The Universe has a rate at which it expands — called the Hubble constant. The problem is that the two most precise ways to measure it give different numbers. One method, using the early light of the Universe (the cosmic microwave background), gives one value. The other, based on observations of distant stars in the present day, gives another, slightly higher value. The difference is small, but it stubbornly refuses to go away. This is known as the 'Hubble tension.'

In the new work, scientists suggested that maybe the issue isn't measurement errors, but that gravity on vast distances doesn't work exactly as we think. They abandoned the idea of dark energy (the mysterious force usually invoked to explain accelerated expansion) and instead modified the geometry of spacetime itself. To do this, they used a theory called symmetric teleparallel gravity. In this theory, gravity arises not from the curvature of space, but from its torsion, as if space were not a smooth sheet but a fabric that can be stretched in different ways.

To test the models, the scientists compared them with a large dataset. They used observations of the ages of old galaxies (which tell us about expansion in the past), type Ia supernova explosions (these flashes serve as 'standard candles' for measuring distances), and baryon acoustic oscillations — imprints of sound waves in the early Universe that provide a cosmic yardstick. The results showed that both models explain the observations as well as standard cosmology. Moreover, the logarithmic model gives a Hubble constant value that sits right between the two conflicting numbers, like a bridge between the early and late Universe. This doesn't fully solve the problem, but it considerably eases it.

This approach recalls an old idea: sometimes, to reconcile disputants, you don't need to pick a side but to change the rules of the game. Here, the rules turned out to be the equations of gravity. And although the final answer is still far off, the very possibility of doing without dark energy and smoothing the contradiction with geometry alone is intriguing.