[PTTG]

In Specter worldlines, previously crude and unscientific approaches to communicating with the dead are refined into functional, reliable and widespread methods.

Specter-1 found a way to allow sensitive electromagnetic sensors and powerful computers to pick up ectoplasmic phenomenon in 1988. The Necrotronic revolution had a wide variety of effects. The current year is 2002.

First, a general look at digital necromancy, or as it is also called, "cyber-spectronics." In these worldlines (but not all,) human neural activity leaves a worn image that persists after death. It is a kind of self-perpetuating hologram, and as a result does not have measurable mass, but is capable of interacting with photons and matter in the region where the deceased person spent the most time. The physical death of the person "decouples" the hologram, allowing it to operate independently. This hologram is the functional core of the ghost.

However, these holograms are almost never energized enough to do anything -- even to think. An activated, or "manifested" spirit has several potential energy levels, all the way from the low end wisp (which is invisible, barely conscious, and may produce a faint glow), all the way up to revenants, which are fully physical copies of the spirit's original form projected by the ghost. Notably, it takes a great deal of energy and effort to speak audibly, let alone to manifest coherent images and forces.

"Natural" manifestations were exceedingly brief, and only few humans have been known to produce enduring, long-lasting ghosts; there have been only a few dozen documented cases in recorded history. In nature, most ghosts dissipate over time without interaction.

Perhaps the most complicated consequence of the development was in law enforcement. Laws were not written with Necrotronics in mind, (this being a high-inertia worldline,) so people have had to interpret the laws creatively. For instance, it is illegal to compel someone to provide evidence. Thus, manifesting the spirit of the deceased cannot be reliant on that spirit providing evidence for a crime.

Ghosts are bound to the locations where they lived, but they have no mass. Experiments involving volunteers have set out to bind a ghost to a small workspace that would then be converted into a rocket payload. Ghosts do not age (they are as they perceive themselves,) nor do they need life support. Others are looking for ways to employ ghosts to provide labor, such as performing small tasks in hostile environments, or non-physical work like programming or writing.

Specter-2 saw the revolution emerge with the dawn of Radio.
Specter-3 is several centuries in after discovering ghosts in the Enlightenment (it seems mana-based here).
Specter-4 has yet to uncover the technology, but it has the same phenomenon. 2016.