Theoretical physics

Two leading candidates for a “theory of everything,” long thought to be incompatible, may be two sides of the same coin.

The irreversibility of time may be a clue as to what makes up the universe’s dark matter.

If a theory can’t be tested, is it still science?

Nima Arkani-Hamed is championing a campaign to build the world’s largest particle collider, even as he pursues a new vision of the laws of nature.

Explore the deepest mysteries at the frontier of fundamental physics, and the most promising ideas put forth to solve them.

At super-low temperatures, a crystal called samarium hexaboride behaves in an unexplained, imagination-stretching way.

By replacing black holes with fuzzballs — dense, star-like objects from string theory — researchers think they can avoid some knotty paradoxes at the edge of physics.

Quantum theorist Christopher Fuchs explains how to solve the paradoxes of quantum mechanics. His price: physics gets personal.

Three physicists have proposed a new solution to one of the deepest mysteries in particle physics: why the Higgs boson has such a tiny mass.