Posted: 18 December, 2008
A question that has been pondered by scientists and philosophers alike could soon be answered, thanks to a mathematical model that explains an anomaly in the early Universe.
WMAP’s all-sky picture of the infant Universe reveals 13.7 billion year old temperature fluctuations (shown as colour differences) that correspond to the seeds that grew to become the galaxies. These variations are 'lop-sided' suggesting asymmetric density variations. Image: NASA / WMAP Science Team.
The notion of space expanding exponentially from a blank canvas in the instant following the so-called Big Bang is known as inflation, and the simplest interpretation of the theory requires the Universe to be uniform in all directions. The energy that permeated the Universe 400,000 years after the Big Bang – essentially an ‘echo’ from the Big Bang – is known as the Cosmic Microwave Background, or CMB, and was mapped in detail by NASA’s Wilkinson Microwave Anisotropy Probe (WMAP), revealing that tiny fluctuations in the CMB seemed to be the same everywhere, fitting with the theory of inflation.
"If your eyes measured radio frequency, you'd see the entire sky glowing. This is what WMAP sees," describes Kamionkowksi. WMAP depicts the CMB as an afterglow of light that has decayed to microwave radiation as the Universe expanded over the past 13.7 billion years.
The problem with inflation, however, is that it predicts the Universe began uniformly, and earlier this year a detailed study suggested that there is in fact a pronounced asymmetry in the CMB, with intensely varied deviations from the average value in one half of the sky than the other. "It's a certified anomaly," remarks Kamionkowski. "But since inflation seems to do so well with everything else, it seems premature to discard the theory."
A representation of the evolution of the Universe over 13.7 billion years. The far left depicts the earliest moment we can now probe, when a period of inflation produced a burst of exponential growth in the Universe. Image: NASA/WMAP Science Team.
The team are now trying to address the remarkable asymmetry within the bounds of inflation. They began 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 by changing the mean value of the inflation, the mean temperature and amplitude of energy variations in space also changed, violating constraints to the homogeneity of the Universe.
So they explored a second energy field, called the curvaton, which has already been proposed to give rise to the density fluctuations observed in the CMB. The team introduced a perturbation to the curvaton field that turns out to affect only how temperature varies from point to point through space, while preserving its average value. This new model suggests more cold than hot spots in the CMB, a predication that will be tested by ESA’s Planck satellite that is scheduled to launch in April 2009.
"Inflation is a description of how the Universe expanded," says Adrienne Erickcek, a graduate student working on the project. "Its predictions have been verified, but what drove it and how long did it last? This is a way to look at what happened during inflation, which has a lot of blanks waiting to be filled in."
Furthermore, the theoretical perturbation that the researchers introduced to the model may also offer the first glimpse at what came before the Big Bang, because it could represent an imprint inherited from the time before inflation. That is, it could be a signature of a structure left over from something that produced our Universe. Perhaps an older universe from which our own Universe was born could explain this anomaly, or could it be due to concurrently existing universes – a Multiverse – in which there are big bangs occurring at different points in the Universe at different times, generating a number of separate universes within our Multiverse?
"All of that stuff is hidden by a veil, observationally," says Kamionkowski. "If our model holds up, we may have a chance to see beyond this veil."
With the launch of Planck not far off we may not have too long to wait for the answers to the questions posed by Kamionkowski and others, and of the nature of how our Universe came to be. The study appears in the 16 December edition of the journal Physical Review D.