Quantum loop gravity proposes a solution to the unification of quantum physics and general relativity, and predicts lots of known particles in the bargain:
NewScientist article and commentary (which can be read without a subscription)
Enter Sundance Bilson-Thompson, a theoretical particle physicist at the University of Adelaide in South Australia. He knew little about quantum gravity when, in 2004, he began studying an old problem from particle physics. Bilson-Thompson was trying to understand the true nature of what physicists think of as the elementary particles - those with no known sub-components. He was perplexed by the plethora of these particles in the standard model, and began wondering just how elementary they really were. As a first step towards answering this question, he dusted off some models developed in the 1970s that postulated the existence of more fundamental entities called preons.
Just as the nuclei of different elements are built from protons and neutrons, these preon models suggest that electrons, quarks, neutrinos and the like are built from smaller, hypothetical particles that carry electric charge and interact with each other. The models eventually ran into trouble, however, because they predicted that preons would have vastly more energy than the particles they were supposed to be part of. This fatal flaw saw the models abandoned, although not entirely forgotten.
Bilson-Thompson took a different tack. Instead of thinking of preons as particles that join together like Lego bricks, he concentrated on how they interact. After all, what we call a particle's properties are really nothing more than shorthand for the way it interacts with everything around it. Perhaps, he thought, he could work out how preons interact, and from that work out what they are.
To do this, Bilson-Thompson abandoned the idea that preons are point-like particles and theorised that they in fact possess length and width, like ribbons that could somehow interact by wrapping around each other. He supposed that these ribbons could cross over and under each other to form a braid when three preons come together to make a particle. Individual ribbons can also twist clockwise or anticlockwise along their length. Each twist, he imagined, would endow the preon with a charge equivalent to one-third of the charge on an electron, and the sign of the charge depends on the direction of the twist.
The simplest braid possible in Bilson-Thompson's model looks like a deformed pretzel and corresponds to an electron neutrino (see Graphic). Flip it over in a mirror and you have its antimatter counterpart, the electron anti-neutrino. Add three clockwise twists and you have something that behaves just like an electron; three anticlockwise twists and you have a positron. Bilson-Thompson's model also produces photons and the W and Z bosons, the particles that carry the electromagnetic and weak forces. In fact, these braided ribbons seem to map out the entire zoo of particles in the standard model. |
