From the quest for the most fundamental particles of matter to the mysteries of dark matter, supersymmetry, and extra dimensions, many of nature’s greatest puzzles are being probed at the Large Hadron Collider.
Image credit: Fermi Lab/Symmetry Magazine
What is the form of the universe?
What is the form of the universe?
Physicists created the Standard Model to explain the form of the universe—the fundamental particles, their properties, and the forces that govern them. The predictions of this tried-and-true model have repeatedly proven accurate over the years. However, there are still questions left unanswered. For this reason, physicists have theorized many possible extensions to the Standard Model. Several of these predict that at higher collision energies, like those at the LHC, we will encounter new particles like the Z', pronounced " Z prime." It is a theoretical heavy boson whose discovery could be useful in developing new physics models. Depending on when and how we find a Z' boson, we will be able to draw more conclusions about the models it supports, whether they involve superstrings, extra dimensions, or a grand unified theory that explains everything in the universe. Whatever physicists discover beyond the Standard Model will open new frontiers for exploring the nature of the universe.
What is the universe made of?
Since the 1930s, scientists have been aware that the universe contains more than just regular matter. In fact, only a little over 4 percent of the universe is made of the matter that we can see. Of the remaining 96 percent, about 23 percent is dark matter and everything else is dark energy, a mysterious substance that creates a gravitational repulsion responsible for the universe’s accelerating expansion. One theory regarding dark matter is that it is made up of the as-yet-unseen partners of the particles that make up regular matter. In a supersymmetric universe, every ordinary particle has one of these superpartners. Experiments at the LHC may find evidence to support or reject their existence.
Are there extra dimensions?
We experience three dimensions of space. However, the theory of relativity states that space can expand, contract, and bend. It’s possible, therefore, that we encounter only three spatial dimensions because they’re the only ones our size enables us to see, while other dimensions are so tiny that they are effectively hidden. Extra dimensions are integral to several theoretical models of the universe; string theory, for example, suggests as many as seven extra dimensions of space. The LHC is sensitive enough to detect extra dimensions ten billion times smaller than an atom. Experiments like ATLAS and CMS are hoping to gather information about how many other dimensions exist, what particles are associated with them, and how they are hidden.
What are the most basic building blocks of matter?
Particle physicists hope to explain the makeup of the universe by understanding it from its smallest, most basic parts. Today, the fundamental building blocks of the universe are believed to be quarks and leptons; however, some theorists believe that these particles are not fundamental after all. The theory of compositeness, for example, suggests that quarks are composed of even smaller particles. Efforts to look closely at quarks and leptons have been difficult. Quarks are especially challenging, as they are never found in isolation but instead join with other particles to form hadrons, such as the protons that collide in the LHC. With the LHC’s high energy levels, scientists hope to collect enough data about quarks to reveal whether anything smaller is hidden inside.
Why do some particles have mass?
Through the theory of relativity, we know that particles moving at the speed of light have no mass, while particles moving slower than light speed do have mass. Physicists theorize that the omnipresent Higgs field slows some particles to below light speed, and thus imbues them with mass. We can’t study the Higgs field directly, but it is possible that an accelerator could excite this field enough to "shake loose" Higgs boson particles, which physicists should be able to detect. After decades of searching, physicists believe that they are close to producing collisions at the energy level needed to detect Higgs bosons.
Image credit: NASA