> For the complete documentation index, see [llms.txt](https://dragoncapsule.gitbook.io/di-er-bu-qiong-ding-jia-yuan/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://dragoncapsule.gitbook.io/di-er-bu-qiong-ding-jia-yuan/3no-ad-2140/3.1-fei-mi-bei-lun.md).

# 3.1 费米悖论

1951年夏天的一个午后，诺贝尔奖获得者、物理学家费米在与朋友讨论地外文明和外星人的问题时，突然冒出一句：“他们都在哪儿呢？”， -- 这句话引出的科学论题，就是著名的“费米悖论”（Fermi Paradox）。

 

费米悖论的隐含之意是：我们的银河系中估计有2000亿到4000亿颗恒星，以及至少1000亿颗行星，理论上讲，人类能用100万年的时间飞往银河系各个星球，那么，外星人只要比人类早进化100万年，那么现在就应该来到地球了。

 

换言之，“费米悖论”表明这样的两难：

* **A. 外星人是存在的**——科学推论可以证明， 外星人的进化要远早于人类，应该已经来到地球并存在某处。
* **B. 外星人是不存在的**——迄今，人类并未发现任何有关外星人存在的蛛丝马迹。


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