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**December 11, 2007**

Freelance researcher Garrett Lisi claims to have uncovered THE theory underlying all the universe's particles and forces — including gravitation. The other fundamental forces of nature are the electromagnetic force; the strong force, which binds quarks together in atomic nuclei; and the weak force, which controls radioactive (beta) decay. Lisi's work suggests that a particular geometry forms the basis of all laws of physics, describing both the contents of the universe and the forces that act on them.

Lee Smolin of the Perimeter Institute for Theoretical Physics described Lisi's work as "fabulous." "It is one of the most compelling unification models I've seen in many, many years," he told *New Scientist*.

Lisi's breakthrough came after he read a paper about E_{8} — a complex, eight-dimensional mathematical pattern with 248 points — and realized that if he could place nature's elementary particles and forces on E_{8}'s 248 points, they might all fit together.

Before tackling E_{8}, however, Lisi examined a hexagonal pattern called G_{2}, and found that it explains how the strong nuclear force works. By labeling points on G_{2} with quarks and anti-quarks of each color, and with various gluons, he found that he could reproduce the way that quarks are known to change color when they interact with gluons, using simple geometry.

For the next simplest pattern in the family, Lisi was able to explain the interactions between neutrinos and electrons by using the star-like F_{4}. While the standard model describes the electroweak force, uniting the electromagnetic and the weak forces, Lisi included two force-carrying particles, called "e-phi" and "omega," to the F_{4} diagram — creating a "gravi-electroweak" force.

By using various "identities" of the 40 known particles and forces, Lisi then filled in 228 points of the E_{8} pattern. He filled the remaining 20 gaps with notional particles; that is, those that some physicists predict are associated with gravitation. With all points on the E_{8} pattern occupied, Lisi transformed it using computer simulations and was able to regenerate the earlier basic patterns describing the quark-gluon relationship and his gravi-electroweak force.

"As far as I have been able to tell, it's a perfect match of tens of thousands of interactions," said Lisi, noting that the model is "without strings, extra space-time dimensions, or other weird inventions that there's no evidence for." Compared with string theory, "this uses baby mathematics," he observed.

"Since E_{8} is perhaps the most beautiful structure in mathematics, it is very satisfying that nature appears to have chosen this geometry," Lisi said.

"Some incredibly beautiful stuff falls out of Lisi's theory," said physicist David Finkelstein of the Georgia Institute of Technology. "I think that this must be more than coincidence and he really is touching on something profound." Finkelstein plans to investigate whether space-time could be described as a quilt woven together from E_{8} patches.

Source: *New Scientist*, Nov. 17, 2007; *Economist*, Nov. 22, 2007.

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218

Start Date:

Tuesday, December 11, 2007