Time is an ancient and contrary mystery. Augustine of Hippo, writing his Confessions in a North African monastery, asked “Who can even in thought comprehend it, so as to utter a word about it? But what in discourse do we mention more familiarly and knowingly, than time?” 時間是古老而永恒的未解之謎。奧古斯丁在北非修道院里寫下他的《懺悔錄》：“誰對此有明確的概念，能用言語表達出來？可是在談話之中，有什么比時間更常見，更熟悉呢？” More than 16 centuries later, many scholars share the feeling, if not the prospect of sainthood. “We don’t even know what time is. But we can measure it really, really well,” says Chris Oates, a physicist at the National Institute of Standards and Technology’s Boulder, Colo., campus. 十六個多世紀(jì)之后，很多學(xué)者都有這種感覺，這當(dāng)然不是作為圣徒的奧古斯丁做出的預(yù)言。“我們完全不知道時間是什么，但是我們能夠非常真實地感受到它的存在。”科羅拉多大學(xué)國家標(biāo)準(zhǔn)和技術(shù)研究院的物理學(xué)家克里斯·奧茨（ Chris Oates）如是說。 His team operates a ytterbium optical lattice clock, one of the latest types of souped-up atomic timepieces. To track the passing seconds, such clocks rely on the fixed frequencies of photons absorbed and emitted by atoms’ electrons as they change energy levels. Recently, scientists have found ways to make these quantum counters even better, by switching from a reliance on microwave frequencies to the faster-paced optical regime and introducing a system of checks that relies on multiple atoms in levitated grids. In a remarkable recent development, the central atomic metronomes are protected from distortion by a method so powerful that physicists formally call it magic. 他的團隊研發(fā)了一種鐿原子光晶格鐘，一種最新的加強版原子鐘。其原理是，當(dāng)質(zhì)子吸收和激發(fā)電子時，因電子的能級改變而產(chǎn)生的電磁波頻率是固定的。最近，科學(xué)家已經(jīng)發(fā)現(xiàn)了數(shù)種改良這些量子計數(shù)器的辦法，只需將微波頻段調(diào)至頻率更快的可見波段，并引入基于懸浮網(wǎng)格的多原子格子系統(tǒng)。最近一項突破性進展是通過一種物理學(xué)家都正式稱為“魔法（magic）”的有效方法使原子鐘核心部分避免失真。 Oates is a member of a worldwide cadre working with such devices at the frontier of clockmaking. His team’s clock loses time at a rate of about one second every few hundred million years. 奧茨處于全球研究原子鐘的前沿。其團隊的原子鐘誤差為1億年內(nèi)不大于1秒。 譯者注：這里用了更科學(xué)的表述，而不局限于英文原文，作為對比平常的原子鐘誤差為十萬年內(nèi)不大于一秒。 Speedy metrology 快速發(fā)展的計量學(xué) Such accuracy is why time is not just one dimension among several but a foundation for defining other fundamental units. The meter’s definition has been defined with increasing accuracy by such things as one ten-millionth the distance on a circular arc from the equator to the North Pole, and by a precision-made “prototype meter” bar of metal alloy kept in Paris. In 1983 the meter officially became the distance light will travel in a vacuum in 1/299,792,458 of a second. The better the stopwatch, the better such definitions can be applied. 這樣的精度解釋了時間不僅是一個普通的維度，也是定義其他基本單位的基礎(chǔ)?！懊住钡亩x越來越精確，最初被定義為“從赤道到北極圓弧長度的一千萬分之一”，并在巴黎保存了一個用金屬合金精確制作的“標(biāo)準(zhǔn)米原器”。1983年“米”被正式定義為“1/299792458秒的時間間隔內(nèi)光在真空中行程的長度”。計時器越精確，對米的定義就越精確。 