What Is Time? 時間是什麼？

🔊His argument is short. The past no longer exists, and the future does not yet exist. Only the present is. But how long is the present? This century is not all present, since most of its years are gone or still to come. The same is true of this year, this day, this hour. Take a single minute: part has already fled and part has not arrived. “If an instant of time be conceived, which cannot be divided into the smallest particles of moments, that alone is it, which may be called present. Which yet flies with such speed from future to past, as not to be lengthened out with the least stay.” He concludes: “The present hath no space.” So the past and future are nothing, and the present is a boundary with no extent. What, then, are we measuring when we say that a time was long?

他的論證很短。過去已經不存在，未來還沒有存在。存在的只有現在。可是現在有多長？這個世紀並不是整個都是現在，因為它大部分的年頭不是已經過去，就是還沒到來。今年、今天、這個小時，也都一樣。拿單單一分鐘來說：一部分已經逃走，一部分還沒抵達。「如果設想有一個時間的瞬間，它不能再被分割成最小的片刻，那麼只有它才可以被稱為現在。然而它以如此的速度從未來飛向過去，以致於沒有絲毫的停留可以把它拉長。」他的結論是：「現在沒有長度。」所以過去與未來是無，而現在是一條沒有寬度的界線。那麼，當我們說一段時間很長的時候，我們量的是什麼？

🔊Augustine’s answer is that we measure something in ourselves. It is not strictly correct, he says, to speak of past, present, and future. One should speak of “a present of things past, a present of things present, and a present of things future,” and these exist in the soul: “present of things past, memory; present of things present, sight; present of things future, expectation.” When I recite a psalm that I know by heart, my expectation reaches forward over the whole of it before I begin. As I go on, what was expected passes through my attention and becomes memory, until expectation is used up and all of it is memory. The long time I measure is a long memory or a long expectation. “It is in thee, my mind, that I measure times.” He called time a stretching of the mind.

奧古斯丁的回答是：我們量的是自己裡面的東西。他說，嚴格來講，說「過去、現在、未來」並不恰當。應該說的是「過去事物的現在、現在事物的現在、未來事物的現在」，而這三者存在於靈魂之中：「過去事物的現在是記憶；現在事物的現在是直觀；未來事物的現在是期待。」當我背誦一首熟記的詩篇，在開口之前，我的期待就向前伸展，涵蓋了整首。隨著我往下背，被期待的東西通過我的注意力，變成記憶；直到期待用盡，全部成了記憶。我量到的那段「長時間」，是一段長的記憶，或一段長的期待。「我的心靈啊，我是在你裡面度量時間的。」他把時間稱為心靈的伸展。

🔊Most philosophers have been unwilling to put time inside the mind, since the world surely had a history before there were minds. But they have disagreed about what sort of thing it is outside. Aristotle tied time to change. “Time is just this—number of motion in respect of ‘before’ and ‘after.’” Where nothing whatever changes, no time passes. Newton needed something firmer for his physics, and declared that “absolute, true, and mathematical time, of itself, and from its own nature flows equably without regard to anything external.” Time, for him, is like an empty container that would go on even if the universe were frozen. His rival Leibniz replied that this is a fiction. Time is the order in which events succeed one another, and to speak of time with no events in it is like speaking of a family tree with no people.

多數哲學家不願意把時間放進心靈裡，因為在有心靈之前，世界肯定已經有了歷史。可是，時間在心靈之外是哪一種東西，他們意見不一。亞里斯多德把時間繫在變化上。「時間就是這個：就『先』與『後』而言的運動之數。」什麼都不變的地方，就沒有時間流逝。牛頓的物理學需要更堅實的東西；他宣稱：「絕對的、真實的、數學的時間，自身依其本性均勻地流逝，與任何外在的事物無關。」對他來說，時間像一個空的容器，就算宇宙凍結了，它也會繼續走。他的對手萊布尼茲回應說，這是虛構。時間是事件彼此相續的次序；談論「裡面沒有任何事件的時間」，就像談論「沒有任何人的族譜」。

🔊In 1908 the Cambridge philosopher J. M. E. McTaggart drew a distinction that has organized the debate ever since. Events can be ordered in two ways. In the first, each event is past, present, or future, and its position is always changing: the death of Socrates was once in the far future, became present, and has been sinking deeper into the past ever since. In the second, events are simply earlier or later than one another, and these relations never change. The death of Socrates is earlier than the birth of Augustine, and it always was and always will be.

1908 年，劍橋的哲學家麥塔加畫出了一個區分，此後這場辯論一直照著它來組織。事件可以用兩種方式排序。在第一種裡，每個事件是過去的、現在的或未來的，而且它的位置一直在變：蘇格拉底之死曾經在遙遠的未來，後來成了現在，從那以後就愈來愈深地沉入過去。在第二種裡，事件之間只有「早於」或「晚於」的關係，而這些關係永遠不變。蘇格拉底之死早於奧古斯丁的出生；它過去一向如此，將來也永遠如此。

🔊The question is which ordering describes reality. On one view, often called presentism, only what is present exists, and the moving “now” is the most basic fact about the world. This agrees with experience and with Augustine’s premise. On the other view, called eternalism, all events are equally real, laid out along the dimension of time as places are laid out in space. “Now” is like “here,” a word that picks out wherever the speaker happens to be. Nothing moves. The first view has to explain what the present moves through and how fast, and the only available answer seems to be one second per second, which says nothing. The second has to explain why it feels so strongly as though time passes.

