And when you get down to the bottom, as far as we can go, they are actually networks of quantum waves. They are empty. Whatever we observe as existing, like this pulpit here, is really the interference patterns of quantum waves of molecular states. What appears to be material, is really non-material. You know the difference between a wave and a particle.
Light waves are electromagnetic waves.
They can travel through empty space in patterns like what happens when you drop a rock into a pool of water. Particles are pieces of things, like a rock. They travel in a particular linear direction. If I throw a rock that way, it doesn't go that way. If a drop a rock into a pool of water, the waves go in all directions at once.