Latest / Talking Science / Neutrinos – The Ghost Particles

Transcript

Neutrinos – The Ghost Particles · Talking Science

0:00
I want you to do something for me. Wherever you
0:03
are right now, whether you're sitting at a desk,
0:05
out for a walk, or just, you know, relaxing on
0:07
the couch, I want you to hold perfectly still.
0:10
Yeah, just for one second. It feels like you're
0:13
doing absolutely nothing. Right. But right now,
0:15
in that single second you just held still, roughly
0:18
100 trillion particles from the sun just passed
0:22
straight through your body. 100 trillion. Yeah.
0:24
Every single second. And you didn't feel a single
0:27
one. I mean, no matter how long you live, you
0:29
will never, ever feel these particles brushing
0:32
past your atoms. It sounds totally like science
0:34
fiction, honestly. It really does. But looking
0:37
through the massive stack of research papers
0:39
and historical notes you sent over for today's
0:41
deep dive uh this is a hard physical reality
0:45
it absolutely is so our mission today is to unravel
0:48
this mystery for you the mystery of these like
0:51
ghost particles known as neutrinos yeah it's
0:54
just a phenomenal story We're going to explore
0:56
how physicists literally predicted this particle
0:59
just to save a foundational law of nature, how
1:02
they finally caught one, the decades -long mystery
1:04
it created about our own sun, and how it's currently
1:08
unlocking the deepest secrets of the universe.
1:11
We are dealing with a piece of the universe that
1:13
is so profoundly reluctant to interact with anything
1:17
that it is essentially invisible to normal matter.
1:21
Which is mind -blowing. But to understand why
1:24
a ghost particle even needed to exist in the
1:26
first place, we kind of have to go back to the
1:28
early 20th century. Right, to a time when the
1:30
world of physics was in a state of absolute existential
1:33
panic. Panic is a good word for it. Oh, it was
1:36
crisis. The whole thing centered around the conservation
1:39
of energy, which is, you know, arguably the bedrock
1:42
principle of physics. Basically the rule that
1:44
energy can never be created or destroyed. Exactly.
1:47
It can change forms, like how the chemical energy
1:50
in a piece of coal turns into thermal energy
1:52
when you burn it. But it can't be created out
1:54
of nothing, and it can never just vanish. The
1:56
cosmic accounting books always have to balance
1:58
perfectly. Which brings us to Beatty Decay. Precisely.
2:02
So physicists were studying this specific type
2:04
of radioactive decay, which happens when an unstable
2:08
atomic nucleus spits out an electron and transforms
2:11
into a slightly different nucleus. Okay. And
2:14
because they knew the precise mass and energy
2:16
of the starting nucleus and the exact mass and
2:19
energy of the resulting nucleus, they could calculate
2:22
exactly how much energy that escaping electron
2:25
should be carrying away. It should be a fixed
2:27
number, right? Right. It should have been one
2:28
specific predictable amount every single time.
2:31
But when they actually measured those escaping
2:33
electrons, the numbers were just a total mess.
2:35
They were coming out with a totally random spread
2:37
of energies. It made no sense. Sometimes the
2:40
energy was a little lower than expected. Sometimes
2:42
it was a lot lower. Energy was simply vanishing
2:45
from the equation. It was completely unaccounted
2:47
for. It's kind of like if you go to an ATM to
2:51
withdraw exactly $100. The bank's computer deducts
2:56
$100 from your account, but the machine spits
2:59
out like $80 one time. Right, or $92 the next
3:03
time. Exactly. And another time it gives you
3:06
$45. And the bank swears the full $100 left the
3:09
vault, but it is definitely not in your hands.
3:12
And no one can figure out where that missing
3:14
cash went. That kind of accounting failure was
3:17
so terrifying to physicists at the time that
3:19
some of the most prominent minds in the field
3:21
were genuinely prepared to concede that the conservation
3:24
of energy might just be wrong. Wow. At the subatomic
3:28
level, they were ready to accept that the universe
3:31
just casually destroyed energy. Which means throwing
3:33
out centuries of physics. But rather than accept
3:37
that, an Austrian physicist named Wolfgang Pauli
3:40
wrote a letter in 1930. And he didn't even present
3:43
this at a formal panel, right? No, not at all.
