What We’ll Find Inside The Atom

The LHC will bring us simplicity by taking us back to the beginning. It will give us a glimpse of the universe as it was at the moment of its birth. That is significant because things were much simpler back then. The only viable (so far) theory is that the universe was born 13.7 billion years ago in a cosmic explosion—the big bang—which created time and space. In this first instant, everything we see today—all the matter and energy that would ever exist—was compressed into an unimaginably small volume. At this moment, two vastly different domains—the inner space of particle physics, as revealed by the microscope tools (largely particle accelerators), and the outer space of cosmology and astrophysics, as revealed by data from earth-based telescopes and space-based telescopes such as the Hubble—were one and the same. As the infant universe expanded and began to cool, forming stars and galaxies, the realms of the small and the large diverged. Things began to get messy.

To figure out what principles undergird the universe, it's necessary to go back to the moment of the big bang and do some experiments. Unfortunately, that's about as easy as getting an interview with Isaac Newton or Alexander the Great. The next best thing is the LHC. It will enable us to replicate some of the conditions of the first few instants of the universe. Not all the conditions at once, of course, but enough to enable us to begin to understand the processes by which the primordial first particles collided and coalesced to form the nuclei and atoms that compose our sun and its planets. Theoretical physicists take insights from the colliders and weave a story of how the smallest components of matter conspire to make the more exotic objects in the sky—the black holes, pulsars, stellar explosions and so forth. By re-creating conditions in the universe moments after the big bang, the LHC will help us forge a coherent description of the universe.

It would be much easier to explain the current state of physics if we had a coherent view, but we don't. Instead, it's necessary to talk about the questions the LHC was built to answer—each question as one piece of a big puzzle. As we go through the questions, the outline of the puzzle will begin to take shape.

Why are there so many particles? So far, colliders such as Fermilab's Tevatron in Chicago or CERN's e+e- collider, both much smaller than the LHC, have given physicists evidence that atoms are not the smallest, most fundamental particles in the universe. That honor now goes to still smaller particles, called quarks and leptons. (It is now believed that all matter is composed of six types of quarks and six types of leptons.) And this is only the beginning—there are neutrinos and muons and Ws and Zs and so forth.

Why is it all so complex? Unquenchable optimism on the part of theoretical physicists leads them to a conviction that beneath this discouraging complexity is a beautiful simplicity. The theorists' hopes are strengthened by the role that the concept of symmetry seems to play when the theoretical ideas are examined mathematically. A kaleidoscope shows a bewilderingly complex pattern, but it can be explained by a simple pattern and system of mirrors. The LHC, physicists hope, will help them see the simple pattern emerging from the confusion of mirrors.

What holds the universe together? Gravity is the force that keeps my feet on the ground, but it's only one of four forces that exist in the universe. Another is electromagnetism, which is familiar to any schoolchild who has fashioned an electromagnet by twisting a wire around a nail and hooking both ends to a battery. Electromagnetism's crucial role is binding quarks and leptons together to make atoms and atoms together to make molecules. The atom's job is simplified by the existence of two other forces: the "strong" and the "weak," which operate in the domain of the nucleus of atoms. What drives physicists crazy is that all four forces don't mix: we've been able to devise theories linking all but gravity. We have a theory of the electromagnetic force, which makes very successful predictions. Similarly, we have a theory of the weak force and a satisfactory theory of the strong force. The crying need is for a theory that unifies all these three forces and that would also include gravity. (This would be the long-sought—but poorly named—theory of everything.) Although gravity seems like an obvious fact of life to the layperson, to the theoretical physicist it is deeply aggravating. Whereas the other three forces—strong, weak and electromagnetic—apparently have a common origin, gravity spoils everything.