Latest / Talking Science / Cosmic Rays – Messengers from Violent Space

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Cosmic Rays – Messengers from Violent Space · Talking Science

0:00
I want you to try something for a second. Just
0:01
hold out your hand, keep it steady, palm up,
0:04
and just look at it. Right, just hold it right
0:07
there in front of you. Yeah. Picture something
0:09
passing straight through your hand, right now,
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roughly once every second or two. You can't feel
0:15
a thing. It isn't sunlight warming your skin,
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and it isn't, well, it isn't the radio waves
0:20
coming from your phone either. It is a tiny,
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incredibly fast -moving particle, and it was
0:25
born a few dozen kilometers above your head.
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And, you know, its origins trace back even further
0:31
than that. That particle is the debris from a
0:34
very violent collision. Right. The original object
0:37
that caused that collision arrived from deep
0:40
space. I mean, it might have been launched by
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a massive star that exploded thousands of years
0:44
ago or blasted out of some cosmic engine that
0:48
nobody has ever quite pinned down. Which is wild
0:51
to think about. It really is. But whatever threw
0:53
it, it crossed the galaxy and slammed into the
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very top of Earth's atmosphere. moving at close
0:58
to the speed of light. And that original incoming
1:01
piece of space debris is called a cosmic ray.
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And it is part of this slow, relentless, invisible
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rain of matter that just never stops. I mean,
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day or night, rain or shine, it has been striking
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the planet for its entire history. Yeah. You
1:19
are quite literally being showered by the cosmos
1:21
right now. Okay, let's unpack this, because right
1:23
out of the gate, we have a naming problem. We
1:25
do, yeah. Based on the stack of sources we're
1:27
looking at for this deep dive, that name, cosmic
1:31
rays, is a massive historical misdirection. It
1:34
really is. It's a remnant from a time when we,
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frankly... fundamentally misunderstood what we
1:40
were looking at. The term was coined in the early
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20th century. Back when physicists were just
1:44
discovering new phenomena left and right. Exactly.
1:47
And because of that, they assumed they were dealing
1:49
with a form of electromagnetic radiation. They
1:52
envisioned something similar to X -rays or gamma
1:54
rays, just sort of radiating down from the sky.
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So they thought they were dealing with light,
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essentially, just really high energy light. Right.
2:01
But these aren't light waves. They are actual
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physical matter. A cosmic ray is overwhelmingly
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a single charged particle. We're talking about
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bare hydrogen nuclei. So protons completely stripped
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of their electrons and just hurled across the
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galaxy. And there's other stuff mixed in too,
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right? Yeah. You also get helium nuclei plus
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a tiny fraction of heavier elements and some
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stray electrons. But the unifying characteristic
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is that they have real mass. They carry an electric
2:29
charge. and they're moving extraordinarily fast.
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So they don't just shine on things, they physically
2:35
smash into them. Precisely. Which brings us to
2:38
how we even... figured out this invisible space
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rain was happening in the first place because
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the 1912 discovery story is fantastic it perfectly
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highlights how science often progresses by looking
2:48
in completely the wrong direction oh absolutely
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early 20th century physicists had these simple
2:52
instruments called electroscopes to measure electric
2:55
charge and they started noticing that the instruments
2:58
were slowly discharging in their sealed labs
3:00
just losing their charge out of nowhere right
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exactly the electroscopes were losing their charge
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as if an unseen radiation was physically knocking
3:09
the electrons loose. Naturally, the working hypothesis
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was that the Earth itself was the source. Scientists
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assumed this radiation was just, you know, seeping
3:19
up from radioactive elements in the rocks and
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soil. Which makes sense. So the logical prediction
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was that if you move the electroscope higher
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up... away from the ground, the discharging effect
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would weaken. That was the thought process, yeah.
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It's like walking into your house, seeing a puddle
3:34
on the floor, and assuming you have a leaky pipe
3:36
in the basement. You start tearing up all the
3:38
floorboards looking for the source, but in reality,
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the roof is caving in. That is a great way to
3:43
put it. And the Austrian physicist Victor Hess
3:45
decided to actually test this assumption. He
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went ahead and strapped his instruments into
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a hot air balloon. Which is such a bold move
3:52
for 1912. It was. He flew repeatedly, eventually
3:56
reaching altitude. Wow. Yeah, and he even scheduled
4:01
a flight during a partial solar eclipse to ensure
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the sun wasn't just acting as some ordinary light
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source responsible for the effect. Very thorough.