問題是：哪一種排序描述的是實在？有一種看法，常稱為「現在論」，主張只有現在的東西存在，而那個移動的「現在」是關於世界最根本的事實。這符合經驗，也符合奧古斯丁的前提。另一種看法，稱為「永恆論」，主張所有事件同樣真實，沿著時間這個維度鋪開，就像各個地點在空間裡鋪開一樣。「現在」就像「這裡」，是一個指出說話者碰巧所在之處的詞。沒有任何東西在動。第一種看法必須解釋：「現在」穿過的是什麼？移動得多快？而唯一說得出來的答案似乎是「每秒一秒」，這等於什麼都沒說。第二種看法必須解釋：為什麼我們如此強烈地覺得時間在流逝？

🔊Einstein’s theory of relativity, published in 1905, gave the eternalists their strongest argument. It showed that two observers moving relative to each other will disagree about which distant events are happening at the same moment, and that neither is wrong. There is no single “now” that spans the universe. If so, there can be no fact about which events, everywhere, are the present ones, and presentism appears to lose its subject. Late in life Einstein wrote to the family of a friend who had just died that for physicists “the distinction between past, present and future is only a stubbornly persistent illusion.”

愛因斯坦在 1905 年發表的相對論，給了永恆論者最強的論證。它顯示：兩個彼此相對運動的觀察者，對於遠處的哪些事件「同時」發生，會有不同的判斷，而兩人都沒有錯。並沒有一個橫跨全宇宙的、單一的「現在」。若是如此，「全宇宙各處，哪些事件是現在的」這件事就沒有事實可言，而現在論似乎失去了它談論的對象。愛因斯坦晚年寫信給一位剛過世的朋友的家人，說對物理學家而言，「過去、現在與未來的區分，只是一個頑固持續的幻覺。」

🔊Physics also deepens a second puzzle. Its basic laws work equally well in either direction of time, and yet eggs break and do not unbreak, and we remember yesterday and not tomorrow. The standard explanation appeals to entropy: the universe began in an extremely orderly state and has been growing more disordered ever since, and the direction of increasing disorder is what we call the future. Why the universe began that way is not known.

物理學還加深了第二個謎。它的基本定律在時間的兩個方向上同樣適用；然而蛋會破，不會復原，我們記得昨天，不記得明天。標準的解釋訴諸熵：宇宙從一個極度有序的狀態開始，此後一直變得更無序；而無序增加的方向，就是我們所說的未來。至於宇宙為什麼那樣開始，沒有人知道。

🔊Classical Chinese thought was little troubled by Augustine’s question and deeply interested in another. The word for the cosmos, 宇宙, is itself a theory of space and time. An early definition runs: “What has gone and what is to come, from of old until now, is called zhou (宙); the four directions with above and below are called yu (宇).” Time and space are named together as the two aspects of everything there is. Within that frame the pressing question was a practical one, what the moment calls for. The word 時 means “time,” “season,” and “timeliness,” and Mencius’s highest praise of Confucius was that he was “the sage who was timely” (聖之時者): he took office when it was right to take office and withdrew when it was right to withdraw. The Greek tradition treated time mainly as something to be measured or explained. Here it is something to be answered, as a farmer answers the seasons.

中國古典思想很少為奧古斯丁的問題煩惱，卻對另一個問題深感興趣。「宇宙」這個詞本身，就是一套關於空間與時間的理論。有一個早期的定義是這樣的：「往古來今謂之宙，四方上下謂之宇。」時間與空間被並列命名，當作一切存在之物的兩個面向。在這個框架之內，迫切的問題是實踐上的：這個時刻要求什麼？「時」這個字的意思是「時間」「時節」，也是「合乎時宜」；孟子對孔子最高的讚語，就是「聖之時者也」：該出仕的時候出仕，該退的時候退。希臘傳統主要把時間當作要被度量或被解釋的東西。在這裡，它是要被回應的東西，就像農夫回應四季。

🔊The metaphysics of time seems remote from life, and it bears on how we live more directly than most of philosophy does. If only the present exists, then the dead are simply nothing, and so is everything you have done. If all times exist, then every moment of your life is permanently part of what there is, and its being over means only that it lies in an earlier part of the whole. People have found comfort in the second picture and some have been horrified by it. Augustine found his own answer by looking inward. He concluded that we are stretched across time, pulled between what we remember and what we expect, and that this stretching is what a human life is. With that conclusion the third unit ends. We have asked what a thing is, whether change is real, whether we are free, and what time is. In each case the plain facts, that ships are repaired, rivers flow, people choose, and the clock moves, turned out to be much less clear than they seemed.

時間的形上學似乎離生活很遠；其實它對我們怎麼活的影響，比哲學的大部分內容都更直接。如果只有現在存在，那麼死者就是單純的無，你做過的一切也是。如果所有的時刻都存在，那麼你生命中的每一刻都永久地是「存在之物」的一部分；它「過去了」，只表示它位於整體當中較早的那一段。有人在第二幅圖像裡找到安慰，也有人被它嚇壞了。奧古斯丁靠著往內看，找到了他自己的答案。他的結論是：我們被拉開、橫跨在時間之上，在記得的與期待的之間被拉扯；而這個「被拉開」，就是人的一生。第三單元就以這個結論結束。我們問過：一樣東西是什麼？變化是不是真的？我們自由嗎？時間是什麼？在每一個問題上，那些明擺著的事實——船會被修補、河在流、人做選擇、時鐘在走——結果都遠不如看起來那麼清楚。