On March 17, a team of astrophysicists announced the physics of what happened in the first one trillionth, of a trillionth of a trillionth of a second after the so-called Big Bang. The American team – also known as BICEP2 – announced these findings of what the science community calls the detection of primordial gravitational waves. As scientists rush to confirm these findings – this would be one of greatest discoveries of the century!
The research team working on BICEP2 has found the signal left in the sky by what may seem as the extreme rapid expansion of space that occurred in the initial infinitesimal fractions of a second after everything came into being. It is the oldest light detectable with telescopes. And the light contains distinct twists or to be more precise - polarization. The BICEP2 telescope is located in the South Pole and this detection of polarized light provides a marker for what physicists call “inflation,” which is that exponential growth spurt in the cosmos in that initial fraction of a second. This discovery is said to be the “proof” of the cosmic inflation that occurred from virtually nothing to the point when the universe was approximately the size of a marble. For the next almost 14 billion years, the universe has continued to expand.
Inflation was first proposed in the early 1980s as an explanation for why the temperature of deep space is the same from any side to one part in one hundred thousands; a suggestion that the extreme expansion created a lack of unevenness to the universe. However, the biggest piece of data inflation brings to the table is that it produces primordial gravitational waves – as theorized by Albert Einstein. These waves, in theory, would leave unique impressions on the oldest light in the universe by polarizing it – which BICEP2 has now discovered.
String gas cosmology, which is based on application of thermodynamics of closed strings in the very early universe, however, offers an alternative component to these inflationary models now “proven” by astrophysicists with the BICEP2 project. It was eight years ago that I along with fellow theoretical physicists predicted the same feature of gravitational waves from the early universe in the framework of string theory.
We predicted that the spectral index of tensor modes (gravitational waves) power spectrum from the early universe should be tilted blue which inflationary models predicted otherwise (zero or with red tilt).Essentially, the power spectrum is a plot of the amount of fluctuation against the angular (or linear) size. These fluctuations are the difference in the two measurements at the corresponding points and in general, they can be the fluctuations of temperature or density or any other kind of measurable quantity.
Spectral index of a source is a measure of the dependence of the power spectrum on frequency. While blue tilts suggests more noises on high frequencies, red tilt suggests more noises on low frequencies. This is like listening to different radio stations with a nondigital radio: As you turn the radio nub to go from one radio station to another one, you may hear noises. If you don’t hear any noises by going to higher or lower frequencies radio stations then that means the power spectrum of these sources has no tilt, otherwise the power spectrum is tilted blue or red depending on one would hear more noises on high or low frequencies receptively.
Over all, it seems its too soon to claim that cosmic inflation as a confirmed theory. What we hope the BICEP2 project scientists will further investigate is the tilt of the polarization of these oldest light waves that have been discovered. It is only then, one can claim the victory of one cosmic theory over the other one!