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And the data completely flipped the script. Completely.
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The data he gathered completely inverted the
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scientific consensus because the discharging
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effect didn't weaken as he ascended. It amplified
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significantly. So the leaky pipe wasn't in the
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basement. The radiation was coming down from
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space itself. Yes, exactly. But if the radiation
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gets stronger, the higher you go, you eventually
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run out of Earth's atmosphere. Yeah. You hit
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the vacuum of space. So the natural next question
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becomes, well. What exactly is out there with
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enough firepower to shoot these massive particles
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at us? Right, and to answer that, we have to
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look at different astrophysical phenomena depending
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on the energy level of the particle. At the lower
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end of the energy scale, a good portion of the
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cosmic rays reaching Earth are actually generated
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locally by our own sun. So the sun is throwing
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particles at us. Yeah, especially during solar
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flares. The sun accelerates streams of charged
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particles outward, and their intensity fluctuates
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with the sun's regular 11 -year cycle. OK, so
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the sun handles the low energy stuff. But to
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get the medium energy galactic cosmic rays, the
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ones that make up the bulk of what strikes Earth,
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things have to get a lot more violent. We have
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to look at the explosive deaths of massive stars.
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Supernovae, yes. Right. When a massive star exhausts
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its fuel and collapses, it triggers a catastrophic
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explosion that flings stellar material outward,
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plowing into the surrounding interstellar gas.
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This creates a supernova remnant, which is an
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expanding shockwave that can persist for tens
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of thousands of years. And this is where the
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acceleration happens. When I was reading the
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sources, it sounded exactly like a game of interstellar
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ping pong. That's a really good analogy, actually.
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To have this charged particle that gets caught
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up in the magnetic fields around this expanding
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shockwave. But it doesn't just ride the wave.
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It gets bounced back and forth across the shock
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boundary. Right, between the approaching layers.
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Yeah, and with... Every single bounce across
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that front, it steals a little bit of kinetic
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energy and speeds up. It just gets whacked back
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and forth across this massive cosmic explosion,
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gaining speed for thousands of years, until finally,
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the magnetic paddles hit it so hard it reaches
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escape velocity, and it gets flung out into the
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galaxy. Physicists refer to that mechanism as
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shock acceleration, and the observational evidence
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strongly supports it. I mean, we can detect the
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specific signatures of radiation we would expect
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if particles were actively being accelerated
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in this exact manner inside known supernova remnants.
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So what does this all mean? We have exploding
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stars playing ping pong with atomic nuclei, shooting
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them across the galaxy. That sounds like the
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absolute ceiling of how crazy the universe gets.
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You'd think so, wouldn't you? But it's not. Because
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supernova shockwaves, as immense as they are
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mathematically run out of steam, their magnetic
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paddles simply aren't strong enough to accelerate
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the most extreme particles we've ever detected.
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And now we step into the genuinely puzzling category,
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which is ultra high energy cosmic rays. To give
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you a sense of scale, we are talking about a
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single subatomic particle, something far too
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small to see or feel, carrying roughly the kinetic
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energy in a well -struck tennis ball. All that
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energy packed into one single proton. That is
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terrifying. It's unbelievable. In 1991, an event
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was recorded that was so extreme, physicists
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informally dubbed it the Oh My God Particle.
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Producing a particle with that much energy requires
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a cosmic accelerator on a scale that completely
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dwarfs a supernova. So if a dying star isn't
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powerful enough, what is? Who is throwing these
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interstellar tennis balls at us? Well, the candidate
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sources are some of the most violent cataclysmic
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phenomena in the universe. One strong candidate
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is active galactic nuclei. Which are black holes,
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right? Right. Supermassive black holes sitting
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at the centers of distant galaxies. They're voraciously
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consuming matter and blasting out highly collimated
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jets of plasma, just colossal energies. Another
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candidate is gamma ray bursts, which are extraordinarily
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brief, violent explosions tied to the collapse
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of massive stars or even colliding neutron stars.
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But I have to push back here for a second, because
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if we caught the oh my God particle, why can't
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we just trace its trajectory backward? Like just
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look back at the exact angle it hit our atmosphere
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and see which black hole or which explosion sits
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at the end of that line. I wish we could, but
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the universe doesn't make it that easy. You have
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to remember, cosmic rays are electrically charged.
