There have been heaps of excitement about the official launch today of the Large Hadron Collider—whether it's visions of protons flying around the world's largest particle accelerator and creaming one another, or for some, the thought of those collisions creating world-destroying black holes.
But if the LHC works exactly the way many scientists hope, the results could be booooooring: finding the Higgs boson—the only particle that's predicted by the current standard model of particle physics but not found—and perhaps a few more expected phenomena along the way. However, nature works in weird ways, especially when you're recreating energies last seen during the Big Bang. So there's a fighting chance that the LHC will be much more than a $10 billion validator: It won't destroy the world, but it certainly could turn the physics world upside-down.
The 5th Dimension (and 6th, and 7th…)
So what would take the entire physics community by storm? How about any physical evidence that supports string theory? For all the hoopla, from amateur physicists who like the idea of universe made of rattling strings to Ph.D.s who understand the crazy calculations involved, no one has ever actually found any solid evidence for string theory. So if you're longing for a surprise, this could be it.
One of the central ideas of string theory is that there are other spatial dimensions than the three we're used to; many string theorists imagine a world with 10 of the things. Extra dimensions tease the imagination and inspire science fiction, but dealing with them in reality often causes a lot of extra explaining, equation adjusting, and overall confusion. The LHC could turn up evidence of extra dimensions—for example, if it shows gravitons slipping into other dimensions. Or, if the LHC does create micro black holes (which will quickly evaporate, not destroy the world), some physicists say that they could study the strange array of subatomic particles the black holes create, and use the decay rates of those particles to tell whether extra hidden dimensions exist.
Into the Dark
Don't forget about our old friend dark matter. Dark matter is so enigmatic—you can't see it, you can't taste it or feel it—that it's bewitching. This mysterious substance that makes up much more of the universe than regular matter may have the right "interaction strength" to show up in LHC experiments. Some hypotheses suggest that the particles produced by collisions will decay into dark matter, which could then be studied.
But there's no guarantee that dark matter can be "thermally created," so it might not even show up at the LHC. And unfortunately, since we don't know what dark matter is made of or how to see it, the collider's experiments could interact with it and we still might not even be able to spot it. Physicists know it interacts only very weakly with other particles, so it would be difficult to tell dark matter from background noise. But if the LHC creates any of the leading candidates to be dark matter—including super symmetic particles like neutralinos—that would be a good sign.
I Never Thought of That!
Some of these potential surprises would validate one model of particle physics over another, or maybe even lend some experimental credence to string theory. But the truly exciting prospect would be the LHC finding something that nobody predicted. Cosmic Variance's post handicapping what will happen at the LHC gives this a 50-50 shot. And if you want to jumpstart the physics world, this is the option for you.
There is one possibility, however unlikely, that probably keeps the physicists most closely connected with the LHC up at night: that they will find nothing. They will smash particles for years on end and find nothing major that they didn'tknow before. This will cause much consternation among particle physicists and much awkwardness for the LHC's boosters. Former CERN chief Chris Llewellyn-Smith told The Telegraph that "it would be a little embarrassing for me, who spent years promoting the LHC and getting it funded." But, he says, it could also force scientists to totally rethink their view of the world, meaning finding nothing could eventually be the most exciting option. Or maybe he's just saying that to cover his ass in advance.