How much of all stuff is empty space?

Tony - That statement is true. The size of an atom is about a hundred thousand times bigger than the nucleus. That's the kind of ratios that we're talking about here. I went to see Oppenheimer last night. It is amazing. There's a really nice scene in it where Oppenheimer is talking to his future wife Kitty, and he's talking about how most of what's in their hand is empty space. There's nothing there between the nucleus, the electrons that they're orbiting around, except of course the fields. We say it's nothing, but there's actually the electromagnetic field that's there. And that's why, when we perceive a solid hand or a solid table or whatever, we're really perceiving the electromagnetic field. So it's not really empty. There's a field there.

Chris - So when you press down on a surface, the reason your hand doesn't go straight through a surface, despite the fact that 99.999999% of the surface is empty space, is because my electrons around my atoms in my hand are coming close to the electrons around the atoms in the desk, and like charges repel. So the minus electrons repel the minus electrons and push back on me as hard as I'm pushing on them.

Tony - Exactly. And that's the field that you are feeling. But actually what's really interesting is we can ask about actual empty space and stuff that's got nothing in it, and ask, is there really anything there? If I go out into space and I create a vacuum, is that really empty? And actually perhaps not, because we think it has something which is called vacuum energy, which is actually the thing that's accelerating the universe. So it all comes together in one wonderful place.