Latest / Talking Science / Living in Space – What Zero-G Does to the Body

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Living in Space – What Zero-G Does to the Body · Talking Science

0:00
So picture that classic pop culture image of
0:02
space travel. You know the videos I'm talking
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about, right? Oh, absolutely. The ones where
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they're just floating around. Yeah, exactly.
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Astronauts floating serenely through the cabin
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of a spacecraft doing these like slow motion
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somersaults. Laughing as they sip those little
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spherical blobs of water right out of the air.
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Right. I mean, it looks like the ultimate playground
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up there. It just looks like this pure, unadulterated
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freedom from the heavy kind of plotting reality
0:26
we all live in down here. It really does look
0:28
fun. But. Contrast that image of serene freedom
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with the, well, the rather jarring reality we
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found in our source material today for this deep
0:37
dive. Yeah, the hidden truth about that weightless
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playground is a lot darker. It is. Because your
0:44
body, my body, the listener's body, we did not
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evolve to float. Every single one of your ancestors,
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stretching back billions of years, lived their
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entire existence under the constant, steady downward
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pull of Earth's gravity. Right. And when you
1:00
take that invisible pole away, the human body
1:02
doesn't just, you know, enjoy the ride. It quietly,
1:07
systematically starts to come undone. It's kind
1:10
of terrifying. It actively unravels. I mean,
1:12
the bones, the muscles, the cardiovascular system.
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They aren't passive structures just hanging out
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inside you. Right, they're doing a job. Exactly.
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They are dynamic systems that are actively tuned
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to fight a 24 -7 battle against a force that
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is suddenly entirely missing. Okay, let's unpack
1:30
this. Because before we can truly understand
1:33
how the body falls apart up there, we really
1:35
have to grasp the physical reality of what the
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body is actually experiencing in space. Which
1:40
is very counterintuitive. It really is. And that
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starts with busting a major myth about gravity.
1:45
itself, specifically this idea of zero gravity
1:48
that we hear constantly in movies and the news.
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Yeah, scientifically speaking, that phrase is
1:53
highly misleading, especially when we're talking
1:55
about the International Space Station. Because
1:57
gravity hasn't just vanished up there. No, it
1:59
hasn't vanished at all. At the altitude of the
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space station, which is roughly 250 miles above
2:05
the surface, Earth's gravity is still very much
2:09
present. Wow. In fact, it's about 90 % as strong
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as it is right where you are sitting right now.
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The technical term for what astronauts experience
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isn't zero gravity. It's actually microgravity.
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But wait, if the gravitational pull is still
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90 % as strong up there, why aren't they just
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pinned to the floor of the station? Like, why
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are they floating? It's a great question. It
2:29
is entirely about their sideways motion. Okay.
2:32
The space station and every astronaut inside
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of it is in a state of permanent free fall. Free
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fall. Yeah. They are orbiting, which means they
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are moving horizontally. So incredibly fast.
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We're talking roughly 17 ,500 miles per hour.
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That is insane. Right. So as gravity pulls them
2:49
down toward the ground, the curve of the Earth
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essentially falls away beneath them at the exact
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same rate. Oh, I see. So they are endlessly falling
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around the planet. Exactly. And because the station
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and the people inside are falling at the exact
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same speed, there is no sensation of weight.
3:05
That's wild. OK, so imagine you're in an elevator
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at the very top of a tall skyscraper. If the
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cable snaps and the elevator plummets, for those
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few seconds before you hit the bottom... You
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would float inside the cabin. Right. You and
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the elevator are falling together. Gravity is
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still pulling you down, but because the floor
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of the elevator isn't pushing back... up against
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your feet, you feel entirely weightless. That's
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a perfect way to picture it. This position is
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really just an elevator that never hits the ground.
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So the astronauts are not beyond gravity's reach.
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They just aren't feeling its mechanical resistance
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anymore. And that absence of resistance, like
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the sheer lack of having to bear any actual weight.
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is what triggers this massive cascade of biological
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alarms, right? Right. Starting deep within the
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skeletal system. It does. I mean, we tend to
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view our skeleton as the static scaffolding of
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a building. Like, it's just hard, dead stuff
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holding us up. Yeah, just rocks inside our bodies.
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Right. But our bones are highly active living
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tissue, and they operate on a very strict use
4:05
-it -or -lose -it system. Okay, so down here
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on Earth, every time you stand up or walk...
