Temporal shields is a theoretical technology that can protect against weapons of a temporal nature, that is, weapons which used some aspect of time-based technology to its advantage. Temporal shields can also be used as a term to describe a shielding mechanism against changes in the flow of time.
Temporal shielding was originally designed by the crew of the USS Voyager in an alternate timeline. In this timeline, Voyager was under attack while in Krenim space from chroniton torpedoes, a weapon which passed straight through the shields. It was later discovered that as these torpedoes were in a state of temporal flux, the shields in their present state were useless.
Lieutenant Commander Tuvok and Seven of Nine worked on a way to modify the shields, and eventually succeded when they found out the temporal varience of the torpedoes by scanning one lodged in a Jeffries tube, changing the shield frequency to match it, and setting the deflector to the inverse of the pulse.
While the temporal shields worked as planned during a Krenim attack, they had the added effect of protecting the ship against changes made in the timeline, specifically changes made by the Krenim temporal weapon ship. The shielding mechanism caused a level nine disruption in the flow of spacetime, enough to affect Annorax's calculations when he attempted to use his weapon ship to alter time to such a degree, he accidently returned the Krenim Imperium to a pre-warp state. These shields were given to the Nihydron and the Mawasi ships, and Chakotay suggested that research was going on to extend the shields to protect those races' homeworlds, though he was probably bluffing to Annorax. The temporal shields around the fleet were ultimately taken offline so that when the temporal weapon ship erased itself from history, as a result of Voyager's kamikaze run, everything could be restored as intended. (VGR: "Year of Hell, Part I" and "Part II").
- There is no evidence that these exist in the "normal" timeline. However, it would be reasonable to assume that this, or a similar mechanism, must exist on 29th century timeships.