Gravitational waves, not inflation, possibly caused the birth of galaxies

Scientists believe that in the very early universe, everything was incredibly tiny, chaotic, and full of random energy ripples, known as quantum foam.

It was a state where spacetime was unstable, and fundamental particles were continually appearing and disappearing in an extreme, high-energy environment.

Then, during a brief but dramatic period called inflation, the universe expanded at an extraordinary speed, stretching those tiny ripples into larger patterns. Some estimates suggest during inflation the universe grew by 10⁶⁰ times, and that too within a second.

Over billions of years, these stretched ripples grew into clumps of matter, forming the first stars and galaxies. Eventually, they created a massive network of galaxies and dark matter called the cosmic web, which spans the entire universe today.

A new study suggests that the cosmic web could have formed without relying on inflation driven by a scalar field. Instead, it proposes a novel mechanism that suggests that inflation arises from gravitational wave amplification.

The many problems with inflation theory

Inflation is believed to have laid the foundation of everything there is out in space. However, nobody knows when it happened, why it happened, or what caused it. Plus, scientists don’t have any solid evidence to confirm whether it happened.

There is an endless number of questions that the inflation theory doesn’t answer. This is why scientists have also been exploring other potential events or factors that could have led to the formation of the cosmic web.

The study authors have developed a mathematical model that suggests that quantum foam itself released gravitational waves that kept on spreading and amplifying over time. Their activity resulted in the creation of patterns in space that eventually shaped the cosmic universe.

Inflation triggered by gravitational waves

In the newly proposed model, inflation is believed to have been caused by a de Sitter space-time, where gravitational waves naturally come from quantum vacuum fluctuations and matter fluctuations are created through secondary effects of these gravitational waves. A de Sitter space describes an expanding universe with no matter (like galaxies or stars).

The researchers also explain how this gravitational wave-driven inflation might have ended. They suggest that as gravitational waves continued to amplify and collide, this led to conditions where small disturbances in space (scalar perturbations) become much larger than gravitational waves.

Then possibly a phase came when radiations dominated space, limiting the activity of gravitational waves and therefore bringing an end to inflation.

“We derive the necessary conditions under which scalar perturbations become significant and much larger than the tensor modes, and we identify a natural mechanism to end inflation via a transition to a radiation-dominated phase,” the study authors note.

Without a doubt, this alternative model is intriguing, but further research is needed to gather more evidence in its favor. Hopefully, future research works will shed more light on this strange possibility of inflation without inflation.

The study is published in the journal arXiv.