Time

“Time” is the most used noun in the English language, yet it remains a mystery. We’ve just completed an amazingly intense and rewarding multidisciplinary conference on the nature of time, and here’s my stab at a top ten list partly inspired by our discussions: the things everyone should know about time.
“時間”是英語中使用最頻繁的一個詞，但人們對它依然所知甚少。我們剛剛進行了一場關于時間本質的、激烈而有意義的跨學科討論會。受到這場討論的啟發(fā)，我將試圖開列如下這個“十大清單”：關于時間，每個人都該知道的十件事。

Time Exists

1. Time exists.
1.時間確實存在。

Might as well get this common question out of the way. Of course time exists — otherwise how would we set our alarm clocks? Time organizes the universe into an ordered series of moments, and thank goodness; what a mess it would be if reality were complete different from moment to moment. The real question is whether or not time is fundamental, or perhaps emergent. We used to think that “temperature” was a basic category of nature, but now we know it emerges from the motion of atoms. When it comes to whether time is fundamental, the answer is: nobody knows. My bet is “yes,” but we’ll need to understand quantum gravity much better before we can say for sure.
如果你覺得這個問題太過普通，大可以跳過它。時間當然存在——否則我們怎么上鬧鐘呢？時間將宇宙有序地組織起來——謝天謝地，否則我們的世界就會亂成一鍋粥了。真正的問題其實是：時間究竟是我們這個宇宙的基本組成要素，還是只是偶然出現的。我們曾以為“溫度”是自然的基本要素之一，但現在我們知道它其實是原子運動的附加產物。而對于“時間是否是宇宙的基本要素”，回答是：沒人知道。我認為它是，但要確認這一點，我們得先對量子引力有更好的理解。

Past and Future

2. The past and future are equally real.
2.過去與未來都是真實的。

This isn’t completely accepted, but it should be. Intuitively we think that the “now” is real, while the past is fixed and in the books, and the future hasn’t yet occurred. But physics teaches us something remarkable: every event in the past and future is implicit in the current moment. This is hard to see in our everyday lives, since we’re nowhere close to knowing everything about the universe at any moment, nor will we ever be — but the equations don’t lie. As Einstein put it, “It appears therefore more natural to think of physical reality as a four dimensional existence, instead of, as hitherto, the evolution of a three dimensional existence.”
并不是所有人都接受這個觀點，但是大家應該接受。憑直覺，我們認為“現在”是真實的，“過去”只存在于書中，而“未來”尚未發(fā)生。但物理學告訴我們一個驚人的事實：過去與未來的每一刻都存在于當下。在我們的日常生活中要理解這一點很難，因為我們無從知曉宇宙中每一刻所發(fā)生的全部事件——但是數學方程可不會說謊。就像愛因斯坦說的：“長久以來，我們都把物質世界看成是一個不斷發(fā)展的三維存在，但將它看成一個四維存在似乎更為自然一些?！?/div>

Different Time Experience

3. Everyone experiences time differently.
3.每個人對時間的體驗是不同的。

This is true at the level of both physics and biology. Within physics, we used to have Sir Isaac Newton’s view of time, which was universal and shared by everyone. But then Einstein came along and explained that how much time elapses for a person depends on how they travel through space (especially near the speed of light) as well as the gravitational field (especially if its near a black hole). From a biological or psychological perspective, the time measured by atomic clocks isn’t as important as the time measured by our internal rhythms and the accumulation of memories. That happens differently depending on who we are and what we are experiencing; there’s a real sense in which time moves more quickly when we’re older.
從生物學和物理學角度來說都確有其事。物理學上，牛頓曾提出過經典的、普適的時空觀，但后來愛因斯坦提出，人們身上時間的流逝跟他們在空間中的運動方式（尤其是當運動速度接近光速時）和引力場（尤其是靠近黑洞時）緊密相關。從生物學或心理學的角度來看，由原子鐘計量的精確時間并不如人體內在節(jié)律和記憶所計量的時間那樣重要。而受到個人身份和經歷的影響，每個人的生物節(jié)律都是不同的。隨著年齡的增長，我們確實會有“時間過得更快”的感覺。

Live in the Past

4. You live in the past.
4.我們活在過去。

About 80 milliseconds in the past, to be precise. Use one hand to touch your nose, and the other to touch one of your feet, at exactly the same time. You will experience them as simultaneous acts. But that’s mysterious — clearly it takes more time for the signal to travel up your nerves from your feet to your brain than from your nose. The reconciliation is simple: our conscious experience takes time to assemble, and your brain waits for all the relevant input before it experiences the “now.” Experiments have shown that the lag between things happening and us experiencing them is about 80 milliseconds.
準確地說，是活在80毫秒前。用一只手碰碰你的鼻子，同時用另一只手去碰你的腳，你會覺得這兩件事是同時發(fā)生的。但這正是不可思議之處——顯然，信號從你的腳傳到你的大腦應該要比從你的鼻子到大腦花費更多時間。不過這一點很容易弄明白：我們的意識需要時間來收集信息，而大腦要等收集到所有相關信息之后才能體驗到“現在”。實驗表明，從事件真正發(fā)生到我們的大腦體驗到事件的發(fā)生，中間大約有80毫秒的時滯。

Memory

5. Your memory isn’t as good as you think.
5.你的記憶力并不像你想的那么好

When you remember an event in the past, your brain uses a very similar technique to imagining the future. The process is less like “replaying a video” than “putting on a play from a script.” If the script is wrong for whatever reason, you can have a false memory that is just as vivid as a true one. Eyewitness testimony, it turns out, is one of the least reliable forms of evidence allowed into courtrooms.
我們的大腦記憶過去的機制和想像未來的機制是非常相似的。這個過程更像是“照著劇本演戲”而不是“重放錄像帶”，如果劇本出錯了（不管是什么原因引起的），你就會得到一段虛假的記憶，而它和真實的記憶一樣生動清晰。因此，目擊者的證詞其實是法庭上出示的所有證據中最不靠譜的一種。

