The writer HG Wells, who first imagined time machines
and alien invasions, had a nightmare of a future world
where atoms were weaponized.
In his book called "The World Set Free", written in 1913,
he coined the phrase atomic bombs
and loosed them on helpless civilian populations.
He set his vision of a nuclear war between England and Germany
in the impossibly distant future of the 1950s.
[music playing]
[bomb exploding]
In 1933, the Hungarian physicist, Leo Szilard,
was contemplating becoming a biologist.
Dr. Szilard?
Are you quite all right in there?
NEIL DEGRASSE TYSON: He read Wells's novel,
and it started him thinking.
Szilard knew that atoms are made of protons and neutrons
on the inside and a skittering vale
of electrons on the outside.
Suddenly, while waiting for the light
to change at this intersection in London,
he was struck by the thought, if he could find a sufficiently
large amount of an element that would emit two neutrons
when it absorbed one, it would sustain
a nuclear chain reaction.
Two would produce four, four would produce eight, and so
forth, until enormous amounts of energy in the nucleus
itself could be liberated.
Not a chemical reaction, but a nuclear one.
[alarm wailing]
[bomb exploding]
[music playing]
This was the moment our world changed.
Leo Szilard also knew the power of exponentials,
and if a neutron chain reaction could be triggered down there
in the world of the atom's nucleus,
then something like Wells's imaginary atomic bomb
might be possible.
He shuddered at the thought of this destructive capability.
It was just the latest development
on a continuum of violence that began long, long before.
50,000 years ago, all humans were roving
bands of hunter-gatherers.
They communicated over limited areas
by calling to one another, that is, at the speed of sound,
around 750 miles per hour, but over longer distances,
they could communicate only as fast as they could run.
Around 12,000 years ago, about the same time as the invention
of agriculture, they developed the power
to kill at a longer distance.
The kill radius expanded to the arc of an arrow
launched by a bow, and they could kill
one person with a single arrow.
Our ancestors were not particularly warlike
because there were so few people and so much room
back then that moving on was preferable to armed conflict.
Their weapons were used almost entirely for hunting.
Their identification horizon was likely small,
only with the other members of their band of 50 or 100 people.
But their time horizon took a giant leap.
They worked long and hard planting crops
in the here and now, so several months
later, they could harvest them.
They postponed present gratification
for later advantage.
They began to plan for the future.