After all, our universe — the way we experience it — might not be the only version out there. The idea of a parallel universe explains it all!
It was the year 1954 when a young Princeton University doctoral candidate named Hugh Everett III came up with the idea of a parallel universe.
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In quantum mechanics, a parallel universe is a new universe that exists alongside our own, although undetectable.
Hugh Everett developed the idea for his Ph.D. thesis – and the theory held up. According to his work, we are living in a multiverse of countless universes, full of copies of each of us.
He suggests quantum effects can cause the universe to constantly split. Based on his idea, every decision we make creates new universes, one for all possible outcomes.
In a multiverse reality, some universes branch off of ours the same way our universe branches off of others. Within these parallel universes, our actions have had different outcomes than the ones we know. In another universe, the Nazis won World War II and Joesph Stalin won the noble peace prize.
About 13.7 billion years ago, all that we know existed was an infinitesimal singularity. Then, according to the Big Bang theory, something triggered it to expand and inflate in three-dimensional space. As the immense energy of this initial expansion cooled, the light began to shine through. Eventually, the small particles began to form into the larger pieces of matter we know today, such as planets, stars, and galaxies.
As far as our technology allows us to understand, our Universe is mind-bogglingly vast. Including photons and neutrinos, it contains some 10^90 particles, clumped and clustered together into hundreds-of-billions-to-trillions of galaxies, all scattered across the cosmos in a sphere some 92 billion light-years in diameter. And that limit is set by the distance that light has had the ability to travel since the instant of the Big Bang.
This is the reality of our universe which may be one out of an infinite number of other universes.
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With his many-world interpretation, Everett was trying to answer a rather sticky question related to quantum physics: Why does quantum matter behave erratically? The quantum world is the smallest one science has detected so far.
The particles that exist on this tiny level of reality have a way of taking different forms, arbitrarily. For example, photons act as particles and waves. Imagine a friend acts and looks like a solid when you glance at him/her, but when you looked back again, he’d taken a gaseous form.
This is known as the Heisenberg Uncertainty Principle. It means that we affect the behavior of quantum matter just by observing it. And that means a quantum particle doesn’t exist in one state or the other, but in all of its possible states at once. The state of an object existing in all of its possible states at once is called the superposition.
Everett suggests that measuring a quantum object does not force it into one understandable state or another. He says a measurement taken of a quantum object causes an actual split in the universe. The universe is literally duplicated, splitting into one universe for each possible outcome from the measurement.
Bottom line: The parallel universe theory proposes that the universe of which we are a part is not the only universe and that there are, in fact, an infinite number of universes that all co-exist in some higher dimensional multiverse.
However, as of now, there’s no evidence to back this theory up, and the hypothesis remains untestable.