THE NEXT BIG STEPS FOR SCIENCE“In an attempt to explain this behaviour,
physicists have come up with a new type
of particle: WIMPS”
If they exist,
billions of dark
matter particles
are passing
through your body
every second.
Only around100,000
a year interact with
the atoms inside
your body.terraelectronvolts
is the record-breaking energy with which
the new souped-up Large Hadron Collider
is smashing particles together in an attempt
13 to unlock the secrets of dark matter.litres of water are needed to
shield the subterranean Large
Underground Xenon dark
matter detector from being
contaminated by radiation
from the Earth’s surface.strings carrying 264,979
detectors were
lowered 2,500
metres below
the surface of the Antarctic
ice to hunt for evidence of
dark matter annihilations.86
DARK MATTER
IN NUMBERS
Compact Halo Objects, the idea is that
there are big objects, such as black
holes, ghosting unseen through the
Milky Way. When we add up all the
mass we ca n see, we a ren’t including
them, hence why we underestimate
the mass of the Galaxy.Q
What are scientists doing to
find dark matter?A
How do you find something that
is, by definition, hidden from
view? You certainly can’t see it. To
make things worse, WIMPs are so
ghostly that they almost always pass
st raight t h rough nor mal matter –
including any detector you build
to snare one.
To put it into perspective, dark
matter is so abunda nt t hat billionsof dark matter particles are streaming
unhindered through you every single
second. And yet, on average, in any
five-minute period, only one of these
dark matter particles interacts with an
atom of nor mal matter in you r body.
This idea t hat da rk matter pa r ticles
do occasionally deign to interact wit h
normal matter is the basis for the Large
Underground Xenon experiment deep
under the surface of South Dakota.
Scientists have commandeered an
abandoned gold mine and set up a
dark matter detector 1.6km down.
Consisting of 370kg of liquid xenon
shielded by 264,979 lit res of water, it
is designed to pick up t he occasional
WIMP interacting with the xenon.
Should a WIMP recoil off a xenon
atom, the atom is accelerated through
the liquid, causing a flash that can be
picked up by the surrounding banks
of super-sensitive cameras.
Scientists might also be able to
detect da rk matter when it interacts
with itself in a process known as
annihilation. When this happens, it is
thought a cascade of ‘normal’ particles
is produced a nd we should be able to
pick that up. One such experiment is
the Alpha Magnetic Spectrometer
(AMS-02) cu r rently st rapped to t he
International Space Station. It is trying
to pick up evidence of atomic sh rapnel
coming f rom WIMP a nnihilations
near the galactic centre.
The Sun could help too. As the
biggest thing in the Solar System it
should be acting as a giant cosmic
vacuum clea ner, sweeping up da rk
matter particles as it treks through the
Galaxy. Some of the dark matter
particles should annihilate inside the
Sun, producing a stream of normal
particles. Unfortunately, the Sun is so
dense that almost all of these daughter
particles remain trapped inside.
However, one type of particle –
neutrinos – would make it out and
travel across space to us. Experiments
such as IceCube, stationed on
Antarctica, are set up to gather these
tell-tale signals.
Then there is the Large Hadron
Collider (LHC). On 5 May 2015, the
experiment began smashing protons
together after a two-year shutdown5 hidden, it ca nnot interact wit h
light. In a n attempt to explain t his
behaviour, physicists have come up
with a new type of particle: Weakly
Interacting Massive Particles (WIMPs).
They are ‘weakly interacting’ because
they don’t interact with light and
‘massive’ as they interact via gravity.
When astronomers run computer
simulations of a Universe that evolves
wit h da rk matter in t he for m of
WIMPs, they get a structure that is a
pretty solid match for the distribution
of gala xies t hat we see today. A t heor y
for physics beyond the Standard
Model called supersymmetry also
seems to fit with this picture.
Other explanations have been
considered in the past, including
MACHOs. Standing for MAssive