Cosmos

Resync by manugutito

The dream of becoming a citizen of the cosmos

was born here, more than two millennia ago,

in the city of Alexandria,

named after and conceived by its dead conqueror,

Alexander the Great.

The Ptolemys, the Greek kings

who inherited the Egyptian portion of Alexander's empire,

built this library

and its associated research institution.

Rarely, if ever,

before or since,

has there been a government that was willing to spend

so much of its gross national product

on the acquisition of knowledge.

And it paid off.

Big time.

Every ship entering Alexandria's harbor

was searched-- not for contraband,

but for books that might be copied and stored here,

in what was then the greatest library on Earth.

Here, Eratosthenes, one of the chief librarians,

accurately calculated the size of the Earth

and invented geography.

Pythagoras.

Hypatia.

Euclid.

Euclid set forth the precepts of geometry

in a textbook that remained in use for 2,300 years.

The Old Testament Bible comes down to us

mainly from the Greek translations made here.

The original manuscripts of the masterpieces

of Greek comedy and drama, poetry,

science, engineering,

medicine and history--

the total work product

of the awakening of ancient civilization-- were kept here.

Estimates vary on the total number of scrolls.

They range from 500,000

to nearly a million.

And all of it...

all of this

is but a tiny fraction of the information

that you have at your fingertips at this very moment.

The collective knowledge of our species,

our own electronic Library of Alexandria,

may be accessed by anyone who has a device

and the interest and the freedom to do so.

This was not true in Alexandria,

where knowledge belonged to the elite.

So in the fourth century AD,

when the mob came to destroy the library

and the genius of classical civilization,

there were not enough people to defend it.

What will happen the next time the mob comes?

We've come a long way together,

traveling from deep inside the heart of an atom

clear out to the cosmic horizon,

and from the beginning of time to the distant future.

I think we're ready to perform an experiment.

It's not the kind of experiment that requires a laboratory.

You can do it in your head.

It's called a "thought experiment."

Pick a star--

any one of the hundreds of billions of stars

in our Milky Way Galaxy,

which is just one galaxy

out of the hundred billion in the known universe.

How about that star?

Or that one?

Okay, this one.

It's orbited by dozens of planets and moons.

Suppose, on one of them,

there lives an intelligent species,

one the ten million life-forms on that planet,

and there's a subgroup of that species

who believe they have it all figured out--

their world is the center of the universe,

a universe made for them,

and that they know everything they need to know about it--

their knowledge is complete.

How seriously would you take their claim?

Our ancestors believed

the universe was made for them.

It was natural to assume that we were at the center.

After all, it looks like the Sun and stars

all revolve around us.

We still speak of the Sun "rising."

The architecture of our language, myths and dreams

comes from that prescientific age.

This is our planet as it was known then,

just before Columbus set sail.

This first globe of the Earth was cutting-edge

when Martin Behaim made it in 1492.

Like everyone else, he believed

that the jigsaw puzzle of geography was complete.

There were three continents...

Europe, Africa and Asia,

and only the great world ocean in between.

Behaim had no clue that North and South America even existed.

It's easy to feel smug, right?

Well, the fact is Martin Behaim knew infinitely more

about his world, the Earth,

than we know about ours, the universe.

A recent lesson in humility

will serve to illustrate.

In 1912, Victor Hess made a series of voyages

into the sky above Austria,

and found the thing that scientists love best...

a mystery that defied understanding

in terms of conventional scientific wisdom.

And even today,

a century later, we are still searching

for a complete explanation of what Hess found.

A new kind of energy had recently been discovered,

radioactivity.

It was given off

by certain elements, like radium.

But it was also found in the air,

even far away from radioactive rocks.

It was everywhere.

Where did this strange energy come from?

No one knew.

Hess suspected that it might come from above the Earth.

To test his hypothesis, he carried radiation detectors

high into the sky.

During a risky ascent in a hydrogen balloon,

he attained an altitude of more than three miles.

When he reached the thin, cold,

upper half of the atmosphere...

he found that the radiation

was more than twice as strong as on the ground.

The radiation must be coming from above.

That's why its intensity was weaker on the ground--

the Earth's atmosphere was absorbing most of it.

Some thought that the radiation might come from the Sun.

To test that idea, Hess timed one of his ascents

to coincide with a solar eclipse.

But the eclipse had no effect on the radiation.

Hess also found that the radiation

was just as strong at night as in daylight.

It was coming from above, but not from the Sun.

What Hess did not know

was that the solar wind doesn't move that quickly.

And so, for the wrong reason,

he came to the right conclusion.

Hess had discovered cosmic rays--

showers of subatomic particles that crisscross the universe

at literally the speed of light.

Without the shielding effect of the Earth's atmosphere,

they would be lethal.

Some cosmic rays can carry as much energy

as a bullet fired from a rifle.

It would take decades to trace those cosmic rays

back to a death of unimaginable violence.

The cosmic rays that Victor Hess detected

in the skies above Austria posed a mystery to scientists.

Radioactivity in minerals on Earth--

like uranium ore--

comes from the disintegration of atoms.

But cosmic rays were of a different nature.

They were far more powerful

than anything known in Hess's world.

Scientists wondered for two decades

what could possibly produce cosmic rays.

Enter Fritz Zwicky,

the most brilliant man you've never heard of.

In 1933, he and a colleague discovered

that some stars flare up to become as bright

as their entire galaxy for a few weeks,

before fading out again.

Fritz Zwicky was the first person

to understand what just happened.

He correctly surmised that this is the way

a massive star dies-- it blows

its guts out into space.

He called this kind of stellar death a "supernova"...

and predicted that the dying star would shrink

from about a million miles across to only ten.

This corpse would be so dense

that a single grain of it would weigh as much

as the Great Pyramid in Egypt.

It would consist almost entirely

of subatomic particles called neutrons,

so he named these bizarre objects "neutron stars."

And 35 years after Zwicky predicted their existence,

astronomers began to find them.

We call them "pulsars"

when they spin rapidly and emit regular pulses of radio energy.

Supernovas and neutron stars could account

for a wide range of cosmic rays,

but not the most energetic ones.

Nothing yet known to science

can explain them, and we're fine with that.

It's one of the things I love about science,

we don't have to pretend we have all the answers.

Zwicky also came up with the idea

that the gravity of a galaxy warps the fabric

of space around it, to act like a lens.

This distorts and magnifies light