When physicists talk about the universe, they don’t really mean the entire universe. They’re referring to the observable universe. And that’s not much. It’s just the part we’ve so far been able to see. When physicists talk about the multiverse or parallel universes, they are referring to distinct hypothesized models for the universe. These are all proposed theories, not facts confirmed through deduction. Let’s take a look at some theories on what constitutes parallel universes.
The models
Bubble Universes or Baby Black Hole Universes
There are other distant parts of the universe we will never be able to observe because they’re very far away from us. These universes could also be inside black holes. All the universes, according to this theory, have their own physical laws and exist as separate entities.
Membranes and extra dimensions
String theorists have been trying long and hard to figure out how many dimensions our universe has; they’ve not been successful yet. They have proposed another theory in which the space we consider our universe is actually a 3-dimensional surface, but it is part of a larger universe with 9 spatial dimensions. There could also exist numerous other 3-dimensional surfaces or “membranes.”
There is a lot that modern physicists do not understand about quantum mechanics. Using quantum mechanics, they’ve theorized that every time-space is real, and that they branch out in every possible way. That is, everything you could ever imagine is happening, but we wouldn’t know it because we are stuck in one reality, unable to access other realities.
The observable universe contains approximately 1,090 particles with photons and neutrinos clumped together to form 2 trillion galaxies. Each galaxy comes with another trillion stars inside, which extends outside for 46 billion light-years. According to the Big Bang theory, the universe is constantly expanding, and this should make it possible for us to observe more galaxies as time goes by.
The argument against parallel universes
Astrophysicist Ethan Siegal believes there are limitations to the concept that space-time goes on forever. According to science, our universe is 14 billion years old. So the age is not infinite, which brings down the number of possibilities where the particles could rearrange themselves.
According to Mr. Siegal’s theory, the particle expansion that happened after the Big Bang has considerably slowed down, unlike in the beginning, when the expansion was happening at an exponential rate. This means the multiverses scattered across the universe could have distinct inflation rates, and so the possibility that another you living a similar life to your own could be almost impossible.
“Even setting aside issues that there may be an infinite number of possible values for fundamental constants, particles, and interactions, and even setting aside interpretation issues such as whether the many-worlds-interpretation actually describes our physical reality,” Siegal said in a Medium post. “The fact of the matter is that the number of possible outcomes rises so quickly — so much faster than merely exponentially — that unless inflation has been occurring for a truly infinite amount of time, there are no parallel universes identical to this one.”
Mr. Siegal says this in an optimistic fashion and asks his readers to live their lives because they are unique, and to treasure that fact.
Parallel universes as presented in science fiction
Parallel universes have been a staple in sci-fi. Given below are some works containing the theory of parallel universes.
- Flatland: A Romance of Many Dimensions by Edwin A. Abbott (1884)
- Men Like Gods by H.G. Wells (1923)
- The Chronicles of Narnia by C.S. Lewis (1950)
- The Dark Tower by Stephen King (1982)
- Back to the Future movie series (1985)
- Stranger Things TV series (2016)
- Anime: Digimon, Dragon Ball and Sonic the Hedgehog
- DC and Marvel Universes