The metrology of time is not holding still. In the April-June issue of Reviews of Modern Physics, experimental physicist Hidetoshi Katori of the University of Tokyo and theorist Andrei Derevianko of the University of Nevada, Reno declared dramatic ambitions for a record-breaking atomic clock based on emissions from mercury atoms. 而對時間的度量并非一成不變的。在4月至6月召開的“回顧現(xiàn)代物理會議”上，東京大學(xué)的實驗物理學(xué)家秀敏香?。℉idetoshi Katori ）和內(nèi)華達大學(xué)理論物理學(xué)家安德烈·杰列維揚科（Andrei Derevianko）表示他們（從理論上）論證了一種基于汞原子激發(fā)態(tài)的原子鐘，并對其破紀(jì)錄很有信心。 “If someone built such a clock at the Big Bang and if such a timepiece survived the 14 billion years, then the clock would be off by no more than a mere second,” they note in the paper. That is actually conservative. The goal formally is to lose or gain no more than one out of every billion billion seconds. That is one second in about 32 billion years, and is 10 to 100 times better than any existing clocks. “如果有人能在大爆炸時做了這么一個鐘，并且能保存140億年，其誤差也不會超過1秒?！彼麄冊谡撐闹新暦Q。事實上這還是保守估計。嚴(yán)格地說其誤差為每艾秒誤差不超過1秒，即大約320億年內(nèi)不超過1秒，這比目前任何鐘表的精度都高10-100倍。 In scientific shorthand, the proposed mercury clock would reach a fractional uncertainty of at most one part in 1018 — it would run for 1,000,000,000,000,000,000 seconds before being one second awry. 在數(shù)學(xué)縮略詞中這表示汞原子鐘達到了10的18次方分之一的精度，即在發(fā)生1秒的誤差前它已經(jīng)正常工作了 1000000000000000000秒。 Already, atomic clocks have come a long way. While experimental clocks are moving ahead, a device called the NIST-F1 is the official U.S. timekeeper. It’s accurate to a few parts in 1016. It occupies a large first floor room in Building One at NIST’s Boulder campus. The dominant feature is a shiny steel vacuum chamber 8 feet high. Inside is a laser-controlled fountain of cesium atoms chilled to near absolute zero. The atoms rise in clumps about as large as a man’s thumb and, responding to gravity, fall back through a cavity in a tunable microwave generator. 原子鐘“其路漫漫”。實驗原子鐘正在不斷更新進步，美國標(biāo)準(zhǔn)計時器名叫NIST-F1，其精度達為10的16次方分之幾。它占據(jù)了美國國家標(biāo)準(zhǔn)技術(shù)研究所（NIST）博爾德分部“建筑一”一樓的大塊地盤。其顯著特征是有一個8英尺高的鋼制真空室，里面由激光將銫原子冷卻到接近絕對零度。這些原子聚集成簇大得像人的拇指，在重力作用下落并經(jīng)過一個裝有可調(diào)微波發(fā)生器的腔體。 Oscillations within the cesium atoms are akin to the to-and-fro of the balance wheel in an old wristwatch, but it is the microwave generator that communicates with the outside world. Just as the ticking of a watch arises from the escapement mechanism connected to the gears and hands, oscillations within the cavity are recorded electronically. 銫原子的振蕩有點像老式手表來回擺動的擺輪，但是是通過微波發(fā)生器和外部交換信息。就如擒縱機構(gòu)和齒輪、指針之間的接觸使得手表發(fā)出滴答聲一樣，腔體內(nèi)的振蕩是電子化記錄的。 By itself, the microwave generator would drift off time. So with each passage of the atoms, the generator checks to be sure its pulsations exactly match the signal from a chosen energy transition in the atoms’ electron clouds — an electromagnetic wave that beats 9,192,631,770 times a second. 微波發(fā)生器自身會發(fā)生時間偏差。發(fā)生器要對原子的每個通道進行檢查確保其振蕩要和選擇的電子云能量（大約是每秒振蕩9192631770次的電磁波）保持精確一致。 