Part of the laser system used by scientists at Imperial College to measure the shape of the electron. Photograph: Joe Smallman/Imperial College

Scientists
at Imperial College London have made the most accurate measurement yet
of the shape of the humble electron, finding that it is almost a perfect
sphere, in a study published in the journal Nature
this week. The experiment, which spanned more than a decade, suggests
that the electron differs from being perfectly round by less than
0.000000000000000000000000001 cm. This means that if the electron was
magnified to the size of the solar system, it would still appear
spherical to within the width of a human hair.

The
physicists from Imperial’s Centre for Cold Matter studied the electrons
inside molecules called ytterbium fluoride. Using a very precise laser,
they made careful measurements of the motion of these electrons. If the
electrons were not perfectly round then, like an unbalanced
spinning-top, their motion would exhibit a distinctive wobble,
distorting the overall shape of the molecule. The researchers saw no
sign of such a wobble.

The
researchers are now planning to measure the electron’s shape even more
closely. The results of this work are important in the study of
antimatter, an elusive substance that behaves in the same way as
ordinary matter, except that it has an opposite electrical charge. For
example, the antimatter version of the negatively charged electron is
the positively charged anti-electron (also known as a positron).
Understanding the shape of the electron could help researchers
understand how positrons behave and how antimatter and matter might
differ.

Research
co-author, Dr Jony Hudson, from the Department of Physics at Imperial
College London, said, “We’re really pleased that we’ve been able to
improve our knowledge of one of the basic building blocks of matter.
It’s been a very difficult measurement to make, but this knowledge will
let us improve our theories of fundamental physics. People are often
surprised to hear that our theories of physics aren’t ‘finished’, but in
truth they get constantly refined and improved by making ever more
accurate measurements like this one.”

The
currently accepted laws of physics say that the Big Bang created as
much antimatter as ordinary matter. However, since antimatter was first
envisaged by Nobel Prize-winning scientist Paul Dirac in 1928, it has
only been found in minute amounts from sources such as cosmic rays and
some radioactive substances.

Imperial’s
Centre for Cold Matter aims to explain this lack of antimatter by
searching for tiny differences between the behaviour of matter and
antimatter that no-one has yet observed. Had the researchers found that
electrons are not round it would have provided proof that the behaviour
of antimatter and matter differ more than physicists previously thought.
This, they say, could explain how all the antimatter disappeared from
the universe, leaving only ordinary matter.

“The
whole world is made almost entirely of normal matter, with only tiny
traces of antimatter. Astronomers have looked right to the edge of the
visible universe and even then they see just matter, no great stashes of
antimatter. Physicists just do not know what happened to all the
antimatter, but this research can help us to confirm or rule out some of
the possible explanations,” said Professor Edward Hinds, research
co-author and head of the Centre for Cold Matter at Imperial College
London.

Antimatter
is also studied in tiny quantities in the Large Hadron Collider at CERN
in Switzerland, where physicists hope to understand what happened in
the moments following the Big Bang and to confirm some currently
unproven fundamental theories of physics, such as supersymmetry. Knowing
whether electrons are round or egg-shaped tests these same fundamental
theories, as well as other theories of particle physics that even the
Large Hadron Collider cannot test.

To
help improve their measurements of the electron’s shape, the
researchers at the Centre for Cold Matter are now developing new methods
to cool their molecules to extremely low temperatures, and to control
the exact motion of the molecules. This will allow them to study the
behaviour of the embedded electrons in far greater detail than ever
before. They say the same technology could also be used to control
chemical reactions and to understand the behaviour of systems that are
too complex to simulate with a computer.

SOURCE: Imperial College London