Exordium is a method of communication, wherein its participants create a "tunnel" or link through spacetime to exchange knowledge across temporal loci. The many-worlds interpretation of quantum mechanics is assumed, and allows participants to form neural links with their past, future, and alternate selves via the instigation of quantum superposition states in their neural implants. Galiana and Skade use this system to obtain and modify inertial suppression technology and take various precautionary actions to eliminate the existential threat of the Inhibitors.
One limitation of the technology appears to be the total informational capacity of the superposition states—each instance of communication makes subsequent attempts more difficult in an effect described similarly to the build-up of static interference. It is unknown whether this limitation holds only for each individual repeat participant (which seems more likely) or for the entire process independent of the participants. Also never explicitly stated is the exact effect of the process' acausal nature, though it is implied that it cannot be used to directly violate causality. Instead, each use of the Exordium creates a new timeline in which the message is received. The original timeline in which the message was sent continues as before.
A similar system to the Exordium is used in Chasm City by the race known as "grubs" to achieve faster-than light communication. It does this by grouping all messages ever sent into a massive far-future archive (known as "Galactic Final Memory") and sending them back to their recipients. It uses the local gravitational background as a key, making it impossible for other recipients to read the messages and gives the device a "range" of a few thousand light years. This also means, however, that the technology cannot be used to send information to other times. It also appears affected by the interference effect which damages the Exordium.