The original version of this story appeared in Quanta Magazine.
Suppose you want to empty a box. Really, truly empty it. You remove all its visible contents, pump out any gases, and—applying some science-fiction technology—evacuate any unseeable material such as dark matter. According to quantum mechanics, what’s left inside?
It sounds like a trick question. And in quantum mechanics, you know to expect a trick answer. Not only is the box still filled with energy, but all your efforts to empty it have barely put a dent in the amount.
This unavoidable residue is known as ground-state energy, or zero-point energy. It comes in two basic forms: The one in the box