Like many other people, I have occasionally wondered if there is a parallel version of me out there, living on some parallel Earth in some parallel universe. Parallels of us or even a parallel Earth is suggested by dreams and mirror reflections in everyday life. Not surprisingly, there are cultural references to parallel universes, such as the “Mirror, Mirror” episode of the original Star Trek television series.[1] In that episode, main character Captain Kirk and cohorts find themselves in a parallel universe where conquest is favored over peace. Could there be a parallel universe with a parallel Earth and maybe parallel versions of me and people I know? I have my doubts for a couple reasons.
To clarify, a parallel universe should contain a parallel Earth, since that’s the only location of civilization that we know of in our own universe. Otherwise, when seeing just the stars that are similar to our own universe, how would we know for sure it’s not our own universe? Anyhow, that parallel Earth should have humans on it like the humans here and should probably be called Earth. The features of that parallel Earth should convince us that it is a copy of our own Earth. The history of humanity there should resemble the history of humanity here. Basically the parallel universe should seem like an alternate copy of our reality.
First of all, there’s the obvious shortcut, namely the “many worlds” interpretation of quantum physics.[2] In this interpretation, every distinct outcome of every distinct quantum event from our universe (or others), supposedly gives rise to its own version of the universe. This would have started at the beginning of the universe. I’ll admit, the idea sounds intriguing. And if we wanted to open some kind of “doorway” between our Earth and a parallel Earth, the many worlds interpretation could make that outcome more likely. After all, each copy of the universe would have meaningful similarity to every other copy. However, our one universe that we live in now, really has a lot in it. I can’t imagine all the energy in our universe (including matter) being multiplied by the number of distinct universes there would be. And the number of these slightly-varied universes would become ridiculously huge, long before life began anywhere. I’m simply not sold on the idea.
What about the existence of a parallel universe at all, not some insane number of them? Can a parallel universe exist? Presumably, the laws of physics would basically behave there the same way they do here. Why? More optimistically, why not? Being a universe, that copy could very well be made of the same space-time material (what else would a universe be made of?). The same subatomic particles that make up Earth and humans now, also existed under somewhat different conditions, like when our universe was much smaller and younger, and had a greater energy density. We might reasonably expect these necessary particles to exist in another universe too, if it exists. Optimistically, we might also expect stars and planets of a parallel universe to form the same way as here, as well.
Granted, a parallel universe may be possible for all we know, does the idea even make sense? The history of any given country on Earth is likely to include events that were very close to having a very different outcome. A slight change somewhere could have significantly affected human history, in spite of (e.g.) no drastic change in the Earth itself. Now consider this happening on the scale of the universe. Even if the parallel universe started out identical to our universe, whatever subtle differences in conditions led to it being different, would have billions of years to accumulate. The point at which the universes are no longer meaningfully similar would likely be before the Earth came into existence. Or if the copies diverged more recently, why should we expect the time of divergence to lead to a universe meaningful to us? It just seems arbitrary to me, that it would treat our planet as special.
But could we still find a parallel universe with a parallel Earth? If we did encounter something seemingly parallel to us in another universe, it would have less to do with similar cosmic history but instead would be more due to the likelihood of a planet like ours existing with humans on it. Just like many stars of a given category of size and temperature exist due to the laws of physics, we might also attribute anything parallel to us to the laws of physics. A parallel would exist simply because something like us is that likely anyhow (which would be why we even exist). It would just be a random coincidence. So we can probably forget the existence or profound meaning of a truly parallel universe with a meaningfully parallel Earth.
So a parallel universe as such seems unlikely, in my opinion at least. But that may not be a bad thing. I may be the only me in existence anywhere. That makes me unique. The same could be said for every one of us. So we’re all special. In that case, no parallel me from another universe is trying to take my spot here. Now if we can just rule out the possibilities of unauthorized clones, shapeshifting aliens, and human-impersonating robots, then I’ll feel even safer. At least I still have a unique birthmark. Wait – they could have just read about it in this blog entry. They may be updating their appearance to include that birthmark as you read this. Maybe I can find a nice cave to hide in.
References
[1] https://memory-alpha.fandom.com/wiki/Mirror,Mirror(episode)
[2] https://en.wikipedia.org/wiki/Many-worlds_interpretation
(c) Copyright 2021 by Mike Ferrell
Odd STEM 