In a parallel universe system (previously discussed here and here), portals are mechanical door frames that, when activated, cause a copy of your universe to appear on the other side. You and your parallel-universe doppelganger initially mirror each other's actions, but after some small amount of time, due to quantum fluctuations (don't worry about it), the two universes de-sync. After that point, there's just two of every object, but the two universes can evolve in different trajectories.

The question is: what's the best-possible naming scheme for these parallel universes? Traditionally in stories with multiple universes, this is not explained ("I'm from Earth 187"). However, simply calling the Nth universe we come across "Earth N" isn't going to work in this case. Here's why.

Every time you make a portal, you not only duplicate the current universe, but all other existing universes. After all, if you have a portal you set up last week in your basement (let's say, to an "Earth 2"), and you open a new portal in your attic to an Earth 3, then of course your house in Earth 3 has a basement with a portal in there that leads to an Earth 4. Note that this 4th universe doesn't have a portal in their attic, because you set the attic portal up after the basement portal de-synced.

(Please, please don't argue in your answer that the portals don't actually work this way. This is easy to misunderstand, so if you think every portal needs to connect to the same universe, or it goes on infinitely, or some other reason why the whole premise is flawed, just don't write an answer. It's not helpful.)

In summary, every time any portal turns on, the number of universes doubles. I considered giving every universe an ID, and then when a new portal opens, adding a 0 to the end of every ID on one side of the portal and a 1 to the end of every ID on the other side. However, an ID with a number of digits equal to the number of portals is way too long and cumbersome to use in day-to-day life. And if you shorten it by converting from binary to decimal, then every time someone opens a portal, everyone in every universe has to memorize a completely new set of digits.

Note that the arrangement of portals isn't always a straight line, either, so numbering them from 1 to 2^N is out. For instance, you could open a third portal in your living room to Earths 5 through 8. Now Earth 1 connects directly to Earth 2, Earth 3, and Earth 5, while all other universes are more than one portal away from Earth 1. An ideal naming system would give connected worlds similar names.

To summarize, a perfect naming system would be

  • Robust (every universe's name should not change drastically when a new portal opens)
  • Concise (I won't give a character limit, since maybe keywords work better or something, but it needs to be memorizable when there are, say, 20 open portals, or roughly a million total worlds)
  • Local (every universe's name should be similar to the names of the other universes that it's connected to).

A fully-perfect solution probably doesn't exist, and it's easy to come up with solutions that do extremely well on 1 out of the above 3 criteria. What I really want is a naming convention that does pretty well on all 3 counts.

  • $\begingroup$ Comments are not for extended discussion; this conversation has been moved to chat. $\endgroup$
    – Monty Wild
    Commented Feb 25, 2020 at 20:27
  • $\begingroup$ Can a new portal connect to an existing world, If I am in earth 1 and earth 2 already exists can I build another portal connecting 1 and 2? $\endgroup$
    – John
    Commented Feb 25, 2020 at 20:30
  • $\begingroup$ So we're just supposed to ignore the fact that it would probably take millions of years for quantum effects to become macroscopically significant (if they ever do)? $\endgroup$
    – Muuski
    Commented Feb 25, 2020 at 22:21
  • $\begingroup$ @John No. @ Muuski Not true. Non-isolated quantum systems are generally chaotic - slight perturbations propagate exponentially up to, and past, human length scales. Within days or weeks (this is a complete guess), the weather will be different on either side of the portal. And if we assume that the most significant source of differences between the worlds is human decision-making, then we only need to consider how long it would take for this expanding difference to reach the scale of neurons. I'd guess it would take only minutes or hours. $\endgroup$ Commented Feb 26, 2020 at 13:55
  • $\begingroup$ so if you have a door connecting 1 and 2 and someone ones a new portal between 2/2 does the portal in one of the paired "2"s disappear? $\endgroup$
    – John
    Commented Feb 26, 2020 at 20:27

17 Answers 17



Refers to the world you get when you start from your current world via gate 23, leave there via gate 12 and so on. Numbers are simply world unique gate identifiers. It does not really matter what they are based on as long as the identifier clearly refers to a specific gate within the world it is used in. The example would probably be based on order of creation but identifiers based on location, time of creation, or anything work just as well.

But they must be permanent. You assign the identifier before you open the gate and never change it. This way all gates have the same identifier regardless of direction. So if you have travelled to 23:12:24:78:123, your original world will be uniquely identified and reached by path 123:78:24:12:23.

And if inhabitants of 23:12:24:78:123 tell you about the wonders of world alpha:calcutta:7, you can after returning home identify just append the path to 23:12:24:78:123:alpha:calcutta:7. Which is convenient.

You can also do other operations with names. The name of world 23:12 in world 23:12:4:8 would be 8:4. World 23:12:8 would be 8:4:8.

This naming is robust. Opening new portals has no effect of previous paths. Opening portal 24 just means that you can now go to world 24:23:12:24:78:123 that starts very similar to 23:12:24:78:123.

System is concise. Since the path is minimal information needed and each gate needs to be uniquely identified, this is the most concise possible system.

System is as local as possible. Worlds directly connected vary by single identifier. Worlds connected to current one have single identifier. Worlds connected to world 23:12 are 23 and 23:12:*.


The system can be adjusted for moving gates thru other gates. While you cannot ever change names without breaking the system, you can extend them. The extension needed is simply the path the gate travelled. Since such paths are unique under this system, the only problem is detecting stale paths using the old name which must be updated with the new name.

Upstream stale paths can be recognized because they leave the origin system thru a gate that is no longer there. People in the origin system simply must record the the old and new name and tell travelers to update their path correctly.

Downstream stale paths can be recognized because they arrive from the new gate using the stale name. So they can also be easily updated.

This can be automated and be done by computers integrated into the gates communicating with equipment all travellers are required to carry using standardized protocols set before the first gate was opened.


A comment by Justin Thyme the Second made clear that such automated information system is necessary even if gates cannot be moved thru other gates. Since all the names are only locally valid they must be updated to reflect the path they travel to remain valid. While this is trivially simple to do, you do not want to rely on people remembering to do it.

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    $\begingroup$ Credit where credit's due, I think Stig Hemmer and Separatrix both had very similar ideas to this, but this was the most concrete for me. My current solution is a combination of two solutions: this one, plus a non-relative numbering scheme. This scheme is maximally robust (it never changes), as well as clear and local, but a relative naming system is convoluted when you want to give each person and universe an identity. For that, and for formal data reasons, there should also be a binary/hex number system that adds digits with every new portal. $\endgroup$ Commented Feb 25, 2020 at 17:23
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    $\begingroup$ But that problem does not seem to come up if you just name all the gates in some order in each universe. If it is order of creation then gates 1,2,3 in universe A are the same as 1,2,3 in universe B. Of course universe B now has portal 4 leading to universe C but that doesn't cause a problem. $\endgroup$
    – Daron
    Commented Feb 25, 2020 at 17:42
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    $\begingroup$ Something that complicates this system a bit was mentioned by OP in a comment on the question: Apparently portals can be carried through other portals. That wouldn't necessarily change the names of worlds relative to each other, but it would still make it extremely hard for any character to actually find the correct portal to go through. Even if you wrote numbers onto the portals directly, you could still carry a portal through another portal, place it next to the identically named portal in that world, play a shell game with the portals and it becomes impossible to find the right world. $\endgroup$ Commented Feb 25, 2020 at 17:50
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    $\begingroup$ Much better. The only problem would be if a portal can connect to already existing universe, which has been suggested in some of the answers, because once that happens, the scheme goes down the toilet. If portal 24 on your world opens to an existing universe that already has 24 portals, then the path numbering isn't symmetrical. You might go out 23:12:24:78:123, but you'd have to come back 123:78:25:12:23. If closed loops are impossible, there's no issue. $\endgroup$ Commented Feb 25, 2020 at 17:54
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    $\begingroup$ @AlexG Sadly that makes no sense in addressing systems like this but the people would still totally be making that joke. Pretty good. $\endgroup$ Commented Feb 26, 2020 at 23:59

You do realize your mathematical problem here, yes?

