Do we actually know how magnets work? - Rachel Yang · TED-Ed
揭秘磁铁如何工作，了解磁性背后的物理原理，适合练习科技和自然类词汇与表达。
In the early 1900s, physicists Niels Bohr and Hendrika Johanna van Leeuwen separately discovered something shocking.
20世纪初，物理学家尼尔斯·玻尔（Niels Bohr）和亨德里卡·约翰娜·范·莱文（Hendrika Johanna van Leeuwen）分别发现了某些令人震惊的现象。
According to every known rule of physics, magnetism was impossible.
根据所有已知的物理规律，磁现象本应是不可能存在的。
This finding made no sense.
这个发现完全无法理解（或：这个结果毫无逻辑可言）。
Humans had relied on magnetic compasses for
人类长期以来一直依赖磁性指南针来进行导航。
a thousand years, and anyone who had ever held two magnetized metals could tell you that some invisible force was acting on them.
一千年过去了，任何曾经接触过两块被磁化过的金属的人都会告诉你：有一种无形的力量在作用于它们之间。
Bohr and van Leeuwen knew they were missing something— but what?
玻尔和范李文意识到他们遗漏了某些东西——但究竟是什么呢？
By the 1920s, physicists had learned quite a bit about the fundamentals of matter.
到了20世纪20年代，物理学家们已经对物质的基本原理有了相当深入的了解。
They knew that every material is made of atoms, each comprised of a nucleus containing protons and orbited by electrons.
他们知道，所有物质都是由原子构成的；每个原子都包含一个原子核，原子核内含有质子，而电子则围绕原子核运动。
They also knew that both of these particles have a few fundamental properties, including a small amount of mass,
他们还知道，这两种粒子都具有一些基本的性质，其中包括微小的质量。
an electrical charge, and some amount of magnetism.
它带有电荷，并具有一定的磁性。
The origin of these intrinsic properties remains an ongoing mystery.
这些内在属性的起源仍然是一个未解之谜。
But the result is that every electron and proton is a tiny magnet that works just like their full-size counterparts.
不过，其结果是：每一个电子和质子都像一个微小的磁体一样，其工作原理与它们“全尺寸”的同类粒子完全相同。
Both have invisible magnetic fields that radiate out in closed loops from one end to the other.
这两种物质都拥有看不见的磁场，这些磁场以闭合的环路形式从一端辐射到另一端。
These magnetic poles are attracted to the dense field lines of the opposite pole of other magnets, and repelled by fields flowing in the opposite direction.
这些磁极会被其他磁体相对极处的密集磁场线吸引；同时，它们也会被方向相反的磁场排斥。
Of course, researchers still had questions.
当然，研究人员仍然有一些疑问。
What determines the direction of these magnetic fields?
是什么决定了这些磁场的方向呢？
And if every atom is composed of tiny magnets, why isn't everything magnetic?
如果每个原子都是由微小的磁体组成的，那么为什么万物不具有磁性呢？
The answers emerged with the birth of quantum mechanics: a new branch of physics exploring how the laws of nature work differently at the sub-atomic level.
这些问题的答案随着量子力学的诞生而浮现。量子力学是物理学的一个新分支，它研究自然法则在亚原子尺度上的运作方式。
In 1926, a pair of Dutch physicists discovered that— in addition to mass, charge, and magnetism— particles had another fundamental property:
1926年，两位荷兰物理学家发现：除了质量、电荷和磁性之外，粒子还具备另一种基本属性。
quantum spin.
量子自旋（quantum spin）。
This is a confusing label because while nothing is actually spinning, spin does refer to a kind of innate direction that influences a particle’s behavior.
这个标签确实容易引起混淆：虽然实际上没有任何东西在旋转，但“旋转”这个词仍然指的是某种内在的“方向性”，这种方向性会影响粒子的行为。
And in the 1930s, Nobel Prize laureate John H.
20世纪30年代，诺贝尔奖得主约翰·H·（John H.）……
Van Vleck discovered that this property held the answer to countless questions about magnetism— including Bohr and van Leeuwen’s.
范弗莱克发现，这一特性为关于磁性的无数问题提供了答案，其中包括玻尔和范李文提出的那些问题。
Basically, the direction of a particle’s spin determines the direction of its magnetic field.
简单来说，粒子自旋的方向决定了其磁场的方向。
And since electrons have much stronger magnetic fields than protons, the direction of their spin determines whether or not something is magnetic.
由于电子的磁场强度远大于质子，因此电子的自旋方向决定了某物体是否具有磁性。
If enough of a material's electrons spin in the same direction, their many tiny magnetic fields will align,
如果某种材料中有足够多的电子以相同的方向旋转，它们所产生的众多微小磁场就会相互对齐。
turning the material into a magnet with a field pointing in that direction.
通过这种处理方式，该材料会被转化为一个磁体，其磁场方向正好与所需的方向一致。
The more aligned electrons, the stronger the magnet.
电子的排列越整齐（即它们的自旋方向越一致），磁体的磁力就越强。
On the other hand, if a material is full of electrons with competing spins their fields cancel each other out,
另一方面，如果某种材料中的电子都具有相互竞争的自旋（即自旋方向相反），那么这些电子产生的磁场会相互抵消。
leaving you with something non-magnetic.
因此，最终剩下的物质应该是非磁性的。
Most elements have electrons that come in pairs and spin in opposite directions, which is why most materials aren’t magnetic.
大多数元素的电子都是成对存在的，并且它们的自旋方向相反；这就是为什么大多数材料不具备磁性的原因。
But iron, nickel, cobalt, and a few rare metals prefer to leave some of their electrons unpaired.
然而，铁、镍、钴以及一些稀有金属更倾向于让它们的电子保持未配对的状态（即这些电子没有与其他电子形成化学键）。
This doesn’t automatically make them magnetic— just because their electrons are unpaired doesn’t mean they always spin in the same direction.
这并不意味着这些物质一定具有磁性；仅仅因为它们的电子处于未配对状态，并不意味着这些电子总是朝相同的方向旋转。
However, they can be nudged into alignment by interacting with neighboring atoms.
然而，通过与邻近原子的相互作用，它们可以被促使达到排列整齐的状态。
And researchers can kick-start this process by applying a strong magnetic field or by heating and cooling the material inside a weaker magnetic field.
研究人员可以通过施加强磁场，或者在对材料进行加热和冷却的同时使其处于弱磁场中，来启动这一过程。
These metals will stay magnets permanently unless their electrons are scrambled by intense heat or an extremely strong magnetic field.
除非这些金属的电子受到高温或强磁场的干扰而发生混乱，否则它们将永远保持磁性的特性。
But this magnetization process can make anything magnetic temporarily.
不过，这种磁化过程可以让任何物体暂时具备磁性。
Felix Bloch and Edward Mills Purcell took advantage of this in 1945 when they invented nuclear magnetic resonance spectroscopy.
费利克斯·布洛赫（Felix Bloch）和爱德华·米尔斯·珀塞尔（Edward Mills Purcell）在1945年发明核磁共振光谱技术时，正是利用了这一原理。
This technology uses a strong magnetic field to temporarily align a material's protons, then a weaker field to knock specific molecules out of alignment.
这项技术利用强磁场暂时使材料中的质子排列整齐，随后通过弱磁场使某些特定分子重新恢复到无序状态（即不再保持整齐的排列）。
The machine then tracks the electromagnetic energy expended by the jostled protons as they realign, allowing researchers to map the material's molecular structure.
随后，该机器会监测那些被碰撞后重新排列的质子所释放的电磁能量，从而帮助研究人员绘制出这种材料的分子结构图。