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Because of that charge, they interact with the
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weak magnetic fields that thread through interstellar
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and intergalactic space. So they don't fly in
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a straight line. Exactly. As they travel over
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millions of light years, their paths are constantly
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nudged, bent, and deflected. By the time a cosmic
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ray arrives at Earth, its direction of travel
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is completely scrambled. It points nowhere near
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its actual... origin. It's like trying to figure
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out who launched a pinball by only looking at
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the very last bumper it hit before falling down
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the drain. Yeah. The information is just lost.
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But the sources do point out something called
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the GZK cutoff, which seems to offer a pretty
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major clue. It acts as a physical limit on how
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far these ultra -high energy particles can actually
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travel. Yes. The GZK cutoff is a crucial piece
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of the puzzle. It's named after the physicists
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who calculated it. And the concept fundamentally
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relies on the fact that intergalactic space is
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not a perfect vacuum. Oh, right. It is filled
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with the cosmic microwave background, which is
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the faint leftover radiation from the Big Bang.
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So space is filled with this sea of ancient microwave
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photons. Yes. ultra high energy cosmic ray traveling
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near the speed of light, that background radiation
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becomes a very dense hazard. When the proton
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collides with the microwave photon, the sheer
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energy of that collision actually creates a new
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particle, a pion out of the kinetic energy. Just
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following Einstein's E equals MC squared. Exactly.
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The particle is literally converting its own
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speed into new mass. It's hitting a cosmic speed
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bump, bleeding off massive amounts of energy
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with every collision. Right. The physics dictate
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that because of these constant energy sapping
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collisions, an ultra high energy particle cannot
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travel across the entire observable universe
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and still arrive with all that energy intact.
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If it reaches us with the energy of a tennis
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ball, it simply couldn't have been traveling
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for very long. Meaning whatever fired it at us
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has to be in our galactic neighborhood. Yeah.
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It narrows the search radius drastically. It
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really does. It is wild to think about. But let's
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bring this journey all the way home. We've traced
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these particles from distant black holes, navigating
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magnetic fields and slamming into background
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radiation. Let's look at the final millisecond
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of the journey, which is hitting Earth. Because
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they don't just float down to the surface, do
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they? No, not at all. The arrival is incredibly
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dramatic. When that primary cosmic ray hits Earth's
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atmosphere, it triggers what we call an air shower.
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An air shower. Yeah. The primary particle collides
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with the nucleus of a nitrogen or oxygen atom
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tens of kilometers up. The collision completely
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shatters both the incoming particle and the atmospheric
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nucleus. It creates a massive spray of secondary
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particles. It initiates a massive cascade, yeah.
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Among that initial spray are short -lived particles
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called pions. Those pions decay almost immediately
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into lighter particles, including neutrinos,
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which are so ghost -like they pass straight through
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the entire planet without hitting anything. They're
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passing right through the Earth. Right. But the
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pions also decay into muons. Meanwhile, the rest
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of the debris from that very first collision
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keeps rocketing downward, striking more atmospheric
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nuclei, shattering them and multiplying. By the
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time the cascade reaches ground level, that one
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single incoming particle has created a shower
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of millions of secondary particles spread across
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an area the size of several football fields.
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And out of all that debris, I really want to
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focus on the muon. Because that is the specific
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particle passing through your hand right now.
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Muons present this incredible physics puzzle.
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They are essentially heavy electrons, but they
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are inherently unstable. They have an incredibly
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short lifespan. It's like a ticking time bomb
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falling from the sky with a timer that is that
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way too short. I mean, even traveling at near
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the speed of light, a muon created high in the
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atmosphere should explode and vanish before it
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ever reaches the ground. You're totally right.
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By classical mechanics, it shouldn't survive
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the trip. The distance is too great for its microscopic
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lifespan. Yet we detect millions of them reaching
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sea level constantly. So how does the time bomb
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reach the ground without detonating? What's fascinating
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here is that the answer is a real -world demonstration
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of Einstein's special relativity. Because these
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muons are traveling at speeds extremely close
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to the speed of light, time itself genuinely
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passes more slowly for them relative to an observer
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standing on the ground. So time dilation isn't
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just a sci -fi concept. It physically stretches
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the muon's lifespan. It does. From the muon's
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own frame of reference, it lives its standard,
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incredibly brief life. No extra time has passed
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for it. But from our frame of reference on Earth,
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that exact same brief lifetime is stretched out.
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The muon's internal clock is ticking so slowly
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that it has plenty of time to cover the tens
13:19
of kilometers down to the surface before it decays.
