Are there places we will never reach, no matter how hard we try?

頑張っても届かない場所はあるか

Turns out there are.

答えは「ある」

Even with science fiction technology, we are trapped in our pocket of the Universe.

SF的な技術があっても

How can that be? And, how far can we go?

出られない領域がある

We live in a quiet arm of the Milky Way; A spiral galaxy of average size,

それはなぜか

– about 100,000 light years across –

どこまで行けるのか

consisting of billions of stars, gas clouds, dark matter, black holes, neutron stars,

私たちは天の川銀河にいる

and planets, with a supermassive black hole in the galactic centre.

直径約10万光年の渦巻き銀河で

>From afar, our galaxy seems dense, but in reality, it consists, mostly, of empty space.

ここにたくさんの星 ガス雲

With our current technology, sending a human to the closest star, would take thousands of years.

ダークマター ブラックホール

So, our galaxy is pretty big.

中性子星 惑星があり

The Milky Way is not alone, though.

中心には巨大ブラックホールがある

Along with the Andromeda galaxy, and more than fifty dwarf galaxies,

密度が濃く見えるが

it's a part of "The Local Group";

実際はほとんどが空の空間だ

a region of space about ten million light years in diameter.

現在の技術では近くの星まで

It is one of the hundreds of galaxy groups in the "Laniakea Supercluster",

数千年かかる

which, itself is only one of millions of superclusters,

それくらい銀河は大きい

that make up the observable universe.

銀河は他にもある

Now, let's assume, for a moment, that we have a glorious future;

アンドロメダや他の銀河が合わさり

humanity becomes a type three civilisation,

局部銀河群となり

does not get wiped out by aliens,

その直径は1000万光年

and develops interstellar travel based on our current understanding of physics.

ラニアケア超銀河団の中の一つだ

In this best case scenario, how far could we possibly go?

これも超銀河団の中の一つで

Well; the local group.

それらが宇宙を構成する

It's the biggest structure that humanity will ever be a part of.

ここで 輝く未来が来たと仮定しよう

While it's certainly huge, the local group accounts for only 0.00000000001 % of

人類はタイプ３の文明となり

the observable universe.

宇宙人にも潰されず

Let this number sink in for a moment.

現代物理で可能な技術を発展させた

We are limited to a hundred billionth of a percent of the observable universe.

この場合 どこまで行けるのか？

The simple fact that there is actually a limit for us, and that there is

銀河群の中までだ

so much universe that we will never be able to touch, is kind of frightening.

これが人類に支配できる最大領域だ

Why can't we go further?

十分広いが これは宇宙全体の

Well, it all has to do with the nature of nothing.

0.00000000001％

Nothing, or empty space, isn't empty but has energy intrinsic to itself;

でしかない

so-called "quantum fluctuations".

想像できるだろうか

On the smaller scale, there is constant action, particles and antiparticles

人類が行けるのは

appearing and annihilating themselves.

宇宙の10兆分の１に限られている

You can imagine this quantum vacuum as a bubbling part:

これが限界ということは

with denser, and less dense regions.

宇宙の大きな可能性にも

Now, let's go back 13.8 billion years when the fabric of space

触れられないことになる

consisted of nothing at all.

なぜそこが限界か

Right after the big bang, in an event known as cosmic inflation, the observable universe

それは無の性質と関係している

expanded from the size of a marble to trillions of kilometres, in fractions of a second.

空の空間は実際は空ではなく

This sudden stretching of the universe was so fast and extreme,

エネルギーを持っている

that all those quantum fluctuations were stretched as well,

量子ゆらぎという現象だ

and subatomic distances became galactic distances,

小さな世界は常に活動し

with dense and less dense regions.

粒子と反粒子が現れては消えている

After inflation, gravity began to pull everything back together.

この量子的な真空は 言わば

At the largest scale, the expansion was too quick and powerful

密度の偏った泡だ

to overcome but in smaller scales, gravity emerged victorious.

ここで 宇宙が真に無だった

So, over time, the denser regions, or pockets, of the universe,

138億年前に戻ってみよう

grew into groups of galaxies, like the one we live in today.

ビッグバン直後 空間は膨張して

Only stuff inside our pocket – The Local Group – is bound to us gravitationally.

宇宙はビー玉大から１兆キロまで

But wait, what is the problem then?

一瞬で広がった

Why can't we travel from our pocket, to the next one?

この宇宙の膨張が急激だったため

Here, dark energy makes everything complicated.

量子ゆらぎも引っ張られ

About six billion years ago, dark energy took over.

その密度の偏りが宇宙に反映された

It's basically an invisible force or effect, that causes,

濃い所と薄い所ができた

and speeds up the expansion of the universe.

