Subatomic comets

It was almost as incredible as if you fired a 15-inch shell at a piece of tissue paper and it came back and hit you.

One of the coolest moments in the history of science. I’d put it in the top 10 “whoa, now that is weird!” observations of all time, I think.

The quote is from Ernest Rutherford, commenting on how bizarre it was that some alpha particles were bouncing off foil at acute angles. Alpha particles go through foil, if you aim the beam right at the foil … which is all anyone had bothered to do at that point. He and a colleague decided to check for bouncy alphas if they fired them at an angle, but they really didn't expect to see any rebounds. When they did, they were pretty gobsmacked, and Rutherford made his famous comment.

It was this observation that forced Rutherford to realize that atoms must have a super-teensy dense nucleus, because the only way to explain the observation was if some alpha particles were passing close enough to atomic nuclei to get flung onto a new course, like a comet slingshotting around the Sun — a subatomic comet. This insight is how Rutherford earned the moniker “father of the atom.”