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♪ ♪
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NARRATOR:
They're the most mysterious
particles ever discovered,
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{\an1}tiny ghosts hidden in our world.
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00:00:14,871 --> 00:00:20,005
{\an1}Now scientists are on a mission
to unlock their secrets.
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{\an1}They're called neutrinos.
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{\an1}The story of their discovery
is almost impossible to believe.
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DAVID KAISER:
If they had bolted the detector
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{\an1}in place, the nuclear bomb
would've
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{\an1}just smashed it to smithereens.
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NARRATOR:
With links to a dramatic
Cold War defection.
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FRANK CLOSE:
He disappeared through
the Iron Curtain,
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{\an1}and for five years,
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{\an1}disappeared off the face of the
planet.
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NARRATOR:
And astonishing experiments
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{\an1}that keep defying
the laws of physics.
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KERSTIN PEREZ:
Even as someone who builds these
experiments for a living,
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{\an1}it just seems mind-blowing
that they ever work.
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NARRATOR:
Today, scientists are using
neutrinos
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{\an1}to probe the edges
of our detectable universe.
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{\an1}They're on a mission to reveal
a hidden world
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{\an1}of "Particles Unknown."
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{\an1}Right now, on "NOVA."
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♪ ♪
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NARRATOR:
We live in a world of matter...
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{\an1}a realm of tiny particles
far smaller than atoms
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{\an1}that build the universe
that we know.
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{\an1}But there is a mystery.
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{\an1}Scientists theorize there
exists a hidden, parallel world
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of particles...
So-called dark matter.
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{\an1}So far, no one has managed
to detect a single one.
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{\an1}But now there might be a way.
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{\an1}Of all the particles scientists
have discovered,
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{\an1}the most elusive, on the very
edge of detectability,
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are neutrinos.
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♪ ♪
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KAISER:
Neutrinos are really
remarkable particles.
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{\an1}There are trillions
and trillions of them
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{\an1}streaming through our bodies,
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{\an1}and we don't even notice.
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{\an1}They are kind of ghost-like,
and yet they're everywhere.
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NARRATOR:
Everywhere and nowhere.
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{\an1}Neutrinos are so ghostly,
they can pass
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{\an1}through solid matter as if
it didn't exist.
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{\an1}And yet they hold the secrets
to why the stars shine
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{\an1}and what our universe
is made of.
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{\an1}RAY JAYAWARDHANA:
The reason we care about these
elusive particles
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{\an1}is because they do play a
fundamentally important role
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in the universe,
in the nature of matter...
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{\an1}in some of the most violent
cosmic phenomena.
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NARRATOR:
First theorized in the 1930s,
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{\an1}they would soon become linked
to nuclear secrets
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{\an1}and a dramatic Cold War
defection
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{\an1}behind the Iron Curtain.
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{\an1}He goes off to Europe
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{\an1}and never returns.
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NARRATOR:
Now the quest
to detect neutrinos
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{\an1}has triggered vast experiments
all over the globe.
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{\an1}Even as someone who builds these
experiments for a living,
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00:03:31,671 --> 00:03:34,238
{\an1}it just seems mind-blowing
that they ever work.
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NARRATOR:
Today, scientists are on the
cusp
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{\an1}of an astonishing discovery.
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{\an1}Tantalizing evidence
suggests neutrinos
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{\an1}could be a doorway
between our world of matter
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{\an1}and the hidden world of
dark matter,
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{\an1}waiting to be discovered.
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{\an1}GEORGIA KARAGIORGI:
It would be a game-changer.
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{\an1}What exactly are these
particles?
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{\an1}What is its role in the
evolution of our universe?
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NARRATOR:
The quest for answers
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{\an1}has driven scientists
to the edge
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{\an1}of what is experimentally
possible
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{\an1}to reveal a universe
we've never seen before.
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♪ ♪
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NARRATOR:
Fermilab, in Batavia, Illinois.
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{\an1}World-renowned physics
laboratory.
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{\an1}Thousands of scientists
build enormous experiments
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{\an1}to probe the very smallest
particles
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{\an1}that make up our universe.
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{\an1}(indistinct chatter)
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{\an1}Leading one of the teams
is Sam Zeller.
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Hi, team.
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{\an7}My interest in physics started
when I signed up
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{\an7}for a field trip to come
to Fermilab in high school.
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{\an1}It just blew my mind.
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{\an1}From that point on, I was
a particle physicist.
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♪ ♪
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{\an1}It turns out that
the universe can be described
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{\an1}by a small number
of subatomic particles.
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♪ ♪
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NARRATOR:
Today, scientists have
discovered
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{\an1}17 basic particles
that make up our universe.
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♪ ♪
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{\an1}Some are the building blocks
of atoms.
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{\an1}Others are the things
that hold matter together.
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{\an7}It's an understanding of
our world that physicists call
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{\an7}the Standard Model.
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{\an8}PEREZ:
The Standard Model of
particle physics
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{\an7}describes the most fundamental
constituents of matter
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{\an7}and how they interact
with each other.
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{\an7}It is in fact the most
mathematically well-defined
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{\an7}physical theory we as humans
have ever written down.
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♪ ♪
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NARRATOR:
For 50 years,
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{\an1}the Standard Model
has withstood test after test,
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{\an1}confirming the hierarchy of all
the fundamental particles.
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(device beeping)
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{\an1}But one type remains
far more mysterious than others.
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{\an1}They're called neutrinos.
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JAYAWARDHANA:
A neutrino is a
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{\an7}type of elementary particle,
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00:06:12,238 --> 00:06:16,305
{\an7}a basic fundamental building
block of the universe,
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00:06:16,338 --> 00:06:20,405
and they come in
three different flavors.
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KARAGIORGI:
Neutrinos are everywhere.
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00:06:22,071 --> 00:06:24,871
{\an1}They are produced in the sun.
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{\an7}There are neutrinos that were
left over after the Big Bang.
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{\an1}Humans emit neutrinos.
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CLOSE:
Neutrinos have got no
electric charge.
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{\an7}They've almost got no mass
at all.
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00:06:38,571 --> 00:06:40,505
{\an7}They're as near to nothing
as you can imagine.
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{\an1}They're so reluctant
to interact with stuff,
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{\an1}they pass through the Earth
as if it wasn't there.
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NARRATOR:
And yet, at Fermilab,
scientists are constructing
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00:06:51,538 --> 00:06:53,905
{\an1}a complex two-stage experiment
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{\an1}with the means to create them
and study them.
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{\an8}♪ ♪
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{\an7}In its first stage,
a powerful ring of magnets
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00:07:03,738 --> 00:07:07,405
{\an7}accelerates positively charged
particles called protons
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00:07:07,438 --> 00:07:13,471
{\an7}to colossal speeds, sending
them smashing into a target.
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00:07:13,505 --> 00:07:16,505
{\an7}The collision creates a shower
of new particles,
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00:07:16,538 --> 00:07:21,471
{\an7}including a powerful beam
of neutrinos.
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00:07:21,505 --> 00:07:25,071
{\an7}150 trillion per second pass
through the Earth
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{\an7}at nearly the speed of light,
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00:07:26,971 --> 00:07:29,271
{\an7}racing towards the second
stage...
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00:07:29,305 --> 00:07:32,138
{\an7}three giant neutrino detectors.
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00:07:33,905 --> 00:07:38,271
{\an1}The largest is called ICARUS.
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Once complete,
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00:07:39,605 --> 00:07:42,405
{\an1}this immense tank filled with
a web of electronics
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{\an1}and cryogenic liquid
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{\an1}will be bombarded by hundreds
of trillions of neutrinos,
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{\an1}all in the hope of catching
just one each minute.
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♪ ♪
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{\an1}That alone will be a remarkable
achievement.
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(device beeping)
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{\an1}But the scientists
have even bigger ambitions.
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00:08:03,538 --> 00:08:07,471
ZELLER:
One of the big goals here at
Fermilab is to try to search
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00:08:07,505 --> 00:08:09,505
{\an1}for possibly a new type of
neutrino
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{\an1}that no one has yet observed.
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00:08:13,371 --> 00:08:14,747
NARRATOR:
Experiments have hinted
there could be
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00:08:14,771 --> 00:08:17,038
{\an1}an even more elusive neutrino
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00:08:17,071 --> 00:08:20,538
{\an1}beyond the three types already
known to exist.
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00:08:20,571 --> 00:08:23,738
{\an1}Some have suggested
that it could be a link
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00:08:23,771 --> 00:08:25,971
{\an1}to a hidden realm of particles
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{\an1}that could finally lead
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00:08:27,571 --> 00:08:31,605
{\an1}to new discoveries beyond
the Standard Model.
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00:08:31,638 --> 00:08:33,838
ZELLER:
If we found evidence
for a new type of neutrino,
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00:08:33,871 --> 00:08:35,905
{\an1}that would be really astounding.
157
00:08:35,938 --> 00:08:37,381
{\an1}That's what gets me excited
in the morning.
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00:08:37,405 --> 00:08:38,781
{\an1}That's what gets me coming
in to work.
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00:08:38,805 --> 00:08:41,571
{\an1}It would be a major
and massive discovery.
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NARRATOR:
Making that discovery would be
groundbreaking.
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{\an1}Because while ordinary neutrinos
are extremely hard to detect,
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00:08:52,605 --> 00:08:57,471
{\an1}this fourth type of neutrino
could break the Standard Model.
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{\an1}What brought them to this
moment...
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00:09:01,205 --> 00:09:04,105
{\an1}and possibly to the brink
of upending
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{\an1}one of the bedrocks of
modern physics?
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♪ ♪
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{\an1}That story begins almost 100
years ago
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{\an1}half a world away.
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00:09:16,638 --> 00:09:19,338
In Rome.
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00:09:21,771 --> 00:09:25,238
{\an1}Physicist and historian
Professor David Kaiser
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{\an1}has traveled here,
to the place where,
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00:09:27,705 --> 00:09:30,638
in the 1930s,
scientists were investigating
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{\an1}the inner workings of the atom.
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KAISER:
For millennia,
for thousands of years,
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{\an1}people had come to believe that
the world was made of atoms,
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{\an7}and those atoms were
the smallest thing there was.
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00:09:43,938 --> 00:09:45,538
{\an7}In fact, the word atom
even means
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{\an7}"unbreakable" or "indivisible"...
The smallest piece.
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♪ ♪
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NARRATOR:
But by the early 1900s,
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00:09:52,405 --> 00:09:55,805
{\an1}scientists had revealed
a deeper hidden structure.
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00:09:57,338 --> 00:10:00,805
KAISER:
If you think about an atom,
it's about a nanometer,
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00:10:00,838 --> 00:10:04,305
{\an1}about a billion times smaller
than a meter, roughly.
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00:10:04,338 --> 00:10:07,371
{\an1}The inside, the deep core of
an atom, the nucleus,
185
00:10:07,405 --> 00:10:11,505
{\an1}is about 100,000 times smaller
than that.
