This premise conjures up images from 1950s B movies, but seems to be quickly climbing the ranks in the paranormal community. Originally postulated as a proposed explanation for the sporadic behavior of UFOs, most notably supported by Jaques Vallee and J. Allen Hynek as an alternative "hypothesis" to the Extraterrestrial Hypothesis. Hypothesis being a loose term and not intended in the scientific definition, being that the inter-dimensional hypothesis is not falsifiable or testable though experiment.
(Note: for more information on the continous misuse of scientific terms by the paranormal field, see Pork Rhine's article)
This concept has been adopted by paranormal investigators, seeking a possible explanation for what they classify as Intelligent Hauntings and more commonly Shadow People. The classification of intelligent haunting refers to an interactive entity, such as a poltergeist or a demonic entity. Unlike the residual haunting, these beings are fully aware and cognizant. Shadow people (shadow men/ shadow beings/ shadow figures) are featureless silhouettes ans are typically considered "evil entities". The vortices. This notion, they feel, is supported by string theory, there-by making the inter- dimensional hypothesis scientific. What they fail to understand is that even if these extra dimensions exist ( there are no experiments capable of confirming these dimensions and are purely hypothetical) they are thought to be extremely small, as in possibly below the scale of quarks and strings.
I believe this misunderstanding lies in the term dimension itself, being confused for a parallel world instead of the measure of spacial extent, because if you consider it in the light of the correct definition, it literally makes no sense.
In conclusion, while it may sound pedantic, learn your terms or you won't be taken seriously.