NIST is now working on a successor, called F2. With an improved cooling system and superior way of moving the atoms through the microwave chamber, it will be about four times better and will beat out the current record for a long-term timekeeper, a clock in the United Kingdom that is accurate to about two parts in 1016. NIST正在研制其后繼者，稱為F2。隨著冷凍技術(shù)的進步和用微波腔移動原子的便捷性提高，F(xiàn)2的性能將提高大約4倍，并且將打破目前英國原子鐘長期保持的10的16次方分之2的記錄。 Such astonishing accuracy is no mere intellectual exercise. Recent advances in timekeeping have brought practical payoffs in the design of better global positioning systems that triangulate locations on Earth by measuring distance via radio-signal travel time, as measured by satellite-borne atomic clocks. Further progress should lead to instruments able, from the slowing or speeding of time’s passage due to shifts in gravity, to improve maps of the planet’s interior and to find mineral deposits or detect the movements of deep magma. Pure research on Earth and in space may gauge to almost unimaginable exactness the stability (or drift) of supposed constants of physics that not only affect nuclear decay, but also, some astronomers say, may have worked differently in distant eras. 這樣驚人的精度不僅僅是吃飽了沒事干，最近計時器的進步為設(shè)計更好的全球定位系統(tǒng)奠定了基礎(chǔ)，定位的依據(jù)就是通過星載原子鐘計算無線電信號在一定時間里運動的距離，將地球分為若干個三角形區(qū)域。計時器的進一步發(fā)展可以導(dǎo)致探測儀器的進步，比如測量由于引力變化導(dǎo)致的時間加快或減慢，行星地質(zhì)地圖的細(xì)致化，尋找礦床或者探測深層巖漿的移動。一些天文學(xué)家表示，對地球和宇宙的純理論研究表明物理常數(shù)難以想象的穩(wěn)定性（或發(fā)生偏移）并不單只影響核衰變，也可能在遙遠的過去發(fā)生不同作用。 譯者注：常用的物理常數(shù)構(gòu)成了所謂的精細(xì)結(jié)構(gòu)常數(shù)，倘若其值大一點點或者小一點點都會使得宇宙在大爆炸后向不同的方向發(fā)展，那樣的話，不要說沒有人類，有沒有地球，能不能形成重元素都是個問題。 Ticking gears 瘋狂的時鐘 By historic standards, clock progress is now frenzied. 從歷史上看，現(xiàn)在鐘表的進步簡直可以用瘋狂來形容。 People have long kept track of time by monitoring processes that change measurably in a steady way. Early peoples monitored the seasons by the motion of the sun and moon. An 11th century Chinese water clock, its gears driven by a steady stream, might lose or gain 10 minutes a day — an accuracy of about a part in 100. Large, stable swinging pendulums in the 1600s were good to a few seconds a day. Eighteenth century navigation clocks that were the pride of the British Navy weren’t much better. They lost or gained a minute or less per month, an accuracy of about one in 10,000, but they did it while tossing about in ships at sea. Quartz clocks and watches, paced by electrically stimulated crystals vibrating at about 32,768 times per second, were developed in the late 1920s. They keep time to within a second per day, better than a part in 105. 人們長期以來都是通過監(jiān)控某個恒定可測的變化過程來記錄時間的。早期人類通過太陽和月球的運動來區(qū)分四季。11世紀(jì)的中國水運儀象臺，其齒輪由恒定水流驅(qū)動，一天里的誤差為10分鐘，即精度大約為百分之一。17世紀(jì)大而穩(wěn)定的擺鐘一天的誤差縮小至幾秒。18世紀(jì)英國皇家海軍引以為傲的航海鐘并沒有更好到哪去。它們每月的誤差為1分鐘，即精度約為萬分之一，但是它們是應(yīng)用在呼嘯的大海上的。20世紀(jì)20年代發(fā)明了石英鐘表，其原理是石英在電力激發(fā)下會發(fā)生晶體振動，大約每秒32768次。