Are we really in a bubble?

For the first time, cosmologists are attempting to test the multiverse theory – the idea that multiple alternative universes exist inside their own bubbles. [caption id="" align="alignleft" width="200" caption="Signatures of a bubble collision at various stages in the analysis pipeline. A collision (top left) induces a temperature modulation in the CMB temperature map (top right). The 'blob' associated with the collision is identified by a large needlet response (bottom left), and the presence of an edge is highlighted by a large response from the edge detection algorithm (bottom right) Credit Stephen Feeney/UCL"][/caption]

Any modern theories of fundamental physics predict that our own universe is contained inside a bubble, and that the multiverse will contain other bubbles, each containing a universe. But until now, no-one has known how to efficiently search for signs of bubble universe collisions – and therefore proof of the multiverse.

However, scientists from University College London, Imperial College London and the Perimeter Institute of Theoretical Physics have detailed how to search for signatures of other universes in the cosmic microwave background (CMB) radiation. Physicists are now looking for disk-like patterns which could provide tell-tale evidence of collisions between other universes.

“It’s a very hard statistical and computational problem to search for all possible radii of the collision imprints at any possible place in the sky,” said Dr Hiranya Peris from UCL. “But that’s what pricked my curiosity.”

The team ran simulations of how the sky would look with and without cosmic collisions and developed an algorithm to determine which fits best with CMB data from NASA’s Wilkinson Microwave Anisotropy Probe (WMAP).

The algorithm – created by UCL PhD student Stephen Feeney – imposes very strict rules on whether the data fits a pattern or whether the pattern is down to chance. This avoids human cherry-picking patterns in data that might just be coincidental.

“It’s all too easy to over-interpret interesting patterns in random data,” said Dr Daniel Mortlock from Imperial. “We took great care to assess how likely it was that possible bubble collision signatures we found could have arisen by chance.”

The research – published in Physical Review Letters and Physical Review D – is not conclusive enough to rule out the multiverse, or to definitively detect bubble collision imprints. However, new data from ESA’s Planck satellite could help solve the problem.

“The work represents an opportunity to test a theory that is truly mind-blowing: that we exist within a vast multiverse, where other universes are constantly popping into existence,” said Feeney.