膨張後は 重力が物同士を引っ張った

We don't know why, or what dark energy is, but we can observe its effect clearly.

大きい規模では膨張力が強かったが

In the early universe, there were larger, cold spots around the local group,

小さい規模では重力が勝った

that grew into clusters with thousands of galaxies.

そしてその後密度が濃かった所には

We are surrounded by a lot of stuff, but none of those structures and galaxies

現在のような銀河群ができあがった

outside of the local group are gravitationally bound to us.

集まった銀河群は

So the more the universe expands, the larger the distance between

重力によって繋がっている

us and other gravitational pockets becomes.

では 何が問題なのか

Over time, dark energy will push the rest of the universe away from us,

なぜ別の群に行けないのか

causing all the other clusters, galaxies, and groups to eventually become unreachable.

ダークエネルギーが原因だ

The next galaxy group is already millions of light years away,

約60億年前 それは始まった

but all of them are moving away from us, at speeds we can't, ever, hope to match.

目に見えない力によって

We could leave the local group, and then fly through intergalactic space,

膨張が加速を始めたのだ

into the darkness, but we would never arrive anywhere.

なぜなのかはわからないが

While we will become more and more stranded, the local group will become more tightly bound,

影響は確かにある

and merge together to form one giant elliptical galaxy, with the unoriginal name "Milkdromeda"

最初 銀河群の周りには空間があり

in a few billion years.

銀河は集団で存在していた

But it becomes even more depressing:

周りにもそんな集団があった

at some point, the galaxies outside the local group, will be so far away,

しかしそれらの外の銀河団とは

that they will be too faint to detect, and the few photons that do make it to us,

重力では繋がらないため

will be shifted to such long wavelengths, that they will be undetectable.

宇宙が膨張するほど

Once this happens, no information outside of the local group will be able to reach us.

その距離は離れていくことになる

The universe will recede from view.

ダークエネルギーはこれを加速させ

It will appear to be dark and empty in all directions, forever.

他の銀河群への旅を不可能にする

A being born in the far future in Milkdromeda,

数百万光年先の銀河群が

will think there is nothing but its own galaxy in the entire universe.

さらに加速的に遠ざかっているのだ

When they look far into empty space, they will only see more emptiness and darkness;

銀河群を出て 闇の中までは行けるが

they won't be able to see the cosmic background radiation,

辿り着く場所はない

and they won't be able to learn about the Big Bang.

一方 時間が経つにつれて

They will have no way of knowing what we know today;

銀河群はより密集し

the nature of the expanding universe, where it began, and how it will end.

数十億年後 合体して一つの巨大銀河

They will think the universe is static and eternal.

ミルクドロメダになる

Milkdromeda will be an island in the darkness, slowly getting darker and darker.

別のことも起きる

But still, with its trillions of stars, the local group is certainly

他の銀河群は遠く離れていくと

large enough for humanity.

見えなくなっていく

After all, we still haven't figured out how to leave our solar system,

光子が少なくなり 波長も伸びるため

and we have billions of years to explore our galaxy.

見づらくなるのだ

We have the incredible luck to exist at the perfect moment in time to see,

やがて外からの情報は届かなくなり

not only our future but also our most distant past.

宇宙の景色は変わる

As isolated and remote as the local group is, we can perceive the entire universe,

暗くて 何も見えなくなる

grand and spectacular as it is right now.

永遠に

This video was sponsored by SquareSpace.com/nutshell

将来 ミルクドロメダ人は

Do you feel isolated in a humongous universe?

宇宙はこの銀河だけだと思うだろう

Why not set up a website or blog and share your thoughts with other

宇宙を見てみても

humanoids around you?

何もない暗闇があるだけだ

Squarespace lets you do that with easy-to-understand tools

宇宙背景放射もないため

very quickly and without any knowledge of web design.

ビッグバンに気づかない

You can also use the code "NUTSHELL" to save 10 % and support Kurzgesagt

私たちが知ることを知らない

in making more videoes about our place in the universe.

宇宙の膨張も

Thanks so much for the help with the video to Ethan Siegel.

始まりも 終わり方も

Follow his astronomy blog here.

彼らは宇宙は永遠だと考えるだろう

You can support us directly at Patreon or get Kurzgesagt merch here.

そして孤独なミルクドロメダは

It really helps.

ゆっくり闇に包まれていく

It is awesome that you watched this far, so we have made a playlist for you about more universe stuff.

それでもこの銀河群の星は

Subtitles made by Sebastian Winkelmann

人間にとって十分多い

Subtitles by the Amara.org community

と言っても 太陽系から出る方法も