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Your bones bear your weight. And your body senses
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that mechanical stress at a cellular level. And
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it continuously rebuilds the bone to ensure it's
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dense enough to handle the load. But in space,
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in that endless elevator drop we just talked
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about, the body realizes it just doesn't need
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to fight gravity anymore. Exactly. From an evolutionary
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standpoint, the human body is incredibly efficient,
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almost to a fault, really. Wait, Amy. Well, why
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expend valuable energy and metabolic resources
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maintaining thick, heavy bones if you don't actually
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need them to hold you up? Oh, wow. So it just
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gives up on them. Pretty much. The moment that
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mechanical stress disappears, the cells responsible
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for building new bone just slow down, while the
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cells responsible for breaking down old bone
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kick into overdrive. That's crazy. The body actively
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dismantles its own scaffolding. The bones literally
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dissolve, shedding vast amounts of calcium directly
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into the bloodstream. And the rate at which this
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happens is just staggering. Our sources note
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that astronauts can lose 1 to 2 percent of their
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bone mass every single month they are in orbit.
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It's massive. That is a highly accelerated form
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of osteoporosis. Which we usually associate with
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aging, right? Where bones become brittle and
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fragile over a span of decades. Exactly. But
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in microgravity, this severe bone thinning is
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happening to peak condition. Extremely fit adults
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in a matter of mere months. And the muscles follow
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that exact same... use it or lose it trajectory,
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especially the postural muscles. Oh yeah, the
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muscles in your calves, your thighs, your core,
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your lower back, they are basically unemployed
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up there. What's fascinating here is how the
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space agencies are actually forced to combat
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this rapid decay. Because exercise on the space
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station, it isn't a recreational activity to
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just pass the time. No. It is essential, strictly
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prescribed medicine. Astronauts strap themselves
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into specialized treadmills and resistance machines
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using these heavy bungee cords to simulate the
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downward pull of gravity. And they have to engage
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in this intense, sweat -inducing workout for
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roughly two hours every single day. Two hours?
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Every single day, just to trick the body into
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maintaining its structural integrity. They are
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artificially forcing the bones and muscles to
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work against resistance. Basically desperately
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sending a biological signal that says, hey. Don't
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dissolve yet. We still need you. Exactly. But
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wait, I have a question about this. If they are
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working out for two hours a day with heavy resistance,
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shouldn't that completely solve the problem?
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I mean, two hours of heavy lifting and running
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is significantly more exercise than most people
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do on Earth in a given week. You would definitely
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think so. But no, it doesn't completely halt
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the decay. Really? Yeah, it mitigates the worst
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of it, sure, but astronauts still lose mass.
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What that stubborn, unavoidable loss tells us
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is that we fundamentally underestimate the 24
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-7 workout that gravity provides for free. That
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makes sense. From the moment you roll out of
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bed to the moment you lie back down, gravity
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is constantly demanding that your cardiovascular
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system, your muscles, and your bones maintain
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themselves. So you don't even have to go to a
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gym to benefit from it. Just standing in your
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kitchen. you know, making coffee, is a constant
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physical engagement with a planetary force. Exactly.
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Take that persistent load away, and two hours
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on a space treadmill is barely a band -aid. Okay,
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so the skeleton is falling apart because it lacks
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resistance, but the human body isn't just a solid
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frame. We are essentially a complex plumbing
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system. A very complex one, yeah. We're full
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of fluids, blood, water, plasma. And normally
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down here, gravity anchors those fluids, pulling
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them downward into our legs and our lower body.
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Which means your cardiovascular system has to
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work incredibly hard, constantly pumping against
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that downward pull to force blood back up to
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keep your brain oxygenated. Right. Your heart
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is a muscle perfectly calibrated for the gravity
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of Earth. So what happens when that fluid is
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suddenly let off the leash in microgravity? The
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heart doesn't immediately get the memo, does
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it? Nope. It keeps pumping with the exact same
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upward force, expecting to fight gravity. But
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with no gravity pulling the blood down, a massive
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volume of fluid rapidly drifts upward, pooling
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in the chest and the head. It's like imagine
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a water balloon that's only half full. If you
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squeeze the bottom half of that balloon... all
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the water is forced upward, making the top half
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bulge out super tight. Yes, that's essentially
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exactly what is happening to the body's fluids.
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And the physical changes from this fluid shift
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are immediate and totally visible. Astronauts
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develop these puffy, rounded faces. The veins
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in their necks bulge out. It looks very uncomfortable.
