What categories of age-handling on return from alternate realities are there?

Question

In traditional Elfland stories, and in C.S.Lewis' Narnia, when a character enters the alternate reality they start with their current age and age normally in that reality, but on return to their origin while they retain their memories, their age is 'corrected' to their origin calendar: some folks crumble into dust, the Lewis characters are no older.

Re-entering Narnia, the children are not 'corrected' to their last time in Narnia, but start at their latest 'real' age again. (I don't know what happens to someone re-entering Elfland.)

In contrast, a harder sci-fi approach would have a character ageing according simply to the number of days experienced, regardless of the time distortion between two realities - a bit like travelling near the speed of light.

1. Are there established terms for these models?
2. Are there other models?

Answer 1

In classical fairy stories, people who entered a hill of the fae for a single night of partying would return and find that many years had passed in the real world, without themselves having grown any older. Usually, their spouses have died and their children have grown up. Ursula Le Guin has a science fiction version of this in her 1964 short story "The Dowry of the Angyar" (aka "Semley's Necklace"), where time dilation makes many years pass at home while Semley is away on a trip to a distant star.

You mention Narnia, where many years pass in the fantasy land while only a day or so pass in the real world, with visitors reverting in age upon exiting. I am not familiar with other stories with this exact model.

There are, however, many stories where time passes far more quickly in the fantasy world than in the real world, as in Narnia, but visitors don't revert in age. For example, in Stephen Donaldson's Thomas Covenant books, roughly a decade passes in the Land for each week between Covenant's visits. Similarly, in A. Merrit's 1924 book The Ship of Ishtar, the protagonist visits a fantasy world several times during a single night, with several weeks passing in the fantasy world between each visit and the last visit lasting many months, still in the course of the one night in our world. That there is no ageing reversal is seen from that fact that wounds that heal in the fantasy world don't reopen when he returns to the real world.

Also common is that there is no time differential at all. This is e.g. the case with Lord Dunsany's The King of Elfland's Daughter (1924) and Susannah Clarke's Jonathan Strange and Mr. Norrell (2004).

I believe I have also read stories where the time differential is chaotic with time sometimes passing faster, sometimes slower, in the fantasy world. I can't however, immediately think of one, other than Roger Zelazny's Amber books, which has many worlds each with their own pace of time, and if you don't know that, you can get pretty surprised about how much or little time has passed elsewhere during a visit.

If there are other models used in fantasy, I am not aware of them.

Answer 2

There are a lot of options, depending on your world

Depending on the rules of your portal world and the specific method in which you enter it, almost all aging scenarios are possible and many have been done before. Rather than list all the examples, I'm going to look at one scenario, and calculate the aging options in it.

We are going to look at the scenario presented by Jumanji: Welcome to the Jungle. In this movie, a group of kids magically transported into a video game, where their bodies are transformed into video game characters.

Here are the questions we can ask in this scenario:

• Does time pass in the real world while they are in the game?
• Do they return to Earth at the same time they left?
• Do their earth bodies age while they are in the game?
• Do their game avatars age?
• Is the rate of time passing the same in game as on Earth?

With these 5 questions, we can have at least 120 different versions of aging between the two worlds. (The last question could be reworded to have more than two states)

So depending on how your worlds work, there could be a lot of options to explore. You could probably also just use the questions from above and answer it about your own scenario as well.

Answer 3

There are three main approaches that I know of.

Fixed Time

There's no difference in time between alternate worlds. Time passes at the same constant rate for both places, so a year in World A is the a year in World B. Useful if you're doing a lot of world jumping between locations, like Planar Travel in a D&D inspired-setting, or something of that nature. Also helps to keep the protagonists with the ability to jump between planes from abusing the time dilation for their own end.

Time Dilation

This is the 'Hour Inside, Year Outside' model, where time is dilated between the two worlds. This is a model usually used for travel to the fae realms, and also a good pick for science fiction due to time dilation because of near lightspeed travel. This can be used alternatively, that is Earth can move at a faster rate or Earth or Earth can move at a slower rate. This also has two subcategories: Fixed vs Variable.

• Fixed: The rate of the time dilation is a constant, that is for every hour on Earth, a year passes in the fae realm or something of that nature. Because this is a constant ratio, this is useful for hard magic systems and also the de facto for science fiction. Be very careful with who you allow access to cross worlds with this one, because computer programmers will happily install server farms to take advantage of this. Among other things.

• Variable: The rate of time dilation is not a constant. When spending time in either realm, either years could pass on the other side or possibly even seconds, seemingly at whim and cannot be controlled, except perhaps by beings of great power on either side of the worlds. This is appropriate for soft magic systems. Also not as dangerous to give access to cross worlds because the whimsical nature of the time dilation will serve as an adequate warning against all but the most desperate of travelers.

• Shifting Variable: (Thanks to SRM for pointing this out) The rate of time dilation isn't constant, but it shifts on a predictable pattern. I've never seen this used, but it is a viable derivative that requires different handling than the previous two, as it doesn't have the benefits of Fixed all the time and doesn't have the problems of Variable.

No Time Passes

This is the last approach, and also a very difficult one to work with. No time passes means that when the main character changes worlds, no time whatsoever has passed. That is, the two world run wholly independent of each other and time only passes when the main character is there. This must be handled very carefully, as the nature of this dilation means that (traditionally) only the protagonist can be given access to this power and a suitable explanation has to be given as to why this actually works. That said, it's an entirely suitable approach for certain types of stories, though also the rarest.