The speed of light in a vacuum is also the speed limit of existence. For everything. Even the laws of physics. If the sun disappeared right now, Earth would continue to orbit for eight minutes before noticing and flying off into space, the exact opposite of a cartoon character running off a cliff. Ole Roemer first measured this universal upper limit back in 1676, when the most advanced light source was the oil lamp. Well, that's a lie. The most advanced light source was the mass-conversion fusion lamp, the same as it was through every moment of human history. But the best light source we'd built at the time was waiting until something died, squeezing it, and setting the death-goo on fire.
"Wow, humanity, that's good too, really."
Roemer was observing the orbit of Io, one of Jupiter's moons, and noticed that the time between eclipses changed as Earth moved toward and away from the satellite. He worked out that light must have a finite speed and did the math on observations spanning the solar system, and his result was off by only 25 percent. That is stunning. He was the first person to nail down the speed of light, and he did it before Newton had published classical mechanics. When others stared into the sky, they saw gods, or pretty shapes. Roemer stared down the universe until it confessed its greatest limitation. He worked out one of the greatest problems of existence using a couple of pieces of melted sand.
Horrebows Basis AstronomiÃ¦ via Wikimedia Commons
"And that Death Star's thermal exhaust port could be a problem."