Start with one universe and 1 portal. It gets turned on, two universes, both with portals.

You turn on your portal again. Four universes, all with portals. One of them activates. Eight universes. Two of them are turned on one right after the other. Thirty-two universes. Three of them turn on portals. Now 256 universes, all with portals. Ten portals get turned on the next day: 662,144 universes. The next day is a quiet one; only 50 of those universes turn on their portals.

You're now at 2.9514 x 1020 universes. How many of them decide to turn on their portals?

It doesn't matter what kind of numbering or naming system you chose; you'll very quickly realize you've run out of any kind of practical method.


Additional problem: how can you know what name your universe is? If opening a portal causes all the universes as they currently exist to duplicate exactly, then how do the "new" universes know they're new, especially if they're created as a result of someone else triggering a portal in a universe no longer connected to yours?


In response to the suggestions about naming schemes:

Just for giggles, let's suppose of those 2.9514e20 universes I mentioned previously, 100 activate portals. Now we're at 3.74e50 universes. Another 100 activate: 4.74e80 universes that require unique names. Now, bit of a problem: there's only an estimated 1080 atoms in the universe. Now keep going on this process. There will come a point where the information required to store the universe's name will exceed the information available in the universe. Probably a lot sooner than you think.

How much of your universe are you dedicating to just keeping the name written down somewhere?

Let's suppose it takes a nanosecond to update record name in a universe and transmit that information on to the connected universe(s) so it knows to update its name as well and pass it on. And, to play fair, we'll only consider the 2.9514e20 universes, so all of them have free atoms to actually build a computer and have memory and such. It will take about 9,359 years for information to propagate through the existing network. Which, of course, will soon reach the heat death of the universe to let everyone one that another portal opened somewhere and the name changed. Again. And doesn't take into account any time needed for coin flips.

And that's passing information from one universe to another in a nanosecond. A time span in which light will move in a vacuum about 30 centimeters.


The name change thing is going to create a problem on its own. Once any universe opens a portal, information has to be sent to other universes to update designations. Now imagine a situation where in any given second, there's a 1 in a trillion chance any given universe will open a portal. Which is, obviously, a very small chance.

With 3e20 universes, that means that in any given second there will be on average 300 million portals opened. And you're going to get the announcement your name has changed. Three hundred million times. Per second. Now imagine what's happening the next second.

  • $\begingroup$ True, it'll rapidly blow up to infinity, but I'm hoping that there's some naming scheme out there which will at least make for easy differentiation between worlds that are within a few portals of each other. Like, sure, there are 2^800 worlds or whatever, but your world is only connected to 3 of them, and each of those 3 worlds only has 2-5 portals in it, or whatever. So the point is, realistically, while your world might have a full, 800 character ID that they put on tax forms and stuff, people will only need a name long enough to tell Joe apart from Joe-from-the-other-side-of-that-portal. $\endgroup$ Commented Feb 24, 2020 at 18:27
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    $\begingroup$ No, there isn't, because how do you know what universe you're in to begin with? $\endgroup$ Commented Feb 24, 2020 at 18:33
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    $\begingroup$ @GiladM, but how does that information propagate? Right now, there is Universe A, with a portal to B, which has portals to C₁ and C₂. I open a portal in A. There are now A₁, A₂, B(A₁), B(A₂), C₁(A₁), C₂(A₁) C₁(A₂), and C₂(A₂) How do the new instances of C learn which they are? $\endgroup$
    – Matthew
    Commented Feb 24, 2020 at 18:52
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    $\begingroup$ @Matthew Whenever you open a portal, exactly half of all worlds will be on your side, and half will be on the other side. You go to every portal in your world (or the International Registry of Portals or whatever) and tell them that you flipped tails. They tell whoever's on the other side of each of your world's portals. Now repeat. The person they just told goes to their portal registry, and so on. $\endgroup$ Commented Feb 24, 2020 at 18:58
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    $\begingroup$ And then, of course, along comes the politicians, activists, and protesters who all hire lawyers and sue the person who opened up the new portal, causing them to have to change all of their stationary. $\endgroup$ Commented Feb 24, 2020 at 21:52

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:

  1. 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.

EDIT1 Coinflip debacle: OP pointed out the coin-flip nature of naming these universes. The only way you can guarantee that this method works is by hoping you win every coin flip, which is what every version of you will attempt to do. So, we have complicated solutions to this as well:

Dictionaries: Who cares about coin flips? Every 'you' will think they're from the root universe. Being the headstrong guy you are a coin-flip doesn't define you. So, you and your duplicate can formalize a dictionary for what you consider to be your universe and root universes below it, creating a more complex hierarchy of universes that will lead to a self-propagating accumulation of ego. This will only make itself more complicated for more and more universes created. The dictionary part of this comes into play because your Earth 0-0 is someone else's Earth 0-2-5, so you'll need to make a pretty comprehensive Excel spreadsheet to document every universe.

Finite coin flips: You and all your duplicates stop making portals after some number of iterations. Do your coin-flip war, make a single static definition that everyone will have to deal with. If you were 0-2, now you are 0-2-0-0, and you'll have to deal with it until the next update comes out and all the yous can go on a portal spree again, and flip your coins again.

That's all I've got so far - will add more ideas if I come up with any.

  1. 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!

