Home
登錄
註冊
Loading...
聽力練習
聽力練習
/
Video
/
Science Channel
/
The Universe's GREAT WALL | Space's Deepest Secrets | Science Channel
The Universe's GREAT WALL | Space's Deepest Secrets | Science Channel
選擇學習模式:
查看字幕
選詞
重寫單字
Highlight:
3000 Oxford Words
4000 IELTS Words
5000 Oxford Words
3000 Common Words
1000 TOEIC Words
5000 TOEFL Words
字幕 (195)
0:02
The Boss Great Wall is the largest
0:04
cosmic structure ever discovered.
0:08
It owes its origin to a super huge cloud
0:11
of gas that collects in the early
0:13
universe.
0:16
But why does this material clump
0:18
together here in the first place?
0:31
Astronomers believe that the answer lies
0:33
at the moment of the universe's
0:35
creation.
0:38
At a time when everything in existence
0:40
fits into a space far smaller than an
0:43
atom.
0:45
The tiniest sliver of a fraction of a
0:47
second after the big bang, 110 trillion
0:50
trillion trillionth of a second, the
0:53
universe underwent an inflationary
0:55
period where it went from about the size
0:57
of a proton, a subatomic particle, to
1:00
roughly the size of a grain of sand.
1:02
Now, I know that doesn't sound like
1:03
much, but you got to realize this is a
1:05
factor of a million billion billion
1:08
times. This is a huge expansion.
1:11
This moment of inflation
1:14
sews the seed that grows into the Great
1:16
Wall.
1:20
Trillionth of a second after the Big
1:22
Bang, the cosmos is a ball of energy
1:24
where weirdness rules.
1:28
Minute random fluctuations in this super
1:31
hot soup create a pattern of hotspots on
1:34
subatomic scales.
1:39
As the universe expands,
1:42
it stretches out the tiny hot spots over
1:45
a cosmic scale,
1:49
energy condenses into matter, which
1:52
provides the seeds
1:54
for huge cosmic structures like the
1:57
clouds of hydrogen that feed the
1:59
galaxies and the Great Wall.
2:03
The inflation of the universe pulled
2:05
parts of the universe that were close
2:07
together wildly apart. If you had a
2:11
region of the universe that had a little
2:12
bit more stuff in it than average next
2:14
to a spot that had a little bit less
2:16
stuff than average, given enough time,
2:18
they would have smoothed each other out.
2:20
But the inflation of the universe ripped
2:22
them apart and they became frozen in
2:24
place.
2:28
Tiny fluctuations at the moment of the
2:30
universe's creation. unlock the genesis
2:33
of the largest structure in the cosmos.
2:37
What is the invisible force that molds
2:39
trillions of stars into the Great Wall's
2:42
distinctive shape?
2:47
The Great Wall is 6 billion lightyear
2:50
from Earth.
2:52
This is too far away for telescopes to
2:54
see in detail how it joins together.
2:58
But clues exist closer to home that can
3:01
help astronomers unlock the mystery.
3:05
>> Despite its ridiculous size and
3:07
forbidding distance, the Great Wall is
3:10
made of the same things we see around
3:11
us. We can learn about that and then
3:14
extrapolate that to understand how the
3:16
Great Wall itself behaves.
3:19
Our Milky Way galaxy is just one of a
3:22
cluster of over 30 closely spaced
3:24
galaxies known as the local group.
3:30
And the local group is just a single
3:32
fragment of an even greater collection
3:35
of hundreds of galaxy clusters.
3:40
Astronomers call this type of structure
3:42
a supercluster.
3:45
The Milky Way is part of a supercluster
3:48
that is 100 million light years wide.
3:52
And superclusters pop up everywhere that
3:55
astronomers look. Almost every galaxy is
3:58
part of a supercluster and there are
4:01
millions of these superclusters in the
4:03
universe. Each one of them has tens to
4:06
hundreds of thousands of galaxies in
4:08
them. And each one of those galaxies has
4:11
billions of stars.
