Confirming Einstein?

Guest Post by Sourendu Gupta, TIFR, Mumba

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.

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