We Know All The Particles And Forces That We’re Made Of

Annual Question: 

Sean Carroll

Sometimes news creeps up on us slowly. The discovery of the electron by J.J. Thomson in 1897 marked the first step in constructing the Standard Model of Particle Physics, an endeavor that culminated in the discovery of the Higgs boson in 2012. The Standard Model is a boring name for a breathtaking theory, describing quarks, leptons, and the bosons that hold them all together to make material objects. Together with gravity, captured by Einstein's general theory of relativity, we have what Nobel Laureate Frank Wilczek has dubbed the Core Theory: a complete description of all the particles and forces that make up you and me, as well as the sun, moon, and stars, and everything we've directly seen in every experiment performed here on Earth.

There is a lot we don't understand in physics: the nature of dark matter and dark energy, what happens at the Big Bang or inside a black hole, why the particles and forces have the characteristics they do. We certainly don't know even a fraction of what there is to learn about how the elementary particles and forces come together to make complex structures, from molecules to nation-states. But there are some things we do know—and that includes the identity and behavior of all of the pieces underlying the world of our everyday experience.

Could there be particles and forces we haven't yet discovered? Of course—there almost certainly are. But the rules of quantum field theory assure us that, if new particles and forces interacted strongly enough with the ones we know about to play any role in the behavior of the everyday world, we would have been able to produce them in experiments. We've looked, and they're not there. Any new particles must be too heavy to be created, or too short-lived to be detected; any new forces must be too short-range to be noticed, or too feeble to push around the particles we see. Particle physics is nowhere near complete, but future discoveries in that field won't play a role in understanding human beings or their environment.

We'll continue to push deeper. There's a very good chance that "particles and forces moving through spacetime" isn't the most fundamental way of thinking about the universe. Just as we realized in the 19th century that air and water are fluids made of atoms and molecules, we could discover that there is a layer of reality more comprehensive than anything we currently imagine. But air and water didn't stop being fluids just because we discovered atoms and molecules; we still give weather reports in terms of temperature and pressure and wind speed, not by listing what each individual molecule in the atmosphere is doing. Similarly, a thousand and a million years from now we'll still find the concepts of the Core Theory to be a useful way of talking about what we're made of.

Could we be wrong in thinking that the Core Theory describes all of the particles and forces that go into making human beings and their environments? Sure, we could always be wrong. The Sun might not rise tomorrow, we could be brains living in vats, or the universe could have been created last Thursday. Science is an empirical enterprise, and we should always be willing to change our minds when new evidence comes in. But quantum field theory is a special kind of framework. It's the unique way of accommodating the requirements of quantum mechanics, relativity, and locality. Finding that it was violated in our everyday world would be one of the most surprising discoveries in the history of science. It could happen—but the smart money is against it.

The discovery of the Higgs boson at the Large Hadron Collider in 2012 verified that the basic structure of the Core Theory is consistent and correct. It stands as one of the greatest accomplishments in human intellectual history. We know the basic building blocks of which we are made. Figuring out how those simple pieces work together to create our complex world will be the work of many generations to come.


[ Fri. Dec. 18. 2015 ]