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The fact that the muon makes it to your hand
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is tangible, physical proof that relativity is
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happening all around us. It's beautiful, isn't
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it? It is, but these particles aren't just doing
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physics tricks. They have real -world impacts.
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They physically interact with human biology and
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our technology. Let's talk about the occupational
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hazards, starting with flight crews, because
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the atmosphere shields. those of us on the ground,
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but if you fly long -haul at high altitudes,
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you lose a lot of that shield. You do, and this
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is especially pronounced on polar flight routes.
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Why the poles? Well, Earth's magnetic field deflects
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a lot of cosmic rays, but those magnetic field
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lines funnel inward at the poles, offering far
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less shielding than you get at the equator. Because
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of this, flight crews on polar routes accumulate
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a noticeably higher dose of cosmic radiation.
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They're actually classified as occupational radiation
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workers in several countries. Like they're monitored
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similarly to technicians in a nuclear power plant.
14:17
Exactly. Airlines use specialized software to
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model and track the cumulative radiation exposure
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for their crews so they can manage their roster
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safely. And, you know, this challenge scales
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up massively for astronauts. Oh, I bet. Once
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you leave the protection of Earth's atmosphere
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and magnetic field entirely, cosmic ray exposure
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becomes one of the primary medical and engineering
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hurdles for long -duration space missions. Like,
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say, a trip to Mars. And it isn't just our bodies
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at risk. It's our silicon, too. A cosmic ray
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can cause a phenomenon in our computers called
14:48
a single event upset. And when I was reading
14:51
how this actually works mechanically, it just
14:53
completely blew my mind. It is a really profound
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intersection of astrophysics and microelectronics.
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Basically, a computer chip is made of billions
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of microscopic transistors, tiny electrical switches
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holding a charge to represent a zero or a one.
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Right. When a secondary cosmic ray particle passes
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through the silicon of a chip, it can deposit
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kinetic energy. Right. That energy knocks electrons
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loose in the silicon, creating a sudden microscopic
15:19
surge of electric charge. If that tiny surge
15:22
hits the right transistor, it alters the voltage
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just enough to flip the switch. It literally
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changes a zero to a one. It does. And most of
15:31
the time, flipping a random bit of memory is
15:33
totally harmless. Your laptop might briefly glitch
15:35
or maybe a single pixel in an image renders incorrectly
15:38
and the system just moves on. Right. No big deal.
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But in highly sensitive systems, think aircraft
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avionics, satellite control. That is wild. Now,
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there's also a lot of noise online about cosmic
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rays causing climate change. And I want to tackle
16:03
this because it's easy to read a headline and
16:05
jump to conclusions. Yes, it is. Let's separate
16:08
the actual science from the Internet speculation
16:09
here. Can these space particles actually change
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our weather? Well the hypothesis centers on cloud
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formation. As cosmic rays pass through the atmosphere,
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they strip electrons from molecules, creating
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ions. The idea is that these charged ions act
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as seeds, helping water vapor condense to form
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tiny aerosols, which eventually grow into clouds.
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Okay, so more cosmic rays would mean more clouds,
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which would reflect sunlight and cool the Earth.
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That's the theory. And the CERN Particle Physics
16:39
Laboratory actually built a massive controlled
16:42
chamber to test this. They did, yeah, in an experiment
16:45
called CLOUD. And the laboratory results showed
16:47
that, yes, ionization from cosmic rays can indeed
16:51
enhance the formation of aerosol particles under
16:53
highly specific controlled conditions. It works.
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In a lab, yes. But we must bridge the gap between
16:59
a controlled chamber and the actual atmosphere.
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The particles formed by this process in the lab
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are often too small to act as effective cloud
17:07
condensation nuclei in the chaotic, dynamic environment
17:11
of Earth's actual climate system. So it's a fascinating
17:14
mechanism, but it's not the secret driver of
17:17
global climate behavior. Right. It remains a
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debated topic, not a confirmed driver. Got it.
