測量定義時間 | 諾獎得主Wilczek專欄_風聞
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作者 | Frank Wilczek（麻省理工學院教授、2004年諾貝爾獎得主）
翻譯 | 梁丁當**、胡風**
來源：蔻享學術
時間是什麼？時間在根本上到底是連續的，還是由某種尚未探測到的離散單元組成的？儘管我們對時間的測量越來越精確，但我們依然不理解時間的本質。
時間的精確測量是物理學的一項輝煌成就，現在仍是個激動人心的前沿領域。
Accurate measurement of time is one of the glories of physics, and one of the most exciting frontiers of current research.
在歷史的長河中，人類大部分時候都是利用太陽和月亮來計時的。地球自轉一週構成我們的“一天”，繞着太陽公轉一圈便是我們的“一年”，而地球和月球的華爾茲則給了我們“月”的概念。日晷利用物體在陽光下的投影來測定時辰，但它也有明顯的缺陷，比如陰天多雲的時候，它就不管用了。
For most of history, people measured time using the sun and moon. Earth’s rotation gives us the day, its revolution around the sun gives us the year, and its dance with the moon gives us the month. Sundials used the shadow cast by the sun to track the hours, but they had drawbacks; for one thing, they didn’t work on cloudy days.
對於更短的時間，人們在數個世紀中都是用沙漏和水鍾來計量的，但它們的精確度容易受到温度和濕度變化，以及振動的影響。到了中世紀，機械鐘出現了，它由擺錘與精巧的齒輪系統構成，代表了當時的技術巔峯。到了20世紀初，這些基於擺錘和彈簧的時鐘進一步演變成各種做工精妙的鐘表，但它們仍然擺脱不了摩擦的影響。摩擦會妨礙鐘擺移動，還會導致零件損耗。
To measure briefer periods of time, hourglasses and water clocks served for many centuries, even though changes in temperature, humidity and vibration could throw them off. Mechanical clocks using falling weights and elaborate systems of gears were a high point of medieval technology. By the early 20th century, clocks with pendulums and springs had evolved into remarkable, beautifully contrived instruments. But even these clocks were subject to friction, which affects their movements and wears away their parts.
而對電磁場和物質的更深入理解，讓人們能夠製造更精準的時鐘。電子的流動取代了流沙或滴水，電磁場取代了齒輪，微小的石英取代了彈簧。目前最先進的時鐘利用原子或分子的振動來測量時間。最精確的原子鐘即便經過了相當於宇宙年齡那麼長的時間，誤差都不會超過1秒。
Increased understanding of electromagnetism and of matter in general made even better clocks possible. Flows of electrons replaced flows of sand or water; electromagnetic fields replaced gears; tiny quartz crystals replaced springs. Today’s cutting-edge clocks are based on measuring the vibrations of atoms and molecules. The most precise atomic clocks are so accurate that, over a period of time equivalent to the whole history of the universe to date, they would be off by less than one second.
當今這些精通量子力學的鐘表匠還在追尋着更高的計時精度。比如，原子核的振動比原子整體的振動更快，因此有可能利用原子核的振動來計時，製造出比原子鐘更準的原子核鍾。精度更高的時鐘可以幫助物理學家判斷時間在根本上到底是連續的，還是由某種尚未探測到的離散單元組成的。更精密的時鐘有着廣泛的用途，比如開發更好的GPS系統，或是探測引力波。
Today’s quantum horologists are looking to improve things further. For instance, it might be possible to monitor atomic nuclei, which vibrate faster than whole atoms. More accurate clocks would help physicists determine whether time is truly continuous or fundamentally granular, made from units yet to be detected. More tangible applications of better timekeeping abound as well, from developing better GPS systems to detecting passing gravitational waves.
雖然這些時鐘千差萬別，它們給出的時間卻是一致的。我們很容易把這個事實當成理所當然，但其實它是非常不可思議的。人的情緒不同時，感受到的時間流逝速度也不同，可能是白駒過隙，也可能是度日如年。但事實上時間在極為嚴格地均勻流動，這是一個現實世界的客觀性質，不受人主觀意識的影響。
It is an amazing fact, too easily taken for granted, that all these radically different sorts of clocks agree with one another. In different moods we might feel time’s flow to be a surge or an ooze, but its rigorous uniformity is an objective feature of physical reality.
儘管我們對時間的測量越來越精確，但我們依然不理解時間的本質。在古羅馬神學家、哲學家奧古斯丁（Augustine）的名著《懺悔錄》（Confessions，撰寫於397-398年）的第11章中，我們可以找到一段關於時間的最佳哲學討論。奧古斯丁是一位基督教主教，一位信徒問了他一個讓人頭疼的問題：“上帝創造世界之前在做什麼？” 奧古斯丁曾考慮過類似這樣的回答：上帝在為那些窺探天機的人準備地獄。然而他最終決定認真對待這個問題，並觸及了它的根源。
Even as we get better at measuring time, however, its nature remains hard to grasp. One of the best philosophical discussions of time can be found in chapter 11 of St. Augustine’s “Confessions,” written in 397-398. Augustine was a Christian bishop, and one of his parishioners asked him a vexing question: “What was God doing before creation?” Augustine considered, but rejected, the answer “He was preparing hell for those who pry into mysteries.” Instead, he took the question seriously—and got to its root.
奧古斯丁指出，每當我們使用“以前”或者“以後”這樣的術語時，我們都在談論時間，可它的本質卻似乎很神秘：“時間是什麼？如果沒人問我，我知道，可如果我試圖去解釋它，卻又做不到。”但是奧古斯丁發現了一個道理，其中藴含了後來相對論和量子理論的一個核心思想：如果要理解一樣事物，你就必須考慮它是如何測量的。正如他所説：“如果我們不能測量，那它就什麼都不是。”
Whenever we use terms like before and after, Augustine reasoned, we are speaking of time, whose essence seems mysterious: “What is time? If no one asks me, I know, but if I try to explain it, I cannot.” But he discovered a principle that anticipates a major theme of relativity and quantum theory: To understand what something is, you must think about how it is measured. As Augustine puts it, “What we measure not, is not.”
按照這個邏輯，奧古斯丁關於“什麼是時間”這個問題的答案很簡單：“時間就是時鐘所測量的東西。”根據這樣的理解，那個信徒的問題就解決了：因為在上帝創世之前沒有時鐘，所以就沒有時間。在當今物理宇宙學中，類似的問題依然存在，比如“大爆炸之前發生了什麼？”也許奧古斯丁的回答仍然是我們能給出的最好答案：在無法測量時間的背景下討論什麼是“以前”，是毫無意義的。
Following this logic, Augustine’s answer to “What is time?” is simple: “Time is what clocks measure.” With that understanding, the parishioner’s question dissolves. Before creation there were no clocks, and without clocks there could be no time. Today, in physical cosmology, the parishioner’s question is still with us, in the form “What happened before the Big Bang?” I suspect that Augustine’s answer might still be the best one we have: To ask about “before,” in that timeless context, is literally senseless.
作者簡介：**Frank Wilczek：**弗蘭克·維爾切克是麻省理工學院物理學教授、量子色動力學的奠基人之一。因在夸克粒子理論（強作用）方面所取得的成就，他在2004年獲得了諾貝爾物理學獎。
版權聲明：本文經授權轉載自微信公眾號「蔻享學術」。
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