A spacecraft traveling at 99 percent the speed of light toward Alpha Centauri would cross 4.3 light-years in what feels like ...

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 dilation. Length contraction. The fact that time moves faster at your face than it does at your feet. These are all experimentally verified consequences of the Special Theory of Relativity, ...