J. Robert Oppenheimer
might be the most important physicist
to have ever lived.
He never won a Nobel Prize,
but he changed the world more than most Nobel Prize winners.
Under his leadership,
the best physicists of the 20th century
built the atomic bomb
forever changing the course of history.
- If there is another world war,
this civilization may go under.
- [Derek] He has affected every war waged
and every peace settled since the end of World War ii.
He also created a way for humanity to destroy itself.
- Now I am become death,
the destroyer of worlds.
- [Derek] This video is about how to build an atomic bomb,
the life of Oppenheimer,
and why serious scientists were worried about the explosion
setting fire to the atmosphere,
ending all life on earth.
Part of this video is brought to you by Wren.
When J. Robert Oppenheimer was 21,
he placed an apple laced with toxic chemicals
on the desk of his physics tutor.
The tutor, Patrick Blackett,
was an experimentalist and he had hounded Robert
to do more of what he thought
Robert wasn't very good at, experimental work.
Oppenheimer had already been spending his days in a corner
of JJ Thompson's basement laboratory,
attempting to make thin films of beryllium,
which were used to study electrons.
But Oppenheimer was clumsy and not good at this work.
He was soon avoiding his duties in the lab,
spending his time listening to lectures
and reading physics journals.
It was 1925 and the 21 year old Oppenheimer was becoming
fascinated by the new field of quantum mechanics.
Despite being surrounded by brilliant physicists
like Rutherford and Chadwick,
Oppenheimer was deeply unhappy.
He wrote, "I'm having a pretty bad time.
The lab work is a terrible bore,
and I'm so bad at it that it's impossible to feel
that I'm learning anything."
A friend walked in on him,
lying on the floor of his room,
which he called "A miserable hole",
groaning and rolling from side to side in emotional anguish.
It was in this state that Robert
attempted to poison Blackett.
The specifics are lost to history.
There are conflicting reports if Oppenheimer used cyanide
or something he found in the lab,
which would've just made Blackett sick.
This story sounds unbelievable,
but Oppenheimer himself confirmed it.
Luckily, Blackett did not eat the apple,
but the attempted poisoning became known
to the Cambridge University authorities.
Robert's parents were visiting their son
from the US at the time,
and Julius Oppenheimer successfully lobbied Cambridge
not to press criminal charges. Due to his family's wealth,
Robert wasn't even expelled from Cambridge
on the condition that he had periodic counseling sessions
with a psychiatrist in London.
(train horn blaring)
In the summer of 1926,
Robert traveled to the University of Göttingen.
The chairman of the department was Max Born,
who just two years earlier had coined the term,
"Quantum Mechanics".
Born was reportedly a thoughtful and gentle teacher
and had nurtured the work of Werner Heisenberg,
Wolfgang Pauli, Enrico Fermi,
and Eugene Wigner,
basically the who's who of quantum mechanics.
The class that Oppenheimer was in was also extraordinary,
including luminaries like Paul Dirac and John Von Neumann,
where the academic culture at Cambridge focused on
experimental physics.
Göttingen was all about theoretical physics,
and under Max Born's mentorship,
Oppenheimer thrived.
His mental health improved,
and he found a community of people who were
as obsessed with physics as he was.
On November 14th, 1926,
Robert wrote to Frank, his younger brother,
"You would like Göttingen.
I find the work hard, thank God,
and almost pleasant."
Robert was thriving and his talent was being recognized.
Born later wrote,
"He was a man of great talent and he was conscious
of his superiority in a way which was embarrassing
and led to trouble."
When Oppenheimer was 23,
he graduated with his PhD in physics.
He wrote his thesis in German on the quantum theory
of continuous spectra.
All in all,
he published more than a dozen papers
in the two years he was at Göttingen.
Many of them expanded upon the work of Werner Heisenberg,
who was just three years older than Oppenheimer.
The two eventually met in 1927,
the same year Heisenberg published his groundbreaking paper
on the Quantum uncertainty principle.
