The cosmic vision of Dante was that of the Middle Ages. Besides the sun and moon, they knew only five planets. Beyond the planets was the sphere of fixed stars against which they moved. They believed that the visible stellar panorama, unlike the earth, was immutable and immortal.
Above the sphere of the fixed stars was the PRIMUM MOBILE, the First Mover, that is God which he depicts as an intense point of light encircled by nine moving choirs of luminous angels. This sphere imparted motion to the visible universe.
"The providence that integrates the whole
Keep in perpetual stillness by its light
That heav'n wherein the swiftest heav'n does roll;
Music of the Spheres: The still point by William Zeitler
Lastly came the EMPYREAN which he envisioned in the shape of the rose. This sphere was beyond time and space where God dwelt with his angels and saints. "The Empyrean Heaven, because of its Peace, bears the similitude to the Divine Science, which is full of Peace; which endures no conflict of opinion or of sophistical arguments, on account of the most excellent certainty of its subject, which is God. And of this He Himself speaks to His disciples: 'My peace I give to you: my peace a live unto you.'" (The Banquet, Ch. 11)
Dante believed that the spheres emitted music as he states:
"The wheel Thou mak'st eternal through innate
Desire for Thee, no sooner took mine ear
With strains which Thou dost tune and modulate."
"The 'Music of the Spheres' was an understanding of the Cosmos that held sway for about 2000 years. According to this view, each of the planets rode on giant crystal spheres, and each of these planetary crystal spheres emitted a musical sound as they moved. The combined sound of all the planets was "the Music of the Spheres". (William Zeitler)
Although this is not true from a scientific viewpoint, it is still true from a theological perspective. Whatever order there is in the universe expresses God's love and the creature desire, conscious or otherwise, to return to it Maker. Music is basically a rhythm emanating from the powers of attraction (love) expressing harmonious movement. Man hears music in the rhythms of nature and expresses them as melodies which vary with the sensitivities of each culture. We can, therefore, say that the rhythms of the planets are an expression of God's music because he is the creative love which moves them around and around with variation in orbit by his fullness of being which is music itself. We do not hear this music with our ears but we perceive their motions with our eyes which we can translate into music.
Unlike Dante, we live in a relativistic universe, a vast flow of matter and energy and without definite boundaries. Although our astronomical view of the cosmos is truer and majestic, it is a monistic view where matter/energy is primary. On the other hand, Dante's universe is dualistic, made up of matter and spirit, God and creatures, and its dimensions are both visible and invisible. "Dante's journey through the celestial realms is not a trip to other physical 'worlds' as in modern science fiction, but a kind of ecstatic cosmic dance through the increasingly abstract realm of light and motion. Hence, luminescent choirs of angels fill the celestial space with heavenly harmonies--the mythical 'music of the spheres.'" 93
3_Dante's Love for Beatrice