It gets stranger. Our sun is relatively young in the lifespan of the universe. There are far older stars with far older Earth-like planets, which should in theory mean civilizations far more advanced than our own. As an example, let’s compare our 4.54-billion-year-old Earth to a hypothetical 8-billion-year-old Planet X. +^$FA4<~
情况变得复杂了。太阳相对于宇宙来说还很年轻，理论来讲年老恒星的类地行星上外星文明应该比地球文明更先进。假设有一个80亿年的行星X，我们用它和我们4.54亿年的地球做比较。
