3 November 2018 | NewScientist | 29gravitational waves emitted as a pair of
distant black holes spun into one another.
The misgivings of Jackson’s group, based
at the Niels Bohr Institute in Copenhagen,
Denmark, began with this press conference.
The researchers were surprised at the
confident language with which the
discovery was proclaimed and decided
to inspect things more closely.
Their claims are not vexatious, nor do
they come from ill-informed troublemakers.
Although the researchers don’t work on
gravitational waves, they have expertise in
signal analysis, and experience of working with
large data sets such as the cosmic microwave
background radiation, the afterglow of the big
bang that is spread in a fine pattern across the
sky. “These guys are credible scientists,”
says Duncan Brown at Syracuse University
in New York, a gravitational wave expert who
recently left the LIGO collaboration.
Gravitational waves are triggered by the
collision of massive objects such as black holes
or neutron stars. They travel for billions of
years, alternately squeezing and stretching
the space-time in their path. Spreading out
in all directions, they get weaker as they go,
but they can be detected on Earth with a
sufficiently sensitive instrument.
The LIGO collaboration built two such
instruments, the Hanford detector in
Washington state and the Livingston detector
in Louisiana. A third, independent instrument
called Virgo, located near Pisa, Italy, joined the
others in 2017. These “interferometers” shoot
lasers down two long tunnels, then reflect
them back in such a way that the pulses should
arrive at the same time. Passing gravitational
waves will distort space-time, making one
tunnel longer than the other, and throwing
off the synchronisation.
By the time the waves wash over Earth, they
are extremely weak, and the sort of change in
tunnel length we expect is equivalent to about
a thousandth of the diameter of a proton.
That is far smaller than the disturbances that
come from background seismic tremors and
even the natural thermal vibrations of the >T
HERE was never much doubt that we
would observe gravitational waves
sooner or later. This rhythmic squeezing
and stretching of space and time is a natural
consequence of one of science’s most
well-established theories, Einstein’s general
relativity. So when we built a machine capable
of observing the waves, it seemed that it would
be only a matter of time before a detection.
In point of fact, it took two days. The Laser
Interferometer Gravitational-Wave
Observatory collaboration, better known as
LIGO, switched on its upgraded detectors on
12 September 2015. Within 48 hours, it had
made its first detection. It took a few months
before the researchers were confident enough
in the signal to announce a discovery.
Headlines around the world soon heralded one
of the greatest scientific breakthroughs of the
past century. In 2017, a Nobel prize followed.
Five other waves have since been spotted.
Or have they? That’s the question asked
by a group of physicists who have done their
own analysis of the data. “We believe that LIGO
has failed to make a convincing case for the
detection of any gravitational wave event,” says
Andrew Jackson, the group’s spokesperson.
According to them, the breakthrough was
nothing of the sort: it was all an illusion.
The big news of that first sighting broke on
11 February 2016. In a press conference, senior
members of the collaboration announced that
their detectors had picked up the signature of