Time moves slower the closer you are to Earth. In his theory of general relativity, Einstein explained that the gravity of a large mass, like Earth, distorts the space and time around it.

In 2010, researchers placed two precise atomic clocks, one 33 centimetres higher than...

Einstein's special theory of relativity applies only to steady, unchanging motion through space-time, not accelerating motion like an object falling toward Earth.

• It troubled Einstein that his theory didn't include gravity, and his battle to incorporate it made symmetry central to hi...

Albert Einstein did not think about symmetry when he wrote his first relativity papers in 1905. He was considering several seemingly unrelated puzzles and connecting the dots.

• Einstein realized that the speed of light - a speed that stayed constant - was a measurable manifestation of...