The constancy of the speed of light is a pillar of modern physics, but questions persist about its absolute universality.

The Sagnac effect, first observed over a century ago, remains central to our understanding of relativistic kinematics and the operational definitions of simultaneity. Fundamentally, this effect arises ...

110 years ago today, Albert Einstein published his General Theory of Relativity, which redefined the relationship between matter and gravity. Suddenly, our mysterious universe made a little more sense ...

The speed of light has been one of science’s most trusted markers of stability. For more than a century, the idea that light moves through space at a constant speed has supported some of physics’ most ...

The idea was first hypothesized about 70 years ago. In a bizarre repercussion of Albert Einstein's Special Theory of Relativity, objects traveling close to the speed of light appear flipped over. The ...

In October 2015, a young mathematician named Clemens Sämann was flying home to Austria from a conference in Turin, Italy, when he had a chance encounter. He found himself seated beside Michael ...

The 1919 total solar eclipse provided the first empirical test of Albert Einstein's general theory of relativity, specifically measuring how the Sun distorts light from background stars. General ...

The original version of this story appeared in Quanta Magazine. Two blind spots torture physicists: the birth of the universe and the center of a black hole. The former may feel like a moment in time ...