I'm putting this up as a response/solution to Keith Morrison's answer.
In short: you're kind of done for. Numbering anything, whether it is parallel universes or fruits in grocery stores, is complicated once you have enough of them. What's the difference between one apple and another apple? What makes an apple Apple 1 vs Apple 2? Also, even if there are a finite/countable number of apples, how countable is it?
My solutions are way more complicated and I'd argue way more subjective. To an extent, I don't even recommend it because numbering might be easier to understand and less likely to garble up. I have two ideas:
- Nomenclature based on portal creation route: I don't want to get myself bogged down in your portal creation system to other parallel universes (as you said, we shouldn't base our answers on that). But I'd like to provide an example similar to the one you've given.
- What if you had 2, 4, 10, or even 1000 portals to different universes in your Earth 1? Let's not even step into Earth 2 or anything - how would you number these? My solution to this problem is to name every universe on the basis of its portal creation. So, your Earth 2 would actually be Earth 1-1, as your first portal in your origin universe leads to it. If you want to get properly computer-science-y about it, maybe a better name would be Earth 0-0.
- What about a portal in Earth 2 to Earth 5 (working off of your own example, as Earth 4's portal is in Earth 3)? This universe can be labeled Earth 0-0-0.
- What if you want to label the parallel universe that is accessed by the 2nd portal of your 4th portal of the 3rd portal of your origin universe? This universe is therefore Earth 0-2-3-2.
If you want to fit more numbers per digit of your parallel universe address/naming system, maybe name all of these universes in hexadecimal (base 16 as opposed to base 10 numbers). Basic structure of name is therefore (in terms of bad context-free-grammar):
E->O O->P P-> int|O|P|Null
This also raises questions like whether portals in different parallel universes lead to the same parallel universe, creating a new mess: The Inter/Intra-relations of Parallel Universes. So, could Earth 0-2-4 be the same as Earth 2-1-9? If so, how do we know that? Does this naming convention help at all? Is it even related to what we're discussing? Or does it just serve to confuse? These are questions you'll have to answer if you pick this option.
- Event-based nomenclature: I'd like to point out that I dislike this idea more than the other one. In this case, you're labeling each universe on the basis of important universe-defining events that happened here that differentiate it from others. Earth 1 and 2 might be very similar universes (same laws of nature, positioning of stars, etc.) but maybe computers aren't programmed in binary in that Earth 2 - but in every other sense the computers work the same way (accessing Facebook is the same in both these universes). Or, maybe in Earth 3 the French Revolution didn't succeed, leading to a vastly different political atmosphere in their present day, but computers are still binary. Depending on what differences exist in these universes, you can make a naming convention that suits it. So, if we only take these 2 events as defining factors in a universe, then Earth 1 could be Earth 00, with Earth 2 being Earth 01, and Earth 3 being Earth 10, raising the possibility of an Earth 11 (where the French revolution failed and computers don't use binary). Unlike the previous point, this example is more absolute and less 'relative'.
If the order of portal creation doesn't determine which universe you go to (i.e. you can make >1 portals to the same destination universe from the same origin universe) then this is a great naming convention. Only issue: What are the defining factors of a universe? A countless number of events happen every day on our planet, let alone others, and there could very well be universes where Earth doesn't exist at all. So how do we know that the use of binary and the French Revolution succeeding/failing are important enough to define a universe? Realistically we don't, but you write your own story so you can choose.
I hope my solutions were not too verbose - I'm open to any questions/clarifications. The biggest differences between the 2 solutions I provided is that option 1 is potentially relative with respect to other universes, whereas option 2 is a more absolute definition but how the definition is constructed is incredibly complex. I hope this helps!
