Why Empty Space Isn't Empty

The story

Quarky builds the emptiest box in the universe: no air, no light, no dust, nothing. But when Quarky peeks inside with a quantum magnifying glass, the box is fizzing! Pairs of tiny particles keep popping into existence and vanishing again, like bubbles in soda that appear from nowhere. Quarky learns that empty space is really a busy, buzzing quantum foam, and that fizz is strong enough to push two mirrors together.