Could there be another you in another world or is that “you” really someone else? Why is this important?
Before I answer those questions, I want to look at the idea of the Doppelgänger. A Doppelgänger is an identical copy of someone who is out there in the world somewhere, and the story goes that if ever they meet, one of them will die. Although the word is German, this idea exists in English folklore, where they are referred to as “fetches”. On the whole it’s confined to mythology although the internet has meant that it has become easier for people to find their doubles nowadays, which is not quite the same thing as there is no sense of bad luck or misfortune associated with it. There is also the very strange case of Emelie Sagee, a teacher at a school in what is now Latvia, in the nineteenth century, who would allegedly have a ghostly copy of herself appear beside her, mimicking all her movements, when she felt tired or ill. This may naturally itself be a fabrication.
At first glance you might also find the idea of parallel universes to be equally fanciful. However, there are good reasons for believing in them. The physical constants which allow us to exist at all in this Universe are very finely tuned. For instance, if the force bonding atomic nuclei together was slightly weaker the only chemical element would be hydrogen and “life as we know it” would not exist. If this is the only Universe, we would more or less be forced into believing in a Designer, i.e. God, because it seems to be so precisely arranged. However, any universe without life in it would not have anyone living in it to notice that the physical constants were any different. Consequently, one solution to this problem is to propose the existence of multiple universes where those constants are different from how they are here. In almost all those universes, even where there are stars, there are no rocky planets and no chemical compounds, although I would still hold out for the possibility that there could be life forms or at least conscious beings made out of ionised hydrogen.
By © User:Colin / Wikimedia Commons, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=30044004
Leaving that possibility aside for now, given that we’re more or less forced to choose between the Design Argument and the Multiverse, I opt for the latter. Given also that there’s no reason why there shouldn’t be universes where the laws of physics vary a bit less than would be required to rule out the existence of organic life forms entirely, it seems plausible that there would be a plethora of other universes which are more or less like this one in various ways.
Many of these universes would be very similar indeed to this one, to the extent that they would contain counterparts of ourselves, which brings me back to the question of doppelgänger. The issue is, are we the same person in all these other “dimensions” or are we just a load of almost identical clones? What would it mean for us to be the same person elsewhere? What would it mean for us not to be?
There are two main philosophical theories about this. One is counterpart theory, which is the idea that those people in the other universes are very similar to us but not the same people. The other is known as “cross-world identity”, or “transworld identity”, which is the idea that we are the same people in them. I personally believe in the latter.
The problem with cross-world identity is that there doesn’t seem to be a definite way to identify the people involved as the same in different universes. I was born in Canterbury, did two degrees in philosophy, got married to Sarada, lived in Leicester, had two children and became a herbalist. There is presumably a parallel universe where I did a doctorate in biochemistry, ended up working for a biotech company in Cambridge, and had no children. This goes against my values because of my political beliefs, but those could also have been different. It goes further than that though, because there seems to be no reason for identifying this random individual in another universe with me even if she has everything in common with me. She wouldn’t have been born in Canterbury because she would be from a possibly identical copy of Canterbury on a different planet in a different universe. She wouldn’t even live on Earth or in the Milky Way.
If at some point in the future, a twin Earth appears billions of light years away from here which repeats our history perfectly, apparently the same individuals would be born on it and live identical lives. These people would in a sense have nothing in common with us. They wouldn’t be us. This is of course the classic problem with the idea of the resurrection of the dead and judgement day. A person dies and their body is cremated or rots away. The atoms making up their body become incorporated in all sorts of other life forms, including human beings. Those human beings also die and their bodies are also destroyed. Then comes the Day of Judgement and all the bodies of everyone who has ever lived are reconstituted and reanimated. But if these bodies are made of the same matter, there is no way that two complete bodies can be made up, particularly if cannibalism was involved, or possibly blood transfusion or organ transplants. Therefore the resurrected human race cannot be the same as the original human race unless they happened to have died the night before or were cryonically preserved or something. God then goes on to judge these people, completely unfairly, since they have just been called into existence and have done nothing their originals have done, so why are they responsible?
