Unit_3 Can we know the universe

CAN WE KNOW THE UNIVERSE?—REFLECTIONS ON A GRAIN OF SALT

Carl Sagan

我们能了解宇宙吗？——关于一粒盐的思索

1. Science is a way of thinking much more than it is a body of knowledge. Its goal is to find out how the world works, to seek what regularities there may be, to penetrate to the connections of things—from subnuclear particles, which may be the constituents of all matter, to living organisms, the human social community, and thence to the cosmos as a whole. Our intuition is by no means an infallible guide. Our perceptions may be distorted by training and prejudice or merely because of the limitations of the phenomena of the world. Even so straightforward a question as whether in the absence of friction a pound of lead falls faster than a gram of fluff was answered incorrectly by Aristotle and almost everyone else before the time of Galileo. Science is based on experiment, on a willingness to challenge old dogma, on an openness to see the universe as it really is. Accordingly, science sometimes requires courage—at the very least the courage to question the conventional wisdom.

科学与其说是一种知识体系，不如说是一种思考方法。其目的是弄清世界的运行机制，寻求其间可能存在的规律，洞察事物之间的联系——从构成一切物质的亚核粒子，到生物有机体，人类社会群体，以至整个宇宙。我们的直觉并非是绝对可靠的向导。我们的认识可能会因为训练和偏见，或者仅仅由于世界各种现象的局限而受到扭曲。在伽利略时代之前，亚里士多德等其他许多人连在没有摩擦的情况下一磅铅是否比一克羽毛落得快这样一个直截了当的问题也不能正确回答。科学的产生基于实验，基于向旧的教条挑战，基于公开承认宇宙的现实。因此，科学有时需要勇气——至少要敢于怀疑传统的学识。

2. Beyond this the main trick of science is to really think of something: the shape of clouds and their occasional sharp bottom edges at the same altitude everywhere in the sky; the formation of a dewdrop on a leaf; the origin of a name or a word—Shakespeare, say, or “philanthropic”; the reason for human social customs—the incest taboo, for example; how it is that a lens in sunlight can make paper burn; how a “walking stick” got to look so much like a twig; why the Moon seems to follow us as we walk; what prevents us from digging a hole down to the center of the Earth; what the definition is of “down” on a spherical ear th; how is it possible for the body to convert yesterday’s lunch into today’s muscle and sinew; or how far is up—does the universe go on forever, or if it does not, is there any meaning to the question of what lies on the other side? Some of these questions are pretty easy. Others, especially the last, are mysteries to which no one even today knows the answer. They are natural questions to ask. Every culture has posed such questions in one way or another. Almost always the proposed answers are in the nature of “Just So Stories”, attempted explanations divorced from experiment, or even from careful comparative observations.

除此之外，科学的主要诀窍是实实在在地思考一些问题：云的形状以及偶然可见的云层在同一高度的鲜明边缘；叶片上形成的露珠；一个名字或者一个词的

起源，比如说，Shakespeare(莎士比亚)或philanthropic(仁慈)是怎样产生的; 人类各种社会习惯形成的原因——例如有关乱伦的禁忌；阳光下的透镜为什么能使纸张燃烧；“拐棍”怎么看上去如此像树枝；为什么月亮似乎跟着我们走；是什么使我们掘洞不能掘到地心；在球形的地球上“下方”的定义是什么；身体如何把昨天的午餐转化为今天的体力和精力；宇宙究竟有多大——是无穷大，还是有边界，询问宇宙的另一边究竟是什么有没有意义？上述的问题有些很容易回答，而另一些问题，尤其最后一个问题，是至今也没人知道答案的谜。这些都是自然要问的问题。世界上每一文化群体都以这样或那样的方式提出过这些问题。所提供的答案几乎都带有“就这么回事”的性质，而试图做的解释总是脱离实验，甚至没有经过细心的比较观察。

3. But the scientific cast of mind examines the world critically as if many alternative worlds might exist, as if other things might be here which are not. Then we are forced to ask why what we see is present and not something else. Why are the Sun and the Moon and the planets spheres? Why not pyramids, or cubes, or dodecahedra? Why not irregular, jumbly shapes? Why so symmetrical, these worlds? If you spend any time spinning hypotheses, checking to see whether they make sense, whether they conform to what else we know, thinking of tests you can pose to substantiate or deflate your hypotheses, you will find yourself doing science. And as you come to practice this habit of thought more and more you will get better and better at it. To penetrate into the heart of the thing—even a little thing, a blade of grass, as Walt Whitman said—is to experience a kind of exhilaration that, it may be, only human beings of all the beings on this planet can feel. We are an intelligent species and the use of our intelligence quite properly gives us pleasure. In this respect the brain is like a muscle. When we think well, we feel good. Understanding is of ecstasy.

