一开始，什么都没有。然后，大约137亿年前，宇宙形成了。我们仍然不知道这一切发生的确切条件，以及是否有一个时间之前。但是利用望远镜观测和粒子物理模型，研究人员已经能够拼凑出宇宙生命中主要事件的大致时间线。在这里，我们来看看我们的宇宙最重要的历史时刻，从它的婴儿期到最终的死亡。
In the beginning, there was nothing. Then, around 13.7 billion years ago, the universe formed. We still don't know the exact conditions under which this happened, and whether there was a time before time. But using telescope observations and models of particle physics, researchers have been able to piece together a rough timeline of major events in the cosmos's life. Here we take a look at some of our universe's most important historical moments, from its infancy to its eventual death.
大爆炸（The Big Bang）
加州理工学院的理论物理学家肖恩·卡罗尔（Sean Carroll）在接受《现场科学》（Live Science）采访时说，这一切都是从大爆炸开始的，大爆炸“是时间上的一个瞬间，而不是空间中的一个点”。具体地说，这是时间本身开始的时刻，从那一刻起，所有的后续瞬间都被计算在内。尽管它有着众所周知的绰号，但大爆炸并不是真正的爆炸，而是一个宇宙极其炽热和稠密，空间开始一下子向各个方向向外扩展的时期。虽然大爆炸的模型说宇宙是一个无限小的密度无限小的点，但这只是一种手摇的方式，说我们不太清楚当时发生了什么。数学上的无穷大在物理方程中没有意义，所以宇宙大爆炸确实是我们目前对宇宙理解的崩溃点。
It all starts at the Big Bang, which "is a moment in time, not a point in space," Sean Carroll, a theoretical physicist at the California Institute of Technology, told Live Science. Specifically, it's the moment when time itself began, the instant from which all subsequent instants have been counted. Despite its well-known moniker, the Big Bang wasn't really an explosion but rather a period when the universe was extremely hot and dense and space began to expand outward in all directions at once. Though the model of the Big Bang states that the universe was an infinitely small point of infinite density, that's just a hand-wavey way of saying that we don't quite know what was going on then. Mathematical infinities don't make sense in physics equations, so the Big Bang is really the point at which our current understanding of the universe breaks down.
宇宙膨胀时代（Cosmic inflation era）
宇宙的下一个诀窍就是迅速变大。在宇宙大爆炸后的第一个0.0000000000000000000000001（1秒前有30个0的小数点）内，宇宙的大小可能会呈指数级膨胀，从而将之前密切接触的宇宙区域分开。这个被称为膨胀的时代仍然是假设性的，但是宇宙学家喜欢这个想法，因为它解释了为什么遥远的空间区域看起来如此相似，尽管它们被巨大的距离隔开。早在2014年，一个研究小组认为他们在早期宇宙的光中发现了这种膨胀的信号。但后来的结果却是更为平凡的东西：干扰星际尘埃。
The universe's next trick was to grow really big really fast. Within the first 0.0000000000000000000000000000001 (that’s a decimal point with 30 zeros before the 1) seconds after the Big Bang, the cosmos could have expanded exponentially in size, driving apart areas of the universe that had previously been in close contact. This era, known as inflation, remains hypothetical, but cosmologists like the idea because it explains why far-flung regions of space appear so similar to one another, despite being separated by vast distances. Back in 2014, a team thought they had found a signal of this expansion in light from the early universe. But the results later turned out to be something much more mundane: interfering interstellar dust.
夸克胶子等离子体（Quark-gluon plasma）
时间开始后几毫秒，早期宇宙真的很热——我们说的是7万亿到10万亿华氏度（4万亿到6万亿摄氏度）的高温。在这样的温度下，被称为夸克的基本粒子，通常被紧紧地束缚在质子和中子内部，自由地四处游荡。胶子携带着一种被称为强力的基本力，与这些夸克混合在一种弥漫于宇宙的浑浊的原始流体中。研究人员已经设法在地球上的粒子加速器中创造了类似的条件。但这种难以实现的状态只持续了几秒钟，无论是在地球上的原子破碎机还是在早期宇宙中。
A few milliseconds after the beginning of time, the early universe was really hot — we're talking between 7 trillion and 10 trillion degrees Fahrenheit (4 trillion and 6 trillion degrees Celsius) hot. At such temperatures, elementary particles called quarks, which are normally bound tightly inside of protons and neutrons, wandered around freely. Gluons, which carry a fundamental force known as the strong force, were mixed in with these quarks in a soupy primordial fluid that permeated the cosmos. Researchers have managed to create similar conditions in particle accelerators on Earth. But the difficult-to-achieve state only ever lasted a few fractions of a second, in terrestrial atom smashers as well as in the early universe.
