Monday, 5 November 2012
Galaxies could give glimpse of the instant time began
Relativity describes gravity as a curve in the geometry of space and time. This mostly works, but quails at the quantum scale of the very start of the big bang, when everything was infinitely dense.
Enter loop quantum gravity theory, which says space-time is underpinned by a network of loops in which no distance can be smaller than 10-35 metres, a unit known as the Planck length. This banishes infinite densities. The theory also implies that the universe was born in a big bounce, not a big bang, due to the collapse of a previous universe.
Now Abhay Ashtekar, Ivan Agullo and William Nelson of Penn State University in University Park have used loop quantum gravity to examine what structures would emerge as the universe bounced into being.
This time-zero era is not covered by conventional cosmology, which says that galaxies and galaxy clusters originated during inflation, an expansion that began about 10-36 seconds into the universe's existence. As space expanded, the theory goes, it stretched quantum variations in the energy field driving inflation, leading to regions of high density matter, which went on to seed galaxies and larger structures.
However, the team says that the energy field should have existed in a weak form before inflation, at the very start of time in our universe.
Fluctuations would have arisen in that first quantum instant, which is set at 10-44 seconds. These would have survived inflation, and the spectrum of sizes of the galaxies and galaxy clusters that they led to would match data from galaxy surveys and the cosmic microwave background – relic radiation from the big bang/bounce.
"Perturbations could be generated during the bounce," agrees Neil Turok of the Perimeter Institute for Theoretical Physics in Waterloo, Ontario, Canada, but he doubts some of the team's other assumptions.
Although the new hypothesis makes similar predictions to conventional cosmology, the tight curve of space-time at the moment of the bounce could distort some fluctuations in a way that would show up in the cosmic microwave background and in the positions of galaxies.
We would have to be lucky though. The value of the original energy field is unknown, and for most of the possibilities there would be no discernible distortion. But if the field has just the right strength, and the distortion shows up, it would suggest that the big bounce and loopy space-time are real – and provide a glimpse of the earliest possible instant of time. "It would tell us the conditions of the quantum universe at its birth," says Ashtekar.