Washington: Is our universe just one of many? The idea may sound a bit bizarre, but it could be a reality, scientists say.

The possibility that we live in a multiverse arises from a theory called eternal inflation, which posits that shortly after the Big Bang that formed the universe, space-time expanded at different rates in different places, giving rise to bubble universes that may function with their own separate laws of physics.

The idea has seemed purely hypothetical until now. In a new study, published in the journals Physical Review Letters and Physical Review D, a team of researchers suggested that if our universe has siblings, we may have bumped into them.

Such collisions, they said, would have left lasting marks in the cosmic microwave background (CMB) radiation, the diffuse light left over from the Big Bang that pervades the universe, LiveScience reported.

"It brings the idea of eternal inflation and bubble collisions into the realm of testable science," said research team member Daniel Mortlock, an astrophysicist at Imperial College London. "If it's not testable, it's hard to even call it science."

Mortlock and the team looked for the best available CMB observations for signs of bubble universe collisions, but didn't find anything conclusive.

If two universes had collided, it would have left a circular pattern behind in the cosmic microwave background, they said.
"If you imagine two ordinary soap bubbles colliding, then the surface where they intersect is going to be a circle, so that's the key signature we're looking for in the CMB," Mortlock said.

For their study, the researchers developed a computer algorithm to analyse CMB observations for patterns that would fit. In data from NASA's Wilkinson Microwave Anisotropy Probe (WMAP), the programme found four regions in the universe that were flagged as promising.

However, statistical analyses suggested these patterns were likely to be random, resembling the circular shapes of collisions simply by coincidence.

The idea of other universes out there is mind-bending, but scientists say in some ways it actually makes sense.
"It helps explain some of the strange coincidences about our own universe," Mortlock said. "Why is our universe so amenable to life?"

Many of the fundamental constants in our universe, such as the strength of gravity and the speed of light, seem perfectly calibrated to produce a universe in which galaxies, stars, planets and even life can form.

If any of these constants had been tweaked at all, the universe would likely be empty, with no stars and no life. But if our universe is one of many, then the fact that it's so perfectly tuned for life isn't such an unlikely coincidence.

"One possibility is there are multiple different universes with different laws, and some are not right for life and so life doesn't evolve, and some are right for life and so creatures evolve and make measurements and ask deep, twisty questions like this," Mortlock said. "For that reason [the theory] is very appealing."