According to Harvard University's Howard Georgi, however, there's at least the theoretical possibility that some matter in the universe is not made of particles at all. Georgi has dubbed the mind-bending matter "unparticle stuff," and hopes that we may see signs of it at the Large Hadron Collider (LHC), a super high energy proton collider due to come online in Europe later this year.

The odds of any unparticle stuff turning up at the LHC are extraordinarily slim, but if it does, we'll know it by an unusual signature. It will appear as though some of the energy from the collider's high energy experiments is carried away by a fractional number of otherwise invisible particles. So if LHC experimentalists happen to see signs of 3.34 ghostly particles, for example, they could be on the track of unparticle matter.

Unparticle stuff may go the way of countless other defunct predictions of exotic phenomena. Unlike the Higgs boson, which many physicists believe will be one of the LHC's great discoveries, there's no compelling reason to expect unparticle stuff to exist at all. But at some level that's the lot of a good theoretical physicist. After all, a theorist who restricts their imagination to merely the likely possibilities probably isn't trying hard enough.

Just what unparticle stuff would be like is hard to say, even for Georgi. "This stuff is so weird and I so far have such a tiny little theoretical window into its properties," says Georgi, "that I really don't know what a teacup full of it would look like or whether it would be good for anything. I hope eventually to understand it well enough to give a better answer."

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