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    $\begingroup$ Good idea! Happily, my intention was that no two portals can ever lead to the same universe. Each time a portal is activated, you just duplicate every universe. You never somehow get back to a universe you already had. I need to think about your path-name concept a bit more, but it seems super promising. $\endgroup$ Commented Feb 24, 2020 at 19:08
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    $\begingroup$ The major shortfall seems to be that if your name changes when a portal opens, it changes disastrously. Say you're in Earth 1-2 (as in, from Earth Null, you go through the first portal, then take the second portal of that world), which has one portal (the one leading back to Earth 1). But now someone opened the second portal in 1-2, and your coin came up tails, which means you're not the original (which gets to stay 1-2), you're the copy. Your new designation is 1-2-2, and poor Earth Null on your side of the portal is now 1-2-2-1-1. $\endgroup$ Commented Feb 24, 2020 at 19:13
  • $\begingroup$ So if I'm understanding this correctly, you're saying that you start in Earth 1 (not in Earth 0 aka Earth Prime). This means that with respect to the root, you're in Earth 0-0 because we're counting from 0 onwards. Then you step through the second portal in Earth 1 to enter Earth 0-0-1. This means that in all the universes that exist so far there are 2 portals. The question this raises to me is that if Earth 0 also has 2 portals, does Earth 0-1 lead to Earth 0-0-1? This was the mess I already described in my answer. Can you please explain what you mean by a coin-flip? I don't understand it. $\endgroup$
    – arpanet101
    Commented Feb 24, 2020 at 19:23
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    $\begingroup$ ... who believes they're looking through a portal that they made.. flip a coin... OH OK that's pretty funny lol. Imagine having the fate of your universe being determined by a coin flip. I'm going to edit my answer - lmk what you think. $\endgroup$
    – arpanet101
    Commented Feb 24, 2020 at 19:44
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    $\begingroup$ Your fix seems fairly realistic, which is to say, confusing for everyone involved :P $\endgroup$ Commented Feb 24, 2020 at 20:52

If these universes exist in an n-dimensional space such that some parallel universes are "closer" than others (either requiring extra power to the portals to go to more distant ones or to traverse intermediate universes first)...

Then the best namespace design is a coordinate system. This will work up to the double digits for the number of dimensions (note that I don't mean "dimensions" as in xyz+space here, just the number of different factors that describe one universe's adjancency to another). You won't be able to hash these universes coordinates to come up with a more human-readable name either (since hashes can't be reversed to the original coordinaes). If the extent of any single dimension is low, then something like a "guid" might be possible to make it smaller, either using hex or some other number base. So it's possible a name will consist of a long paragraph of comma-separated numbers.

If there is no dimensionality (all universes are directly reachable from all other universes), then there is no reasonable namespace convention possible.

If on the other hand, each portal retains it's connection, then you don't need a namespace, you need a map. And it's unclear that it would have to become complicated... human-meaningful names would be chosen for each portal by consensus among the two universes relevant to that portal. And governments would likely crack down on the creation of new portals, it would become strictly regulated. Idiots would be opening new portals to try to get back together with a girlfriend whose original had already broken up with them (even though the doppelganger would be exactly the same for our purposes). People would be trying to get away with murder (and abducting doppelgangers to prove they were still alive). Etc.

So I expect the map would remain rather small, with portals numbering in the thousands or tens of thousands at most.

  • $\begingroup$ Good point, I think you're right. It'll end up as a map, and people will have to look at subway-map-like graphs to figure out how to get from one place to another. What I want to know is, how do you answer the question, "which world are you from?" It's a bit analogous to "where do you live?" You could give them directions to your house, but it's more convenient in a lot of cases to have an address. So I think your map idea needs to go hand-in-hand with a naming system for the worlds, not just the portals. $\endgroup$ Commented Feb 24, 2020 at 19:17
  • $\begingroup$ @GiladM I live on left-stream of the Goathead portal. Or "15 portals away" if you just want to give the distance. It'd become unmanageable if too many are created but I honestly think there are limiting factors there. $\endgroup$
    – John O
    Commented Feb 24, 2020 at 21:53
  • $\begingroup$ The other issue is that when a new portal opens, you need new names for the portals (i.e. now that there are 2 Goathead portals, how would you distinguish them? The portal that one is to the left of and the other is to the right of might be several portals away, so figuring out which you're talking about from context would be a nightmare.) They'd have to keep renaming them, wouldn't they? That's the difficult part. Otherwise it's like towns: nobody memorizes all of them, they look at a map instead. But towns don't need to constantly change their names. $\endgroup$ Commented Feb 24, 2020 at 22:12
  • $\begingroup$ @GiladM The first portal opens. People are just from the left/right universe. Then a second portal opens... the first portal is named Carsplat. Everyone is left/right of that. The other two portals can also be named (though they are duplicates of each other). Probably some really boring 3 year long committee process. People are left/right of those. And so on. If you want to watch a show with this, it was called Counterpart (single portal). It was watchable. $\endgroup$
    – John O
    Commented Feb 24, 2020 at 22:44
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    $\begingroup$ Hang on, that profile icon looks suspiciously familiar... $\endgroup$
    – CJ Dennis
    Commented Feb 25, 2020 at 4:53

The growth is exponential, so any naming convention would need to match that exponential growth. Therefore, I propose the following binary structure for names:

  • The initial Earth is Earth Prime.
  • The first duplicate is Earth Null.
  • The second duplication will be counted in Binary - Earth 0 and Earth 1.
  • Every subsequent duplication is then given an additional value slot. For instance, the third duplication of the Earths will be given a two-digit moniker - Earth 00, Earth 01, Earth 10, and Earth 11 respectively. The fourth duplication will have eight designations - 000, 001, 010, 011, 100, 101, 110, and 111.
  • When world are duplicated, the new world arranged numerically, earlier duplicate sets first. In other words, in a fourth duplication, the 000 position is occupied by the replicated Earth Prime, 001 by Earth Null, 010 by 0, 011 by 1, 100 by 00, 101 by 01, 110 by 10, and 111 by 11.

Thus, in order to figure out what duplication set you are in, you check the number of digits and add one. An Earth with a 40-digit binary code, for instance, will be part of the 41st duplication. Then, you use the binary code itself to figure out what world number you are along that line. Simple, concise, and information dense. (Save for the first two Earth, which must be given special conditions as they don't fit the pattern.)

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    $\begingroup$ How do you know what Earth you are? If everything is exactly duplicated, why do you assume you're Earth Null rather than Earth Prime? $\endgroup$ Commented Feb 24, 2020 at 18:34
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    $\begingroup$ @KeithMorrison Flip a coin. No, honestly, flip a coin. If you can't tell any other way, than it doesn't matter which is which, and you just need to decide one for the naming scheme to work. So flip a coin. $\endgroup$
    – Halfthawed
    Commented Feb 24, 2020 at 18:36
  • $\begingroup$ And who flips the coin? $\endgroup$ Commented Feb 24, 2020 at 18:39
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    $\begingroup$ Flipping a coin works to tell the difference, but it doesn't solve the problem of sudden, drastic name changes. You used to live in Earth 101. Now the 8th portal opened and you flipped tails, so now the one on the other side of the portal gets to stay Earth 101 and you're now Earth 00000101. Admittedly, though, just adding zeroes to the start is pretty tame as far as name changes go. Maybe a shorthand like 8-101 for "the 8-digit number with leading zeroes, then 101"? $\endgroup$ Commented Feb 24, 2020 at 18:41
  • $\begingroup$ @GiladM Well, it's only a problem if you're the duplicate, so I guess the trick is to just not be the duplicate. On a serious note, there is no naming convention that will get around the fact that, yes, you'll be changing names very, very frequently. $\endgroup$
    – Halfthawed
    Commented Feb 24, 2020 at 18:47

Strictly local names.

As pointed out in Keith Morrison's answer, trying to give everybody globally unique names is not going to work. At all.

Justin Thyme the Second's answer points out that most people will consider themselves to be from Earth. The original.

Taken together I think that every Earth will name itself "here". So you are "Gilal M from here". Most people will stay at home.