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00:10:11,538 --> 00:10:15,238
{\an1}So we're really zooming in
powers of ten, powers of ten,
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00:10:15,271 --> 00:10:17,305
{\an1}getting to unimaginably
tiny scales.
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00:10:17,338 --> 00:10:20,938
NARRATOR:
During the early 20th century,
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00:10:20,971 --> 00:10:26,071
{\an1}scientists discovered the atom's
tiny nucleus contained protons,
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00:10:26,105 --> 00:10:29,338
particles with
a positive electric charge.
191
00:10:29,371 --> 00:10:31,838
{\an1}These protons held in place
192
00:10:31,871 --> 00:10:35,205
{\an1}a cloud of negatively charged
electrons
193
00:10:35,238 --> 00:10:37,771
{\an1}that formed the atom's
outer limit.
194
00:10:40,971 --> 00:10:43,471
{\an1}It seemed that protons
and electrons
195
00:10:43,505 --> 00:10:46,505
{\an1}were the only two components
of all atoms...
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00:10:46,538 --> 00:10:50,638
{\an1}permanent and fixed.
197
00:10:50,671 --> 00:10:54,505
{\an1}But scientists had also found
something shocking:
198
00:10:54,538 --> 00:10:59,305
{\an1}some types of atoms seemed
to break apart.
199
00:10:59,338 --> 00:11:01,105
KAISER:
That was just jaw-dropping.
200
00:11:01,138 --> 00:11:03,971
{\an1}Literally, it contradicts
the name of the thing itself.
201
00:11:04,005 --> 00:11:05,605
{\an1}Atoms are supposed to not
break down.
202
00:11:05,638 --> 00:11:07,705
♪ ♪
203
00:11:07,738 --> 00:11:11,905
NARRATOR:
It was as though certain atoms
had too much energy.
204
00:11:11,938 --> 00:11:16,005
{\an1}The nucleus would
spontaneously transform
205
00:11:16,038 --> 00:11:19,538
{\an1}and spit out an electron.
206
00:11:19,571 --> 00:11:22,871
{\an1}This phenomenon was
a type of radioactivity
207
00:11:22,905 --> 00:11:26,338
{\an1}known as beta decay.
208
00:11:26,371 --> 00:11:27,805
JAYAWARDHANA:
It appeared to be
209
00:11:27,838 --> 00:11:32,038
{\an1}this sort of mysterious energy
leaking from or emanating from
210
00:11:32,071 --> 00:11:34,471
certain atoms.
211
00:11:34,505 --> 00:11:38,105
{\an8}NARRATOR:
This process was remarkable
in itself,
212
00:11:38,138 --> 00:11:40,171
{\an7}but when scientists measured
the energy
213
00:11:40,205 --> 00:11:44,505
{\an7}of the electrons from beta
decay, something was wrong.
214
00:11:44,538 --> 00:11:48,738
KARAGIORGI:
One of the basic principles
in all sciences
215
00:11:48,771 --> 00:11:53,005
{\an1}is that energy can change
from one form to the other,
216
00:11:53,038 --> 00:11:56,071
{\an1}but the total sum must be
conserved.
217
00:11:56,105 --> 00:11:58,338
♪ ♪
218
00:11:58,371 --> 00:12:03,371
NARRATOR:
This is the principle
of conservation of energy.
219
00:12:03,405 --> 00:12:05,805
{\an1}From collisions in the
macro world
220
00:12:05,838 --> 00:12:07,905
to the behavior
of tiny particles,
221
00:12:07,938 --> 00:12:12,638
{\an1}the principle states that
energy should never disappear.
222
00:12:12,671 --> 00:12:16,005
{\an1}But when scientists measured
the energy of the electrons
223
00:12:16,038 --> 00:12:20,638
{\an1}from beta decay, that's exactly
what seemed to happen.
224
00:12:20,671 --> 00:12:24,938
KARAGIORGI:
So every time, rather than
having energy conserved,
225
00:12:24,971 --> 00:12:26,238
{\an1}what they were seeing is that
226
00:12:26,271 --> 00:12:29,038
{\an1}some amount of energy
would be missing.
227
00:12:29,071 --> 00:12:33,205
NARRATOR:
Where was the energy going?
228
00:12:33,238 --> 00:12:35,938
{\an1}It seemed that the particles
themselves were breaking
229
00:12:35,971 --> 00:12:40,005
{\an1}the fundamental rules
of physics.
230
00:12:42,805 --> 00:12:44,705
♪ ♪
231
00:12:44,738 --> 00:12:49,938
{\an1}In 1926, a young Italian
physicist called Enrico Fermi
232
00:12:49,971 --> 00:12:54,105
{\an1}was working at the University
of Rome's Physics Institute.
233
00:12:55,705 --> 00:12:57,538
{\an1}It was here that Fermi probed
234
00:12:57,571 --> 00:13:01,571
{\an1}into the developing field
of nuclear physics.
235
00:13:04,005 --> 00:13:05,481
KAISER:
Enrico Fermi was really
a towering figure
236
00:13:05,505 --> 00:13:06,671
{\an1}of 20th-century physics...
237
00:13:06,705 --> 00:13:08,414
{\an1}by any measure, one
of the greatest physicists
238
00:13:08,438 --> 00:13:09,871
{\an1}of the 20th century.
239
00:13:09,905 --> 00:13:12,605
This is the site
where Fermi built what became
240
00:13:12,638 --> 00:13:16,238
{\an1}an absolutely world-class group
of researchers.
241
00:13:16,271 --> 00:13:18,005
NARRATOR:
They were known
242
00:13:18,038 --> 00:13:20,571
{\an1}as the Via Panisperna Boys.
243
00:13:20,605 --> 00:13:22,371
KAISER:
This is really an iconic
photograph.
244
00:13:22,405 --> 00:13:24,181
{\an1}It captures them in the middle
of what would become
245
00:13:24,205 --> 00:13:26,238
{\an1}world-changing research.
246
00:13:26,271 --> 00:13:28,038
{\an1}Fermi himself was remarkably
young...
247
00:13:28,071 --> 00:13:30,238
{\an1}he was just 26 years old,
248
00:13:30,271 --> 00:13:32,571
{\an1}and already he'd been made
the big senior professor
249
00:13:32,605 --> 00:13:35,638
{\an1}around which this young group
would come together.
250
00:13:35,671 --> 00:13:38,705
{\an1}They referred to Fermi as the
Pope, he was the great leader.
251
00:13:38,738 --> 00:13:43,005
{\an1}Rasetti was next in line,
he was a cardinal.
252
00:13:43,038 --> 00:13:44,081
{\an1}The person taking the
photograph,
253
00:13:44,105 --> 00:13:45,505
{\an1}the very young Bruno Pontecorvo,
254
00:13:45,538 --> 00:13:46,938
{\an1}the youngest member of the
group,
255
00:13:46,971 --> 00:13:51,105
{\an1}they called him the Puppy.
256
00:13:51,138 --> 00:13:56,205
{\an8}NARRATOR:
The group's ideas would have
a profound impact on the world.
257
00:13:57,338 --> 00:13:58,838
{\an8}♪ ♪
258
00:13:58,871 --> 00:14:01,871
{\an8}In October 1931,
259
00:14:01,905 --> 00:14:04,505
{\an7}they invited a group of the
world's leading physicists
260
00:14:04,538 --> 00:14:09,038
{\an7}to a conference held at the
Physics Institute.
261
00:14:09,071 --> 00:14:11,638
{\an7}High on the agenda was
the problem
262
00:14:11,671 --> 00:14:14,738
{\an8}of the missing
radioactive energy.
263
00:14:16,505 --> 00:14:18,671
{\an7}One scientist at the conference,
264
00:14:18,705 --> 00:14:23,971
{\an7}the famous Wolfgang Pauli,
proposed a radical idea.
265
00:14:24,005 --> 00:14:26,905
KAISER:
Wolfgang Pauli had written
a letter to colleagues.
266
00:14:26,938 --> 00:14:29,471
{\an1}And he put forward what
he called a desperate remedy,
267
00:14:29,505 --> 00:14:33,338
{\an1}a "versweifelten Ausweg"...
It was just ridiculous.
268
00:14:33,371 --> 00:14:35,271
{\an7}And he says so in his letter.
269
00:14:35,305 --> 00:14:38,571
{\an7}It's a really quite
strange-sounding idea.
270
00:14:38,605 --> 00:14:41,105
{\an1}What if there was a new type
of particle in the world
271
00:14:41,138 --> 00:14:44,805
{\an1}that no one had ever seen
or detected before?
272
00:14:44,838 --> 00:14:46,771
{\an8}♪ ♪
273
00:14:46,805 --> 00:14:51,338
{\an8}NARRATOR:
Pauli suggested that instead
of just an electron,
274
00:14:51,371 --> 00:14:54,071
{\an7}perhaps there was an
unknown particle
275
00:14:54,105 --> 00:14:58,671
{\an7}that was carrying away the
missing energy.
276
00:14:58,705 --> 00:15:00,771
KAISER:
Very few people seem to have
been convinced
277
00:15:00,805 --> 00:15:02,638
{\an1}that this was the right way
to go.
278
00:15:02,671 --> 00:15:05,405
At that time,
physicists were quite confident
279
00:15:05,438 --> 00:15:07,571
{\an1}there existed two basic kinds
of particles,
280
00:15:07,605 --> 00:15:09,338
{\an1}electrons and protons.
281
00:15:09,371 --> 00:15:14,071
{\an1}But Pauli was suggesting,
"Let's make this enormous leap."
282
00:15:14,105 --> 00:15:18,071
NARRATOR:
A new particle of matter
seemed a step too far.
283
00:15:18,105 --> 00:15:19,638
♪ ♪
284
00:15:19,671 --> 00:15:23,571
{\an1}But for Enrico Fermi,
the Pope of Via Panisperna,
285
00:15:23,605 --> 00:15:29,105
{\an1}he took the wacky idea
and ran with it.
286
00:15:29,138 --> 00:15:32,005
{\an1}Fermi dedicated the next
two years of his life
287
00:15:32,038 --> 00:15:34,971
{\an1}to describe the obscure
ghost particle.
288
00:15:35,005 --> 00:15:38,271
{\an1}It would be neutral,
and carry no electric charge.
289
00:15:38,305 --> 00:15:42,438
{\an1}It would be tiny,
far smaller than an electron.
290
00:15:42,471 --> 00:15:47,171
{\an1}And it would pass through atoms
as if they weren't there at all.
291
00:15:47,205 --> 00:15:50,805
{\an1}He named the particle
the neutrino,
292
00:15:50,838 --> 00:15:54,105
Italian for
"little neutral one."
293
00:15:56,505 --> 00:15:59,805
KAISER:
This was a really quite
remarkable step.
294
00:15:59,838 --> 00:16:02,238
{\an1}But many physicists,
Fermi included, thought
295
00:16:02,271 --> 00:16:03,547
{\an1}that it should be nearly
impossible...
