Name: 【TED-Ed】What light can teach us about the universe - Pete Edwards
Uploaded: 2014-08-27T08:59:28.000Z
Duration: 4 min 7 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...

Humans have been discussing these questions

for as long as they've been around without ever reaching much agreement.

Today, cosmologists are working hard to find the answers.

But how can anyone hope to find concrete answers to such profound questions?

And how is it possible to explore and study something as huge as the universe,

most of which we'll never be able to reach?

And although light from distant parts of the universe

it carries six unique messages that, when put together,

can disclose an amazing amount of information to astronomers

Just as sunlight can be split up into the familiar rainbow,

splitting the light from distant objects exposes different patterns of colors

This distinctive light barcode can reveal not only an object's composition,

but also the temperature and pressure of its constituent parts.

There's even more we can discover from light.

If you've ever stood on a train platform, you might have noticed

that the train sounds different  depending on its direction

with the pitch ascending  when it approaches you

But this isn't because the train conductor is practicing for a second career.

Rather, it's because of something called the Doppler effect

where sound waves generated by an approaching object are compressed,

while those from a receding object are stretched.

Sound does not travel through a vacuum. In space, no one can you hear you scream!

But the same Doppler effect applies to light whose source is moving at exceptional speed.

If it's moving towards us,  the shorter wavelength

While light from a source that's moving away

will have a longer wavelength, shifting towards red.

So by analyzing the color pattern in the Doppler shift of the light

from any object observed with a telescope, we can learn what it's made of,

how hot it is and  how much pressure it's under,

as well as whether it's moving,  in what direction and how fast.

And these six measurements, like six points of light,

The first person to study the light  from distant galaxies was Edwin Hubble,

and the light he observed was redshifted.

The distant galaxies were  all moving away from us,

and the further away the were, the faster they were receding.

Hubble had discovered our universe is expanding,

providing the first evidence for the Big Bang theory.

Along with the idea that the visible universe has been constantly expanding

one of this theory's  most important predictions

is that the early universe consisted of just two gases: hydrogen and helium,

And this prediction can also be tested with light.

If we observe the light from a remote, quiet region of the universe and split it,

we do indeed find the signatures of the two gases in just those proportions.

Although we know the visible universe is expanding,

But recent measurements of light from distant dying stars

show us that they're farther away than predicted.

So the expansion of the universe is actually accelerating.

and many scientists believe that something is dark energy,

making up over 2/3 of the universe and slowly tearing it apart.

Our knowledge of the behavior of matter and the precision of our instruments

means that simply observing distant stars can tell us more about the universe

But there are other mysteries, like the nature of dark energy