It's a sad but inescapable fact some of the greatest advances in science have come
from humanity's more destructive impulses.
German chemist, Fritz Haber for example, figured out how to fix nitrogen from the atmosphere
to create gigantic bombs, used to kill people in the World War I
But his technology was also used to make the world's first synthetic fertilizers, which revolutionized
how the world feeds itself.
Gunpowder, similarly, was discovered by ancient Chinese alchemists, but was developed by Europeans
who used it to conquer half of the world.
None of these is science's fault.
When we discovered powerful truths about the universe, it's up to us to decide how to use them
because they can either be boons to humanity or banes.
And there's probably no better example of this than the work done by The Manhattan Project,
the years-long multinational effort to develop an atomic bomb during World War II.
It took 2 billion dollars, roughly 25.8 billion of today's dollars, and a hundred percent of the smartest
chemists, physicists, and engineers in the US, UK, and Canada to develop and build four nuclear weapons.
First, "The Gadget", the test bomb that was detonated in the desert of New Mexico.
Second, "Little Boy", which was dropped on Hiroshima, Japan.
"Fat Man", dropped on Nagasaki, Japan.
And the fourth bomb, that was thankfully never used.
It's because of those bombs that we now live in a world, where humans have the wherewithal to destroy
ourselves, and every other living thing on the planet.
And though they effectively ended World War II, atomic bombs started the Cold War
which was almost fifty years of everybody walking around worried that they were going to be
incinerated at any moment.
But the Manhattan Project is responsible for humanity gaining a lot of information about the atom
and really quickly.
If it hadn't been for this top-secret bomb development program, all those physicists wouldn't have been able
to collaborate to make this science happened.
And it's science that we're still learning from today.
Before we invented atomic bombs, humans destroyed each other and each other's stuff using
conventional bombs, casings full of explosives like Trinitrotoluene — that's TNT or ammonium nitrate
or some cocktail of different explosive substances.
When they're detonated, conventional bombs release most of their energy in the form of a blast
a wave of super pressurised air, that moves out from around the bomb faster than the speed of sound
which is why they make that big booming sound.
After the initial blast, which might be accompanied by a fireball, depending on what the bomb is made of
a vacuum is created around the site of the explosion, and air rushes in to fill it, creating a blast wind
that sucks everything into the detonation site.
By comparison, an atomic bomb uses an unstable radioactive isotope of uranium or plutonium
as the explosive.
If you fire a single neutron at a single atom of one of those radioactive isotopes, it can split the atom
and shoot out other neutrons, which in turns, split neighbouring atoms, creating a chain reaction
of split atoms in a process called nuclear fission.
All of these happens in about one picosecond, and then an unbelievable amount of energy and heat is released.
The release is so powerful because it unleashes energy from the most powerful force known to physics:
The rightly named "Strong Force".
Strong Force is what holds an atom's nucleus together, pulling protons and neutrons close to one another,
but also keeping them from getting too close. It's a very tense dynamic kind of sub-atomic push and pull.
To give you an idea of what's it like when energy from this force is released,
one kilogram of nuclear fission fuel can release twenty million times more energy than a kilogram of TNT.
About 50% of the energy released in a nuclear detonation is a blast, like a conventional bomb
35% is released as heat, and about 15% is nuclear radiation, in the form of
gamma rays, neutrons, and alpha and beta particles.
The radioactive pulse emitted when an atomic bomb is detonated continues to linger
after a blast, in the form of nuclear fallout —
a kind of dust made up of unused and spent fuel that's begun the process of radioactive decay.
Until 1932, nobody knew that any of this was even possible.
That's when German-Jewish physicist, Leo Szilard first theorised that nuclear materials could be used
to create energy and a chain reaction much like a chemical chain reaction.
Mind you, this was six years before anyone even knew about fission, but Szilard thought that the key was
the neutron, which was just been discovered.
If you could get a neutron from one atom could be used to caused an energy producing reaction
in another atom releasing more neutrons that could generate more reactions.
And if the reaction was discovered that could free that first neutron, somebody can use it to create
a pretty flipping sweet bomb.
So Szilard used the idea to patent the world's first atomic bomb, not because he planned on
making one, but because if he had the patent for it, nobody else could make it.
Smart guy.
In 1936, Szilard turned his patent over to British goverment, so it could be classified under
British secrecy laws, to keep it out of the hands of the Nazis, who had come to power in Germany.
And like many others who became involved in developing the atomic bomb, Szilard would
later campaign feverishly against it ever being used.
But from the perspective of many scientists, particularly those who knew what life was like under the
Nazis and Italian fascists, not solving the scientific puzzle of nuclear fission was no longer an option.
Because by the time World War II broke out in Europe, Szilard's hunch that fission was possible,
had been proven by a team of physicists in Berlin.