但是科学的头脑以挑剔的态度检验世界，似乎有许多其他的世界存在，似乎有一些事物本应出现在这里。于是，我们不得不问：为什么我们看见的是眼前的事物而不是其他别的什么东西。为什么太阳、月亮和行星呈球状? 为什么它们不呈角锥体，立方体或十二面体? 为什么不呈不规则的乱七八糟的模样? 为什么世界上万物是如此对称? 如果你花时间构想一些假设，检查看它们是否有意义，是否与我们知道的其他什么理论相符合，考虑一些你能用来证实或摒弃你的假设的实验，那么你将发现自己在从事科学。当你逐渐养成勤于思考的习惯时，你将越来越善于思考。要透彻地领悟一件事物，哪怕是一桩小事——比如惠特曼所说的一片草叶，也会经历一种喜悦，这种喜悦，在整个世界的所有生灵中只有人类才能感受到。人类是智慧的种群，恰当地利用才智令我们愉快。在这方面大脑的功能与肌肉相似。我们思维敏捷的时候，感觉也舒畅。理解具有令人心醉神迷的魅力。

4. But to what extent can we really know the universe around us? Sometimes this question is posed by people who hope the answer will be in the negative, who are fearful of a universe in which everything might one day be known. And sometimes we hear pronouncements from scientists who confidently state that everything worth knowing will soon be known—or even is already known—and who paint pictures of a

Dionysian or Polynesian age in which the zest for intellectual discovery has withered, to be replaced by a kind of subdued languor, the lotus-eaters drinking fermented coconut milk or some other mild hallucinogen.

但是我们对我们周围的宇宙真正能了解到什么程度? 一些希望得到否定答案的人有时候提出这样的问题，这些人害怕有朝一日宇宙中的一切或许会真相大白。有时我们听到一些科学家发表的宣言，他们充满信心地宣称，每一件值得弄清的事物将很快会为大家所知，或者说有些已经众所周知。他们描绘的是狄奥尼修斯和波利尼西亚时代的图画，在这些画中，人们对知识探索的热情已经衰退，取而代之的是一种被征服的怠惰，成了饮用发酵椰子汁和其他一些温和迷幻剂的安逸度日者。

5. Let us approach a much more modest question: not whether we can know the universe or the Milky Way Galaxy or a star or a world. Can we know, ultimately and in detail, a grain of salt? Consider one microgram of table salt, a speck just barely large enough for someone with keen eyesight to make out without a microscope. In that grain of salt there are about 1016 sodium and chlorine atoms. This is a 1 followed by 16 zeroes, 10 million billion atoms. If we wish to know a grain of salt, we must know at least the three-dimensional positions of each of these atoms. (In fact, there is much more to be known—for example, the nature of the forces between the atoms—but we are making only a modest calculation.) Now, is this number more or less than the number of things which the brain can know?

我们还是来探讨一个较为容易回答的问题吧：不要问我们是否能了解宇宙或银河系，也不问有关恒星或世界的问题。我们是否能完全而详尽地了解一颗盐粒的成分呢? 假设有一微克食盐，不借助显微镜，其大小只是敏锐的视力才能看见的小微点。在这样一粒盐中，有1016个钠原子和氯原子。也就是说，其原子数为1后接16个零，共有1万万亿个原子。如果我们想了解一粒食盐，我们必须至少了解这些原子中每一个原子的三维位置。(事实上，需要了解的情况要多得多——比如原子之间力的性质——但我们这里只是进行一种简单的计算。)那么，这个数目究竟是大于还是小于人脑现在所能了解的事物的数量?

6. How much can the brain know? There are perhaps 1011 neurons in the brain, the circuit elements and switches that are responsible in their electrical and chemical activity for the functioning of our minds. A typical brain neuron has perhaps a thousand little wires, called dendrites, which connect it with its fellows. If, as seems likely, every bit of information in the brain corresponds to one of these connections, the total number of things knowable by the brain is no more than 1014, one hundred trillion. But this number is only one percent of the number of atoms in our speck of salt.

