(音乐)
You probably already know everything is made up of little tiny things called atoms or even that each atom is made up of even smaller particles called protons, neutrons and electrons. And you've probably heard that atoms are small. But I bet you haven't ever thought about how small atoms really are. Well, the answer is that they are really, really small. So you ask, just how small are atoms? To understand this, let's ask this question: How many atoms are in a grapefruit? Well, let's assume that the grapefruit is made up of only nitrogen atoms, which isn't at all true, but there are nitrogen atoms in a grapefruit. To help you visualize this, let's blow up each of the atoms to the size of a blueberry. And then how big would the grapefruit have to be? It would have to be the same size of -- well, actually, the Earth. That's crazy! You mean to say that if I filled the Earth with blueberries, I would have the same number of nitrogen atoms as a grapefruit? That's right! So how big is the atom? Well, it's really, really small! And you know what? It gets even more crazy. Let's now look inside of each atom -- and thus the blueberry, right? -- What do you see there? In the center of the atom is something called the nucleus, which contains protons and neutrons, and on the outside, you'd see electrons. So how big is the nucleus? If atoms are like blueberries in the Earth, how big would the nucleus be? You might remember the old pictures of the atom from science class, where you saw this tiny dot on the page with an arrow pointing to the nucleus. Well, those pictures, they're not drawn to scale, so they're kind of wrong. So how big is the nucleus? So if you popped open the blueberry and were searching for the nucleus ... You know what? It would be invisible. It's too small to see! OK. Let's blow up the atom -- the blueberry -- to the size of a house. So imagine a ball that is as tall as a two-story house. Let's look for the nucleus in the center of the atom. And do you know what? It would just barely be visible. So to get our minds wrapped around how big the nucleus is, we need to blow up the blueberry, up to the size of a football stadium. So imagine a ball the size of a football stadium, and right smack dab in the center of the atom, you would find the nucleus, and you could see it! And it would be the size of a small marble. And there's more, if I haven't blown your mind by now. Let's consider the atom some more. It contains protons, neutrons and electrons. The protons and neutrons live inside of the nucleus, and contain almost all of the mass of the atom. Way on the edge are the electrons. So if an atom is like a ball the size of a football stadium, with the nucleus in the center, and the electrons on the edge, what is in between the nucleus and the electrons? Surprisingly, the answer is empty space. (Wind noise) That's right. Empty! Between the nucleus and the electrons, there are vast regions of empty space. Now, technically there are some electromagnetic fields, but in terms of stuff, matter, it is empty. Remember this vast region of empty space is inside the blueberry, which is inside the Earth, which really are the atoms in the grapefruit. OK, one more thing, if I can even get more bizarre. Since virtually all the mass of an atom is in the nucleus -- now, there is some amount of mass in the electrons, but most of it is in the nucleus -- how dense is the nucleus? Well, the answer is crazy. The density of a typical nucleus is four times 10 to the 17th kilograms per meter cubed. But that's hard to visualize. OK, I'll put it in English units. 2.5 times 10 to the 16th pounds per cubic feet. OK, that's still kind of hard to figure. OK, here's what I want you to do. Make a box that is one foot by one foot by one foot. Now let's go and grab all of the nuclei from a typical car. Now, cars on average weigh two tons. How many cars' nuclei would you have to put into the box to have your one-foot-box have the same density of the nucleus? Is it one car? Two? How about 100? Nope, nope and nope. The answer is much bigger. It is 6.2 billion. That is almost equal to the number of people in the Earth. So if everyone in the Earth owned their own car -- and they don't -- (Cars honking) and we put all of those cars into your box ... That would be about the density of a nucleus. So I'm saying that if you took every car in the world and put it into your one-foot box, you would have the density of one nucleus. OK, let's review. The atom is really, really, really small. Think atoms in a grapefruit like blueberries in the Earth. The nucleus is crazy small. Now look inside the blueberry, and blow it up to the size of a football stadium, and now the nucleus is a marble in the middle. The atom is made up of vast regions of empty space. That's weird. The nucleus has a crazy-high density. Think of putting all those cars in your one-foot box. I think I'm tired.
你也许已经知道所有的东西 都是由微小的原子组成。 你可能还知道每一个原子是由更小的 叫做质子,中子和电子的微粒组成 也许你听说过原子很小。 我打赌,你从未想过它究竟有多小。 答案是,它们非常非常非常小。 你提出问题了,到底原字有多小呢? 为了去理解它,让我们先提出一个问题: 一个柚子包含多少原子? 首先我们假设柚子完全由氮原子构成, 虽然不准确,但柚子中确实有氮原子。 为了便于观察,我们把原子放大到 一个蓝莓大小。 那总体柚子又会是多大呢? 它会跟地球的个头差不多。 天啊!难道地球装满蓝莓的数量 会和柚子中的氮原子一样多? 的确如此!那么原子究竟有多小? 它小到 超出了你的 想象。 现在让我们看看原子内部,也就是蓝莓。 你会发现 原子有一个核心。 其中包含着质子和中子, 外围的是电子。 如果原子是地球中的蓝莓, 那么原子核又有多大呢? 你可能在物理书上看过原子的描绘, 原子核是箭头所指的小点。 这些图不是按比例画的, 所以并不准确。 那么真实的原子核多大呢? 如果你在蓝莓的内部 搜索原子核, 结果是一无所获。 因为我们看不到它! 如果我们把原子,也就是蓝莓 放大到房子的尺寸。 想象下有两层房屋那么高。 我们在其中寻找原子核, 它就如一粒尘埃。 所以想要真正看清原子核, 还要把蓝莓放大到橄榄球场大小。 想象一下,橄榄球场大小的原子。 在它的正中间, 你终于找到了原子核! 而它只有玻璃弹子大小。 如果现在你都没有被震撼到, 那再来设想下原子中的质子,中子,电子。 质子和中子组成了原子核, 几乎占了原子全部比重。 在原子边缘的是电子。 一个橄榄球场大小的原子, 原子核在中心,而电子在边缘, 那么两者之间又是什么呢? 虚空。 (风声) 没错,空无一物! 在原子核和电子之间存在着大片空洞区域。 严格的说来还有电磁场, 但从物质的角度看,还是空洞。 而这空洞区域正是在 蓝莓之中,而蓝莓又是在 如地球大小的柚子之中。 更奇异的是, 事实上原子的大部分质量集中在原子核, 虽然电子也有一定质量, 但是可以忽略。 那么原子核的密度是多少? 你会觉得不可思议。 典型的原子的密度是 4乘以10的17次方千克/立方米。 很难设想,那么换作英制单位是 2.5乘以10的16次方 磅/立方英尺。 如果还是很难想象, 那么打个比方。 一个30厘米立方的盒子, 一辆重两吨的汽车, 我们需要多少量汽车的原子核 装在一个盒子里 才能达到一个原子核的密度? 一辆,两辆,还是一百辆? 都不是。 结果大得多。 需要62亿辆。 这差不多是世界人口总数。 所以如果每个人都拥有一辆车, 我们假象, 把这些车都装进盒子里, 就差不多相当于一个原子核的密度。 把世界上每一辆车都装进一30厘米立方的盒子中, 你才得到原子核的密度。 我们回顾一下。 原子极其渺小。 柚子中的原子是地球中的蓝莓。 原子核更是出奇的小。 把蓝莓放到大橄榄球场大小, 原子核就是其中的玻璃弹子。 原子内存在广阔的虚空。 很不寻常。 原子核有极高的密度。 想想盒子里装的那些车。 我洗洗睡了。 (打哈欠)