So in 1939 influential physicists, including Szilard, Albert Einstein, who was Jewish and had
escaped Nazi Germany, and Enrico Fermi, who had just escaped fascist Italy with his Jewish wife
started pressing president Franklin Roosevelt to start an atomic research program before the Nazis solved
the puzzle first.
Roosevelt responded by bringing together the brightest minds in physics, chemistry, and engineering
to research how to make weapons out of uranium and plutonium,
an element that doesn't occur in nature but can be made from uranium-238.
It became known as the Uranium Committee.
A lot of the most impressive and difficult science that we associate with what'd later be known as
The Manhattan Project was actually done by this committee, which included both military and civilian types
including Nobel Laureates, Ernest Lawrence, Harold Urey, and Arthur Compton.
And at first nobody was even trying to make a bomb.
They were just trying to figure out how to isolate enough of the right kind of uranium to create the chain reaction
that Szilard had envisioned.
Because the problem is, that most of the world's uranium doesn't come out of the ground,
ready to be made into a nuclear weapon, actually that does not sound like a problem to me
That sounds like a good thing.
Naturally occurring uranium is actually a mixture of two isotopes, or forms of uranium with different
numbers of neutrons in their nuclei: uranium-235 and uranium-238.
Because they have different numbers of neutrons in their nuclei, they respond differently to having a neutron
shot at them. Uranium-235 will bump up to uranium-236, which is really unstable, and will therefore undergo
fission a lot more readily than uranium-238, which just absorbs that extra neutron, and becomes uranium-239
which is super stable and not fissile at all.
So most of the time and money involved in the community research was spent figuring out how to
enrich uranium, that is how to separate the uranium-235, which makes up less than one percent of the world's
natural uranium, from the uranium-238.
The community eventually discovered that this could be done by combining uranium with fluorine to form a gas
that could be filtered to extract the isotope that they wanted.
But then, they had to figure out how much uranium-235 was needed to achieve critical mass.
The smallest amount of fissile material necessary to sustain a nuclear chain reaction
After that, they just had to figure out how fast a neutron had to be fired at the uranium atom to trigger a reaction
None of this research was easy, as you could imagine. But the physicists succeeded in answering all those
questions over the course of just a couple of years.
By 1942, with these early puzzles solved, the project was turned over to the United States Army Corps of engineers,
and move to facilities given the codename Manhattan District.
The research actually continued at three labs at separate regions of the country, one in Oak Ridge, Tennessee;
one in Los Alamos, New Mexico; and another near Richland, Washington.
As the labs worked on enriching fuels and basically inventing a whole new technologies to go inside the bombs,
the project eventually came together at Los Alamos, where young American physicist,
Robert Oppenheimer with the magnificent title Coordinator of Rapid Rupture oversaw the bomb-making
operation itself.
And Los Alamos actually made two such devices, one fueled by uranium, and the other by plutonium
The very first bomb, The Gadget, was a plutonium fuelled bomb that was detonated in the desert in
Southern New Mexico, in July 16th of 1945, in an event codenamed Trinity, was the very first atomic explosion
ever to occur on earth.
When it went off in early morning, observers ten miles away immediately felt the heat of the blast and said that
it was brighter than the sunrise.
The test was a complete success, but afterwards, Oppenheimer famously said it brought to mind
the passage from Hindu scripture.
I remembered the line from the Hindu scripture, the Bhagavad-Gita
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."
We all know what happened next,
within a month of that test, the plutonium bomb was dropped on Nagasaki,
and the uranium bomb on Hiroshima,
killing at least 185,000 people.
Soon, the war was over and the Atomic Age was beginning, a time when if you wanted to,
you could spend every second of your day worrying about whether the world was going to get blown up
by people who happened to have gotten their hands on a whole bunch of enriched uranium.
It also held the beginning of the Cold War, a period of about 50 years,
in which the United States and the USSR had nuclear warheads pointed at each other
all the time, everyday. It was terrifying and very tense.
But the research done during the Manhattan Project was huge in helping develop nuclear energy,
which has had its ups and downs.
But it's incredible technology nevertheless.
We also have the Manhattan Project to thank for the entire field of nuclear medicine,
where radioactive materials are used in medical imaging, diagnosis and treatments, like for some kinds of cancer.
Even modern stem cell research has its roots in the Manhattan Project.
And of course, the new understandings of the atom that we obtained in just a few short years
brought about enormous advances in nuclear chemistry and nuclear physics,
the might otherwise have taken generations.
Basically in the 1930s and 40s we did the impossible.
We took the smallest, most seemingly indivisible particle in the universe,
and we found a way to split it.
Also, we could make the worst weapon we ever imagined.
But we've used that knowledge for a lot of goods since then
so i think the take-home here is:
Science can be complicated,
but so can history.
Thank you for watching this possibly frightening, hopefully enlightening episode of SciShow.
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