Confirming Einstein ?

This is a guest column by Sourendu Gupta, TIFR, Mumbai

UPI today picked up what is probably its first ever news story about lattice gauge theory. This is a method of dealing with a quantum field theory which is usually applied to problems where nothing else works, and is heavily dependent on modern supercomputers. The news is about an application to computing the mass of a proton by Stephan Duerr and his collaborators. If you are not familiar with particle physics and field theories, then think of it as computing Avogadro's number to three digit precision using as input only the standard model of particle physics.

Quantum field theories inherit infinities from classical theories of matter: most well-known of which is the infinity encountered in Lorentz's theory of the electron. Because of such infinities, classical theories cannot manage to explain the structure of matter, ie, the masses of elementary particles, and their basic interactions. However, quantum theories can remove these infinities and make precise predictions about physical quantities. The process by which this is done is called renormalization.

In the 1970's Kenneth Wilson exploited a deep connection between quantum theory and statistical mechanics to understand the physics of renormalization. Since then his insights have permeated all theories of matter and started a quiet revolution which has gone largely unnoticed outside the world of theoretical physics. However, Wilson's way of understanding renormalization has provided solutions to many outstanding problems: the computation of Avogrado's number starting from particle physics being just one.

Mass media, however, recognize Einstein as the sole repository of genius in the sciences. Hence the connection with him in UPI's report, and the invocation of his name by media science in general. To the extent that particle physics uses relativistic quantum field theories, the report by UPI is certainly not wrong. E=mc² is certainly important (again, for the umpteen millionth time) and the supercomputers used most definitely treat the theory on a space-time lattice. However these are not the most exciting things about the result reported.

For those who attend the Lattice Meeting each summer, the exciting aspect of this work is that it is one of several this year which compute the masses of the proton and other hadrons with high accuracy. Lattice gauge theory is now testably one of the most accurate methods of dealing with quantum field theory.

You might expect such a powerful technique to have other things to say. It does. Other works have begun to predict new and as yet unobserved hadrons, some of which may well be seen at the LHC, the Beijing synchrotron, the Jefferson lab or the Japanese collider J-PARC. Results from lattice QCD are also important in tests of CP violations, for which one half of this year's Nobel prize in physics was awarded.

Interestingly, the other half of the same Nobel prize is closely related to another prediction of lattice gauge theory: that of a phase transition to a completely new state of elementary particle matter; one in which there are no hadrons. The reverse phase transition is expected to have occurred within the first microsecond of the history of the universe. This kind of matter may already have been created in a lab: the RHIC. It will be studied further in the LHC.

We are now firmly in the era of lattice gauge theory as a major tool in the box of tricks for theoretical particle physics. This is the place where quantum physics, relativity and supercomputing come together. The newspaper report you saw may have got it wrong, but it wasn't completely wrong.