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And simultaneously, their legs thin out dramatically
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because a huge percentage of their fluid volume
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has just evacuated the lower body. I read that
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it's affectionately known among astronauts as
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the chicken leg effect. Yeah, exactly. Chicken
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legs. So they get plucky faces and skinny legs.
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And the sources say they also constantly feel
9:02
like they have a severe head cold because all
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that fluid congestion stuffs up their sinuses.
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Mm -hmm. Constantly congestion. But I mean, it
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sounds highly uncomfortable, sure. But a stuffy
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nose and puffy cheeks don't exactly sound like
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mission ending catastrophes that would stop us
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from going to Mars, right? Well, a stuffy nose
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isn't mission ending, no. But the pressure behind
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that stuffiness, that absolutely could be. Wait.
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Really? Yeah, because the fluid isn't just settling
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in their sinuses. It is increasing the overall
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intracranial pressure, so the pressure inside
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the skull. And the brain is encased in solid
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bone, so when extra fluid rushes in, it has literally
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nowhere to expand. So that rising pressure begins
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to press forward against the back of the eyeballs.
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Wait, so it physically alters the shape of the
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eye? It physically flattens the globe of the
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eye from the inside out. Oh, wow. While simultaneously
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squeezing the optic nerve. It is a condition
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currently being heavily researched, often called
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spaceflight -associated neuroocular syndrome.
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That sounds intense. It is. Many astronauts find
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that their vision noticeably degrades during
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long missions. They become farsighted. They struggle
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to read instruments. And do their eyes go back
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to normal when they get home? Not always. For
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some astronauts, these structural changes to
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the eye are permanent. Their vision never fully
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returns to its pre -flight baseline, even years
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after returning to Earth. This raises an important
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question for space agencies, because how can
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we send people on a three -year Mars mission
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if they might go blind on the way? That is terrifying.
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But OK, so we can measure the bones shrinking
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on a scan, and we can clearly observe the fluid
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shifting and pressing against the eyes. Right.
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But the absolute most dangerous roadblocks to
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deep space travel are actually completely invisible
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to the naked eye. Ah, yes, the radiation. Exactly.
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Because once a crew leaves Earth's immediate
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orbit, they hit a wall of invisible threats,
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primarily high -energy cosmic radiation. It's
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true. Down here on the surface, we are blissfully
11:03
unaware of just how hostile the universe really
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is because we are wrapped tightly in two protective
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blankets. The atmosphere being one of them? Right.
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The atmosphere physically absorbs a lot of radiation,
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but the heavy lifting is actually done by Earth's
11:15
massive magnetic field. Okay, so how does that
11:18
work? It acts as an enormous deflector shield
11:21
that stretches far out into space, and it routes
11:24
highly charged solar particles and cosmic rays
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safely around the planet. Even the International
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Space Station, right? Right. Orbiting a few hundred
11:32
miles up, it's still tucked safely inside that
11:34
magnetic shield. Exactly. They get a higher dose
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than we do on the ground, but they are still
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protected. Okay, here's where it gets really
11:41
interesting. If you picture the Earth's magnetic
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field as a giant invisible umbrella, as long
11:46
as you're standing under it, you stay dry. Good
11:49
analogy. But the moment a crew sets course for
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the moon... or embarks on a multi -month journey
11:54
to Mars, they step completely out from under
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that umbrella. And they are instantly caught
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in a torrential, unending downpour of deep space
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radiation. And unlike muscle loss, You cannot
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exercise away radiation damage. No, you absolutely
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cannot. We are talking about galactic cosmic
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rays here. Incredibly fast, heavy particles that
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tear right through human tissue. Like tiny bullets.
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Literally. On a cellular level, they smash through
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DNA strands, causing complex double -strand breaks
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that the body's repair mechanisms just struggle
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to fix. Which means a huge cancer risk. Exactly.
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This drastically raises the lifetime risk of
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developing cancer. It damages the central nervous
12:33
system. And it can even... accelerate cognitive
12:35
decline. But the logical solution to protect
12:38
the crew would just be to build a thicker spacecraft,
12:41
right? Yeah. Like just line the walls with thick
12:44
lead or water to block the radiation. You would
12:46
think so, but that runs into the absolute most
12:49
unforgiving rule of rocket science. Which is?