其誤差為每天小于1秒，即比萬分之一強些。 Then along came atomic clocks, following the beat of quantum mechanics, the laws that govern the energies of electrons bound to nuclei. Every 10 years since the first one debuted in 1949, based on oscillations in the ammonia molecule, the accuracy has increased by about 10 times. Recently, things have gone even faster. 伴隨著量子力學(xué)的橫空出世，核子與電子間的作用法則被揭示，之后就輪到原子鐘獨領(lǐng)風(fēng)騷了。自1949年首個原子鐘（以氨分子為磁振源）面世以來，原子鐘的精度每十年就幾乎提高十倍。近年來，其增速更快了。 While devices like the NIST-F1 use atomic signals of microwave frequency with billions of cycles per second, newer clocks, including Oates’, rely on light waves beating a million times faster. The new approach “is like having a ruler with more divisions,” says Tom O’Brian, NIST’s chief of the divisions of Time and Frequency and of Quantum Physics. “The pace of improvement is skyrocketing.” 諸如NIST-F1的儀器運用的原子信號是頻率為數(shù)十億赫茲的微波，新式時鐘包括奧茨的都是運用頻率快上百萬倍的光。NIST時間與頻率部及量子物理部的負(fù)責(zé)人湯姆·布萊恩表示新方法就好比“有了一把精確度更高的尺子”，“其發(fā)展速度真是和坐火箭一樣?！? A further development, the lattice clock, has been imagined only in the last decade, with rapid progress in the last five years. For now, related devices called single ion optical clocks, which key in on solitary electrically charged atoms such as aluminum, are the most accurate. However, lattice clocks’ use of many atoms simultaneously, with a strong combined signal, appears to give these clocks the ultimate edge. 進一步發(fā)展的晶格鐘是在過去十年才被構(gòu)想出來，在過去五年取得了實質(zhì)性進展。目前將這種網(wǎng)格裝置稱為單離子光學(xué)鐘，其關(guān)鍵在于孤立帶電原子比如鋁，它們的精度最高。但是晶格鐘通過一個強信號同時操縱多個原子，使得它們有一個終極邊界。 Katori says his team in Tokyo hopes to have the first clock with one part in 1018 accuracy working within five years. A look at how the record-setting mercury clock would work reveals the basics of all contemporary neutral-atom lattice clocks. 香取說其在東京的團隊希望在五年內(nèi)制作出首個精度達到10的18次方分之一的原子鐘。通過觀察這個汞原子鐘是如何工作的將奠定目前所有中性原子晶格鐘的基礎(chǔ)。 At a glance, the proposed clock is a bewildering laser beam jubilee — but there is underlying order. 乍看上去這個目前仍停留在紙上的時鐘就是一簇眼花繚亂的激光束聚在一起過節(jié)，但是其本質(zhì)是有序的。 The action starts with a system of cooling lasers that bathe a thin vapor of mercury atoms in what is called “optical molasses” to slow their motion. Temperatures hit a few millionths of a degree above absolute zero, a coolness at which each atom drifts roughly at the walking speed of ants. But even at that slow speed, the motion causes a slight blur in the atoms’ collective optical signals. 通過冷激光系統(tǒng)給汞蒸氣“洗冷水浴”減緩汞原子的運動使其成為所謂的”光學(xué)粘團（optical molasses）”。溫度可以達到只比絕對零度高百萬分之幾度，使得每個原子的運動都像螞蟻爬一樣慢。但是即便是如此慢的速度，其運動仍將引起原子團光信號的輕微模糊。 The cooling lasers propel the chilled atoms gently into a zone where another laser system’s beams cross one another. The interacting light waves, sometimes doubled up by mirror systems, form a tiny three-dimensional array of shimmering energy fields. 冷激光將冷卻原子推入一個存在互相垂直激光的區(qū)域?；ハ嘧饔玫墓獠ǎㄓ袝r可以通過鏡像系統(tǒng)達到增強）形成一個小型三維能量場。 