The “Universe 25” experiment, conducted by American scientist John Calhoun, is one of the most alarming studies in the history of science. It aimed to explain human societies through the behavior of a mouse colony. Calhoun created an “ideal world” for hundreds of mice, known as the “Paradise of Mice,” where they had abundant food, water, and ample living space. Initially, he introduced four pairs of mice, which quickly reproduced, causing the population to grow rapidly. However, after 315 days, their reproduction rate significantly declined. When the population reached 600, a hierarchy emerged, and the so-called “wretches” appeared. Larger rodents began attacking others, leading to psychological collapse in many males. Consequently, females became aggressive towards their young and did not protect themselves. Over time, the females exhibited increasing aggression, isolation, and a lack of reproductive drive. This led to a low birth rate and higher mortality among younger rodents. A new class of male rodents, termed “beautiful mice,” emerged. They refused to mate or fight for territory, focusing only on food and sleep. Eventually, “beautiful males” and “isolated females” dominated the population. Calhoun described the death phase in two stages: the “first death,” marked by a loss of purpose beyond mere existence, and the “second death.” Juvenile mortality reached 100%, and reproduction ceased entirely. Despite abundant food, cannibalism and homosexuality increased among the mice. Two years into the experiment, the last baby mouse was born, and by 1973, the last mouse in Universe 25 had died. Calhoun repeated the experiment 25 times, with the same outcome each time. Calhoun’s work has been used to model social collapse and serves as a significant reference in urban sociology studies.