Go with your GUT

A series of exchanges on a mailing list led me to write a fairly long piece about the theory of relativity, quantum mechanics and grand unified theories (GUTs.) With a little bit of editing, I’ve turned it into my first science blogpost!

Since the time of Newton with his Laws of Motion to present day science, one simple understanding has prevailed. Forces acting upon bodies are what keeps the world going. Literally and figuratively.

While in our everyday life, we can encounter all kinds of forces like the friction when you’re trying to push that heavy table across the floor, to the difficulty you have carrying a heavy package up a flight of stairs, there are only four fundamental forces in nature. All other forces are just manifestations of these four.

Solar System

The one we most commonly encounter and which most people will readily identify is the gravitational force. Gravity is a force that acts between any two bodies that have a mass. It is the force that holds the stars in their places, the solar system together, keeps the moon orbiting the earth, not to mention all the TV satellites that allow us to watch Cartoon Network anywhere in the world (more or less.)

That package I talked about earlier is so hard to carry up a flight of stairs because gravity is pulling down on it and you need to overcome gravity with your legs and arms to get the package up! Just imagine, the entire planet Earth is pulling down at that package and you can beat it with a little effort!

That fact illustrates an important point about gravity. It is the weakest of the four fundamental forces. The strongest of them all is what physicists in a total lack of originality have named the “strong” force (sometimes also referred to as the strong interaction.) This force is what was thought to hold protons and neutrons together inside an atomic nucleus. Today there is a different understanding of that, but more on that later.

The next strongest force is the electromagnetic interaction on which a lot (if not all!) of our modern technology is based on. In fact, practically all the forces we experience in daily life besides gravity are due to electromagnetic interactions!

Electromagnetism is the interaction between charged particles and the electrical and magnetic fields that this creates. If the electromagnetic interaction were stronger than the “strong” force, the protons (which are all positively charged) would fly apart due to repulsion and there would be no possibility of a nucleus forming.

But then, why does the electromagnetic interaction have any effect all? If the “strong” nuclear force is so overwhelming, shouldn’t it wipe out any effect of any other forces? That’s true. And the answer to that is the range at which the forces operate. The “strong” nuclear force is very very strong, but the scale and range it works on is very very small. It falls off to virtually zero beyond a couple of femtometers. (1 million billionth of a meter or 10E-15 meters!)

Today’s understanding of the strong force is that it is a force that affects quarks, the actual fundamental blocks that make up protons and neutrons and the residual effect is seen as a force between protons and neutrons! Lets quit while we can still understand things and move on to the last force in this mixed bag! 🙂

The “weak” force (weak interaction) is another force that manifests itself on the nuclear level. Obviously it gets its name from the fact that it is much much weaker than the “strong” force and weaker than even electromagnetism. Like the “strong” force it also operates on a vanishingly tiny scale (about 10E-18m.) At the risk of being dismissive, most of what the “weak” interaction achieves is of interest only to physicists. About the only physical phenomenon you’re likely to have heard of or encounter (and even then probably only in a physics or chemistry text) is that is due to the “weak” interaction is that of beta decay.

What’s this GUT all about then?