Those who are not shocked when they first come across quantum theory can not possibly have understood it.
It was thought for a time that atoms were the smallest bits of matter. Now scientist can see that atoms are made of electrons around a dense nucleus made of protons and neutrons, which are in turn made of quarks of different flavours.
However, these subatomic particles are unimaginably small compared to the size of the entire atom. The following excerpt from The Particle Adventure (see the Resources page for the link) gives an excellent idea of the scale.
If we drew the atom to scale and made protons and neutrons a centimeter in diameter, then the electrons and quarks would be less than the diameter of a hair and the entire atom’s diameter would be greater than the length of thirty football fields.
Atoms, the particles that make up everything in our physical world – whether they are in the solid, liquid, gas, or plasma state – are themselves 99.99999% empty space. In addition to this, the space between the atoms can be vast compared to the size of the atoms themselves.
Everything we conventionally consider to be “real” is made of tiny particles that consist of mostly empty space separated by even more space.
What we consider to be empty space makes up the majority of our world, and yet we pay little attention to it. We focus almost exclusively on the surface level, the illusion of solidity. But I think the space from which everything in our physical reality is born contains worlds even more wonderful and beautiful than our physical one.