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If you take a piece of wood and put it next to another piece of wood, nothing happens.
如果你把一块木头放在另一块木头旁边，什么也不会发生。
And if you take a piece of granite and put it next to another rock, still nothing.
如果你把一块花岗岩放在另一块岩石旁边，依然什么也没有发生。
But if you take this piece of iron and put it next to this other piece of iron, magic! I mean, magnet.
但是如果你把这块铁放在另一块铁旁边，那就不一样了！我是说，磁力。
Magnetic objects are able to magically attract at long distance
磁性物体能够在远距离以不可思议的方式吸引，
because they generate magnetic fields that extend invisibly out beyond the object.
因为它们产生的磁场是不可见的，并延伸到物体之外。
But the mystery is this: where do magnetic fields come from? well that's easy, Henry!
但问题是：磁场是从哪里来的？这很简单，亨利！
We've known for a long time that electricity and magnetism are really just two sides of the same coin,
我们很久以来就知道电和磁力其实只是一枚硬币的两面，
kind of like mass and energy or time and space, and they can be transformed into each other.
就像质量和能量或者时间和空间，它们可以相互转化。
In fact, magnetic fields are basically just what electric fields become
事实上，磁场基本上就是带电物体
when an electrically charged object starts moving!
开始运动时所产生的电场！
That makes sense for explaining why a current of electrons flowing through a wire causes this compass needle to move,
这就解释了为什么电子流过导线会导致罗盘指针移动，
or how currents in the earth's outer core generate the geomagnetic field,
也解释了地核中的电流是如何产生地磁场的，
but a bar magnet or the compass needle itself are just pieces of metal
但条形磁铁或罗盘指针本身只是一片
without any electrical current running through them.
没有电流流过的金属。
Or are they? At a microscopic level,
或者它们是？在微观层面上，
there are loads of electrons whizzing around in the atoms and molecules that make up any solid.
有大量电子在构成任何固体的原子和分子中飞来飞去。
Right! This brings up an excellent point,
对！这就引出了一个很好的观点，
The magnetic behavior of any everyday object is influenced by a fascinating combination of effects
任何日常物体的磁性行为都受到
ranging from the level of particles to atoms, collections of atoms, and collections of collections of atoms.
从粒子水平到原子、原子集合和原子集合等各种效应的迷人组合的影响。
First, individual particles. Unlike the everyday workings of gravity and electricity,
首先，单个粒子。与日常的重力和电的作用不同，
permanent magnets can only be fully understood as a quantum mechanical effect.
永久磁铁只能被完全理解为一种量子力学效应。
In much the same way that particles like electrons and quarks
就像电子和夸克这样的粒子
have fundamental properties called mass and electrical charge,
具有被称为质量和电荷的基本属性一样，
most particles also have another intrinsic property, called "tiny magnet".
大多数粒子还有另一个内在属性，叫做“微小磁铁”。
Just kidding, it's called an "intrinsic magnetic moment,"
开个玩笑，它被称为“本征磁矩”，
but really, that's just technical mumbo-jumbo saying that particles with electric charge also happen to be tiny magnets.
但实际上，这只是技术上的空话，带电荷的粒子恰好也是微小的磁铁。
If you want to know WHY they're tiny magnets, well,
如果你想知道为什么它们是微小的磁铁，那么，
you might as well ask WHY do particles have charge in the first place,
你不妨先问问为什么粒子会有电荷，
or why do objects with energy and momentum attract gravitationally? No one knows.
或者为什么有能量和动量的物体会有引力吸引呢？没有人知道。
We just know these things are true/that is how the universe works.
我们只知道这些事情是事实/这就是宇宙的运作方式。
Exactly, and since the 1920s, we've known that each individual electron or proton is basically a tiny magnet.
没错，从20世纪20年代开始，我们就知道每个电子或质子基本上都是一个微小的磁铁。
Which brings us to the level of atoms.
从而我们认识了原子的世界。
An atom is a bunch of positively charged protons with a bunch of negatively charged electrons whizzing around them.
原子是一束带正电的质子，周围是一束带负电的电子。
The proton tiny magnets are about 1000 times weaker than the electron ones,
质子微磁体比电子微磁体弱1000倍左右，
so the nucleus of the atom has almost no effect on the magnetism of the atom as a whole.
所以原子核对原子整体的磁性几乎没有影响。
And you might think that since many (though not all) of the electrons are also moving,
你可能会想，因为许多（虽然不是全部）电子也在运动，
like the current in a wire, they would generate magnetic fields from that motion.
就像导线中的电流一样，它们会从这个运动中产生磁场。
Indeed they do, and these are called "orbital" magnetic fields.
确实如此，这些被称为“轨道”磁场。
Except, these don't usually contribute to the magnetic field of an atom.
但是，这些通常不会促进原子磁场的形成。
Here's why: Electrons in atoms are accurately and complicatedly described by quantum mechanics,
原因如下：量子力学精确而复杂地描述了原子中的电子，
but the gist of the story is that electrons congregate in shells around the nucleus.
但故事的梗概是电子聚集在原子核周围的壳层中。
The electrons in any filled shell zoom equally in all directions
任何填充壳中的电子在所有方向上相等地变焦，
and so the currents they generate cancel out and generate no magnetic field.
因此它们产生的电流抵消并且不产生磁场。
These electrons also come in pairs whose tiny magnets point in opposite directions and also cancel.