17:24
With all these phenomena, from bit flips to time
17:26
-traveling muons, how are scientists actually
17:29
studying this? I mean, how do you catch something
17:31
invisible that moves at the speed of light? The
17:34
detection methods span an incredible range of
17:37
engineering. At the smallest scale, you have
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cloud chambers. You fill a sealed container with
17:41
a supersaturated vapor, often alcohol. When a
17:44
charged cosmic ray zips through, it ionizes the
17:46
gas, creating a visible, thin trail of condensation
17:49
along its path. You can actually build one for
17:52
a high school science class and watch cosmic
17:53
rays with your own eyes. It's amazing you can
17:56
just see it on a desk. But to catch the oh -my
17:58
-god particles, a desktop box doesn't work because
18:01
they are so incredibly rare. You really need
18:04
scale. The sources mention the Pierre Auger Observatory
18:08
in Argentina, which monitors an area the size
18:10
of Rhode Island. Yeah, the scale is massive.
18:13
They use arrays of water tanks to detect the
18:15
secondary particles hitting the ground, but they
18:18
pair them with specialized telescopes pointed
18:20
at the night sky. Wait, why telescopes? Because
18:23
when a massive air shower cascades through the
18:25
atmosphere, the charged particles excite nitrogen
18:28
gas in the air, causing it to emit a faint ultraviolet
18:31
fluorescence. The telescopes literally watch
18:34
the sky glow for a fraction of a second. Here's
18:37
where it gets really interesting, though. Because
18:39
if you want to detect the ghostly neutrinos that
18:41
are produced in these air showers, you look down,
18:44
not up. And you use a full cubic kilometer of
18:47
solid ice in Antarctica at a facility called
18:49
IceCube. IceCube is a masterpiece of extreme
18:52
engineering. Neutrinos interact so rarely with
18:55
matter that you need a colossal target just to
18:57
catch one. They drilled deep into the ultra -clear
19:01
ancient glacial ice at the South Pole and buried
19:04
thousands of optical sensors. And the mechanism
19:07
here is incredible. When a high -energy neutrino
19:10
actually happens to collide with an atom in the
19:12
ice, it produces a secondary particle, like a
19:15
muon. But here is the trick. The speed of light
19:19
in a vacuum is the absolute speed limit of the
19:22
universe. But light travels significantly slower
19:25
through solid ice. Precisely. The newly created
19:28
particle is ejected from the collision moving
19:30
faster than the local speed of light in that
19:32
specific icy medium. Right. Just as an aircraft
19:35
exceeding the speed of sound creates a sonic
19:37
boom, this particle exceeding the speed of light
19:40
in ice creates an optical sonic boom. It emits
19:43
a faint cone -shaped flash of blue light called
19:45
Cherenkov radiation, and the sensors in the ice
19:47
detect that blue flash, pointing all the way
19:50
back to the particle's origin. The scale of human
19:52
engine... The continuity required to capture
19:53
these signals is truly profound. It really is.
19:56
So let's recap this journey. A physical piece
19:59
of an atom is forged in the explosive death of
20:02
a massive star, or maybe blasted from a supermassive
20:05
black hole. It gets ping -ponged across the galaxy,
20:08
navigates twisting magnetic fields, bleeds energy
20:10
crashing into ancient microwave radiation, and
20:13
eventually shatters against our upper atmosphere.
20:15
The debris cascades down, stretches the very
20:18
fabric of time to prove Einstein right, silently
20:21
passes through your hand, and maybe flips a bit
20:25
of data in your laptop. It is a tangible connection
20:27
between the most violent events in the cosmos
20:30
and our everyday reality. And, you know, I want
20:32
to leave you with a final thought to ponder,
20:34
building directly on the GZK cutoff we discussed
20:36
earlier. Ah, the cosmic speed bump. Exactly.
20:40
If a cosmic micrise background forces ultra high
20:43
energy particles to constantly lose energy, it
20:46
acts as a strict physical boundary. It means
20:48
the absolute most powerful, mind -bogglingly
20:51
energetic, oh -my -god particles must originate
20:54
from relatively nearby. Right, they can't travel
20:57
forever. They cannot have traveled from the distant
20:59
edges of the universe. Which raises a very important
21:02
question. What kind of unseen, unimaginably violent
21:06
astrophysical monsters are lurking right here
21:08
in our own cosmic backyard, just waiting to be
21:11
discovered? That is a brilliant, slightly terrifying
21:14
thought to leave on. The next time you're on
21:16
a long flight and the cabin crew doesn't mention
21:18
the cosmic radiation because it's just a Tuesday
21:20
for them, or the next time you look up at a seemingly
21:23
empty night sky. Remember, the space above us
21:26
is never truly empty. Every second a tiny piece
21:29
of ancient cosmic violence is raining down, passing
21:32
quietly straight through the palm of your hand.
21:34
Thanks for diving deep with us.