The Higgs bosun is something that theoretical physicists have proposed must be needed. Basically they started asking the question how does a particle know what its mass should be. The Higgs is the particle which tells all the other particles the answer. Although how it knows I do not know.
It’s in the news a lot lately because the Large Hadron Collider is exploring the range of energies (ie. masses) where it is predicted to be. And there are hints that they have seen it too.
Basically the Higgs Boson is the ‘king’ of particles (or the God, which is why some people call it the God Particle), that lets other particles have mass, which lets other things in physics work like gravity. It is only theoretical, because it is probably too tiny or too fast to have been found yet.
But they’ve been looking for it by smashing lots of particles together at the Large Hadron Collider in Switzerland. One of the scientists said last month that they should know whether it exists or not before the end of this year! It’ll be exciting whether or not we find it, because we’ll either have solved the problem, or have to come up with a new idea to test.
A ‘boson’ is a kind of particle that causes a force. So the electromagnetic force is caused by photons, the strong nuclear force is caused by gluons, and the weak force (that causes radioactivity) has three bosons , W+, W- and Z (they get the worst names).
There are only four fundamental forces, so physicists predicted that their must be a boson that causes gravity… the graviton, which you may notice isn’t called the Higgs boson!
The Higgs is supposedly the boson that gives the other particles mass. Gravity and mass are actually separate things, so they kind of need two bosons.
The Higgs was predicted by the Standard Model, which even told us where to look for it, which they are doing in particle accelerators.
Both CERN and the Tevatron in America have said they have seen signs of the Higgs but not conclusive proof yet. Like Leila says, they know that if they don’t see it in a certain place (actually at a certain energy) then it probably doesn’t exists and we may need to rewrite our physics!