**Sundance Osland Bilson-Thompson** is an

AustraliaAustralia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...

n theoretical

particle physicistParticle physics is a branch of physics that studies the existence and interactions of particles that are the constituents of what is usually referred to as matter or radiation. In current understanding, particles are excitations of quantum fields and interact following their dynamics...

. He has developed the idea that certain

preonIn particle physics, preons are postulated "point-like" particles, conceived to be subcomponents of quarks and leptons. The word was coined by Jogesh Pati and Abdus Salam in 1974...

models may be represented

topologicallyTopology is a major area of mathematics concerned with properties that are preserved under continuous deformations of objects, such as deformations that involve stretching, but no tearing or gluing...

, rather than by treating preons as pointlike

particlesIn particle physics, an elementary particle or fundamental particle is a particle not known to have substructure; that is, it is not known to be made up of smaller particles. If an elementary particle truly has no substructure, then it is one of the basic building blocks of the universe from which...

. His ideas have attracted interest in the field of

loop quantum gravityLoop quantum gravity , also known as loop gravity and quantum geometry, is a proposed quantum theory of spacetime which attempts to reconcile the theories of quantum mechanics and general relativity...

, as they may represent a way of incorporating the

Standard ModelThe Standard Model of particle physics is a theory concerning the electromagnetic, weak, and strong nuclear interactions, which mediate the dynamics of the known subatomic particles. Developed throughout the mid to late 20th century, the current formulation was finalized in the mid 1970s upon...

into loop quantum gravity. This would make loop quantum gravity a candidate

theory of everythingA theory of everything is a putative theory of theoretical physics that fully explains and links together all known physical phenomena, and predicts the outcome of any experiment that could be carried out in principle....

. He was a Visiting Academic at the

University of AdelaideThe University of Adelaide is a public university located in Adelaide, South Australia. Established in 1874, it is the third oldest university in Australia...

, and from 2007 to 2009 he was a full-time academic at the

Perimeter Institute for Theoretical PhysicsPerimeter Institute for Theoretical Physics is an independent, resident-based research institute devoted to foundational issues in theoretical physics located in Waterloo, Ontario, Canada. Perimeter Institute was founded in 1999 by Mike Lazaridis...

in

Waterloo, OntarioWaterloo is a city in Southern Ontario, Canada. It is the smallest of the three cities in the Regional Municipality of Waterloo, and is adjacent to the city of Kitchener....

, Canada.

## Summary of Bilson-Thompson's research

There have been recent claims that loop quantum gravity may be able to reproduce features resembling the

Standard ModelThe Standard Model of particle physics is a theory concerning the electromagnetic, weak, and strong nuclear interactions, which mediate the dynamics of the known subatomic particles. Developed throughout the mid to late 20th century, the current formulation was finalized in the mid 1970s upon...

. So far only the first generation of fermions (leptons and quarks) with correct parity properties have been modelled by Sundance Bilson-Thompson using

preonIn particle physics, preons are postulated "point-like" particles, conceived to be subcomponents of quarks and leptons. The word was coined by Jogesh Pati and Abdus Salam in 1974...

s constituted of braids of spacetime as the building blocks. However, there is no derivation of the

LagrangianThe Lagrangian, L, of a dynamical system is a function that summarizes the dynamics of the system. It is named after Joseph Louis Lagrange. The concept of a Lagrangian was originally introduced in a reformulation of classical mechanics by Irish mathematician William Rowan Hamilton known as...

that would describe the interactions of such particles, nor is it possible to show that such particles are fermions, nor that the gauge groups or interactions of the Standard Model are realised. Utilization of quantum computing concepts made it possible to demonstrate that the particles are able to survive

quantum fluctuationIn quantum physics, a quantum fluctuation is the temporary change in the amount of energy in a point in space, arising from Werner Heisenberg's uncertainty principle.According to one formulation of the principle,energy and time can be related by the relation...

s.

In a 2005 paper, Sundance Bilson-Thompson proposed a model which adapted the

Harari Rishon ModelThe rishon model is the earliest efforts to develop a preon model to explain the phenomena appearing in the Standard Model of particle physics. It was first developed by Haim Harari and Michael A...

to preon-like objects which were extended ribbons, rather than point-like particles. This provided a possible explanation for why ordering of the subcomponents matters (giving rise to colour charge) whereas in the older point-particle preon model (Rishon Model), this feature must be treated as an

*ad hoc* assumption. Bilson-Thompson refers to his extended ribbons as "helons", and his model as the Helon Model.

This model leads to an interpretation of electric and colour charge as a topological quantities (electric as number of twists carried on the individual ribbons and colour as a number of variants of such twisting for fixed electric charge).