296
00:16:03,571 --> 00:16:05,505
{\an1}perhaps impossible forever...
297
00:16:05,538 --> 00:16:10,238
{\an1}to detect such a particle
even if it really exists.
298
00:16:10,271 --> 00:16:13,071
♪ ♪
299
00:16:13,105 --> 00:16:15,605
NARRATOR:
Outside the intellectual fervor
of the lab,
300
00:16:15,638 --> 00:16:17,771
{\an1}fascism was about to cast
a shadow
301
00:16:17,805 --> 00:16:20,538
{\an1}over the neutrino mystery.
302
00:16:20,571 --> 00:16:25,038
{\an1}In 1939, Fermi immigrated
to the U.S.A.
303
00:16:25,071 --> 00:16:27,171
{\an1}and was quickly put to work.
304
00:16:27,205 --> 00:16:29,171
{\an1}He helped to develop
305
00:16:29,205 --> 00:16:31,738
{\an1}the first operational
nuclear reactor
306
00:16:31,771 --> 00:16:36,705
{\an1}that led eventually
to the atomic bomb.
307
00:16:38,438 --> 00:16:43,738
{\an1}But not everybody had forgotten
about the elusive neutrino.
308
00:16:43,771 --> 00:16:46,405
♪ ♪
309
00:16:46,438 --> 00:16:51,871
{\an1}Bruno Pontecorvo, the Puppy of
the Via Panisperna Boys.
310
00:16:51,905 --> 00:16:55,538
{\an1}Upon moving to England
after the Second World War,
311
00:16:55,571 --> 00:16:58,205
{\an1}he continued to think
about neutrinos
312
00:16:58,238 --> 00:17:02,238
{\an1}until his life took
a shocking turn.
313
00:17:02,271 --> 00:17:06,771
CLOSE:
Pontecorvo was a man
who created big ideas.
314
00:17:06,805 --> 00:17:10,605
{\an7}The work that he did on
neutrinos alone
315
00:17:10,638 --> 00:17:12,605
{\an7}could have won him
316
00:17:12,638 --> 00:17:14,905
{\an1}certainly one Nobel Prize,
317
00:17:14,938 --> 00:17:16,805
{\an1}and been a candidate
maybe for two.
318
00:17:16,838 --> 00:17:20,538
NARRATOR:
But it wasn't to be.
319
00:17:20,571 --> 00:17:24,038
{\an1}In 1950, in the midst
of the Cold War,
320
00:17:24,071 --> 00:17:28,738
{\an1}Pontecorvo and his family
mysteriously went missing.
321
00:17:28,771 --> 00:17:30,838
Bruno Pontecorvo
322
00:17:30,871 --> 00:17:33,705
{\an1}disappeared through the Iron
Curtain in 1950,
323
00:17:33,738 --> 00:17:36,405
{\an1}and for five years,
324
00:17:36,438 --> 00:17:38,538
{\an1}disappeared off the face
of the planet.
325
00:17:40,105 --> 00:17:42,605
NARRATOR:
Only after five years
of silence
326
00:17:42,638 --> 00:17:46,105
did he reappear
in the Soviet Union.
327
00:17:46,138 --> 00:17:49,805
♪ ♪
328
00:17:49,838 --> 00:17:52,471
{\an1}So, what happened?
329
00:17:52,505 --> 00:17:55,071
{\an1}Was he kidnapped?
330
00:17:55,105 --> 00:17:58,338
Was he a spy?
331
00:17:58,371 --> 00:18:00,538
{\an1}Professor Frank Close
has spent years
332
00:18:00,571 --> 00:18:05,738
{\an1}researching Pontecorvo and his
mysterious disappearance.
333
00:18:05,771 --> 00:18:10,105
{\an1}He has come to the British
National Archives in London.
334
00:18:11,305 --> 00:18:13,205
{\an1}Earlier in his life,
335
00:18:13,238 --> 00:18:16,438
{\an1}Pontecorvo had been a member
of a communist party.
336
00:18:16,471 --> 00:18:19,171
{\an1}And there are now
British intelligence files
337
00:18:19,205 --> 00:18:21,771
under his name.
338
00:18:21,805 --> 00:18:23,005
CLOSE:
Looking at these
339
00:18:23,038 --> 00:18:25,738
old folders,
they're worn down the sides.
340
00:18:25,771 --> 00:18:27,705
{\an1}They have red stamps,
"top secret."
341
00:18:27,738 --> 00:18:31,371
{\an1}The case of Pontecorvo.
342
00:18:31,405 --> 00:18:34,071
{\an1}It is dripping with intrigue.
(chuckles)
343
00:18:34,105 --> 00:18:35,505
♪ ♪
344
00:18:35,538 --> 00:18:36,905
NARRATOR:
After the war,
345
00:18:36,938 --> 00:18:40,205
{\an1}while working for the
U.K.'s atomic energy program,
346
00:18:40,238 --> 00:18:45,138
{\an1}Pontecorvo devised a method
to try and detect neutrinos.
347
00:18:45,171 --> 00:18:48,171
He reasoned that
nuclear reactors...
348
00:18:48,205 --> 00:18:51,071
{\an1}which derive energy
from splitting atoms...
349
00:18:51,105 --> 00:18:54,771
{\an1}should produce neutrinos in
vast quantities.
350
00:18:54,805 --> 00:18:59,705
{\an1}But the government classified
his paper.
351
00:18:59,738 --> 00:19:04,371
{\an1}Now, I conjecture that this
paper was classified secret
352
00:19:04,405 --> 00:19:09,105
{\an1}because, if you could indeed
detect neutrinos
353
00:19:09,138 --> 00:19:11,338
{\an1}coming from a nuclear reactor,
354
00:19:11,371 --> 00:19:12,971
{\an1}you would be able to work out
355
00:19:13,005 --> 00:19:14,738
how powerful
the nuclear reactor was.
356
00:19:14,771 --> 00:19:16,871
{\an1}So they classified it.
357
00:19:16,905 --> 00:19:19,438
♪ ♪
358
00:19:19,471 --> 00:19:21,471
NARRATOR:
As the Cold War escalated,
359
00:19:21,505 --> 00:19:27,071
{\an1}the U.S.A. became paranoid
of atomic espionage.
360
00:19:27,105 --> 00:19:31,538
{\an1}In 1950, the Rosenberg spy ring
was uncovered.
361
00:19:31,571 --> 00:19:34,671
And it triggered
a communist witch hunt.
362
00:19:37,038 --> 00:19:39,138
{\an1}A secret letter reveals the FBI
363
00:19:39,171 --> 00:19:41,505
{\an1}wrote to a British
intelligence service
364
00:19:41,538 --> 00:19:43,905
{\an1}about Pontecorvo.
365
00:19:43,938 --> 00:19:47,671
CLOSE:
"The FBI now ask if we can send
them any information
366
00:19:47,705 --> 00:19:49,505
{\an1}"which would indicate that
Pontecorvo
367
00:19:49,538 --> 00:19:53,171
may be engaged
in communist activities."
368
00:19:53,205 --> 00:19:57,238
{\an1}The letter was received in
London on the 19th of July.
369
00:19:57,271 --> 00:19:58,671
Five days later,
370
00:19:58,705 --> 00:20:02,338
{\an1}Pontecorvo goes off to Europe
and never returns.
371
00:20:02,371 --> 00:20:03,871
♪ ♪
372
00:20:03,905 --> 00:20:06,905
NARRATOR:
Flight manifests reveal
Pontecorvo and his family
373
00:20:06,938 --> 00:20:10,871
{\an1}flew from Rome, across Europe,
to Helsinki,
374
00:20:10,905 --> 00:20:14,905
{\an1}alongside two suspected
KGB agents.
375
00:20:14,938 --> 00:20:18,738
{\an1}Pontecorvo's son, just
12 years old at the time,
376
00:20:18,771 --> 00:20:22,571
{\an1}revealed they were then driven
across the border to Moscow...
377
00:20:22,605 --> 00:20:25,438
{\an1}with Bruno in the trunk.
378
00:20:25,471 --> 00:20:26,605
CLOSE:
He said to me,
379
00:20:26,638 --> 00:20:29,405
{\an1}"I knew something was up."
(chuckles)
380
00:20:29,438 --> 00:20:34,938
NARRATOR:
Frank believes a Soviet mole
passed the FBI letter to Moscow,
381
00:20:34,971 --> 00:20:40,271
{\an1}who then pressured Pontecorvo
to defect.
382
00:20:40,305 --> 00:20:43,705
{\an1}There's no clear evidence that
he had been a spy,
383
00:20:43,738 --> 00:20:46,371
{\an1}but whatever his reason
for leaving,
384
00:20:46,405 --> 00:20:50,238
{\an1}Bruno's time in the West
was over.
385
00:20:50,271 --> 00:20:51,938
CLOSE:
Was he a spy or not?
386
00:20:51,971 --> 00:20:53,071
{\an1}We don't yet know.
387
00:20:53,105 --> 00:20:54,538
{\an1}In any event, it was clear
388
00:20:54,571 --> 00:20:57,338
that Pontecorvo
was a top-quality scientist
389
00:20:57,371 --> 00:21:00,105
{\an1}who had taken his
brain to the Soviet Union.
390
00:21:06,305 --> 00:21:09,938
NARRATOR:
By 1950, the U.S.A.
and the Soviet Union
391
00:21:09,971 --> 00:21:13,905
were engaged
in a nuclear arms race.
392
00:21:13,938 --> 00:21:18,371
{\an1}With it came a new opportunity
to hunt for neutrinos.
393
00:21:21,171 --> 00:21:25,205
KARAGIORGI:
When a nuclear bomb
goes off,
394
00:21:25,238 --> 00:21:29,938
{\an1}there is this huge cascade
of particles
395
00:21:29,971 --> 00:21:34,171
that spews out:
protons, electrons,
396
00:21:34,205 --> 00:21:37,571
{\an1}a lot of light particles
carrying off energy.
397
00:21:37,605 --> 00:21:40,838
{\an7}And along with these particles
spewing out,
398
00:21:40,871 --> 00:21:44,238
{\an7}lots and lots of neutrinos
come out for free.
399
00:21:45,971 --> 00:21:50,271
NARRATOR:
If neutrinos were real, could
a nuclear weapon finally be
400
00:21:50,305 --> 00:21:52,538
{\an1}the key to detect them?
401
00:21:52,571 --> 00:21:57,638
{\an1}In 1951, a young American
called Fred Reines
402
00:21:57,671 --> 00:21:59,871
{\an1}was working on the
U.S. nuclear program
403
00:21:59,905 --> 00:22:03,438
{\an1}at Los Alamos National
Laboratory.
404
00:22:03,471 --> 00:22:07,705
{\an1}It was here that Reines, along
with his colleague Clyde Cowan,
405
00:22:07,738 --> 00:22:11,338
{\an1}decided to take advantage
of destructive bomb tests
406
00:22:11,371 --> 00:22:16,071
{\an1}to investigate the mystery
of the missing neutrino.