3:45
He wrote it half -jokingly to a conference of
3:47
fellow physicists that he couldn't attend. He
3:50
famously addressed it to, Dear radioactive ladies
3:53
and gentlemen. I love that. Pauli proposed a
3:56
radical desperate guess. He suggested the conservation
3:58
of energy was perfectly intact and that the missing
4:01
energy wasn't vanishing at all. Instead, it was
4:04
being carried away by a brand new unseen particle.
4:07
So basically a ghost taking the missing cash
4:09
from the ATM. Pretty much. He argued this theoretical
4:13
particle had to have no electric charge, an extremely
4:16
small mass, and be so incredibly faint and reluctant
4:19
to interact with matter that it was just slipping
4:22
past every single detector they had. And he actually
4:25
felt guilty about this. Oh, incredibly guilty.
4:28
He stated later that he had done something a
4:31
good theoretical physicist should never do, predicting
4:33
a particle that might never be observed. But
4:36
then Enrico Fermi later built Pauli's idea into
4:39
a formal mathematical theory and gave the particle
4:42
the name we use today. The neutrino. Italian
4:44
for a little neutral one. But Pauli's guilt over
4:47
inventing an unseeable particle lasted for, what,
4:50
25 years? Because it took that long to actually
4:52
catch one. Yeah, and the reason a neutrino is
4:54
so ridiculously elusive comes down to the fundamental
4:57
forces of nature. Neutrinos only interact with
5:00
matter through something called the weak nuclear
5:02
force. And as the name implies, it is extraordinarily
5:06
feeble. Right. And we can contrast that with
5:09
the electromagnetic force, which is essentially
5:11
the traffic cop of the atomic world. Exactly.
5:15
Like when you press your hand against a wall,
5:17
your hand doesn't pass through it because the
5:19
electromagnetic forces in your hand's atoms are
5:22
repelling the electromagnetic forces in the wall's
5:25
atoms. But because neutrinos have absolutely
5:27
zero electric charge, they are completely immune
5:30
to that traffic cop. The electromagnetic force
5:33
doesn't even register them. They don't bounce
5:35
off atoms. They don't get absorbed like light
5:37
does. They glide right through the empty space
5:39
inside atoms. So a single neutrino can pass through
5:43
thousands of kilometers of solid rock or fly
5:46
straight through the entire Earth with only the
5:49
absolute faintest, most statistically improbable
5:52
chance of ever bumping into a nucleus. Most of
5:55
them zip through the planet as if it were entirely
5:57
hollow. Which is why those hundred trillion solar
5:59
neutrinos are streaming through your body right
6:01
now without a trace. Exactly. But wait, let me
6:04
push back on this for a second. If this thing
6:06
is completely immune to electromagnetism and
6:08
can pass right through thousands of miles of
6:11
solid iron and rock, how on earth could a scientist
6:14
in the 1950s possibly build a trap for it? Any
6:18
cage you build, it would just ghost right through.
6:20
Well, that was the exact realization of two physicists
6:23
in 1956, Clyde Cowan and Frederick Raines. They
6:27
knew finesse wouldn't work, so they engineered
6:29
a brilliant brute force solution. Just overwhelming
6:32
numbers. Right. They realized that if the chance
6:34
of catching one neutrino is vanishingly small,
6:37
your only option is to play a numbers game on
6:40
a massive scale. So they built a large tank of
6:43
water. But they laced it with a very specific
6:45
chemical, right? Cadmium chloride. Yeah, the
6:48
chemistry here is what made the trap work. They
6:52
designed the setup so that if a neutrino did
6:54
happen to score a highly improbable direct hit
6:57
on a proton in the water, it would trigger a
6:59
very specific reaction. The collision would produce
7:02
a positron and a neutron. And those two new particles
7:05
are what they actually looked for. Exactly. The
7:07
positron would immediately collide with an electron
7:09
and annihilate, creating a flash of light. And
7:12
then a fraction of a second later, that free
7:14
neutron would be absorbed by the cadmium they
7:17
added to the water, which would release a second
7:19
light flash of light. Oh, wow. Yeah, that specific
7:21
double flash, flash, pause, flash was the unfakable
7:24
fingerprint of a neutrino collision. But a tank
7:27
of laced water alone isn't enough because normal
7:30
background neutrinos are way too rare. So they
7:32
literally took this entire setup and parked it
7:35
right next to a nuclear reactor. A nuclear reactor
7:37
is a massive concentrated source of neutrinos.
7:41
The fission reactions inside a reactor core pump
7:43
out absolutely enormous numbers of them every
7:46
single second. So it's basically a flood. Exactly.
