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".
BBC News - 'Multiverse' theory suggested by microwave background