK—were jointly awarded the Gruber Prize for Cosmology in 2009.
“What the Hubble constant also does is to tell us the expansion rate of the Universe—which is accelerating,” says Jeremy. “This controls the future evolution of the Universe.”
Mould is not the first Australian winner of the Gruber Prize for Cosmology. In 2007 the Australian National University’s Brian Schmidt was jointly awarded the prize for a related discovery that showed that the expansion of the Universe is currently accelerating. Schmidt went on to win the Nobel Prize for Physics in 2011 together with Saul Perlmutter and Adam Riess.