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[ intro ]
We don’t usually think of astronomy as an experimental science.
We imagine astronomers sitting behind telescopes, sure —
or behind computers, staring at pictures of the Hubble, doing a lot of math...
But we don’t normally picture them behind a lab bench.
Except, some astronomers have found ways
to test what we see in space right here on Earth.
They do it with analogue models,
or physical models that mimic
and rely on the same math as something in space.
And those models can seem unconventional.
Because sometimes, studying the universe means
making gas giants from trash cans…
and black holes from sound.
how we’ve studied Jupiter’s clouds /with a garbage can/.
Let’s look at Jupiter.
These clouds have mesmerized us for centuries,
but there’s a lot we don’t know about them.
Like, it’s hard to tell how deep they go since they’re opaque,
and we’re still learning how the patterns can be so stable
when the clouds themselves are in constant motion.
We’ve learned a lot from probes and computer simulations,
but simulations always have assumptions built into them:
You assume things work a certain way and see what happens.
So, we might be able to make virtual planets that /look/ like Jupiter,
but we need a way to know if those virtual planets also /behave/ like Jupiter.
And for /that/, we need experiments.
So, how do you experiment on a planet?
With a giant, water-filled trash can!
See, gases and liquids are both fluids,
and they respond to forces like rotation in similar ways.
So since Jupiter is a big, spinning ball of gas,
you can learn about it with a big, spinning tub of water.
In 2017, a group of scientists filled a huge, industrial trash can with water,
then placed it on a special table where it could spin 75 times per minute.
As the trash planet spun,
the team used a pump at the bottom of the can to circulate water through a series of
With this fairly simple setup,
the team saw water moving /the same way/ gases do on Jupiter.
They even got /stripes/ as regions of water swirled in different directions.
They /also/ noted that the swirls in the water went all the way to the bottom of the can.
And they took that as evidence that Jupiter’s clouds /also/ extend far below the planet’s
outermost layers —
something scientists have been arguing about for /years/.
So, while computers are amazing…
sometimes, a basic setup with some creative scientists will get you a long way.
Now, experimental astronomy can take us beyond gas giants,
too: It can also help us study how /all/ planets form.
Learning how dust clouds turn into planets is one of astronomy’s hardest problems.
We know that a young star’s gravity and magnetic field make orbiting dust clump together
and that /somehow/,
those clumps become planets.
But that can take millions of years, so there are a lot of open questions.
Again, simulations can fill some gaps,
but it’s hard to know if they help us understand the /process/
or are just good at making certain star systems.
So, scientists brought out the balls and springs.
That’s because simulations often simplify the environment near a star by treating the
magnetic fields between nearby grains of dust as /springs/,
which can push the grains apart or pull them together.
The idea is that these fields /move/ dust into orbits full of other material,
leading to clumps that grow into planets.
Which sounds fair enough, but at least for some magnetic fields,
nobody had directly confirmed that springs were actually a good stand-in!
And then came a 2019 paper.
The authors started with a ball and a fixed, vertical post
— representing two dust grains —
and connected them with a spring, representing a magnetic field.
I know what you’re thinking: yes, basically, tetherball.
But then it gets even better, because they took that set up and put it into a tank of
And when the tank spun, the water would rotate like dust around a star.
In the test, the ball started out moving at the same rate as the nearby water, just like
how dust grains would orbit a star.
But then, the magic happened:
Over time, the ball began to move back and forth:
The water pushed the ball into the spring, and the spring pushed the ball out to different
sometimes /way/ out —
just like magnetic fields should push dust into different orbits.
It sounds like a simple test, but this showed that our models are on the right track!
Springs /can/ capture something about how planets form!
I mean, there /are/ a lot of steps between that and a full understanding of planet formation.
But it’s a start, and is helping us learn about something that’s hard to observe directly.
Okay, moving onto black holes.
These bottomless pits of gravity are hard to study because,
once you pass something called the event horizon, not even /light/ can escape them.
And since physics as we know it also breaks down somewhere past that horizon,
computers can’t tell us everything, either.
So we’ve got questions.
For instance, Stephen Hawking predicted that, at the edge of an event horizon,
black holes should produce light —
or what we call Hawking radiation now.
The problem is, the gases /around/ a black hole make a /lot/ of radiation on their own,
which would drown out the kind Hawking predicted.
So we haven’t been able to confirm that that Hawking radiation exists.
Fortunately, teams have studied black holes in the lab through analogue models,
which mimic an event horizon by making a barrier you can cross one way, but not the other.
And some of them make what looks a /lot/ like Hawking radiation.
For instance, in a 2016 paper, one physicist made a model by zapping a cloud of atoms with
until one group of atoms was moving faster than the speed of sound in the cloud.
It was like making a rushing river:
Sound waves could get /into/ this stream,
but not out, since the gas was moving faster than sound travels.
Kind of like how light can get into a black hole but not out.
Then, an amazing thing happened:
Little, random vibrations around the edge of the stream created /sounds/ on either side
of this simulated event horizon —
just like how Hawking predicted /radiation/ would appear around real black holes!
Of course, this isn’t enough to say that Hawking radiation /definitely/ exists, but
this /is/ a point in its favor —
and a way to study what this elusive stuff might be like!
some physicists /do/ say real black holes are /so/ unique, you can’t study them through
but — they’re all we’ve really got right now.
And ultimately, that’s what’s great about these experiments:
It can be hard to impossible to access planets and black holes,
but we’ve got plenty of trash cans, springs, and lasers!
And with clever thinking,
we can use them to study something as complex and distant as space.
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[ outro ]