Probability mirrors were objects created for the purpose of large-scale causal reconciliation by prehistoric Forerunners in their early ages of high technological achivement circa 10,000,000 BCE. They were enormous spheres with perfectly reflective surfaces which reflected light along a short span of time as well as space. This would reconcile space-time in the vicinity of the structure, capturing and adjusting the immediate light of any nearby object and allowing the transit of large amounts of mass without producing major causal damage; a blunt but effective form of reconciliation ideal for use in conjunction with a large number of slipspace portals. The reflections seen by observers aboard a ship near a time-phased mirror were vague and indefinite, often only appearing as small, green glints or outlines of what might have been a distorted version of their own reflection from moments later, or, conversely, another ship reflected eons earlier. They registered on sensors as colder than interstellar space, and echoed back any attempt to analyze their internal composition or structure.
A series of probability mirrors was discovered in Path Kethona by the crew of the Audacity, hidden in a cloaked star system by the ancient Forerunners who had used the mirrors to transport their enormous battle fleet to the satellite galaxy during their campaign to exterminate the Precursors ten million years earlier.
A structure in a Forerunner city within Onyx's Zone 67 possessed a surface reflecting numerous images from different worlds and time periods; however, these may simply have been optical illusions achieved through advanced holography as opposed to proper time-phased mirrors.
List of appearances
- Halo: Silentium (First appearance)
- Halo: Silentium, page 69
- Halo: Silentium, pages 110-112
- Halo: Silentium, pages 119-120
- Halo: Ghosts of Onyx, page 269 ("As they maneuvered closer to one pillar, Kelly banked the ship around its curve and Kurt saw reflected images of a thousand different sunsets—all with varying cloud geometries, some with flocks of migrating birds, or dinosaurs, another had smears of blue spacecraft, and one burned with a supernova that illuminated the twilight... all images captured here. From the past? The future? Both?")