The Paradox of an Infinite Universe · Kurzgesagt – In a Nutshell
视频探讨宇宙是否无限，是否有边界。通过类比橘子表面，解释宇宙可能是一个无边界的有限空间。适合练习英语中的抽象概念和逻辑推理。
Is the universe infinite?
宇宙是无限的吗？
Does it have an edge?
它有锋利的部分吗？
And if so, what would you see if you went there?
如果真是这样，当你去那里的时候，你会看到什么呢？
Today we know that the universe had a beginning 14 billion years ago and that it's been expanding ever since.
如今我们知道，宇宙起源于140亿年前，从那时起它就一直在膨胀。
But something that's expanding should also have an edge, right?
但是，任何正在膨胀的东西都应该具有某种“边界”或“边缘”，对吧？
Well, it sort of does.
嗯，某种程度上确实是这样。
Information can’t travel faster than light.
信息传播的速度不可能超过光速。
That means that we can only see parts of the universe whose light has had time to reach us in the last 14 billion years.
这意味着我们只能看到宇宙中那些光线在过去的140亿年里才来得及到达我们这里的区域。
When we look outwards, what we see is a sphere centered on us, the observable universe.
当我们向外观察时，所看到的是一个以我们为中心的球体——也就是我们所能够观测到的宇宙。
But it gets a tad more complicated
不过情况会变得稍微复杂一些。
– because the universe has been expanding,
因为宇宙一直在膨胀。
we know that the most far away things whose light we can see are actually 45 billion lightyears from us right now.
我们知道，那些我们能够看到其光芒的、距离我们最遥远的天体，实际上距离我们大约有450亿光年之远。
So the observable universe is a sphere with a radius of 45 billion light years.
因此，我们所能观测到的宇宙实际上是一个半径为450亿光年的球体。
It contains around 200 billion galaxies, each with hundreds of billions of stars.
该宇宙包含大约2000亿个星系，每个星系又拥有数千亿颗恒星。
So for us, there is an edge: We are looking at the past until there is just no past left.
对我们来说，有一个优势：我们会不断回顾过去，直到过去彻底消失为止。
This edge is really more like an edge in time and in a sense meaningless.
这种“边缘”其实更像是一种存在于时间中的“边界”，从某种意义上来说是没有意义的。
The real universe is for sure bigger than what we can see.
现实中的宇宙肯定比我们能够看到的范围要广阔得多。
But how much?
但是具体要多多少呢？
There are two options – either the universe is really big but finite, or it’s truly infinite.
有两种可能性：要么宇宙确实非常大但仍然是有限的；要么宇宙真的是无限的。
A finite universe means that, if you want to fill it with ice cream, you can do it.
一个有限的宇宙意味着：如果你想用冰淇淋填满整个宇宙，你是完全可以做到的。
You need a lot of ice cream, but it is a finite amount.
你需要很多冰淇淋，但冰淇淋的数量毕竟是有限的。
But that leads to a weird problem.
但这引发了一个奇怪的问题。
Such a universe should have an edge, a cosmic wall where space ends.
这样的宇宙应该存在一个边界，一道“宇宙墙”——在那里，空间就结束了。
And if there is an edge there should be something outside that edge.
如果存在某种“边界”或界限的话，那么在该边界之外应该还存在其他东西。
But the universe by definition is “all there is”, so how could there be stuff outside all there is?
但根据定义，宇宙就是“一切存在的东西”；那么，在这个宇宙之外，怎么可能还有其他东西存在呢？
Does the idea of something outside of everything even make sense?
某种存在于一切事物之外的东西”这个概念，究竟有没有意义呢？
Except of course there is a physics
当然，这里还涉及物理学原理。
hack: You can have a universe that has no border, but that still could be filled with a finite amount of ice cream.
解释： “Hack”这个概念在这里可以理解为一种假设或理论上的可能性。假设我们存在一个没有边界的宇宙，但这个宇宙中仍然只能容纳有限量的冰淇淋。这种设定实际上是在探讨空间无限性与物质有限性之间的矛盾：虽然宇宙在空间上是无限的，但其内部的物质（如冰淇淋）的数量却是有限的。这种思维方式常用于哲学、科学或文学创作中，用来探讨无限与有限、无限与具体现实之间的关系。
What if the universe is truly finite?
如果宇宙真的是有限的，那会怎么样呢？
Imagine an orange and a really tiny ant.
想象一个橙子和一只非常小的蚂蚁。
The ant can only see a small piece of the skin – just as you can only see a small chunk of the universe.
蚂蚁只能看到皮肤的一小部分；就像你也只能看到宇宙的一小部分一样。
But if the ant starts walking, it will eventually walk around the whole orange and be back to its starting point.
但是，如果那只蚂蚁开始行走，它最终会绕着整个橙子走一圈，然后回到起点。
So the skin of an orange is not infinite – but it doesn’t have a border.
因此，橙子的果皮并不是无限大的，但它也没有明显的边界。
The universe is not like the skin of an orange, but it could be very similar – instead of a sphere,
宇宙并不像橙子的表皮那样，不过它们在结构上可能非常相似；只不过宇宙并不是一个完美的球体而已。
it could be a hypersphere, where 3D-space is curled on itself.
这可能是一个“超球面”（hypersphere）——在这种结构中，三维空间被自身“卷曲”在一起（即三维空间的结构发生了某种特殊的变形）。
Which is impossible for your brain to visualize unfortunately.
遗憾的是，你的大脑无法将这一情景可视化（即无法在脑海中形成相应的图像或画面）。
But the point is: no borders, no outside of the hyper sphere – from our human ant perspective,
但关键在于：没有边界，也就不存在所谓的“超球体”之外的世界。从我们人类微小的视角来看，一切都被这个“超球体”所包含在内。
our whole 3D space is like the peel of the orange.
我们整个三维空间，其实就如同橙子的果皮一样。
If you were aboard a spaceship flying in a straight line, you would eventually come back to Earth.
如果你乘坐一艘沿直线飞行的宇宙飞船，最终你还是会回到地球的。
How does any of this make sense?
这一切到底有什么意义呢？