After traveling through a portal you will gain a modifier to your name like "Gilal M from beyond the Google Portal." Traveling further you become "Gilal M from beyond the MSN then Google Portals." Some sort of abbreviation will be needed for far away travelers.

If you go back through the same portals you will lose modifiers until you reach your home again.

Portal names will only need to be unique for one given Earth.

I would like to expand on Keith Morrison's example to show how hopeless the situation really is. In my example there is only two portals, or so it seems.

Google and MSN are competing to build the first portal. Google wins, but MSN is only a day behind.

On Monday the world splits into Earth-1 and Earth-2. So far, so good.

On both of these worlds, MSN is going to open another portal. Two worlds with pending portals.

Due to random events, MSN on Earth-1 arrives first, but Earth-2 is only an hour or so behind.

On Tuesday, at 9:00am, Earth-1 splits into Earth-1A and Earth-1B. Earth-2 splits into Earth-2A and Earth-2B. On both of these worlds, MSN is going to open another portal. Two worlds with pending portals.

Due to random events, MSN on Earth-2A arrives first, but Earth-2B is only a few minutes behind.

On Tuesday, at 10:00am, Earth-2A splits into Earth-2A1 and Earth-2A2. Everybody else splits too. On both of Earth-2B1 and Earth-2B2, MSN is going to open another portal. Two worlds with pending portals.

Due to random events, MSN on Earth-2B1 arrives first, but Earth-2B2 is only a few seconds behind.

On Tuesday, at 10:10:00am, everybody splits again.

On Tuesday, at 10:10:10am, everybody splits again.

On Tuesday, at 10:10:10.1am, everybody splits again.

After this trilling game of Zeno's World Splitting, there is an infinite number of worlds. And the week has just started.

If this is hard to accept, consider the following scenario. As above, Google and MSN has built portals on every world.

What happens if you first go through the Google portal, then the MSN portal, then the Google portal of that world, then MSN, etc

Will you ever get home? The answer must clearly be no. You cannot get home without retracing your steps, and you never do.

So, you have an infinite number of worlds to visit. Have fun naming them.

  • $\begingroup$ It won't be an infinite number of worlds - there is some non-zero probability that the second ("MSN") portal doesn't open at all, so on at least some subset of the infinitely many potential worlds it will almost surely happen, leaving finitely many worlds. A traveller could alternate between google and MSN portals until they reach one where something prevented MSN from opening a portal at all... and could then retrace their steps and keep alternating until they reach the other universe where the second portal was never opened. That traveller would have enumerated all universes in existence. $\endgroup$
    – Steve
    Commented Feb 25, 2020 at 9:48
  • $\begingroup$ I already considered the subject of infinite worlds in a "hall of mirrors"-type event here. You're correct that it's infinite. There needs to be some oversight over who can set up a portal and when. In your scenario, the infinite chain of universes will arise harmlessly, and then the overseeing body will force the MSN's on Earths 1 and 2 to close their portals, then open them again, one much later than the other, to allow for proper de-sync. $\endgroup$ Commented Feb 25, 2020 at 10:10
  • $\begingroup$ @GiladM, so what stops a universe that doesn't want to follow the rules from simply shutting off the portal to the universe(s) full of the stick-in-the-muds who want a limit on how many times a portal is opened? Once you get a large number of universes, it only has to happen once, and then you're back to infinite numbers. $\endgroup$ Commented Feb 25, 2020 at 17:47
  • $\begingroup$ @KeithMorrison They totally can. I'm not saying it's impossible to have a rapidly-expanding multiverse, I'm just saying it's a mess, and that names aren't super relevant at that point. It would be like the Earth was infinite in size, like there were new countries we were constantly discovering, some of which had diverged from us and now had very different cultures and/or levels of power. It's an interesting premise, just not the one I was considering in this question $\endgroup$ Commented Feb 25, 2020 at 17:59
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    $\begingroup$ The naming convention would indeed be just local. $\endgroup$ Commented Feb 25, 2020 at 18:42

Is there a direct need for a naming convention? It only really makes sense for an outsider, someone who isnt even connected to any of these universes.

When you create the first portal and new universe it is perfectly identical, and from inside the universe there is no way of telling which one is the "prime" universe. Then if you create a new portal you encounter this problem again. Even if you create infinite new universes this way each universe can trace a history back to it creating the first portal, and can therefore assume it is the prime universe.

So instead of trying to name each universe they just communicate with each other. For example they say "I'm connected to 10 universes, and you are connected to 5 universes. We buy some D&D dice, throw them until a number comes up that isnt present in any of our cumulative 15 connected universes and accept that for our universe name". The number of dice coukd rely on the number of cumulative connected universes.

Yes maybe 2 connections down the line there is a universe with the same number, but that doesnt matter much for most travel between the universes you are in.

  • $\begingroup$ They could come up with random names, but the trouble comes from the fact that every time a new portal opens, they all have the same name as their doppelganger universe, so half of them need to come up with new names. It would get super confusing if it wasn't handled in an ordered way $\endgroup$ Commented Feb 24, 2020 at 22:34
  • $\begingroup$ And the reader. It's important to the reader. $\endgroup$ Commented Feb 25, 2020 at 2:59
  • $\begingroup$ The reader *and characters) also have to be aware that Univese 0-2-1-2-1-0-1-2-1-1 is a very different place from Universe 0-2-1-1-1-0-1-2-1-1, you know with 0-2-1-2-1-0-1-2-1-1 being the next best thing to paradise on Earth and 0-2-1-1-1-0-1-2-1-1 being a post-apocalyptic nuclear hellscape ruled by roving gangs of Nazi cannibals. $\endgroup$ Commented Feb 25, 2020 at 15:54
  • $\begingroup$ The inhabitants need to know its DIFFERENT from the time it was cloned, and that its history diverged at the point of cloning, but do they really care about its name? Methinks they would just give it their own nickname. $\endgroup$ Commented Feb 25, 2020 at 17:59

Robert Heinlein dealt with this when crafting the Future History series of books. He solved the problem by assigning each universe a name and a number. He recognized that most changes we deal with are quickly diluted with the randomness of everyday life and not recognized as unique. If the electron in the tip of my finger is spin up in one world and spin down in another, the two are really indistinguishable for all intents and purposes. There's no meaningful way to assign names to worlds whose differences cannot be measured.

Instead, he argued that most important changes occurred at "cusp events." These were events of great importance that shaped the course of humanity. One of those cusp events was who landed on the mooon first. Thus we might be from timeline "Neil Armstrong 67." This let us distinguish individual timelines quickly by cusp events, and then delve into the details of the timeline by number later.

