Quantum theory is notoriously weird. Here’s one case in point: The theory holds that empty space isn’t empty. Instead, it predicts random energy fluctuations that cause evanescent, or virtual, particles to continually pop in and out of the vacuum.
Exploring that oddity, the late Dutch physicist Hendrik B.G. Casimir predicted in 1948 that interactions between virtual particles would be detectable as forces between neutral, but electrically conductive, objects.