The most widespread view of the origin of our Universe is that of the big explosion, commonly known as the Big Bang (BB). We have asked ourselves what happens right after, at the first instants of the universe… the most accepted view among cosmologists is that of an exponential expansion, called the inflation theory.
The BB theory results from doing a backward-in-time evolution to the universe’s expansion. If it is expanding as time moves forward, this implies the universe was smaller, denser and hotter in the distant past. The BB theory predicts that the early universe was much denser and extremely hot, about 273 million degrees above absolute zero, too hot for atoms to exist, only free electrons and hydrogen nuclei – protons and neutrons – where present. After cooling during the expansion, these nuclei and electrons combined to compose the first light atom, the Hydrogen (H). It is now known that hydrogen atoms fill space all over.
One of the signatures expected from this BB event that occurred about 13.7 billion years ago, is the radiation linked to the remains of heat from that period, the so called “cosmic microwave background (CMB)”, emitted only a few hundred thousand years after the Big Bang, much before cosmological structures such as stars or galaxies ever existed. The properties of the CMB radiation allow us to have a look into the conditions in the early universe on very large scales in space-time. BB theory predicts the spectrum of the CMB radiation to have a blackbody form, which was indeed measured with accuracy by the FIRAS experiment.
For the theory of inflation to be fully confirmed, the scientists expect the remaining of the ripples or gravitational waves occurring at the time of the BB event, to induce subtle swirls in the polarization of the CMB. But even with the most sophisticated experiments and devices, this has not been measured. It could be that these swirls are just too faint to be detected, so the model is not entirely discarded, but the absence of this confirmation can open the route to many other competing theories, such as the oscillating universe theory, where the BB was actually a bounce occurring after a contracting period.

Cosmologist Loeb and collaborators at Harvard have predicted an oscillatory pattern in the distribution of matter throughout the cosmos that, if detected, could distinguish between inflation and this oscillatory scenario. What happened right after the BB could gives us some hints on what happened before the BB, helping us elucidate the origin of the BB, which is a mystery by itself.


By: Ines Urdaneta