While you still have to number all your universe, a similar pattern might work: a short synopsis followed by a number. You probably want a coded number like an IPv6 address to track enough details. Our timeline might be Gutenberg, Einstein, Hitler, Neil Armstrong, Oprah Winfrey 2001:0db8:85a3:0000:0000:8a2e:0370:7334

  • 1
    $\begingroup$ This might be helpful hundreds of years after the portals open, but all of the portals share the same history and portals in this setting are invented in the modern day. Which means Neil Armstrong was the first to land on the moon in all of them, since that happened before the portals caused things to diverge between the universes. $\endgroup$ Commented Feb 25, 2020 at 9:53
  • $\begingroup$ But the timelines are not divergent. They are the same timelines. The timeline for America after separation from Britain was the same timeline as Britain. The events on that timeline were different in each country, but the events that occurred during that timeline in Britain were the same, whether you lived in Britain or America. You would have to say 'The Universe in which Neil Armstrong 67 occurred'. But as soon as another clone occurred, there would now be TWO universes in which 'Neil Armstrong 67' occurred in their history. $\endgroup$ Commented Feb 25, 2020 at 18:30

You don't need to name them all

Keith Morrison has already explained the impossibility of naming them all, the argument I'm going to make is that you don't need to.

There's no possible set of circumstances under which you need to identify an arbitrary universe in your set. You only need to identify an universe you can reasonably interact with. The only way to interact with another universe is to pass through a portal to get there. Which means you can address any universe by the path you need to follow to access it.

If you encounter another traveller in a distance universe, you can reverse their path to locate their universe relative to yours.

No name is absolute, everything is relative.

  • $\begingroup$ First of all, Keith assumed that there would be no overarching regulatory system that stops people from constantly opening new portals. If the number of portals is kept to below a reasonable limit, say 20, then every universe could be uniquely identified with a 5-digit hexidecimal number, for instance. More to the point, there will inevitably be people who decide to move 10 or 20 portals away from their home universe. A path that changes with each destination is easy to forget, while a home address can be printed and taken with you. You definitely don't want to get lost when portal-hopping. $\endgroup$ Commented Feb 25, 2020 at 12:21
  • $\begingroup$ @GiladM, I never said it would be easy, you'd definitely need some sort of technological support to record your path if you travel far. $\endgroup$
    – Separatrix
    Commented Feb 25, 2020 at 12:24
  • $\begingroup$ @GiladM, you pointed out that once the universe duplicates, both duplicates can then go on their merry, independent way. So what, precisely, stops someone in one of the duplicates down the line, "generations" removed from the original, just opening portals willy-nilly? $\endgroup$ Commented Feb 25, 2020 at 17:44
  • $\begingroup$ @KeithMorrison Like I said in response to the other answer, due to the branching structure of the universes, they can cut off contact by shutting off a single portal, and then they'll never be able to reconnect (since portals never connect to existing universes). If I were sitting in front of you with a pen and paper, I'd plot out the graph and show you that it's always doable. $\endgroup$ Commented Feb 25, 2020 at 18:04

As long as the two universes are largely the same, you don’t need to differentiate them. You can interact with either interchangeably. What matters is once they start to diverge. So name them based on the first notable divergence you notice: Earth Mom-said-no, Earth the-dog-barked-twice,etc. Over time you may rename some based on more significant divergence. The naming is relative to the person who opens the portal, anyway, so why not embrace that subjective focus in the naming?

  • $\begingroup$ The John Smith opening, the Mary Jane opening, the Peter Faulk opening? $\endgroup$ Commented Feb 25, 2020 at 5:02
  • $\begingroup$ Interesting idea, but when you open more than one portal, you'll have to differentiate that different universe from itself again. So you'll need names like Earth dog-barked-twice-and-4-days-after-the-second-portal-opened-it-was-cloudy. Not a sustainable naming convention with multiple portals in play. $\endgroup$ Commented Feb 25, 2020 at 9:51
  • $\begingroup$ @GiladM I wouldn’t chain the names. Just note why you need to remember this universe and write that down. The path through the gates to get back home matters more than the particular names. $\endgroup$
    – SRM
    Commented Feb 25, 2020 at 16:25

Looking at all the previous answers it seems clear that you can only achieve the things you require, instant naming and single individual IDs (no accessing my facebook or bank account) if you invent a new measurable universal property that is unique to each universe.

Using my hand-held and waveable quantum signature gizmo I can measure each universes paralleism state. This is a simple guid, that the pocket device turns into a naming phrase, like what3Words, but auto generated from the GUID rather than relying on a hand cranked list.

You're still going to run out, over all your parallel universes quite quickly. But you should have enough locally unique names that your characters can't realistically travel far enough to meet a duplicate name.

On duplication, everyone used to live in CorrectHorseBatteryStaple, and now the duplicates live in SpaceBannanaBurningHole. It's annoying that I've become the B universe, but given the quantum signature doesn't change after duplication I've no choice but to believe the device.

How you get the two factor authentication to check my quantum signature is a puzzle I leave up to the bank. But obviously they don't have to actually care what the universe's signature is, just that the person accessing as the same one. So the bank's end could be plugged into, say, a small piece of fairy cake.

  • $\begingroup$ If a new universe is an exact clone of an existing universe, with the same history back to the Big Bang, and if it is a deterministic universe, wouldn't the clone also have exactly the same quantum signature up to that point? The signature between the two universes would diverge from there, but so would their history, so no need for quantum measurement gizmos, just determine who went right and who went left immediately after the clone. $\endgroup$ Commented Feb 25, 2020 at 23:24
  • $\begingroup$ @JustinThymetheSecond I think the other answers make pretty clear why you can't just track which is left and right. $\endgroup$
    – Jontia
    Commented Feb 25, 2020 at 23:51
  • $\begingroup$ It has become increasingly clear that every time a new clone is made it is abundantly clear when you can compare their histories when the clone took place. Everything before that point would be identical. Everything past that point would diverge. On every single duplicated Earth that existed at the point of the clone. The OP has made that clear to me a few times, and I finally realized what the model was that allowed this to happen. Nothing new is created in any clone, nothing different, except an exact duplicate. From there, portals and histories of each Earth can differ substantially. $\endgroup$ Commented Feb 26, 2020 at 1:20

I am trying to envision this as a tree diagram. Start at the root, and you have two branches, say Alice and Bob. Alice splits off, goes her own way, and splits into another branch, Alice and Alice-Mary. Bob goes on, and splits into Bob and Bob-John. Alice-Mary splits off, and has a branch Alice-Mary and Alice-Mary-Jane. The original Alice continues on and splits into another branch, Alice and Alice-Susan. Do the people in the universe Alice-Mary-Jane know anything about the people in Alice-Susan? Or even Bob-John? It seems they would have de-synched and lost connectedness. Or can someone in Alice-Mary-Jane go back to Alice-Mary, then Alice, and then forward again through Alice to Alice-Susan?

If someone can traverse the tree, in order to make sure no spawned universe gets the name of another universe on a different branch, without knowing it, the solution would seem to be an ever-longer-growing name that always references the route along the tree, unless there is an omnipotent 'master cataloger' who can see the entire tree all the time.

If a person could not 'surf the tree', then a duplicate name for two universes on completely different branches would only matter to the omnipotent reader, not to any particular resident of any particular citizen in any universe. To them, they might just as well be called, simply, 'Bob' and 'Alice' and 'Alice-Mary' and 'Mary-Jane'. That is, the name of the spawning world, and the spawned world. Just like married couples today either just take one last name of the other partner, keep their original last name, or take the groom's last name and the bride's last name, not the entire groom's family tree last name, and the bride's family tree last name. Otherwise, when a James-Ming-Nile-Smith married a Mang-Spencer-Wilson-Porter-Sanainil-Popodoupolous, the new child's name would be...