7:49
Their reasoning was that by placing their tank
7:52
in the middle of this staggering flood of neutrinos,
7:54
eventually, purely by statistical chance, one
7:58
of them was going to hit a proton. It's the ultimate
8:00
lottery strategy. I mean, your chances of winning
8:03
with one ticket are effectively zero. But if
8:05
you buy 100 trillion tickets every single second,
8:08
you are guaranteed to get a winning ticket eventually.
8:11
And it worked. They caught those unmistakable
8:14
double flashes. They confirmed Pauli's 25 -year
8:17
-old prediction, which eventually earned Raines
8:19
a Nobel Prize. Incredible. And more importantly,
8:22
this brute force strategy building a huge detector,
8:25
waiting patiently and relying on overwhelming
8:27
numbers, became the foundational method for all
8:30
neutrino physics. So having successfully caught
8:33
neutrinos from a nuclear reactor on Earth, physicists
8:36
naturally turn their attention to the biggest,
8:38
most obvious nuclear reactor in our solar system,
8:41
which is the sun. Right. Deep inside the sun's
8:44
core, nuclear fusion is constantly crushing hydrogen
8:47
atoms together to form helium. This process releases
8:51
the immense energy that powers our solar system,
8:54
and a direct byproduct of that fusion is the
8:58
neutrino. But the journey of a neutrino out of
9:00
the sun is fascinating when you compare it to
9:02
light. It really is. Because the actual photons
9:05
of sunlight created in the sun's core take what?
9:09
tens of thousands of years to slowly bounce and
9:11
diffuse their way out from the unimaginably dense
9:14
core to the visible surface. Yeah, they have
9:16
to fight their way out before they finally escape
9:17
into space. The light warming our faces on a
9:20
summer day was actually generated inside the
9:22
sun tens of thousands of years ago. Which is
9:24
wild to think about, but neutrinos don't bounce.
9:27
No, because they are immune to electromagnetism,
9:30
they don't have to fight their way out through
9:32
the dense solar plasma. They stream straight
9:35
out of the core at nearly the speed of light.
9:38
reach Earth in just eight minutes. Meaning neutrinos
9:41
give us a real -time, completely uncorrupted
9:44
window into what is happening in the core of
9:46
our sun right this very minute. Exactly. And
9:49
to look through that window, a physicist named
9:51
Raymond Davis Jr. built a massive detector in
9:54
the 1960s. He went deep underground into the
9:57
Homestake gold mine in South Dakota. Using the
10:00
miles of rock overhead to shield his experiment
10:02
from cosmic rays and background radiation. Right.
10:05
And he filled a huge tank with 100 ,000 gallons
10:08
of standard dry cleaning fluid. Perclorophthalene.
10:11
Yes. The chlorine in that fluid was the target.
10:14
When a solar neutrino occasionally struck a chlorine
10:16
atom, it would transform it into an atom of radioactive
10:19
argon. So by counting those argon atoms, Davis
10:23
could count the neutrinos. But when he ran the
10:25
numbers, there was a massive discrepancy. Astrophysics
10:29
models dictated exactly how many neutrinos the
10:32
sun's fusion should be producing. But Davis was
10:35
only finding about one third of that predicted
10:37
number. Two thirds of the solar neutrinos were
10:40
simply missing. Two thirds. That's huge. It became
10:43
known as the solar neutrino problem. And it persisted
10:46
for decades. At first, you know, many assumed
10:49
Davis's detector was simply inefficient or just
10:52
broken. Sure. You blame the equipment first.
10:54
Exactly. But in the following decades, totally
10:57
independent experiments came online using different
11:00
detection chemicals like gallium, which were
11:02
sensitive to lower energy neutrinos that Davis's
11:05
chlorine tank couldn't even see. And those new
11:07
gallium detectors found the exact same shortfall.
11:10
Yep. The missing two -thirds were consistently
11:12
missing across the board. That consistency had
11:15
to force a very uncomfortable realization on
11:17
the scientific community. Oh, definitely. Either
11:19
our entire highly verified model of how the sun
11:22
works was fundamentally wrong, or... our understanding
11:25
of this ghost particle was fundamentally wrong.