4:15
The supercluster is the key that unlocks
4:18
why the Great Wall has its distinctive
4:20
shape.
4:23
The Great Wall measures 1 billion
4:25
lightyears across.
4:29
Breaking it apart reveals that it is a
4:31
cluster of four superclusters.
4:35
Two of them are large, densely packed
4:37
tubes,
4:39
each more than 500 million lightyear
4:42
long,
4:44
and two are smaller superclusters, each
4:48
over a thousand times the mass of the
4:50
Milky Way.
4:54
These superclusters join together to
4:57
form a true heavyweight champion of the
4:59
cosmos.
5:01
The largest single object we have ever
5:03
seen.
5:09
Astronomers now know that nine out of 10
5:12
galaxies sit inside a supercluster.
5:17
What mysterious force brings galaxies
5:20
together into these vast structures?
5:26
A clue lies in the way that everything
5:29
moves through the universe.
5:32
Objects attract each other. The more
5:35
massive the object, the greater the
5:38
pull.
5:40
Scientists call this force gravity.
5:44
If the universe is a symphony, then
5:46
gravity is its great conductor. It
5:49
choreographs the dance of everything in
5:51
the cosmos. It brings clouds of gas
5:53
together to form stars, stars together
5:56
to form galaxies, and galaxies together
5:58
to form clusters, including the Great
6:01
Wall.
6:02
>> It sounds simple. Gravity pulls objects
6:05
together
6:07
into ever larger structures.
6:11
But there's a big problem with this
6:13
idea.
6:16
From the Big Bang
6:19
to the galaxies that we see today,
6:23
computers can simulate how the cosmos
6:25
evolved.
6:28
When scientists simulate the formation
6:30
of superclusters,
6:33
these mega structures end up loose as
6:36
gravity isn't strong enough.
6:40
Only when they boost the gravity beyond
6:42
the expected level does matter assemble
6:46
fast enough to form the superclusters
6:48
that we see today.
6:53
So how can objects like the Great Wall
6:56
form if gravity is too weak? The only
7:00
force in the universe that we know that
7:01
brings things together is gravity. When
7:04
it comes to structures as large as the
7:06
Great Wall, there just isn't enough
7:08
gravity in the galaxies together to form
7:10
something that huge. Something else must
7:13
be there underlying all of it, creating
7:15
more gravity than we can account for.
7:18
Where is the missing gravity that the
7:20
universe needs to make the Great Wall?
7:23
And is the Great Wall unique? Or is it
7:28
part of an even larger cosmic structure?
7:34
The Boss Great Wall is a vast collection
7:37
of galaxies that stretches over 1
7:40
billion lightyears across.
7:43
Scientists calculate that the gravity of
7:45
its thousands of galaxies alone is too
7:48
weak to build this immense mega
7:50
structure.
7:53
Where does the extra gravity that's
7:55
needed to construct the Great Wall come
7:57
from?
8:02
Scientists believe that a clue lies in
8:05
the space around galaxies.
8:09
Gravity doesn't just pull on matter,
8:12
it also bends light.
8:18
When powerful telescopes photograph
8:20
dense galaxy clusters,
8:22
the objects around them look distorted.
8:26
This warping of spaceime by a giant
8:29
cluster of galaxies can act like an
8:31
optical lens that magnifies the light of
8:33
galaxies beyond it. These strange
8:35
smeared out images all over the sky.
8:39
These are real. This is actually what
8:40
you would see if your eyes were
8:42
sensitive enough. You would see this in
8:43
the night sky.
8:46
>> But sometimes something weird happens.
8:50
The light that comes from behind
8:52
galaxies bends far more than astronomers
8:55
expect.
8:57
There must be an invisible material with
8:59
huge mass and gravity around these
9:02
galaxies.
9:04
This material could unlock where the
9:06
extra gravity comes from to build mega
9:08
structures like the Great Wall.
9:12
Scientists call it dark matter and they
9:16
estimate that it outweighs regular
9:18
matter by a factor of 5 to 1.
