25 July 2020 | New Scientist | 15TWO sets of measurements to
estimate the rate of the expansion
of the universe conflict with one
another, which may be a sign that
our basic understanding of the
cosmos is wrong. What’s more,
two new attempts by astronomers
to solve this problem have
complicated things further.
The rate at which the universe’s
expansion accelerates is described
by a number called the Hubble
constant. There are two main sets
of data that we use to estimate this
key number: measurements of the
cosmic microwave background
(CMB), which is a relic of the first
light to shine through the cosmos,
and local measurements, which
use observations of supernovae
and other relatively nearby objects
to determine how fast expansion
is carrying them away from us.
But these two estimates don’t
agree: CMB readings from the
Planck satellite indicate that the
expansion is accelerating about
9 per cent slower than the rate
suggested by the supernova data.
Simone Aiola at the Flatiron
Institute in New York and his
colleagues used the Atacama
Cosmology Telescope in Chile to
take new observations, calculating
a Hubble constant that agrees
with the Planck satellite data
(arxiv.org/abs/2007.07288).
This strengthens the argument
that the CMB value of the Hubble
constant is correct, indicating that
either the local measurements
were somehow wrong or that the
two values are actually different
for as yet unknown reasons.“It would be very exciting if
the tension is real,” says Antonella
Palmese at the Fermi National
Accelerator Laboratory in Illinois.
“The hope is that some new
physics will be needed to describe
the universe and we are just
starting to see that now as our
measurements are becoming
more precise.”
Palmese and her colleagues
have used measurements of
gravitational waves – ripples that
stretch and squeeze space-time
because of the movements of
massive objects – to calculate anindependent value of the Hubble
constant. They used data on three
mergers of massive objects
from the Laser Interferometer
Gravitational-Wave Observatory
in the US and the Virgo detector
in Italy (arxiv.org/abs/2006.14961).
Their value is in between the
two others, but the measurements
aren’t precise, so it is compatible
with both. This first attempt
demonstrates that gravitational
waves could be a major help in
solving this mystery.
“It should be very close to
the local measurements, but it
doesn’t rely on the same type of
observation, so if there is some
kind of problem with the local
measurements, we should be
able to find it with gravitational
waves,” says Palmese.
If the observations remain in
tension, it means that the Hubble
constant changed between when
the light in the CMB was emitted
and now. There are many possible
explanations, from unexpected
properties of dark matter and
dark energy to the idea that we
may just live in a strange corner
of the universe. ❚“ The belt could pave the
way for other applications,
such as assisting those
with visual impairments”NGIMAGES
/ALAMYTechnology
Vibrating belt
helps guide the
way for soldiers
DUTCH soldiers are being kitted
out with a belt that allows them
to sense the location of waypoints,
providing hands-free directions.
Haptic navigation tools,
which guide the wearer through
vibration, have been researched
as possible aids for people with
visual impairments, but are also of
interest to the military. A firm called
Elitac Wearables in Utrecht, the
Netherlands, has delivered the first
real product using the technology,
selling 20 of its Mission Navigation
Belts to the Royal Netherlands Army
this month for an undisclosed price.
Existing navigational aids require
soldiers to look down at screens or
listen to audio instructions. Both
have disadvantages: soldiers need
to scan their surroundings at all
times and light from a screen may
betray their position, while verbal
instructions can interfere with other
communications and get drowned
out by background noise.
The belt connects to the soldiers’
existing smart vests, which are
fitted with a radio, GPS and battery.Seven vibrational motors around
the belt continuously indicate the
direction to the next waypoint,
with the location of the vibration
changing as the wearer turns.
Soldiers tested the belts in land
and water vehicles and on foot,
navigating continuously between
modes of travel. The haptic signals
were clear even when running or
traversing rough terrain.
“It has proved its valueconvincingly during field tests,”
says Van Veen, a major in the
Royal Netherlands Army who was
involved in the testing. “Soldiers
reported that they were more aware
of their surroundings and found the
navigational cues very intuitive.”
The belt could pave the way
for other applications, says Martijn
van der Leeden at Elitac’s parent
company Teijin, such as assisting
those with visual impairments and
providing hands-free navigation
for hikers, runners and cyclists, but
Elitac has no immediate plans for
a consumer version. ❚
David HamblingCosmology
Leah Crane
Universe mystery deepens
The universe is constantly expanding, but we aren’t sure exactly how quickly
The universe has
been expanding
since the big bang