There are forces that we see every day that take no energy. How can you have a force that takes no energy?

It all began with me musing as to how a magnet sticks to my refrigerator.

A conversation with some physics folks on Discord helped me sort out my thoughts. I realized that most (but not all) of the forces that I experience on a typical day do not require any external energy.

If I throw a stick, yes, that requires energy. It takes energy from me to throw the stick. Duh.

However, if I stick a magnet to the fridge, no external energy is used to keep the magnet stuck, day after day, year after year. The force of the magnet is constant, but it doesn’t suck up any energy to stay stuck to the fridge.

So what makes up this “magnetic force”? Any physicist worth their salt will tell you that photons transmit electromagnetic force. But magnetism is transmitted by very weird photons.

Here’s where we start our tumble down the rabbit hole.

When you get down to the quantum realm, nature behaves much differently than it does at the human scale of existence. For one thing, particles can wink in and out of existence on such short timescales that they don’t have to obey common sense ideas about the conservation of mass or energy. These are called virtual particles.

The magnetic force that holds my magnet to my fridge is transmitted by a continuous flow of virtual photons. They flicker invisibly between the magnet and the fridge, keeping the fridge and the magnet bound together.

These virtual photons are here-and-gone so quickly that they hide under the limits of Heisenberg’s Uncertainty Principle. Their existence is so brief that nature doesn’t care that they transmit a force. Under cover of the Uncertainty Principle they get away with pulling the magnet and fridge together without requiring any external energy.

But that isn’t the half of what virtual particles do.

Virtual particles hold our world together.

I’ll start at the smallest scale and work up. To get all the way down to the smallest scale, let’s start with a drop of water. An average-sized drop of water has over a trillion billion water molecules in it. That’s right, as inconceivable as a billion water molecules is, it takes over a trillion of those billion water molecules to make a single drop of water.

A water molecule is formed by binding two hydrogen atoms to one oxygen atom (H₂O). Let’s look at just one of the hydrogen atoms (H) in one single H₂O water molecule. That hydrogen atom is composed of a single proton and a single electron. That’s it. It is the simplest atom in our universe. The proton serves as the atom’s nucleus.

The proton is not an elementary particle. It is built from three truly elementary particles called “quarks”. What binds those three quarks together? Virtual gluon particles.

What the heck is a gluon? It is an elementary particle of force. And yeah, it “glues” the quarks together. Give the physicists a break, when they discovered the gluon they had to call it something. “Gluon” is a silly name, but so is “quark”. “Quark” is related to a gibberish line from James Joyce “Three quarks for a Muster Mark”. It is a known fact that physicists get a little goofy when they name something new.

How long can virtual gluons hold quarks together as a proton? A proton will hold together for much longer than the current age of the universe. The virtual gluons that hold those quarks together do all this without an external energy source.

OK. Quarks and gluons are as small as it gets. Let’s start building bigger stuff.

The next step up in size is to bind an electron to our proton to create an atom, a hydrogen atom. “What keeps the electron bound to the proton?” you might ask.

The electron gets bound to the proton because the electron is electrically negative, while the proton is electrically positive. Opposite electrical charges attract each other. “How do they attract each other?” you ask. “With virtual photons,” I answer. Remember, photons are the carriers of the electromagnetic force. In this case, the force is the attraction of the negative electron to the positive proton. The lone proton serves as the hydrogen atom’s nucleus.

A hydrogen atom remains stable because the quarks in its proton are bound together by virtual gluons, and its electron is bound to its proton by virtual photons. Virtual gluons and virtual photons hold each and every atom in the entire universe together.

The next step up in size is combining atoms into molecules. Each and every H₂O water molecule binds two hydrogen atoms to a single oxygen atom. In the language of chemistry, atoms are bound into molecules by ionic and covalent bonds. And guess what? Ionic and covalent bonds are electrical, kept up by a flow of virtual photons. So molecules are held together by virtual photons.

The next bigger step is to put atoms and molecules together to build stuff like metal, wood, milk, flesh, bone, tables, chairs, people, airplanes, yadda, yadda, yadda. Many varieties of bonding make big stuff out of a bunch of atoms and molecules. They’ve got names like metallic bonding, hydrogen bonds, the van der Waals force, ion-dipole bonding, and so on. In one way or another, all of these forces involve the electromagnetic force, and that means virtual photons.

So we’ve got protons, atoms, molecules, and big stuff all held together by continuous flows of virtual gluons and virtual photons. And because these particles are virtual, they require zero energy from any other source. They transmit force for free. That’s what holds together all the stuff in our world. Virtual gluons and virtual photons.

Here’s a parting thought:

When I sit in a chair, gravity is pulling me toward the center of the Earth. The chair applies a force to my butt that keeps me from falling through the chair. The solidity of the chair and the solidity of my body are due to those virtual particles at every scale — from binding quarks into protons, to binding electron(s) to the nucleus of each atom, to binding atoms into molecules, to binding molecules into the stuff that I call “me” and “chair”.

Our world is held together by continuous forces that require no energy. Just like the magnet stuck to my fridge.

We certainly live in a curious world!