After the Big Bang: Image shows the changing rate of expansion of the universe since the Big Bang 13.7 billion years ago. A new study may offer the first clues of what happened prior to the Big Bang.

Credit: NASA

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SYDNEY: The Big Bang is thought to have obliterated all trace of what came before. But astrophysicists now believe that interpreting an imprint from the earliest stages of the universe may provide some clues.

"It's no longer completely crazy to ask what happened before the Big Bang," said Marc Kamionkowski, of the California University of Technology in the USA.

Kamionkowski led a team who have proposed a mathematical model explaining an anomaly in what is supposed to be a universe of uniformly distributed radiation and matter. The study is detailed in the journal Physical Review D.

Exponential expansion

The investigators looked at a phenomenon called inflation, first proposed in 1980, which posits that space expanded exponentially in the instant following the Big Bang.

"Inflation starts the universe with a blank slate," explained graduate student and team member Adrienne Erickcek. The hiccup in inflation, however, is that the universe is not as uniform as the simplest form of the theory predicts it to be. Some parts of it are more variable than others.

Until recently, measurements of the cosmic microwave background (CMB) radiation (a form of electromagnetic radiation that permeated the universe 400,000 years after the Big Bang) were consistent with inflation; miniscule fluctuations in the CMB seemed to be the same everywhere.

But a few years ago, researchers including Krzysztof Gorski of NASA's Jet Propulsion Laboratory, in Pasadena, California, scrutinised data from the U.S. space agency's Wilkinson Microwave Anisotropy Probe (WMAP). They discovered that the amplitude of fluctuations in the CMB is not the same in all directions.

Inflaton and curvaton

"If your eyes measured radio frequency, you'd see the entire sky glowing. This is what WMAP sees," said Kamionkowksi. WMAP depicts the CMB as an afterglow of light from shortly after the Big Bang, which has decayed to microwave radiation as the universe expanded over the past 13.7 billion years.

The probe has also revealed more pronounced mottling – deviations from the average value – in the CMB in one half of the sky than the other.

"It's a certified anomaly," said Kamionkowski. "But since inflation seems to do so well with everything else, it seems premature to discard the theory." Instead, the team looked at the maths behind the hypothesis.

They started by testing whether the value of a single energy field thought to have driven inflation, called the 'inflaton', was different on one side of the universe than the other. But this appears not to have been the case – they found that if they changed the mean value of the inflaton, then the mean temperature and amplitude of energy variations in space also changed.