And if you pump it down to total vacuum and absolute zero and then find a way to keep neutrinos out, you still have virtual particles.
Once I saw the designs for a device called a Casimir engine. The idea was to put two metal plates so close together that virtual particles could not appear between them, resulting in a space with negative energy density relative to the rest of the universe. In other words, a box of nothing.
But would it really be empty? Does spacetime itself or the Higgs field count as something? Physicists spend a lot of time arguing about nothing and still do not understand it fully.
If people want to understand this as well as anybody does, which is not that well, watch this series of videos.
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In theory could you have a box located between virtual particles. It seems that the size of the box would be a major factor relative to what posters had said. A microscopic box so tiny that no known or visible substances could be seen in it by modern technology, is that possible?
YouTube - The Mystery of Empty Space 1