Name: 大歷史速成班。探索宇宙 (Crash Course Big History: Exploring the Universe)
Uploaded: 2021-01-14T05:19:20.000Z
Duration: 14 min 8 s
Description: 【看影片學英語】數萬部 YouTube 影片，搭配英漢字典即點即查，輕鬆掌握單字發音與用法，長久累積看電影不必再看字幕。

Hi, I'm John Green, and this is Crash Course Big History.

Today, we're going to be exploring what happened

to the universe after the Big Bang, particularly,

how you and I and everyone you know emerged from stars.

And we'll also be investigating the burning question

Why can't we just learn about like English kings

Sorry, me from the past, the thing is if you look far back

enough in your family tree, you're going to find not just

like farmers, and foragers, and fish, and microbes,

And I don't mean stars like Kim Kardashian,

who is actually not a star, she is a person.

And to understand how we got from stars to people,

So last episode we went from the very beginning of everything

to the release of cosmic background radiation.

Studying it closely also tells us the age of the universe

and it allows us to see the minute variations in temperature

And it turns out that those tiny differences

So when the universe inflated from much, much smaller

than an atom to the size of a grapefruit in a split second,

there were quantum fluctuations, tiny little blips

And they created those little variations that we see

And as the universe continued to expand--

I mean it is currently larger than a grapefruit--

those variations in density were inflated to such a scale

that gravity was able to take hold and start clumping together

the universe was becoming an increasingly cold

Like temperatures were no longer high enough

to forge new elements, and if hydrogen and helium

nothing would have ever happened ever again.

Our universe would just be a dull, homogeneous place

with some clouds of hydrogen and helium gas floating around.

But what happened is that while the universe on the whole

continued to cool, thanks to those tiny variations

that emerged during inflation, certain pockets of the universe

Indeed, a liberal dose of hot sauce was yet to come.

Hydrogen and helium though are light gases;

So light that they require very little encouragement

But while the explosive force of the Big Bang flings matter

and energy apart, gravity has the ability to pull

tiny pockets of the cosmos back together,

provided it has some wrinkles in the universe to work with.

As gravity sucked hydrogen and helium atoms together,

While the expansion of the universe continued to increase

the density of these pockets also increased.

The vastness of empty space began to be filled

with tiny islands where atoms of hydrogen and helium

Despite being the lightest of all the elements,

the immense amount of all that gas built pressure

Increasing pressure meant increasing temperatures,

suddenly these gassy pockets were burning inside.

It was in this rather uncomfortable state of heartburn

roughly 100 million years after the Big Bang.

By a billion years after the Big Bang, the universe

was starting to look like what we think of as a universe.

An immense vastness littered with hundreds of billions

of galactic islands containing hundreds of billions of stars.

And as recent work with Kepler space telescope has revealed,

for the average person to get a mental picture

Our galaxy, the Milky Way, formed from these

galactic mergers with other galaxies that stopped