Detection at t=0: looking at the beginning of time

Detection at t=0: looking at the very beginning of time, we saw the echoes of the Bang imprinted across the sky.

We’ve all heard the big news yesterday. Scientists spotted the gravitational ripples that left marks in the distribution of energy, which is strong evidence for inflation, but how did they do it?

Polarization means the electric vector of the photon oscillates in a specific direction. B-mode polarization is a pattern in the CMB radiation that can be broken into two components. One, a curl-free, gradient-only component, the E-mode, was first seen in 2002 by the Degree Angular Scale Interferometer (DASI). The second component is gradient-free, curl only, and is known as the B-mode. Cosmologists predict two types of B-modes, the first generated during cosmic inflation, and the second generated by gravitational lensing later, due to light encountering matter on its way. Gravitational waves squeeze space as they travel, and this squeezing produces a distinct pattern in the cosmic microwave background. GWs have a handedness or chirality, much like light waves, and can have left- and right-handed polarizations which makes them very recognizable.

"The swirly B-mode pattern is a unique signature of gravitational waves because of their handedness. This is the first direct image of gravitational waves across the primordial sky," said co-leader Chao-Lin Kuo (Stanford/SLAC).

Inflationary theory predicts the universe expanded exponentially around 10^-34 s after the Big Bang. This rapid expansion gives rise to high-amplitude gravitational waves due to quantum fluctuations that squeeze and expand space. Later on, photons scattering off matter become differently polarized as they travel through the cosmos, but this is not the original signal anymore. What was found is the first type of B-modes, consistent with inflation and gravitational waves in the early universe at the level of 2.7σ which means there’s only about a 2% chance that this detection will go away as more data is taken. So in a sense, this is a victory for the inflation theory, but also this makes it the farthest observation in time, to 10^-36 s after the Big Bang - almost to t = 0. We are almost looking at the birth of the universe. At this time, other than gravity all the other forces of nature (strong, weak and EM) are together. 

"Don't expect implications of BICEP for theory to be immediately clear. Sometimes we need time to think about the consequences of new data!" - Sean Carroll  

The news make Stephen Hawking to quickly claim the victory of a bet with Neil Turok, the director of the Perimeter Institute in Canada, that gravitational waves from the first fleeting moments after the big bang would be detected. Speaking on BBC Radio 4's Today programme, Hawking said the discovery of gravitational waves, announced on Monday by researchers at the Harvard-Smithsonian Centre for Astrophysics, disproves Turok's theory that the universe cycles endlessly from one big bang to another.

See more:

Starts with a Bang

Symmetry Magazine

B-Mode polarization

The announcement at the Harvard-Smithsonian Center for Astrophysics