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338 22 APRIL 2022 • VOL 376 ISSUE 6591 science.org SCIENCEILLUSTRATION: ET CONCEPTUAL DESIGN TEAMA
n underground observatory that could
detect gravitational waves from the
far reaches of the universe is one step
closer to reality. Last week, the Dutch
government said it was prepared to
foot about €900 million of the proj-
ect’s roughly €1.9 billion construction cost if
it is built near the border of the Netherlands,
Germany, and Belgium. The pledge puts the
Dutch proposal for Europe’s so-called Ein-
stein Telescope ahead of rival bids, says Stan
Bentvelsen, director of the Netherlands’s Na-
tional Institute for Subatomic Physics and
a leader of the Dutch proposal. “I think the
Dutch government is sticking its neck out the
farthest,” he says.
Gravitational waves were discovered in
2015 when the ripples in spacetime generated
by a pair of merging black holes were detected
by the Laser Interferometer Gravitational-
Wave Observatory (LIGO), two U.S. detec-
tors each made up of 4-kilometer-long tubes
arranged in an L-shape. By sending a laser
beam down each tube and bouncing it off
mirrors suspended at each end, physicists
can look for fluctuations in the beams’ travel
time, a sign that a passing gravitational wave
has subtly stretched or squeezed the arms.
Researchers at LIGO and Virgo, a detector in
Italy with arms 3 kilometers long, have since
gone on to detect dozens more black hole
mergers, as well as collisions between pairs
of neutron stars.
Now, researchers in Europe and the United
States are thinking about bigger detec-
tors that could survey most of the universe
(Science, 12 March 2021, p. 1089). The most
sophisticated, the Einstein Telescope, might
be able to detect hundreds of thousands of
mergers per year, out to the distant reaches
of the observable universe, or soon after the
big bang. Three overlapping L-shaped detec-
tors, each with arms 10 kilometers long, will
watch for spacetime distortions, and the ob-
servatory will be buried in bedrock several
hundred meters down to insulate it from
the surface noise of wind and traffic. Each
detector arm will contain two laser systems,
including one cooled almost to absolute zero,
giving it sensitivity to longer wavelength
radiation from mergers of very large black
holes, hundreds of times the mass of the Sun.
Last year, the European Union added the
Einstein Telescope to an official wish list of
major scientific facilities known as the Euro-
pean Strategy Forum on Research Infrastruc-
tures, and official project bids are due within
the next 2 to 3 years. Bentvelsen says the
Dutch site—somewhere between the cities of
Maastricht, Liège, and Aachen—has a layer of
soft soil above the bedrock. The contrast be-
tween the layers ensures that most surface vi-
brations would bounce off the bedrock rather
than shake the observatory.
In a recent assessment of new proposals
for public infrastructure, the Netherlands
National Growth Funds Commission cited
the region’s geology as one of its advantages.
Last week, the Dutch Cabinet agreed to pay€42 million for preparatory research and
€870 million for construction, should the site
be chosen. To win the funding, however, the
observatory’s backers in academia and pro-
vincial government also need to show how
the project would benefit local companies.
Bentvelsen appears confident, saying he has
“positive feedback” from a range of compa-
nies and technology institutes in the region.
The Dutch bid has an Italian rival that
would put the Einstein Telescope close to
a former zinc mine near the town of Lula
in Sardinia. It is one of the 30 most seismi-
cally quiet sites in the world, says Michele
Punturo of Italy’s National Institute of
Nuclear Physics, who co-leads the over-
all Einstein Telescope collaboration and is
the scientific coordinator of the Sardinian
proposal. He says he and his colleagues
submitted a request in February to the Ital-ian government for €100 million to develop
detector technology and better scrutinize
the site’s geology. They expect to hear the
outcome in June. “The noises are positive,”
he says.
Punturo is heartened that two separate
governments are showing an interest in
the project, but acknowledges it is not yet
guaranteed. After a board of scientists com-
pares site characteristics, the winner should
emerge from negotiations between national
governments, he says. Construction should
begin in 2026 or 2027, with scientific opera-
tions starting up some 9 years later.
Even after the big pledge, the Dutch willstill have to drum up support from other Eu-
ropean nations. Belgium and Germany have
been involved in preliminary site investiga-
tions but have yet to formally support the
Dutch bid.
And Germany may launch its own bid.
Günther Hasinger, head of the European
Space Astronomy Centre near Madrid, is
spearheading plans for a new astrophysics
center in the state of Saxony, using federal
funds intended for development in eastern
Germany, where the coal industry has de-
clined. Hasinger wants to site the Einstein
Telescope in a strip of granite found in the
region—but only if the site’s geology makes
it “significantly better than the others.” With
a site decision expected in 2025, he and his
colleagues have a few years to find out. jEdwin Cartlidge is a journalist based in Rome.By Edwin Cartlidge
ASTROPHYSICS
Dutch dangle bid for gravitational wave detector
Government pledges to support nearly half the cost of the Einstein Telescope
The Einstein Telescope would be buried several hundred meters underground to insulate it from noise.