Knowledge of quantum mechanics has revealed so much to modern day scientists,
and now it’s a driving force for new technology. But perhaps no quantum term piques curiosity
quite so much as quantum gravity does. It sounds like something straight out of science fiction,
but it’s here in the real world… and a recent breakthrough may well have opened
up a whole new space for future exploration. This is Unveiled, and today we’re exploring
the extraordinary ways that scientists are using gravity to find secrets underground.
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At the broadest level, scanning technology that’s capable of peering below the Earth’s surface is
nothing new. The first ground-penetrating radar (or GPR) systems emerged in the early 1900s,
and we’ve been tweaking and improving them ever since. At its simplest, the technology makes
use of the way that high-frequency radio waves reflect and rebound to build 3D-representative
maps of whatever’s below our feet. Radar waves shot into the Earth will continue
down uninterrupted unless they come across something solid, at which point they bounce back,
the obstruction is registered, and a map is built based on the data.
But there are limitations. GPR only really works with certain materials, for example.
Some soil types, like clay, are much more difficult to penetrate and effectively absorb
radar waves, reducing the length (or depth) to which researchers can probe. There are trade-offs
to be made with the frequency of penetrating waves, too, with lower frequencies generally
able to see further underground… but having to sacrifice accuracy to do so. And finally, GPR
also suffers while scanning smaller rocks and artifacts, which are more difficult for it to
distinguish, or even pick up at all. So-called quantum gravity technology offers an exciting
new option, however. With some believing that it could soon show traditional radar to be extremely
old-fashioned. And researchers at the University of Birmingham in the UK have just put forward a
working design for a quantum gravity sensor. The workings of gravity in general have been
applied to underground mapping before now, using measuring devices known as gradiometers
to convert gravitational influence into readable data that’s then used to position underground
objects. But the principles are today being honed toward a much more effective method.
Details of the quantum sensor design from the Birmingham-based team were published in the
journal “Nature”, in February 2022. According to the report, the cutting edge device bypasses many
of the main problems that previous attempts toward quantum sensors had been beaten by… and, so,
we’re finally able to use the technology (outside of lab conditions) for the first time ever.
The most significant problem until now for quantum gravity sensors has been background
noise. Readings being disrupted (until they’re essentially meaningless) by tiny
vibrations in the ground, which can fuzz up the rebounding waves until they’re indecipherable.
On top of that, the method is generally so sensitive that even small changes in how the
instruments themselves are set up and positioned can have a significant impact, and skew results.
But the quantum design put forward by the University of Birmingham team appears to have
solved all of that. The background noise isn’t an issue anymore, to the point that those behind the
study have successfully used their technique to identify a small tunnel, about three feet
below the ground at Birmingham University. As to precisely how their sensor works,
it involves manipulating the quantum world itself - the realm of the very small. The new quantum
gravity gradiometer uses clouds of atoms as a means for mapping the underground. The atom clouds
are essentially dropped into the Earth, where they’re split into a state of superposition. It’s
then upon their being recombined that researchers can determine gravitational measurements to track
the journey that the atoms have been on, including what structures they’ve met or passed. Any and all
objects beneath the ground exert a degree of gravitational pull, and the sensor can make
sense of all these influences to build a clear picture of what’s actually in the ground - as
though it’s painting a finely detailed landscape of the hidden, subterranean world. In this way,
it’s perhaps a similar process to traditional radar methods, only it can yield far greater
accuracy. The details are far more finely tuned. The technology isn’t totally new for this study,
but the Birmingham University paper does mark the first time that it’s been used outside in a real,
non-lab setting. That’s why the discovery of an otherwise quite uninteresting tunnel is actually
so significant. And, although the tech still needs to be improved, it’s hoped that it will provide a
starting point for researchers to build off of in the future. It’s hoped that future iterations of a
quantum sensor will be much cheaper (to buy and to build), even more reliable, and that they’ll yield
much faster results than anything else that’s currently available. This is just the start,
then, but it's a hugely promising “first version” of what’s to come. As quantum
sensors can reportedly already operate around ten times faster than any current equivalent…
it means that measurements that once took months to process could soon be taking days,
or even hours. In the experiment itself, mapping just the small tunnel, the key locations were
reportedly measured in only a matter of minutes. The finding of the small tunnel may seem a fairly
modest achievement, but it’s actually a huge deal because of the widespread implications and
potential benefits that quantum gravity tech like this could provide. A co-author of the study, Kai
Bongs, has already described the breakthrough as an “Edison moment” in an accompanying statement…
referring to how widely it could impact society. Practical applications for quantum
mapping include that it could help to find hidden chambers under roads or buildings,
to improve infrastructure stability; it could be used to survey sites before building, as well,
to ensure that they’re safe underfoot; and it can therefore help towards making the construction of
everything from railroads to skyscrapers faster and cheaper. There are even proposed uses for it
in relation to natural disasters, too, with it thought that maps made using quantum sensors
could help to better prepare us for volcanic eruptions, and perhaps even earthquakes.
Quite apart from the unpredictability and uncontrollability of non-lab conditions,
it’s also been a struggle to use (or even set up) gravity sensors in outside settings before now
because the sensors (until now) have tended to be large and complex. However, the new design
is improved here, as well, as it’s much more portable. The dramatic drop has even prompted some
suggestions that in the future these high-tech machines might be pushed around with ease, like
lawnmowers. We’re not at that stage yet, but when we are… there will be even more potential uses. In
a world where getting to know what’s underground is as easy as mowing your lawn, there should be
no secrets left unearthed. We should have total knowledge of what’s happening below the surface.
The research was contracted by the UK’s Ministry of Defence,
which indicates another potential future use for it, with scanning underground environments
feasibly becoming a key aid in the military. But elsewhere, it’s thought the technology
could become vital in our quest to better understand the famously underexplored ocean.
Meanwhile, there are plenty of potential uses for it in space, as well. Earlier gravity sensors have
already been used by NASA to analyze the moon, but devices like that put forward in this study could
supercharge what’s possible. For example, we know that if we are to ever live on the moon (or on a
solar system planet) then finding subsurface caves to build bases from could be crucial.
Quantum gravity sensors could be the tool we’ve been waiting for to find those caves en masse.
Underground water sources might also be easier to locate, if we took this kind of tech to Mars,
Europa, or Enceladus, for instance. At present, there are still many advances
that need to be made before most of that is possible, yes, but this is still an exciting time.
Researchers have demonstrated that quantum gravity mapping tech can work outdoors,
that it can be portable and practical, and that it can yield reliable data. The hope is that
quantum sensors will become much more commonplace within the coming years, allowing us to explore
underground with more clarity than ever before. The wide-open field of quantum mechanics is still
a relatively new one, but research within it has already reshaped so many strands of scientific
study. This is just the latest example of how understanding the complex quantum world is helping
us to live and develop in everyday reality. For now, it’s one tunnel, three feet below the ground…
but, in the not-too-distant future, the methods at play here could truly
inspire massive change. And that’s how scientists are using gravity to find secrets underground.
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