Knowing the mind of God: Seven theories of everything

The "theory of everything" is one of the most cherished dreams of science. If it is ever discovered, it will describe the workings of the universe at the most fundamental level and thus encompass our entire understanding of nature. It would also answer such enduring puzzles as what dark matter is, the reason time flows in only one direction and how gravity works. Small wonder that Stephen Hawking famously said that such a theory would be "the ultimate triumph of human reason - for then we should know the mind of God". Read more

Why There Can't Be a Theory of Everything Pierre-Simon de Laplace, the 18th century French astronomer who proposed one of the early theories of the formation of the solar system, famously postulated a "Demon" who had enough information to know what would happen in any place in the universe at any time. It was the height of mechanistic and deterministic hubris in science, and it seemed that it was only a matter of time before physicists would find out everything there was to find out about the way the world works

The Universe in a Grain of Sand There was a flurry of press coverage when the Large Hadron Collider in Switzerland was turned on, and again when it was shut down by a technical problem shortly afterwards. The colliders operation was a much-anticipated event in science, one that could confirm or undermine one of the most successful theories about how the universe is structured. The public attention that it has received is rare for scientific news, perhaps owing to concerns that something celestially dangerous is being cooked up in our backyard.

Although we may believe humans know a lot about the Universe, there are still a lot of phenomena to be explained. A team of cosmologists from the University of the Basque Country are searching for the model that best explains the evolution of the Universe. We usually have an image of scientists who study the Universe doing so peering through a telescope. And, effectively, this is what astrophysicists do: gather data about the observable phenomena of the Universe. However, in order to interpret this data, i.e. to explain the majority of the phenomena occurring in the Universe, complicated calculations with a computer are required and which have to be based on appropriate mathematical models. This is what the Gravitation and Cosmology research team at the University of the Basque Country (UPV/EHU) is involved in: analysing models capable of explaining the evolution of the Universe.

Three researchers have shared this years Nobel Prize for Physics for their work in particle physics on symmetry-breaking and quarks. The Nobel committee has awarded one half of the award to Yoichiro Nambu of the University of Chicago for the discovery of the mechanism of spontaneous broken symmetry in subatomic physics.

Europeans unite to tap early universe for secrets of fundamental physics The future of fundamental physics research lies in observing the early universe and developing models that explain the new data obtained. The availability of much higher resolution data from closer to the start of the universe is creating the potential for further significant theoretical breakthroughs and progress resolving some of the most difficult and intractable questions in physics. But this requires much more interaction between astronomical theory and observation, and in particular the development of a new breed of astronomer who understands both. This was the key conclusion from a recent workshop organised by the European Science Foundation (ESF), bringing together experts in cosmology, astrophysics and particle physics.

Scientists have used a supercomputer to shed new light on one of the most important theories of physics, the Standard Model, which encapsulates understanding of all the material that makes up the universe. This 30-year-old theory explains all the known elementary particles and three of the four forces acting upon them - however, it excludes the force of gravity, which is its shortcoming. Physicists have been trying to find the missing pieces in the jigsaw that would extend the Standard Model into a complete theory of all the forces of nature. However, the landmark findings by researchers at the Universities of Edinburgh and Southampton, and their partners in Japan and the US, confirm the Standard Model to even greater precision than before, deepening the puzzle. The project's enormously complex calculations relate to the behaviour of tiny particles found in the nuclei of atoms, known as quarks. In order to carry out these calculations, the researchers first designed and built a supercomputer that was among the fastest in the world, capable of tens of trillions of calculations per second. The computations themselves have taken a further three years to complete. Their result shows that the Standard Model's claim to be the best theory invented holds firm. It raises the stakes for the riddle to be solved by experiments at the Large Hadron Collider at CERN, which will switch on later this year. Physicists efforts to confront Standard Model predictions using the most powerful computers available with the most precise experiments offer no clues about what to expect.

"An Exceptionally Simple Theory of Everything" is the title of a physics paper submitted to the arXiv library on Nov. 6, 2007 by Antony Garrett Lisi. His theory unifies all fields of the standard model with gravity using a 248 point lattice of E8 geometry. The paper has not yet been peer-reviewed or published in a scientific journal; however, physicist Lee Smolin has described the work as "one of the most compelling unification models I've seen in many, many years."

According to Lisi, the mathematics of the universe should be beautiful and a successful description of nature should be a concise, elegant, unified mathematical structure consistent with experience.

In field theory, all of the observable properties of fundamental particles can be understood as the result of operations acting on a field whose basis is the set of allowed quantum mechanical states. The mathematics of such fields are governed by certain rules (e.g. commutation relations) that define how particles are allowed to interact, and in addition one must specify a mathematical principle, known as the action, that governs how states will evolve with time. Previously, quantum field theory had been able to identify the properties of the Standard Model of elementary particles as corresponding with the mathematics of well-known Lie groups, specifically SU(3) for the strong force and SU(2) x U(1) for the electroweak force. In addition, the mathematics of general relativity is equivalent to that of the Lorentz group, SO(3,1).

Lisi's work identifies a mechanism by which the mathematics of all of the above forces and their associated fundamental particles can be embedded within the mathematical framework of E8, which is the largest of the simple Lie groups. He also specifies an action for the resulting structure which, if correct, would provide the framework for co-evolving gravitational and quantum mechanical interactions, thus providing a solution to the problem of quantum gravity. Since the action he specified contains the normal relations of both quantum mechanics and relativity, this theory is intrinsically consistent with both realms of established physics in the limits where each is individually applicable. In addition, a natural consequence of the triality within E8 is that there should be exactly three families of fermions. The presence of three families is experimentally well-established, but the Standard Model provided no explanation for why exactly three.

Lisi's embedding admits no free parameters. It necessarily predicts as a consequence of the embedding and the structure of E8 the exact number of fundamental particles, all of their properties, their masses, the forces between them, the nature of space-time, and the cosmological constant. The quantum mechanical properties are forced to be true by construction, while the masses should be determinable, in principle, by measuring expectation values of fundamental states over the Higgs component of his field. However, the calculation required to do so is extremely complicated and was not attempted prior to publication. In addition, Lisi's embedding is likely not unique. He embedded the quantum mechanical terms within E8 in a way that minimises mixing between states. It is likely that other "less elegant" embeddings could also be constructed that would unite quantum mechanics and relativity within E8 but give rise to different predictions for particle masses.

In Lisi's theory, there are 20 elements out of the 248 basis elements of the E8 Lie group, which do not correspond to known particles/forces. These require the existence of new particles and force interactions, though the exact number of new particles will depend on the mixing of these basis states with those for the conventionally known particles (such mixing is exactly defined by the structure of E8 but not yet determined). The new fields include two new quantum numbers in the Pati-Salam model, a new Higgs scalar, as well as new fields that mix leptons and quarks and have forces that vary depending on fermion family. Hence, the theory also predicts proton decay. To be consistent with previous observations, Lisi suggests that the masses of any resulting extra particles would need to be too large to have been observed by current particle accelerators. It can be hoped that the mass of at least one of these extra particles will be within the range to be discovered by the soon to be completed Large Hadron Collider.