It's an essential question

幾世紀以來，人類一直想知道

that humans have been wondering about for centuries.

這關鍵問題的答案

But the journey toward an answer

追尋答案的過程

has been a strange one.

卻是段奇異的旅程

If you wanted to know the answer to this question

如果你身在西元前三百年古希臘時期

in third century B.C.E. Greece,

想知道這問題的答案

you might look up at the night sky

你可能就直接仰望夜空

and trust what you see.

然後相信所見即是

That's what Aristotle,

這就是亞里斯多德（Aristotle）

THE guy to ask back then, did.

當時所做的

He thought that since we're on Earth, looking up,

他認為既然我們身在地球上，仰望一切

it must be the center, right?

那我們就是宇宙的中心點，不是嗎？

For him, the sphere of the world

對他而言

was made up of four elements:

這個球體世界的一切由四大元素所構成

Earth,

土

water,

水

air,

空氣

and fire.

火

These elements shifted around a nested set

四大元素繞著

of solid crystalline spheres.

網狀的天球（celestial spheres）在運行

Each of the wandering stars, the planets,

每一顆行星

had their own crystal sphere.

都有自己的天球

The rest of the universe and all of its stars

其餘的宇宙和裡頭的恆星

were on the last crystal sphere.

排列在天球的最外圍

If you watch the sky change over time,

如果你長期觀察天象的變化

you could see that this idea worked fine

你會發現這個理論

at explaining the motion you saw.

確實能解釋你觀察到的天體運行

For centuries, this was central to how Europe

此後的幾個世紀

and the Islamic world saw the universe.

這就是歐洲和伊斯蘭世界的宇宙觀

But in 1543, a guy named Copernicus

直到西元 1543 年

proposed a different model.

哥白尼（Copernicus）提出了不同觀點

He believed that the sun

他認為

was at the center of the universe.

太陽才是宇宙的中心

This radically new idea

這樣激進的新觀點

was hard for a lot of people to accept.

很難讓當時的人們接受

After all, Aristotle's ideas made sense

畢竟亞里斯多德的說法

with what they could see,

才符合他們看到的天體

and they were pretty flattering to humans.

何況還讓人類自我感覺良好

But a series of subsequent discoveries

但之後一系列的發現結果

made the sun-centric model hard to ignore.

讓人越來越難以否定「日心說」

First, Johannes Kepler pointed out

首先是克卜勒（Johannes Kepler）

that orbits aren't perfect circles or spheres.

提出行星運行軌道 並非完美的圓形或球狀

Then, Galileo's telescope caught

之後伽利略（Galileo） 用天文望遠鏡觀察到

Jupiter's moons orbiting around Jupiter,

木星的衛星運行軌道只圍繞著木星

totally ignoring Earth.

完全和地球無關

And then, Newton proposed the theory of universal gravitation,

再來是牛頓（Newton）提出的萬有引力

demonstrating that all objects are pulling on each other.

顯示出所有的物體都互有引力

Eventually, we had to let go of the idea

最終，我們還是要放棄

that we were at the center of the universe.

我們是宇宙中心的想法

Shortly after Copernicus, in the 1580s,

西元 1580 年代，在哥白尼之後不久

an Italian friar, Giordano Bruno,

一個名叫布魯諾（Giordano Bruno）的 義大利修士

suggested the stars were suns

提出恆星們就如同太陽一樣

that likely had their own planets

各自擁有行星群

and that the universe was infinite.

而宇宙是浩瀚無邊的

This idea didn't go over well.

這個論點在當時太過激進

Bruno was burned at the stake for his radical suggestion.

布魯諾因此被判火刑而死

Centuries later, the philosopher Rene Descartes

幾個世紀之後，哲學家笛卡兒 （Rene Descartes）

proposed that the universe was a series of whirlpools,

認為宇宙就像一連串的漩渦

which he called vortices,

他稱為渦流（vortices）

and that each star was at the center of a whirlpool.

每個恆星都在一個漩渦的中心

In time, we realized there were far more stars

隨著時間過去，我們明瞭恆星的數量

than Aristotle ever dreamed.

遠比亞里斯多德想像的更多

As astronomers like William Herschel

當天文學家，如赫雪爾（William Herschel）

got more and more advanced telescopes,

製作了越來越精良的天文望遠鏡

it became clear that our sun is actually

讓人們清楚的看到

one of many stars inside the Milky Way.

太陽不過是銀河裡眾多恆星之一

And those smudges we see in the night sky?

而那些我們在夜空中看到的煙狀物

They're other galaxies,

則是其他的星系

just as vast as our Milky Way home.

就和我們所在的銀河一樣廣大

Maybe we're farther from the center than we ever realized.

也許我們和宇宙中心的距離 比我們所知的更遙遠

In the 1920s, astronomers studying the nebuli

在西元 1920 年代， 天文學家研究星雲（nebula）

wanted to figure out how they were moving.

想弄清楚星雲的運行方式

Based on the Doppler Effect,

基於都卜勒效應（Doppler Effect）

they expected to see blue shift

天文學家預期會在朝我們移動的星雲中

for objects moving toward us,

觀察到藍移（blue shift）現象

and red shift for ones moving away.

而遠離的會出現紅移（red shift）現象

But all they saw was a red shift.

但他們只觀察到紅移現象

Everything was moving away from us, fast.

表示所有星雲正快速遠離地球

This observation is one of the pieces of evidence

這觀測數據

for what we now call the Big Bang Theory.

正是支持「大爆炸理論」的證據之一

According to this theory,

根據這個論點

all matter in the universe

宇宙中所有一切

was once a singular, infinitely dense particle.

曾經只是一個無窮大、密度極高的粒子

In a sense, our piece of the universe

某種意義上可說

was once at the center.

我們曾經在宇宙的中心

But this theory eliminates the whole idea of a center

不過這理論完全消滅了中心論

since there can't be a center to an infinite universe.

因為無窮大的宇宙是不會有中心點的

The Big Bang wasn't just an explosion in space;

大爆炸並不只是在空間裡的爆炸

it was an explosion of space.

而是空間的爆炸

What each new discovery proves

每個新發現都證明

is that while our observations are limited,

即使我們的觀測的方式有限

our ability to speculate and dream

但推論和夢想宇宙的能力

of what's out there isn't.

並不受限

What we think we know today can change tomorrow.

我們今日所知可以改變明日

As with many of the thinkers we just met,

就如我們剛談到的那些思想家

sometimes our wildest guesses

有時最瘋狂的想像

lead to wonderful and humbling answers

能引導出美妙謙卑的答案

and propel us toward even more perplexing questions.

同時促使我們追尋更進一步的複雜問題