By all accounts,
the pair got along well.
There was no way to know that just 15 years later,
they would be deadly rivals attempting to build
the first nuclear bomb.
Oppenheimer for the USA
and Heisenberg for Nazi Germany.
At the time,
it was thought that getting significant amounts of energy
out of radioactive atoms was impossible.
Ever since the discovery of radioactivity
by Henri Becquerel, Marie Curie,
and Pierre Curie in the late 1890s,
it was known that radioactivity was a passive process.
Unstable atoms would just decay at random,
unpredictable times,
and surely there was no way to control that.
In 1933, Ernest Rutherford,
Oppenheimer's old boss from Cambridge wrote that,
"Anyone who expects a source of power
from the transformations of these atoms
is talking moonshine."
That same year,
Albert Einstein said,
"That there is not the slightest indication
that nuclear energy will ever be obtainable.
It would mean that the atom
would have to be shattered at will."
So how would you break an atomic nucleus?
Well, you could take a proton
and accelerate it through a large electric field
and then smash it into a nucleus.
This is exactly what John Cockcroft
and Ernest Walton did in 1932.
They accelerated protons into lithium nuclei,
breaking them apart.
The pair would later win a Nobel Prize for this work,
but a proton is positively charged,
so it's repelled by all nuclei,
which are also positively charged.
So to give them a hope of overcoming this barrier,
Cockcroft and Walton had to use 250,000 volts
to accelerate the protons.
Even then, only about one in a billion protons
actually hit and split a lithium nucleus,
so this would not be an effective way to get energy.
But there is another way.
In 1932, the neutron was discovered
this subatomic particle that's about 0.1%
heavier than a proton,
and it has no electric charge,
so a neutron would not be repelled from a nucleus.
And in 1933,
Leo Szilard was thinking about how you could use neutrons
to split nuclei.
"It suddenly occurred to me that if we could find an element
which is split by neutrons and which would emit two neutrons
when it absorbed one neutron,
such an element if assembled sufficiently large mass,
could sustain a nuclear chain reaction."
But the thing is,
nobody knew if there was an element
that had a kind of nucleus that would do that.
On the 29th of January, 1939,
Louise Alvarez, a promising young physicist,
was getting a haircut while reading
"The San Francisco Chronicle",
and suddenly he got outta the chair
halfway through the haircut and ran to Oppenheimer's office.
Alvarez read an article about how two German chemists,
Otto Hahn and Fritz Strassmann
had successfully split an atom of uranium
by bombarding it with neutrons.
Oppenheimer was not impressed.
"That's impossible."
He reportedly told the Young Alvarez
proceeding to mathematically prove on his blackboard
why fission could never be achieved.
But the next day,
Alvarez had repeated the experiment
and invited Oppenheimer to see it.
Alvarez later recalled that,
"In less than 15 minutes,
he not only agreed that the reaction was authentic,
but also speculated that in the process,
extra neutrons would boil off.
That could be used to split more uranium atoms
and thereby generate power or make bombs."
When a single atom of uranium-235 splits apart,
it loses a little bit of mass,
which is released as energy.
Following Einstein's mass energy equivalence.
That is a tiny amount of energy,
about 20 times less than the amount required
to raise a grain of sand,
the thickness of a piece of paper.
But atoms are also tiny.
In a one kilogram lump of uranium,
there are about a trillion, trillion atoms,
so the energy quickly adds up.
Soon, almost everyone was convinced in August of 1939,
Einstein, who just six years earlier
believed that nuclear bombs were impossible,
signed his name to a letter
addressed to President Franklin Roosevelt.
The letter actually written by Szilard warned Roosevelt
of the possibility of nuclear weapons.
It also pointed out that Germany had access to uranium
from the mines in Czechoslovakia,
which was recently taken over by the Nazis.
Roosevelt began an informal uranium committee
to discuss this topic,
but then for two years, nothing happened.
