as to the correct interpretation of Nietzsche's doctrine continues to this day. Precursors The discovery of the laws of thermodynamics in the 19th century restarted the debate among scientists and philosophers about the ultimate fate of the universe, which brought in its train many questions about the nature of time. Eduard von Hartmann argued that the universe's final state would be identical to the state in which it had begun; Eugen Dühring rejected this idea, claiming that it carried with it the necessary consequence that the universe would begin again, and that the same forms would repeat themselves eternally, a doctrine which Dühring viewed as dangerously pessimistic. , on the other hand, argued in favour of a cyclical system, additionally positing the spatial co-existence of an infinite number of identical worlds. Louis Auguste Blanqui similarly claimed that in an infinite universe, every possible combination of forms must repeat itself eternally across both time and space. Nietzsche's formulation Nietzsche may have drawn upon a number of sources in developing his own formulation of the theory. He had studied Pythagorean and Stoic philosophy, was familiar with the works of contemporary philosophers such as Dühring and Vogt, and may have encountered references to Blanqui in a book by Friedrich Albert Lange. He was also a fan of the author Heinrich Heine, one of whose books contains a passage discussing the theory of eternal return. Nevertheless, Nietzsche claimed that the doctrine struck him one day as a sudden revelation, while walking beside Lake Silvaplana. The first published presentation of Nietzsche's version of the theory appears in The Gay Science, section 341, where it is proposed to the reader as a thought experiment: Nietzsche expanded upon this concept in the philosophical novel Thus Spoke Zarathustra, later writing that eternal return was "the fundamental idea of the work". In this novel, the titular Zarathustra is initially struck with horror at the thought that all things must recur eternally; ultimately, however, he overcomes his aversion to eternal return and embraces it as his most fervent desire. In the penultimate chapter of the work ("The Drunken Song"), Zarathustra declares: "All things are entangled, ensnared, enamored; if you ever wanted one thing twice, if you ever said, 'You please me, happiness! Abide, moment!' then you wanted all back ... For all joy wants—eternity." Interpretation Martin Heidegger points out that Nietzsche's first mention of eternal recurrence in The Gay Science