A photon emitted from a star a billion light-years away arrives at a telescope having experienced no time whatsoever. Not ...

In 1916, only a year after Albert Einstein had published his general theory of relativity, Karl Schwarzschild used mathematical calculations to show this: If sufficient mass could be placed into an ...

Tiny “Ferris wheels” made from light and extremely cold particles could allow researchers to test a facet of Albert Einstein’s theory of relativity on unprecedentedly small scales. Theories of special ...

Tracking time is one of those things that seems easy, until you really start to get into the details of what time actually is. We define a second as 9,192,631,770 oscillations of a cesium atom.

Time travel has shifted from pure fantasy to a serious, if highly constrained, topic in modern physics. The equations that describe gravity, quantum fields and the structure of spacetime now allow ...

A spacecraft traveling at 99 percent the speed of light toward Alpha Centauri would cross 4.3 light-years in what feels like months to its crew, while decades tick by on Earth. That asymmetry is not ...