Discworld (world) - Magic

Magic

See also: Unseen University and Witches (Discworld)

Magic is the principal force on the Discworld, and operates in a similar vein to real-world elemental forces such as gravity and electromagnetism. The Disc's "standing magical field" is essentially the local breakdown of reality which allows a flat planet on the back of a turtle to even exist. The force called "magic" is really just a function of the relative absence of reality in the local area, much in the same way that the absence of heat is described as "coldness." Magic warps reality in much the same way as the real universe's gravity warps its space-time. The act of performing magic is, essentially, telling the universe what you want it to be like, in terms it can't ignore. This is very draining to magic-users, due to Discworld science's Law of Conservation of Reality (which states it takes the same effort to do something with magic as it would to do it mundanely). This is why most Discworld wizards store magic in a staff (with a knob on the end) which is a sort of capacitor for magical energy.

On the Discworld, where magic has more in common with particle physics than Houdini, high-level background magic (most likely a reference to real-world background radiation) occurs when a very powerful spell hits, creating a myriad of sub-astral particles that severely distort local reality. Building a house in (or even walking into) a region where this has happened is extremely dangerous as it is mentioned that an individual may not remain the same species, shape or level of sanity, as they were when they entered. Medium levels cause odd effects, such as coins landing on their edges and turning into caterpillars. Areas with larger than normal quantities of background magic tend to display unusual qualities, even for the Disc. Very high quantities of magic can knock a hole in Discworld reality, leading to an invasion by Lovecraftian monstrosities from the Dungeon Dimensions, or, almost as bad, the world of the Elves. In the Discworld universe, magic is broken into elementary particulate fragments in much the same way that energy and other forces are in real-world quantum physics. The basic unit of Discworld magic is the thaum (from the Greek thauma, marvel), equal to the amount of mystical energy required to conjure up one small white pigeon, or three normal-sized billiard balls. Several SI-modifiers have been applied to it (e.g. millithaum, kilothaum) in the books. Magic can be measured with a thaumometer, which is described as a black cube with a dial on one side. A standard thaumometer is good for up to a million thaums, beyond that level, Discworld reality starts to break down. The thaum also appears to be a particle; the Discworld physics equivalent of the atom. "Splitting the thaum" revealed that it was in fact composed of numerous sub-particles, called resons ("thingies") which in turn are created from a combination of up to five "flavours": up, down, sideways, sex appeal, and peppermint (see the real-world quarks).

In the opening books, the number eight is generally significant and has magical properties on the Disc, (e.g. the number of the colour of Magic, octarine) and should never be spoken by wizards especially in certain places. Doing so may allow the ancient dungeon dimension creature "Bel-Shamharoth the sender of eight" to break through (this is taken to a somewhat-extreme end in one book, as even the narrator takes great pains to avoid saying the word). On the other hand, eight turns up in many places one would expect the number seven in the real world (e.g. the Discworld week contains eight days, not seven). After The Colour of Magic, both the colour and the number eight no longer appeared as dangerous.

The Disc's magical field is centred on the Cori Celesti. Everyday natural forces, such as light and magnetism, are muffled by the power of the Disc's magical field, and rather than a magnetised needle, navigators on the Disc use a compass with a needle of the magical metal octiron, which will always point towards Cori Celesti. Light is so oddly affected by magic that, as it passes into the Disc's atmosphere, it actually slows down from millions to hundreds of miles an hour. One odd effect of this is that the Disc has time zones, when, as a flat world, it shouldn't. Another effect is that, as reported in Thud!, the red- and blue-shifting of light becomes noticeable when travelling at speeds of merely a hundred and twenty miles per hour.