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Mass. Every single ounce you launch into space
12:54
requires a massive amount of fuel. Right, of
12:57
course. So building a spacecraft with walls thick
13:00
enough to act as a proper radiation shield would
13:02
make the ship so incredible. Wow. So the physics
13:09
of propulsion and the biology of radiation damage
13:11
are currently just in a standoff. Pretty much.
13:14
We haven't solved it yet. But the sources also
13:16
highlight invisible threats that aren't physical
13:19
or cellular at all. There are subtler, deeply
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human challenges to leaving the planet, starting
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with something as simple as figuring out which
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way is up. Yeah, the human balance system is
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entirely dependent on gravity. Right, the inner
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ear. Exactly. Deep inside your inner ear is the
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vestibular system, which uses small fluid -filled
13:37
canals to tell your brain your orientation. So
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when you tilt your head on Earth, gravity pulls
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on that fluid, sending a signal. Right. But in
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microgravity, that fluid just floats. So your
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eyes might tell your brain you are floating upside
13:50
down in the cabin, but your inner ear is sending
13:53
completely chaotic, nonsensical signals because
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it has no gravity to anchor it. That sounds nauseating.
13:59
Oh, it is. This conflict causes space adaptation
14:02
syndrome. For the first few days in orbit, many
14:05
astronauts experience profound, debilitating
14:08
nausea and sickness until the brain eventually
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learns to just ignore the inner ear entirely.
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Which is wild that the brain can just choose
14:15
to ignore an entire sensory organ. It's very
14:17
adaptable. But once that physical sickness fades...
14:20
The psychological reality sets in. I mean, we
14:22
are deeply social earthbound creatures. I'm sure.
14:25
So being sealed inside a small metal container,
14:28
essentially the volume of a large house or like
14:31
a few school buses with the exact same three
14:34
or four people for years takes an immense toll.
14:37
There is no fresh air, no wind, no varying landscapes.
14:40
And on the space station, at least astronauts
14:43
can look out the window. Right. They can look
14:45
out the cupola window and see the Earth filling
14:47
their entire field of view. Yeah, it's vibrant,
14:50
it's huge, and it's incredibly psychologically
14:52
comforting. But on a mission to Mars, the sources
14:55
paint a terrifyingly isolated picture. As the
14:58
spacecraft travels, the Earth just shrinks. It
15:02
does. Eventually, our entire planet, everyone
15:05
you know, the entire history of our species,
15:07
is reduced to a single distant point of light
15:10
in an endlessly black sky. You are utterly alone.
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and you cannot return home in an emergency, you
15:17
are locked into orbital mechanics. Keeping a
15:19
crew mentally well, cooperative, and sharp under
15:22
that level of profound, inescapable isolation
15:25
is an entirely different puzzle from keeping
15:28
their bones strong. It is a psychological pressure
15:30
cooker. Complete. So given the DNA damage from
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radiation, the dissolving skeleton, the flattening
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eyeballs, and the immense psychological strain,
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it really begs the question, Are we fundamentally
15:43
doomed to stay here? Like, is human spaceflight
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an evolutionary dead end because we are just
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too biologically fragile for the environment?
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Well, if you only look at the decay, it definitely
15:55
seems that way. But the silver lining in all
15:58
this data lies in the profound resilience of
16:01
human biology. Okay, that's good news. Yeah,
16:03
the human machine is phenomenally adaptable.
16:05
When astronauts return to Earth's gravity, they
16:08
are undeniably weak. I mean, they often have
16:11
to be physically carried out of the landing capsule
16:13
because their cardiovascular systems can't even
16:15
pump blood to their brains quickly enough when
16:17
they stand up. Right, because their heart is
16:19
used to microgravity. Exactly. But the damage
16:21
is not a permanent state. So once that heavy
16:24
downward gravitational load applies itself again,
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the biological alarm bells immediately start
16:29
ringing in reverse. Exactly. The body realizes
16:32
the mechanical stress has returned and says,
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hey, we need these systems online immediately.
