By most scientific accounts, the Universe began with the expansion of
an intensely hot and dense “something”—hotter than the cores of most
stars, denser than the nucleus of any atom. Precisely what that event
was is unknown, though it might have been nothing more than a quantum
fluctuation in a vacuum. Today’s leading scientists reason that in the
beginning—most likely between 10 and 15 billion years ago—a singularity
released an outward burst of pure, radiant energy.

     With time’s passage, the Universe cooled and thinned. That cooling is
noted in the film’s changing colors: bluish early on, gradually yielding to
reddishness later—scientifically, blue is hotter than red (despite artists
often depicting the opposite), and the movie remains faithful to technically
correct color throughout.

     The first hundred centuries saw radiation reign supreme. Space was
literally inundated with energetic photons of light, x rays and gamma rays
(in white). Eventually, as the fireball waned, elementary particles of
matter (black) emerged—not from magic, rather from the decay of pure
energy. At the start of this billion-year interval, radiation dominated, but by
its end matter was in firm control.

     What the movie depicts here are the primordial moments of the
Universe that are very much now over and done, perhaps never to occur
again. It is remarkable that science can model such events, which films
like this one help us visualize.

     With the march of time, the expanding Universe continued to grow
cooler, thinner, and darker. Hydrogen and helium atoms formed when
elementary particles, then less frenzied, bound together. About a billion
years later, the first stars and the cores of galaxies emerged when gravity
forced gargantuan numbers of atoms into much larger clumps. The
youthful Universe was probably stringy and lumpy, with huge filaments of
matter surrounding vast voids of emptiness.

     The movie’s scene has shifted from a submicroscopic view in Module 1
to a macroscopic view in Module 2. Now depicted is large-scale cosmic
structure.

     How the galaxies originated is not well known. The role played by dark
matter is theoretically unclear, and astronomers have been unable to find
evidence of galaxies in the act of formation. Most galaxies likely came
forth in the first few billion years, and many have continued changing ever
since. Details are sketchy since their youthful exuberance lays beyond the
reach of our best telescopes.

     Even when galaxies evolve, their changes are agonizingly slow, at least
compared to the duration of our civilization. Fortunately, movies can
speed those changes, portraying possible evolutionary scenarios—
including one now favored by most astronomers called “hierarchical
assembly” that gravitationally groups individual galaxies into great
clusters.

     Telescopes are time machines and astronomers are historians.
Looking out into space is equivalent to looking back into time. As we
observe the Universe, our view is delayed. That’s because the speed of
light is finite—it takes time for light to travel in space. As a result, by
probing objects far away we can reconstruct a picture of earlier times.
That’s what this movie attempts to do.

     What astronomers have found is that galaxies ruled much of the first
few billion years of the Universe—they were nearly everywhere.
Especially prominent among the earliest galaxies were the quasars—
extraordinary powerhouses of energy that lit up the far away and the long
ago. We now see them in their blazing youth, though only faintly since
they currently reside billions of light-years distant.

     At the heart of most galaxies lurk their “central engines”—probably
huge black holes that consume matter at prodigious rates. But before
swallowing sometimes whole stars, the violent environments surrounding
the holes launch huge jets of fast-moving gas. Such supermassive events
are alien to anything familiar to us now on or near Earth.

     The abnormal power and peculiar character of these mostly distant
cosmic objects imply that the Universe was once more robust than it is
today. The first few billion years must have been a tumultuous period,
quite unlike the more tranquil state surrounding us now in space and time.

     Galaxies and more galaxies continue to populate our movie’s view of
the adolescent Universe. Myriad stars were surely strewn throughout the
galaxies, but the galaxies themselves would have dominated the scene if
anyone could have been there to witness events unfolding.

     Spiral galaxies spanning a hundred-thousand light-years, with huge
“arms” emanating from near their cores. Comparably sized elliptical
galaxies shaped like gigantic footballs and elongated cigars. And irregular
galaxies, often dwarfed by their bigger cousins, with strange shapes
harking back to ancient events—leftovers that managed to avoid falling
into the full-fledged galaxies, or perhaps dregs remaining after dramatic
encounters among their bigger members.

     Evolutionary events likely created the many varied types of galaxies
seen in the nighttime sky. Whether those events were dictated by intrinsic
factors (such as black holes in galaxy cores), or environmental factors
beyond galaxies per se, is unknown. Galaxy research is among the most
exciting frontiers of science today.

     One kind of change widespread among the galaxies was enormous
collisions that greatly rearranged the spread of stars and gas within them.
Such mergers and acquisitions probably helped to develop the diverse
galaxies now residing close to us—including our own Milky Way in which
we live.

