What if the Big Bang didn't begin with a singularity? This point of infinite density, which so divides physicists, could be avoided. A new approach to quantum gravity suggests that the universe may have emerged without this problematic concept, by simply modifying Einstein's theory.
This idea posits that gravity itself, at extreme energies, could have triggered the initial expansion of the cosmos without adding extra ingredients.
Einstein's theory, general relativity, works remarkably well in most situations, but it predicts singularities at the Big Bang and inside black holes. These points where density and temperature become infinite are a sign that the theory is pushed beyond its limits. To address this, physicists from the University of Waterloo and Perimeter Institute have explored an extension called quadratic quantum gravity.
This new theory behaves remarkably well at the highest energies, unlike general relativity. It proposes that primordial inflation, that phase of rapid expansion of the universe, could be a direct consequence of gravity itself, without the need for a hypothetical field.
The resulting model matches current data very well, sometimes better than standard inflation models. What surprised the team was how naturally an inflationary phase emerged once the theory was treated in a coherent framework. This changes our view of the early universe: instead of adding elements to gravity, it already contains the necessary ingredients.
To test this idea, scientists rely on primordial gravitational waves and the cosmic microwave background, that fossil glow from the very beginning of the universe. If future observations detect particular patterns in these signals, it could confirm that quadratic quantum gravity is the right path. The team plans to refine their predictions and compare them with upcoming data.
This research, published in
Physical Review Letters, thus opens a promising new avenue for understanding the first moments of our universe without resorting to infinite singularities. The next step will be to distinguish this model from more standard inflation theories through precise observations.