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Before his death on March 14, theoretical physicist Stephen Hawking was deep in thought about the possibility of universes that exist well beyond our own -- places with completely unknown galaxies, stars, and planets.

While there's no evidence yet of any such parallel universes, also known as a multiverse, Hawking had been working with fellow theorist Thomas Hertog to prove that it's possible to observe the cosmos and find evidence of these mysterious places. Hertog continues to research the deeper questions of the universe at the Institute for Theoretical Physics at the University of Leuven in Belgium.

Their paper, which Hertog says has been sent to a leading journal for formal review, is available online and was last updated by Hawking and Hertog on March 4. It builds upon Hawking's 1983 theory about the Big Bang -- the event many scientists believe prompted the beginning of our 13.8 billion-year-old universe.

SEE ALSO:Stephen Hawking hosted a party for time travelers, but no one came

But this earlier theory didn't satisfy Hawking because it was untestable, requiring an experiment that would account for an infinite number of potential universes. So Hawking sought a solution.

"'Let’s try to tame the multiverse', he told me a year ago," said Hertog, over email, about Hawking's research plans.

This paper creates a "coherent testable scientific framework," said Hertog, which will guide scientists on their quest to find evidence of other universes, something that currently only exists in the realm of science fiction. Using complex mathematics, Hawking and Hertog assert that future research missions -- whether using assets on Earth or in space -- should be able to pick up evidence of powerful gravitational waves from the Big Bang.

A time-scale representation of the Big Bang (beginning on the left) and the proceeding development of the universe.Credit: nasa

Observatories on Earth have detected gravitational waves from colliding black holes and stars, but not yet from the Big Bang.

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According to Hertog, finding evidence of the Big Bang would lend critical support to the idea that other such events created other universes -- a reality that would momentously alter our understanding of space, and ourselves.

"That constitutes a significant extension of our notion of physical reality," Hertog said.

Hertog acknowledged that some cosmologists will argue that a multiverse doesn't exist because it simply can't be tested. But perhaps now, it can.

"This is a very interesting idea that will no doubt stimulate further discussion among early universe researchers," said Avi Loeb, chair of the Harvard Astronomy Department and director of Harvard's Institute for Theory and Computation, in an interview.

Loeb, however, was skeptical about the research roadmap put forward in the forthcoming paper. Hawking, he said, was doing some "preliminary" thinking in his final weeks based upon theories that aren't yet widely accepted.

"It's just an approach that's questionable," said Loeb. "It's not exactly Kosher."

via GIPHY

Previously, some theorists thought the multiverse couldn't be proven false because of the notion that "anything that can happen will happen an infinite number of times," Loeb said.

Hawking and Hertog, at least, provide an argument that the multiverse can eventually be proven true or false.

"I like the Hawking and Hertog concept much more," said Loeb. "But more work is needed to flesh it out in more detail."

Stephen Hawking never won a Nobel Prize for his research. But if future research missions can capture evidence of gravitational waves from the Big Bang passing through our universe -- and potentially lend credence to the wild reality of parallel universes -- it might justify such an award being given to researchers that follow in his path. (Nobel Prizes are not given posthumously.)

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