早期（The early epoch）
在宇宙大爆炸后的几千分之一秒左右，在下一阶段有很多动作。当宇宙膨胀时，它冷却了，很快条件就足够让夸克聚集成质子和中子。宇宙大爆炸一秒钟后，宇宙的密度下降到足以使中微子——最轻、相互作用最少的基本粒子——能够在不撞击任何物体的情况下向前飞行，从而形成了科学家尚未探测到的宇宙中微子背景。
There was a lot of action in the next stage of time, which began around a few thousandths of a second after the Big Bang. As the cosmos expanded, it cooled, and soon conditions were clement enough for quarks to come together into protons and neutrons. One second after the Big Bang, the universe's density dropped enough that neutrinos — the lightest and least-interacting fundamental particle — could fly forward without hitting anything, creating what's known as the cosmic neutrino background, which scientists have yet to detect.
第一个原子（The first atoms）
在宇宙生命的最初3分钟里，质子和中子融合在一起，形成了氢的同位素，称为氘、氦和极少量的次轻元素锂。但是一旦温度下降，这个过程就停止了。最后，在宇宙大爆炸38万年后，物质冷却到足以使氢和氦与自由电子结合，形成第一个中性原子。先前与电子相撞的光子现在可以不受干扰地移动，形成宇宙微波背景（CMB），这是1965年首次探测到的这个时代的遗迹。
For the first 3 minutes of the universe's life, protons and neutrons fused together, forming an isotope of hydrogen called deuterium as well as helium and a tiny amount of the next-lightest element, lithium. But once the temperature fell, this process stopped. Finally, 380,000 years after the Big Bang, things were cool enough so that hydrogen and helium could combine with free electrons, creating the first neutral atoms. Photons, which had previously run into the electrons, could now move without interference, creating the cosmic microwave background (CMB), a relic from this era that was first detected in 1965.
黑暗时代（The dark ages）
在很长一段时间里，宇宙没有发出任何光。这一时期持续了大约1亿年，被称为宇宙黑暗时代。由于天文学家对宇宙的认识几乎完全来自星光，所以这个时代仍然极难研究。没有星星，很难知道发生了什么。
For a very long time, nothing in the universe gave off light. This period, which lasted around 100 million years, is known as the Cosmic Dark Ages. This epoch remains extremely difficult to study because astronomers' knowledge of the universe comes almost entirely from starlight. Without any stars, it's difficult to know what went on.
第一颗星（The first stars）
在大爆炸之后的大约1.8亿年，氢和氦开始坍缩成大球体，在它们的核心产生了地狱般的温度，照亮了最初的恒星。宇宙进入了一个被称为“宇宙黎明”或“再电离”的时期，因为早期恒星和星系辐射的热光子将星际空间中的中性氢原子分裂成质子和电子，这个过程被称为电离。再电离究竟持续了多久还很难说。因为它发生得太早，它的信号被后来的气体和尘埃所掩盖，所以科学家们能说的最好的解释是，它在大爆炸之后大约5亿年就结束了。
By around 180 million years after the Big Bang, hydrogen and helium began to collapse into large spheres, generating infernal temperatures in their cores that lit up into the first stars. The universe entered a period known as Cosmic Dawn, or reionization, because the hot photons radiated by early stars and galaxies broke neutral hydrogen atoms in interstellar space into protons and electrons, a process known as ionization. Just how long reionization lasted is difficult to say. Because it occurred so early, its signals are obscured by later gas and dust, so the best scientists can say is that it was over by around 500 million years after the Big Bang.