This is the lattice. Its standing waves rise and fall but do not propagate. When the fields’ energies are diagrammed, they take on a pattern that looks a bit like the hollows in egg cartons. These nodes trap and hold the atoms — ideally one atom per energy well — in perfectly aligned ranks. The entire array of atoms is levitated in a tiny near-vacuum about 100 micrometers across, roughly the thickness of a page in a glossy magazine like this one. Most important, the trapping lasers whose beams produce the lattice will be set to a “magic frequency” — a recent breakthrough in the field — to grip the atoms in place while not distorting the shapes of their electron clouds. 這就是所謂的“晶格”。它形成了起起落落的駐波但是并不傳播。當(dāng)能量場被繪制出來時，它看起來有點像凹下去的蛋箱。那些凹下去的節(jié)點就好像陷阱能抓住原子（理想狀態(tài)是一個能量阱一個原子），且所有的陷阱都完美地在同一級別上。完整的原子陣列懸浮在一個微小的近真空環(huán)境中，大約100微米長寬，厚度大概是一頁雜志的厚度。最重要的是，用以俘獲原子形成網(wǎng)格的激光束被設(shè)置在了一個“魔法”頻率，快要突破場的極限但能陷住原子同時不改變其電子云分布。 All that is preamble to the key step. A clock laser will, a bit faster than once per second, illuminate the atoms, adjusting itself as needed to match the frequency at which they most easily absorb and emit light. Lasers may be popularly considered the essence of precision optics and purity of color. But at the esoteric edge of the timekeeper’s craft, they are too wobbly to keep time by themselves. Thus the clock laser’s orderly light waves are paced by the atomic metronome — just as a drill sergeant keeps troops in precise cadence. 以上才代表關(guān)鍵步驟剛剛開始。原子鐘所用激光（頻率比1赫茲快些）照射在原子上，讓原子調(diào)整自身以匹配其吸收或激發(fā)激光的最佳頻率。激光具有良好的光學(xué)精密性和單色性。但是在這個原子鐘的裝置里，它們還是太不穩(wěn)定了不能靠自身確保時間。因此用原子節(jié)拍器對其調(diào)節(jié)使其有序，就好像教官喊節(jié)拍一樣。 Just one more big step: reading the clock. Though this clock relies on visible light, optical waves flicker far too fast, nearly a million billion times per second, for electronic circuits to count one by one. So, the clock laser is keyed in turn to yet another recent invention, what’s called an optical comb laser. It is many thousands of lasers in one. Its multiple wavelengths, when plotted, look like the teeth of a comb, stretching across a vast frequency range. Optical combs were a big reason another scientist at NIST, John Hall, shared a Nobel Prize in 2005. 下一個重要步驟是：讀取時間。盡管原子鐘用的是可見光，光學(xué)波頻率很大，接近1拍赫茲，而電子線路是一個一個計數(shù)的。所以還應(yīng)用到了另一項最新技術(shù)，即所謂的“光梳（光頻率梳）”。它是數(shù)千束激光集合在一起，自然就有多種波長，將它們繪制出來看起來就像梳子的梳齒一樣，涉及的頻譜也很寬廣。光梳也是NIST另一科學(xué)家約翰·霍爾（John Hall）和另外兩位科學(xué)家共享2005年諾貝爾物理學(xué)獎的一個重要原因。 The comb’s function is akin to a transmission’s gears. By synchronizing one of the optical teeth with the clock laser, atomic clockmakers force the other teeth to become equally stable. That way one of those in the microwave domain can be selected to deliver a countable beat, a million times slower. 光梳的作用和傳動裝置中的齒輪一樣重要。通過將激光和光梳某個梳齒同步，制作者可以使得其他梳齒變得同樣穩(wěn)定。這樣的方法在微波領(lǐng)域能用來減慢光頻率一百萬倍，使得其變得可測量。 