The Law of Contagion is a psionic law and phenomenon that states that a psychic link exists between two objects or persons that have been in physical contact with one another due to the exchange of trace amounts of cuil flux. Flux is innately tied to a person's identity, more unique than a fingerprint- it is the entire manifestation of a person's identity and personality, given color, properties, even taste and smell. Some skilled psions are able to take advantage of the Law of Contagion by using this trace flux on an object to apply an ability on a person regardless of distance, using just the psionic connection between the trace flux and the main person. Trace amounts of flux can remain in extended periods of time in objects because flux decays in a means similar to half-lives, where smaller amounts of flux take longer to decay; not enough to be useful for any abilities on the psion's part, but enough to be detected by a skilled esper.
The Law of Contagion has many uses; psionically tracking someone using a lock of their hair for example, or applying a curse to someone after finding a sample of their blood. Generally, abilities applied using the Law of Contagion are significantly weaker than if they were applied within an ability's typical range.
How long a person's flux remains in trace amounts in an object after exposure depends on several factors: time, flux conductivity, ECF, and amount of flux. The longer a person is exposed to an object, the longer their flux trace will last within it; for example, a piece of jewelry a person is wearing would have a much longer trace than the ground they walk on (possibly more so if the jewelry has a flux conductive material like gold). Flux conductivity also plays an important role; since organic tissue conducts flux well, disembodied parts of a person such as lost limbs or their blood can last much longer (especially since items like these also have very long exposure times to their flux); conversely, flux will decay significantly faster inside a flux insulator like salt. ECF also plays a factor, since flux takes longer to decay the higher the cuils present, and shorter when exposed to negative cuils. Finally, how much flux there is during the exchange matters; a psion in shrouded flow is going to have a very detectable trace as opposed to a normal person, though even non-psionic people can leave a trace detectable by a skilled psion if its strong enough from time exposure or ECF. And of course, psions or other entities with an abnormally large amount of flux will leave abnormally large traces, sometimes even large enough to be detected via cuilsight.
|Faint||Recent footprints, recent briefly touched surfaces, etc|
|Weak||Recent area stood or sat in, recent surface with prolonged contact, place where an ability was used|
|Moderate||Small or external body part (hairs, nail clippings, skin) if the person isn't wearing a flux insulator, recently worn clothes or clothing scraps, a flux-heavy ability (>7%)|
|Strong||Bodily fluids (blood), sentimental items, pieces of flesh (up to 1/4 lb), clumps of hair, any worn frequently worn flux conductors like jewelry (if the person isn't wearing an insulator), flux-intensive abilities (>20%)|
|Special||Body parts, metacreated objects, tulpas, remains, large amounts of blood, larger amounts of flux or psychic constructs|
Naturally, many learned psions are cautious about potentially leaving behind traces that could be used to track them or do harm unto them. Expelling flow reduces the strength of their traces significantly, but it's also possible to cleanse traces of a person's flux, or prevent them from leaving certain traces altogether. This is typically done by exposing the object with the trace to a flux insulator such as salt or the smoke of a smudgestick. Of course, any exposure to negative cuils such as from normantium is going to be highly effective.
There are also ways to prevent one from leaving certain traces; certain abilities that repel flux are able to, as well as certain 'charms' of a flux insulator material worn on the body, such as a hair pin jewlery with salt crystals that prevents hair from becoming traces.
Using the Law of Contagion
The Law of Contagion can be used by certain psionic abilities to apply abilities to people regardless of their distance from the psion, so long as the psion has a flux trace of the person that they can detect and use. There are some caveats, however; for starters, abilities that use the Law of Contagion cannot be awakened with. The Law of Contagion can only be utilized by psions that know about the law, and either create new abilities that use it, or modify existing abilities to use it. In addition, abilities applied using the Law of Contagion are significantly weaker than they would be if applied traditionally.
Detecting and using flux traces is an ESP ability. Espers will be able to detect flux traces at a more sensitive level than anyone else, and detecting weaker or near-expiring traces becomes a more difficult task the further away from ESP your aptitude is. Metacreators and neuroinvaders have the most trouble detecting flux traces, though any psion can do it.
The Trace Detection (ESP) common ability is a prerequisite ability for any ability that utilizes the Law of Contagion. These abilities typically require consent.