[icegreentea]

There are voids. A lot of voids. A good deal of matter (even solid) are actually 'nothing'. If you take materials science, you get the 'atoms made of hard ball' approximation of the world (which usually yields pretty good answers), and even then, the densest you can get anything like 75% matter or something. And that's severely high-balling it (the ball radius approximates the electron cloud as a hard continuous shell, when it's really actually mostly just empty.

[foob]

These voids are actually full of a crazy mess of virtual particles that exist within time/energy uncertainty. Empty space isn't really a meaningful concept when you're dealing with field theories.

When you study quantum field theory one of the first mind blowing things that you learn is that an electron at rest can be thought of as a superposition of an infinite number of somewhat classical scenarios. For instance, the electron can shoot of a virtual photon, which creates an electron/positron pair, which annhilate and create a new photon, which is then absorbed by the original electron. These processes can be arbitrarily complex; just imagine substituting in the whole process we just described for the electron that was pair produced- you can do that as many times as you want. These things are all ocurring at once. This leads to the necessity of renormalization and in turn a great joke. What is positive infinity plus negative infinity? If you ask a mathematician he'll tell you that it's undefined. If you ask a physicist he'll tell you it's the mass of the electron.

[ars]

Actually ALL mater is nothing.

In between atoms is nothing. Inside atoms (between the electrons and the nucleus) is more nothing. Electrons are point particles and have no size. In between the protons and neutrons of the nucleus is nothing. Inside a proton are quarks, and between those quarks is nothing. Quarks themself are point particles and have no size.

So in total 100% of matter is empty space.