"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.
“时间”是英语中使用最频繁的一个词，但人们对它依然所知甚少。我们刚刚进行了一场关于时间本质的、激烈而有意义的跨学科讨论会。受到这场讨论的启发，我将试图开列如下这个“十大清单”：关于时间，每个人都该知道的十件事。

1. Time exists.
时间确实存在。

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.
如果你觉得这个问题太过普通，大可以跳过它。时间当然存在——否则我们怎么上闹钟呢？时间将宇宙有序地组织起来——谢天谢地，否则我们的世界就会乱成一锅粥了。真正的问题其实是：时间究竟是我们这个宇宙的基本组成要素，还是只是偶然出现的。我们曾以为“温度”是自然的基本要素之一，但现在我们知道它其实是原子运动的附加产物。而对于“时间是否是宇宙的基本要素”，回答是：没人知道。我认为它是，但要确认这一点，我们得先对量子引力有更好的理解。

2. The past and future are equally real.
过去与未来都是真实的。

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这个观点，但是大家应该接受。凭直觉，我们认为“现在”是真实的，“过去”只存在于书中，而“未来”尚未发生。但物理学告诉我们一个惊人的事实：过去与未来的每一刻都存在于当下。在我们的日常生活中要理解这一点很难，因为我们无从知晓宇宙中每一刻所发生的全部事件——但是数学方程可不会说谎。就像爱因斯坦说的：“长久以来，我们都把物质世界看成是一个不断发展的三维存在，但将它看成一个四维存在似乎更为自然一些。”

3. Everyone experiences time differently.
每个人对时间的体验是不同的。

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.
从生物学和物理学角度来说都确有其事。物理学上，牛顿曾提出过经典的、普适的时空观，但后来爱因斯坦提出，人们身上时间的流逝跟他们在空间中的运动方式（尤其是当运动速度接近光速时）和引力场（尤其是靠近黑洞时）紧密相关。从生物学或心理学的角度来看，由原子钟计量的精确时间并不如人体内在节律和记忆所计量的时间那样重要。而受到个人身份和经历的影响，每个人的生物节律都是不同的。随着年龄的增长，我们确实会有“时间过得更快”的感觉。

4. You live in the past.
我们活在过去。

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.
准确地说，是活在80毫秒前。用一只手碰碰你的鼻子，同时用另一只手去碰你的脚，你会觉得这两件事是同时发生的。但这正是不可思议之处——显然，信号从你的脚传到你的大脑应该要比从你的鼻子到大脑花费更多时间。不过这一点很容易弄明白：我们的意识需要时间来收集信息，而大脑要等收集到所有相关信息之后才能体验到“现在”。实验表明，从事件真正发生到我们的大脑体验到事件的发生，中间大约有80毫秒的时滞。

5. Your memory isn't as good as you think.
你的记忆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.
我们的大脑记忆过去的机制和想像未来的机制是非常相似的。这个过程更像是“照着剧本演戏”而不是“重放录像带”，如果剧本出错了（不管是什么原因引起的），你就会得到一段虚假的记忆，而它和真实的记忆一样生动清晰。因此，目击者的证词其实是法庭上出示的所有证据中最不靠谱的一种。

6. Consciousness depends on manipulating time.
意识的存在有赖于处理时间的能力。

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.
对于人的意识来说，许多认知能力都是重要的，而这些方面我们并没有完全弄清。但有一点可以确定：处理时间和可能性的能力是决定性的。和水生动物不同，陆生动物的感官场建立在视觉的基础上，可以延展好几百米远，因此它们有时间考虑各种行动并选择最好的一种。语法的产生让我们可以谈论假想的未来。如果没有想象不同的时间的能力，意识将不可能产生。

7. Disorder increases as time passes.
随着时间的流逝，宇宙的无序程度会上升。

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?
在过去与未来的所有差别——记忆、衰老、因果、自由意志——背后，隐藏着一个核心事实，那就是宇宙是从有序逐渐走向无序的。或者如物理学家所说：“熵（动力学方面不能做功的能量总数）在不断增加。”达到无序状态（高熵）比达到有序状态（低熵）的途径要多，因此熵的增加看起来再正常不过。但要解释宇宙曾有过的低熵状态，就必须回溯至最初的宇宙大爆炸。我们仍然不能回答如下问题：为何在大爆炸之时熵如此低，以及熵增如何导致了记忆、因果以及其他一切。

8. Complexity comes and goes.
复杂性增加又减少。

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.
除了神创论者，大多数人都能够明白“有序（低熵）”和“复杂”的区别。熵在不断增加，但复杂状态是短暂的；复杂性以复杂的方式增加和减少，这一点也不令人意外。复杂结构存在的“意义”之一就是使各种过程——比如生命起源——中的熵增加。但我们还远未能对这一至关重要的现象有全面的理解。

9. Aging can be reversed.
衰老的过程是可逆的。

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."
我们都会老去，这也是这世界走向无序的趋势的一部分。但必然的熵增是针对整个宇宙而言，对宇宙的个别部分而言并非必然如此（否则我们就不可能造出冰箱了）。倒转有机体的时间流逝只是一项技术挑战，从物理学角度来说并不是不可能的。并且在某些有机体上我们已经取得了一些进展：干细胞，酵母菌，甚至老鼠和人体肌肉组织。一位生物学家曾告诉我：“你我肯定不会永生，但我们的孙辈就不一定了。”

10. A lifespan is a billion heartbeats.
动物的寿命大约是十亿次心跳的时间。

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.
复杂的有机体会死去。对个体来说这是个悲哀的事实，但在更高的层面上这是必须的：旧的总要为新的让路。值得注意的是，自然界存在着关于动物体型和新陈代谢的一套简单比例法则：体型更大的动物活得更久，但新陈代谢也更慢，表现出来就是心跳会更慢。这些效应相互抵消，结果就是从鼩鼱（一种外形似鼠的小型哺乳动物）到蓝鲸，各种动物的寿命都差不多是15亿次心跳的时间。从这个意义上来说，所有物种都经历了“相同的时间”——至少是在我们掌握了第9条并获得永生之前。