I just don't think it would be practical to have any kind of a 'descendant' naming convention, so go with some simple, unique name for each world, and keep track of it with some form of tree diagram in the appendix or the front fly for the omnipotent reader.

  • $\begingroup$ Travel between the universes is possible, and internet connectivity across portals makes running into distant parallel selves a reality sometimes (don't worry, there's some kind of protocol in place to prevent widespread identity theft). For this reason, it would help both to have a colloquial "first name" for each universe to tell it apart from its neighbors, as well as an ideal universal "last name" which is, for fringe cases of distant universes coming into contact, completely unique and well-ordered. $\endgroup$ Commented Feb 24, 2020 at 21:38
  • $\begingroup$ One of us is really, really confused. My interpretation was, first, that hese were branching universes. A new portal leads to another branch, and the existing universe is cloned PAST that branch, going forward, but he past history is not cloned. That is, the history of the two universes (the two clones) has exactly the same non-cloned past. So if, in my example, someone from Alice-Mary goes back to Alice, then the root, then back up to Bob and Bob-John, they go through EXACTLY the same (not cloned versions) as someone going from Alice-Susan to Alice to root to Bob to Bob-John. $\endgroup$ Commented Feb 25, 2020 at 1:04
  • $\begingroup$ That is, there is only ever just one Bob, the Bob universe is not re-cloned every time another Alice-Sussie-Margaret-Whatever-Whatever is spawned and cloned. Bob going FORWARD can clone and spawn, Bob going backward can not. Otherwise, there is absolutely no direct causal connection between Bob-(the new cloned) and the Root-(new cloned), except for something that happens IN THE FUTURE, well after the first spawning and clone.. $\endgroup$ Commented Feb 25, 2020 at 1:12
  • $\begingroup$ It's like a planet suddenly appearing in our solar system today, because of something that happened in Andromeda today but can be traced back through all time to the big bang, and then forward again to out time. causation can not be because of something that happens in the future. Bob can not be cloned because some future universe is cloned. $\endgroup$ Commented Feb 25, 2020 at 1:14
  • $\begingroup$ Looked at another way,in your construction, a traveler from Alice-Mary-Jane can go back and forward to Bob-John, but a traveler from un-cloned Alice can not go back to Bob-John, because Bob-John had not been cloned yet, not until AFTER Alice was cloned. Bob-John was cloned AFTER Alice-Mary. So Bob-John would appear in the cloned Alice-Mary universe, but not the before-cloned Alice universe. Methinks history can not be backwards cloned and spawned, the branch has to go forward only. So no PREVIOUS cloned worlds have to be renamed - they don't ever get cloned again in ANYONE"S history.. $\endgroup$ Commented Feb 25, 2020 at 1:28

This is answer 2, because the more I think about it, the more I realize that no one in any universe would allow their 'Earth' to change names. Either that, or these inhabitants would not be humans.

John Smith, born Jan. 31 2010 in Liverpool, England, Earth would be John Smith, born Jan. 31 in Liverpool, England, Earth after the first clone. Both of them. The parents would be John Smith Sr. and Mary Jones. And the parents would be exactly the same. Indistinguishable. But after the clone, John Smith Jr. marries Henry, but John Smith Jr. marries Henrietta. And John Smith Sr. and Mary Jones break up and divorce. But John Smith Sr. and Mary Jones live happily into their retirement until death. In their minds, in their psyche, they were all born on Earth. Period.

And then, another universe is cloned. John Smith Jr. born on Earth (not Earth 1, or Earth001, or whatever, but Earth - that is what his birth certificate and legal documents state, very clearly) now has four clones. Each one born Jan. 31 in Liverpool, England, Earth, with John Smith and Mary Jones as parents, born on Earth. Not one of them would change their names, just because anther clone exists with the same name, somewhere else. Every clone is exactly the same person. Same DNA. Not one of them is going to change their names. These are the names they were born with, and have a right to. So which one is going to allow their history to be re-written? The place of birth, the name of the place where they were born, doesn't change. It is and always will be Earth. Unless you re-write every clone universe history. Everything in the past stays the same, no matter how the future changes. What has happened, has happened. The Earth is named Earth, and it will not change.

Are (were) the deceased grand-parents thus clones? Or are they the same person? The clones didn't exist until AFTER the earths are cloned. How can dead and fully decomposed people thus end up cloned? They didn't exist before. Or does cloning a universe clone everything that happened in the past? What would that even mean? Would a clone from one earth, traveling through the portal, consider their parents on 'the other side' still as their parents? After all, their DNA came from them. They came from the same womb. So how does a person completely change their heritage, when their heritage doesn't really change? They are all descendants of Earth. One Earth.

No, I am afraid the Earth would always be called Earth, every one of them. Unless any future inhabitants of one earth decided to call it something else, and then the name would be unique and meaningful to them, unrelated to any arbitrary naming 'convention'. Maybe the inhabitants of one Earth might come up with nicknames for the OTHER Earths, but I guarantee you, if we are talking about humans, they would be derogatory and completely unacceptable to the OTHER Earth's inhabitants.

If these are humans, you are stuck with Earth. Every last clone of them. And they would be right. Every instance would be properly called Earth.

The naming convention is strictly for the convenience of the omnipotent author and reader, not the inhabitants of the story. There would be no 'coin flipping', no 'lots cast'. It is entirely at the discretion of the author, entirely for the author's own purpose, as the omnipotent overseer, trying to bring order to chaos.

  • 1
    $\begingroup$ The naming convention isn't just for the reader's benefit - it's essential for their society to function. You don't want your parallel universe self to be able to access your bank account or your Facebook page. If your parallel self travels to your Earth and commits a crime, you and the Interdimensional Police both need a way to convey that it wasn't you who did it. As the universes diverge, this naming scheme becomes increasingly crucial - they'll develop different populations and cultures, and we'll need names for Earths like we need names for nations. $\endgroup$ Commented Feb 25, 2020 at 10:03
  • $\begingroup$ I understand the conundrum with identity and identity theft. But the bank accounts would be identical until the clone. It wouldn't matter which bank account you accessed from a time before the clone. The bank account numbers would be exactly identical. The bank balance would be exactly identical. The only way to avoid identity theft between inhabitants AFTER the cloning, and after the desyncing, would have to be on some basis other than biological or place-of-birth metrics. Would you retroactively change a bank account number, and allocate the bank balance, between future clones? $\endgroup$ Commented Feb 25, 2020 at 18:17
  • $\begingroup$ Clone 1 John Smith "I earned all that money in MY universe before I was cloned, so it is all mine'. John Smith clone 2 "No I earned all of that money before the clone, so it is all MINE.' Just coming up with a naming convention is not going to solve the problem of financially splitting the economies, and then merging them into some form of mega-universal-financial-system. But all births going forward from the clone would NOT share identical DNA, nor have a doppelganger in any other universe. Only the existing-at-clone-time people would. $\endgroup$ Commented Feb 25, 2020 at 18:21

Lots of people here seem to be overcomplicating it. Use binary fractions as a starting point:

  • Earth 1 splits into Earth 1.0 and Earth 1.1.
  • Earth 1.0 splits into Earth 1.00 and Earth 1.01.
  • Earth 1.1 splits into Earth 1.10 and Earth 1.11.

