Since atoms are mostly "empty space,"

[longship]

26. Sigh! No! It is an expression of Quantum Electrodynamics.

You cannot pass your hand through a wall (without hurting your hand somewhat severely) because the electrons in the outer shells of the atoms in your hand repel the same in the wall.

You stand on the floor of your house because the force of gravity which holds to the Earth (and to the floor) is many orders of magnitude weaker than the electrodynamic forces repelling you from falling through the floor.

Things are solid because of their compact atomic arrangement which is mostly static, held by atomic bonds that hold the material together. This also is quantum electrodynamics. As is light, as is radio, as are X-rays, as are gamma rays, as is computers, as is chemistry, as is biology. QED is almost everything we experience in the universe, except gravity.

Gravity is exceptionally weak, but over distances all the other forces of nature average out to zero.

The other two known forces of nature, the Weak and Strong nuclear forces are strangers to our daily experience, but without the first stars wouldn't shine, and without the second matter couldn't exist in a stable form. They also take part in certain exotic physics experiments to measure their attributes. The LHC at CERN comes to mind, among others. We don't experience them since they only act at very short distances, e.g., within an atom's nucleus.

This is all putting it simply. But that's my answer. I am sure some DUers could improve on it. (on edit: as I see some already have. :hi