If we take out all the matter, neutrinos, dark matter, cosmic rays, and radiation from the deepest parts of the voids, the only thing left is empty space. I know it sounds like a paradox, but the voids are full of the vacuum of space-time. And crucially, that's not nothing.
That's because the vacuum of space-time has something inside of it. Or on top of it. Or within it. Or kind of existing within its fundamental fabric. Look, it's kind of hard to precisely describe with words what's going on, but I'm talking about the quantum fields. In quantum field theory, the particles that make up our existence, like electrons and top quarks and neutrinos and even the dark matter aren't really particles.\
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