However different the criteria for art and for science are, there are also points in common between them, inasmuch as people working in both fields are driven by curiosity. It is a matter of exploring connections that others have yet to recognize and designing structures that hitherto did not exist.
György Ligeti, 1991

György Ligeti's interest in mathematics and the natural sciences accompanied him throughout his life. He often compared his working methods as a composer with those of scientific research while emphasising the differences between the two fields. The Poème Symphonique for 100 metronomes is both a "musical ceremony" and an experiment in hearing psychology. Ligeti's interest in high-precision machines and clockwork manifests itself in Clocks and Clouds for textless women's choir and orchestra, whose title he borrowed from an essay by the philosopher Karl Popper. In 1984, Ligeti first saw computer-generated fractal images, which immediately fascinated him. He got to know personally one of the most influential researchers of fractal geometry and chaos theory, Benoît B. Mandelbrot, who coined the term "fractal" in 1975. Ligeti worked intensively with fractal-like musical structures, as used in the fourth movement of the Piano Concerto.