Well, are otherworlds, other worlds? If it's plausible to speculate on the actual existence of the apparently mythical polytheistic god, by postulating that there were not really supernatural gods but flesh-and-blood 'Â€Â˜gods'Â€Â“ technologically advanced extraterrestrials in other words Â€Â“ then it open up a can of worms. What about the rest of the apparently mythical menagerie like the Fairy-Folk? Okay, let's give them a fair-go too because fairies, like dragons, are nearly universal throughout all cultures from Polynesia to Asia to the American Indians to, and of course, the Northern Europeans. Fairies and elves (Fairy-Folk in general) equal the modern UFO 'Greys', or the modern UFO 'Â€Â˜Greys' equate to the mythological but actual and historical Fairy-Folk, to unite past and present.
A fairly common thread in mythology is someone coming across or visiting or being taken (kidnapped even) to some sort of magical land or place inhabited by exotic, even supernatural, beings, often god-like deities and/or often the Fairy-Folk types. However, upon return to their natural world, there's no apparent similarity between the interval of time that person thought they spent in that enchanted realm and the elapsed time between that person exiting their normal abode for enchantment-land and re-entering their natural world later on down the line. For every day or week or month that person spends in the land of enchantment, perhaps a year or more of their natural world time passes. For example, we have the mythological (or is it?) enchanted land of the Otherworld.
The 'Other World' (Slavic) or 'Otherworld' (Irish, Welsh and Celtic) in mythology tends to be a mysterious, enchanted, fabulously wealthy land, a land of fantastic pleasures, the land of (usually dispossessed*) gods, goddesses, and Fairy-Folk that is literally out of this world. It's sort of like the Promised Land that resides towards the west, located in the oceans or beyond the seas. Note it's the 'Â€Â˜Otherworld', not the 'underworld' two different concepts.
The Otherworlds (in generalÂ€Â“ they're quite a few of them) tend to be places of rebirth where the dead get resurrected back to the land of the living. Call those rising-from-the-dead, sort of like what Jesus Christ (an extraterrestrial 'Â€Â˜god') did, though he's but one of many 'gods' with that talent according to mythology.
While fairies are known throughout the cultures and mythologies of the world, such as with the Maoris of New Zealand, they tend to be most associated with the Irish, Celtics and Welsh. Further, Fairy-Folk tend to be extremely long lived (quasi-immortal, like the mythological gods), maybe even really immortal (or as close to it as makes no odds) in their Otherworld, again depicted as a land of eternal youth.
The Celtic / Irish / Welsh Otherworld is kind of like the ancient Greek Elysium (or Elysian Fields), a land of paradise also situated just somewhere to the West, but without the bit about being dead, although apparently some get to Elysium without dying. Regardless, in Elysium you're granted immortality or become immortal, which is kind of like a rebirth, although death and rebirth were certainly Otherworld themes part of the Otherworld environment.
My general or overall interpretation of the Otherworld(s) is that it's a high-tech, quasi-utopian planet in another (probably not too far away in astronomical interstellar terms) solar system, inhabited by quasi-immortal, shape-shifting beings we tend to call the modern UFO abduction era 'Greys' or the equivalent, the historical Fairy-Folk, perhaps even home to some of the more traditional 'gods' associated with our mythologies.
Relevant to the case history immediately below, it's worth noting that the Fairy-Folk (as well as the gods) have the ability to be seen only by those who they want to be seen by, just like the Norse Valkyries can only be seen by a Viking warrior about to die in battle before being escorted to (a sort of Norse Otherworld called) Valhalla. There the Viking warriors are resurrected and live to fight another day for the Norse gods like Odin in the coming final battle known as Ragnarok. This ability by Fairy-Folk and the gods and associated hangers-on to be visible to only those they wish to be visible to have a parallel in modern UFO abduction lore. Abductions can take place right under the nose of those who aren't participants. They see and hear nothing, though by all rights they should have. The abductees usually are made unaware of the experience some sort of mental block though such deliberate attempts at amnesia haven't been entirely successful, otherwise the UFO abduction phenomena or scenario wouldn't be such a major and ongoing topic.
Case History #1: An unseen woman (obviously a Fairy-Folk or 'Â€Â˜goddess' of some sort) except to an Irishman called Conla, lures him away to the Otherword in a ship of glass, a crystal coracle, never to be seen again. Now a coracle is normally a small round boat composed of wickerwork or interwoven laths covered with skin or canvasÂ€Â“ it's not made of glass or crystal! The 'Â˜boat' used by Conla in his voyage with the invisible woman to the Otherworld sounds a lot more like a shiny metallic round UFO IMHO.
