Imagine you went to a bank that is willing to loan you any amount of money you want, but only for a very short amount of time. You can borrow one dollar, but only for a second. You can borrow one million dollars, but you have to give it back in one-millionth of a second. There’s very little satisfaction in that, except that you can say that you were a millionaire for an eye blink. Yet this is what happens at the subatomic level to hold protons and neutrons together.
Protons and neutrons borrow energy from the universe, from the environment around them, and the laws of physics allow them to do so, but only for a very short period of time. Technically this energy borrowing violates what’s called the law of conservation of energy. Protons and neutrons use the energy they borrow and create a new particle called a pi meson, and just like our banking example the universe takes this energy back quickly as the pi meson decays and disappears quickly.
This particle weighs less than a proton but more than an electron, it’s weight is in the middle of these two particles, and that’s why it was given the “meson” part of its name. In Latin meso is a prefix meaning “middle.” It’s called a pi meson because theoretically in the Greek alphabet it’s Pi’th particle of this type discovered. Instead of calling it a pi meson it’s name is usually abbreviated as “pion.”
Imagine a pitcher in a baseball game. In order to get the ball over the plate the pitcher takes a big step toward the catcher when making the throw. Imagine two pitchers having a high speed catch with one another. With each throw they take a big step toward each other in order to throw the ball as fast as possible and they never take any steps back. Inevitably they approach each other as the catch continues. This is the type of catch that protons and neutrons have with each other, throwing pions back and forth, and causes them to stick together.
At the subatomic level particles actually carry forces between other particles. There’s no analogy for this in everyday life, but at such small scales, several thousand billionths of a meter, energy is borrowed, used, and subsequently lost over short periods of time and creates the force fields that hold matter together.