What happened when the universe began 14 billion years ago is one of the biggest mysteries in physics. This is not easy to prove, because, in the early stages, the universe was full of dense plasma: a gas composed of charged particles containing electrons and protons (these particles together with neutrons form the nucleus). Photons (light particles) hit the mixture and bounce violently with other particles, unable to escape.
When the universe expands and the density is low enough, photons can finally escape and light starts to move freely. This event occurred 380,000 years after the Big Bang and was called “reorganization” and produced the first snapshot of the formation of the universe. Much of our understanding of the early universe is based on the radiation left over from the Big Bang. But recombination is like a wall: we cannot directly explore earlier eras with telescopes, because the light was captured at that time.
Several projects are now trying to understand the Big Bang with the help of gravitational waves (waves in the structure of space-time). Some new project aims to detect ultra-high frequency such waves and may lead to the discovery of new physics.
The gravitational waves recently discovered in the Ligo/Virgo experiment, the ripples in the structure of time-space, opened a new window for observing the universe. They enable us to study phenomena where gravity rather than light is the main factor. The gravitational waves discovered so far are called astrophysical gravitational waves: they are produced by relatively new physical processes, such as the merging of black holes.
The wave type that may have formed in the early universe is called cosmic gravitational wave, which has not been discovered yet. These waves propagate freely after they are formed; they act as a spirit to break the barriers of reorganization and provide unique tools for exploring the early universe. Astrophysics gravitational waves come from a certain direction, while cosmic waves come to us from all possible directions, corresponding to different regions where they originated in the past, so it is difficult to identify.
Using our currently available technology, we can even detect the smallest changes in the high-frequency range (although we have not captured any gravitational waves), but we still need to make some improvements to it to identify gravitational waves from the early universe. their project is to support the development of this technology.