- [Narrator] The universe is everything.
From the tiniest particles,
to the largest galaxies,
to the very existence of space, time, and life.
But how did it all begin?
The origin of the universe is the origin of everything.
Multiple scientific theories
plus creation myths from around the world
have tried to explain its mysterious genesis.
However, the most widely accepted explanation
is the Big Bang theory.
The Big Bang theory states that the universe began
as a hot and infinitely dense point.
Only a few millimeters wide, it was similar
to a supercharged black hole.
About 13.7 billion years ago
this tiny singularity violently exploded.
And it is from this explosion, this bang,
that all matter, energy, space, and time were created.
What happened next were two major stages
of the universe's evolution.
Called the radiation and matter eras,
they're defined by key events
that helped shape the universe.
First came the radiation era,
named for the dominance of radiation
right after the Big Bang.
This era is made of smaller stages call epochs
that occurred within the universe's
first tens of thousands of years.
The earliest is the Planck epoch.
No matter existed in the universe at this time,
only energy and the ancestor
to the four forces of nature, the superforce.
At the end of this stage, however,
a key event occurred in which gravity
split away from the superforce.
Next came the grand unification epoch,
named for the three remaining unified forces of nature.
This epoch ended when one of those forces,
called strong, or strong nuclear, broke away.
Then the inflationary epoch began
during which the universe rapidly expanded.
Almost instantly it grew from the size of an atom
to the size of a grapefruit.
The universe at this time was piping hot
and it churned with electrons, quarks, and other particles.
Then came the electroweak epoch,
when the last two forces, electromagnetic and weak,
finally split off.
During the next stage, the quark epoch,
all of the universe's ingredients were present,
however, the universe was still too hot and dense
for subatomic particles to form.
Then, in the hadron epoch, the universe cooled down enough
for quarks to bind together and form protons and neutrons.
In the lepton and nuclear epics,
the radiation era's last two stages,
the protons and neutrons underwent a significant change.
They fused and created nuclei.
And in doing so, they created the first
chemical element in the universe, helium.
The universe's new ability to form elements,
the building blocks of matter,
queued the matter era.
Much as the name suggests, the matter era's defined
by the presence and predominance
of matter in the universe.
It features three epochs that span billions of years.
The vast majority of the universe's life span,
and includes the present day.
The first was the atomic epoch.
In this stage, the universe's temperature
cooled down enough for electrons
to attach to nuclei for the first time.
Called recombination, this process helped create
the universe's second element, hydrogen.
This hydrogen, along with helium atoms,
dotted the universe with atomic clouds.
Within the clouds, small pockets of gas
may have had enough gravity to cause atoms to collect.
These clusters of atoms, formed during the galactic epoch,
became the seedlings of galaxies.
Nestled inside those galaxies, stars began to form.
And in doing so, they queued the latest
and current stage of the universe's development,
the stellar epoch.
The formation of stars then caused
a tremendous ripple effect
and helped shape the universe as we know it.
Heat within the stars caused the conversion
of helium and hydrogen into almost all
the remaining elements in the universe.
In turn, those elements became the building blocks
for planets, moons, life,
everything we see today.
This ecosystem of everything was only possible
because of the many stages in the universe's development.
While countless questions about the origins
of our universe remain, it's only a matter of time
for some long-sought answers to emerge.