Theoretical physics

Testing the multiverse hypothesis requires measuring whether our universe is statistically typical among the infinite variety of universes. But infinity does a number on statistics.

Newly discovered particles are forcing physicists to extend their simple picture of subatomic interactions or replace it with a more nuanced understanding.

Physicists have begun to explore the idea that mass and length may not be fundamental properties of nature. The hypothesis could help to avoid the conclusion that our world is just a weird bubble in an endlessly foaming multiverse.

Katherine Freese, a physicist who will soon lead the Nordic Institute for Theoretical Physics, reflects on the hunt for dark matter and how dark matter heating may have produced the first stars.

Surprising oil drop experiments suggest that the quantum world may not be as strange as advertised.

A new theory explains the seemingly irreversible arrow of time while yielding insights into entropy, quantum computers, black holes, and the past-future divide.

A conversation with the mathematical physicist Freeman Dyson on quantum electrodynamics, climate change and his latest pet project.

Scientists report the possible discovery of primordial gravitational waves, ripples in space-time that carry a record of how the universe began.

New calculations suggest physicists may someday discover a fundamental theory of gravity, but it could require a radical new perspective on the universe.