March 17, 2014
A great Discovery! By finding small spiral patterns in the Cosmic Microwave Background (CMB), scientists have proven the existence of gravitational waves and 35 years after it has been theorised, the inflation of the early universe. This marks a tremendous step toward understanding the universe and probably the earliest point in past that we will ever get to study.
Universe, from the Big Bang and cosmic inflation to what it is today, its growth accelerated by dark energy. Credit: NASA/WMAP
In 1980, Alan Guth predicted that a small fraction of a second after the Big Bang, the universe began to grow at an enormous rate, faster than the speed of light. This is known as the cosmic inflation. Ever since it was theorised, the evidence for inflation has been expected to be found in the Cosmic Microwave Background (CMB) radiation.
The CMB is a remnant radiation originating from early ages of our universe. For the first 380,000 years, the universe was extremely hot and dense, which prevented photons to travel freely. It is counter-intuitive that something so hot doesn't glow, but that's exactly what happened. Only after the universe expanded enough to cool down did the light "escape". Now, we see this radiation as the CMB across the whole sky.
Today, a team led by John M. Kovac of the Harvard-Smithsonian Center for Astrophysics in Cambridge, USA, announced they have found the evidence of gravitational waves in the CMB. The team analysed data from the Background Imaging of Cosmic Extragalactic Polarization (BICEP2) telescope for almost three years before publishing it in The Astrophysical Journal. With the discovery of this magnitude, the team wanted to make sure they really had their facts right while at the same time fearing one of the many competing teams would beat them to the discovery.
"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 Kovac.
CMB is divided, or polarised, into two patterns, meaning that microwaves had a preference to vibrate in one direction more than another. This polarisation was theorised to have been caused by gravitational waves that were created during the cosmic inflation. As gravitational waves travelled through the space, they stretched it in one direction and squeezed in another, so when microwaves travelled through that space, the direction of their polarisation got twisted.
One of these two patterns caused by gravitational waves is called B-mode or curl-mode, characterised by spirals. By finding the B-mode pattern, physicists have proven that gravitational waves exist and this in turn proves they were created during the theorised period of rapid inflation.
B-mode pattern in the polarisation of the CMB, caused by gravitational waves. Credit: CfA/BICEP2
As a theory, cosmic inflation is used to describe why is the CMB, with the exception of tiny variations in temperature, mostly uniform across the entire sky.
The BICEP2 is a detector that's based at the South Pole, where the thin, dry air provides excellent conditions for measuring small differences in temperature of the CMB that led to discovering spirals mentioned above.
Measure of the swirliness of the polarisation – the ratio of the gravitational wave fluctuations in the CMB to the fluctuations caused by perturbations in the density of matter – called parameter r, was not expected to be higher than 0.11, yet the BICEP2 measured it to be 0.20. Higher r value indicates that inflation took place even earlier than some models predicted, one trillionth of a trillionth of a trillionth of a second after the Big Bang, which in turn means the universe had even higher energies than thought.
If BICEP2 measurement of r is correct, this would mean that energy
levels during the inflation were high enough for strong interaction,
weak interaction and electromagnetism to be one force of nature. This is
predicted by the Grand Unified Theory, which some models of inflation
omitted, since they don't include such an energy scale.
The discovery is yet to be confirmed by other teams, but if it gets confirmation, it will be one worth of the Nobel prize.
"I'm sure there will be lots of discussion about galactic foregrounds and whether they could possibly be fooling us, be totally different than we'd expected," said Kovac. "But our paper goes into some detail on using all the best available models for what galactic foregrounds ought to look like, and why what we see doesn't look like that."