So about a year ago, physicists at CERN announced the discovery of the Higgs boson (or more technically, a “Higgs-like particle” that has now been confirmed to be the Higgs) in the LHC. And you probably haven’t heard much about the collider since then. Part of that is because the the discovery (or non-discovery) of the Higgs at the energies the LHC was probing at was one of the biggest tests of the Standard Model of Particle Physics, which was one of the major selling points of building the LHC in the first place. And since February of this year, the LHC has been shut down to allow for technical improvements that will turn it into an even more energetic detector (and in particle physics, the more energetic you are, the more you can see). If you’re really tuned into CERN, you may know that in November of last year, researchers announced observations of a rare kind of meson decay into muons (which are like heavier electrons).
But part of the reason also seems to be that the results from before the shutdown don’t give physicists much new to theorize on. The Higgs boson was discovered to have the mass predicted by the Standard Model, and so served as a great test of that. But that also means it doesn’t really offer anything new for theorists. And though the muon decay hasn’t been verified yet to the statistical significance that particle physicists consider to mean a discovery, what has been found so far still fits into the Standard Model. Neither of these findings fit into most of the common models of supersymmetry, which is believed to be a necessary component of string theory, which is currently the dominant idea to go beyond the Standard Model to a “theory of everything”.
Experimental testing is basic to science, and theories are routinely disproved, so what would be a problem? Before the LHC was turned on, physicists described finding the Higgs and nothing else as a “worst case scenario”. Physicists know the Standard Model is wrong because they can’t use it to get sensible predictions to describe extreme scenarios, like black holes or conditions immediately after the Big Bang. Only finding the Higgs at the LHC doesn’t give any new data for theorists to work with and it may even disprove some versions of string theory, which could be a big blow to a large part of the physics community.
Compare the situation to when Lord Kelvin (supposedly) said “There is nothing new to be discovered in physics now. All that remains is more and more precise measurement.” In 1900, it could have been considered a reasonable statement. Physicists had finished developing the classical theories of mechanics and electromagnetism and they hadn’t observed things they couldn’t explain, like how electrons could stably orbit atomic nuclei. It was only when new experiments were defying their predictions that they realized their theories were wrong and needed to develop new ideas.
If the LHC doesn’t find anything else, there’s no obvious future theory to work with. It also may be hard to justify government spending for the next particle collider to get new data if the physicists have no idea what to expect. Of course, I might be premature here, since the LHC is only halfway through its life and I don’t think there were many other predicted results that would be found before the upgrade.
Science has a good article from before the LHC started it’s test runs that covers this (and is the source of the picture above). You have to a Science account to see it (they’re free!) or access it from a place that has a subscription to the journal, like a library or university.