Theory of Everything

How do things work?

This incredibly innocent question has led scientists down a centuries-long path, leading to a set of a limited number of rules (laws of physics) that govern everything.

The number of rules continues to dwindle. How? Each rule has the potential to merge with another rule, as it eventually turns out to be a part of the same phenomenon.

Having 50 equations that tell you how things work is useful, but what if you could get this number down to five? How about four? What’s the smallest number of rules you could have that describes how the universe is governed?

Taking a complex phenomenon and explaining why it happens at a very simple level has incredible value for humanity. If we know how things work at a fundamental basis, we understand things well enough to predict outcomes. If we can predict outcomes, we may also be able to manipulate them. By understanding the laws of physics, we can do much more to make life better.

It’s no wonder that great thinkers have been working on unifying and simplifying rules for a long, long time. We’ve long sought order to explain what we saw, going all the way back to ancient astronomical observations and star observatories like Stonehenge.

Around 2700 years ago, Thales of Miletus sought a natural explanation for the world, suggesting that there were explanations for things beyond the whims of the gods. His suggestion was that everything was made of one substance, and that substance was water.

This idea that the world could all be made up of one type of substance was an attempt at a simplifying, unifying principle. Democritus took this a step further by proposing that there was a tiny underlying particle that made up everything, and that these particles were individual, or (the Greek word for indivisible) atomos.

Democritus had laid the foundation for an idea that everything could be explained in terms of something very fundamental—or rather, what everything was made of could be explained. It was a start.

Twenty centuries later, give or take, Isaac Newton put two and two together to show that the force that held the Moon in place around the Earth (and held every other celestial body in place) also caused things to fall to the ground here on Earth. Newton came up with equations, too, so that you could predict what would happen when something fell.

This was huge! Two seemingly different forces were really one thing, and now there was an equation to explain how it all worked. Could this be done again?

This time, the world only had to wait about two centuries to find the answer. Michael Faraday pointed out that electricity and magnetism were actually the same thing, just manifesting in different ways. James Clerk Maxwell created a framework to explain how this happened, including equations that were incredibly useful in predicting how things worked with this new force scientists call electromagnetism.

Electromagnetism’s streamlining was taken a step further another century later. Now, when I grew up, I learned about four fundamental forces of physics. These were gravity (the weakest), followed by electromagnetism, the weak nuclear force, and the strong nuclear force.

We’ve talked a bit about electromagnetism and gravity, and both of these forces are pretty intuitive. If you want to find out why electromagnetism keeps things from falling through your hand, I wrote a bit about that phenomenon here:

The nuclear forces, though, are pretty nonintuitive. They happen at the tiniest of scales, and we experience reality at scales many billions of times bigger.

The strong force binds the nucleus together, overcoming the repulsive electromagnetic force (protons are all positive, so they want to push one another apart). You can see how much stronger the so-called strong force is by thinking about how electromagnetism unsuccessfully tries to blast the nucleus apart all the time.

The weak force—so called because it’s much, much weaker than the strong nuclear force, even though it’s much stronger than electromagnetism—is responsible for radioactive decay. It might be surprising to learn that the weak nuclear force and electromagnetism are really the same force.

How? Physicists say that EM (electromagnetism) and the weak force have a hidden symmetry that isn’t visible at low energy levels we experience most of the time. The two forces behave completely differently. However, if you can produce more than 246 GeV, like in particle colliders, the distinction between these forces disappears. The electroweak force emerges.

Incidentally, physicists are very bad at naming things.

If electromagnetism and the weak force are one and the same at insanely hot temperatures (high energy levels), what about the strong force? This turns out to be a very exciting frontier right now, as physicists seek to prove that the two nuclear forces are actually manifestations of the same force, which is also the same thing as EM.

If you hear the term Grand Unified Theory (or GUT for short), that’s what physicists mean. There are good reasons to think this will prove to be the way things work. Unfortunately, getting enough energy to test the theory is far beyond our current capabilities, as the conditions were ripe just shortly after the Big Bang.

If the GUT turns out to be true, that leaves only one more force to tie into the mix: gravity. Trying to get gravity to play nice with the other forces has proven frustratingly elusive so far, so the quest for the Theory of Everything (TOE) continues.

There’s one final unification worth mentioning, perhaps: that of space and time. Einstein’s brilliant leap to suggest that these two concepts were really the same thing has been truly fundamental in our 20th and 21st century understanding of how things work.

This isn’t the same thing as unifying all the fundamental forces—that’s what the Theory of Everything is—but it’s an amazing way of simplifying nature, of showing how two things that don’t really seem like the same thing, very much are the same thing. I wrote about that idea here.

This is a very big question for today, but let me ask it anyway. How will our understanding of the universe change if the Grand Unified Theory or the Theory of Everything is proven? Why do physicists insist on GUT and TOE as abbreviations for these important ideas?