8 | New Scientist | 23 November 2019
A VAST simulation of the universe
is digitally recreating the lives
of stars, black holes and galaxies.
Approximately 1 billion light
years across, it is modelling tens
of thousands of galaxies.
Richard Bower at Durham
University in the UK and his
colleagues started the simulation
last week. It will run non-stop for
50 days across 30,000 computer
processors in both Durham
and Paris developed by tech
firm Intel. The simulation is
30 times larger than one the
team ran in 2015, which led to
predictions about the mergers
of supermassive black holes.
The new simulation includes
the physics of all the “normal”
matter such as the atoms
and molecules that make up
humans and Earth, as well as
the mysterious dark matter that
forms around 85 per cent of the
universe but which we haven’t
yet been able to directly observe.
It also incorporates the physics
of star and black hole formation,
and the conditions at the start of
the universe. “We set the initial
conditions, represented byhundreds of billions of particles in
play, and then we let the universe
go,” says Bower.
The team will look at galaxies
by breaking them up into blocks
about 3000 light years across. One
objective is to try to understand
rare objects in the universe, such
as galaxies that are so distant from
Earth that they are invisible to
many telescopes. By simulating
what the universe looked like at
different points in time – at half
or a quarter of its present age,
say – the team can test theories
about how galaxies are relatedto the growth of black holes, and
what happens when they die.
Simulating individual galaxies
in sufficient detail is a challenge.
“If you try to do a calculation
where you have less detail in
the galaxy, then you really can’t
understand the rate at which stars
are going to form,” says Bower.
Another difficulty in simulating
the internal structure of galaxies,
which contain gas, dust andbillions of stars, is that there are
huge uncertainties about their
underlying physics.
“The physics is so complicated
that any small mistake could lead
to a very wrong prediction,” says
Romain Teyssier at the University
of Zurich in Switzerland. He was
part of a team behind a massive
universe simulation in 2017 that
contained 25 billion galaxies,
focusing on dark matter.
The paradox is that although
we don’t know what dark matter
is, its physics is simple to model.
That is because it doesn’t seem
to interact with anything or itself
except through gravity, which is
why we don’t see it emitting light
or other radiation.
In contrast, we don’t know very
accurately how stars form or how
much energy is released when a
star goes supernova, says Bower.
To check the accuracy of the
virtual universe, the team will
compare simulated features to
the observed universe to check
for discrepancies. Teyssier says
this is like weather forecasting,
in which actual observations
are used to refine predictions. ❚NASA
/SWIFT/AURORE
SI
MONNETNews
MaterialsBlasting lead with
lasers makes it
really strongLEAD just got an upgrade. When it is
quickly compressed with powerful
lasers, the typically weak element
gets 250 times stronger, making it
tougher than hardened steel.
The difference between strong
and weak materials has to do with
how the atoms move against one
another. When the atoms are
arranged so that they can slide
across each another easily, like they
typically are in lead, the material issoft and pliable. When they cannot
move around so easily, like in iron,
the material is hard and strong.
Andy Krygier at the Lawrence
Livermore National Laboratory in
California and his colleagues tested
the properties of lead that is quickly
pushed to incredibly high pressures
using lasers at the lab’s National
Ignition Facility.
Applying significant pressure also
applies heat, so the researchers had
to devise a setup that would allow
the lead to reach pressures higher
than those in Earth’s core without
melting. They did this using a
special gold tube, which had ahigher melting point, into which
they fired 160 laser beams. Those
beams heated up the tube to about
1,000,000°C, sending a high-
pressure shock wave through a
sample of lead. At the same time,
they measured the lead’s strength
using X-rays.
They found that after a few tens
of nanoseconds, once the apparatus
had reached its highest pressures,
the lead had become 250 timesstronger (Physical Review Letters,
doi.org/dfdk). “We can hold it at this
pressure just long enough to make
a measurement before it explodes,”
says Krygier.
As well as teaching us how
materials behave at high pressures,
like those inside planets, these sorts
of experiments could help create
shielding that becomes strong
when it is hit. “Designing new
armour for war-fighters or for tanks
or even for satellites that run into
small meteors depends on our
ability to understand dynamic
strength,” says Krygier. ❚
Leah CraneCosmologyGiant virtual universe
A simulation of the universe, 1 billion light years across, is looking
at how galaxies form and die, reports Donna Lu“We can hold it at this
pressure just long enough
to make a measurement
before it explodes”Tens of thousands of galaxies
are included in a digital model
of the cosmos