2 November 2019 | New Scientist | 35got stuck into the mathematics, they made a
remarkable discovery. The aether that fit best
into their model was one that matched the
demands cosmologists made of dark matter.
“The result,” says Złosnik, “was general
relativity with a dark matter dust.”
They published that result in late 2018.
At about the same time, Richard Battye at
the Jodrell Bank Centre for Astrophysics
in Manchester, UK, published a paper
suggesting the aether could explain dark
energy as well. He and his team followed
in Złosnik’s footsteps, using an expanded form
of Jacobson and Mattingly’s Einstein-aether
theory to see how such models tallied with
cosmological data.
They found that there is hope for the aether
here, but no definitive evidence. “You can
construct something that works,” says Battye,
“but they are not ruled in.” The problem is that
although some Einstein-aether models match
the raw data, we don’t yet know how to
distinguish them from any other suggestion
for dark energy, he says. “It doesn’t come up
with a unique prediction: something this
predicts that nothing else predicts,” says
Battye. “At least not yet.”Heart of darkness
The most exciting outcome would be for the
aether to explain both dark matter and dark
energy in one fell swoop. Such a mathematical
tour de force remains far off, but some
researchers have suggested that Złosnik’s
work could eventually lead us there.
Whether the aether actually does make up
dark matter, dark energy or both, the dark
sector may be the best place to look for clues,
says Blas. “It opens a window of detection to
the aether.” We could check any experiment
that probes the properties of dark matter to
look for signs of a preferred frame, he says.
If anything does turn up, it would be an
irony of truly cosmic proportions. More than
a century after its banishment from the realm
of respectable science, the aether could be the
very thing we need to help make sense of the
universe. In the graveyard of failed ideas,
something ethereal is stirring. ❚At this point, 20 years on, Jacobson is a
little pessimistic about the aether’s prospects.
But cosmologist Niayesh Afshordi of the
Perimeter Institute in Canada hasn’t given up
hope. “The fundamental reasons to look at
aether are still valid,” he says. He thinks we
have been looking for it in the wrong kinds
of experiments. So far, most work has tried
to uncover the aether’s effect by zooming in
to the mooted atoms of space-time, or else
by studying higher energies and faster speeds
in the hopes that relativity breaks down.
Afshordi believes we need to reverse our
approach, looking for anomalies at lower
energies and across larger distances. It may
be that zooming out will allow us to see the
bigger picture. In the context of the aether,
that means using experiments that look
at interactions with radiation from the
moments after the big bang, or with
gravitational waves of even lower
frequency than those glimpsed so far.
Even if Afshordi is wrong and no such
evidence turns up, some physicists think
we already have a good enough reason to
turn to the aether.
According to the best data we have, 95 per
cent of the universe is made of invisible
substances whose identity remains unknown.
General relativity can describe their behaviour,
but offers no answers as to what they might
be. With a mystery of that size awaiting
resolution, no theoretical model is off the
table. But how do we even know that these
dark substances are out there?
If we observe the way visible matter moves
about inside clusters of galaxies, gravity tells us
there must be extra, but unseen, dark matter
lurking within them. And if we look at the rate
of the universe’s expansion, gravity says that
something mysterious, dubbed dark energy, is
causing that expansion to accelerate. We have
lots of models for what they could be, we just
lack any conclusive answers.
One tantalising possibility is that the aether
could fill in the gaps. If true, we might be able
to connect the two biggest challenges to
Einstein’s general relativity – quantum gravity
and these dark influences – via the very thing
that Einstein’s special relativity banished.
Tom Złosnik, a cosmologist at the Czech
Academy of Sciences in Prague, is one of those
looking to achieve that goal. Like Jacobson,
his original intention was to paint a unified
picture of quantum gravity that incorporated
an aether-like field. But as he and his colleaguesBrendan Foster is a freelance
writer based in St Paul,
Minnesota“ The aether
could be the
very thing we
need to help
make sense of
the universe”