In 1941, Roosevelt upgraded the informal
uranium committee to the S-1 committee,
which would report directly to the White House.
The explicit goal was to develop an atomic bomb,
and in May, 1942,
Oppenheimer was hired onto the committee
to be the coordinator of rapid rupture.
So why was he selected?
(dramatic music)
Well, after completing his PhD,
Oppenheimer became a physics professor,
first at UC Berkeley, and then at Caltech,
the brilliance he had shown
under Max Born's tutelage didn't fade.
Indeed, it blossomed into a remarkable
but strange physics career.
In the 15 years after finishing his PhD,
Oppenheimer made important contributions to everything from
nuclear physics to quantum field theory,
and even astrophysics.
He had a number of Nobel Prize winning ideas.
One of his students, Willis Lamb,
became a Nobel laureate,
but Oppenheimer himself was nominated three times,
but never actually won the Nobel Prize.
When asked why he thought that Oppenheimer
never won the Nobel Prize,
Murray Gell-Mann said that,
"He didn't have Sitzfleisch"
A German word that translates to sitting flesh.
The ability to sit down in a chair for a long time
and do the hard work.
"He never wrote a long paper or did a long calculation.
He didn't have the patience for that."
Wolfgang Pauli also said,
"His ideas are very good,
but his calculations are always wrong."
But Oppenheimer was amazing with people.
He was a natural and charismatic leader,
and this combination,
his charisma and his ability to generate great ideas
would serve him well in the next phase of his life.
(upbeat music)
On the 18th of September, 1942,
general Leslie Groves was put in charge
of the Manhattan Project.
- I was responsible for the development of the atomic bomb.
- [Derek] On day one, he ordered 1200 tons of uranium ore.
The next day,
he ordered to buy the Oak Ridge site
where the ore would be refined.
The next month in a surprising move,
he chose Oppenheimer to be the science director
of the soon to be established Los Alamos laboratory.
Oppenheimer had just been selected to be the chief architect
of the atomic bomb.
The military establishment had concerns.
Oppenheimer did not have a Nobel Prize,
so would the scientists hired for the project,
respect his opinion,
and follow his leadership?
Oppenheimer also had no prior administrative experience
over a large project like this.
Furthermore, he was a theoretical physicist,
who according to Isidor Rabi,
"Was a very impractical fellow.
He didn't know anything about equipment."
And then there was the problem
of Oppenheimer's political stance.
He had links to the Communist Party,
including his wife, Catherine,
who was a member of that party.
But Groves was impressed by Oppenheimer.
He valued his overwhelming ambition.
He also knew that Oppenheimer's ability to understand
problems not just in physics,
but chemistry, engineering,
and metallurgy would be invaluable.
Groves thought that Oppenheimer was a "Real genius."
Saying that why Oppenheimer knows about everything.
"He can talk to you about anything you bring up.
Well, not exactly.
He doesn't know anything about sports."
The two men couldn't have been more different.
Oppenheimer weighed half as much as Groves
despite both of them being nearly six feet tall.
Ideologically, Oppenheimer was a communist.
Groves, a staunch conservative,
but Groves was convinced that Oppenheimer
would be the person that would build the atomic bomb
before the Nazis,
and that was all that mattered.
Isador Rabi later commented that,
hiring Oppenheimer for this role was
"A real stroke of genius
on the part of General Groves,
who was not generally considered to be a genius."
The Manhattan Project needed a location.
Somewhere isolated to keep the project secret
safe from enemy attack.
And while no one wanted to admit it,
somewhere that was sparsely populated,
just in case there was an accident,
Oppenheimer proposed Los Alamos, New Mexico.
He had fallen in love with the harsh desert in the mountains
of New Mexico when he was in his twenties.
In 1929, Oppenheimer wrote to a friend.
"My two great loves are physics and New Mexico.
It's a pity they can't be combined."
But Oppenheimer had severely underestimated the logistical
challenge ahead.
