Try as they might, scientists can’t truly rid a space or an object of its energy. But what “zero-point energy” really means is up for interpretation.

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 is associated with fields, such as the electromagnetic field, and the other is associated with discrete objects, such as atoms and molecules. You may dampen a field’s vibrations, but you cannot eliminate every trace of its presence. And atoms and molecules retain energy even if they’re cooled arbitrarily close to absolute zero. In both cases, the underlying physics is the same.

...read more at quantamagazine.org