407
00:22:16,105 --> 00:22:17,514
KAISER:
Reines went back to a question
408
00:22:17,538 --> 00:22:19,771
{\an1}that had been kind of
abandoned in the decades
409
00:22:19,805 --> 00:22:21,438
{\an1}before the Second World War,
410
00:22:21,471 --> 00:22:24,071
{\an7}the question of, could
physicists ever actually detect
411
00:22:24,105 --> 00:22:28,571
{\an7}these very strange, elusive,
ghost-like particles?
412
00:22:28,605 --> 00:22:34,005
NARRATOR:
They called their mission
Project Poltergeist.
413
00:22:34,038 --> 00:22:36,271
{\an1}For detecting the neutrino,
the good news was,
414
00:22:36,305 --> 00:22:38,805
{\an1}you could calculate the chance
of doing it.
415
00:22:38,838 --> 00:22:41,605
{\an1}And the bad news was,
it was almost zero.
416
00:22:41,638 --> 00:22:47,038
NARRATOR:
Reines and Cowan needed to tip
the odds in their favor,
417
00:22:47,071 --> 00:22:50,871
{\an1}and knew a nuclear bomb test
could be the key.
418
00:22:50,905 --> 00:22:54,205
{\an1}An atom bomb should produce
thousands of times
419
00:22:54,238 --> 00:22:57,938
{\an1}more neutrinos than even
the biggest nuclear reactor.
420
00:22:59,005 --> 00:23:02,471
{\an1}But it also created a problem.
421
00:23:02,505 --> 00:23:04,438
{\an1}If they had bolted
the detector in place,
422
00:23:04,471 --> 00:23:05,514
the nuclear bomb would've just
423
00:23:05,538 --> 00:23:07,238
{\an1}smashed it to smithereens.
424
00:23:07,271 --> 00:23:08,771
{\an1}So instead, the proposal
425
00:23:08,805 --> 00:23:11,705
{\an1}was to dig a shaft about
150 feet deep
426
00:23:11,738 --> 00:23:13,705
{\an7}right near where the bomb
would eventually
427
00:23:13,738 --> 00:23:16,771
{\an7}be detonated above ground.
428
00:23:16,805 --> 00:23:18,705
{\an8}NARRATOR:
The team planned to drop
429
00:23:18,738 --> 00:23:24,005
{\an7}a detector down the shaft to
avoid the shockwave of the bomb.
430
00:23:24,038 --> 00:23:27,005
{\an8}KAISER:
Inside that shaft, they would
pad the bottom with foam
431
00:23:27,038 --> 00:23:30,471
{\an7}and feathers and kind of, like,
mattress cushions.
432
00:23:32,805 --> 00:23:34,871
{\an1}It was, I mean...
(chuckles)
433
00:23:34,905 --> 00:23:36,905
{\an1}...a creative, ambitious,
434
00:23:36,938 --> 00:23:39,305
{\an1}and maybe slightly crazy kind
of idea
435
00:23:39,338 --> 00:23:41,138
{\an1}to try to catch these neutrinos
in the midst
436
00:23:41,171 --> 00:23:43,871
{\an1}of this very dramatic,
very worldly set of events
437
00:23:43,905 --> 00:23:46,005
{\an1}in the early years of the
Cold War.
438
00:23:46,038 --> 00:23:47,738
♪ ♪
439
00:23:47,771 --> 00:23:50,171
NARRATOR:
Work digging the shaft
had begun,
440
00:23:50,205 --> 00:23:53,538
{\an1}but the head of physics
at Los Alamos was concerned
441
00:23:53,571 --> 00:23:56,871
{\an1}that the experiment
couldn't be repeated.
442
00:23:56,905 --> 00:24:01,005
{\an1}He urged the team
to find another way.
443
00:24:01,038 --> 00:24:04,871
{\an1}Couldn't they use
a nuclear reactor instead?
444
00:24:04,905 --> 00:24:09,338
{\an1}Late one evening, Reines
and Cowan had a realization.
445
00:24:12,105 --> 00:24:15,571
{\an1}In the same way that the nucleus
of an atom could decay
446
00:24:15,605 --> 00:24:19,538
{\an1}and release a neutrino,
they knew in theory
447
00:24:19,571 --> 00:24:23,238
{\an1}the process should be
reversible.
448
00:24:23,271 --> 00:24:27,638
{\an1}On the rare occasion a neutrino
could interact with a nucleus,
449
00:24:27,671 --> 00:24:30,871
{\an1}it should produce two new
particles,
450
00:24:30,905 --> 00:24:34,105
called a neutron and a positron.
451
00:24:34,138 --> 00:24:37,238
{\an1}And if they traveled
through the right medium,
452
00:24:37,271 --> 00:24:40,638
{\an1}those two telltale particles
should produce
453
00:24:40,671 --> 00:24:44,171
{\an1}two distinctive flashes
of light.
454
00:24:44,205 --> 00:24:48,705
KARAGIORGI:
So Reines and Cowan
built a detector,
455
00:24:48,738 --> 00:24:53,571
{\an1}essentially a big tank filled
with a solvent
456
00:24:53,605 --> 00:24:55,571
{\an1}that could pick up
457
00:24:55,605 --> 00:25:00,205
{\an1}this two coincident signal blip
458
00:25:00,238 --> 00:25:03,305
{\an1}deep under a nuclear reactor.
459
00:25:03,338 --> 00:25:08,671
♪ ♪
460
00:25:08,705 --> 00:25:11,505
NARRATOR:
After five years of experiments,
461
00:25:11,538 --> 00:25:16,571
in 1956,
finally, they got their answer.
462
00:25:18,938 --> 00:25:21,438
♪ ♪
463
00:25:21,471 --> 00:25:24,971
{\an1}They recorded the two
telltale flashes of light.
464
00:25:25,005 --> 00:25:26,771
♪ ♪
465
00:25:26,805 --> 00:25:29,505
{\an1}For the first time,
they saw evidence
466
00:25:29,538 --> 00:25:32,538
{\an1}of the elusive neutrino.
467
00:25:32,571 --> 00:25:35,038
{\an7}What they had done was
a remarkable achievement,
468
00:25:35,071 --> 00:25:38,371
{\an7}one that seemed impossible.
469
00:25:38,405 --> 00:25:39,571
♪ ♪
470
00:25:39,605 --> 00:25:41,205
KAISER:
Neutrinos exist.
471
00:25:41,238 --> 00:25:44,138
{\an1}They're real and they're part
of the world.
472
00:25:44,171 --> 00:25:46,171
{\an1}They're not only a clever idea.
473
00:25:51,038 --> 00:25:52,838
{\an1}Knowing neutrinos exist
474
00:25:52,871 --> 00:25:55,205
{\an1}put a whole extra set
of investigations
475
00:25:55,238 --> 00:25:57,338
{\an1}on a kind of firmer path.
476
00:25:57,371 --> 00:25:59,138
♪ ♪
477
00:25:59,171 --> 00:26:04,838
NARRATOR:
If neutrinos were pouring from
nuclear reactors on Earth,
478
00:26:04,871 --> 00:26:06,405
{\an1}then surely they would
be generated
479
00:26:06,438 --> 00:26:10,905
{\an1}in abundance in the largest
nuclear furnaces of all.
480
00:26:12,471 --> 00:26:15,105
Stars.
481
00:26:15,138 --> 00:26:16,771
KAISER:
For a long, long time,
482
00:26:16,805 --> 00:26:19,605
{\an1}scientists have been wondering,
what makes the stars shine?
483
00:26:19,638 --> 00:26:22,971
{\an1}What drives that enormous
output of energy?
484
00:26:23,005 --> 00:26:24,738
♪ ♪
485
00:26:24,771 --> 00:26:30,405
KARAGIORGI:
People theorized that our sun
is like a giant nuclear reactor,
486
00:26:30,438 --> 00:26:34,705
{\an1}except, rather than heavier
elements breaking down
487
00:26:34,738 --> 00:26:38,338
{\an1}into smaller ones
and releasing energy,
488
00:26:38,371 --> 00:26:41,771
{\an1}you have lighter elements
that fuse together
489
00:26:41,805 --> 00:26:43,171
{\an1}through nuclear fusion.
490
00:26:43,205 --> 00:26:45,838
♪ ♪
491
00:26:45,871 --> 00:26:47,471
NARRATOR:
In the heart of the sun,
492
00:26:47,505 --> 00:26:50,938
{\an1}tremendous heat and pressure
force hydrogen nuclei
493
00:26:50,971 --> 00:26:53,838
to fuse together to make helium.
494
00:26:55,471 --> 00:27:00,405
And, in theory,
vast quantities of neutrinos
495
00:27:00,438 --> 00:27:05,805
{\an1}that pass freely through the sun
and out into space.
496
00:27:09,071 --> 00:27:12,538
{\an1}So if we could detect neutrinos
from the sun,
497
00:27:12,571 --> 00:27:16,705
{\an1}we could learn about
the processes that fuel it.
498
00:27:16,738 --> 00:27:21,738
{\an1}We could peek inside the core
of our sun.
499
00:27:24,905 --> 00:27:28,171
{\an8}NARRATOR:
In the historic gold mining
town of Lead,
500
00:27:28,205 --> 00:27:31,938
{\an1}people descend into the depths
of the Earth.
501
00:27:31,971 --> 00:27:33,838
{\an1}(indistinct chatter)
502
00:27:33,871 --> 00:27:36,638
NARRATOR:
But no longer to mine
precious metal.
503
00:27:36,671 --> 00:27:41,338
They're hunting for neutrinos.
504
00:27:41,371 --> 00:27:44,371
{\an1}It was here in 1965
505
00:27:44,405 --> 00:27:47,505
{\an1}that an experimentalist
called Ray Davis
506
00:27:47,538 --> 00:27:52,005
{\an1}came to try and prove
what makes the sun shine.
507
00:27:52,038 --> 00:27:54,271
KAISER:
Ray Davis got very excited
508
00:27:54,305 --> 00:27:57,405
{\an1}that there is this new thing
in the world called a neutrino.
509
00:27:57,438 --> 00:28:00,338
{\an1}He began realizing that other
kinds of nuclear reactors
510
00:28:00,371 --> 00:28:03,105
{\an1}that occur throughout
the universe, like stars,
511
00:28:03,138 --> 00:28:06,105
{\an1}they should be spewing out these
neutrinos all the time.
512
00:28:06,138 --> 00:28:10,905
NARRATOR:
But catching them wouldn't
be easy.
513
00:28:10,938 --> 00:28:14,405
{\an1}Calculations showed
that neutrinos from the sun
514
00:28:14,438 --> 00:28:17,805
{\an1}would be so faint, a detector
near the Earth's surface
515
00:28:17,838 --> 00:28:21,105
{\an1}would be overwhelmed
by background radiation.
