The interdimensional hypothesis (IDH or IH), is an idea advanced by Ufologists such as Jacques Vallée that says unidentified flying objects (UFOs) and related events involve visitations from other “realities” or “dimensions” that coexist separately alongside our own. It is an alternative to the extraterrestrial hypothesis (ETH). IDH also holds that UFOs are a modern manifestation of a phenomenon that has occurred throughout recorded human history, which in prior ages were ascribed to mythological creatures.
Although ETH has remained the predominant explanation for UFOs by UFOlogists, some UFologists have abandoned it in favor of IDH. Paranormal researcher Brad Steiger wrote that “we are dealing with a multidimensional paraphysical phenomenon that is largely indigenous to planet Earth”. Other UFOlogists, such as John Ankerberg and John Weldon, advocate IDH because it fits the explanation of UFOs as a spiritistic phenomenon. Commenting on the disparity between the ETH and the accounts that people have made of UFO encounters, Ankerberg and Weldon wrote “the UFO phenomenon simply does not behave like extraterrestrial visitors.”
Some UFO proponents accepted IDH because the distance between stars makes interstellar travel impractical using conventional means and nobody had demonstrated an antigravity or faster-than-light travel hypothesis that could explain extraterrestrial machines. With IDH, it is unnecessary to explain any propulsion method because the IDH holds that UFOs are not spacecraft, but rather devices that travel between different realities.
One advantage of IDH proffered by Hilary Evans is its ability to explain the apparent ability of UFOs to appear and disappear from sight and radar; this is explained as the UFO entering and leaving our dimension (“materializing” and “dematerializing”). Moreover, Evans argues that if the other dimension is slightly more advanced than ours, or is our own future, this would explain the UFOs’ tendency to represent near future technologies (airships in the 1890s, rockets and supersonic travel in the 1940s).
Jacques Vallée proposes that there is a genuine UFO phenomenon, partly associated with a form of non-human consciousness that manipulates space and time. The phenomenon has been active throughout human history, and seems to masquerade in various forms to different cultures. In his opinion, the intelligence behind the phenomenon attempts social manipulation by using deception on the humans with whom they interact.
Excerpts from Wikipedia entries; Interdimensional Hypothesis and Jacques Vallée.