     Galaxies like our Milky Way are colossal disks, resembling double
sombreros clapped brim-to-brim. They are colossal for two gee-whiz
reasons: Even if you could run at the speed of light, it would take about a
hundred-thousand years to cross one such galaxy. And there are more
stars—about a hundred billion—in a single galaxy than all the people who
have ever lived on Earth.

     Rotation is the prime reason that spiral galaxies are not more
spherical. Their original shapes have been distorted not only by close
encounters with other nearby galaxies, but also by the spin of the
whole system of stars, gas, and dust comprising such galaxies. Rotation can
compete with gravity on large scales.

Stars are the most obvious members of any normal galaxy. And the
globular star clusters are among the richest of such star groups.
Inhabiting the halo regions around the edges of such galaxies, the
globulars are remnants of earlier times when galaxies originated. They
contain information about the age of galaxies, and probably hints and
clues about how the galaxies came to be.

     Don’t hesitate to pause the film midway through this module. Take a
close look at the grand and glorious spread of matter and radiation
throughout these magnificent galaxies, whose animations here are based
on real data. Spiral galaxies are among the most spectacular objects in
all of Nature—and we live in the suburbs of one of them.

     Within the disks of galaxies is where the action is today. There, the
“life cycle” of stars is played out. New stars emerge from stellar nurseries,
middle-aged stars mature by going about their daily business of shining,
and old stars die when their fuel runs out. Stars do pass through
developmental and evolutionary stages much like life itself, but in simpler
ways and over much, much longer timescales.

     The concept of stellar evolution well explains the odd array of stars and
stellar systems scattered throughout the Milky Way: Interstellar clouds
light-years across, gaseous nebulae that are signposts of star birth, bright
red, yellow, and blue stars, some that are giants, some dwarfs, and some
torn apart, all amid debris fields of star remnants that are markers of
stellar death.

     Stellar evolution enables astronomers to date a whole panoply of
stellar objects—from stars and nebulae, to pulsars and supernovae.
Without a theory of stellar evolution, we would witness a huge unrelated
zoo of objects strewn in space. With stellar evolution, we enjoy a more
powerful intellectual position, ordering each of them into a consistent
temporal sequence along an arrow of time.

     The Milky Way’s contents are all so active, so changing: The many
varying interrelationships among the diverse components of stellar and
interstellar matter in our galaxy compose nothing less than a “galactic
ecosystem”—an evolutionary posture nearly as intricate and delicate as
life in a tidal pool or a tropical forest.

     Although scientists know little about galaxies, by contrast they know
much about stars. One of the best understood aspects of stellar evolution
is the way that stars create heavy elements, such as carbon, nitrogen and
oxygen needed for life.

     Deep in the hearts of stars, lighter nuclei fuse into heavier nuclei.
Helium and carbon are easy for many stars to produce, but heavier
elements—like oxygen, silicon, and up thru iron—are made only in the
most massive stars. The biggest stars (much more massive than the Sun)
then explode at death, expelling those heavy elements into the
surrounding interstellar regions. Such supernovae are among the most
titanic events in all of Nature.

     In addition to the heavy elements, supernovae often leave behind
remnants of erstwhile stars. The ultimate end-states of stellar evolution
are truly bizarre, yet include some of the most fascinating objects actually
seen in space: Dense and white-hot dwarf stars the size of planets.
Denser and rapidly spinning neutron stars the size of cities. And even
smaller black holes which trap matter forever.

     On and on, the stellar evolutionary cycle churns, enriching and
fertilizing interstellar space with heavy elements that sow the seeds of
later-generation stars—as well as planets. Indeed, from the ashes of dead
stars come the origins of new ones. Without the heavy elements made
inside stars, both life on Earth and Earth itself would not exist.

     With only 5 minutes left in our 12-minute journey across the arrow of
time, the Sun finally emerges. Some 5 billion years ago, a galactic cloud
in the outskirts of the Milky Way began contracting—possibly the result of
chance, or perhaps in response to some larger trigger, such as the
concussion of an ancient supernova. The result was the origin of our star
and its attendant planets, including Earth.

     The birth of the planets and their mottled moons is a challenging,
as-yet unsolved problem. Most of our knowledge of the Solar System’s
formative stages comes from studies of galactic clouds, fallen meteorites,
and the Sun and Moon. In recent years, scientists have also gotten closer
views of the planets with robotic space probes, and have found alien
planets circling nearby stars.

     The Jovian planets—Jupiter, Saturn, Uranus, and Neptune—are
galactic frag-ments frozen in time. They are not massive enough to have
become stars, yet too massive to have condensed rocky surfaces. They
formed via gravitational infall, much like stars, and preserve the pristine
properties of the early Solar System.

     The smaller Terrestrial planets—Mercury, Venus, Earth, and Mars—
formed mostly by accreting myriad debris left over from the Sun’s
formation. They have evolved a great deal over billions of years, cooling
and crystallizing hard rocky surfaces while outgassing atmospheres and
sometimes oceans. At least one of these small planets spawned life.

