Over the years, we’ve developed many ingenious methods in our unending quest to map out the
universe around us. And for decades, a proposed role for the moon in our efforts has been that
it would make for an excellent place to build an observatory, to house traditional, visual
telescopes. But, more recently, we’ve discovered that it can also be used in other ways.
This is Unveiled, and today we’re exploring how the moon’s
orbit is helping us to map the universe.
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To better understand the moon’s role in mapping space, we first have to think about gravitational
waves. Gravitational waves were theorized far before they were actually confirmed. And,
as with so many other concepts of the universe, it was Albert Einstein who first proposed them, back
when he was crafting his most famous theories on spacetime. He thought that sufficiently energetic
events in space would cause gravitational waves, which are ripples in spacetime (similar to ripples
in a lake). Einstein’s first predictions were made in the early 1900s, but it wasn’t until the
year 2015 that researchers were able to directly measure gravitational waves for the first time,
as they passed by Earth - a feat achieved by the Laser Interferometer Gravitational-Wave
Observatory, or LIGO, which is the main focal point for an ongoing international project.
While gravitational waves are created by massive and destructive cosmic events, as
Einstein said - events like black holes colliding and supernova explosions - by the time they reach
us they’re more like tiny vibrations. But still, they’ve become absolutely vital in plotting
“what’s what” and “where’s where” in the universe. The successful measurement of gravitational waves
is already widely held as one of the most significant breakthroughs in recent times,
giving researchers (as it has) an entirely new way to observe space. Before they had
gravitational waves, astronomers relied almost solely on radiation - such as visible light and
microwaves - to measure and observe objects. But gravitational waves are independent from all that.
So much so, it’s been said that the introduction of gravitational waves
was like science and cosmology being gifted with an entirely new sense. Before,
we had only sight to view the universe, but now we have sound to hear it.
It's not like these are especially loud sounds, though. When gravitational waves pass through
Earth, they’re totally indecipherable for most of us. They’re tiny, subatomic murmurings. But
this means that, in some cases, researchers can use the waves to essentially see objects that
are normally invisible. Black holes, for example, are traditionally only noticeable by the effect
they have on objects around them… but now, they can be detected via gravitational waves, too,
by tracing the waves back to their source. This is extremely intricate science, however. Which is
why it’s good news that a new way has recently been developed to measure gravitational waves,
with greater accuracy. And it’s a method that makes use of our very own moon.
Although theories have been around since the late 1970s, it was in 2013 that a team at Columbia
University showed that gravitational waves might affect the orbits of binary systems specifically.
A binary system is any system in space where two objects orbit a common center of gravity.
Binary star systems, for example, have two stars rotating around each other instead of one solitary
star, like our sun in the solar system. But binary systems don’t need to be based on stars alone.
Any two objects can pair together in this way, which is why the Earth and moon can
be said to be in a binary orbit, as well. What’s important for today’s video, though,
is that there are slight differences to be found in the orbits of binary objects before and after
a gravitational wave passes through them. It’s as though the waves leave a trail of cosmic evidence
in their wake, which can then be converted into information. Wave experts can extract data about
the strength of the waves, for example, and can therefore predict what might’ve caused them,
and where and how far away from us that cause may have originated. Regarding the moon and Earth,
then, the moon’s orbit is very slightly affected by the gravitational waves that reach us… and so,
seeing as researchers can measure the lunar orbit to within a centimeter, we have a sure-fire,
near-perfect way of tracking gravitational waves right on our doorstep. And therefore
a close-to-home base from which to paint a picture of the rest of the universe.
This new application of the science comes following research by physicists Diego
Blas and Alexander Jenkins, published in the journal “Physical Review Letters”, in March 2022.
And, at this early stage it’s thought that by essentially converting the moon into a beacon for
gravitational waves, we could soon be measuring those waves with significantly more accuracy.
In some ways it’s like we’re finally seeing (or hearing) the universe in high definition.
Thanks to this new technique, it’s hoped that we should soon be detecting
more gravitational waves than ever before, and seeing them clearer than ever before, as well.
Which is exciting for a number of reasons, and especially for anyone interested
in producing a “map of the universe”. What’s particularly important about gravitational waves
is that they provide us with unchanging, reliable markers in space, that aren’t affected very much
by the surrounding cosmos. While more traditional astronomy relies on radiation, we know that much
of it can be distorted. Light can pass through dust clouds, for example, and dim as a result…
or it can be altered and bent by gravity, so that what we see through our telescopes
isn’t a true representation of what’s really there. But gravitational waves, by comparison,
travel through the universe relatively unhindered and reach us in near pristine condition.
But still, why are they so useful in the first place? Again, it has to do
with their uniformity. If you know how to read a gravitational wave, then you know how to read
a constant of space. It can reveal to you details about anything from the
expansion of the universe to the most violent and formative physical events that happen within it,
and it can even provide a glimpse into the very first moments and birth of the universe, too.
But really, those are only the possibilities that researchers can currently imagine. By
viewing waves through the lens of lunar orbit, we’re truly looking at space in a whole new way…
which could also lead to whole new discoveries. Naturally, one of the best parts about this
research is that it doesn’t require us to build anything new to put it to use. The
moon’s orbit has always been there. We don’t need to affect it in any way, we just need to keep a
close eye on it… and automatically we’ll gain a better understanding of gravitational waves
(and the universe) as a result. And, although the calculations involved are difficult,
we have everything we need already in place. When NASA first put humans on the moon during
the Apollo program, one part of the mission that’s often forgotten is that astronauts left
mirrors on the lunar surface. Today, researchers on Earth can simply fire lasers at those mirrors
and wait for the light to reflect back, to determine exactly how far away the moon is
at any given moment. We already have a firm grip on how the lunar orbit works, then, it’s just that
by pairing it with gravitational wave activity we’re applying that knowledge in an all-new way.
Of course, we know that it’s not as though the Earth-moon setup is the only binary system around.
Astronomers do (and will) apply similar methods to other binaries, too. Anything that helps to clear
the fog with gravitational waves is certainly worth pursuing. But it still feels particularly
notable, hopeful, and exciting that our greatest wave detector could well be bound to our own sky.
The unerring presence of the moon is already a source of comfort for many, but now it truly is
a bridge between us and the rest of the cosmos. We’re using it to hear space more loudly and
clearly than ever before… and that’s how the moon’s orbit is helping us map the universe.
What do you think? Is there anything we missed? Let us know in the comments, check out these other
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