11:27
Well, the resolution to this mystery proved that
11:29
Pauli's ghost particle was far more complex than
11:32
he ever imagined. Because it turns out, the neutrino
11:35
is a shapeshifter. Physicists eventually discovered
11:38
that there isn't just one type of neutrino. There
11:41
are actually three distinct types, which the
11:44
field refers to as flavors. You have the electron
11:46
neutrino, the muon neutrino, and the tau neutrino
11:50
and the crucial piece of the puzzle here is that
11:52
the specific nuclear fusion happening inside
11:54
the sun only produces one of those flavors the
11:58
electron neutrino right And Davis' dry -cleaning
12:01
fluid detector in the gold mine, along with the
12:04
gallium detectors that followed, were chemically
12:06
designed to only react with electron neutrinos.
12:09
They were completely blind to the muon and tau
12:11
flavors. Okay, so it's like the sun is standing
12:13
way over there and it throws an apple at the
12:15
Earth. I like this analogy, yeah. But while that
12:18
apple is flying through the vacuum of space,
12:20
it randomly morphs into a banana, then it morphs
12:23
into a pear, and then it morphs back into an
12:26
apple. By the time it hits the Earth, it could
12:27
be any of the three fruits. But Davis's detector
12:30
was a net specifically built to only catch apples.
12:33
That's spot on. The missing two -thirds of the
12:36
neutrinos were never actually missing. They had
12:38
just changed their identity during the eight
12:40
-minute journey from the sun to the earth. That
12:42
is just so weird. It's a genuine quantum phenomenon
12:45
known as neutrino oscillation. As the neutrino
12:48
travels, its identity isn't fixed. It flips back
12:52
and forth, governed by quantum wave interference
12:54
between the different possible states of the
12:56
particle. Wow. So to prove this was actually
12:59
happening, we had to build a net capable of catching
13:01
the bananas and the pears, essentially. And that
13:04
happened in the early 2000s with the Sudbury
13:07
Neutrino Observatory in Canada. Right. They built
13:10
this detector deep inside a working nickel mine.
13:13
But instead of cleaning fluid, they filled an
13:15
enormous acrylic sphere with a thousand tons
13:18
of heavy water. And just to clarify, normal water
13:21
has standard hydrogen, just one proton. But heavy
13:24
water uses an isotope of hydrogen called deuterium,
13:27
right? which has a proton and a neutron. Exactly.
13:30
That extra neutron in the heavy water molecule
13:32
changes everything. It allows the heavy water
13:35
to be broken apart by a specific type of collision
13:38
called a neutral current interaction. that is
13:42
sensitive to all three flavors of neutrinos,
13:44
not just the electron flavor. So when they turned
13:47
the detector on and tallied up the electron,
13:49
muon, and tau neutrinos together, the books balanced
13:52
perfectly. They did. The total count matched
13:55
the original astrophysics predictions for the
13:57
sun exactly. the sun was working exactly as we
14:00
thought it was our incomplete understanding of
14:03
the neutrino causing the deficit yes but proving
14:06
that neutrinos oscillate carried a massive paradigm
14:09
shifting implication for physics because for
14:12
a particle to oscillate and change flavors as
14:14
it moves through space Quantum theory dictates
14:17
that it must experience time, and therefore it
14:19
must have mass. Which completely shattered the
14:22
standard model of particle physics, didn't it?
14:24
Oh, it broke it. Up until that point, the fundamental
14:26
assumption was that neutrinos were perfectly
14:28
massless, traveling exactly at the speed of light,
14:31
just like photons. But finding out they shapeshift
14:33
proved they have weight. The mass is incredibly
14:36
tiny, but it's unequivocally not zero. This discovery
14:40
actually earned a Nobel Prize in 2015. And finding
14:43
the precise mass of these three flavors remains
14:46
one of the most intense active frontiers in particle
14:49
physics today. And what's amazing is that the
14:51
necessity of building these giant subterranean
14:54
vats of weird fluids to catch shape -shifting
14:57
particles led physicists to construct the most
15:00
colossal scientific instruments on the planet.
15:03
Truly colossal. And entirely by accident, these
15:06
giant underground caverns turned into a brand
15:08
new way to observe the cosmos. The scale really
15:11
is staggering. Consider Japan's Super Kamiokande
15:13
Observatory. It is buried deep under Mount Aikana
15:16
to block out cosmic rays, housing a massive cylinder.
