時間是什麼?
The earliest time measurements were observations of cycles of the natural world, using patterns of changes from day to night and season to season to build calendars. More precise time-keeping, like sundials and mechanical clocks, eventually came along to put time in more convenient boxes. But what exactly is it that we’re measuring? Is time something that physically exists, or is it just in our heads? At first the answer seems obvious— of course time exists; it constantly unfolds all around us, and it’s hard to imagine the universe without it.
最早出現的時間測量 是觀察自然世界的循環, 用白天到黑夜、一季到下一季的 改變模式,來建立出日曆。 更精確的時間記錄,比如日晷 以及機械時鐘,最終都出現了, 把時間放在更方便的盒子中。 但,我們在測量的到底是什麼? 時間有實體的存在嗎? 還是它只是我們腦中的想像? 一開始,答案似乎很明顯—— 時間當然存在; 它經常會出現在我們的周邊, 很難想像沒有時間的宇宙。
But our understanding of time started getting complicated thanks to Einstein. His theory of relativity tells us that time passes for everyone, but doesn’t always pass at the same rate for people in different situations, like those travelling close to the speed of light or orbiting a supermassive black hole. Einstein resolved the malleability of time by combining it with space to define space-time, which can bend, but behaves in consistent, predictable ways.
但,要歸功於愛因斯坦, 我們對於時間的了解開始變複雜。 他的相對論告訴我們, 對每個人,時間都會過去, 但過去的速度就會因情況而異了, 比如在接近光速旅行的情況, 或是在超大質量的黑洞 旁邊運行的情況。 愛因斯坦解決了時間的 可塑性(延展性), 將時間與空間結合, 來定義「空間—時間」, 它可以被彎曲, 但行為仍然是一致、可預測的。
Einstein’s theory seemed to confirm that time is woven into the very fabric of the universe. But there’s a big question it didn’t fully resolve: why is it we can move through space in any direction, but through time in only one? No matter what we do, the past is always, stubbornly, behind us. This is called the arrow of time.
愛因斯坦的理論似乎確認了 時間是被織入到宇宙織物中的。 但還有一個大問題, 是這個理論沒有完全解決的: 為什麼在空間中我們 能朝任何方向移動, 但在時間中的方向只有一個? 不論我們怎麼做,過去始終都 很固執地留在我們身後。 這就是所謂的時間箭頭。
When a drop of food coloring is dropped into a glass of water, we instinctively know that the coloring will drift out from the drop, eventually filling the glass. Imagine watching the opposite happen. Here, we’d recognize time as unfolding backwards. We live in a universe where the food coloring spreads out in the water, not a universe where it collects together.
當一滴食物色素被滴入一杯水中, 我們直覺上就知道, 該色素會從水滴中擴散出來, 最終充滿整個杯子。 想像一下相反的狀況。 在這裡,我們認為 時間是反向呈現的。 我們所住的宇宙中, 食用色素散佈在水中各處, 而不是集合起來成一滴的。
In physics, this is described by the Second Law of Thermodynamics, which says that systems will gain disorder, or entropy, over time. Systems in our universe move from order to disorder, and it is that property of the universe that defines the direction of time’s arrow.
在物理上, 可以用熱力學第二定律來描述它, 該定律說的是,系統會 隨著時間得到混亂或是熵。 在我們宇宙中的系統, 會從有秩序變成混亂, 正是宇宙的這項特性 定義了時間箭頭的方向。
So if time is such a fundamental property, it should be in our most fundamental equations describing the universe, right? We currently have two sets of equations that govern physics. General relativity describes the behavior of very large things, while quantum physics explains the very small. One of the biggest goals in theoretical physics over the last half century has been reconciling the two into one fundamental “theory of everything." There have been many attempts —none yet proven— and they treat time in different ways. Oddly enough, one contender called the Wheeler-DeWitt equation, doesn’t include time at all.
所以,如果時間 是這種根本的特性, 它就應該要出現在 我們用來描述宇宙的 最根本的方程式當中,對吧? 目前,我們有兩組 支配物理的方程式。 廣義相對論描述 大型物體的行為, 而量子物理解釋非常小的物體。 在過去半個世紀, 理論物理最大的目標之一, 就是將兩者調解整合 成為單一的「萬物之理」。 許多人嘗試過,卻沒一個被證明—— 它們都以不同的方式來看待時間。 很怪的是,其中一個角逐者是 惠勒—德威特方程式, 它完全沒有納入時間。
Like all current theories of everything, that equation is speculative. But as a thought experiment, if it or a similarly time-starved equation turned out to be true, would that mean that time doesn’t exist, at the most fundamental level? Could time just be some sort of illusion generated by the limitations of the way we perceive the universe? We don’t yet know, but maybe that’s the wrong way of thinking about it. Instead of asking if time exists as a fundamental property, maybe it could exist as an emergent one.
和目前所有的萬物之理一樣, 該方程式純屬理論推測。 但就思想實驗來說, 如果它或同樣缺乏時間的方程式, 最後證明是真的, 那是否意味著時間不存在於 最根本的層級上? 時間是否可能只是一種幻覺, 因我們受限於對宇宙的感知方式 而產生出來的幻覺? 我們還不知道答案, 但也許那是錯誤的時間思考方式。 不問時間是否真的是 一種根本特性的存在, 而是問它是否是 一種突顯特性的存在。
Emergent properties are things that don’t exist in individual pieces of a system, but do exist for the system as a whole. Each individual water molecule doesn’t have a tide, but the whole ocean does.
突顯的特性不存在於 系統中的個別部分, 而是存在於整個系統當中。 個別的水分子沒有潮汐, 但整體的海洋卻有。
A movie creates change through time by using a series of still images that appear to have a fluid, continuous change between them. Flipping through the images fast enough, our brains perceive the passage of time from the sequence of still images. No individual frame of the movie changes or contains the passage of time, but it’s a property that comes out of how the pieces are strung together. The movement is real, yet also an illusion. Could the physics of time somehow be a similar illusion?
電影透過時間創造出改變, 使用一系列靜態影像, 各影像間有著流暢、連續的改變。 只要非常快速翻動這些影像, 我們的大腦就認為靜態影像序列 是有的時間經過的。 電影中沒有任何一個畫格會改變, 單一畫格也不包含時間經過, 但當各部分被串接在一起時, 就會產生出時間這種特性。 動作是真實的,同時也是種幻覺。 時間的物理有沒有可能 在某種層面上也是類似的幻覺?
Physicists are still exploring these and other questions, so we’re far from a complete explanation.
物理學家仍然在探究 這些及其他問題, 我們離完整的解釋還很遙遠。
At least for the moment.
至少目前是如此。