This question has plagued physicists and cosmologists for years.
An essential clue turned up in 1964 and it is only recently,
following further discoveries and advances in technology, that
it has become possible to exploit the clue and perhaps identify
the culprit. The clue was the discovery that Nature contains
a tiny imbalance, a tendency for the behaviour of certain
‘strange’ particles, such as the electrically neutral K
o
not
to be mimicked precisely by the antimatter counterpart,
the K
¯
o
.
The strange particles had been discovered in 1947 among
the debris arising when cosmic rays hit the upper atmosphere.
The realization that there is exotic stuff in the universe had
helped inspire the building of particle accelerators, which
were capable of producing strange particles, such as K-mesons,
in abundance. Thus it was that in 1964 a team of physicists
at Brookhaven National Laboratory in New York discovered
that about one in a million times, the matter and
antimatter accounts in the K-meson decays failed to
balance.
The nature of this asymmetry is so subtle that investigating it has
been one of the most demanding and delicate measurements in
modern physics. The breakthrough came following the discovery in
1977 of the first examples of ‘bottom’ particles and the realization
that they are in effect heavier versions of strange particles. As the
strange particles can distinguish between matter and antimatter, so
the bottom particles might too. Indeed, when the discovery of
bottom and top quarks confirmed that nature has indeed made
three generations of quarks, and of antiquarks, the resulting
equations surprisingly seemed to imply that an asymmetry between
matter and antimatter for bottom particles was almost inevitable.
The subtle asymmetry between K
o
and K
¯
o
was predicted to be rather
large for their bottom analogues, the B
o
and B
¯
o
. Could the existence
of three generations, and in particular of bottom quarks, somehow
hold the key to the conundrum? As bottom particles are abundant
103
Exotic matter (and antimatter)