The Multiverse Theory - Relevant or hoax?

** Based on Hawking's book, The Grand Design **

What is the Multiverse Theory?

Quantum Superposition and Multiple Universes: Explained

The existence of multiple universes or parallel universes is one of the most popular and sought-after theories in the sci-fi world. From the existence of wormholes to bubble universes, this theory has made it to the top of the list of most controversial scientific theories ever developed. But in this post, we're about to discuss its scientific significance with quantum mechanics.

The Multiverse concept was officially brought up by Erwin Schrodinger, most famous for his wave function equation of a system, and of course, the famous Schrodinger's Cat thought experiment. According to Schrodinger, the ultimate outcome of an event, until observed, can take up all possible outcomes, and they all happen simultaneously, a phenomenon called Quantum Superposition. The concept of quantum superposition suggests that in the case of the origin of our universe, there should exist alternate (parallel) universes where the conditions are different from our universe. A universe with a repulsive gravitational force or one where the Planck's constant is some other value!!

But this was not the only explanation for the existence of multiple universes. Richard Feynman's sum over histories, which says that in quantum mechanics, no particle has a single history or path, rather it has every possible history, each with its own probability. 

Theory of Alternate Histories

In Stephen Hawking's book The Grand Design, he gives a detailed description of Feynman's sum over histories and how it can be applied to a whole system, like our universe. 

According to Feynman's sum over histories, if we consider the history of a particle or the path which it followed (its path), the particle does not have a single history, rather it will have different histories for different possible states of the particle. Of course, this concept of alternate histories is solely based on quantum mechanics and seems to conflict with classical ideas with only one single history for a particle or a system. 

The key point here is that all of these probable histories are dependent on what we actually observe. In other words, when we really think about the history of our universe by going backwards from our present state, we do not find a single path, instead, we find that it has an infinite number of histories that are dependent on our observation. We were convinced that the universe had a single definite history because we actually observed our present state of the universe.

When we piece it all together, Schrodinger's implication of parallel universes, i.e, quantum superposition and Feynman's sum over histories applied to the universe's history, all compliments the existence of a multiverse. 

This is a bold speculation to develop from quantum mechanical principles, but according to the Big Bang hypothesis, the universe was initially at the subatomic level, before it started expanding. So it is reasonable to analyze its history based on quantum mechanics, and also because it's our only tool in studying phenomena at a subatomic scale. 

However, the answer to the question of whether this theory will ever be proved or not is out of scope right now. The reason is that we don't know for sure if we'd actually be able to find a parallel universe where our earth is actually green or a multidimensional universe that intelligent species have taken over. 

But most importantly, we can't even imagine the consequences of such a discovery, good or bad. 

We're not even sure if we'll discover such universes ever because it could create an imbalance in nature itself; as in the case of time travel, and our primitive human minds are not ready for parallel universes and overriding spacetime!!