[bomb exploding]
- I'm a historian of nuclear weapons.
[bomb exploding]
And today I'm here to talk about the science
behind Oppenheimer.
[upbeat music]
So that's a scene of them assembling the gadget.
This is clearly based on some pictures that have come out,
and they're not a ton of pictures
showing this level of assembly
that have been declassified and released.
All the pictures we have of this are black and white.
The people who actually saw it described it
as being a sort of peach colored, a sort of tan colored.
Each of those wedges are several layers of high explosive.
So there are sort of variants of TNT
called explosive lenses, and they are putting them
around the plutonium sphere that powers the whole thing.
This is about the size of a grapefruit
So plutonium's solid metal.
Imagine you had a piece of steel and I said,
push it on all sides to make it smaller.
You need to shrink it by half its size
exactly symmetrically.
Each of these are the detonators.
When they all go off,
they're gonna start a shockwave through this device.
It's gonna start going in, in, in.
Inside that little sphere of plutonium
is an even tinier sphere of polonium and beryllium.
This thing, if you compress it, will shoot out some neutrons
that's meant to just start the reaction.
You push the whole thing together
and make an atomic bomb explode.
This is called implosion.
One of the things we see in the movie
is the final assembly of the gadget.
This is based on actual footage that was taken at the time.
Even the lighting looks like
in the historic footage that we have.
This is a hundred foot tower.
They have brought the explosive sphere
out to the test site by the tower
and they put a big tent around it.
You need this thing to be as controlled as possible.
If you got a pebble in there, it could deform the shock wave
by just enough to make the whole thing either not work
or not work very well.
So they want this to be a very pristine sort of environment,
which is hard to do when you're in the middle of the desert.
They're putting in in this scene
what's called the tamper plug.
The goal is to have this sit right around the plutonium core
in the middle of the bomb.
This is a delicate operation.
This tamper plug arguably is worth $400 million
in 1945 money.
They don't wanna mess this up,
because once you put the plutonium in there,
every little step of getting it closer to being a bomb
makes it a little bit more dangerous to be around
and radioactively, you know, problematic.
This core is like on the edge of being explosive.
It's also radioactive, it's also hot.
Plutonium in that quantity is so radioactive
that it's about 80 degrees Fahrenheit.
They're dropping it through the center of the bomb.
They've made a sort of trap door basically
into the bomb so that the lens on top can come out.
You can drop this thing in.
In real life, they went to put it in and it didn't fit.
Oh my God, have we totally messed this up?
Wait a minute, wait a minute.
It had to be the right temperature for it to fit.
The outer part was cooler than the inner part was,
and so they had to wait for them
to reach the same temperature,
and then it just slid into place.
So there had to be one person left in the tower
to set it all up at the very end, stay with the bomb,
do the final connections, and then head back.
And this was, of course, a very stressful job.
They had previous mock-ups
that were set off by lightning in the distance,
so they were in a very precarious state here.
There's a scene before the actual Trinity test
where General Groves is asking Oppenheimer
about the possibility of this test destroying the world.
- [Groves] There's a chance that when we push that button,
we destroy the world?
- One of the real concerns was this problem
of what they called atmospheric ignition.
What if the nitrogen and oxygen in the atmosphere
fuse together and release energy?
Could they release enough energy
that that would trigger more nuclear fusion
that then goes over the entire globe
and leaves at a burnt horrible cinder?
Turns out that kind of equation is really hard to do,
but let's imagine that it's like 100 times easier
than we think it is.
We can sort of make very conservative extrapolations
and we find it's probably not gonna happen.
- Chances are near zero.
- Near zero.
- What do you want from theory alone?
- Oppenheimer is giving the correct scientist's answer.
They basically concluded
it would be less than one in 3 million, something like that.
In the 1970s, weapon scientists redid those calculations.
Could you set the earth on fire if you wanted to?
Yes, but you need bombs
that would be hundreds of thousands of times
more explosive than any bombs we ever made.
And you'd need to have a much higher proportion
of the ocean be made out of a rare isotope called deuterium,
a different type of hydrogen.
If you had this, you could indeed turn the earth into a sun.
The detonation took place very late at night.
They wanted to see exactly how bright it was,
and it's gonna be harder to see that in the daytime
when you're competing with the actual sun.
They actually had recommended
that the bombs be dropped on Japan at night
because they would be more psychologically stunning.
But for logistical reasons,
they were dropped in the morning on both of the cities.
So those numbers you see are nixie tubes.
Those are a pre-digital way to display numbers.
It's a very nice period-appropriate touch.
So at this point, the gadget, as they called it,
is fully assembled.