Since the integer part is redundant, we can use it to count the number of otherwise-ambiguous trailing decimals.

  • Earth 0 -> Earth 1.0 and Earth 1.1
  • Earth 1.0 -> Earth 2.00 and Earth 2.01.
  • Earth 1.1 -> Earth 2.10 and Earth 2.11.

Since you said

Every time you make a portal, you not only duplicate the current universe, but all other existing universes

we're doubling the number of universes each time, which basically means adding a digit after the decimal.

The observation which simplifies this whole scheme (if you are willing to complicate this particular aspect) is that the name of every universe changes each time there is a split. Luckily this is a change which is entirely predictable and easy to read.

Example, Earth 2.10 and Earth 2.11 both used to be called Earth 1.1 at some point in the past.

One might argue, philosophically, that Earth 2.10 and Earth 2.11 both always have existed, but before the split happened they were identical and interchangeable. (Arguably, this is what the "many worlds" interpretation of quantum physics is really saying, the universe doesn't "split" when Schoringer's cat either dies or survives, both timelines are eternal and the apparent "split" is just recognising the point at which they start to disagree.)

The hard part of your situation is a communications issue: if EVERY world splits when ANYWHERE opens a portal, you need to agree on the ORDER of splits events if everyone is to agree on a naming scheme.

  • $\begingroup$ I agree, it seems like binary (possibly shortened to hex for readability) is the way to go. This is the 3rd or 4th answer to suggest that, though with a slight formatting difference being the addition of a decimal point. I think, if anything, the need to name them in the correct order (due to this leading digit convention) makes this a little less convenient than plain ol' binary $\endgroup$ Commented Feb 25, 2020 at 12:11

I would use both IDs and path history.

When a portal opens, it automatically assign a random UUID ( https://en.wikipedia.org/wiki/Universally_unique_identifier ) to the door. It won't be able to identify every existing door but will at least allow to differentiate the close ones and avoid that multiple active doors have the same name in the same universe. Each universe keeps track of its own open doors and their IDs.

Then, when you travel, you keep track of every door you go through. When someone ask you where you come from, you describe the reverse path:

  • You leave your universe through door X, then go to the next through Y, then Z. When you meet someone in the last universe, you can explain that you are from Z-Y-X.

You could also describe your universe by giving all the IDs of the doors open in it:

  • "I'm from ABQJZ, you know it ?".

Of course, in the infinity of universes that will be created, there will be a huge number of universes with "ABQJZ" doors, but what are the odds that they will be close to you ? If the guy just went though 10 portals to get to your universe, chances are the universe ABQJZ saved in your database is the same than his.

It's not foolproof but I think it's efficient enough for navigation and keeping tracks of the universes around you.

EDIT : Clarification on UUID

An UUID actually looks like this : 07d84f17-f0cd-41da-a103-970974a17d11.

I've replaced it by a letter in my answer for clarity (but apparently failed !) and space. Someone going though three doors would mark his path as :


  • $\begingroup$ Unfortunately, the odds of two neighboring universes sharing the same names for their portals is very high. Take the simple case of a universe ABC that wants to open a portal D. Now it and its parallel self across D are both called ABCD. And they're right next to each other. That would cause no shortage of confusion. $\endgroup$ Commented Feb 25, 2020 at 10:32
  • $\begingroup$ I'm giving examples with letters for simplicity but if you use actual UUIDs (en.wikipedia.org/wiki/Universally_unique_identifier) it shouldn't be a problem. It's my fault if it wasn't clear. $\endgroup$
    – Jemox
    Commented Feb 25, 2020 at 11:03
  • $\begingroup$ UIUDs don't save you in this case. The odds of 2 UIUDs ending up the same in reality is basically 0, but if you're perfectly cloning existing worlds, they'll end up with the same UIUD, and will need to generate a new number. $\endgroup$ Commented Feb 25, 2020 at 12:06
  • $\begingroup$ It depends on what the doors are able to detect. Maybe you'll need another dose of handwavium at this point, but if you manage to attribute an 'unique ID' to the actual opening (and not the door) then my system could work. Maybe each portal has a unique and stable property that the door can measure and use for identification. Some kind of frequency or quantum index (blabla)... You door perpetually actualize its own indice but it never changes, until one door is cloned and the new aperture doesn't have the exact same physical property (and thus a new "id" is generated). $\endgroup$
    – Jemox
    Commented Feb 25, 2020 at 13:18
  • $\begingroup$ OOps. I copied it down wrong. What number comes after '97' again? Never mind, I made an error in entering it, and I am now in 07d84f17-f0cd-41da-a103-970974a17d11.de12f6c7-fab9-4021-bcf2-ba6978a4acc0.5a2a53c9-cff6-4c60-846b-f150101a1d78 Just try to find the mistake. $\endgroup$ Commented Feb 25, 2020 at 18:46

Terrian, Elevation, Latitude, Longitude

I'd recommend the T.E.L.L. (time, elevation, latitude, longitude -- popularized in 'Travellers') of when and where the split from the 'primary' timeline occurred, and an (Left, Right) ordinal indicating which of the several possible simultaneous branches this one is. Because doors duplicate, there are only two : by right-hand rule ('Right' the door knob is on the right, 'Left' on the left) This coordinate is local. So, the next branch would be relative to the new timeline.

A fully-qualified world name starts with the earliest time, and continues appending TELL-suffixes up to the most recent leaf.

Shorthand for Convenience

For short-hand, the closest city and year works. For example: AthensApril179Right : Byzantium238Left

This can be simplified further if only one door was ever opened in Athens. In that case, AthensLeft or AthensRight is sufficient.

On the other extreme, if hundreds of doors have been opened in Berlin the name can offer the necessary detail (up to the limits of your ability to know when and where the door opened). Examples : Berlin1931April26-0135, 0136, 0137 -- in that case, it may be easier to shorthand the event everyone is going to : BerlinOlympics-0135

Simplest Form

The shortest version will be the TELL of the most recently opened door in this universe. Since time marches forward, there should always be only one "most recently opened" door.

In your example :

  • 'Earth 1' is BasementJan2020Right,
  • 'Earth 2' is AtticFeb2020Right,
  • 'Earth 3' is AtticFeb2020Left, and
  • 'Earth 4' is BasementJan2020Left (if I have the order right).

Alt-names. I think this is your set-up :

  • E1 :
    • E1 (also called E2)
    • E3
  • E4

Uniqueness of Synonyms for the Same World

Because of the time and location component, MyHomeTownBasementJan2020Right is pretty unique in all of the multiverse. It doesn't matter that the proper short name, after opening the door in the attic in MyHomeTownAtticFeb2020Right -- both names are highly unlikely to conflict with another in the multiverse.


Let's say that both AtticFebruaryLeft and BasementJanuaryLeft both decide to go to the same neighbor's house and open a door. In the unlikely event that both of these timelines open a door so close to the same location that you can't measure a difference, and so close to the exact same time that you can't measure a difference.

