How do you know you’re a person who has lived your life, rather than a just-formed brain full of artificial memories, momentarily hallucinating a reality that doesn't actually exist? That may sound absurd, but it’s kept several generations of top cosmologists up at night. They call it the Boltzmann brain paradox.
你该如何得知 你是过着现有人生的一个人, 还是一个装满人工记忆的 初生大脑, 用不存在的现实暂时迷惑着你呢? 听起来可能有些奇怪, 但是这让好几代 顶级宇宙学家彻夜难眠。 他们将其称为玻尔兹曼大脑悖论 (Boltzmann Brain Paradox)。
Its namesake, Ludwig Boltzmann, was a 19th century physicist operating in a period when scientists were passionately debating whether the universe had existed for an infinite or finite time. Boltzmann’s main claim to fame was revolutionizing thermodynamics, the branch of physics that studies energy. He put forward a new interpretation of entropy, which is a measure of the disorder of a system. A glass is an ordered system, whereas a shattered glass is disordered. The second law of thermodynamics states that closed systems tend towards disorder: you won’t see a shattered glass return to its pristine state.
它的名字源自 一位 19 世纪的物理学家 路德维希·玻尔兹曼 (Ludwig Boltzmann), 当时,科学家们激烈地讨论着 宇宙已经存在了无限长的时间, 还是有限长的时间。 令玻尔兹曼成名的主要成就是 他为热力学带来了革命性突破, 热力学是物理学中研究能量的分支。 他创造了熵的全新阐释, 熵描述了系统的无序程度。 一块玻璃是一个有序系统, 而一块碎玻璃是一个无序系统。 热力学第二定律主张 一个孤立系统会向无序状态演变, 比如,一块碎玻璃不会回到原状。
Boltzmann’s insight was applying statistical reasoning to this behavior. He found that a system evolves to a more disordered state because it’s more likely. However, the opposite direction isn’t impossible, just so unlikely that we’ll never witness things like scrambled eggs turning raw.
玻尔兹曼的发现是 利用统计原理解释这一现象。 他发现之所以说一个系统会逐渐 趋于无序,只是因为可能性更大, 然而,逆向也是有可能的, 只是可能性微乎其微,所以 我们从未见证过炒蛋变生的情况。
But if the universe exists over an infinitely long time, extremely unlikely events will happen, including complex things forming out of random combinations of particles. So what does that look like in a hypothetical infinitely old universe? In this unremarkable stretch of near-nothingness, about eight octillion atoms randomly come together to form a replica of the Thinker made of pasta. It instantly dissolves. Over here, these particles suddenly form something like a brain. It’s filled with false memories of a lifetime up to the present moment, when it perceives a video saying these very words, before decaying. And finally, by random fluctuations, all the particles in the cosmos concentrate in a single point, and an entire new universe spontaneously bursts into existence. Of those last two, which is more likely? The brain, by far— despite all its complexity, it’s a blip compared to an entire universe. Every one universe produced by random fluctuations has equivalent odds to heaps upon heaps of insta-brains. So by this reasoning, it seems extremely more likely that everything you believe to exist is actually a brief illusion, soon to be extinguished.
但是,如果宇宙已经 存在了无限长的时间, 极端不可能事件也有可能发生, 包括从粒子的随机组合中 形成复杂物体。 那么在一个假想的无限宇宙中 是什么样的呢? 在这接近虚无的历史长河中, 大约 8 乘 10 的 27 次方个原子 随机组合到一起,形成了一个 由意面做成的《思想者》复制品。 然后它瞬间分解了。 接着,这些粒子突然组成了 一个类似大脑的东西。 它盛满了虚假的一生记忆, 直到此时此刻, 直到在它消失前接收到这个视频, 说着这些话。 再举个例子,宇宙中的 所有粒子随着随机波动 汇集到一个点, 然后一个全新的宇宙 自发地横空出世。 刚说的两个想法, 哪个更有可能呢? 大脑的可能性大得多, 虽然非常复杂,比起 整个宇宙可太微不足道了。 每一个由随机波动产生的宇宙 有同样的可能性 在这些速成大脑上层层堆叠。 因此,非常有可能 所有你相信存在的物体 都是一个短暂的幻象, 稍纵即逝。
Boltzmann didn’t get quite that far in his thinking; the brains themselves were introduced by later cosmologists building on his work. But they, like just about everyone else, were pretty sure that they themselves weren't just ephemeral brains. So the paradox was: how could they be correct and the universe be eternal? The resolution is something most take for granted today: that our universe has not existed forever, but rather time and space started with a Big Bang.
玻尔兹曼在他的想法中 并没有到达这一步, 大脑本身的理论由后续宇宙学家 基于他的成果得出。 但是这些宇宙学家们, 就和大多数人一样, 非常确信他们本人 并不只是转瞬即逝的大脑。 因此,这个悖论为:如果他们是对的, 宇宙怎么会是永恒的呢? 答案是我们如今 默认的一个“事实”: 我们的宇宙不是永恒存在的, 时间和空间始于宇宙大爆炸。
So that’s the paradox over and done with, right? Well, maybe not. In the last century, scientists have found evidence supporting the theory of the Big Bang everywhere we look. Yet while we know that the Big Bang happened, no one knows what, if anything, preceded and caused it. Why did the universe begin in such an extremely ordered, and unlikely, state? Is our universe in an unending cycle of creation and collapse? Or might we be in one of many universes expanding within a multiverse?
悖论就这么被解决了,对吧? 不一定。 上个世纪,科学家们 发现了一些证据 处处证明了宇宙大爆炸理论。 然而,虽然我们知道 宇宙大爆炸发生了, 但是无人知晓在它之前发生了什么, 或者由什么导致。 为什么宇宙始于如此 极端有序又不太可能的状态呢? 我们的宇宙是不是处于一个 创造崩塌的循环之中呢? 我们的宇宙会不会是多元宇宙 正在膨胀的其中之一呢?
In this context, Boltzmann’s paradox has found renewed interest by contemporary cosmologists. Some argue that leading models for where the universe came from still imply that Boltzmann brains are more likely than human brains, suggesting something’s amiss. Others counter that slight modifications of the cosmological models would avoid the problem, or that Boltzmann’s brains can’t actually physically form. Some researchers even attempted to calculate the probability of a brain popping out of random quantum fluctuations long enough to think a single thought. They got this incredible number whose denominator is 10 to a number about a septillion times larger than the number of stars in the universe. The Boltzmann brain paradox, despite its absurdity, is useful because it creates a bar that models have to rise to. If, compared to numbers like this one, the current state of the universe is exceedingly unlikely, something in the model is almost certainly wrong. Unless you’re the one who is wrong...
在这种环境下,当代宇宙学家 对玻尔兹曼悖论产生了新的兴趣。 有人说,宇宙来源的主流模型 依旧在说明玻尔兹曼大脑 比人脑更有可能, 说明了有什么东西不对。 有人反对说,对宇宙论 模型的轻微修改 就能避免这个问题, 或者证明玻尔兹曼大脑 无法从实际上物理存在。 有的研究人士甚至试图计算出 从随机量子波动中 产生一个大脑的概率, 时间足以思考一个想法。 他们得到了 这样一个惊人的数字, 分母为 10,次方为 比宇宙恒星数量大 10 的 24 次方的数字。 尽管玻尔兹曼大脑悖论 有点离谱, 但是由于它为模型创造了一个标杆, 还是十分有用的。 如果参照这个数字, 宇宙现在的状态 极为不可能出现, 证明这个模型 肯定有地方不对。 除非你就是那个不对的人……