Heisenberg Uncertainty Principle
Werner Heisenberg discovered something unsettling about the fundamental nature of reality: a single electron doesn't have a single location or a single speed. It has a range of locations and a range of speeds, all at once.
This is the uncertainty principle—not a limitation of our measuring tools, but a feature of existence itself. "For any fungible collection of instances of a physical object," quantum physics tells us, "some of their attributes must be diverse."
Two electrons in the same position can have different speeds. Two electrons moving at the same speed can occupy different positions. The result is that an electron's typical behavior is to spread out gradually in space, like a thought that refuses to stay still. The particle exists as a collection of possibilities, all real, all simultaneous.
What we think of as a single, definite thing turns out to be many things at once.