这篇论文用极简模型把费米悖论推到了宇宙尺度，对地外文明和SETI感兴趣的人会看到一种全新的约束视角——看完你会重新思考“我们为什么孤独”。
哈特-蒂普勒猜想认为，如果银河系中存在其他技术文明，它们应该已经发射了自我复制的冯·诺依曼探测器，但我们的存在表明这并未发生，从而反证地外文明不存在。最新研究将这一计算扩展到宇宙尺度，建立了一个仅含三个参数的简化模型（自发产生率、传播速度和起始时间）。模型发现，若传播速度为0.1倍光速，且每百万星系中有一个产生自我复制探测器，则今天宇宙的一半已被“感染”；若传播速度接近光速，则每十亿星系中有一个即可。该研究为地外文明的存在提供了极严格的约束，并探讨了人择原理的含义。
The Cosmological Hart-Tipler Conjecture
Self-reproducing automata, so-called von Neumann machines, have been repeatedly estimated to be capable of traversing the Galaxy many times given its age. Our mere existence thus seems to exclude an aggressive variant of such a probe having ever been launched in the Milky Way. The Hart-Tipler conjecture considers this to represent contra-positive evidence to the hypothesis that other extra-terrestrial technological entities have emerged in our galaxy. Recently, several authors have extended interstellar colonization calculations to cosmological volumes, but these models are loaded with specific assumptions about behavior and emergence times. Here, we present a bare-bones model of generic artificial infections (such as but not limited to von Neumann probes) at cosmological scale in order to maximize interpretability, an approach closer to the original spirit of the Hart-Tipler calculations. Our model has just three parameters, a spontaneous spawn rate, a propagation speed (u) and a start time for the calculation. Accounting for cosmological expansion, we find that half the Universe is infected by today for u=0.1c propagation starting 4.5 Gyr after the Big Bang if the spawn rate exceeds approximately once per million galaxies. For near-c propagation, this becomes a billion galaxies. Over 99.9% of cosmological volumes are filled with 0.1c if even 1-in-100,000 galaxies have ever spawned an infection. The "cosmological Hart-Tipler" problem therefore offers a remarkably sharp minimal-model constraint on the prevalence of aggressive, self-propagating technological behavior. We explore its implications, such as how anthropic reasoning implies such infections occur and its fine-tuning nature.