You know what’s really keeping me down?
Gravity.
Everywhere I go, there it is.
Scientists noticed this too, and since 2000
have used satellites to map the Earth’s
gravitational field.
Now they’ve developed a new instrument that
uses quantum phenomena to deliver the most
accurate measurements yet.
You may be wondering what point there is to
mapping the Earth’s gravity.
If you’ve taken high school physics you
probably learned that Earth’s gravity pulls
things toward its center at a rate of 9.8
m/s2.
It turns out that while that’s a good enough
approximation for the kinds of math problems
you’ll tackle in high school, it’s not
entirely accurate.
The Earth’s gravitational pull isn’t uniform,
it varies from one place to another, and it
can change over time.
What might cause the Earth’s gravity to
change?
Well, gravity is directly related to mass,
and the more massive an object is, the more
it pulls on other objects.
And what has a lot of mass that covers most
of the Earth and can shift around?
That’s right, water.
There are other things that can contribute
to a change in Earth’s gravity, but the
shifting mass of water is the biggest factor.
If a glacier melts or water gets trapped underground,
its mass will be redistributed.
So measuring the minute changes in the gravitational
field is a way to track what Earth’s water
is doing, and how the water cycle is being
affected by climate change.
Previous NASA missions like GRACE and its
successor GRACE-Follow On used twin satellites
to map the field.
The principle was one satellite would follow
the other, and as they passed through fluctuations
in the gravitational field, they would get
closer or farther apart.
Measuring the change in distance would tell
scientists how the gravity over that part
of the world differed.
But since the goal is always more accuracy
and precision, NASA teamed up with the company
AOSense, Inc. to try an entirely different
approach.
The new prototype sensor uses about 100 million
cesium atoms sealed in a vacuum near absolute zero.
This keeps the atoms insulated from outside
factors that may affect the measurements.
The only force pulling on these atoms is gravity.
Thanks to the bizarre nature of quantum physics,
these atoms are coaxed into behaving like
light waves.
Lasers can split and send these waves down
different paths, and as they travel they interact
with gravity.
Finally the waves meet up again, and when
they do, they form an interference pattern
where some sections of the waves have a higher
amplitude while others have a lower amplitude.
By studying this interference pattern, the
instrument can determine how gravity affected
the atoms with unprecedented accuracy.
While past atom-based instruments needed components
the size of a room, the new sensor is small
enough to fit on a spacecraft.
That doesn’t mean it’s sacrificing sensitivity;
during testing, the device reported different
gravitational measurements after the scientists
came back from their lunch break... because
it was detecting the added mass from the food
in their stomachs.
And once it’s up in space, the sensor will
map the Earth’s gravity 10 times more precisely
than GRACE-Follow On, at four times the spatial
resolution.
An instrument like this could have uses beyond
Earth one day, like measuring the interiors
of other planets, moons, and comets.
It could also be tuned to detect gravitational
waves in new frequency ranges that we haven’t
been able to see yet.
Whatever it ends up being used for, the new
instrument is an ingenious application of
scientific principles to solve a problem and a testament to just how clever scientists
are.
Gravity mapping satellites can also help us
probe the Earth's secrets, like what’s happening
under Antarctica.
Maren has a video on that here.
If you liked this video, let us know down
in the comments, and make sure to subscribe
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Thanks for watching and I’ll see you next
time.
