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).
 The interdimensional hypothesis (IDH or IH), is an idea advanced by Ufologists such as Jacques Vallée and this idea is outdated.