You can tell that because the wires are sticking out the top
on the front, that's called the X Unit,
that's the firing unit, it's assembled.
To set off this kind of bomb,
you have to send a high voltage electrical signal
to 32 separate places at exactly the same time.
Nanosecond tolerances on the timing to have it work right.
And then they have a wire
going all the way back to base camp.
And if you hit the big button on the wire.
- Detonator charged.
- [Alex] You're telling the bomb,
go ahead and explode, and it will.
[nuke exploding]
In the movie Oppenheimer,
the Trinity test is one of the climax moments.
It's ridiculously bright,
much, much brighter than the actual sun.
What Oppenheimer's putting on here are welding goggles,
and these are so dark
that you really can't see anything in them
except something that is as bright as the sun.
There were a few people at the Trinity Test
who'd looked at the explosion
without anything over their eyes.
One of them, by accident, he dropped his goggles,
and one of them on purpose.
They both suffered from what was called flash blindness,
temporary blindness.
You'll see a big dark spot
over your vision for quite some time.
There were people who were relatively close,
thousands of yards.
Oppenheimer in the sort of control bunker,
much closer than a lot of the outlying ones.
Most of the people that were instructed to lay down
away from the blast so that they don't turn around
and either get knocked over or get a face full of dust.
So the Trinity test was heavily, heavily documented
both by pressure gauges and cameras
with telephoto lenses from a very far distance,
but some of them were closer in bunkers.
Anytime you see a closeup
and it's sort of like a wall of fire,
there are shots from the actual Trinity test
that looked pretty similar to that.
Interestingly, on some of the very earliest shots
where they were trying to get
the very first moments of the fireball,
it was hot enough that it burned holes in the film.
This particular shot is interesting
because this is what they call in the business a rope trick.
And they only show up when you can take pictures
that are 1,000 frames per second or something like this.
You have a tower with a bomb on it
and it's got wires stabilizing the tower,
and there's a little tendril of the fireball
that's going faster than the rest
because it's blowing up the wire as it goes down there.
No one at Trinity could have actually seen this.
What you're seeing here is the complex interaction
that happens when the blast wave hits the ground,
goes straight down, bounces back up,
and then intersects with that blast wave coming out.
There's a really big difference
in how the blast wave behaves
from a bomb that's right on the ground
from one that's a little bit in the air.
They want this, what's called the mach stem,
to have a wide area of destruction.
That's how you maximize the blast pressure,
detonating very high above the ground.
They're gonna use that data
to set the altitude of the atomic bomb over Japan.
When they went into the Trinity test,
their sort of best guess
was it would maybe be 4,000 tons of TNT.
It ended up being more powerful than they thought
by a factor of like 5, 20,000 tons of TNT equivalent.
This is enough to destroy a sort of medium-sized city.
If you're a much bigger city, like say New York City,
it's enough to destroy like Midtown.
So this is one of the reasons why Trinity is so important.
It's not just it works.
They find out it works really well.
So the Manhattan Project is this gigantic endeavor.
It's this massive industrial project
and employs like 500,000 people.
It's like 1% of the civilian labor force,
and it cost like $2 billion in their money,
which is like 1% of the whole cost of World War II.
They use 1% of all the electricity in the country
to make these weapons.
They're building an industry in like two and a half years,
and the output of that industry
is a very tiny amount of material.
A 6 kilogram plutonium core, 13.5 pounds,
that's the one they first test at Trinity.
About 64 kilograms, so about 120 something pounds
of highly enriched uranium, uranium 235,
that's for the bomb that's gonna be dropped on Hiroshima.
And then they have one more plutonium core.
That's the one they're gonna end up dropping on Nagasaki.
So all of that effort
is to make these three cores for the bombs.
And they had one more bomb in the pipeline.
They ended up never sending it, the war ended.
Many of these people talked about this
as the best years of their life in some ways.
They had a lot of fun,
and some of them felt quite guilty about that
after Hiroshima and Nagasaki.
Oppenheimer's a really complicated character.
What he said he regretted was that after World War II,
they continued to make more weapons
and they continued to make bigger weapons
and they continued to make the kind of world
that he thought would ultimately put
civilization itself in danger.
- In the years to come,
it will be possible to kill 40 million American people
by the use of atomic bombs in a single night.
- [Alex] He knew in 1945 that there were ideas on the table
for bombs that would be thousands of times more powerful,
and that the nations of the world
could all get them if they wanted them,
and that a war with bombs of that big
could be fatal for the entire species.
And so that's the sort of paradox of Oppenheimer,
this person who wants peace, but he does it through war.