(gentle music)
In 1943, Oppenheimer estimated
that he'd need about six scientists
supported by a handful of engineers
and technicians to make a bomb.
He was off by two orders of magnitude.
764 scientists would end up
working for the Manhattan Project.
302 of which would work at the Los Alamos site.
Over 600,000 people in total were involved
with the making of the atomic bomb.
By this point, making the atom bomb didn't seem impossible.
It seemed likely.
On the 2nd of December, 1942,
a team of physicists at the University of Chicago
led by Enrico Fermi created the world's
first artificial nuclear reactor Pile-1.
It consisted of 45 tons of uranium and uranium oxide
and 330 tons of graphite blocks.
Horrifyingly enough.
It was located under the stands of the football field.
It generated about half a watt of power,
and if you can make a nuclear power plant,
you can make a bomb.
The only real difference between the two
is how many neutrons hit the next atom,
causing it to split and release more neutrons.
If on average that number is one,
there will be a stable self-sustaining chain reaction,
but it won't grow.
If it's less than one,
the reaction will die down,
and if it's more than one,
the reaction will grow.
This is known as the multiplication factor, K.
Nuclear reactions are similar to pandemics in this way.
The simplest way to make a nuclear bomb
is to get enough fissile material close together
that it creates a runaway chain reaction.
That amount is known as the critical mass.
With uranium-235,
you need about 52 kilograms.
Forming a sphere with a diameter of 17 centimeters.
If you use plutonium-239,
the critical mass is much smaller,
only around 10 kilograms,
which would create a sphere only 10 centimeters wide.
For the first few years,
the scientists worked on a bomb with a gun type design.
Inside a gun type bomb,
you have two slabs of uranium-235,
both of which are below the critical mass.
Then using a conventional explosive like cordite,
you rapidly fire one towards the other.
So the combined mass is higher than the critical mass.
When the uranium bullet is about 25 centimeters away,
the nuclear chain reaction begins
resulting in an atomic explosion.
Despite the simple design,
it is not very efficient.
Only a small percentage of the uranium undergoes fission,
so the total yield of the bomb is much smaller.
You also run into some unexpected problems,
like how do you make sure the uranium
slides smoothly through the barrel?
Well, you use oil to lubricate the barrel,
but all the synthetic oils the scientists tried
would dry up.
In the end,
the only oil they could find that would work
was the oil from sperm whales.
Only about 0.7% of naturally occurring uranium is U235,
the fissile fuel for nuclear bombs.
When U235 absorbs a neutron,
it briefly becomes U236,
and then it rips itself roughly in half
and releases on average 2.4 neutrons per fission.
But when you get uranium outta the ground,
most of it is U238,
which doesn't undergo fission.
So to make a nuclear bomb,
the scientists use gigantic mass spectrometers
to separate out and concentrate the U235,
and the resulting substance was uranium
with a much higher concentration of U235.
In other words, it was enriched.
There was another option though.
In early 1941,
a new element was discovered or rather synthesized.
When a neutron is absorbed by a nucleus of uranium-238,
it turns into uranium-239.
U239 is unstable,
so it decays into Neptunium,
which then becomes plutonium.
There are three things that matter for this story.
First is that plutonium-239
is a great fuel for a nuclear bomb.
It has a critical mass of only about 10 kilograms.
Second, it is cheaper to make than to separate uranium-235
and third, it reacts too quickly
to be used in a gun type device.
It would fizzle,
meaning only a tiny fraction of the fuel
would undergo fission.
But there is a way to make a bomb using plutonium.
Critical mass changes depending on the density
of the material.
Under normal pressure conditions,
six kilograms of plutonium-239 won't explode.
But if you compress it,
the atoms get closer together and the chance of a stay
neutron hitting the nucleus increases.
So the higher the density, the lower the critical mass.
So if you set off conventional explosives
around a ball of plutonium,
you can get it compressed enough
to start a nuclear chain reaction.
And this was the whole idea behind
the implosion bomb design.
There are a couple ways to cheat lowering the critical mass.
