人类存在的概率微乎其微The Probability of Human Existence Is Infinitesimally Small
Brett：这里还有一个思考角度，对那些认为外星人就在那里、将来某天会来拜访我们的人来说，这个角度在数学上相当吓人。
我们之前谈到，已知宇宙中存在着数万亿颗行星，其中有些甚至可能适宜生命诞生。想象一下，从我们这些有智慧的人类，到我们能想象到的最简单的细菌之间，只隔着 100 个独立的进化步骤。这当然不是事实——要让生物存活至今、让我们今天得以存在，可能得发生上百万次甚至更多的不同突变——但我们就假定只有 100 步。
再想象一下，这 100 个独立步骤中，每一步发生的概率都只有十分之一。事实上，真实概率可能更接近百万分之一，但我们就大方一点，算它是十分之一。
这样一来，我们就得到了一条概率链：十分之一乘以十分之一，再乘以十分之一……一共乘 100 次。也就是 10 的 100 次方分之一——即 1 除以 1 后面跟 100 个零。这个数字，远超我之前提到的那些关于行星的天文数字。
换句话说，按这套推演，我们得以出现的概率小到微乎其微。而它竟然真的发生过一次——这本身就足以让我们惊叹不已。
Brett: Here’s another way to think about it that is mathematically frightening for the people who think that the aliens are out there and they’re going to visit us sometime in the future.
We were talking earlier about trillions of planets that exist throughout the known universe that might even be friendly for life to arise. Imagine that between us as intelligent human beings and the most simple form of bacteria that we can imagine, there are only 100 independent evolutionary steps. Now that’s not true—a million or more different mutations probably had to happen to allow the organisms to survive such that we exist today—but let’s make it only 100.
Imagine that each of those independent steps had a probability of just one in 10 happening. Now, in fact, it’s probably more like one in a million, but we’ll be generous and say one in 10.
Now what we have is a chain of probability: one in 10, times one in 10, times one in 10…100 times. This is one over 10, all to the power of 100—which is one over one followed by 100 zeroes. That number swamps the astronomical number I was talking about with planets earlier on.
In other words, the probability of us arising in this particular argument is infinitesimally small. The fact that it’s happened once should blow our minds.