     All signs point to an Earth that formed nearly 5 billion years ago.
Initially cold, our planet heated enough to melt completely, partly from
without because of intense asteroid bombardment but mostly from within
owing to serene radioactive decay. The result was a differentiated planet,
with hot metal at its core, volcanic basalt in its mantle, and a genuine hell
on its early surface.

     During its first billion years of existence, Earth’s interior evolved, its
crust solidified, and much of its atmosphere escaped. Change was initially
rampant, with energy flows surging on our young planet. Although that
change slowed thereafter, it produced mountain ranges, oceanic trenches,
and atmospheric rejuvenation. All this environmental change set the stage
for the origin of life.

     Theoretical insights and laboratory simulations suggest that life is a
logical result of known scientific principles operating among simple atoms
and molecules. The common chemical content pervading all life on Earth
is our best evidence that every living thing dates back to a single-celled
ancestor. Fossils imply that those first cells probably arose in Earth’s
soupy sea several billion years ago.

     However, the details of life’s origin—thought to be a natural
consequence of acids and bases interacting in an energy-rich
environment—are not yet in hand. A sizeable gulf separates the early
chemical evolution of life’s essential contents from the later biological
evolution of the first living cells.

     For the first few billion years, life remained starkly unicellular,
resembling the microscopic algae found today in backyard swimming
pools. Originally eking out a living by extracting energy from captured
organic chemicals in Earth’s primordial ocean, some life-forms eventually
began using energy from the Sun. Not for any known purpose or design,
talented single cells rather took advantage of chancy opportunities to
utilize sunlight directly. Nature selected those that could best survive and
therefore replicate, a hallmark of biological evolution.

     Photosynthesis—the most frequent chemical reaction on Earth
today—was perhaps the greatest single metabolic invention in history.
Fossils imply that it began some 3 billion years ago, at which time oxygen
slowly began accumulating in our atmosphere. Geology provides the
evidence with its reddish iron sediments.

     Complexifying advances were underway, yet none evident without a
micro-scope. Notably, symbiosis—the mutually beneficial union of different
organisms—granted some microbes a fuel-rich nucleated center about 2
billion years ago.

     All through this billion-year interval, and for much of the next billion
years as well, the living scene on Earth remained much the same. To be
sure, change was still at work on our planet: Oceanographic change,
meteorological change, geological change. But generation after countless
generation, life-forms remained unicellular and fragile, while bathed in a
watery environment.

     Much of life’s history on Earth is a long temporal sequence of
microscopic chemical entities erratically drifting through the ages so long
as to be measured in millions of millennia. Yet all of it—all of life ever
found, now alive or fossilized—shares the same basic composition.

     A mere two dozen building blocks—4 nucleotide bases and 20 (plus a
rare one) amino acids—combine to fashion genes and proteins in all of life
today. Despite the multitude of biological structures and their countless
functions in our fabulously rich biosphere, every single living thing ever to
have existed on Earth has apparently housed the same fundamental
makeup. Only the numbering and ordering of the basic acids and bases
distinguish a human from a mouse, a duck from a daisy, no matter how
complex life eventually became.

     Within a billion years of the present, unicellular life had already existed
on Earth for more than two billion years. Its basic cells had become ten
times larger, vastly more sophisticated, and perhaps more diverse
functionally. More advanced life was evolving from simple life, though
both coexisted as the movie animates.

     But that’s pretty much all there was to life a billion years ago. Primitive
oceanic life flourished, though not much else. No plants yet adorned the
landscape. No animals were crawling, swimming, or flying near the
surface. And, certainly, by no means were men and women even on the
evolutionary horizon.

     Cellular organization represents a distinct evolutionary advance. By a
billion years ago, specialized cells were communicating, sharing
resources, and working together as a team. Their collaboration led to a
dramatic rise in complexity—multicellular life.

     While chronicling the rich natural history of life on Earth, buried fossils
and mapped genomes record that life rather suddenly became enormously
varied and widespread around 500 million years ago. A rapid surge in
numbers and diversity of living organisms came forth—a population
explosion of the first magnitude.

     Fish swimming in the seas, plants coming ashore, amphibians quickly
following, birds taking to the sky—pervasive species throughout the
biosphere of land, sea, and air, but only within the past 10% of our planet’s
history. In turn, animals mastered the land hardly 200 million years ago—
with but 10 seconds to go in this movie. Mammals, mobility, stereoscopic
vision, hominids, bipedality, manual dexterity, intelligence, culture, civilization, technology, . . .

     . . . whereupon, when sentient beings reflect back on the grand
evolutionary worldview of the Universe that gave us life, we find that:

     In this 12-minute movie that captures all of cosmic history at the video
rate of 30 frames per second, Homo sapiens appear within the last frame
of the last second.