I happen to have an answer to that, but I mention it here to illustrate that it seems fair to claim that the almost or even completely identical people in parallel universes are not in fact us. What exists to link us to them? They’re in different universes!
There does, however, seem to be a much more ordinary-seeming situation which makes sense of it. At one point I was a baby in a hospital in Canterbury. I am now a 49-year old typing a blog entry in Loughborough. At first sight the answer to the question “Is a baby in a hospital in Canterbury the same person as a 49-year old blogger in Loughborough?” is an obvious “no”. However, clearly it is the case because the first person turned into the second one. Put more normally, the first person became the second one. There is a succession of moments from my infancy to my middle age and in each moment I’m the same person as I was in the moment immediately preceding. The same could apply to parallel universes. In each successive parallel universe, perhaps adjacent, I am the same person, so I’m the same person as myself in any possible world where I exist.
I’ve described existence through a lifetime as an “ordinary-seeming situation”, and of course it is. What might not be as obvious is that just as living one’s life is what we all do, and it’s entirely ordinary even if one is oneself extraordinary, it’s just as ordinary to exist as a single individual in many parallel universes, or at least, that’s how it seems to me. However, there are still a couple of problems with this.
One is the question of what happens if there are “gaps” in one’s existence. That is, there are some universes where one exists and others which are initially identical apart from one’s existence. If there is a way of ordering parallel universes, and I think there is in the form of relative probability, our births are, to quote Eric Idle “amazingly unlikely”, and therefore it wouldn’t be surprising if there were very probable nearby universes where one doesn’t exist, then more improbable and therefore more distant universes where one doesn’t. It could be argued that this never happens in someone’s lifetime. I would argue, though, that it does. It happens, for example, every time we fall into a dreamless sleep. There is a sense in which we don’t exist during that time, although anyone who wanted could easily call us back into existence just by giving us a shake. However, and this applies to identity through time as well, there are overlapping characteristics in a lifetime which guarantee identity proceeds in a fairly steady stream, and arguably parallel universes interrupt that stream. Bringing them into the picture, it seems that characteristics can be so altered that I could arbitrarily identify myself with a rock on the third moon of a planet in the Andromeda galaxy which was destroyed when its sun went supernova six billion years ago. This is not so. In the same way as there are overlapping characteristics through a lifetime, so are there overlapping characteristics in parallel universes. The point does come when claiming that one is a particular thing or person is simply false.
Why is this important?
It’s important for various reasons. I am of course currently quite preoccupied with the Mandela Effect – the discrepancies between groups of people regarding their memories of well-known events, such as Shirley Temple having been dead since 1939 as opposed to her survival until this century and the existence of a fifty-first US state called Superior consisting of northern Wisconsin and Michigan. It’s entirely plausible that these are mere memory effects. However, if transworld identity can be made to work, another explanation is possible, namely that other versions of oneself are living in parallel universes where the state of Superior does exist and where Shirley Temple did in fact die nearly eight decades ago. Those other versions of oneself would often have such memories. It’s equally possible that there are versions of oneself whose memories of such events are incorrect, and that I may be such a version.
If transworld identity is plausible, containing no logical flaw that would make it impossible to be true, there is then a plausible explanation for the Mandela Effect. This is that events which are true in parallel universes create accurate memories which in special circumstances become mixed up and transferred into one’s mind in other universes. The veil which leads us only to perceive this world occasionally blows aside or rips, and we glimpse those other realities. If this happens to a sufficiently extreme degree, we might no longer be said to be the same person, because all the important memories would change to those from other universes, and those might even turn out all to be true in a particular parallel universe.
Then again, and this is ignored by many people although it’s as important, maybe our memories are becoming less reliable because we use Google, Wikipedia and digital media too much. I think this is also true, and will be going into that in a bit too.