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It’s probably hard to ignore the very obvious green algae taking up most of your screen.
But for the moment, I want you to try. Look away from the closterium and instead, shift your focus
to the area that surrounds it. At first, it may not seem that interesting. It’s just a sea of
dark blue, interrupted only by tiny little dots. But unlike the completely static closterium, those
tiny little dots are wiggling around in frantic, uncoordinated directions like they’re
dancing to a million different soundtracks played at once. There are organisms in the
world of the microcosmos that move in concerted, directed ways, but this is definitely not that.
Now let’s focus on the closterium. Look towards the tip of the algae, where there are round barium
crystals wiggling around in the same random way that those particles we saw before were.
We’re going to see that type of motion over and over again today because it’s all over the
microcosmos, found in and around many different types of organisms. And this kind of random motion
may seem almost too trivial to discuss, leading at best to an end where I mull over the way that
randomness seems to pop up everywhere like some kind of unifying force that shapes our lives
through millions of tiny coincidences. Except, well, there’s no point waiting
until the end to say all that because the reason we want to talk about this weird,
wiggling motion is that this randomness really does tie us together, not metaphorically, but
very, very literally and physically. This motion that you see is a proof of something fundamental
not just to life, but to existence itself. This movement is proof of atoms.
It’s easy to take the existence of atoms for granted now, in the same way that it’s easy to
take the existence of microbes for granted. Once you know about them and how they shape the world,
and you've been told about them since you were a child,
it’s impossible to see the world as existing without them.
But our knowledge of both is relatively recent,
even if it’s built on work that spans millennia. And just as the microscope has been
essential to our understanding of microbes, it has played an important role in understanding atoms.
Long before the existence of the microscope though, there was an idea.
In the fifth century BCE, a Greek philosopher named Democritus proposed that if you kept
breaking matter down further and further, you would eventually reach something that could no
longer be broken down. That indivisible thing was what he called atomos, which meant “uncuttable”.
Democritus’ theory was in opposition to the ideas of Aristotle and Plato,
who believed that the world was composed of four basic elements: earth, wind, air, and fire.
So what does Democritus have to do with the tiny little
wobbles of the pigments inside this stentor? For that, we have to flash forward to 1827.
This was an exciting time for anyone interested in diving deep into what matter was made of. The end
of the 18th century had seen important advances in our understanding of matter. And in 1803,
the scientist John Dalton drew upon these ideas to propose that each chemical element
could be described by a particular atom. The atom became a useful tool in developing new
theories about how our world is built, and 19th century physicists used it to describe a theory of
gasses that assumed they were composed of many, many tiny particles constantly moving around.
But these theories weren’t proof. If anything, they raised more questions about how to think
about atoms. Should we think of atoms as just some kind of mathematical metaphor,
or were they something real? And how could we find proof of something as unseeable as an atom?
The answer, it would turn out, would come thanks to a botanist named Robert Brown.
Brown wasn’t setting out to solve the problem of atoms. It was the summer of 1827,
and he was trying to clear up some questions he had about the tiny particles that burst
out of pollen grains like this one. So he did what we’re doing right now:
he brought out his microscope, and looked at some tiny things under it. While we didn’t have
those pollen particles on hand, we imagine that what he saw was similar to these oil droplets,
which came from the body of a dying copepod. He said simply, “While examining the form of
these particles immersed in water, I observed many of them very evidently in motion,”.
Curious about this motion, Brown proceeded to do a number of different experiments. He looked at
pollen from other plants and saw the same motion. He looked at pollen from dead plants and saw the
same motion. He even moved on to inorganic materials like rocks and saw the same motion.
In water, everything wiggled, even if it wasn’t living. And that meant the motion wasn’t something
biological, it was rooted in something else. These random movements are what we now call
Brownian motion. And in the decades that followed his observation, physicists began to study it
in earnest so they could understand the forces that shaped the movement.
For example, one scientist noted that smaller particles exhibited faster motion compared to
larger ones, which you can see at play here in the crystals lying within this amoeba,
with the larger crystals moving more slowly compared to the smaller ones5.
But Brownian motion’s biggest impact would come in 1905 when a scientist theorized
that the movement of the particles Brown had watched was the result of other smaller
particles colliding into them. That scientist, you probably know the name of, it was Albert Einstein.
And those smaller particles were water molecules, composed of
atoms that are packed with energy. And because of that energy, the water molecules are constantly
moving and colliding. Sometimes they collide with each other. And sometimes they collide into other
larger particles, which move erratically in response. That is Brownian motion, a movement
shaped by atoms and their kinetic energy. Einstein’s theories were built on equations,
but they provided a framework that would allow experimentalists to use Brownian motion as a
way to see atoms and their energy at work. And ultimately, it was the French scientist Jean
Perrin who put these theories to the test, using a new microscope called the ultramicroscope to
not only study Brownian motion and confirm the equations that drove Einstein’s theory, but also
to estimate the size of water molecules.
All of that discovery was made possible because a
botanist wanted to study some pollen. Robert Brown was operating in a realm
that is familiar to us here on Journey to the Microcosmos. He was exploring an invisible world.
But what he studied and what he described helped us find an even more invisible world, one that was
still invisible under his microscope, except that it was responsible for everything he was
seeing, not just the motions of the pollen grains, but the pollen grains themselves and anything else
that was under his microscope, outside his microscope, and even the microscope itself.
What he found in those wiggles—what you’re seeing now in the same motion more than a century later,
is an invisible world that built an entire universe.
Thank you for coming on this journey with us as we explore the unseen world that surrounds us.
And thank you again to Endel for sponsoring this episode.
Endel is an app that takes everything we know about sound,
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The goal of Wind Down is to help you transition from an active day to a
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They are our Patreon patrons. We love what we do at Journey to the Microcosmos, this team
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If you want to see more from our master of microscopes, James Weiss,
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