Time Slips and Parallel Dimensions
Unlike residual hauntings, certain ghosts appear to offer us a glimpse into another time or universe, while also acting with apparent intelligence. One theory to explain this phenomenon is that the witness is, by some unknown mechanism, peering either through time or into a parallel universe; although the ideas aren't mutually exclusive. Many interesting reports have come out of unsuspecting citizens who suddenly find themselves encountering another reality. Oftentimes the event is said to begin with an eerie fog or strange lights, but not always. What is consistent is that there are witnesses who claim to have been surprised to see anachronistic vehicles and devices where they do not belong, and people that appear inexplicably out of place--people who almost always react to the witnesses with the same shock that they feel.
Mainstream scientists have long postulated that time travel could be possible, and the idea of a multiverse full of similar Earths has gained popularity of late; but what scientists lack so far is a way to test these theories. Perhaps they need look no further than people who claim to have experienced the paranormal.