16:36
So the fluids redistribute downward. taking the
16:39
dangerous pressure off the optic nerve. The inner
16:42
ear recalibrates to the downward pull and a normal
16:45
sense of balance slowly returns. Yeah, and the
16:47
bones. The cells responsible for building bone
16:49
wake back up and the skeleton gradually rebuilds
16:53
its density. Muscles regrow and regain their
16:56
earthly strength. The sources do mention that
16:58
this recovery process can take months. And there
17:01
is a possibility that a tiny percentage of the
17:03
lost bone density never fully returns. But by
17:06
and large, the body manages to knit itself back
17:09
together. It does. And if we connect this to
17:11
the bigger picture, every single astronaut who
17:13
spends an extended period in microgravity is
17:16
acting as a volunteer in a grand high -stakes
17:19
medical experiment. How so? Well, by closely
17:22
observing exceptionally fit, healthy individuals
17:25
rapidly deteriorate in a predictable way and
17:27
then successfully recover, scientists are learning
17:30
invaluable lessons about ordinary medical conditions
17:32
down here. Oh, right. Because the accelerated
17:34
bone loss in space perfectly mimics osteoporosis
17:38
on Earth. Exactly. And the rapid muscle wasting
17:41
perfectly mimics the atrophy seen in elderly
17:44
patients or individuals confined to long -term
17:47
bed rest. So by studying the exact cellular mechanisms
17:50
of how astronauts lose bone, and more importantly,
17:53
how they heal, Researchers are developing better
17:55
targeted therapies for the frailties of aging
17:58
right here on Earth. That's amazing research.
18:01
It really is. So every time you, the listener,
18:03
just stand up from your chair right now and walk
18:05
across the room, you are actively participating
18:08
in the exact life -sustaining biological process
18:12
that space agencies are spending billions of
18:15
dollars to study in orbit. That's a great way
18:17
to think about it. So what does this all mean?
18:19
When we look at all these sources, The core realization
18:22
is really a complete reframing of our relationship
18:25
with this planet. We are conditioned to think
18:27
of gravity as a burden. Wow, totally. It's the
18:29
thing that makes heavy boxes hard to lift. It's
18:32
the force that makes our legs ache at the end
18:34
of a long workday. It's what we have to physically
18:36
drag ourselves up against every morning when
18:38
the alarm goes off. But the reality revealed
18:40
by space travel is that gravity is actually an
18:43
invisible life support system. It is a fundamental
18:46
matrix that we are biologically plugged into.
18:49
It dictates the architecture of our skeleton.
18:51
It manages the precise circulation of our blood.
18:54
It grounds our sense of... Physical reality and
18:57
balance. It's basically performing essential
19:00
structural maintenance on your body every single
19:03
second of your life. Every second. And if we
19:06
want to travel to Mars, if we truly want to become
19:09
an interplanetary species, our biggest hurdle
19:12
isn't just engineering a more powerful rocket
19:14
engine. Right. We have to figure out how to artificially
19:18
replicate a fundamental force of nature. that
19:22
we have taken completely for granted for our
19:24
entire evolutionary history. Which leaves us
19:26
with a truly fascinating question to ponder.
19:28
Oh, what's that? Well, everything we've discussed
19:31
today revolves around fully grown adults whose
19:33
bodies were forged in Earth's specific 1G environment,
19:36
venturing briefly into space. But what about
19:39
the future? If our bodies are this intimately
19:42
tuned to Earth's gravitational pull, what would
19:45
happen to the first generation of humans born
19:48
on Mars, where the gravity is only about a third
19:50
as strong as it is here? Oh, wow. Or like a child
19:54
born on the moon, where it's even weaker. Exactly.
19:56
If they grew up without that constant, heavy
19:59
workout from birth, their bodies would develop
20:01
entirely differently. Their bones would be significantly
20:04
less dense, optimized only for a much lighter
20:07
world. Their hearts would be weaker, never having
20:09
needed to pump blood against Earth's heavy pull.
20:12
So if a child born on Mars decided as an adult
20:16
to visit their ancestral home planet... Could
20:18
they even survive the trip down to the surface?
20:21
Right. Would the crushing weight of Earth's gravity
20:24
simply be too much for a Martian -grown body
20:26
to endure? They might be effectively trapped
20:29
on Mars forever by the sheer reality of their
20:31
own biology. That is profound. We spend billions
20:34
building rockets to escape the Earth, only to
20:36
find out that the Earth... is quite literally
20:38
built into our bones. It really is. Well, thank
20:41
you so much for joining us on this deep dive.
20:43
As you go about the rest of your day, maybe take
20:45
just a moment to appreciate that heavy feeling
20:48
of your feet pressing firmly into the floor.
20:51
You aren't just walking. You are actively enjoying
20:53
the constant life -giving embrace of the planet.
20:56
Forget the serene floating and the slow -motion
20:59
somersaults. Exactly. Down here, heavy is healthy.
21:02
Take care of yourselves, and we will catch you
21:04
on the next one.