World riddle
The term "world riddle" or "world-riddle" has been associated, for over 100 years, with Friedrich Nietzsche (who mentioned Welträthsel in several of his writings) and with the biologist-philosopher Ernst Haeckel, who, as a professor of zoology at the University of Jena, wrote the book Die Welträthsel in 1895–1899, in modern spelling Die Welträtsel (German; "The World-riddles"), with the English version published under the title The Riddle of the Universe, 1901. The term "world riddle" concerns the nature of the universe and the meaning of life. The question and answer of the World Riddle has also been examined as an inspiration or allegorical meaning within some musical compositions, such as the unresolved harmonic progression at the end of Also sprach Zarathustra (1896) by composer Richard Strauss. View of Nietzsche Friedrich Nietzsche referred to the "World Riddle" (Welträthsel) in several of his writings; however, his direct influence was limited to a few years, by his failing health. Emil du Bois-Reymond Emil du Bois-Reymond used the term "World Riddle" in 1880 for seven great questions of science, such as the ultimate nature of matter and the origin of simple sensations. In a lecture to the Berlin Academy of Sciences he declared that neither