大型结构（Large-Scale structure）
这里是宇宙开始进入商业领域的地方，或者至少是我们今天所熟知的商业领域。早期的小星系开始合并成更大的星系，在大爆炸后大约10亿年，在它们的中心形成了超大质量的黑洞。明亮的类星体，在120亿光年之外产生强烈的光信号灯，被打开了。
Here's where the universe gets down to business, or at least the familiar business we know about today. Small early galaxies began to merge together into larger galaxies and, around 1 billion years after the Big Bang, supermassive black holes formed in their centers. Bright quasars, which produce intense beacons of light that can be seen from 12 billion light-years away, turned on.
宇宙的中年（The universe’s middle years）
在接下来的几十亿年里，宇宙继续进化。来自原始宇宙的密度较高的点在引力作用下把物质吸引到自己身上。这些慢慢成长为星系团和长串的气体和尘埃，形成了今天可以看到的美丽的丝状宇宙网。
The universe continued to evolve over the next several billion years. Spots of higher density from the primordial universe gravitationally attracted matter to themselves. These slowly grew into galactic clusters and long strands of gas and dust, producing a beautiful filamentary cosmic web that can be seen today.
太阳系的诞生（Birth of the solar system）
大约45亿年前，在一个特定的星系中，一团气体云坍缩成了一个围绕着它的环系统的黄色恒星。这些光环合并成八颗行星，加上各种彗星、小行星、矮行星和卫星，形成了一个熟悉的恒星系统。在这一过程中，位于中央恒星第三位的行星要么在这一过程中保留了大量的水，要么彗星随后带来了大量的冰和水。
About 4.5 billion years ago, in one particular galaxy, a cloud of gas collapsed down into yellow star with a system of rings around it. These rings coalesced into eight planets, plus various comets, asteroids, dwarf planets, and moons, forming a familiar stellar system. The planet third from the central star managed to either retain a ton of water after this process, or else comets later delivered a deluge of ice and water.
地球与人类（Earth and humanity）
在第三个，水世界，在38亿到35亿年前（取决于你问谁），微小的，简单的微生物眨眼间就存在了。这些生命形式出现并进化成神奇的海怪和巨大的食叶恐龙。最终，大约20万年前，直立的生物出现了，它们能够惊叹于我们神秘的宇宙，并发现整个宇宙是如何形成的。
On that third, watery world, between 3.8 and 3.5 billion years ago (depending on whom you ask), tiny, simple microbes winked into existence. These life-forms emerged and evolved into wondrous sea monsters and gigantic, leaf-eating dinosaurs. Eventually, about 200,000 years ago, along came upright creatures capable of marveling at our mysterious universe and discovering how the whole thing came to be.
终曲（或者不是 ?）【The end (or not?)】
上方图片指标的翻译：
Big crunch theory：大紧缩理论 closed universe：封闭宇宙
TIME：时间 open universe ：开放宇宙
EXPANSION:膨胀 maximum expansion：最大膨胀
当然，事情还没有结束。物理学家们仍然不太清楚宇宙将要发生什么。这取决于暗能量的细节，暗能量是一种驱动宇宙分裂的神秘力量，其性质尚未得到很好的测量。在一个可能的未来，宇宙将继续永远膨胀，足够长的时间，所有星系中的所有恒星都将耗尽燃料，甚至黑洞也将蒸发为零，留下一个充满惰性能量的死宇宙。或者，引力最终会克服暗能量的扩张力，以一种被称为大紧缩的反向大爆炸的方式把所有物质拉回到一起。另一方面，暗能量可以加速一切离其他一切越来越远的东西，造成所谓的大裂口，在这个大裂口中，宇宙实际上撕裂了自己。
Of course, that isn't the end of things. Physicists still don't quite know what's in store for the universe. That depends on the details of dark energy, a still-mysterious force driving apart the cosmos and whose properties have not been well measured. In one possible future, the universe will continue to expand forever, long enough that all the stars in all the galaxies will have run out of fuel, and even black holes will evaporate into nothing, leaving behind a dead cosmos permeated by inert energy. Or, gravity will eventually overcome dark energy's expansionary force, pulling all matter back together in a sort of reverse Big Bang known as the Big Crunch. Alternatively, dark energy could accelerate everything apart farther and farther from everything else, creating what's known as the Big Rip, in which the cosmos literally tears itself apart.
