It took 3.8 billion years, but we got there in the end. For most of the history of life on Earth, life was pretty dull. Then humans evolved, and things got interesting.
One of the defining features of our species is our ability to make connections. From birth, we can’t help but recognise patterns. Arrangements of dark and light resolve into faces, sounds into voices. Some of these patterns become more abstract rules about the world – day follows night, things fall down. They allow us to draw inferences about things: a stone falls, therefore an apple will too.
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What goes for us individually applies to our species as well. The history of science is the history of seeing ever deeper connections between apparently unrelated phenomena. Newton recognised that the same force that causes an apple to fall also keeps the moon in orbit: gravity. Faraday and Maxwell showed that electricity and magnetism were two sides of the same coin; electromagnetism itself was later united with the weak nuclear force, responsible for things like beta decay.
Each of these unifications reduces the number of separate physical theories required to understand the universe, leading many to believe that it may eventually be possible to unify all of them into a single theory – a much-vaunted theory of everything.
Is that a realistic prospect? Could we, a species of ape with a brain evolved for survival on the African savannah, really figure out the whole thing?
“We’ve understood an enormous amount about how the world works in an extremely short period of time, cosmically speaking,” says Sean Carroll, an astrophysicist at the California Institute of Technology in Pasadena. A century ago, we didn’t know that other galaxies existed, or that the universe is expanding, he says. And that’s just the start. In the past 100 years we have discovered most of quantum mechanics, a whole zoo of new particles, the existence of dark matter and dark energy – and we have woven these and other empirical observations into a series of very successful theories about how the universe works. “At this rate, we have every reason to think we can understand it all someday,” says Carroll.
Or maybe not. Chimps, smart as they are compared with, say, tortoises, will never grasp quantum theory, or even recognise the need for such a theory. And although we are smarter than chimps, why shouldn’t there be concepts that are too big or too complex for our brains to handle? In some senses, such unknowables do exist. Turbulent fluids, stock markets, crowd dynamics, even the functioning of our own brains are all impossible for us to fathom without the help of computer models.
Even if we are capable of understanding everything, there’s much work to be done. Our two most successful physical theories – general relativity, which deals with very large things, and quantum mechanics, which deals with very small ones – are maddeningly hard to unify.
Similarly, we know of four fundamental physical forces: electromagnetic, weak nuclear, strong nuclear and gravity. Three of these forces play nicely with each other in the form of the standard model, our best description of how fundamental particles interact. The odd one out? Gravity.
Unifying gravity and the standard model would be a huge step towards a theory of everything. Our best shot so far is string theory, which recasts all phenomena as the result of tiny vibrating strings interacting with each other. The problem is, we don’t have a good way to test it. And without verification by experiment, how can we say we really “understand” it?
Nonetheless, there’s no reason to think we won’t eventually be able to test our theories and understand the cosmos, says Peter Woit, a mathematician at Columbia University in New York.
So what happens when we do fully understand the cosmos? If knowledge is power, how powerful will it make us? Woit says there’s an outside possibility that some insight will lead to a Star Trek future of warp drives and wormholes. But it could just as easily show why these things are impossible.
A theory of everything could also have profound cultural impacts, perhaps telling us that we are, after all, the centre of the universe (see “Was the universe made for us?“), or a holographic projection from the edge of it. What is sure is that we will keep on striving. “The point of searching for a theory of everything isn’t to do things,” says Carroll. “It’s to understand how the world works. Discovery is its own reward.”
Read more: “The human universe: Exploring our place in space”
This article appeared in print under the headline “Can we understand everything?”
