of his universe from the depths of Hell in the centre of the Earth, up the purifying mountain of Purgatory and through the celestial layers, Dante pierces the shell of the primum mobile and bursts through the skin of the world to come face to face with God, ‘the Love that moves the Sun and the other stars’. For medieval thinkers this spiritual domain was the primary realm of the Real with the physical realm serving as a secondary and rather pale reflection. Just what it meant to have a ‘place’ outside physical space was a question that much exercised medieval minds – no scholar of the Middle Ages believed that Heaven lay literally beyond the stars. Yet whatever the philosophical difficulties, scholars of the time insisted that physical space was not the totality of reality but one half of a larger metaphysical whole.
This dualism of body and soul – matter and spirit – was mirrored in a dualism that was believed to exist between the terrestrial and celestial realms. Again, following the Greeks, medieval natural philosophy held that the two regions were qualitatively distinct regions: in the terrestrial realm things were made up from the four mundane elements, earth, air, fire and water; those in the celestial realm (stars, planets, comets and so on) were composed of a fifth element, or quintessence, also known as the æther. Everything in the terrestrial realm was subject to decay and death, those in the heavens were believed to be eternal, prone neither to decay nor change. Subtleties compounded, for the celestial realm was not itself homogeneous. Ascending from the surface of the Earth medieval cosmology posited that in each successive sphere things became more ethereal. In effect, celestial space exhibited a vector of grace: the closer one got to God, the more ‘pure’ the region was said to be. Within the scheme of medieval cosmology, celestial space thus served as a mediating zone between the purely material realm of the Earth and the purely spiritual realm of the Empyrean. To put it another way, the celestial heaven of the planets and stars stood as a metaphor for and pointer to the religious Heaven of God and the soul, and the whole of medieval thinking rejoiced in this analogy.
But what if terrestrial space and celestial space were not qualitatively distinct? What if the cosmos was a homogeneous domain? Just such an idea began to bubble into European consciousness during the fifteenth century forming the seeds of what would become, in the seventeenth, a full-blown reconfiguration of Western cosmological thinking.
The first person to express this vision in anything like its modern form was a cardinal of the Roman Catholic Church, Nicolas of Cusa, who completed in 1440 a masterpiece of scientific proleptics entitled On Learned Ignorance. The universe Cusa proposed had no crystal spheres and no hierarchy of planets; in one daring swoop he abolished the distinction between the ‘base’ Earth and the ‘ethereal’ heavens, positing that the stars and planets were also mundane material bodies. Cusa’s cosmos was infinite – ‘unbounded’ is the word he used – a space in which all regions were materially and spiritually on par. He even suggested that other stars were peopled by other physical beings, an idea that would not be broached again for 150 years. Cusa’s ideas were too radical for most of his contemporaries, but in the sixteenth century the tectonic plates of the Western psyche began to shift, resulting in the work of Copernicus and all that came after him.
Why was such a shift occurring? After all, the medieval world picture had held stable as a philosophical construct for more than a thousand years. The telescope had not yet been invented, astronomical observations were not qualitatively better, the Ptolemaic model continued to yield reasonable results. Cosmological technologies were not perceived to be failing. So what was going on? Astronomy wasn’t undergoing a crisis, nonetheless underlying conceptions of how reality might be were beginning to change. We know this primarily not from what scientifically minded thinkers were saying but from what painters were doing. Long before the rise of science a new Western attitude to space was apparent in the realm of art, and to understand the cosmological transformation wrought by Galileo and Newton in the seventeenth century it is instructive to turn first to the frescoes of Giotto. Here we can see explicitly the spiritual stakes that were coming into play as Europeans began to feel their way out of a medieval world.
Along with medieval philosophy, medieval art focused on the numinous realm of the soul. Art also was iconic, aiming to represent the spiritual order beyond the material world. One way of conveying that order was through scale; thus Christ would be the largest figure in a painting, with angels next in size, followed by saints and martyrs, then ordinary human beings. Backgrounds too were iconic; gold and azure represented Heaven, whose value was viscerally present in exorbitantly expensive gold leaf and lapis lazuli pigments. Depth was almost absent from these images. But in the late twelfth century representation began to undergo a subtle transformation with a gradual interest in three-dimensionality starting to emerge. This new style reached a crescendo with Giotto’s work in the Arena Chapel in Padua in which he depicted a sequence of near-life-sized images recounting the life of Christ. What is immediately startling about these Christ Cycle frescoes is their sense of physical presence. Figures look solid and are anchored to the ground as if compelled by gravity. We are clearly no longer in Heaven but on Earth. Everyone appears at the same scale: Christ and humans and angels. Flat blue and gold backgrounds are replaced by attempts at genuine landscapes; there are mountains, trees and carefully observed studies of animals. Buildings seem to be leaping out of the surface. True, they are not entirely convincing, but one feels here that the artist is striving to convey three-dimensional space.
All this was in keeping with a revivified interest in the natural world. After the hiatus of the early Middle Ages, scholars had begun to recover the science and mathematics of ancient Greece, and during the thirteenth century the study of nature underwent a renaissance. With his careful attention to empirical detail, Giotto reflected this novel scientific bent. For artists and their patrons (many of whom were leaders of the Catholic Church) the observations of the outer eye were becoming more interesting than the revelations of the inner eye. In short, visual attention was shifting towards the material realm.
Paradoxically, this refocusing from spirit to matter was given credence by a novel theological development and it is here that science and religion intersect in a uniquely Western way. As Europeans recovered the heritage of the Greeks one thinker they increasingly encountered was Pythagoras, a mathematician and mystic who had dreamed the dream that would become modern physics. In the fifth century BCE Pythagoras posited that the structure of the world was determined by mathematics: ‘All is number’, he famously declared. A small band of medieval thinkers took Pythagorean precepts and transformed them into a Christian context, giving rise to the then-novel idea that God had created the material world according to mathematical rules.
Among God’s primary tools was Euclidean geometry and in 1267 the Franciscan friar Roger Bacon argued in a treatise to Pope Clement IV that artists ought to follow their Creator and construct images accordingly with geometric relationships. Bacon called the new style ‘geometric figuring’ and he proposed that the Church encourage painters to adopt it as a matter of principle. Artists who did so would not just be rendering Creation truthfully, Bacon said, they could also serve a powerful propaganda purpose, for according to him the techniques of three-dimensional verisimilitude were so psychologically powerful that viewers beholding such images would believe they were actually witnessing the scenes depicted. They would believe they were really seeing, for example, Christ raising Lazarus in front of them. To put this into current parlance, Bacon was suggesting that ‘geometric figuring’ acted as a kind of virtual reality and, as he saw it, this medieval VR would have the power to convert unbelievers to the Christian faith.
From the fourteenth through sixteenth centuries artists elaborated Bacon’s vision with ever-greater finesse, a movement that culminated in the formalisms of ‘linear perspective’. The consequences of this representational revolution reached far beyond the painted surfaces of the churches from which it began. Art historian Samuel Edgerton has argued that ‘geometric figuring’ retrained European minds to see space in a Euclidean sense and that in this respect Renaissance artists from Giotto through Raphael paved the way for the physicists who came after them. Edgerton’s thesis helps make sense of a historical conundrum, for following Aristotle most Western thinkers pointedly rejected a Euclidean view of space. As physicist and science historian Max Jammer has stressed, such a view of space was not ‘thought reasonable until the seventeenth century’. No other culture we know of has conceived of its cosmic scheme in