Physics

A recent experiment shows how quantum mechanics can make heat flow from a cold body to a hot one, an apparent (though not real) violation of the second law of thermodynamics.

A surprise discovery announced a month ago suggested that the early universe looked very different than previously believed. Initial theories that the discrepancy was due to dark matter have come under fire.

Paradoxically, a small galaxy that seems to contain none of the invisible stuff known as “dark matter” may help prove that it exists.

Gravitational waves have opened up new ways to test the properties of black holes — and Einstein’s theory of gravity along with them.

The renowned British physicist, who died at 76, left behind a riddle that could eventually lead his successors to the theory of quantum gravity.

By 1913, Albert Einstein had nearly completed general relativity. But a simple mistake set him on a tortured, two-year reconsideration of his theory. Today, mathematicians still grapple with the issues he confronted.

The amount of energy infusing empty space seems too small to explain without a multiverse. But physicists have at least one alternative left to explore.

Two teams of researchers have made significant progress toward proving the black hole stability conjecture, a critical mathematical test of Einstein’s theory of general relativity.

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