人脑究竟能了解多少呢? 人脑中有1011个神经元，它们的线路成分和转换器负责大脑的电子和化学活动的功能。一个典型的脑神经元大约有1000个微线路，称为树突, 它将一个个神经元连接起来。如果人脑中的每一点信息与这些连接物中每一点相对应（这似乎很可能），那么大脑可知的事情的全部总量不超过

1014，也即100万亿。而这个数量只是我们所知的一小粒盐的原子数量的百分之一。

7. So in this sense the universe is intractable, astonishingly immune to any human attempt at full knowledge. We cannot on this level understand a grain of salt, much less the universe.

因此从这种意义上讲，要了解宇宙是很棘手的，对任何饱学之士也毫不例外。在这一程度上，我们不能了解一粒盐，对宇宙更是知之甚少。

8. But let us look more deeply at our microgram of salt. Salt happens to be a crystal in which, except for defects in the structure of the crystal lattice, the position of every sodium and chlorine atom is predetermined. If we could shrink ourselves into this crystalline world, we could see rank upon rank of atoms in an ordered array, a regularly alternating structure—sodium, chlorine, sodium chlorine, specifying the sheet of atoms we are standing on and all the sheets above us and below us. An absolutely pure crystal of salt could have the position of every atom specified by something like 10 bits of information. This would not strain the information-carrying capacity of the brain.

但是让我们更深地了解一下这一微克食盐。盐碰巧是一种晶体，其中除了有缺陷的晶体点阵结构之外，所有钠原子与氯原子的位置都预先定了位。如果我们可以缩小身体进入这个水晶的世界，我们可以看见一排排原子形成有序的点阵，呈一种有规律的交替结构——钠原子、氯原子、氯化钠原子，这些点阵结构详细地勾画出我们所站的这一层原子以及在我们头上、头下的所有原子层的示意图。绝对纯净的盐晶体中可以找到上述结构的每一种分子状况，由大约10个信息单位确定。这将不会超过大脑的信息携带量。

9 If the universe had natural laws that governed its behavior to the same degree of regularity that determines a crystal of salt, then, of course, the universe would be knowable. Even if there were many such laws, each of considerable complexity, human beings might have the capacity to understand them all. Even if such knowledge exceeded the information-carrying capacity of the brain, we might store the additional information outside our bodiesーin books, for example, or in computer memoriesーand still, in some sense, know the universe.

如果宇宙有什么自然规律控制自己的行为，就像决定盐晶体的规律一样，那么，宇宙当然会是可知的。即使有许多这样的自然规律，每一规律都相当复杂，人类也有可能理解所有这些规律。即使这些知识超过人脑的信息携带量，我们仍然可以将另外一些信息存储在我们的体外——比如存储在书本里，或计算机内存里——这样，从某种意义上讲，我们仍然可以了解宇宙。

10 Human beings are, understandably, highly motivated to find regularities, natural laws. The search for rules, the only possible way to understand such a vast and complex universe, is called science. The universe forces those who live in it to understand it. Those creatures who find everyday experience of muddled jumble of events with no predictability, no regularity, are in grave peril. The universe belongs to those who, at least to some degree, have figured it out.

对于寻找宇宙规律和自然法则，人类具有高度的积极性，这不难理解。探索这些规则，理解这样一个巨大而复杂的宇宙的惟一可能方法我们称之为科学。宇宙迫使那些生活在其中的人去理解它。那些每天都发现自己生活在混乱的日常事件中，没有预见性、没有规律性的人处于极为危险的境地。宇宙属于那些至少在某些程度上理解它的人。

11 For myself, I like a universe that includes much that is unknown and, at the same time, much that is knowable. A universe in which every thing is known would be static and dull, as boring as the heaven of some weak-minded theologians. A universe that is unknowable is no fit place for a thinking being. The ideal universe for us is one very much like the universe we inhabit. And I would guess that this is not really much of a coincidence.

就我自己而言，我喜欢宇宙既包括许多未知事物，同时也包括许多可知的东西。宇宙中要是一切事物都成了已知的东西，那将成为一个静止乏味的世界，枯燥得如同某些缺乏头脑的神学家的天堂。而不可知的宇宙是不适宜思考的人居住的。我们需要的理想的宇宙非常像我们目前居住的宇宙。我倒愿意认为这并不真的是一种巧合。