The entire known Universe — from the smallest constituents of the atoms to the largest superclusters of galaxies — have a lot of things in common. Although the scales differ by some 50 orders of magnitude, the laws that govern the grandest scales of the cosmos are the very same laws that govern the tiniest particles and their interactions with one another on the smallest known scales. We study, however, these two scales in entirely different ways; the largest scales can only be studied with great telescopes, using the natural cosmic laboratory of outer space, while the smallest scales require the largest, most powerful machines ever constructed here on Earth: particle accelerators! The largest of them is the Large Hadron Collider (LHC), which is also by far the most powerful.
Although many scientists were hoping that the LHC finds something new, exciting and unexpected, it was mainly constructed to find the last missing piece of the Standard Model: the Higgs Boson. There are many types of fundamental particles in the Universe, but we can divide them into three general categories: fermions (like quarks and electrons), gauge bosons (like the photon), and the Higgs, a unique, fundamental scalar particle. The standard model, of course, does not include gravity. But the real Universe has gravity, and it is assumed that whatever the full, fundamental theory of the Universe is, it incorporates all of the known forces, gravity included. When it comes to gravity, General Relativity is considered as a low-energy, large-scale (compared to the Planck length, at least) approximation of a more fundamental, fully quantum treatment of gravity, which is simply beyond the scope of our current theoretical tools. But there is a new idea gaining traction in recent years when it comes to making a quantum field theory (QFT) of gravity: asymptotic safety. Without going into any mathematical detail, you can think of it as a mathematical toolbox that allows you to incorporate gravitation into your QFT.
There’s a very important reason we care about this: if we understand how to incorporate gravity into QFT, and we’ve measured the masses of all the standard model particles except one, we can theoretically predict what the mass of that one remaining particle needs to be in order for physics to work properly at all energies! But if we can predict that mass, and the actual mass of the Higgs boson turns out to be anything else, either higher or lower, then that means there must be something new in the Universe in order for physics to be self-consistent. Now, here’s the truly amazing thing: the mass of the Higgs boson was correctly calculated to be 126 GeV back in 2009, before the LHC was turned on.
So, if asymptotic safety is right, and the work done in the 2009 paper is right, then an observation of a Higgs Boson with a mass of 126 GeV, with a very small uncertainty (±1 or 2 GeV), would be towering evidence against supersymmetry, extra dimensions, technicolor, or any other theory that incorporates any new particles that could be found by any accelerator that could be built within our Solar System.
Fast-forward to July 2012, when the discovery of the Higgs Boson — confirmed to be a single, fundamental scalar particle of spin-0 — was announced. According to the combined ATLAS+CMS data (both major detectors), a Higgs of mass somewhere between 125 and 126 GeV was detected with a (robust) significance of 6-σ, with an uncertainty of around ±1 GeV. In other words, those of you who followed the excitement in July may have witnessed the last fundamental particle physics discovery we will ever make. There still may be more out there, but the Higgs Boson could have very well been the last unfound fundamental particle accessible to colliders.
There are still more questions to answer, more physics to learn and more to explore even with the LHC, including questions about dark matter, the origin of neutrino mass, and the lack of strong CP-violation. But there might not be anything more to learn — at least, in terms of fundamental, new particles — from doing particle physics at higher and higher energies.