U.S. Energy Information Agency
The carbon atom: beware, distances in this image may not be accurately portrayed.
I still remember sitting in chemistry and learning about atoms — you know, tiny protons and neutrons in a nucleus being orbited very, very far away by some even tinier electrons.
But the distances are truly vast. The nucleus is only about 1/50,000th of the width of the overall atom. Therefore the firm ground that your chair is sitting on right now is 1 part matter to 100 million million parts empty space. How in the world is this possible?
The question flashed through my mind but I was soon diverted, probably by the prospect of blowing something up in class. It’s always lingered at the back of my mind, but I’d never found a good answer. Turns out scientists couldn’t answer this simple, but profound puzzler until just a few decades ago.
I came upon an explanation recently, reading Robert Matthews’ most-excellent Q&A: Cosmic conundrums and everyday mysteries of science:
The situation is even more curious, as the attractive force between the atoms that make up matter should have led to everything collapsing in a trice. The fact that we are here to ponder this question shows that nature has some way of preventing it from happening.
The answer to this difficulty did not emerge until the mid-1960s, when the theorist Freeman Dyson showed that, if atoms become too closely packed, their clouds of electrons start to interact with each other, creating a repulsive force. There comes a point where this outward “degeneracy pressure” exactly balances the attraction between the atoms and matter becomes stable.
Estimates for the strengths of these two effects suggest that this balance point comes when solids are a few times denser than water — which is just what we see.