Unparticle Physics

By Anne Pawsey

What with quantum physics, particle physics and astrophysics to keep them occupied (not to mention the search for the grand theory of everything, oh and string theory) you’d have thought physicists had enough on their plates without inventing yet another type of physics. But that is exactly what they’ve gone and done - it’s called “unparticle physics”.

Unparticle physics is based on the concept of scale invariance, the idea that something looks identical no matter how big it is.

You can get some idea of this by looking at what is called a ‘fractal’. For example, the image below contains many repetitions of the same form, so you'll see the same shapes, no matter how far you zoom in or out.

Professor Howard Georgi of Harvard University recently published a paper on what he calls “unparticle stuff”, the idea being that this unparticle stuff is also scale invariant.

Professor Georgi explains, “It is a phenomenon that has been understood mathematically for a long time, in the sense that we know of theories that have the peculiar property of scale-invariance. It is hard to describe this because it is so different from what we are used to. For us it makes a big difference whether we measure masses in grams or kilograms. But in a scale-invariant world, it makes no difference at all.”

One example of a scale invariant particle is a photon, the particle which carries light. Photons don’t have mass so if you multiply all photon energies by say 1000 they would still look identical. Unfortunately this doesn’t work with particles that do have mass, which would look and behave differently. But as it is impossible for a scale invariant object to have mass, Professor Georgi calls them “unparticle stuff”.

We don’t see the unparticles because they don’t interact with normal matter at low energies, so we miss their effects. However, it might be possible to see them using the new LHC (Large Hadron Collider) at CERN. At this point, it gets, as the professor says, “weird”. Even we at Null threw down our hats in exasperation trying to understand this one, but persevere if you must…

The idea is to look for missing energy and momentum in collisions. This missing energy is normally thought to be carried away by neutrinos (they are so nearly massless it makes no difference), which go straight through the detector. The unparticle stuff would look like a fractional number of neutrinos carrying the energy away. Phew.

Go to Anne's page for more physics phun.

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