Watch an animation of a black hole shooting jets of particles through a "collapsing star at nearly the speed of light" and ...

The speed of light is constant, or so textbooks say. But some scientists are exploring the possibility that this cosmic speed limit changes, a consequence of the nature of the vacuum of space.

Einstein’s theory of relativity shows us that time isn’t constant,it stretches or contracts based on speed and gravity. But ...

Even in vacuum conditions, light can move slower than its maximum speed depending on the structure of its pulses.

Specifically, Einstein's theory that light travels at a constant speed underpins the popular Theory of Relativity as well as our models for understanding what happened after the Big Bang.

Let’s explore how constant this speed of light fundamental constant really is. One of the most fundamental physics facts is that the speed of light in a vacuum is constant for all observers.

Because space-time warps to accommodate the constant speed of light, a person traveling through space at near lightspeed would age more slowly than all the other humans waiting back on Earth.

Many things in life are constant. The crushing sense of disappointment after finishing a bar of chocolate, for example. The unpredictability of 2016. And, of course, the speed of light.

The speed of light may not be constant, a possibility that could have broad implications for fields of cosmology and even astronomy, say physicists.

The speed of light is constant, or so textbooks say. But some scientists are exploring the possibility that this cosmic speed limit changes, a consequence of the nature of the vacuum of space. The ...