516
00:28:21,138 --> 00:28:26,605
{\an1}His only option was to go
to the bottom of a mine.
517
00:28:26,638 --> 00:28:30,405
{\an1}Beneath almost a mile of solid
rock, Davis's team built
518
00:28:30,438 --> 00:28:32,905
{\an1}a steel tank the size of a house
519
00:28:32,938 --> 00:28:35,671
{\an1}and filled it with
100,000 gallons
520
00:28:35,705 --> 00:28:38,305
{\an1}of dry-cleaning fluid.
521
00:28:40,371 --> 00:28:43,438
In theory,
if a neutrino from the sun
522
00:28:43,471 --> 00:28:47,638
{\an1}collided with a chlorine atom
inside the tank,
523
00:28:47,671 --> 00:28:52,271
{\an1}it would cause a reaction
that Ray Davis could detect.
524
00:28:52,305 --> 00:28:55,905
CLOSE:
Here was something
that was completely fresh.
525
00:28:55,938 --> 00:28:58,071
{\an1}Nobody knew anything about it.
526
00:28:58,105 --> 00:29:02,638
{\an1}But the key thing was that
if neutrinos hit chlorine,
527
00:29:02,671 --> 00:29:04,605
{\an7}which you could get in
cleaning fluid,
528
00:29:04,638 --> 00:29:06,205
{\an7}it would turn the atoms
of chlorine
529
00:29:06,238 --> 00:29:08,871
{\an7}into a radioactive form
of argon.
530
00:29:08,905 --> 00:29:10,405
{\an7}And that's when Davis
got excited,
531
00:29:10,438 --> 00:29:13,805
{\an1}because he was a radiochemist,
and for him,
532
00:29:13,838 --> 00:29:19,771
{\an1}detecting radioactive forms
of argon was easy street.
533
00:29:21,205 --> 00:29:23,005
NARRATOR:
Scientists had calculated
534
00:29:23,038 --> 00:29:26,605
{\an1}that around a million trillion
neutrinos from the sun
535
00:29:26,638 --> 00:29:30,871
{\an1}should pass through Davis's tank
each minute.
536
00:29:30,905 --> 00:29:33,305
{\an1}But the probability
of them hitting the fluid
537
00:29:33,338 --> 00:29:37,171
{\an1}and making an argon atom
was so small,
538
00:29:37,205 --> 00:29:39,505
{\an1}Ray Davis could only expect
to find
539
00:29:39,538 --> 00:29:42,205
{\an1}ten individual atoms of argon
540
00:29:42,238 --> 00:29:46,538
{\an1}from ten neutrino collisions per
week.
541
00:29:46,571 --> 00:29:49,505
JAYAWARDHANA:
His task was almost impossible.
542
00:29:49,538 --> 00:29:52,838
{\an1}Many of his own physicist
colleagues doubted
543
00:29:52,871 --> 00:29:55,105
{\an1}this experiment would ever work.
544
00:29:55,138 --> 00:29:57,105
♪ ♪
545
00:29:57,138 --> 00:29:58,547
CLOSE:
He was having to convince people
546
00:29:58,571 --> 00:29:59,814
{\an1}that out of these millions
and millions and millions
547
00:29:59,838 --> 00:30:02,071
{\an1}and millions of atoms
inside this tank,
548
00:30:02,105 --> 00:30:05,538
{\an1}he could identify
the collisions of one or two
549
00:30:05,571 --> 00:30:08,938
{\an1}and convince you that these were
neutrinos coming from the sun.
550
00:30:08,971 --> 00:30:13,438
NARRATOR:
Around each month,
Davis flushed out the giant tank
551
00:30:13,471 --> 00:30:16,138
{\an1}to extract the argon atoms.
552
00:30:17,471 --> 00:30:19,371
{\an1}To everybody's amazement,
553
00:30:19,405 --> 00:30:21,938
he found them.
554
00:30:21,971 --> 00:30:26,171
{\an1}(machine whirring)
555
00:30:27,205 --> 00:30:29,738
{\an1}But there was a problem.
556
00:30:29,771 --> 00:30:34,138
{\an1}Instead of detecting the number
of atoms that theory predicted,
557
00:30:34,171 --> 00:30:37,371
{\an1}his measurements fell short.
558
00:30:37,405 --> 00:30:38,981
KAISER:
They knew the target number
based on
559
00:30:39,005 --> 00:30:41,671
{\an1}the nuclear physics
theoretical explanation
560
00:30:41,705 --> 00:30:43,305
{\an1}of how stars shine,
561
00:30:43,338 --> 00:30:46,271
{\an1}and that led to a very
particular target number.
562
00:30:46,305 --> 00:30:48,371
{\an1}And Davis's remarkable
experiment
563
00:30:48,405 --> 00:30:51,105
{\an1}kept coming in not close to it,
not 80 percent,
564
00:30:51,138 --> 00:30:54,005
{\an1}but only at one-third
of that target number.
565
00:30:54,038 --> 00:30:57,338
NARRATOR:
What happened?
566
00:30:57,371 --> 00:30:59,571
{\an1}Had the experiment gone wrong?
567
00:30:59,605 --> 00:31:03,071
{\an1}Another scientist carried out
a blind trial
568
00:31:03,105 --> 00:31:05,971
{\an1}to test the accuracy
of Ray's atom detection.
569
00:31:06,005 --> 00:31:10,305
KAISER:
A colleague put in
500 kind of rogue atoms
570
00:31:10,338 --> 00:31:12,238
{\an1}without telling Davis
the number.
571
00:31:12,271 --> 00:31:14,405
{\an1}And Davis was able to go through
the whole process,
572
00:31:14,438 --> 00:31:15,938
sift it through,
573
00:31:15,971 --> 00:31:18,014
{\an1}and he counted exactly the
number that had been put in.
574
00:31:18,038 --> 00:31:21,738
NARRATOR:
If the experimental results
were accurate,
575
00:31:21,771 --> 00:31:24,671
{\an1}then perhaps scientists
had gotten their theory
576
00:31:24,705 --> 00:31:28,005
{\an1}about neutrinos from the
sun wrong.
577
00:31:28,038 --> 00:31:29,614
CLOSE:
Everybody was blaming
everybody else.
578
00:31:29,638 --> 00:31:31,271
{\an1}There were even suggestions,
579
00:31:31,305 --> 00:31:34,571
{\an1}has the sun already burnt out
in the core?
580
00:31:34,605 --> 00:31:36,138
{\an1}It was just an enormous puzzle.
581
00:31:36,171 --> 00:31:39,205
{\an1}All these advances in
understanding how stars shine,
582
00:31:39,238 --> 00:31:41,438
{\an1}and then hitting this kind of
brick wall
583
00:31:41,471 --> 00:31:44,938
{\an1}where theory and experiment just
would not agree with each other.
584
00:31:47,338 --> 00:31:51,838
NARRATOR:
The puzzle became known as
the solar neutrino problem.
585
00:31:54,271 --> 00:31:56,405
♪ ♪
586
00:31:56,438 --> 00:31:58,038
1970,
587
00:31:58,071 --> 00:32:00,505
20 years since Bruno Pontecorvo
588
00:32:00,538 --> 00:32:03,505
{\an1}defected to the Soviet Union.
589
00:32:03,538 --> 00:32:05,005
♪ ♪
590
00:32:05,038 --> 00:32:07,038
{\an1}Even after all that time,
591
00:32:07,071 --> 00:32:10,938
{\an1}his life behind the Iron Curtain
remained shrouded in secrecy.
592
00:32:12,738 --> 00:32:15,838
{\an1}But in a government lab outside
Moscow,
593
00:32:15,871 --> 00:32:18,405
{\an1}Pontecorvo worked tirelessly
to explain
594
00:32:18,438 --> 00:32:21,571
{\an1}the puzzling behavior
of neutrinos.
595
00:32:24,105 --> 00:32:28,205
{\an1}He suggested that instead
of just one,
596
00:32:28,238 --> 00:32:32,405
{\an1}there may be two or even three
different kinds of neutrino...
597
00:32:32,438 --> 00:32:36,905
{\an1}known as different flavors.
598
00:32:36,938 --> 00:32:40,038
♪ ♪
599
00:32:40,071 --> 00:32:43,338
{\an1}If this wasn't strange enough,
he calculated that something
600
00:32:43,371 --> 00:32:47,371
{\an1}peculiar might happen as they
traveled through space.
601
00:32:50,405 --> 00:32:55,538
{\an1}A neutrino would always be born
as one definite flavor,
602
00:32:55,571 --> 00:32:59,671
but over time,
it would change its identity.
603
00:32:59,705 --> 00:33:03,905
{\an1}It would transform,
mixing back and forth
604
00:33:03,938 --> 00:33:08,105
{\an1}between the three different
types.
605
00:33:08,138 --> 00:33:12,238
This was called
neutrino oscillation.
606
00:33:12,271 --> 00:33:16,838
♪ ♪
607
00:33:16,871 --> 00:33:20,371
{\an7}Pontecorvo's idea really is,
it's, it's sort of delicious.
608
00:33:20,405 --> 00:33:25,005
{\an1}These neutrinos could be not
taking one identity,
609
00:33:25,038 --> 00:33:28,538
{\an1}dropping that, adopting another
one, dropping that,
610
00:33:28,571 --> 00:33:30,211
{\an1}but going into this even
stranger mixture,
611
00:33:30,238 --> 00:33:33,105
{\an1}where they're in neither
and both states at once.
612
00:33:33,138 --> 00:33:35,638
NARRATOR:
It was a bold idea.
613
00:33:35,671 --> 00:33:37,805
{\an1}No other fundamental particle
614
00:33:37,838 --> 00:33:41,305
{\an1}seemed to spontaneously change
its identity.
615
00:33:41,338 --> 00:33:43,771
{\an1}But if neutrinos were
transforming into flavors
616
00:33:43,805 --> 00:33:46,971
{\an1}that Ray Davis's detector
couldn't see,
617
00:33:47,005 --> 00:33:50,238
{\an1}it might explain why
two-thirds of the neutrinos
618
00:33:50,271 --> 00:33:53,305
{\an1}from the sun appeared
to be missing.
619
00:33:55,171 --> 00:33:56,938
{\an7}But there was a catch.
620
00:33:56,971 --> 00:33:58,905
{\an7}The Standard Model,
621
00:33:58,938 --> 00:34:02,305
{\an7}the most precise scientific
theory in human history,
622
00:34:02,338 --> 00:34:05,938
{\an7}made one important prediction
that stood in the way.
623
00:34:08,271 --> 00:34:09,771
{\an8}PEREZ:
The Standard Model anticipated
624
00:34:09,805 --> 00:34:12,338
{\an7}neutrinos would be
completely massless.
625
00:34:12,371 --> 00:34:15,771
{\an7}They would have no mass at all,
much like the photon of light.
626
00:34:15,805 --> 00:34:18,405
{\an7}And if they had no mass,
627
00:34:18,438 --> 00:34:21,205
{\an7}that meant that they could not
oscillate.