Then two completely unrelated sets of NeighborsMarch2020 have been created. It's possible to disambiguate by prefixing the parent world :

AtticLeft-NeighborsMarch, or BasementLeft-NeighborsMarch

  • $\begingroup$ For a system with dozens of branch points, it seems really cumbersome to do this over binary. Sure, it's more detail, but it's less a "name" for each world and more a complete description. Not really what I'm looking for $\endgroup$ Commented Feb 24, 2020 at 23:45
  • $\begingroup$ @GiladM I added shorthand that I think might work. $\endgroup$ Commented Feb 25, 2020 at 0:10
  • $\begingroup$ What happens if two portals are opened at the same time and the same room but different houses? And the attic in Earth 4 does not have a portal, nor would any 'descendant clone earth', but every attic cloned from any descendant of Earth 3 would. So some worlds would have an AtticFeb2020-A and others would not. And, really, how would one state their 'place of birth, including Earth designation'? Someone AFTER the clone, easy. But someone born BEFORE the clone? What designation do they give? What would be on their birth certificate? The 'name' of their world wouldn't exist until AFTER the clone. $\endgroup$ Commented Feb 25, 2020 at 4:22
  • $\begingroup$ But EVERY universe cloned from that time forward has a portal called MyHomeTownAtticFeb2020Right. So how do you differentiate one portal named MyHomeTownAtticFeb2020Right in one universe,and another portal named MyHomeTownAtticFeb2020Right in a future cloned universe? Methinks the naming convention can not be named after the portal itself, but after the number of clonings. $\endgroup$ Commented Feb 25, 2020 at 18:03

Okay, answer number 3. We have been looking at this wrong. It IS indeed a binary tree diagram, but the root is not at the FIRST Earth that existed, The tips of the branches are the Earths, The node just indicates 'another clone occurred'.

Start at the beginning, with one earth. Neither 1 nor 0. Just earth, because no other exists.

Then another Earth is cloned. So we have Earth 1 and Earth 0. Earth 0 does not exist as Earth 0 until another earth is formed to be Earth 1. Until then, it is just Earth. But the node is NOT at earth 1 OR 0, it is one level above. We have to add a bit to indicate the creation of the portal, the two clones. Earth 0 is now earth 00. The clone is earth 01. The Earths are the TIP of the end branches, the LSB 0 and 1. Two Earths. The address as it were, NOT the node. The node represents that a new portal appeared anywhere on any of the branch tips (or Earths), causing everything to duplicate, not a portal on any particular Earth. That is, it represents the duplication, not the portal. Thus, the added 0 on the most significant bit represents the creation of the portal, the beginning of the added branch between 'old' and 'new'. (For the sake of clarity, I will call them 'old' branches and 'new' branches, even though they could not, in reality, be differentiated into 'old' and 'new'. EITHER could be labeled as a '1' or '0', but thereafter would ALWAYS be a '1' or '0' in the tree as their LSB, odd or even.)

A clone happens on EITHER earth, so the tree is duplicated. Now there are four Earths, not two, at the branch tips. That is, there are four branch tips, not two. Two 'old' ones, and two 'new' ones. So now a new branch starts from the top of the tree, not the bottom. And not from the portal on any Earth. The portal and where it exists or what Earth it exists on is irrelevant. What is important is that all of the Earths are cloned into exact duplicates. There are two more Earths, named Earth 0 and Earth 1, identical to the old Earth 0 and Earth 1, but another branch from the node has been created. The 'old' Earths now stay Earth 00 and Earth 01. But the new Earths become Earth 10 and Earth 11. The branch is NOT from the original earth, but from the added branch. The least significant bit of the Earth name does not change.

(It doesn't matter where the portal is, or on what Earth the portal is, or how you get from one Earth to another. This is not a road map between Earths through portals, but a tree diagram for a naming convention. Every time you clone, the number of Earths doubles, no matter how you get to them or where they are on the road map.)

So another clone happens from anywhere. The existing branches all exist, and the new branch would also be labeled as 00 and 00 and 10 and 11. But now we have to add an additional Most Significant Bit node further out on the existing tree, to indicate the split into old and new. The old Earths would be 00, 01, 10, 11, but now duplicated and renamed into 000, 001, 010, and 011 and the identical new earths would be 100, 101, 110, and 111.

Another clone forms, from anywhere, any Earth, on the tips. The new branch does NOT start at that tip, but at the tree root. An entirely new copy of the tree is formed. The eight old Earths are named 000, 001, 010, 000, 100, 101, 110, 111, but now they are divided into old 000, 001, 010, 000 100, 101, 110, 111 and new 000, 001, 010, 000 and 100, 101, 110, 111, so they are named with an additional MSB and are now called 0000, 0001, 0010, 0000, 0100, 0101, 0110, 0111 and new 1000, 1001, 1010, 1000 1100, 1101, 1110, 1111.

But wait, these can be shortened into Hex digits. 0000 is Hex 1, 0001 is Hex 2, 0010 is Hex 3, and so on up to 0111 is Hex E and 1111 is Hex F. So now the names of these Earths are EarthH1, EarthH2, EarthH3 EarthH4 ... Earth HE and Earth HF.

So clone the tree again, and the new names at the branch tips becomes EarthH00, EarthH01, EarthH01, EarthH02, EarthH03 ... EarthH0D, Earth0E, EarthH0F, EarthH10, EarthH11, EarthH12, EarthH13 ... Earth H1E, EarthH1F.

With a four digit Hex notation, by the time you get to HexFFFF, you have named 16^4 or 65,536 different Earths. AN 8 digit Hex notation gives you 16^16 or 4,294,967,296 names.

Except, of course, who wants to be named EarthHBAD? Or EarthHBADBAD? Or even EarthHBADFAD? Methinks they would all get nicknames, instead.


The advantage of this system is that you can clearly identify when the histories diverged. Every universe had the same history up until the first clone. So every universe that was 'odd' had a divergent history from the 'even' between the first and second clone.

Every universe that had the first two digits '00' had the same history up until the clone that generated a third digit. Likewise every universe with a "01', a '10', and a '11' first LSB digits would have identical histories.

Then after the next clone, every universe would match histories up until the next digit was added. Those with a '0' added would start to have a divergent history from those with a '1' added.

Then they would all go through two divergent histories each identically into two streams at the next clone, which add another '0' or '1' to the name, indicating a desynch in the histories. At the next clone, every universe that had 'history 0101' would be identically cloned into two '10101' and '00101'.

That is, universes 10 1110 and 11 1110 had identical histories up throughout the iterations 1110 (they were identical clones up to that time), and diverged only when the digit fifth from the right got added. However, a universe with designation 10 0110 diverged from all the universes with '110' as the first three LSBs up to the next clone of the fourth digit from the right (ie. 1110 vs 0110).

Two earths 1110 0101 and 0110 0101 were cloned and desynched or diverged after the eighth cloning, having shared the exact same pre-cloned history up until then.

So after another cloning, there would be four Earths, Earth 0 0110 0101, Earth 0 1110 0101, Earth 1 0110 0101, and Earth 1 1110 0101, with identical histories up until two clonings ago. In this way, an omnipotent accountant could track when the financial obligations diverged between two entities, be they individuals or corporations, on diverging Earths.


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