In Philip Pullman's His Dark Materials and The Book of Dust trilogies, Dust or Rusakov particles are particles associated with consciousness that are integral to the plot. Dust features in the multiverse written about in these trilogies and companion books. In these universes, Dust is attracted to consciousness, especially after puberty; the Church within the series associates Dust with original sin and seeks its end. Pullman described Dust in an interview as "an analogy of consciousness, and consciousness is this extraordinary property we have as human beings".
Dust was previously known (in Lyra Belacqua's universe) as "Rusakov particles" named after their discoverer, Boris Mikhailovitch Rusakov. Rusakov discovered a field permeating the universe that enabled consciousness, before the discovery of Dust; its existence was predicted, as:
In an alternate universe, Mary Malone researches dark matter, referring to it as "Shadows". The name "Shadows" was given to the particle by her colleague, Oliver Payne, in references to Plato's Allegory of the Cave,: ch. 4 involving "shadows on the wall". When she communicates with Shadows by interfacing with her detector, it confirms that they are the same as Dust and dark matter.[a] The Mulefa, who are able to see Dust directly, use the word "sraf" accompanied by a leftward flick of the trunk (or arm for humans) to describe it.
Dust came into being when living things became conscious of themselves; but it needed some feedback system to reinforce it and make it safe, as the mulefa had their wheels and the oil from the trees. Without something like that, it would all vanish. Thought, imagination, feeling, would all wither and blow away, leaving nothing but a brutish automatism; and that brief period when life was conscious of itself would flicker out like a candle in every one of the billions of worlds where it had burned brightly.— The Amber Spyglass: ch. 34
Dust is attracted to objects that have been formed by consciousness, and can be viewed by special photographic emulsions. It is particularly attracted to consciousnesses that have matured; in the case of humans in Lyra's world, this happens when their Dæmon is fixed in shape. For the mulefa, this happens when adolescents start using wheels. Dust is also what connects humans to their dæmons. If the bond between a child and their dæmon is severed (as through Intercision), both the child and the dæmon will eventually die. If the separation occurs after Dust has settled on the person (that is, after adolescence), the person becomes a lifeless shell.
In Pullman's trilogy, Angels are formed when Dust condenses. These angels only appear as winged humans because that is what is expected of them; in reality, they have more complex shapes, similar to "architecture".
Dust is able to communicate with humans via several methods shown throughout His Dark Materials and The Book of Dust, including by use of alethiometers. Mary Malone is able to construct a computer program that, when paired with a detector, can communicate with Dust by typed questions. Later, Mary uses I Ching divination, which Lyra confirms to be a method of communicating with Dust.[b]
An alethiometer is a truth telling device which can answer any question. The word is derived from the Greek words aletheia (truth) and meter (measure). In Lyra's world, six alethiometers were constructed. Also known as symbol readers, alethiometers have a ring of 36 standard symbols, but are all different; some, for example have more elaborate decoration. Over the course of the books, several alethiometers are shown being read, including by Lyra Belacqua, Hannah Relf, and Fra Pavel.
Each symbol on the rim of an alethiometer has several levels of meaning; for example, the anchor can mean steadfastness, hope, the sea, or other interpretations. To phrase a question, three adjustable levers are pointed at symbols, and the reader has to hold the level of meaning for each symbol in their head. A fourth lever, made of an alloy sensitive to Dust, swings around, stopping on different symbols to give an answer, with the number of times it stops at a given symbol indicating the level of meaning intended.
In La Belle Sauvage, it is said that no more alethiometers can be built, as their construction depends on a rare metal being subjected to special treatment, knowledge of which has been lost. Oxford has an alethiometer in its library, which is read by Hannah Relf, various other universities have one, and one is missing. After the Magisterium attempts to steal one, a secret society opposed to their actions is able to obtain it, and give it to Relf to use on their behalf. The missing alethiometer is found by Malcolm Polstead in the pack of Gerard Bonneville, and given to the Master of Jordan College, for safekeeping. In Northern Lights, it is this alethiometer which is given by the Master to Lyra, who is able to read it intuitively. At that point in the story, only two other alethiometers are known to survive.
Within the books, Dust came into existence when consciousness did; it was created by consciousness, as well as being conscious. Occasionally, Dust condensed into Angels; the first of these was called The Authority, who told all the angels that subsequently condensed that he was the creator of the multiverse.
About 33,000 years prior to the time of the books, Dust had induced changes in sapient species, including humans and mulefa, to allow them to interact better, conferring more consciousness. For the mulefa, this was the start of their oral history and memory as a species. When asked directly, Dust states that this was done by rebel angels for vengeance over the war in heaven.[c]
300 years before the start of His Dark Materials, scientists in Cittagazze had created the Subtle Knife, which allowed them to travel between worlds. However, explorers were not meticulous about closing the cuts in the fabric between worlds, and Dust was lost into the void between universes through the cracks of these windows. At that time, the mulefa noticed that their trees – which depend on Dust for fertilisation – had started producing fewer seeds.