In 1954, a grad student named Hugh Everett was enjoying the evening drinking sherry with his friends in the student hall at Princeton University. Suddenly! An idea occurred to him that quantum effects split up the universe constantly. Then further he carried the idea in his Ph.D thesis. According to Everett’s thesis, We exist in a multiple of innumerable worlds packed with clones of each all of us. Today we know this idea by the Theory of Parallel Universe. Even though Max Tegmark remarked his work as remarkable as Einstein’s theory of relativity, but Niels Bohr, a famous physicist of Everett’s time and among the fathers of quantum mechanics, did not consume the idea. Everett afterward quit physics and joined the Pentagon, where his work was to maximize the potential deaths of Soviets in nuclear war while saving Americans.
Tragically, he did not continue further research on his theory, but we see more scientists came up supporting or opposing it.
According to the supportive argument;
Since there is no confirmation about space’s shape and size, the many other universes may exist somewhere. And even they don’t know about our existence.
Another theory is present, based on the research by Alexander Vilekin, a cosmologist at Tufts University. It says that just like our universe inflated. As a result, Big-Bang, there is a possibility that more universes came into being, and they might be in a repetitive form.
Stephen Hawking, the well-known physicist, published a paper in May 2018, just a few months before he died. In his paper, he discussed the idea of the parallel universe as well. He stated in an interview at Cambridge University that, “We are not down to a single, unique universe, but our findings imply a significant reduction of the multiverse to a much smaller range of possible universe.
Those who argue against the theory state that even though space-time can go forever, but since the universe is 14 billion years old, it is obvious the universe’s age is not infinite. This also simply puts limits on the possibility that particles rearrange themselves and even have our alternatives.
So this theory will remain an idea until some solid evidences prove it.