A scientific paper seeking to unify physics with a "theory of everything" and posted this month has attracted attention as much for its bold claim as for its author: a 39-year-old surfer and snowboarder with no university affiliation.
Garrett Lisi has worked as a snowboard instructor in Nevada and a hiking guide in Hawaii, according to a story in this week's New Scientist, and also writes on his personal blog "the best thing there is to do on this planet is surf."
Which makes him an unusual candidate to write a paper entitled "An Exceptionally Simple Theory of Everything," which was posted on the arxiv scientific paper forum on Nov. 6.
But Lisi also has a PhD in physics from the University of California and received support for his work from the Perimeter Institute at the University of Waterloo and funding from the U.S.-based Foundational Questions Institute.
Perimeter professor Lee Smolin described Lisi's work to the New Scientist as "fabulous" and "one of the most compelling unification models I've seen in many, many years."
In short, Lisi's paper tries to find a mathematical way to unite the interactions of all the particles in the universe, from force-carrying particles called bosons to fermions like electrons and quarks, which combine to make up matter.
Standard Model comes up short
The most agreed-upon theory to date — the Standard Model of particle physics — explains the interactions of matter with three of the four fundamental forces of nature: electromagnetism, the strong nuclear force (which binds the parts of a nucleus together), and the weak nuclear force (which allows for the radioactive decay of particles).
Where it's come up short is in explaining the fourth force: gravity. For the 30 years since the Standard Model was proposed, scientists have come up with a number of theories to unite the gravity of Einstein's theory of general relativity with the Standard Model, including string theory, which reduces the forces and matter of the universe to tiny one-dimensional filaments called strings that vibrate in 10 dimensions.
But critics of String Theory, Lisi included, argue it is virtually untestable and bears no resemblance to the world we live in. As Lisi writes in his paper: "A successful description of nature should be concise, elegant, unified mathematical structure consistent with experience."
Lisi's theory attempts to explain the relationship between the particles of the universe with the points on a complex, eight-dimensional mathematical pattern called E8.
E8 is an example of a Lie group. Lie groups were invented by 19th-century Norwegian mathematician Sophus Lie to define objects that have the underlying characteristics of symmetry. Spheres, cylinders and cones are familiar examples of symmetrical shapes that belong to Lie groups.
E8 is the most complex exceptional Lie Group — a 453,060 by 453,060 matrix that exists only in abstract mathematics. It's so complex, its structure wasn't completely unravelled until earlier this year, when a U.S. supercomputer took 77 hours to provide a solution to the formula.
Difficult math hides 'beautiful' structure
While the math behind the theory may be maddeningly complexfor the layman, Lisi said the relationship between E8 and the particle soup of quantum physics fulfils his hope that, as he writes, "the mathematics of the universe should be beautiful."
"Since E8 is perhaps the most beautiful structure in mathematics, it is very satisfying that nature appears to have chosen this geometry," he told the New Scientist.
Since its publication, Lisi's story has attracted the attention of the media, while his theory has been alternately applauded and jeered in the scientific community.
Perimeter Institute researcher Sabine Hossenfelder said Lisi's paper "has the potential to become a very important contribution" and "is worth further examination" but was cautious in her assessment.
"I find it hard to make up my mind on Garrett's model because the attractive and the unattractive features seem to balance each other," she wrote in her blog backRe(Action).
"To me, the most attractive feature is the way he uses the exceptional Lie-groups to get the fermions together with the bosons. The most unattractive feature are the extra assumptions he needs to write down an action that gives the correct equations of motion."
'A huge joke,' critic contends
String theorist and former Harvard professor Lubos Motl had the harshest criticism, writing in his blog the Reference Frame that "the visually intriguing and colorful paper is a huge joke.
"For people like … Garrett Lisi, it is not hard to unify everything with everything else because they don't know any difference between different concepts in physics," Motl wrote.
Lisi's paper itself strikes a cautious tone and suggests some of the paper's findings — including a host of new particles predicted mathematically but so far undetected — might be proven or disproven using the Large Hadron Collider, a powerful particle accelerator expected to begin running in 2008.
"The lack of extraneous structures and free parameters ensures testable predictions, so it will either succeed or fail spectacularly," he wrote.