Now, a pause to ponder magic. By the 1990s it was clear that laser lattices would allow a probe laser to gaze at a throng of trapped atoms long enough to get a better reading on their signal than is possible with a fountain clock such as the F1. The lattice would also prevent collisions among the atoms, a key source of distortion in microwave fountain clocks. 現(xiàn)在我們停下來思考一下所謂的“魔法”。20世紀(jì)90年代人們就已經(jīng)知道激光網(wǎng)格能讓探測激光在足夠長的時間里陷住一大群原子以便能獲得比F1那種噴泉鐘更準(zhǔn)確的信號。同時網(wǎng)格能避免原子間的互相碰撞，而這是噴泉鐘產(chǎn)生微波信號干擾的關(guān)鍵原因。 譯者注： fountain clock噴泉鐘，顧名思義就是以原子噴泉為原理的原子鐘，比如文中提及的F1，為何叫噴泉呢？文中也提到，將原子上拋和下落過程中要經(jīng)過諧振器，這個上拋和下落和噴泉相似，物理學(xué)家因此命名。 However, lattices come with a price. Their oscillating electromagnetic fields typically and severely distort atomic energy levels. One can easily guess how badly a violin would go off tune if someone squeezed its belly and twisted its scroll just as the violinist was striving for a delicate note. 可是網(wǎng)格造價昂貴，而所需的振蕩電磁場嚴(yán)重的扭曲了原子能級。我們不難想象一個小提琴共鳴器受到擠壓、琴弦受到扭曲時后果有多糟糕，所以小提琴手對此都很注意，原子鐘也一樣。 In 2001, Katori and colleagues began publishing proposals that there might be a cure. Perhaps there could be certain frequencies of trapping fields that would displace the boundaries of one key energy transition by exactly the same degree. Katori’s insight, bolstered by calculations by Derevianko and others, offered a way to grab that violin roughly yet leave one selected note unwavering. 2001年香取及其合作者開始研究解決辦法。也許俘獲場的某一頻率能同等程度地代替一個關(guān)鍵能級跳躍的閥值。香取的觀點被杰列維揚科和其他人的計算證實了，他們提供了一種能夠抓住“小提琴”而不改變其音質(zhì)的方法。 In conversations with Katori, Nobelist Hall said such frequencies sounded like magic. Some journal editors initially resisted when formal papers referred to magic. But the name stuck. 霍爾在和香取交談時談到這樣的頻率聽起來就像魔法。當(dāng)正式論文提及“魔法”時一些雜志編輯起先還很反對呢。但是這個名字還是保留下來了。 Magic frequencies give lattice clocks accuracy a billion-fold better than they would otherwise manage. “That is nine orders of magnitude,” Derevianko says. “That is magic happening.” 魔法頻率使得晶格鐘比其他形式的原子鐘精確十億倍。“那可是九個數(shù)量級呢，”杰列維揚科說，“可不就是魔法啊。” Katori calls it “a gift from nature.” 香取則稱它是“大自然的禮物”。 With magic frequencies soon discovered for several atoms suitable to trapping in lattices, physicists now had an army of atoms, says Jun Ye of JILA, an institute that NIST and the University of Colorado operate jointly. “A million-man army is better than a one-man army.” 魔法頻率能很快發(fā)現(xiàn)一些原子適合被晶格俘獲，物理學(xué)家現(xiàn)在有了一支原子軍隊，JILA （NIST與科羅拉多大學(xué)聯(lián)合建立的實驗天體物理實驗室）的葉軍如是說，“一百萬人的軍隊就是比一個人的軍隊好?！? Ye’s group operates a strontium-based lattice clock. In 2007 he interlinked, via optical fiber, his clock with a calcium-based lattice clock in Oates’ lab at NIST. The two researchers were able to cross-check the time to an accuracy of one in 1016, an exercise proving that such clocks can be interlinked over electronic and optical circuits. 葉的團隊研發(fā)了鍶原子晶格鐘。2007年通過光學(xué)纖維他將他的原子鐘和NIST奧茨的鈣原子晶格鐘連接起來。