 As an example, the speed of light is 186,000 miles a second, but that's in a vacuum. It can slow down by 25% in water. But relativity keeps anyone from measuring the speed of light from point A to point B. The fact is, the more we know, we discover how little we know. Scientists recently found an ancient structure in the Baltic Sea. They don't know who built it, probably around 10,000 years ago. And there are other structures around the world and we're clueless as to who built them.