The theory that parallel universes exist is termed the multiverse theory. The multiverse theory challenges the older single universe theory by claiming that many universes exist. The multiverse theory was first proposed by physicists in the twentieth century as a way of explaining several baffling aspects of quantum mechanics, a field of physics that seeks to describe the behavior and structure of matter and the physical universe at the small scale level of fundamental particles.
One of the earliest versions of the multiverse theory was the "many-worlds interpretation" of quantum mechanics proposed by physicist Hugh Everett in 1957.
According to Everett's "many-worlds interpretation" of quantum mechanical phenomena such as the so-called universal wave function, many and perhaps infinite worlds exist as alternate histories and futures of our known universe, and each universe is real.
However, Everett conceived of the parallel universes representing alternate histories of our given universe as existing independently without influencing or interacting with each other.
Everett's many-worlds interpretation effectively denies the concept of wave function collapse which suggests, under the single universe theory, that each time a quantum measurement is made only one of the myriads of alternative histories of our universe is actualized.
According to Everett, our multiverse is constantly branching into multitudes of equally real universes in which all possible alternative histories are actualized.
Thus, in an Everett many-worlds multiverse, there exists a universe in which you were not born and another in which you were born. There exists a universe in which you died a car crash last week and another in which you became president of the United States. In some universes, Hitler won the Second World War, and in others the Russians nuked Washington at the height of the Cold War.
According to Everett's interpretation, universes representing all possible alternate histories of our world exist as parallel non-interacting universes.
The idea that parallel universes do not influence each other at all was the major point of criticism of Everett's theory because from the scientific perspective the idea of parallel non-interacting universes is a non-testable hypothesis.
"Critics question the reality of other universes [in Everett's many-worlds interpretation], since they do not influence our universe... 'Many Interacting Worlds' approach is different..."
But a research team including Professor Howard Wiseman, Dr. Michael Hall, both from Griffith University's Center for Quantum Dynamics, and Dr. Dirk-Andre Deckert from the University of California, have proposed a radically new approach to the proposal that parallel universes exist.
The "many interacting worlds" (MIW) theory proposed by the team seeks to make the many-worlds interpretation a testable scientific theory.
According to the research team, in a study titled "Quantum Phenomena Modeled by Interactions between Many Classical Worlds," first published on October 23, 2014, in the journal Physical Review X, parallel universes exist, and they influence each other. The interaction between parallel universes, according to the physicists, is what we observe as the weirdness of quantum mechanics.
The researchers proposed that similar parallel universes exert subtle repulsive forces on each other.
"Any explanation of quantum phenomena is going to be weird, and standard quantum mechanics does not really offer any explanation at all—it just makes predictions for laboratory experiments," Wiseman told the Huffington Post. "Our new explanation... is that there are ordinary (non-quantum) parallel worlds which interact in a particular and subtle way."
The scientists offered a three-point summary of the MIW theory in an article published on the Griffith University website.
- The universe we experience is just one of a gigantic number of worlds. Some are almost identical to ours while most are very different;
- All of these worlds are equally real, exist continuously through time, and possess precisely defined properties;
- All quantum phenomena arise from a universal force of repulsion between 'nearby' (i.e. similar) worlds, which tends to make them more dissimilar.
"The beauty of our approach is that if there is just one world our theory reduces to Newtonian mechanics, while if there is a gigantic number of worlds it reproduces quantum mechanics," Hall said. "In between it predicts something new that is neither Newton's theory nor quantum theory. We also believe that, in providing a new mental picture of quantum effects, it will be useful in planning experiments to test and exploit quantum phenomena."
When Motherboard asked Wiseman whether the new theory means that humans might in the future interact with "nearby" parallel universes, Wiseman said it at least moves the idea away from the realm of "pure fantasy."
"It's not part of our theory," he said. "But the idea of interactions with other universes is no longer pure fantasy."
But many experts, including theoretical physicists Dr. Lawrence Kraus, from the Arizona State University (ASU), expressed skepticism about the "many interacting worlds" hypothesis.
According to the Huffington Post, a well-known Czech Republic physicist said that although the researchers "managed to present some ideas that [were] at least slightly original," their proposals were yet "another example of the fact that such efforts are a hopeless enterprise and a huge waste of time."
But several other experts described the theory as an "exciting new idea."
"They give very nice analyses of particular phenomena like ground-state energy and quantum tunneling," Charles Sebens, and expert in the philosophy of physics at the University of Michigan in Ann Arbor, told Nature."I think that together they do a nice job presenting this exciting new idea."
Dr. William Poirer, chemistry professor at Texas Tech University in Lubbock, described the theory as an "an important contribution."
"There is no experimental evidence to support this yet, but if true, it means that their theory will make different experimental predictions than standard quantum mechanics does," Poirer said.
Responding to critics, Wiseman said his team had not expected to change the minds of researchers "who are completely happy with their own interpretations of QM." But he said he hoped that others would be sufficiently interested in starting to work on its implications.
"I think there are many [physicists] who are not happy with any of the current interpretations," Wiseman said, "and it is those who will probably be most interested in ours. I hope some will be interested enough to start working on it soon, because there are so many questions to answer."
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