兩位研究者就可以以10的16次方分之一的精度反復(fù)核對時間，這證明這樣的原子鐘可以通過電學(xué)和光學(xué)電路連接起來。 Beyond the tock 滴答聲的背后 Such advances are the latest step in humankind’s ancient drive to measure how long it takes things to happen, whether for a season to pass or an automobile equipped with GPS navigation to drive 10 feet as monitored by the changed time for a radio signal to reach and return from two distant satellites whose locations are known. A one in 1018 clock would allow location to a matter of inches — on Mars using satellite transceivers at Earth. 如此的進步是人類從古至今試圖測量時間的最新進展，無論是季節(jié)的變遷還是裝有GPS導(dǎo)航的汽車都離不開時間的變化，后者即是根據(jù)兩個已知位置的遠距離衛(wèi)星來回收送無線電信號來確定的。比如火星和地球各有一個衛(wèi)星收發(fā)無線電，則一個精度達到10的18次方分之一的原子鐘就可以幫忙定位到英寸大小的物體。 The European Space Agency aims to make the International Space Station a platform for fundamental discovery with lattice clocks. That agency, along with the French space agency, has already begun a mission called ACES, or Atomic Clock Ensemble in Space. Its aim is to install on the space station a laser-cooled cesium microwave clock, with accuracy of about one in 1016. 歐洲航天局（ESA）想通過使用晶格鐘使得國際空間站成為一個基礎(chǔ)研究的平臺。歐洲航天局和法國太空署已經(jīng)開始了一項名叫ACES的項目，全稱是“Atomic Clock Ensemble in Space（原子鐘組合在太空）”（譯者注：一般直譯為“太空鐘”）。其目的是在空間站組裝一臺精度為10的16次方分之一的激光冷卻銫原子微波原子鐘。 Linking to ground clocks based on different atoms and atomic transitions in a worldwide network, the timekeeper will probe fundamental laws of physics to high accuracy, says Luigi Cacciapuoti of ESA’s astrophysics and fundamental physics division. Under scrutiny will be such esoterica as the constancy of the speed of light in all directions, and Einstein’s equivalence principle declaring that gravity and acceleration have the same effects on time and physical processes. With shuttles retired, the first such clock could be delivered by a Japanese or other automated transfer vehicle as early as 2014. ESA天文物理和基礎(chǔ)物理部的路易吉·卡恰波蒂（Luigi Cacciapuoti）表示，如果將太空鐘的原子鐘與地面各種基于不同原子和原子躍遷的原子鐘納入一個全球范圍的網(wǎng)絡(luò)，那么計時器就使得人類可以以高精度探測物理基本定律。比如我們可以在各個方向上驗證光速是否是恒定不變的，愛因斯坦的等效性原理認(rèn)為重力場與以適當(dāng)加速度運動的參考系是等價的（無論是時間上還是物理過程上）。隨著航天飛機的退役，首個這樣的原子鐘最早將于2014年將通過日本或者其他自動運載飛船運往國際空間站。 Stephan Schiller of Heinrich-Heine-Universit?t in Düsseldorf, Germany, and colleagues, in a program called Space Optical Clocks, hope to put aboard the station around 2020 an optical lattice clock 10 times as accurate. They look forward to comparing the relativistic effect of Earth’s gravitational field on time with that of the sun. Some theories suggest that Earth, with its iron core and other heavy, neutron-rich matter, may very slightly affect time’s passage differently than the neutron-poor hydrogen that dominates the sun. 杜塞爾多夫·海因里?！ずＤ髮W(xué)（簡稱杜塞爾多夫大學(xué)，位于德國杜塞爾多夫）的斯蒂芬·席勒（Stephan Schiller ）極其合作者正在進行一項名叫“太空光學(xué)鐘（Space Optical Clocks）的項目，希望在2020年左右建成一個精度比目前高10倍的光晶格鐘。他們期望將地球引力場引起的相對論效應(yīng)和太陽的相對論效應(yīng)相比較。一些理論認(rèn)為地球由于擁有鐵質(zhì)核心和其他重元素物質(zhì)，將略微影響時間通道使得它和輕元素（主要是氫）組成的太陽表現(xiàn)出不同的相對論效應(yīng)。 