How to Travel Faster Than Light Without Really Trying
It’s often said that nothing can travel faster than light, but that’s only part of the story.
The speed of light, c, is an absolute physical constant. No matter where you are in the Universe, or how fast you’re moving relative to something else, the speed of light in a vacuum is always the same. That’s often taken to imply that nothing can travel faster than light, but things aren’t quite so simple. It turns out there are several ways things can travel faster than light, depending on what you mean by a “thing,” “faster-than-light,” and “travel”.
One way is to note that the immutable speed of light only applies to light in a vacuum. When light travels through a material, its effective speed is reduced. This is often given by an index of refraction, n, where the effective speed of light is c/n. (And n is pretty much always greater than 1.) For example, when light travels through water, its speed is about 0.75c. Because of this, it is possible for particles to “break the light barrier” in a material while still traveling less than c.
For example, in nuclear reactors electrons are emitted with so much energy that they are traveling at…
