Can Anything Go Faster Than the Speed of Light?

A student recently asked me, “When do you think we’ll finally beat the speed of light?”

Like many, he assumed that in a world where we constantly work to make things bigger, better, faster—from our technology to our athletic performances—the speed of light was also something we would eventually be able to best.

Not everything is a record waiting to be broken, though. Sometimes the universe pumps the brakes.

What is the speed of light?

The speed of light, the fastest moving thing we know of, is 299,792,458 meters per second in a vacuum. That’s over 186,000 miles per second.

But physicists didn’t always know light traveled at a finite speed. In fact, physicists once thought light did not have a speed at all but rather traveled instantaneously. Naively, this assumption seems reasonable—I don’t have to wait for the light to reach my eyes once I flip the light switch.

Traveling at over 186,000 miles per second in a vacuum, light is the fastest-moving thing we know of.

In the early 1600s, the Dutch scientist Isaac Beeckman tried to test the assumed instantaneous nature of light by investigating whether observers from different locations saw the flash from a gunpowder explosion sooner or later. His results were inconclusive for reasons we now understand—his terrestrial distances were too small to measure a difference in arrival time.

Around 50 years later, the astronomer Ole Romer noted a difference in the times measured between the eclipses of Jupiter’s moons depending on the position of the Earth. When the Earth was moving away from Jupiter, the downtime between each eclipse—that’s when the moon traverses in front of the gas giant planet from our perspective—was increased by about seven minutes compared to when Earth was moving toward Jupiter. He suggested this difference might be due to a difference in light travel times. Romer measured a value of ~220,000,000 meters per second which, considering his set up, is really pretty good.

In the 1800s, James Clerk Maxwell began to work out the mathematical framework for how electromagnetic radiation, classical optics, and electric circuits work—a framework now known as Maxwell’s Equations. His work revealed that light was an electromagnetic wave and that electromagnetic waves traveled at a consistent speed—the speed of light.

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