628
00:34:21,238 --> 00:34:24,438
NARRATOR:
If neutrinos had no mass,
629
00:34:24,471 --> 00:34:27,371
{\an1}one of Albert Einstein's most
important theories
630
00:34:27,405 --> 00:34:31,438
{\an1}predicted that neutrinos could
not possibly oscillate.
631
00:34:34,171 --> 00:34:35,914
KAISER:
There is this mind-boggling
phenomenon
632
00:34:35,938 --> 00:34:37,971
{\an1}from Einstein's relativity
633
00:34:38,005 --> 00:34:40,438
{\an1}that says that a clock
that is moving closer
634
00:34:40,471 --> 00:34:41,938
{\an1}and closer to the speed of light
635
00:34:41,971 --> 00:34:45,271
{\an1}will tick at a slower
and slower rate.
636
00:34:45,305 --> 00:34:47,771
{\an1}If that clock were moving
literally at the speed of light,
637
00:34:47,805 --> 00:34:49,338
{\an1}it would never tick at all.
638
00:34:49,371 --> 00:34:51,438
{\an1}No time would pass
for that object
639
00:34:51,471 --> 00:34:53,905
{\an1}that moves at exactly
the speed of light.
640
00:34:53,938 --> 00:34:56,838
NARRATOR:
According to Einstein's
theories,
641
00:34:56,871 --> 00:34:59,205
{\an1}the faster a particle travels,
642
00:34:59,238 --> 00:35:02,938
{\an1}the more its internal clock
slows down.
643
00:35:02,971 --> 00:35:08,205
{\an1}A particle with no mass can only
travel at the speed of light,
644
00:35:08,238 --> 00:35:10,371
{\an1}which is where time stops.
645
00:35:13,038 --> 00:35:15,671
{\an1}So if a neutrino had zero mass,
646
00:35:15,705 --> 00:35:18,505
{\an1}it would not experience
the passage of time,
647
00:35:18,538 --> 00:35:24,305
{\an1}and would never be able
to change.
648
00:35:24,338 --> 00:35:26,671
{\an1}If a particle has zero mass,
649
00:35:26,705 --> 00:35:30,405
{\an1}what that means is that its
internal clock is not ticking.
650
00:35:30,438 --> 00:35:34,438
{\an1}There's no way for that
particle to experience time.
651
00:35:34,471 --> 00:35:36,405
{\an1}If there's no passage of time,
652
00:35:36,438 --> 00:35:39,471
{\an1}then how could they change over
time from one identity
653
00:35:39,505 --> 00:35:42,105
to another?
654
00:35:42,138 --> 00:35:45,638
NARRATOR:
If neutrino oscillation
was real,
655
00:35:45,671 --> 00:35:49,071
{\an1}neutrinos must have some mass.
656
00:35:49,105 --> 00:35:54,438
{\an1}But could the Standard Model
really be wrong?
657
00:35:54,471 --> 00:35:57,605
♪ ♪
658
00:35:57,638 --> 00:36:01,405
{\an7}Throughout the 1950s and '60s,
clues from experiments
659
00:36:01,438 --> 00:36:04,805
{\an1}performed at CERN,
alongside Fermilab,
660
00:36:04,838 --> 00:36:08,905
{\an1}helped to lay the foundation
of the Standard Model.
661
00:36:08,938 --> 00:36:12,671
What they found
revolutionized our understanding
662
00:36:12,705 --> 00:36:15,438
{\an1}of the particles that make up
our universe.
663
00:36:15,471 --> 00:36:19,405
FILM NARRATOR:
By means of this machine,
it is possible to see
664
00:36:19,438 --> 00:36:20,581
the tracks
of sub-nuclear particles,
665
00:36:20,605 --> 00:36:23,971
{\an1}the smallest particles
known to man:
666
00:36:24,005 --> 00:36:26,938
{\an1}the electron, the positron,
667
00:36:26,971 --> 00:36:29,671
{\an1}the photon, and the neutrino...
668
00:36:32,305 --> 00:36:34,305
NARRATOR:
Over the years, work at CERN
669
00:36:34,338 --> 00:36:36,305
{\an1}led to groundbreaking
new technologies:
670
00:36:36,338 --> 00:36:40,671
medical advances like PET scans;
671
00:36:40,705 --> 00:36:44,571
{\an1}even the birth of
the World Wide Web.
672
00:36:46,871 --> 00:36:51,371
{\an1}Perhaps CERN's biggest success
came in 2012.
673
00:36:51,405 --> 00:36:54,471
{\an1}Nearly 50 years after the
Standard Model was proposed,
674
00:36:54,505 --> 00:36:57,571
{\an1}physicists detected the
final particle
675
00:36:57,605 --> 00:37:01,938
{\an1}it predicted... the Higgs boson.
676
00:37:03,238 --> 00:37:05,371
{\an1}I think we have it.
677
00:37:05,405 --> 00:37:07,371
{\an1}(cheers and applause)
678
00:37:16,705 --> 00:37:19,371
NARRATOR:
Finally, all the pieces needed
679
00:37:19,405 --> 00:37:22,171
{\an1}to describe the detectable
physical universe
680
00:37:22,205 --> 00:37:25,738
{\an1}seemed to be in place.
681
00:37:25,771 --> 00:37:29,271
{\an1}Along with the Higgs boson,
there are force carriers,
682
00:37:29,305 --> 00:37:32,138
{\an1}like the photon of light.
683
00:37:32,171 --> 00:37:36,371
{\an1}Quarks, which form
the nuclei of atoms.
684
00:37:36,405 --> 00:37:41,938
{\an1}Leptons, including the electron,
muon, and tau.
685
00:37:41,971 --> 00:37:46,405
{\an1}And three corresponding flavors
of neutrinos.
686
00:37:46,438 --> 00:37:49,238
KAISER:
It is a map of what's out there,
687
00:37:49,271 --> 00:37:52,405
{\an7}what we're made of,
and how we fit... all of us.
688
00:37:52,438 --> 00:37:55,538
{\an7}We are made of these things.
689
00:37:55,571 --> 00:37:57,205
{\an1}And that is a kind of basic
understanding
690
00:37:57,238 --> 00:37:59,138
{\an1}of nature, of our own world,
691
00:37:59,171 --> 00:38:01,705
{\an1}that I, I think is, is just a
remarkable
692
00:38:01,738 --> 00:38:03,938
{\an1}human achievement.
693
00:38:05,705 --> 00:38:07,971
NARRATOR:
And yet, for all its success,
694
00:38:08,005 --> 00:38:10,938
{\an1}the Standard Model had
no equations to explain
695
00:38:10,971 --> 00:38:15,005
{\an1}how or why the neutrinos
would have mass.
696
00:38:19,705 --> 00:38:23,038
For Ray Davis
and his missing solar neutrinos,
697
00:38:23,071 --> 00:38:27,571
{\an1}it seemed an unsolvable paradox.
698
00:38:28,871 --> 00:38:32,238
{\an7}For decades, Davis persists,
699
00:38:32,271 --> 00:38:35,338
{\an7}but he still only finds
one-third of the neutrinos
700
00:38:35,371 --> 00:38:38,271
{\an7}that were supposed to be coming
from the sun.
701
00:38:39,738 --> 00:38:43,138
{\an7}Well, we've been carrying
on this experiment
702
00:38:43,171 --> 00:38:45,971
{\an7}for about 20 years right here.
703
00:38:46,005 --> 00:38:51,305
{\an7}But we're still observing a
low flux of neutrinos.
704
00:38:52,805 --> 00:38:56,571
{\an8}NARRATOR:
Eventually, the problem
is too big to ignore.
705
00:38:56,605 --> 00:39:00,805
{\an8}In the 1990s,
scientists in Canada and Japan
706
00:39:00,838 --> 00:39:05,205
{\an7}construct a new generation of
supersized neutrino detectors
707
00:39:05,238 --> 00:39:07,971
{\an7}to finally settle the mystery.
708
00:39:08,005 --> 00:39:10,871
{\an1}(explosion roars)
709
00:39:10,905 --> 00:39:15,505
{\an1}One of them lies deep beneath
Japan's Ikeno Mountain.
710
00:39:15,538 --> 00:39:19,271
{\an1}Scientists fit 11,000
light detectors
711
00:39:19,305 --> 00:39:21,671
to the inside of
a gigantic container
712
00:39:21,705 --> 00:39:28,205
{\an1}and fill it with 50,000 tons of
ultra-pure water.
713
00:39:28,238 --> 00:39:34,638
{\an1}This $100 million detector
is named Super-K.
714
00:39:34,671 --> 00:39:38,271
{\an1}The Super-K experiment ended up
being a game-changer.
715
00:39:38,305 --> 00:39:41,938
NARRATOR:
In the rare event that
a neutrino collides
716
00:39:41,971 --> 00:39:44,571
{\an1}with the liquid in Super-K,
717
00:39:44,605 --> 00:39:46,405
{\an1}the reaction produces
a trail of light
718
00:39:46,438 --> 00:39:49,405
{\an1}which the sensors can pick up.
719
00:39:49,438 --> 00:39:51,405
{\an1}Unlike Davis's detector,
720
00:39:51,438 --> 00:39:54,738
{\an1}this signal allows scientists
to calculate
721
00:39:54,771 --> 00:39:57,205
{\an1}which type of neutrino has hit
722
00:39:57,238 --> 00:39:59,105
{\an1}and the direction it came from.
723
00:39:59,138 --> 00:40:02,405
{\an1}Super-K allows scientists
724
00:40:02,438 --> 00:40:05,838
{\an1}to test the theory
of neutrino oscillation
725
00:40:05,871 --> 00:40:08,305
{\an1}by catching them from
a new source:
726
00:40:08,338 --> 00:40:10,038
{\an1}the Earth's atmosphere.
727
00:40:10,071 --> 00:40:12,805
♪ ♪
728
00:40:12,838 --> 00:40:15,505
{\an1}Theory suggests that
when radiation from space
729
00:40:15,538 --> 00:40:18,871
{\an1}hits the atmosphere,
it creates neutrinos
730
00:40:18,905 --> 00:40:23,238
{\an1}that travel directly through
the Earth.
731
00:40:23,271 --> 00:40:26,038
{\an1}Some travel a short distance,
732
00:40:26,071 --> 00:40:30,538
{\an1}but others will come from
the other side of the planet
733
00:40:30,571 --> 00:40:33,671
{\an1}to reach the detector.
734
00:40:33,705 --> 00:40:36,238
{\an1}If the neutrinos are not
changing,
735
00:40:36,271 --> 00:40:38,438
{\an1}the combination of flavors they
record
736
00:40:38,471 --> 00:40:41,071
{\an1}coming from a short distance
will be the same
737
00:40:41,105 --> 00:40:44,338
{\an1}as those coming from afar.
738
00:40:44,371 --> 00:40:47,805
{\an1}If they are changing over
a long distance,
739
00:40:47,838 --> 00:40:53,038
{\an1}the combination of flavors will
be different.
