Music of the Spheres in nLab
In ancient times, Musica Universalis or Music of the Spheres referred to a philosophical concept that regards proportions of orbits in the solar system as exhibiting a cosmic harmony (Plato 380BC).
My initial inclination was to call this book The Music of the Spheres, but I was dissuaded from doing so by my diligent publisher, who is ever mindful of the sensibilities of librarians. (Ravenel 86, p. xv)
For the last 50 years one of the basic problems in algebraic topology has been the determination of the homotopy groups of spheres (Mahowald-Ravenel 87, Sec. 1)
As is well known, it is our manifest destiny as 21st century algebraic topologists to compute homotopy groups of spheres. (Wilson 13, p. 1)
One of the most fundamental problems in topology is to determine the set of homotopy classes of continuous based maps between spheres. (Isaksen-Wang-Xu 20, Sec. 1)