On Wednesday, CERN is expected to announce that the Large Hadron Collider has found evidence that the Higgs boson exists with something on the order of 99.99% certainty. The Standard Model of particle physics has predicted the existence of the Higgs since 1967, so why is finding it such a big deal?
The reason the Standard Model of particle physics is called the "Standard Model" of particle physics is that it's been predicting the existence of particles that were later verified experimentally since the mid-1960s. Quarks, for example, were predicted to exist by the Standard Model and then experimentally detected decades later. Same with the tau neutrino, which was predicted to exist in 1977, had a detector built to look for it in the early 1990s, and was detected in 1997.
This is what's so great about the Standard Model: it doesn't just explain existing phenomena in particle physics very very well, it's also able to say "there should be this sort of particle" and physicists can build a detector to go look for it and it'll be right where the model says it'll be.The tau neutrino was the second to last Standard Model particle to be experimentally verified.
The last particle is, of course, the Higgs boson, and even though its existence was predicted in 1964, it's taken this long to start looking for it because of the massive amounts of energy required to create one. And while we're fairly confident that the Higgs exists and the Standard Model can (finally) be completed, there's no guarantee that this is how physics works, which is part of the reason why finding the Higgs is so important: if it's where the Standard Model predicts, that's what we expect. If it's not, physics has some work to do.
It might seem like with the rest of the Standard Model experimentally verified, putting together the last piece is just not that big of a deal. And if the Standard Model really did explain everything, than that might be the case. The problem is, the Standard Model only explains almost everything, and that "almost" includes a lot of stuff that's kind of really super important. Here's a sampling:
- Gravity: The Standard Model can't explain it.
- General Relativity: The Standard Model can't explain it.
- Dark Energy: Most of the energy present in the universe is dark energy, or vacuum energy, and the Standard Model is way off in accounting for all of it.
- Neutrinos: The Standard Model says that neutrinos don't have mass. Experiments show that neutrinos have mass.
- Antimatter: The Standard Model says that matter and antimatter should have been created in approximately the same amounts, and it can't explain where all the antimatter has gone.
Yeah, this looks kinda bad, but the thing to keep in mind is that for just about every single other thing the Standard Model is spot-on. It's been great. And this is why finding the Higgs is so important.
If the Higgs is exactly where the Standard Model predicts that it's going to be (which seems likely at this point), then the Standard Model gets to keep its self-consistency and physicists have to move on from it and start looking for other ways to explain gravity and relativity and stuff, probably by relying on getting more power from the LHC over the next few years to search for even more exotic particles.
If, however, it turns out that the Higgs has substantially different characteristics than what the Standard Model predicts, there's a chance that it might offer some new avenues to explore without having to move on to an entirely new sort of physics.
Arguably, physicists are more excited for the latter possibility: that the Higgs will open up physics beyond the Standard Model instead of just confirming it.