My momma done told me ... when I was a boy ... that when she was growing up on a Wisconsin farm, the corn would grow so fast in late summer you could hear it grow — it was noisy. Being a suburban kid, and a born skeptic, I didn't believe her at first. An April Fool's joke?
She explained that at the height of the growing season, little fibrous strands on any given stalk of corn will snap on occasion, maybe once a week or so. But when you have a whole field of many thousands of stalks of corn, the field crackles like a campfire.
So, in that Wisconsin farmhouse, late at night in the dog days of summer during the Depression, with the windows of her bedroom wide open, she used to fall asleep listening to the corn grow ... crackling, crackling, all night long.
This was a lesson in statistics: very rare events happen all the time. I thought of it years later, reading how radio astronomers map our galaxy.
The vast, star-forming clouds in our Milky Way Galaxy's spiral arms are mostly made of hydrogen atoms — simply, one electron circling one proton. They both spin on their axes like tops, usually in parallel directions. But very rarely, the electron will flip and spin in the opposite (or anti-parallel) direction from its proton. When this happens, the atom emits a light wave at a wavelength of 21 centimeters — a radio frequency.
It only happens to a given hydrogen atom every 10 million years or so, but because our galaxy contains trillions of hydrogen atoms, it happens everywhere, all the time. So radio astonomers can map the galaxy, because the Milky Way softly hums with radio noise, all night, all day, for billions of years.
