But if the Universe is "everything", does that mean it includes the things that we don't know that we don't know exist?

但，假如宇宙指的是「所有的一切」，那代表它包含了我們未知並且不確定是否存在的事物嗎？

Or even the things that we believe exist but haven't yet seen or observed?

或是一些我們相信其存在，但還沒見過或是觀測到的事物嗎？

For example, is the future a part of the universe?

舉個例子，未來是否是宇宙的一部分呢？

In physics, we usually distinguish between these two notions of universe as 1) the "observable universe," which is everything whose existence we've thus far been able to confirm or observe, or could in principle observe if we point our telescopes at it.

在物理學上，我們通常會區分宇宙為兩種概念。其一，「可觀測宇宙」，指的是到目前為止，能確定它們的存在、可觀測到的事物，或是用望遠鏡原則上可以觀測到的。

And 2) "The Universe" with a capital U, or, "The Whole Universe," which is everything that exists, has existed, or will exist, any time, anywhere, regardless of whether or not we're aware of it yet (or ever will be).

其二，「The Universe」，其中 U 是大寫，也稱為「整個宇宙」，指的是現在存在，已經存在一段時間，或是即將發生的事，包含任何時間，任何地點，不管我們是否有發現注意到，或是永遠也不會注意到的所有事物。

Of course, the main reason for this distinction is so that we can talk scientifically about parts of the universe we haven't yet been able to observe,

當然，因為有這樣的區分，所以我們可以以科學的角度來探討宇宙間我們還沒辦法觀測的部分，

and the two biggest reasons we might not have been able to observe a piece of the universe yet are either it's in the future or it's so far away that light from it hasn't had time to reach us—yet.

而我們無法觀測到宇宙的這些部分有兩大原因，它們不是還在未來、尚未發生，就是太遠了，遠到現在光還沒辦法傳到達我們這。

To explain: As far as we know, the universe had a beginning and is now around 13.8 billion years old.

來解釋一下：就我們所知，宇宙有個起始點，到現在已經約 138 億年這麼老了。

Light takes time to travel through space, so anywhere too far away from us just isn't visible yet in the same way that thunder from a distant lightning strike isn't audible—until you wait long enough.

光線在宇宙間傳輸需要時間，所以離我們太遠的東西，我們就還沒辦法看到。跟打雷一樣，你會看到遠方有閃電，但還聽不到聲音。

If you were blind, the thunder would be the first sign you have of the storm's existence, though once you hear it, you can infer that the storm must have existed all along.

假如你看不見，打雷是讓你知道暴風雨存在的第一個訊號。一旦聽到雷聲，你就可以推論暴風雨的確是一直存在的。

So within the observable universe, what do we know "exists"?

所以在可觀測宇宙內，我們怎麼知道事物是「存在」的呢？

Pretty much just three things: spacetime, particles, and the physical laws that describe how spacetime and those particles interact to give rise to gravity and matter and forces and everything else.

大概是靠這三樣東西來判定：時空、粒子、描述時空和粒子如何相互作用以產生重力、物質、力，以及其他一切的物理定律。

It's open for debate whether or not mathematics is a part of the universe or if it exists "outside" the universe in some sort of mathematical heavens,

至於數學算是宇宙的一部分，還是存在於宇宙外部的某種數學天堂，就還在爭辯中，

but if you think that mathematics exists and if "The Universe" is everything that exists, then, well... I'll leave that up to you.

但假如你認為數學存在，而宇宙包含了所有事物，那麼... 這就由你自己來判斷。

There's one other thing, though—you may have heard of parallel universes, or "Multiverses," an idea proposed by researchers or sci-fi fanatics that perhaps what we think of as "The Universe" is actually just a small piece of a larger thing which is really "everything there is".

還有一件事，你也許聽說過平行宇宙，或是「多重宇宙」。這想法是由一些研究員或科幻狂人所提出，指的是也許我們想像的宇宙僅僅是真正「所有事物」的一小部分。

But that's another verse of the story.

但這又是個另外的故事了。