Name: Mysteries of a Dark Universe
Uploaded: 2014-04-23T13:48:47.000Z
Duration: 25 min 1 s
Description: Thousands of YouTube videos with English-Chinese subtitles! Now you can learn to understand native speakers, expand your vocabulary, and improve your pronunciation...

Advanced passive voice

Cosmology, the study of the universe as a whole, has been turned on its head by a stunning

discovery that the universe is flying apart in all directions at an ever-increasing rate.

Is the universe bursting at the seams? Or is nature somehow fooling us?

The astronomers whose data revealed this accelerating universe have been awarded the Nobel Prize

And yet, since 1998, when the discovery was first announced, scientists have struggled

to come to grips with a mysterious presence that now appears to control the future of

On remote mountaintops around the world, major astronomical centers hum along, with state

of the art digital sensors, computers, air conditioning, infrastructure, and motors to

Deep in Chile's Atacama desert, the Paranal Observatory is an astronomical Mecca.

This facility draws two megawatts of power, enough for around two thousand homes.

What astronomers get for all this is photons, tiny mass-less particles of light. They stream

in from across time and space by the trillions from nearby sources, down to one or two per

second from objects at the edge of the visible universe.

In this age of precision astronomy, observers have been studying the properties of these

particles, to find clues to how stars live and die, how galaxies form, how black holes

But for all we've learned, we are finding out just how much still eludes our grasp,

how short our efforts to understand the workings of the universe still fall.

Cosmology, the study of the universe as a whole, goes back to the ancient Greeks.

With no telescopes or other optical instruments to probe the stars... observers constructed

models designed to make sense of what they saw.

Their earliest theories stated that all matter in the Universe is composed of some combination

Each arises from opposing properties of heat and cold, dry and wet, acting upon more primitive

Aristotle took it a step further. He held that the universe is divided into two parts,

the realm of Earth, in which everything is composed of the four substances, and the realm

These bodies are made up of a fifth substance, unchanging and incorruptible, called aether

The Greek idea that the universe is a series of concentric circles, with Earth at the center,

yielded to a wealth of new discoveries about the universe.

Located in a giant wheel of stars and gas, a galaxy.

Bound by gravity to a local group of 30 galaxies.

Bound, in turn, to a cluster of over a thousand galaxies, and to a supercluster with tens

This, our cosmic region, takes up a volume about 100 million light years across, set

within a larger pattern of galaxy filaments, superclusters, and enormous empty voids.

Earth is but a speck, within a firmament so vast we can scarcely imagine it.

For all we've learned from snatching photons, the most basic nature of the universe has

only grown more mysterious. Ironically, modern models have recalled the mysterious fifth

element conjured by the Greeks to explain a universe that appears to move in ways not

To understand the predicament now faced by scientists, let's see how they got there in

A hundred years ago, most astronomers believed the universe consisted of a grand disk, the

Milky Way. They saw stars, like our own sun, moving around it amid giant regions of dust

The overall size and shape of this "island universe" appeared static and unchanging.

That view posed a challenge to Albert Einstein, who sought to explore the role that gravity,

a dynamic force, plays in the universe as a whole.

There is a now legendary story in which Einstein tried to show why the gravity of all the stars

and gas out there didn't simply cause the universe to collapse into a heap.

He reasoned that there must be some repulsive force that countered gravity and held the

He called this force the "cosmological constant." Represented in his equations by the Greek

letter Lambda, it's often referred to as a fudge factor.

In 1916, the idea seemed reasonable. The Dutch physicist Willem de Sitter solved Einstein's

equations with a cosmological constant, lending support to the idea of a static universe.

Now enter the American astronomer, Vesto Slipher.

Working at the Lowell Observatory in Arizona, he examined a series of fuzzy patches in the

sky called spiral nebulae, what we know as galaxies. He found that their light was slightly

It's similar to the way a siren distorts, as an ambulance races past us.

If an object is moving toward Earth, the wavelength of its light is compressed, making it bluer.

If it's moving away, the light gets stretched out, making it redder.

12 of the 15 nebulae that Slipher examined were red-shifted, a sign they are racing away

Edwin Hubble, a young astronomer, went in for a closer look. Using the giant new Hooker

telescope in Southern California, he scoured the nebulae for a type of pulsating star,

called a Cepheid. The rate at which their light rises and falls is an indicator of their

By measuring their apparent brightness, Hubble could calculate the distance to their host

Combining distances with redshifts, he found that the farther away these spirals are, the

faster they are moving away from us. This relationship, called the Hubble Constant,

showed that the universe is not static, but expanding.

Einstein acknowledged the breakthrough, and admitted that his famous fudge factor was

The discovery revolutionized astronomy because it redefined the universe as a dynamic realm.

But if he were around today, Einstein would be surprised to see his own failed idea return.

If the universe is expanding, it must have emerged from a dense and hot primordial state.

A cosmic fireball, we now call the big bang, would have supplied the initial kick.

Even as the universe expanded, gravity began drawing matter together into a web-like structure

If there's enough matter out there, will gravity oneday reign in the big bang, and cause the

To find out, astronomers renewed Hubble's quest to precisely measure the cosmic expansion

Working with the Hubble space telescope, and giant new observatories on land, they sought

to measure distances far deeper than Hubble ever could.

People are talking about doing precision cosmology for the first time. Because it used to be,

"Cosmology, well we have a rough idea of how big the universe is, maybe to a factor of

two or three." But now with these new measurements we're really getting a handle on the overall

Subtitles ListPlay Video

Mysteries of a Dark Universe

dark

light

big

show