Cosmic Dawn & Cosmic Questions‏

COSMIC QUESTIONS

National Geographic

http://www.nationalgeographic.com/cosmic-dawn/questions-index.html

[To see the graphics and illustrations 

of this exposition on our Cosmos

go to the direction indicated above.  

The following text

is the transcript of that presentation.

In the 20th century the universe 

became a story—a scientific one. 

It had always been seen as static and eternal. 

Then astronomers observed 

other galaxies flying away from ours, 

and Einstein’s general relativity theory 

implied space itself was expanding

—which meant the universe 

had once been denser. 

What had seemed eternal now 

had a beginning and an end. 

But what beginning? 

What end? 

Those questions are still open.

HOW DID OUR UNIVERSE BEGIN?

Some 13.8 billion years ago 

our entire visible universe 

was contained in an 

unimaginably hot, dense point, 

a billionth the size of a nuclear particle. 

Since then it has expanded

—a lot—fighting gravity all the way.

INFLATION

In far less than a nanosecond 

a repulsive energy field inflates space 

to visible size and fills it with a soup 

of subatomic particles called quarks.

AGE: 10ˆ-32 MILLISECONDS

SIZE: INFINITESIMAL TO GOLF BALL

---

EARLY BUILDING BLOCKS

The universe expands, cools. 

Quarks clump into protons and neutrons, 

the building blocks of atomic nuclei. 

Perhaps dark matter forms.

AGE:    .01 MILLISECONDS

SIZE:  0.1-TRILLIONTH PRESENT SIZE

--

FIRST NUCLEI

As the universe continues to cool, 

the lightest nuclei, 

of hydrogen and helium, arise. 

A thick fog of particles blocks all light.

AGE:     .01 TO 200 SECONDS

SIZE:   1-BILLIONTH PRESENT SIZE

---

FIRST ATOMS, FIRST LIGHT

As electrons begin orbiting nuclei, creating atoms, 

the glow from our infant universe is unveiled. 

This light is as far back as our instruments can see.

AGE:    380,000 YEARS

SIZE:    .0009 PRESENT SIZE

--

THE “DARK AGES”

For 300 million years 

this cosmic background radiation 

is the only light. Clumps of matter 

that will become galaxies glow brightest.

AGE:   380,000 TO 300 MILLION YEARS

SIZE:    .0009 TO 0.1 PRESENT SIZE

___

GRAVITY WINS: FIRST STARS

Dense gas clouds collapse under their own gravity

—and that of dark matter—to eventually form galaxies and stars. 

Nuclear fusion lights up the stars.

AGE:   300 MILLION YEARS

SIZE:   0.1 PRESENT SIZE

--

ANTIGRAVITY WINS

After being slowed for billions of years by gravity, 

cosmic expansion accelerates again. 

The culprit: dark energy. Its nature: unclear.

AGE:  10 BILLION YEARS

SIZE:   .77 PRESENT SIZE

TODAY

The universe continues to expand, 

becoming ever less dense. As a result, 

fewer new stars and galaxies are forming.

AGE:     13.8 BILLION YEARS

SIZZE:  PRESENT SIZE

HOW WILL IT END?

Which will win in the end, gravity or antigravity? 

Is the density of matter enough for gravity 

to halt or even reverse cosmic expansion, 

leading to a big crunch? 

It seems unlikely—especially 

given the power of dark energy, 

a kind of antigravity. 

Perhaps the acceleration in expansion 

caused by dark energy will trigger a big rip 

that shreds everything, from galaxies to atoms. 

If not, the universe may expand 

for hundreds of billions of years, 

long after all stars have died.

WHAT IS OUR UNIVERSE MADE OF?

Stars, dust, and gas

—the stuff we can discern—

make up less than 5 percent of the universe. 

Their gravity can’t account 

for how galaxies hold together. 

Scientists figure about 

24 percent of the universe 

is a mysterious dark matter

—perhaps exotic particles 

formed right after inflation. 

The rest is dark energy: 

an unknown energy field 

or property of space 

that counteracts gravity, 

providing an explanation 

for observations that 

the expansion of space 

is accelerating.

The Universe

Dark energy 71.5%

Dark matter 24%

Gas 4%

Planets and stars 0.5%

WHAT IS THE SHAPE OF OUR UNIVERSE?

Einstein discovered 

that a star’s gravity 

curves space around it. 

But is the whole universe curved? 

Might space close up on itself 

like a sphere or curve the other way, 

opening out like a saddle? 

By studying 

cosmic background radiation, 

scientists have found 

that the universe 

is poised between the two: 

just dense enough 

with just enough gravity 

to be almost perfectly flat, 

at least the part we can see. 

What lies beyond we can’t know.

Observable Universe

The universe began 13.8 billion years ago. 

Because it has been expanding ever since, 

the farthest observable edge 

is now 47 billion light-years away.

The Unknown Beyond

What we can’t see. 

The possible shapes are:

Sphere    Saddle     Flat

DO WE LIVE IN A MULTIVERSE?

What came before the big bang? 

Maybe other big bangs. 

The uncertainty principle holds 

that even the vacuum of space 

has quantum energy fluctuations. 

Inflation theory says 

our universe exploded 

from such a fluctuation

—a random event that, odds are, 

had happened many times before. 

Our cosmos may be one

in a sea of others just like ours

—or nothing like ours. 

These other cosmos 

will very likely remain forever 

inaccessible to observation, 

their possibilities limited 

only by our imagination.