Can timekeeping possibly continue a tenfold improvement every decade? There are many orders of magnitude before timekeeping would reach the smallest increment allowed by known physics — called the Planck time, 10-43 seconds. To even approach it seems out of reach. 計時器真的能每十年提高十倍嗎？在計時器達到物理學(xué)允許極限（即所謂的普朗克時間，10的負(fù)43次方秒）之前仍有很多個數(shù)量級的精度可以提升，甚至它就很難達到。 As for boosting precision relatively modestly by bringing today’s atomic lattice clocks into ultraviolet or even X-ray domains, several technical hurdles stand in the way. 至于通過將今天的原子晶格鐘引入紫外甚至X射線頻段以提高精度，目前仍有數(shù)個技術(shù)難題有待解決。 While atomic clocks depend on the activity of electrons in an atom’s outer boundaries, there may be other processes to tap — nuclear processes. Within an atom’s nucleus, neutrons and protons jostle and change energy according to quantum mechanics, too. Calculations suggest, for instance, that in the nucleus of the isotope thorium-229 is a transition that should emit ultraviolet rays. If that signal can be confirmed, and stimulated, a laser frequency comb might lock on to it and produce a lower frequency beat that could be fed into an electronic counter. 原子鐘原理是基于原子外層電子的運動，也許有其他方法來振蕩，比如核反應(yīng)。在原子核內(nèi)，中子和質(zhì)子堆疊在一起，同樣也根據(jù)量子力學(xué)互相交換能量。舉例來說，計算表明，釷-229的原子核內(nèi)存在著能發(fā)出紫外線的轉(zhuǎn)變過程。如果那個信號能被加強，受激放大，一個激光頻率梳可能對其鎖定并產(chǎn)生一個更低頻率的振蕩使得電子計數(shù)器能夠計數(shù)。 “This is a very important development, as the nuclei are very well isolated from external perturbations,” says Derevianko. It may open a path “toward the ultimate clock.” “這是一個十分重要的進步，因為原子核和外界擾動很好的隔絕開了?！苯芰芯S揚科說。這或許開拓了一條“通往終極時鐘”的道路。 Only time will tell. 這只有交給時間去證明了。 A laser jubilee 激光亂舞 From the outside, a lattice clock appears to be a dizzying array of lasers, but (as shown in one type of strontium clock at right) each laser has a role in reading the time from atomic oscillations. 從外面看，一個晶格鐘看起來是一系列眼花繚亂的激光，但是（如展示的鍶原子原子鐘）每束激光都有各自的作用，用以從原子振蕩中讀取原子時。 Thousands of strontium atoms are cooled by a system of blue lasers. 數(shù)千個鍶原子被藍激光冷卻。 Red lasers further cool and shrink the cloud of atoms. 紅激光進一步冷卻并縮小原子云區(qū)域。 An infrared laser system traps the atoms, locking them into pancake-shaped wells. 紅外線激光俘獲原子，將它們陷在晶格阱中。 Another red laser, the “clock” laser, bathes the atoms, causing many of them to become excited. 另一束紅激光，所謂的“時鐘”激光，將給原子“泡澡”，使它們受激。 A blue laser probes the cloud; emitted light reveals how many atoms became excited. 一束藍激光探測電子云，受激光顯示有多少原子受激發(fā)。 The clock laser adjusts to properly keep pace based on the atoms’ excitations. Light from the clock laser is passed through a “frequency comb,” allowing the light’s ticks to be read. 時鐘激光和受激原子保持頻率一致。時鐘激光通過一個頻率梳，使得光能夠被讀出。 |
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時過“時”遷：過去一千年里計時器的精度發(fā)生了翻天覆地的進步，過去中國水運儀象臺一天的誤差達到10分鐘，而最近五年科學(xué)家期望制造出從宇宙大爆炸至今都不會產(chǎn)生大于1秒誤差的原子鐘。圖表的具體信息沒有翻譯，我們只需要知道計時器的精度在這一千年里的變化趨勢就行了。 
