The speed of light is one of the most famous constants in physics, yet it has never been directly measured in the way most people assume. All experiments rely on round-trip measurements and built-in ...

Everyone knows the number for the speed of light — but almost nobody knows the uncomfortable truth behind it. Measuring light in one direction requires perfectly synchronized clocks, and that’s the ...

The universe has a speed limit, and it's the speed of light. Nothing can travel faster than light — not even our best spacecraft — according to the laws of physics. So, what is the speed of light?

Here, a calcite crystal is struck with a laser operating at 445 nanometers, fluorescing and displaying properties of birefringence. Unlike the standard picture of light breaking into individual ...

Chris Impey receives funding from the National Science Foundation and the Hearst Foundation. Curious Kids is a series for children of all ages. If you have a question you’d like an expert to answer, ...

The principle of relativity, as initially described by Galileo, posits that the laws of physics remain consistent regardless of an observer's relative motion. Einstein's special relativity ...

The speed of light in vacuum, commonly denoted c, is a universal physical constant important in many areas of physics. Its exact value is defined as 299792458 metres per second (approximately 300000 ...

The Parker Solar Probe, currently the fastest human-made object, travels at 0.05% the speed of light (approximately 330,000 mph). Reaching 1% the speed of light requires an immense amount of energy ...