“You are both fools. You cannot see thoughts, or angels. One is an abstract, the other a fantasy. To compare the two would be silly. Of course, using inferential logic, we can detect the existence of thought by the evidence of its actions, just as I detected the existence of a new form of radiation! Seeing no evidence of God or angels, and applying Occam’s Razor we can effectively rule out God or angels with metaphysical certainty. By the way Mr. Astronaut, you have cancer.” -Pavel Cherenkov (allegedly)
It’s true that nothing can move faster than the speed of light, but only if you’re in a vacuum. Once you’re in a material, like water, glass, or even the atmosphere, all you need to do is make your particles move faster than the speed of light in that medium and all the rules change. By moving faster than light, you force these relativistic particles to emit photons in all directions — Cherenkov radiation — which forces them to slow down.
The Advanced Test Reactor core, Idaho National Laboratory. Image credit: Argonne National Laboratory.
This Cherenkov radiation can be detected by an observatory designed to do exactly this! Since very high energy cosmic rays strike our world and move through the atmosphere, we can detect these Cherenkov photons as their signature, and work to reconstruct where they came from and what caused them.
An artist’s concept for the conceptual design of the Cherenkov Telescope Array. Image credit: G. Pérez, IAC.
Ground has been broken just this year on the first telescopes as part of the massive Cherenkov Telescope Array (CTA); come find out what science we’re poised to learn from this massive undertaking!