外星人在哪里？
外星人在哪里？
宇宙应该充满外星生命
Naval: 既然我们谈到外星人，让我们简单讨论一下费米悖论。对于不了解的听众来说，恩里科·费米是参与曼哈顿计划的著名物理学家。他说过：“外星人在哪里？”
宇宙如此之大，可能有很多行星能够支持某种形式的生命。难道我们不应该已经看到它们了吗？
Brett: 几乎每颗恒星周围都有一系列行星，很像我们自己的太阳系。像银河系这样的典型星系中存在的恒星数量大约是2000亿颗，尽管估计数字高达约4000亿颗。我们能够看到的星系数量大约在2000亿到3000亿之间。
可观测宇宙只是整个宇宙的一小部分，这意味着行星的数量绝对是天文数字。
当然，考虑到这些数字，情况必然是不仅存在适合生命的行星，而且宇宙应该充满比我们先进得多、比我们落后得多，以及一些与我们发展水平相似的文明。
那么它们在哪里呢？
Where Are the Aliens?
The universe should be teeming with aliens
Naval: Let’s talk briefly about the Fermi paradox since we’re talking about aliens. For listeners who don’t know, Enrico Fermi was a famous physicist who was part of the Manhattan Project. He said, “Where are the aliens?”
The universe is so large and there are probably so many planets that are capable of supporting life of some kind or another. Shouldn’t we have seen them by now?
Brett: Around almost every star there is a contingent of planets much like our own solar system. The number of stars that exist within a typical galaxy like the Milky Way is something like 200 billion, although the estimates go up to about 400 billion. The number of galaxies that we can see is around 200 to 300 billion.
The observable universe is just a small fraction of the entire universe, which means that the number of planets is absolutely astronomical.
Surely, given these numbers, it has to be the case that there are not only planets out there that are suitable for life but that the universe should be teeming with civilizations far more advanced than ours, less advanced than ours, and some that are similar in advancement to ours.
So where are they?