In a subsequent paper from 2006 Bilson-Thompson,

Fotini MarkopolouFotini G. Markopoulou-Kalamara is a Greek theoretical physicist interested in foundational mathematics and quantum mechanics. She is a faculty member at Perimeter Institute for Theoretical Physics and is an adjunct professor at the University of Waterloo.Markopoulou received her Ph.D...

, and

Lee SmolinLee Smolin is an American theoretical physicist, a researcher at the Perimeter Institute for Theoretical Physics, and an adjunct professor of physics at the University of Waterloo. He is married to Dina Graser, a communications lawyer in Toronto. His brother is David M...

suggested that in any of a class of

quantum gravityQuantum gravity is the field of theoretical physics which attempts to develop scientific models that unify quantum mechanics with general relativity...

theories similar to

loop quantum gravityLoop quantum gravity , also known as loop gravity and quantum geometry, is a proposed quantum theory of spacetime which attempts to reconcile the theories of quantum mechanics and general relativity...

(LQG) in which

spacetimeIn physics, spacetime is any mathematical model that combines space and time into a single continuum. Spacetime is usually interpreted with space as being three-dimensional and time playing the role of a fourth dimension that is of a different sort from the spatial dimensions...

comes in discrete chunks, excitations of spacetime itself may play the role of preons, and give rise to the standard model of particle physics as an emergent property of the quantum gravity theory.

Consequently, Bilson-Thompson

*et al.* proposed that loop quantum gravity could reproduce the standard model. In this scenario the four forces would already be unified. The first generation of fermions (leptons and quarks) with correct charge and parity properties have been modelled using preons constituted of braids of spacetime as the building blocks.

Bilson-Thompson's original paper suggested that the higher-generation fermions could be represented by more complicated braidings, although explicit constructions of these structures were not given. The electric charge, colour, and parity properties of such fermions would arise in the same way as for the first generation. The model was expressly generalized for an infinite number of generations and for the weak force bosons (but not for photons or gluons) in a 2008 paper by Bilson-Thompson, Hackett, Kauffman and Smolin.

### Criticism

Lubos MotlLuboš Motl is a Czech theoretical physicist who keeps a blog commenting on physics, global warming and politics. His scientific research concentrated on string theory, of which he has been a passionate defender. He proposed Matrix string theory in 1997.Motl was born in Plzeň, Czech Republic...

points out sarcastically that the proposed interpretation of the ribbon diagrams leaves unexplained almost every feature of actual standard model particles.

How do you get fermions and their chiralA chiral phenomenon is one that is not identical to its mirror image . The spin of a particle may be used to define a handedness for that particle. A symmetry transformation between the two is called parity...

gauge interactions, you may still want to ask? For example, the muon neutrino is an octopus handcuffed in one way. Other particles correspond to other kind of knots created from trinions. Surely, the more advanced questions - why do the particles live in three dimensions as opposed to a string with defects, why are the animals fermions, why are they described by spinors, why there are any gauge groups at all, why the fermions have the right representation properties, and why there is any del-slashIn the study of Dirac fields in quantum field theory, Richard Feynman invented the convenient Feynman slash notation...

, any covariant derivativeIn mathematics, the covariant derivative is a way of specifying a derivative along tangent vectors of a manifold. Alternatively, the covariant derivative is a way of introducing and working with a connection on a manifold by means of a differential operator, to be contrasted with the approach given...

, the Lorentz invariance, or anything else for that matter - are details that will be fully resolved in a simple followup of this paper.

## External links

- University of Adelaide
- Sundance Bilson-Thompson (Perimeter Institute for Theoretical Physics)
- You are made of space-time (
*New Scientist*New Scientist is a weekly non-peer-reviewed English-language international science magazine, which since 1996 has also run a website, covering recent developments in science and technology for a general audience. Founded in 1956, it is published by Reed Business Information Ltd, a subsidiary of...

12 August 2006)
- Topological preon models: a braid new world
- Bilson-Thompson, S. O.;
*A topological model of composite preons* submitted to Phys. Lett. B (2005)
- Bilson-Thompson, S. O.; Markopoulou, F.; and Smolin, L.
Lee Smolin is an American theoretical physicist, a researcher at the Perimeter Institute for Theoretical Physics, and an adjunct professor of physics at the University of Waterloo. He is married to Dina Graser, a communications lawyer in Toronto. His brother is David M...

*Quantum Gravity and the Standard Model*, published in Class. Quant. Grav.24:3975-3994 (2007).
- Sundance Bilson-Thompson's blog