8 June 2019 | New Scientist | 35didn’t find favour at the time, but faced
with a number of intractable problems in
fundamental particle physics, researchers
such as Broussard and Berezhiani have begun
to embrace it again. In fact, says Berezhiani, we
may already have seen signs of its existence.
Most clearly, they believe, its fingerprints
can be glimpsed in the behaviour of the
neutron, one of the three particles atoms
break down into. Over time, neutrons outside
an atomic nucleus decay into the other two –
electrons and protons – in the process of beta
decay. For decades, we have been trying to
work out exactly how long these so-called free
neutrons live before they decay, and we have
been getting strangely conflicting results.
There are broadly two ways of measuring
the lifetime of a free neutron – by bottle and
by beam. The bottle experiment is fairly
straightforward. You use a weak magnetic field
to herd neutrons into what is called a bottle
trap. Then you wait a certain amount of time
before counting how many neutrons are >PATRY
K^ HARDZ
IEJ^
ST
UDIOA key symmetry in particle physics was
parity, which mandated that everything
should stay the same even if all positions
and orientations were flipped as though
in a mirror. Lee and Yang proposed an
experimental test for parity violations. When
Chinese-American physicist Chien-Shiung
Wu built and ran the experiment, she found
that parity could occasionally be violated.
This was so significant a discovery that Lee
and Yang (though not Wu) were awarded the
Nobel prize in physics the very next year.
Lee and Yang also came up with a rather
off-the-wall explanation. They suggested
that parity was in fact conserved, and only
appeared to be violated because we were
looking at half the picture. “They suggested
parity is broken in our universe only because
there is another sector where parity is broken
in the opposite direction,” says Zurab
Berezhiani at the University of L’Aquila in
Italy. “So it’s retained overall.”
This concept of a “mirror matter” world
“ We may
already have
seen signs of
its existence in
the behaviour
of the neutron”