What is time, and why does it seem to flow in only one direction? This video explores modern physics’ take on time—from the ...

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.

OUR most accurate clocks are probing a key tenet of Einstein’s theory of relativity: the idea that time isn’t absolute. Any violation of this principle could point us to a long-sought theory that ...

From Hawking's black holes to the GPS in your pocket, Einstein's theory endures. On November 25, 1915, amidst the turmoil of World War I, a short, three-page paper was published in the journal ...