15:20
tank filled with 50 ,000 tons of ultra -pure
15:22
water. And the walls of that tank are lined with
15:24
over 11 ,000 individual light sensors, all staring
15:27
into the pristine pitch -black water, waiting
15:30
for a single microscopic flash of what is called
15:33
Cherenkov light. Cherenkov light is a really
15:35
fascinating physical effect. When a high -speed
15:38
jet plane travels through the air faster than
15:40
the speed of sound, it compresses the sound waves
15:43
ahead of it, creating a shock wave that we hear
15:45
as a sonic boom. Right. And light has a universal
15:48
speed limit in a vacuum. But when light travels
15:51
through a medium like water, it slows down by
15:53
what? About 25 percent. Building on that, if
15:57
a high energy particle like an electron knocked
15:59
loose by a neutrino collision zips through that
16:02
tank faster than light can travel through that
16:03
same water, it creates an optical shockwave.
16:06
An optical sonic boom. Exactly. Compresses the
16:09
light waves ahead of it, producing a faint directional
16:12
flash of blue light. The optical sonic boon is
16:15
Cherenkov light. So in February of 1987, those
16:18
sensors were sitting in the dark, waiting for
16:20
those blue flashes, when several underground
16:23
detectors around the world suddenly registered
16:25
a brief, intense burst of neutrinos. It was a
16:28
flurry of flashes in the water, far above the
16:30
normal background rate, all clustered within
16:32
a span of about 13 seconds. Hours later, astronomers
16:36
looking through traditional telescopes spotted
16:38
a sudden, brilliant point of light in a nearby
16:41
galaxy called the Large Magellanic Cloud. A massive
16:44
star had collapsed and exploded in an event we
16:47
now call Supernova 1987A. Right. But the incredible
16:51
part is the underground detectors caught the
16:54
burst of neutrinos hours before the optical telescope
16:56
saw the flash of light. Which sounds backward,
16:59
but the mechanics of a dying star perfectly explain
17:02
this head start, right? Exactly. When the massive
17:05
core of a star exhausts its fuel, it collapses
17:07
in on itself, creating unimaginable density.
17:10
The light generated by that explosive, fiery
17:12
collapse is entirely trapped by that density.
17:15
The photons physically have to fight and bounce
17:17
their way out through the turbulent outer layers
17:19
of the dying star. A chaotic process that delays
17:23
the light by hours. But the neutrinos are born
17:25
the exact millisecond the core collapses. And
17:28
because they don't interact with the star's dense
17:30
outer layers, they just go straight through the
17:33
explosion instantly. They get a massive head
17:35
start. They cross 168 ,000 light years of space
17:38
and hit our underground detectors on Earth. Hours
17:41
before the light from the explosion finally broke
17:43
free and arrived at our telescopes. So these
17:46
giant tanks of water literally function as an
17:49
early warning system for a dying star. Yes. This
17:52
single event birthed the entire field of neutrino
17:56
astronomy. We were no longer restricted to observing
17:58
the universe solely through light. We could now
18:00
look at it through the lens of ghost particles.
18:03
But to push this new field of astronomy to its
18:05
absolute limits, physicists realized they needed
18:08
a detector far larger than any cavern they could
18:11
possibly excavate. They required a volume of
18:13
clear material so massive that it could only
18:16
be found in nature. And they found it in Antarctica.
18:19
The Ice Cube Observatory, which is just an absolute
18:22
engineering marvel. I mean, instead of building
18:23
a tank, they melted over 80 holes, each one and
18:27
a half kilometers deep, straight down into the
18:29
pristine Antarctic ice sheet. It's brilliant.
18:31
They lowered strings containing thousands of
18:34
sensitive optical detectors down into those holes
18:36
before the water refroze. By doing this, they
18:39
effectively turned a full cubic kilometer of
18:42
solid ancient ice into a single massive neutrino
18:45
telescope. A full cubic kilometer of ice looking
18:48
for that faint blue Cherenkov flash. But with
18:51
a detector that massive, how do they differentiate
18:54
a neutrino flash from random cosmic radiation
18:56
hitting the ice? The mechanism they use is really
18:59
clever. Background radiation, like muons created
19:02
by cosmic rays, rains down from the sky above.
19:05
But neutrinos can easily travel entirely through
19:07
the Earth. So the IceCube sensors are programmed
19:10
to look specifically for flashes of light moving
19:12
upward through the ice from the bottom to the
19:14
top. Oh, wow. They use the entire bulk of the
19:16
planet Earth as a filter to block out the noise
19:18
from above. Exactly. Coming up from below has
19:21
to be a neutrino. That is so smart. And using
19:24
this setup in 2017, IceCube caught an incredibly
19:27
high energy neutrino moving through the ice.
