A team of scientists led by expert Raúl Jiménez, ICREA researcher at the University of Barcelona's Institute of Cosmos Sciences (ICCUB), in collaboration with the University of Padua (Italy), has presented a revolutionary theory about the origins of the Universe. The study, published in the journal Physical Review Research, introduces a radical change in the understanding of the first moments after the Big Bang, without relying on the speculative assumptions that physicists have traditionally assumed.
Unravelling the mystery of the origins of the Universe
For decades, cosmologists have worked under the inflationary paradigm, a model that suggests that the Universe expanded extremely rapidly, in a fraction of a second, thus paving the way for everything we observe today. But this model includes too many adjustable parameters-the free parameters-which can be modified. Scientifically, this poses a problem, as it makes it difficult to know whether a model is truly predicting or simply adapting to the data.
In a significant breakthrough, the team has proposed a model in which the early Universe does not require any of these arbitrary parameters. Instead, it begins with a well-established cosmic state called De Sitter space, which is consistent with current observations of dark energy.
Gravitational waves: the key to understanding cosmic structure
The new model does not rely on hypothetical fields or particles such as inflation. It suggests that natural quantum fluctuations in space-time, gravitational waves, were sufficient to seed the small density differences that eventually gave rise to galaxies, stars, and planets. These ripples evolve non-linearly, interacting and generating complexity over time, allowing for verifiable predictions with real data.
"For decades, we have tried to understand the early moments of the Universe using models based on elements we have never observed", says Raúl Jiménez. "What makes this proposal exciting is its simplicity and verifiability. We are not adding speculative elements, but rather demonstrating that gravity and quantum mechanics may be sufficient to explain how the structure of the cosmos came into being".
Understanding the origin of the Universe is not just a philosophical question, but helps us answer fundamental questions about who we are and where we come from. This new proposal offers a minimalist but powerful, elegant and potentially refutable vision. This is science at its best: clear predictions that future observations-such as measurements of gravitational waves and cosmic structure-can confirm or reject.
These new results suggest that we may not need speculative elements to explain the cosmos, but only a deep understanding of gravity and quantum physics. If the model is confirmed, it could mark a new chapter in the way we think about the birth of the Universe.
Reference article:
Bertacca, Daniele; Jiménez, Raúl; Matarrese, Sabino; Ricciardone, Angelo. "Inflation without an inflaton" . Physical Review Research, July 2025. DOI: 10.1103/vfny-pgc2.
