The lack of convergence between quantum laws and gravitation remains a persistent problem in physics. A recent advance, materialized by a new equation, however opens a path to bring these fields closer together.
The work of a team of physicists focuses on a fundamental concept of general relativity: geodesics. These paths, which naturally follow the curvature of space-time according to the mass of objects, could be modified if one considers that space-time itself has quantum properties. By applying quantum principles to the description of curvature, the researchers have developed a new approach to these paths.
Schematic representation of a classical geodesic and a q-desic in a curved space-time. The dotted line shows the quantum deviation.
Credit: Oliver Diekmann, TU Wien
This method led to the establishment of the so-called "q-desic" equation. It indicates that in a quantum space-time, particles do not follow exactly the shortest paths predicted by classical theory. Very subtle deviations appear in their trajectories. This result opens the possibility, in principle, of detecting quantum effects by observing the motion of free objects in space.
These differences are extremely weak when considering only the gravity of a single body, on scales far too small to be measured. However, the equation takes an interesting turn when the cosmological constant, associated with the accelerated expansion of the Universe, is integrated into it. In this case, the gaps between classical and quantum trajectories become significant at very large cosmic distances.
Thus, on scales on the order of several billion light-years, the predictions of this new equation could differ notably from those of standard general relativity. This equation could also help interpret certain astronomical observations, like the rotation speed of spiral galaxies. It represents a step towards possible observational tests for quantum gravity theories.
The study, published in
Physical Review D, proposes more than a theoretical framework. It identifies a potentially observable effect that could help distinguish between different approaches seeking to unify quantum physics and gravitation. The researchers hope that further developments will allow refining these predictions and confronting them with cosmic data.