STRENGTH OF GRAVITY HAS REMAINED CONSTANT FOR BILLIONS OF YEARS

Remains of a Type Ia supernovae (G299.2-2.9). Image Credit: X-ray: NASA/CXC/U.Texas/S. Park et al, ROSAT; Infrared: 2MASS/UMass/IPAC-Caltech/NASA/NSF.

byANDY FLEMING

Australian astronomers have combined all observations of supernovae ever made to determine that the strength of gravity has remained unchanged over the last nine billion years.

Newton's gravitational constant, known as G, describes the attractive force between two objects, together with the separation between them and their masses. It has been previously suggested that G could have been slowly changing over the 13.8 billion years since the Big Bang.

If G has been decreasing over time, this would mean that Earth's distance to the Sun was slightly larger in the past, meaning that we would experience longer seasons now compared to much earlier points in Earth's history.

But researchers at Swinburne University of Technology in Melbourne have now analysed the light given off by 580 supernova explosions in the nearby and far Universe and have shown that the strength of gravity has not changed.

A DISCOVERY WITH PROFOUND GRAVITY

The 10-meter South Pole Telescope and the BICEP (Background Imaging of Cosmic Extragalactic Polarisation) Telescope are shown against the Milky Way. BICEP2 recently detected gravitational waves in the cosmic microwave background, a discovery that supports the cosmic inflation theory of how the universe began. (Image credit: Keith Vanderlinde, National Science Foundation)

Approximately fourteen billion years ago, our universe burst into existence in an extraordinary event that initiated the Big Bang. In an infinitesimally small fraction of a second, the universe expanded exponentially to a truly gargantuan size, inflating far in excess of the views of our most powerful telescopes. All this, of course, was just a theory.

Astronomers from the Background Imaging of Cosmic Extragalactic Polarisation (BICEP2) radio telescope at the South Pole have announced the first direct evidence for this cosmic inflation. Their data also represent the first images of gravitational waves, or ripples in space-time, a major prediction of Einstein’s 1915 Theory of General Relativity, in effect his theory of gravity. They have been described as the "first tremors of the Big Bang." Finally, the data confirm a deep connection between the (until now) irreconcilable pillars of modern physics: quantum mechanics and general relativity itself.

"Detecting this signal is one of the most important goals in cosmology today. A lot of work by a lot of people has led up to this point," said John Kovac (Harvard-Smithsonian Centre for Astrophysics), leader of the BICEP2 collaboration.

These ground-breaking results came from observations by the BICEP2 telescope of the cosmic microwave background - a faint glow left over from the Big Bang. Tiny fluctuations in this afterglow provide clues to conditions in the early universe. For example, small differences in temperature across the sky show where parts of the universe were denser, eventually condensing into became polarized too.