Parallel universes are no longer just a feature of a good sci-fi story. There are now several scientific theories that support the idea of parallel universes beyond our own. However, the multiverse theory remains one of the most controversial theories in science.
Our universe is unimaginably large. There are hundreds of billions, if not trillions, of galaxies spinning through the universe, each containing billions or trillions of stars. Some researchers studying models of the universe speculate that the diameter of the universe could be 7 billion light years in diameter. Others think it could be infinite.
Science fiction loves the idea of a parallel universe
But is that all there is to it? Science fiction loves the idea of a parallel universe and the idea that we could only live one of an infinite number of possible lives. However, multiverses are not reserved for “Star Trek”, “Spiderman” and “Doctor Who”. A true scientific theory examines, and in some cases supports, the case for universes beyond, parallel, or distant but mirroring our own.
Multiverses and parallel worlds are often argued in the context of other major scientific concepts such as the Big Bang, string theory, and quantum mechanics.
ETERNAL INFLATION, THE BIG TRACK THEORY AND PARALLEL UNIVERSES
•About 13.7 billion years ago, all we know was an infinitesimal singularity. Then, according to the big bang theory, it burst into action and inflated faster than the speed of light in all directions for a tiny fraction of a second.
•By the time 10^-32 seconds had passed, the universe had exploded outwards to 10^26 times its original size in a process called cosmic inflation.
•All before the actual expansion of matter that we usually think of as the Big Bang itself, which was the result of all this inflation: As inflation slowed down, there was a flood of matter and radiation that created a classic big bang fireball and began to form atoms, molecules, stars and galaxies that populate the vast space that surrounds us.
•This mysterious process of inflation and the Big Bang has convinced some researchers that it is possible, or even very likely, that there are multiple universes.
Theory of eternal inflation
According to theoretical physicist Alexander Vilenkin of Tufts University in Massachusetts, inflation did not end everywhere at the same time. While everything we can detect from Earth has ended 13.8 billion years ago, cosmic inflation is actually continuing elsewhere. This is called the theory of eternal inflation. And as inflation ends at a certain point, a new universe of bubbles emerges, Vilenkin wrote for Scientific American in 2011.
These bubble universes cannot contact each other because they are constantly expanding. If we were to go to the edge of our bubble where it might bump into another bubble universe, we would never reach it because the edge is moving away from us faster than the speed of light and faster than us could ever travel.
But even if we could reach another bubble, according to eternal inflation (combined with string theory), our known universe, with its physical constants and habitable conditions, could be quite different from the hypothetical bubble universe next to our own.
“This picture of the universe, or the multiverse as it is called, explains the long-standing mystery of why the constants of nature seem to be fine-tuned for the origin of life,” Vilenkin wrote. “The reason is that intelligent observers only exist in those rare bubbles where, by pure chance, the constants are just right for life to evolve. The rest of the multiverse remains barren, but there’s no one to complain about that.”
QUANTUM MECHANICS AND PARALLEL UNIVERSES
•Some researchers base their ideas about parallel universes on quantum mechanics, the mathematical description of subatomic particles. In quantum mechanics, there are all possible different states of existence for small particles at the same time the “wave function” encapsulates all these possibilities.
•When we really look, we only ever observe one of the possibilities. According to the Copenhagen interpretation of quantum mechanics, as described in the Stanford Encyclopedia of Philosophy, we observe the result when the wave function “collapses” into a single reality.
•But many-worlds theory instead proposes that every time one state or outcome is observed, there is another “world” in which a different quantum outcome becomes reality. This is a bifurcated arrangement in which our perceived universe bifurcates moment by moment into almost infinite alternatives.
These alternate universes are completely separate and unable to intersect, so while there may be countless versions of you living a life that’s slightly or wildly different from your life in this world, you’d never know it.
Something Deeply Hidden: Quantum Worlds and the Emergence of Spacetime
In his book “Something Deeply Hidden: Quantum Worlds and the Emergence of Spacetime” (Dutton, 2019), physicist Sean Carroll wrote the “boldest” theory of many worlds. He also argued that it was the most straightforward theory, though not without wrinkles.
One of the wrinkles is that the idea of many worlds is not really falsifiable. This is an important part of scientific thinking and is how the scientific community develops ideas that can be explored through observation and experimentation. If there’s no opportunity to find evidence against a theory, it’s bad for science as a whole, science journalist John Horgan argued in a blog post for Scientific American.