The Science of Discworld IV

flat top of a semi-infinite cylinder, extending downwards for ever (shades of ‘turtles all the way down’). Anaxagoras accepted that the Earth was flat, but Archelaus insisted it was saucer-shaped, which is why we don’t all see the Sun rising and setting at the same time.
    Most ancient natural philosophers preferred the theories of Aristotle and Ptolemy, who placed the Earth where any sensible person naturally would: at the centre of things. Plutarch, in a work about the Man in the Moon – the apparent face formed by the darker regions – wrote that the head of the Stoics, Cleanthes, urged that Aristarchus should be called to account for lack of piety towards the gods. Why? Because he had dared to set ‘the hearth of the universe’ (Earth) in motion, and suggested that the heavens are static whereas the Earth rotates in ‘an oblique circle’ and – even worse – spins on its axis.
    The heliocentric theory found favour with just one of Aristarchus’s successors, Seleucus of Seleucia, a hundred years later. By then, the Greeks were aware that the Earth is round, and Eratosthenes obtained a fairly accurate estimate of its size by observing the altitude of the midday Sun at Alexandria and Syene, present-day Aswan.
    One variant Egyptian creation myth, the Ogdoad, replaces the primal mound by a cosmic egg. The Milky Way emerged from the ocean of chaos as a mound, associated with the goddess Hathor. A heavenly goose laid an egg on the mound, and inside it was Ra. Later, when the cult of the god Thoth rose to prominence, the goose mutated into an Ibis, an aspect of Thoth.
    The image of the cosmos as an egg is common to many cultures. Typically either the universe or important deities come into existence when the egg hatches. The egg may be all that initially exists, or it may rest on a primal ocean. In Hindu mythology the
Brahmanda Purana
, a Sanskrit religious text, describes the cosmic egg at length. Here
brahm
means either ‘cosmos’ or ‘expanding’ and
anda
means ‘egg’. The
Rig Veda
refers to
hiranyagarbha
, ‘golden womb’. This floated in nothing until it fragmented into two parts, heaven and Earth. In Chinese Buddhism, Taoist monks told of a god called Pangu, born inside the cosmic egg, who broke it into heaven and Earth when he emerged. In Japanese mythology, a cosmic egg floats in a vast sea.
    The Finnish epic
Kalevala
has a novel slant on creation, which it attributes to a duck that laid fragments of an egg on the knee of the air goddess Ilmatar:
    One egg’s lower half transformed
And became the Earth below,
And its upper half transmuted
And became the sky above.
From the yolk the Sun was made,
Light of day to shine upon us;
From the white the Moon was made,
Light of night to gleam above us.
    This extract exemplifies a common feature of many myths: they are human-centred. They explain the vast, enigmatic cosmos in terms of a familiar everyday object. An egg is round, like the Sun and the Moon. A living creature emerges from it, so the egg functions as a symbol for the source of all life. Crack one open, and you see two main colours: yellow yolk, and white. These just happen to be the colours of the Sun and the Moon. It is no wonder that images of this kind became so widespread. It just takes a certain combination of logic and mysticism, akin to the Egyptian association between the Sun god and a dung-beetle because both pushed a ball around.
    The same combination is characteristic of Discworld narrativium; it is why so much on Discworld ‘makes sense’ even though it is about wizards, witches, trolls, vampires, elves and magic. All you need is a small amount of ‘suspension of disbelief’, as they say in science fiction circles. After that, everything is perfectly sensible. The main difference in ancient times was that there was very little disbelief to suspend. The universe-centred way of thinking was confined to a few deep thinkers in a few cultures.
    As Greek civilisation became subsumed under the Romans, the main centres for the study of the natural world moved to Arabia, India, and China. Europe entered a lengthy period often referred to as the Dark Ages, a name that suggests (correctly) that we know very little about them, and also (incorrectly) that this is because nothing much happened on an intellectual level. There was a lot of scholarly effort, but most of it went into theology and rhetoric. What we now consider to be fledgling science struggled.
    It is often claimed that in