For one thing,
you surround the sphere with a material that reflects
neutrons decreasing the amount of nuclear fuel
you need to start a chain reaction.
You can also have a neutron source,
something that kick starts the chain reaction.
For the first implosion bomb,
scientists created a device called the urchin,
which was a tiny pellet weighing just seven grams,
and it would sit at the heart of the bomb.
It was made of beryllium and polonium
separated by a layer of nickel and gold.
The idea was that when the explosives detonated,
the shockwave would mix the beryllium and polonium together,
and then the alpha particles from polonium
would cause the beryllium to release a flood of neutrons,
which would set off the nuclear chain reaction.
At least that was the hope.
An atomic bomb had never been made before.
Oppenheimer and the rest of the scientists at Los Alamos
needed to act quickly.
It was already 1945,
and Truman wanted to test the weapon
before the start of the Potsdam conference.
That's where Truman, Churchill,
and Stalin would come together to plan the post-war piece.
The conference began on the 17th of July.
The earliest date that everything could be ready
for the bomb was just one day earlier.
So that is when the test was scheduled.
It was Codenamed Trinity.
The night before Oppenheimer was nervous.
There were so many things that could go wrong.
The last test firing of the explosives
without the actual plutonium core was a failure.
To calm himself,
he recited a stanza from the Bhagavad Gita,
the sacred Hindu poem.
He had actually translated the Gita from the original
Sanskrit in himself.
In battle, in forest,
at the precipice in the mountains,
on the dark great sea,
in the midst of javelins
and arrows in sleep,
in confusion, in the depths of shame,
the good deeds a man has done before defend him.
Perhaps more terrifying than the idea of the bomb
not working was that it would work too well.
Around 1942, Oppenheimer discussed with Arthur Compton
a terrible possibility that a nuclear test
could end the world.
The worry was that the nuclear bomb
would create temperatures so hot that fusion would occur.
A tiny fraction of the atmosphere,
just one part in 2 million is hydrogen gas.
But the worry was that at high enough temperatures
and pressures that hydrogen could fuse to together
releasing energy,
this energy would fuse more hydrogen.
It could also break apart the hydrogen
from water vapor causing that to fuse as well.
That would release even more energy
causing yet more fusion until the entirety
of the Earth's atmosphere would become a giant fusion bomb.
Recalling his conversations with Oppenheimer in 1959,
Compton said, "Nor was this all that Oppenheimer feared.
The nitrogen in the air is also unstable,
though in less degree.
Might not it, too, be set off by an
atomic explosion in the atmosphere."
Most of the scientists quickly realized
how unlikely this scenario was,
and they continued on with the project,
so no one took the idea too seriously.
But the thought of starting a fusion reaction with a fission
weapon would become very important after the war.
(dramatic music)
The Trinity test was scheduled for 4:00 AM
but it was delayed due to a storm.
So at 5:29 and 21 seconds, the gadget,
the world's first nuclear bomb detonated,
the high explosive squeezed the core of plutonium inwards.
The shockwave mixed the beryllium and polonium
releasing a flood of neutrons.
The urchin worked.
It jump started the nuclear reaction,
and now there was no way to stop it.
Just six kilograms of plutonium created an explosion
that was equivalent to nearly 25,000 tons of TNT.
The New Mexico mountains were illuminated
brighter than in daytime.
The shockwave was felt from over 160 kilometers away.
The mushroom cloud rose to 12 kilometers into the sky.
It was so hot that the desert sand melted
into a glassy mineral, now known as trinitite.
Fortunately, the blast did not set fire to the atmosphere.
On August 6th, 1945,
the Boeing B29 Flying Fortress dropped little boy,
a gun type nuclear bomb with 64 kilograms
of enriched uranium.
The nitro cellulose ignited pushing the slugs
of uranium-235 together,
tipping it over its critical mass.
The blast from the explosion equivalent
to 15,000 tons of TNT,
killed nearly 70,000 people.
