Theoretical physics

A recently proposed experiment would confirm that gravity is a quantum force.

The theoretical physicist Joe Polchinski, who died February 2, left a tremendous professional and personal legacy, says a friend and collaborator.

Cosmologists have shown that it’s theoretically possible for a contracting universe to bounce and expand. The new work resuscitates an old idea that directly challenges the Big Bang theory of cosmic origins.

For decades, physicists have struggled to create a quantum theory of gravity. Now an approach that dates to the 1970s is attracting newfound attention.

A complete classification could lead to a wealth of new materials and technologies. But some exotic phases continue to resist understanding.

The mother of all string theories passes a litmus test that, so far, no other candidate theory of quantum gravity has been able to match.

Edward Witten reflects on the meaning of dualities in physics and math, emergent space-time, and the pursuit of a complete description of nature.

Physicists theorize that a new “traversable” kind of wormhole could resolve a baffling paradox and rescue information that falls into black holes.

The universe has not cooperated with physicists’ hopes. In desperation, many are looking for new ways to search for surprises at the Large Hadron Collider.