Physicists are quietly testing wild new theories that treat a hidden fifth dimension as more than science fiction, suggesting it could steer how gravity, dark matter and even cosmic history unfold.

Imagine a world where you can only move forwards and backwards along a line. You’d see nothing but single points in front of you, and nothing but single points behind you—a one-dimensional world. Now ...

The Higgs boson was supposed to be the final piece of the Standard Model puzzle. Confirmed at the Large Hadron Collider in 2012, it completed a theoretical framework decades in the making. But a ...