Another 70,000 would die from burns and radiation poisoning
in the following months.
Three days later,
an implosion type bomb, like the gadget,
was dropped on Nagasaki
killing an estimated 80,000 more people.
More than 95% of the 225,000 people killed
in the bombings of Hiroshima and Nagasaki were civilians.
Most were women and children.
In 1965, recalling the moments after the Trinity test,
Oppenheimer said that he thought of another verse
from the Ghita.
- He knew the world would not be the same.
Few people laughed,
few people cried.
Most people were silent.
I remembered the line from the Hindu scripture,
the (speaking foreign language).
The Vishnu is trying to persuade the prince
that he should do his duty
and to impress him takes on his multi-armed form and says,
'Now I am become death the destroyer of worlds.'
I suppose we all thought that one way or another.
- [Derek] After the war,
Oppenheimer was a national hero.
His portrait was on the cover of Time Magazine,
and he became a household name.
In 1947, he became the director
of the Institute of Advanced Study at Princeton.
He also became the chairman
of the General Advisory Committee,
where he became an advisor on nuclear weapons
related issues.
He used his position to argue for arms control.
(dramatic music)
In August, 1949,
the Soviet Union tested their first atomic weapon,
and the US military quickly decided
that the best course of action
was to develop a more powerful bomb.
The hydrogen bomb,
known as "The Super",
Oppenheimer was against the development
of The Super on ethical grounds
and the worry that it would start an arms race.
But Truman's administration pushed through,
and three years later, Ivy Mike,
the first hydrogen bomb was tested in the Marshall Islands.
It had a yield of 10.4 megatons of TNT.
That's 400 times more powerful than the Trinity test.
A hydrogen bomb is actually three bombs in one,
a conventional bomb, a fission bomb,
and a fusion bomb.
The conventional explosives trigger a fission reaction,
which increases the temperature and pressure
enough to fuse deuterium and tritium together,
releasing a huge amount of energy.
In 1961, the Soviet Union tested the Tsar Bomba,
the most powerful explosion ever detonated.
It was another five times more powerful than Ivy Mike
around 2000 times more powerful than Trinity.
This kind of arms race
was exactly what Oppenheimer had feared,
in part, due to his opposition to the hydrogen bomb.
And due to his calls to avert a nuclear arms race,
Oppenheimer was essentially put on trial
to revoke his security clearance.
He had been surveilled while he was working
for the Manhattan Project,
but that surveillance didn't stop after he left.
Many of the wiretaps were illegal and warrantless.
Oppenheimer was questioned about his ties
to the Communist Party,
including his affair with Gene Tatlock,
a Communist party member
while he was leading the Los Alamos lab.
He was essentially accused of treason and espionage.
In December, 1953,
Oppenheimer had his security clearance suspended.
His face now grim and in black and white
was once again on the cover of time.
His security hearings were international news.
In 1964, German playwright Heinar Kipphardt
wrote a play about Oppenheimer's life.
Oppenheimer was sent a copy of this script,
and he hated it so much that he threatened to sue.
He especially despised the final scene where the character
of Oppenheimer realizes the evil of his work.
And I quote,
"We have been doing the work of the devil."
To Oppenheimer, it was always more complicated than that.
- I think that it probably was assumed,
it certainly was always assumed at Los Alamos
that if the war were not over and not clearly
to be brought to a conclusion by the diplomatic means
this weapon would play a part.
At the time, the alternative,
the campaign of invasion was certainly much more terrible
for everyone concerned.
I think that Hiroshima was far more costly in life
and suffering inhumane than it needed to have been,
to have been an effective argument for ending the war.
This is easy to say after the fact.
- In 1965, he was asked about the recent proposal of talks
with the Soviet Union to halt the proliferation
of nuclear weapons,
and his response was,
"It should have been done the day after Trinity.
Later that same year, he was diagnosed with throat cancer.
He was a lifelong smoker,
and he died on the 18th of February, 1967 aged 62.
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