费米悖论最惊悚的解答，是“大过滤器”假说：在文明演化的关键阶段（如掌握核武或超级AI后），存在一道极高的、几乎无法跨越的自我毁灭障碍。宇宙的寂静，或许正是因为无数文明都在此处集体“熄火”。萨根拼命相信有“别人”存在，是因为只要听到一声回响，就能证明那道墙并非不可逾越——人类，或许还有希望...
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