Consciousness and Time

6. Consciousness depends on manipulating time.
6.意識的存在有賴于處理時間的能力。

Many cognitive abilities are important for consciousness, and we don’t yet have a complete picture. But it’s clear that the ability to manipulate time and possibility is a crucial feature. In contrast to aquatic life, land-based animals, whose vision-based sensory field extends for hundreds of meters, have time to contemplate a variety of actions and pick the best one. The origin of grammar allowed us to talk about such hypothetical futures with each other. Consciousness wouldn’t be possible without the ability to imagine other times.
對于人的意識來說，許多認知能力都是重要的，而這些方面我們并沒有完全弄清。但有一點可以確定：處理時間和可能性的能力是決定性的。和水生動物不同，陸生動物的感官場建立在視覺的基礎上，可以延展好幾百米遠，因此它們有時間考慮各種行動并選擇最好的一種。語法的產生讓我們可以談論假想的未來。如果沒有想象不同的時間的能力，意識將不可能產生。

Dissorder and Time

7. Disorder increases as time passes.
7.隨著時間的流逝，宇宙的無序程度會上升。

At the heart of every difference between the past and future — memory, aging, causality, free will — is the fact that the universe is evolving from order to disorder. Entropy is increasing, as we physicists say. There are more ways to be disorderly (high entropy) than orderly (low entropy), so the increase of entropy seems natural. But to explain the lower entropy of past times we need to go all the way back to the Big Bang. We still haven’t answered the hard questions: why was entropy low near the Big Bang, and how does increasing entropy account for memory and causality and all the rest?
在過去與未來的所有差別——記憶、衰老、因果、自由意志——背后，隱藏著一個核心事實，那就是宇宙是從有序逐漸走向無序的?；蛘呷缥锢韺W家所說：“熵（動力學方面不能做功的能量總數）在不斷增加?！边_到無序狀態(tài)（高熵）比達到有序狀態(tài)（低熵）的途徑要多，因此熵的增加看起來再正常不過。但要解釋宇宙曾有過的低熵狀態(tài)，就必須回溯至最初的宇宙大爆炸。我們仍然不能回答如下問題：為何在大爆炸之時熵如此低，以及熵增如何導致了記憶、因果以及其他一切。

Complexity

8. Complexity comes and goes.
8.復雜性增加又減少。

Other than creationists, most people have no trouble appreciating the difference between “orderly” (low entropy) and “complex.” Entropy increases, but complexity is ephemeral; it increases and decreases in complex ways, unsurprisingly enough. Part of the “job” of complex structures is to increase entropy, e.g. in the origin of life. But we’re far from having a complete understanding of this crucial phenomenon.
除了神創(chuàng)論者，大多數人都能夠明白“有序（低熵）”和“復雜”的區(qū)別。熵在不斷增加，但復雜狀態(tài)是短暫的；復雜性以復雜的方式增加和減少，這一點也不令人意外。復雜結構存在的“意義”之一就是使各種過程——比如生命起源——中的熵增加。但我們還遠未能對這一至關重要的現象有全面的理解。

Aging

9. Aging can be reversed.
9.衰老的過程是可逆的。

We all grow old, part of the general trend toward growing disorder. But it’s only the universe as a whole that must increase in entropy, not every individual piece of it. (Otherwise it would be impossible to build a refrigerator.) Reversing the arrow of time for living organisms is a technological challenge, not a physical impossibility. And we’re making progress on a few fronts: stem cells, yeast, and even mice and human muscle tissue. As one biologist told me: “You and I won’t live forever. But as for our grandkids, I’m not placing any bets.”
我們都會老去，這也是這世界走向無序的趨勢的一部分。但必然的熵增是針對整個宇宙而言，對宇宙的個別部分而言并非必然如此（否則我們就不可能造出冰箱了）。倒轉有機體的時間流逝只是一項技術挑戰(zhàn)，從物理學角度來說并不是不可能的。并且在某些有機體上我們已經取得了一些進展：干細胞，酵母菌，甚至老鼠和人體肌肉組織。一位生物學家曾告訴我：“你我肯定不會永生，但我們的孫輩就不一定了。”

Lifespan

10. A lifespan is a billion heartbeats.
10.動物的壽命大約是十億次心跳的時間。

Complex organisms die. Sad though it is in individual cases, it’s a necessary part of the bigger picture; life pushes out the old to make way for the new. Remarkably, there exist simple scaling laws relating animal metabolism to body mass. Larger animals live longer; but they also metabolize slower, as manifested in slower heart rates. These effects cancel out, so that animals from shrews to blue whales have lifespans with just about equal number of heartbeats — about one and a half billion, if you simply must be precise. In that very real sense, all animal species experience “the same amount of time.” At least, until we master #9 and become immortal.
復雜的有機體會死去。對個體來說這是個悲哀的事實，但在更高的層面上這是必須的：舊的總要為新的讓路。值得注意的是，自然界存在著關于動物體型和新陳代謝的一套簡單比例法則：體型更大的動物活得更久，但新陳代謝也更慢，表現出來就是心跳會更慢。這些效應相互抵消，結果就是從鼩鼱（一種外形似鼠的小型哺乳動物）到藍鯨，各種動物的壽命都差不多是15億次心跳的時間。從這個意義上來說，所有物種都經歷了“相同的時間”——至少是在我們掌握了第9條并獲得永生之前。