We're used to thinking of space as the emptiness in which things happen, like an empty warehouse

像是一個倉庫等著被填滿 或是一個宇宙事件發生的舞台

ready to be filled, or a theater stage on which the events of the Universe play out.

但廣義相對論預測了空間不僅僅是片「虛無」

But General Relativity predicts that space is not just emptiness, it's a physical,

它是個物體般動態的東西 而這個預測已經被許多實驗證實了

dynamic thing, and that prediction has been borne out by many, many experiments.

空間之所以可以彎折是因為其中的物質和能量 且扭曲物體在其中運行的路線

Space can bend because of matter and energy, curving the paths of objects that move inside

它會因重力波而振動 也可以膨脹而在空間中創造出更多「空間」

of it.

以上這些現象可以用一個概念來說明： 空間（或是時空）的曲度

It can ripple with gravitational waves And it can expand, creating more and more space

在時空平坦的區域中（像是附近沒有物質或能量）

between two objects.

物體平行移動仍保持平行

All of these phenomena can be described by one idea: curvature of space (or spacetime).

在時空曲度為正的區域中（像是在行星或黑洞附近） 平行移動的物體會相戶接近

In flat regions of spacetime (like, if there's no energy or matter nearby), objects traveling

而時空曲度為負的區域中物體平行移動 （甚至是互相會聚）會相互遠離

along parallel paths stay along parallel paths.

那如果空間是一體的呢？ 如果時空曲度在哪裡都為正

In positively curved regions of spacetime (like near planets or black holes), parallel

那空間只會有一種形狀── 一個距大的超空間馬鈴薯

paths converge, and in negatively curved regions of spacetime parallel paths (or even paths

如果你朝著同一方向不斷行走 那你就會回到你開始的地方

pointed at each other!) diverge.

如果時空在哪裡都是平的 那它的形狀簡單的就是──無限伸直

But what about space as a whole ? If space is positively curved everywhere, then there's

或是類似電玩遊戲裡的無限迴圈

only one shape space can be: a giant hyper-potato.

那如果時空在哪裡曲度都為負 那體育都將行不通

If you went in one direction for long enough, eventually you'd end up in the same place

所以　到底是哪一種呢？

you started.

基本上有兩種方式量測宇宙大尺度的曲度

If space is flat everywhere, its shape could be simple: just extend out straight to infinity.

第一個是量測一個三角形的內角和

Or it could loop around in a periodic way, like in some video games:

如果空間是平的　 那內角和將會是 180 度

And if space is negatively curved everywhere, sports would be impossible

但如果空間是彎曲的話 內角和會因彎曲類型的不同而大於或小於 180 度

So which is it?

宇宙學家已經藉由早期宇宙的照片

There are basically two ways to measure the large-scale curvature of the Universe.

量測照片上三點的特殊關係 來計算所圍成的三角形的內角和

One is to measure the angles inside of triangles.

第二種量測曲度的方法是去 量測造成空間彎曲的東西──

If the space is flat, then the angles will add up to 180 degrees.

宇宙中物質和能量分部的密度

But if the space is curved, those angles will add up to more or less than 180 degrees depending

這也是個已經被宇宙學家所量測的東西

on the type of curvature.

最終的量測結果表示... 宇宙幾乎是平的（只有 0.4% 的誤差）

Cosmologists have done the equivalent of measuring our Universe's triangles by looking at a

但在你對於我們不是生活在一個酷炫的 超空間馬鈴薯上而感到失望前

picture of the early Universe, and studying the spatial relationship between different

讓我來告訴你一個大問題：

points on that picture.

我們居住的宇宙是「平的」 似乎是個巨大、難以想像的巧合

The second way to measure curvature is to measure the thing that causes space to curve

如果宇宙只多出了一點質量或能量 那空間就會朝向一個方向彎曲

in the first place: the density of energy and matter throughout the Universe.

那如果只少了一點質量或能量 空間就會朝向另一個方向彎曲

Which cosmologists have also measured.

但我們所觀測到的來說 宇宙似乎有剛剛好的質量和能量維持平坦

It turns out that in both cases, measurements show the Universe to be… pretty much flat

這完美的比例差不多是 平均每立方公尺內有五個氫原子

(within 0.4% margin of error).

而宇宙中那些沒有東西的部分的原子 就聚集在一起而創造了我們

But before you get disappointed that we don't live in a cool cosmic hyper-potato, let me

但如果平均每立方公尺有六個或四個氫原子

tell you one big problem

那整個宇宙將會彎曲非常多（或非常少）

The fact that we live in a flat Universe appears to be a GIGANTIC, COSMIC-LEVEL COINCIDENCE.

但我們現在仍對宇宙如此平坦的原因毫無概念

If the Universe had just a little bit more mass and energy, space would have curved one

當我們探討宇宙的曲度時，我們的知識就變平了

way.

＜公商時間＞

And if it had just a little bit less mass and energy, space would have curved the other

way.

But we seem to have just the right amount to make space perfectly flat as far as we

can tell.

This perfect amount is the equivalent of five hydrogen atoms per cubic meter of space, on

average.

If instead there were six hydrogen atoms per cubic meter of space on average, or four,

the entire Universe would have been a lot more curved or a lot less .

And we so far have no idea why our universe has the density that it does.

When it comes to the curvature of the universe, our knowledge falls flat.