The quantum mantra revolves around the theory that in physics, anything not forbidden is compulsory - given enough time and/or space. While there is nothing forbidden about an identical twin(s) of yourself existing elsewhere in the cosmos, how compulsory that is depends on what sort of cosmological model you adopt.
You are unique, aren't you? There never has been a person exactly like you before, there isn't now, and there never will be. Maybe! Depending on what's really real in all things cosmological, the odds that there are identical copies of you out there can range from plausible if improbable, to plausible and probable, to in fact near certainty, even certainty. The key issue revolves around the concept of infinity, or near infinity. If one has an infinite number of universes to play around with, and/or infinite time, then every possible history is, sooner or later, somewhere, compulsory.
The idea of a duplicate you or two or three isn't that farfetched. Even on Planet Earth, this tiny speck within the cosmos, you have had, do have, and will have doppelgangers. But those are just look-alikes, not actual duplicates of you down to the nittiest-grittiest detail.
From the outset, some definitions are in order. We have the 'observable universe' which is that part of the entire Universe we can actually see in the here and now. Parts of the Universe that exist, but which light hasn't yet reached us, aren't part of our 'observable universe' - yet. The 'Universe' is all that we can ever know about, regions seen, and regions as yet unseen. Then there is the 'Multiverse' which, if it exists, are a conglomerate of separate Universes, each of which exists as a discrete entity in a three dimensional arena and which we could potentially interact with. Think of separate houses along a street you can visit in turn as separate universes. An overall analogy could be the nucleus part of a liver cell (our 'observable universe'), the entire cell (the Universe), and the grand collection of liver cells - the liver Multiverse as it were. Apart from those, there are parallel (mirror/shadow/alternate) universes which 'exist' - for lack of a better phrase - in other planes of existence and like houses that exist in a time instead of a special sequence, say on the same block of land, one can't easily travel from one to another. There's also the Many Worlds Interpretation variation of parallel universe, and simulated universes.
Firstly, could there be another you or multiple copies of you in the existing Universe? That's plausible, but probably unlikely.
Discussion: The existing Universe could be as near to infinite as makes no odds. It obviously can't be infinite, because it would take an infinite amount of time to expand the Universe to an infinite volume, and we know the Big Bang took place less than 14 billion years ago. And, the Universe can't contain an infinite amount of stuff; otherwise it would have to have an infinite volume to house it all. The fact that our night sky is dark, suggests that there can't be an infinite number of stars and galaxies in our observable universe, otherwise, no matter in which direction you looked, you'd see a star or galaxy and the night sky would be as light as the daytime. However, from our point of view, while not infinite, the Universe is still BIG! And it does contain a lot of stuff. It is within the bounds of possibility that within such a vast space, by chance, there could be a duplicate(s) of you, even more identical to you than any identical terrestrial twin you might happen to have. The odds aren't very high to be honest, but they aren't zero. However, even if an identical copy of you exists elsewhere out there, the probability is far greater that they already have, or someday will. The odds that two copies of you exist right now multiply the odds against by many orders of magnitude. Finally, even if another copy of you exists somewhere out there now, they are in all probability way to far away for the both of you to ever shake hands.
Secondly, could there be another you or multiple copies of you in a cyclic Universe? That's not only plausible, it borders on near certainty.
Discussion: Current cosmological observations suggest that our Universe began some 13.7 billion years ago in a Big Bang. Alas, the expansion of our Universe appears not only not slowing down, but ever accelerating due to something cosmologists and astrophysicists are calling dark energy - which they admit they don't really understand. Anyway, despite dark energy, many cosmologists cling to the concept that eventually the expansion will slow down, halt, and reverse, resulting in ultimately a Big Crunch billions of years in the future. That Big Crunch leads directly to another Big Bang - expansion - contraction - Big Crunch - Big Bang, etc., etc. Thus one has an ever oscillating or cyclic Universe with no beginning and no end. Ah, the concept of infinity (this case in time) rears its head. Since the Universe has already gone through an infinite number of these cycles, as surely as night follows day follows night, anything that could have happened, has happened, and happened an infinite number of times. That includes in infinite number of you, and the life your leading now right down to the last detail an infinite number of times, as well as leading differing lives in every possible variation from the major (marriage, career, children, lifespan, etc.) through to the relatively minor, right down to the highly trivial (like an infinite number of lifetimes absolutely identical to the current one except for one morning when you had an ever so slightly different breakfast cereal). Just think, somewhere in the infinite past, there was a version of you who lived an entire lifetime driving a car and never hit a red light! Again, anything that is within the realm of possibility, even if improbable in the extreme, has happened, and has happened again an infinite number of times. Such is the nature of infinity. The other nice thing about an infinite Universe (whether in time or space) is that all those unsuccessful eggs and sperm, all those failed or un-germinated seeds, all those spores and pollen that never bore fruit, all those lives that never were, all now get their moment in the sun!
There's an interesting variation on the above theme. Most of us are probably familiar with the sci-fi idea of being caught in a time-loop. You repeat an interval of time over again and again, probably until some weird sense of deja vu alerts you that something's not quite right. Expand the idea to the grandest scale possible. Big Bang - expansion - contraction - Big Crunch - Big Bang - expansion, etc. but each cycle isn't a new cycle with a new history and new possibilities rather each cycle is absolutely identical to the one that came before, and the one before that, etc. So, there will be an endless number of you, but there will be no wild new things in your lives, just the same old life, again and again. Maybe that's where we get our now and again sense of deja vu from.
Of course in a cyclic universe, one universe dies before the next is born, so a copy of you in a previous universe is kaput before your universe comes into being, and you will be kaput before the next cycle starts, so there's no meeting of identically like minds.
To be continued...
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