'Multiverse' theory suggested by microwave background

The idea that other universes - as well as our own - lie within "bubbles" of space and time has received a boost.

Studies of the low-temperature glow left from the Big Bang suggest that several of these "bubble universes" may have left marks on our own.

This "multiverse" idea is popular in modern physics, but experimental tests have been hard to come by.

The preliminary work, to be published in Physical Review D, will be firmed up using data from the Planck telescope.

For now, the team has worked with seven years' worth of data from the Wilkinson Microwave Anisotropy Probe, which measures in minute detail the cosmic microwave background (CMB) - the faint glow left from our Universe's formation.

The theory that invokes these bubble universes - a theory formally called "eternal inflation" - holds that such universes are popping into and out of existence and colliding all the time, with the space between them rapidly expanding - meaning that they are forever out of reach of one another.

But Hiranya Peiris, a cosmologist at University College London, and her colleagues have now worked out that when these universes are created adjacent to our own, they may leave a characteristic pattern in the CMB.

"I'd heard about this 'multiverse' for years and years, and I never took it seriously because I thought it's not testable," Dr Peiris told BBC News. "I was just amazed by the idea that you can test for all these other universes out there - it's just mind-blowing."

Dr Peiris' team first proposed these disc-shaped signatures in the CMB in a paper published in Physical Review Letters, and the new work fleshes out the idea, putting numbers to how many bubble universes we may be able to see now.

Crucially, they used a computer program that looked for these discs automatically - reducing the chance that one of the collaborators would see the expected shape in the data when it was not in fact there.

The program found four particular areas that look likely to be signatures of the bubble universes - where the bubbles were 10 times more likely than the standard theory to explain the variations that the team saw in the CMB.

However, Dr Peiris stressed that the four regions were "not at a high statistical significance" - that more data would be needed to be assured of the existence of the "multiverse".

"Finding just four patches is not necessarily going to give you a good probability on the full sky," she explained to BBC News. "That's not statistically strong enough to either rule it out or to say that there is a collision."

Dr Peiris said that data from the Planck telescope - a next-generation space telescope designed to study the CMB with far greater sensitivity - would put the idea on a firmer footing, or refute it. However, the data from Planck cannot be discussed publicly before January 2013.

George Efstathiou, director of the Kavli Institute of Cosmology at the University of Cambridge, called the work "the first serious attempt to search for something like this... from the methodology point of view it's interesting".

He noted that the theories that invoked the multiverse were fraught with problems, because they dealt in so many intangible or immeasurable quantities.

"My own personal view is that it will need new physics to solve this problem," he told BBC News. "But just because there are profound theory difficulties doesn't mean one shouldn't take the picture seriously."

Dr Peiris said that even if these bubble universes were confirmed, we could never learn anything further about them.

"It would be wonderful to be able to go outside our bubble, but it's not going to be possible," she explained.

"They're born close together - that's when the collision happens - and this same inflation happens between the bubbles. They're being hurled apart and space-time is expanding faster than light between them."

But Professor Efstathiou said the search was inherently worth it. He explained: "It would be a pretty amazing thing to show that we have actually made physical contact in another universe. It's a long shot, but it would be very profound for physics."