Now people disappear all the time, and I'm sure that applied in our ancient past as well. A few (more probably back then than now) disappeared through some sort of natural mishapÂ€Â“ being in the wrong place at the wrong time. Most people voluntarily disappear themselves be they criminals on the lam, people dropping out of society, children running away from home, parents running away from each other and their kids and family responsibilities, political refugees, etc. That accounts for probably 99.9% of people seemingly vanishing. But there is a residue, perhaps like Conla above, of people who do vanish under rather mysterious circumstances. In the UFO/abduction area, take for example the October 1978 case of Frederick Valentich, a young pilot flying a private plane on a short trip from Melbourne to King Island under ideal flying conditions. He and his plane vanished from sight while he was in radio contact with Melbourne flight controllers, reporting a UFO hovering over his plane. His transmission ceased at that point go figure. But to this day, neither he nor his plane has ever been seen again.
Case History #2: The Scottish Thomas of Erceldoune, otherwise known as Thomas the Rhymer was escorted by the Queen of Elphame to fairyland (Otherworld) for an apparently brief period, but upon leaving found that seven years had passed.
Case History #3: An Irishman named Oisin had a bit of a fling with the fairy princess Niamh in the mythical Irish land of Tir na nOg (Land of Youth), the land of fairies and elves (Fairy-Folk), a land of eternal youth. It was a mystical place, an island (planet?) that lay beyond the edge of any known maps (outer space perhaps?). Oisin lived with Niamh in the Otherworld for three years, but when longing for, and finally returning home to old Mother Ireland, found that he had returned 300 years later all his friends and family were dead, surviving himself long enough to relate his tale to Saint Patrick.
Now in any sort of modern context or interpretation, regarding those latter two case histories, that's nothing more than Einstein's Special Theory of Relativity's time dilation effectÂ€Â“ the Twin Paradox. The closer you travel towards luminal (speed of light) velocities, the slower time (rate of change) ticks over for you relative to those you left behind who are not travelling at close to luminal velocities. Thus, when you return home, you've aged less relative to those who stayed at home.
To continue with modern parallels, I might broad-brush alien races here which may (or may not) be in cahoots or at least in some sort of association or alliance. We have the chosen few' and the 'victims', in modern terms called the Contactees' and the Abductees', and their associated extraterrestrials, which area.
The modern UFO abductees are associated with the UFO 'Â˜Greys' which in turn might be akin to the mythological Fairy-Folk (lumped collectively together), which might have an association with the Incubi/Succubi and related types prevalent in the Middle Ages.
In the TV show "Stargate: SG-1", the 'Greys' were shown to be the Asgard race, well the Norse. But that's okay for the real Norse too had their elves or Fairy-Folk Their Muspelheim was the land of dark elves; Svartalfeim their world of (run-of-the-mill everyday) elves.
UFO abductions (via the 'Â˜Greys') have Fairy-Folk kidnapping parallels. And just as Fairy-Folk have been associated with the abduction of humans (like say to Otherworld), that applies ditto to the gods who could abduct you and take you upstairs' or 'downstairs'. You could also often be abducted for sexual purposes by the gods. Modern abductions (as in UFO abductions) have a common theme of sex. Sex with, unwilling human victims is nothing new, like in the Middle Ages.
In the past, like around the Middle Ages (though the track record goes all the way back to Mesopotamia around 2400 BC), you had similar tales with respect to the Incubi and Succubi - legend claims that demons both male and female sexually prey on human beings, generally during the night when the victim is sleeping. Incubus/human and Succubus/human couplings are sometimes said to be able to conceive children. The half-human offspring of such unions are sometimes referred to as a cambion. There are exact parallel tales of infant hybrids between humans and the 'Â˜Greys' of UFO abduction fame.
The modern (1950's) flying saucer Contactees are associated with the 'Nordics' otherwise call the Space Brothers' which might have an association with Jesus Christ like varieties of angelic-like 'gods'.
The question is, where stand the standard pantheons of the polytheistic gods or extraterrestrial 'gods' in this scenario? IMHO, somewhere in-between the angelic-like 'Nordics' as physically perfect specimens and the 'Greys' in terms of their personalities and actions, which can be rather callous and uncaring.
In conclusion, Otherworlds as other worlds, and out of this world, is a part of mythology that's relevant to all those interested in astrobiology, ancient astronauts and UFOs.
*Presumably by the rise of Christianity and monotheism forcing the polytheistic 'gods' to pack up their bags, exit stage left, and return homeÂ€Â“ to their Otherworlds.
Science librarian; retired.