19:29
Because of the vast three -dimensional grid of
19:32
sensors, they were able to track the exact trajectory
19:35
of that blue flash and trace the ghost particle
19:38
back to its origin in deep space. They traced
19:42
it back to a blazar, which is a supermassive
19:44
black hole at the center of a distant galaxy
19:46
that is actively devouring matter and blasting
19:50
a highly energized relativist. jet of particles
19:53
out into space. In this specific case, that cosmic
19:56
jet was pointed almost directly at Earth. And
19:59
when IceCube calculated the trajectory, they
20:01
alerted traditional light -based observatories
20:03
to point their telescopes at that exact coordinate
20:06
in the sky. The telescopes observed the blazer
20:08
actively flaring in gamma rays at the exact same
20:11
time the neutrino arrived. This established the
20:14
era of multi -messenger astronomy. For all of
20:16
human history, we have only been able to study
20:18
the universe using one messenger. electromagnetic
20:21
radiation or light. By combining optical telescopes
20:24
with neutrino detectors, we now have an entirely
20:26
new secondary sense to study the most violent,
20:29
extreme, and previously opaque mechanisms in
20:32
the cosmos. And the practical applications of
20:34
mastering this particle aren't just limited to
20:36
deep space either. Physicists are using this
20:39
exact same underlying science right here on Earth.
20:42
Like, remember how Cowan and Raines caught the
20:45
first neutrino by placing a tank next to a nuclear
20:47
reactor? Yeah, today, physicists use smaller,
20:50
highly sensitive neutrino detectors to monitor
20:53
nuclear reactors remotely because the specific
20:56
neutrino output of a reactor core directly and
20:59
unavoidably correlates with the fission reactor.
21:02
actions happening inside, it creates a unique,
21:05
unfakable signature. So you can point a detector
21:08
at a facility and know exactly what specific
21:10
nuclear isotopes they are burning inside, which
21:12
provides an incredibly powerful tool for international
21:15
security and nuclear non -proliferation. A rogue
21:18
state cannot shield or hide their neutrino emissions.
21:21
It's impossible. Furthermore, the planet Earth
21:23
itself is a massive source of neutrinos. Deep
21:26
inside the planet's crust and mantle, radioactive
21:28
elements like uranium and thorium are constantly
21:31
undergoing radioactive decay. Producing what
21:33
geologists call geoneutrinos. Earth ghosts, essentially.
21:37
Earth ghosts, I like that. By detecting these
21:40
geoneutrinos streaming up from beneath our feet,
21:43
geophysicists have a completely novel way to
21:46
measure exactly how much radioactive decay is
21:49
happening inside the Earth. This data is crucial
21:52
for understanding our planet's internal heat
21:54
budget. Because it helps answer fundamental questions
21:56
about how much of the Earth's internal heat is
21:59
left over from its formation versus how much
22:01
is actively being generated today to drive volcanoes,
22:04
plate tectonics, and, you know, the magnetic
22:08
field that protects our atmosphere. It is a remarkable
22:10
century -long arc. We started in 1930. with Wolfgang
22:14
Pauli making an uneasy, desperate guess just
22:17
to balance a math equation. It took a quarter
22:19
of a century in a nuclear reactor just to catch
22:21
one. We spent decades staring at the sun, deeply
22:24
confused, because the particles were shapeshifting
22:27
from apples to bananas in flight. Right. And
22:29
that confusion forced us to rewrite the foundational
22:32
rules of particle physics to give them mass.
22:35
And today, we have turned a cubic kilometer of
22:38
Antarctic ice into a telescope to watch black
22:41
holes in other galaxies. while simultaneously
22:43
using them to x -ray the heat of our own planet's
22:46
core. It is a staggering legacy for a particle
22:49
that physicists originally assumed we would never
22:51
be able to observe. Truly. Which brings us right
22:54
back to you listening to this. As we've been
22:57
talking, you've just been sitting there going
22:59
about your day. But you aren't really sitting
23:02
still. You are standing in the middle of a torrential
23:05
cosmic rainstorm. a hundred trillion invisible
23:10
messengers are still quietly seamlessly crossing
23:14
right through you every single second this is
23:16
ghosting right through it leaves you with a thought
23:19
i really want you to mull over If we as a species
23:22
spent all of human history utterly and completely
23:24
blind to 100 trillion particles passing through
23:27
our bodies every second, right up until we figured
23:30
out how to build the exact right tank of water
23:32
to see a tiny blue flash, what other invisible
23:35
realities or forces might be streaming right
23:37
through you at this very moment, simply waiting
23:39
for us to invent the right detector to finally
23:41
see them?