For decades, scientists have relied on a popular idea called cosmic inflation to explain how the universe began and why it looks like it does today. This theory suggests that the universe expanded at an unimaginable speed just moments after the Big Bang. Despite its popularity, it still faces the problem that no one knows for sure what caused it. Explanations have been proposed, but none have been proven. This led a team of researchers to search for a fundamental way to explain the origins of the universe, leading them to propose an intriguing idea: gravitational waves might just hold the key to better understanding the Big Bang.
The research was published in July 2025 in the Physical Review Journal of the American Physical Society under the title “Inflation without inflaton.” He assembled a team of four scientists whose goal was to propose a new model of the Big Bang theory that could help explain the origins of the universe. They wanted to create a model that didn’t rely on a mysterious inflation particle as the source of the universe’s expansion.
The team proposed that tiny ripples in space-time itself, known as gravitational waves, naturally produced the fluctuations that would later become galaxies and stars. Their calculations show that this process could match what astronomers actually observe, while providing a smooth way for the universe to transition from rapidly expanding to the radiation-filled cosmos we know today. In short, this model could explain inflation without the need for new hypothetical particles.
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How was this new model born?
A galaxy full of stars in space – Triff/Shutterstock
First, researchers turned to quantum physics instead of relying on traditional cosmological models. They examined how tiny ripples in space-time, called gravitational waves, could naturally give rise to density fluctuations. Their model showed that these ripples can appear as a second-order effect of gravitational waves, eventually becoming dominant and shaping the structure of the universe – the stars, galaxies and everything else we see in the night sky. They also studied the inherent instability of the early universe – which could be twice as old as we initially thought – demonstrating that this instability could provide a natural way to end inflation and allow the universe to transition to the radiation-filled state we see today.
Daniele Bertacca, one of the study’s researchers and a professor at the University of Padua, told Space.com: “Too much flexibility in science can be problematic because it makes it difficult to determine whether a model actually predicts something or simply adapts a posteriori to the observed data. » Referring to the advantage of a theory based on gravitational waves rather than a mysterious swelling (a hypothetical particle created by scientists to explain inflation), Bertacca also said: “It is precisely the elegance and simplicity of the proposed model, as well as the absence of free parameters, that are essential. »
What this means for future Big Bang models
artistic image of the solar system with the sun, Earth and planets – Rbkomar/Getty Images
The researchers note that this model, focused on the ripples in space-time that created the beginnings of galaxies and cosmic structure, could still apply today depending on the behavior of our universe. The team wants to see if more observations and future studies further confirm this new model. If they do, it could revolutionize the way we understand the Big Bang theory and the origin of the universe.
The leader of this study, Raúl Jiménez of the University of Barcelona, stressed to Space.com that it is a deep understanding of gravity and quantum physics that motivates the theory and could move it forward. Jiménez emphasized that without taking into account inflation, the new proposed model is minimalist and clear. It provides a solid framework that can then be used for further testing and future predictions.
Daniele Bertacca also said that the theory is good for the field of cosmology as a whole: “Like all theoretical models, ours must be confirmed by measurements and observations that researchers can analyze, evaluate and compare with data from ground and space experiments today and in the near future… These gravitational ripples interact and create complexity over time, leading to testable predictions that researchers can now compare with real data. »
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Read the original article on BGR.