这些电子也成对出现，它们的小磁铁指向相反的方向，也相互抵消。
However, in a half-filled shell, all of the electrons are unpaired
然而，在一个半填充的外壳中，所有的电子都是不成对的，
and their tiny magnets point in the same direction and add up,
它们的小磁体指向同一个方向，并相互叠加，
meaning that it's the intrinsic magnetism of the electrons in the outer shell
这意味着正是外壳中电子的内磁性
that gives an atom the majority of its magnetic field.
给了原子大部分的磁场。
So atoms near the side of any of the major blocks of the periodic table,
因此，靠近元素周期表中任何一个主要单元的原子，
which have full (or nearly full) outer electron shells, aren't very magnetic.
都有完整的（或接近完整的）外层电子壳，它们不是很有磁性。
And atoms in the MIDDLE of the blocks have half-full outer electron shells and are magnetic.
并且在块体中间的原子具有半满的外层电子壳并且是磁性的。
For example, Nickel, Cobalt, Iron, Manganese, Chromium, etc.
例如镍、钴、铁、锰、铬等。
Wait, but chromium isn't magnetic!
等等，铬是没有磁性的！
Ah, but just because an atom is magnetic doesn't mean that a material made up of lots of that atom will be magnetic.
啊，但是仅仅因为一个原子是磁性的，并不意味着由很多原子组成的材料就会是磁性的。
Which brings us to the level of crystals.
从而我们认识了晶体的世界。
When a bunch of magnetic atoms get together to make a solid, they generally have two options.
当一束磁性原子聚集在一起形成固体时，它们通常有两个选择。
One is for all of the atoms to align their magnetic fields with each other,
一个是让所有的原子将它们的磁场彼此对准，
or they can align the magnetic fields in an alternating fashion so that they all cancel out.
或者它们可以以交替的方式将磁场对准，以便它们全部抵消。
The atoms will do whichever one requires less energy.
无论哪个原子需要更少的能量，它都会起作用。
That's why chromium, for example, is a very magnetic atom but a very un-magnetic solid
这就是为什么，例如，铬是一个非常有磁性的原子，但一个非常非磁性的固体
because it's one of the most anti-ferromagnetic materials we know.
因为它是我们知道的最反铁磁性的材料之一。
Iron, on the other hand, is the name-sake of ferromagnetism,
另一方面，铁是铁磁性的代名词，
so it is, unsurprisingly, ferromagnetic. Or, in usual parlance: magnetic.
因此，毫不奇怪，铁是铁磁性的。或者，用通常的说法：磁性的。
Sometimes. The last and final level of magnetism is that of domains.
有时候。最后一级的磁性是磁畴的磁性。
Essentially, even in a magnetic material where the magnetic fields of atoms line up together,
本质上，即使在一个磁性物质中，原子的磁场排列在一起，
it's possible that one chunk of the material will have all its atoms lined up pointing one way,
也有可能一个物质中的所有原子都指向一个方向，
and another chunk will have all its atoms pointing another way, and so on.
而另一个物质中的所有原子都指向另一个方向，依此类推。
If all of these "Domains" are of approximately similar size,
如果所有这些“磁畴”的大小都差不多，
none may be strong enough to force the others to align with it,
那么就没有一个能强大到足以迫使其他磁畴与之一致，
and so a piece of iron, for example, might have no magnetic field at all,
因此，一块铁，例如，可能根本没有磁场，
because of all of the warring magnetic kingdoms within it.
因为所有敌对的磁性王国在它里面。
However, if you apply a strong enough magnetic field/force/pressure from outside the material,
然而，如果你从材料外部施加足够强的磁场/力/压力，
you can help favor one domain/help one domain expand its control over its neighbors,
你可以帮助支持/帮助一个区域扩展它对相邻区域的控制，
and so on until all of the domains have been unified into one kingdom, all pointing in the same direction.
等等，直到所有的区域已经统一成一个王国，所有的域指向相同的方向。
And now, finally, you can rule with an iron fist … I mean, magnet. Exactly!
现在，你终于可以用铁拳统治了……我是说，磁铁。完全正确！
What's remarkable is that magnetism is a fundamentally quantum property amplified to the size of everyday objects:
值得注意的是，磁性本质上是一种量子属性，被放大到日常物体的大小：
every permanent magnet is a reminder that quantum mechanics underlies our universe
每一个永磁体都提醒我们，量子力学是我们宇宙的基础，
in order for any object to be magnetic, it has to have a unified kingdom of magnetic domains,
为了让任何物体都是磁性的，它必须有一个磁畴的统一王国，
each made up of bajillions of magnetic atoms which also need to be aligned with each other,
每个磁畴都由无数的磁性原子组成，这些原子也需要相互对准，
each of which can only be magnetic in the first place if it has an approximately half-filled outer shell of electrons
如果它具有近似半填充的电子外壳，首先它们中的每一个只能是磁性的，
so their intrinsic magnetic fields can align and not cancel each other out.
那么它们的本征磁场可以对准并且不会相互抵消。
Not surprisingly, these criteria are pretty difficult to fulfill,
毫不奇怪，这些标准是很难达到的，
which is why there are only a limited number of suitable materials you can use when you're building a magnet.
这就是为什么当你正在制造一块磁铁时，只有有限数量的合适的材料供你使用，
OR you could just run a current through any electrical conductor and generate a magnetic field that way.
或者，你可以让电流流过任何电导体，通过这种方式产生磁场。
But hey, Why does that work in the first place?
但是，嘿，为什么这在第一时间起作用呢？
Click here to go to over to Veritasium and we'll find out what special relativity
点击这里转到《Veritasium》频道，我们将会发现狭义相对论
and the speed of light have to do with electromagnets. I want to find out.
和光速与电磁铁有关。我想知道答案。
