How do I track time (using a special time system) between two realities that are not necessarily parallel but if a person jumps from one to the other what would the time be in comparison to their original reality and vice versa?

P.S this has been bugging me for a while and was going crazy until I found this site.

  • $\begingroup$ There is no one answer to questions like these, because you invent how your time system works. There is no one scientific answer to it. However, if you pick some properties, it becomes possible to develop something like a time system. For example, one property that is popular is to assume that you can't go back to a previous point before the jump. This requirement provides some mathematical guarantees (montonicity) which can be used to shape your system. Some of them can have interesting implications. $\endgroup$
    – Cort Ammon
    Dec 11, 2019 at 6:39
  • $\begingroup$ For example, a time system based on taking turns might develop into the surreal numbers that Conway devised. They have a curious behavior that some numbers are uncomparable -- the numbers aren't equal, but neither is greater or less than the other. I find all sorts of neat side effects can stem from such toys--- I mean tools. Yes, definitely tools, and not toys. $\endgroup$
    – Cort Ammon
    Dec 11, 2019 at 6:42
  • $\begingroup$ thank you this helped $\endgroup$
    – chewey1239
    Dec 11, 2019 at 6:53
  • $\begingroup$ For example, in "The Lion, The Witch, and the Wardrobe", time in Narnia was very different from time on Earth. It was clearly driven by dramatons, the quantum unit of drama. $\endgroup$
    – puppetsock
    Dec 11, 2019 at 15:02

2 Answers 2


Our literature is full of stories where the impossibility to tell the time between two realities leads to grime results for the main character, who usually travel from here to there and back, just to find that what were for them only few days spent there have resulted on a few hundreds years elapsing here.

From a relativistic point of view if the two realities do not belong to the same space-time frame I think you cannot define time between them. It's like adding up apples and eggs.

  • $\begingroup$ thank you this helped $\endgroup$
    – chewey1239
    Dec 11, 2019 at 6:55
  • 1
    $\begingroup$ Just to add, we also have stories where people go to a different world, spend their life there, and return old and decrepit, yet maybe only a day passed where they are originally from. In general for either of these kinds of stories, it's usually assumed that time in one reality flows "faster" than the other and there is a constant ratio. E.g. 1 day = 1 year. Some stories have a variable time difference which may mean that 1 day = 1 to 7days or even 1day = 1 second to 1 year. In those cases...it's not usually specified how this works, so it often serves as a plot vehicle. $\endgroup$
    – VLAZ
    Dec 11, 2019 at 7:05
  • $\begingroup$ Couldn't the main character just take a shower? Or if pressed for time, wet wipes? $\endgroup$
    – Willk
    Dec 11, 2019 at 13:43

welcome to Worldbuilding!

OK, I'm going to assume tech level of ours or higher, and that you have access to whatever you want (hey - you can go to different worlds, mere baubles are easy!)

So, we're going to need at least 3 atomic clocks (slight problem, they aren't exactly pocket watch size, but let's hand wave that minor issue!). We probably don't really need the level of accuracy here, but let's go for the platinum solution.

The 1st clock we leave in reality 1. It's our "base time" if you will.

Clock 2 goes to reality 2, along with clock 3 which is the one we lug around with us wherever we go.

So, we have an an accurate time piece in both realities, and a clock we're lugging around too.

We now need to start going back and forth between the 2 realities. Obviously, we need to go between our 2 fixed clocks. I'm not sure how many travels we'd need - I vaguely remember 5 data points for a line graph, but more would be better (depending on the time differential, this may be a multi-generational project!). We then try and correlate the differences, possibly seeing if there's a travel time going between the realities with clock 3.

Simple really... :P


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