740
00:40:55,305 --> 00:40:58,138
After two years
of recording data,
741
00:40:58,171 --> 00:41:00,838
{\an1}the team finally has an answer.
742
00:41:02,905 --> 00:41:04,805
KARAGIORGI:
What they were seeing was that
743
00:41:04,838 --> 00:41:07,805
{\an1}one type of neutrinos was
depleting
744
00:41:07,838 --> 00:41:11,705
{\an1}when traveling through
the Earth.
745
00:41:11,738 --> 00:41:16,271
{\an1}The Super-K results combined
with results
746
00:41:16,305 --> 00:41:17,438
{\an1}from another experiment
747
00:41:17,471 --> 00:41:20,971
{\an1}were able to definitively show
748
00:41:21,005 --> 00:41:25,905
{\an1}that neutrinos can change
from one type to the other.
749
00:41:25,938 --> 00:41:28,438
{\an1}For that to happen,
750
00:41:28,471 --> 00:41:31,138
{\an1}you must have non-zero
neutrino mass.
751
00:41:31,171 --> 00:41:35,171
NARRATOR:
The results are groundbreaking.
752
00:41:35,205 --> 00:41:38,305
{\an1}Neutrinos change their identity.
753
00:41:38,338 --> 00:41:41,905
{\an1}Neutrinos have mass after all.
754
00:41:41,938 --> 00:41:43,805
{\an1}And the Standard Model's
prediction
755
00:41:43,838 --> 00:41:48,205
{\an1}of the nature of neutrinos
must be wrong.
756
00:41:48,238 --> 00:41:49,538
KAISER:
With the new input,
757
00:41:49,571 --> 00:41:52,071
{\an1}the evidence that neutrinos
really oscillate,
758
00:41:52,105 --> 00:41:53,571
{\an1}they really change their
identities,
759
00:41:53,605 --> 00:41:56,005
{\an1}therefore they really,
really have a mass,
760
00:41:56,038 --> 00:41:58,805
{\an1}this long-standing,
decades-long challenge
761
00:41:58,838 --> 00:42:00,381
{\an1}to understand the solar neutrino
problem
762
00:42:00,405 --> 00:42:04,205
{\an7}finally fell into place.
763
00:42:04,238 --> 00:42:06,705
{\an8}NARRATOR:
Nuclear fusion in the sun
764
00:42:06,738 --> 00:42:09,938
{\an7}produces one type of neutrino.
765
00:42:09,971 --> 00:42:12,905
{\an7}But on the long journey through
space,
766
00:42:12,938 --> 00:42:14,871
{\an7}the neutrinos oscillate,
767
00:42:14,905 --> 00:42:19,138
{\an7}and turn into a mixture of
all three.
768
00:42:19,171 --> 00:42:21,805
{\an8}On Earth,
769
00:42:21,838 --> 00:42:26,771
{\an7}Ray Davis's detector only
picked out one flavor.
770
00:42:26,805 --> 00:42:31,305
{\an7}His results had been accurate
all along.
771
00:42:34,605 --> 00:42:38,105
37 years after
the experiment began,
772
00:42:38,138 --> 00:42:40,471
{\an1}Ray Davis was awarded the
Nobel Prize.
773
00:42:40,505 --> 00:42:44,605
{\an1}(cheers and applause)
774
00:42:46,505 --> 00:42:50,238
{\an1}For Bruno Pontecorvo
and his theory of oscillations,
775
00:42:50,271 --> 00:42:54,705
{\an1}sadly, the discovery came
too late.
776
00:42:54,738 --> 00:42:56,438
CLOSE:
Nobel Prizes aren't everything,
777
00:42:56,471 --> 00:42:59,371
{\an1}but by the time the oscillations
had been sorted out
778
00:42:59,405 --> 00:43:01,871
{\an1}and the whole thing finally
understood,
779
00:43:01,905 --> 00:43:04,405
{\an1}Pontecorvo was dead.
780
00:43:04,438 --> 00:43:08,438
{\an1}So that's the final tragedy
of his life.
781
00:43:13,371 --> 00:43:17,571
NARRATOR:
After almost 100 years
of research and discovery,
782
00:43:17,605 --> 00:43:20,405
{\an1}today, neutrino physicists face
783
00:43:20,438 --> 00:43:23,138
{\an1}perhaps their biggest
puzzle yet.
784
00:43:23,171 --> 00:43:26,438
{\an1}The Standard Model's equations,
785
00:43:26,471 --> 00:43:29,271
{\an1}which are so precise for
other particles,
786
00:43:29,305 --> 00:43:35,205
{\an1}cannot explain why neutrinos
have mass or why they oscillate.
787
00:43:35,238 --> 00:43:37,405
{\an1}It's a sign that our
understanding of matter
788
00:43:37,438 --> 00:43:39,971
{\an1}is still incomplete.
789
00:43:40,005 --> 00:43:42,171
♪ ♪
790
00:43:42,205 --> 00:43:44,705
{\an1}Today, neutrino experiments are
in overdrive,
791
00:43:44,738 --> 00:43:46,505
{\an1}hunting for clues.
792
00:43:46,538 --> 00:43:48,571
KAISER:
We're in the midst of, really,
793
00:43:48,605 --> 00:43:51,338
{\an1}a neutrino bonanza... I mean,
they're just, they're popping up
794
00:43:51,371 --> 00:43:54,005
{\an1}all over the field of physics.
795
00:43:54,038 --> 00:43:55,838
♪ ♪
796
00:43:55,871 --> 00:43:57,171
NARRATOR:
At the South Pole,
797
00:43:57,205 --> 00:43:59,205
{\an1}scientists have built
798
00:43:59,238 --> 00:44:03,805
{\an1}the largest neutrino detector
on the planet.
799
00:44:03,838 --> 00:44:06,971
{\an1}It's made of more
than 5,000 sensors drilled into
800
00:44:07,005 --> 00:44:10,871
{\an1}a cubic kilometer
of Antarctic ice.
801
00:44:10,905 --> 00:44:13,371
{\an1}It's known as IceCube.
802
00:44:13,405 --> 00:44:15,971
♪ ♪
803
00:44:16,005 --> 00:44:17,405
KAEL HANSON:
IceCube is in this,
804
00:44:17,438 --> 00:44:18,814
{\an1}this huge field around me...
I'm sitting,
805
00:44:18,838 --> 00:44:22,671
{\an1}kind of standing in the middle
of IceCube.
806
00:44:22,705 --> 00:44:24,205
{\an7}It's kind of amazing to think
807
00:44:24,238 --> 00:44:26,871
{\an7}that we were able to haul
something like
808
00:44:26,905 --> 00:44:27,871
{\an7}five million pounds of cargo
809
00:44:27,905 --> 00:44:30,171
{\an1}down to the South Pole... this is
810
00:44:30,205 --> 00:44:32,571
instrumentation,
cables, drill equipment,
811
00:44:32,605 --> 00:44:34,605
fuel...
812
00:44:34,638 --> 00:44:39,671
NARRATOR:
As well as probing neutrino
oscillations,
813
00:44:39,705 --> 00:44:42,071
{\an1}IceCube acts like
a neutrino telescope,
814
00:44:42,105 --> 00:44:43,605
{\an1}catching cosmic neutrinos
815
00:44:43,638 --> 00:44:47,205
from billions
of light years away.
816
00:44:47,238 --> 00:44:48,638
{\an1}This is the universe that
has really
817
00:44:48,671 --> 00:44:51,371
{\an1}only been opened to our eyes
for the last 50 years.
818
00:44:51,405 --> 00:44:52,838
{\an8}♪ ♪
819
00:44:52,871 --> 00:44:56,071
{\an7}There's all kinds of discoveries
that are waiting out there.
820
00:44:57,171 --> 00:45:00,271
{\an8}NARRATOR:
With new experiments like
IceCube,
821
00:45:00,305 --> 00:45:04,005
{\an1}scientists believe that
neutrinos may reveal discoveries
822
00:45:04,038 --> 00:45:06,838
{\an1}beyond the Standard Model.
823
00:45:08,438 --> 00:45:09,938
{\an1}Neutrinos could even help unlock
824
00:45:09,971 --> 00:45:13,671
{\an1}one of the biggest mysteries
in physics today.
825
00:45:13,705 --> 00:45:15,338
♪ ♪
826
00:45:15,371 --> 00:45:18,371
{\an1}It seems that most of what
our universe is made of
827
00:45:18,405 --> 00:45:21,638
is missing.
828
00:45:22,938 --> 00:45:25,538
PEREZ:
The whole quest of
particle physics
829
00:45:25,571 --> 00:45:29,405
{\an1}is to explain the matter
contents of the universe.
830
00:45:29,438 --> 00:45:34,371
{\an1}And we seem to be doing
this phenomenally good job.
831
00:45:34,405 --> 00:45:36,114
{\an1}You crank through the math
of the Standard Model,
832
00:45:36,138 --> 00:45:38,905
{\an1}and everything makes sense.
833
00:45:38,938 --> 00:45:43,105
{\an7}And yet it only describes
some very small fraction
834
00:45:43,138 --> 00:45:45,071
{\an7}of what the universe is made
out of.
835
00:45:47,171 --> 00:45:50,438
NARRATOR:
Looking into space,
836
00:45:50,471 --> 00:45:53,438
{\an1}cosmologists can see
the gravitational influence
837
00:45:53,471 --> 00:45:57,938
{\an1}of a material that binds entire
galaxies together,
838
00:45:57,971 --> 00:46:03,171
{\an1}but that is completely invisible
to their detectors.
839
00:46:03,205 --> 00:46:07,205
Scientists call
this material dark matter,
840
00:46:07,238 --> 00:46:12,771
{\an1}because nothing in the Standard
Model can describe what it is.
841
00:46:12,805 --> 00:46:14,705
{\an1}And yet, it seems to be
842
00:46:14,738 --> 00:46:19,538
{\an1}what most of the matter
in the universe is made of.
843
00:46:19,571 --> 00:46:23,038
CLOSE:
The Standard Model is very good
at describing
844
00:46:23,071 --> 00:46:26,571
{\an7}about five percent
of the universe.
845
00:46:26,605 --> 00:46:29,338
{\an7}95% of the stuff is an utter,
complete mystery,
846
00:46:29,371 --> 00:46:32,605
{\an1}made of dark stuff, whether
it's dark matter or dark energy.
847
00:46:32,638 --> 00:46:36,071
{\an1}And what either of those are,
we don't know.
848
00:46:36,105 --> 00:46:38,271
{\an1}All we really know about
dark matter
849
00:46:38,305 --> 00:46:39,838
{\an1}is that it creates gravity,
850
00:46:39,871 --> 00:46:42,971
{\an1}but it's not interacting
with the instruments
851
00:46:43,005 --> 00:46:46,805
{\an1}that we have used to observe
the universe.
