You hear about parallel universes all the time in science fiction (see Fringe, probably a billion episodes of Star Trek, Stephen King’s Dark Tower series, etc.). But did you know that scientists take parallel universes seriously and consider them possible? There are several types of possible parallel universes. In this series of articles, we are going to look at each of these different types.
Really, Really, Really, Really Far Away
Our universe is huge. Mind-bogglingly, eye-poppingly, throat-stoppingly huge. It is so huge that we are not even sure yet if it is infinite or not. Regardless, the universe is so huge that we can only see a part it.
This is where we need to look at definitions. When we say the universe, we generally mean everything in existence: the entire universe. However, when scientists say “the universe,” they mean all the stuff we can see: the observable universe. The observable universe is smaller than the entire universe. Our range of vision is about 46 billion lightyears in any given direction. So the observable universe is a bubble about 92 billion lightyears across. For scale, the Milky Way is only 100,000 lightyears across, so the observable universe is 92,000 Milky Ways across. Once again: huge.
So, where do the parallel universes come in? Cosmologist Max Tegmark created a taxonomy of possible parallel universes. One type is the stuff outside of the observable universe. The idea is that, in a given volume of space (i.e., something the size of the observable universe), there are only so many possible configurations of matter.
Think of it like K’Nex: there are lots of different pieces, but they only fit together in a certain number of ways. If you build a rollercoaster with your K’Nex, it’s not very likely that somebody else would build the exact same rollercoaster, but there is a small chance. So if enough people build K’Nex rollercoasters, someone else would eventually make almost the exact same thing as you made. It’s the same with observable universes. If there are enough of them, the matter in them can only be arranged in a finite number of ways and you are bound to have near-duplicates.
The issue is, how many parallel observable universes do you need to have a duplicate of our observable universe? As you can expect, it’s a lot. Like, a lot a lot. Like, the next closest duplicate universe is about 10^10^115 meters away from us. That number is even bigger than a googolplex of meters, which I’ll leave to Carl to explain:
If you translate that into lightyears, it shaves a couple zeros off, but it’s not very much. It’s hundreds and hundreds of observable universes away. Tegmark even went so far as to say how far would have to go to find a duplicate of the solar system and its surrounding stars: 10^10^91 meters away. A duplicate of just yourself: 10^10^29 meters away. Much closer, but it still might as well be an infinity away. Even if you allowed for slight variances in the arrangement of matter (like perhaps a blade of grass is missing here or there, or a few letters are missing from some books), it wouldn’t affect the distance calculation that much because those tiny differences don’t amount to the same scale of the total amount of matter. A drop in an ocean doesn’t affect the ocean that much.
Suppose we invented some awesome new technology that allowed us to travel to these parallel universes, despite the absolutely, positively, massively massive distances. What would we find there? Well, pretty much the same thing we have here. Since it involves the exact same entire universe, the laws of physics would be the same. If I were to travel to my duplicate’s house in that universe, I’d find him sitting in his den on his day off of work, typing this very article in his pajamas, while intermittently cleaning his dog hair-filled house. And you would find your duplicate reading this very article, wherever you had been just before you traveled to the parallel universe. Meta, huh?