General relativity

For decades, extremal black holes were considered mathematically impossible. A new proof reveals otherwise.

Tensors are used all over math and science to reveal hidden geometric truths. What are they?

By studying the geometry of model space-times, researchers offer alternative views of the universe’s first moments.

Black holes are inescapable traps for most of what falls into them — but there can be exceptions. The theoretical physicist Leonard Susskind speaks with co-host Janna Levin about the black hole information paradox and how it has propelled modern physics.

Mathematicians prove a theorem that illuminates the geometry of universes with tiny amounts of mass.

For a half century, mathematicians have tried to define the exact circumstances under which a black hole is destined to exist. A new proof shows how a cube can help answer the question.

Inside of a black hole, the two theoretical pillars of 20th-century physics appear to clash. Now a group of young physicists think they have resolved the conflict by appealing to the central pillar of the new century — the physics of quantum information.

For decades, physicists have struggled to develop a quantum theory of gravity. But what if gravity — and space-time — are fundamentally classical?

Astronomers have found a background din of exceptionally long-wavelength gravitational waves pervading the cosmos.