852
00:46:46,838 --> 00:46:49,038
KAISER:
Whatever is filling space,
853
00:46:49,071 --> 00:46:50,971
{\an7}much more of it than the
ordinary matter
854
00:46:51,005 --> 00:46:53,905
{\an8}that makes up us
and our planet and our stars,
855
00:46:53,938 --> 00:46:56,671
{\an8}it's some other,
other kind of particle.
856
00:46:56,705 --> 00:47:00,705
NARRATOR:
Whatever dark matter
particles are,
857
00:47:00,738 --> 00:47:06,338
{\an1}scientists must look beyond the
Standard Model to find them.
858
00:47:06,371 --> 00:47:10,571
{\an1}Neutrinos might be the key.
859
00:47:10,605 --> 00:47:16,305
♪ ♪
860
00:47:16,338 --> 00:47:19,471
{\an1}At Fermilab, for over 20 years,
861
00:47:19,505 --> 00:47:21,705
{\an1}scientists have been
investigating
862
00:47:21,738 --> 00:47:23,738
{\an1}neutrino oscillations.
863
00:47:23,771 --> 00:47:25,905
{\an1}What they've found
864
00:47:25,938 --> 00:47:28,105
doesn't add up.
865
00:47:28,138 --> 00:47:31,405
ZELLER:
The first observation
that something was amiss
866
00:47:31,438 --> 00:47:34,971
{\an1}was in the late 1990s.
867
00:47:35,005 --> 00:47:38,371
{\an7}Something we don't quite
understand is going on.
868
00:47:38,405 --> 00:47:40,805
{\an8}♪ ♪
869
00:47:40,838 --> 00:47:44,605
{\an8}NARRATOR:
At Fermilab, scientists fired
a beam of neutrinos
870
00:47:44,638 --> 00:47:48,605
{\an7}just 500 yards to their
detector.
871
00:47:48,638 --> 00:47:50,471
{\an7}Neutrinos oscillate too slowly
872
00:47:50,505 --> 00:47:52,205
{\an7}for the detector to see them
change
873
00:47:52,238 --> 00:47:54,805
{\an7}over such a short distance...
874
00:47:54,838 --> 00:47:58,705
{\an7}at least according to theory.
875
00:47:58,738 --> 00:48:01,571
{\an7}But the detectors saw
an increase in one type
876
00:48:01,605 --> 00:48:05,038
{\an8}of neutrinos.
877
00:48:05,071 --> 00:48:07,171
{\an7}Neutrinos seem to oscillate
faster
878
00:48:07,205 --> 00:48:11,071
{\an7}than is theoretically possible.
879
00:48:11,105 --> 00:48:12,838
{\an8}KARAGIORGI:
The strange thing
880
00:48:12,871 --> 00:48:18,738
{\an7}that we're seeing is that
neutrinos seem to be
881
00:48:18,771 --> 00:48:22,171
{\an7}changing from one type
to the other
882
00:48:22,205 --> 00:48:24,471
{\an7}much faster than expected.
883
00:48:24,505 --> 00:48:27,838
{\an1}In order for that to happen,
884
00:48:27,871 --> 00:48:29,871
{\an1}we think it's possible
885
00:48:29,905 --> 00:48:33,638
{\an1}that there are extra neutrinos
out there.
886
00:48:33,671 --> 00:48:36,171
NARRATOR:
In addition to the three flavors
of neutrino
887
00:48:36,205 --> 00:48:40,271
{\an1}that the Standard Model
describes,
888
00:48:40,305 --> 00:48:44,071
{\an1}there could be a fourth neutrino
that affects them,
889
00:48:44,105 --> 00:48:47,938
{\an1}making them oscillate faster.
890
00:48:47,971 --> 00:48:52,305
{\an1}Scientists call it
a sterile neutrino,
891
00:48:52,338 --> 00:48:55,871
{\an1}and it's never been directly
detected.
892
00:48:57,871 --> 00:49:00,405
PEREZ:
So we call it a sterile
neutrino,
893
00:49:00,438 --> 00:49:04,805
{\an1}in essence, just because it
interacts even less
894
00:49:04,838 --> 00:49:07,238
{\an1}with other particles than the
regular neutrinos do.
895
00:49:07,271 --> 00:49:09,105
♪ ♪
896
00:49:09,138 --> 00:49:13,738
NARRATOR:
A sterile neutrino would be
the ultimate ghost particle.
897
00:49:13,771 --> 00:49:16,871
{\an1}It would never collide with
atoms in our world.
898
00:49:16,905 --> 00:49:19,638
{\an1}No detector could ever see it.
899
00:49:19,671 --> 00:49:21,771
{\an1}But it may reveal itself
900
00:49:21,805 --> 00:49:26,071
{\an1}through its effects
on the neutrinos we can see.
901
00:49:26,105 --> 00:49:30,871
KARAGIORGI:
The only way that we can tell
they exist
902
00:49:30,905 --> 00:49:34,905
{\an1}is through their effects
on neutrino oscillation.
903
00:49:34,938 --> 00:49:38,605
NARRATOR:
If sterile neutrinos exist,
904
00:49:38,638 --> 00:49:42,038
{\an1}it would break the neat symmetry
of the Standard Model
905
00:49:42,071 --> 00:49:46,171
{\an1}that organizes particles
in groups of three.
906
00:49:46,205 --> 00:49:48,371
{\an1}What if there's a fourth kind
of neutrino,
907
00:49:48,405 --> 00:49:49,605
{\an1}a so-called sterile neutrino?
908
00:49:49,638 --> 00:49:53,138
{\an1}Well, where would you put
that on our map?
909
00:49:53,171 --> 00:49:55,571
{\an1}There's no room to kind of
shoehorn in,
910
00:49:55,605 --> 00:49:58,338
{\an1}to squeeze in a fourth neutrino.
911
00:49:58,371 --> 00:50:02,638
{\an1}So I think there really is a lot
riding on this.
912
00:50:02,671 --> 00:50:07,538
NARRATOR:
If they're real, sterile
neutrinos would have mass,
913
00:50:07,571 --> 00:50:09,938
{\an1}but not interact with our
detectors...
914
00:50:09,971 --> 00:50:13,171
{\an1}just like dark matter.
915
00:50:13,205 --> 00:50:17,938
{\an1}They could be the first particle
of dark matter ever discovered,
916
00:50:17,971 --> 00:50:21,538
{\an1}and through their effects on the
neutrinos we can see,
917
00:50:21,571 --> 00:50:26,705
{\an1}they could give scientists
a window into another world.
918
00:50:26,738 --> 00:50:29,605
KAISER:
The neutrino might be a kind
of link,
919
00:50:29,638 --> 00:50:31,805
{\an1}almost a kind of messenger
or portal
920
00:50:31,838 --> 00:50:35,138
{\an1}to this whole other possible
kind of stuff out there.
921
00:50:38,871 --> 00:50:44,905
NARRATOR:
At Fermilab, scientists
are edging towards the truth.
922
00:50:44,938 --> 00:50:47,438
ZELLER:
I think we're getting
a lot closer.
923
00:50:47,471 --> 00:50:49,738
{\an1}Neutrino physicists are
incredibly patient.
924
00:50:49,771 --> 00:50:52,505
{\an1}It takes a long time for us
to collect our data,
925
00:50:52,538 --> 00:50:55,438
{\an1}and we really want to be sure in
what we're seeing before
926
00:50:55,471 --> 00:50:59,405
{\an1}we potentially make
a very important discovery.
927
00:50:59,438 --> 00:51:01,371
{\an1}We're trying to answer
928
00:51:01,405 --> 00:51:03,538
{\an1}some of the biggest questions
in physics.
929
00:51:03,571 --> 00:51:05,538
{\an1}I think it's really unique
that neutrinos
930
00:51:05,571 --> 00:51:08,305
{\an1}may hold all the answers.
931
00:51:08,338 --> 00:51:10,271
NARRATOR:
What began as a
hypothetical particle
932
00:51:10,305 --> 00:51:13,705
{\an1}that no one thought possible
to detect
933
00:51:13,738 --> 00:51:15,738
{\an1}could now be a key that unlocks
934
00:51:15,771 --> 00:51:20,405
{\an1}what most of our universe
is made of and how it works.
935
00:51:23,005 --> 00:51:24,238
KAISER:
Every time we look up,
936
00:51:24,271 --> 00:51:27,071
{\an1}there seem to be these
very curious neutrinos.
937
00:51:27,105 --> 00:51:28,471
{\an1}They are constantly bedeviling
938
00:51:28,505 --> 00:51:31,305
{\an1}our mental maps of how we carve
up nature
939
00:51:31,338 --> 00:51:32,838
{\an1}and try to dig in and study it.
940
00:51:32,871 --> 00:51:35,205
And that's just
amazingly exciting.
941
00:51:35,238 --> 00:51:38,205
{\an1}So they've gone from, "Maybe
they exist, maybe they don't,
942
00:51:38,238 --> 00:51:39,905
{\an1}we might never know,"
943
00:51:39,938 --> 00:51:43,838
{\an1}to being our surest ticket
to the next step.
944
00:51:43,871 --> 00:51:45,838
KARAGIORGI:
History has shown that
945
00:51:45,871 --> 00:51:48,738
{\an1}with every little bit
of progress,
946
00:51:48,771 --> 00:51:53,438
{\an1}we've learned huge, surprising
things about our cosmos.
947
00:51:53,471 --> 00:51:55,605
{\an1}To me, that's really exciting.
948
00:51:55,638 --> 00:52:00,505
{\an1}And I'm curious to know, where
else could we go?
949
00:52:00,538 --> 00:52:02,805
NARRATOR:
Wherever we go,
950
00:52:02,838 --> 00:52:06,871
{\an1}neutrinos could be our guide.
951
00:52:13,971 --> 00:52:21,971
{\an8}♪ ♪
952
00:52:28,905 --> 00:52:33,971
{\an8}♪ ♪
953
00:52:34,005 --> 00:52:35,647
{\an8}ALOK PATEL:
Discover the science
behind the news
954
00:52:35,671 --> 00:52:37,538
{\an7}with the "NOVA Now" podcast.
955
00:52:37,571 --> 00:52:41,071
{\an7}Listen at pbs.org/novanowpodcast
956
00:52:41,105 --> 00:52:44,271
{\an7}or wherever you find your
favorite podcasts.
957
00:52:44,305 --> 00:52:48,238
{\an8}ANNOUNCER:
To order this program on DVD,
visit ShopPBS
958
00:52:48,271 --> 00:52:51,238
{\an7}or call 1-800-PLAY-PBS.
959
00:52:51,271 --> 00:52:54,138
{\an7}Episodes of "NOVA" are available
with Passport.
960
00:52:54,171 --> 00:52:57,938
{\an7}"NOVA" is also available on
Amazon Prime Video.
961
00:52:57,971 --> 00:53:02,238
{\an8}♪ ♪
962
00:53:12,038 --> 00:53:15,671
{\an8}♪ ♪
80400
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