34 | New Scientist |8 June 2019
mirror world
A universe identical to our own could be hiding in plain sight.
Michael Brooks steps through the looking glass
A
T FIRST glance, everything looks
familiar. The clock ticks placidly on
the wall, cars motor along outside
your window, the magazine in your hand has
the same eye-catching cover. But something
is wrong. The clocks are running backwards.
Cars are driving on the wrong side of the road.
The article you are reading is written back to
front. Suddenly, it clicks. You are looking at
your own reflection.
The uncanny world on the other side of
the mirror may not seem real to you. But
Leah Broussard thinks parallel universes
where everything is flipped might be very
real indeed. Along with her colleagues at Oak
Ridge National Laboratory in Tennessee, she
is on the hunt for a universe that is identical
to our own, but flipped so that it contains
mirror atoms, mirror molecules, mirror stars
and planets, and even mirror life. If it exists,
it would form a bubble of reality nestling
within the fabric of space and time alongside
our own familiar universe, with some particlescapable of switching between the two.
After decades of tantalising hints about its
existence, the first experiments aiming to
go through the looking glass are about to get
under way. Finding such a mirror universe
would not only transform our view of reality,
but could also answer questions about our
own universe that have puzzled scientists
for decades. “The implications would be
astounding,” says Broussard.
Physicists have found new worlds before.
In 1928, Paul Dirac realised that the equations
of quantum mechanics allowed for the
existence of particles with properties beyond
those anyone had seen before. He predicted
that a whole new family of them was lurking
in the universe, made up of particles identical
to those we knew but with opposite electrical
charges. This hidden world of antimatter
doubles the number of fundamental particles
known in the universe.
That’s not all. In 1933, Swiss astronomer
Fritz Zwicky observed that the rotationsof galaxy clusters suggested that they
were experiencing a stronger gravitational
pull than could be coming from nearby
visible matter.
In the 1970s, US astronomer Vera Rubin
observed this same effect across a range
of galaxies and clusters. Today we think
the “dark” matter causing this extra pull
outnumbers regular matter 5:1. But we have
never found this missing stuff, despite decades
of dedicated direct and indirect searches.
Antimatter and dark matter have entered the
scientific mainstream. But perhaps the most
ambitious new world has spent 60 years in the
shadows. In 1956, Chinese physicists Tsung Dao
Lee and Chen Ning Yang made a remarkable
prediction about the way physics works. Until
then, it had been assumed that all physical
processes must obey certain fundamental
symmetries, meaning they remain the
same when other things around them change.
The way a ball responds to Earth’s gravity,
for example, is unaffected by its colour.Features Cover story