"Long before it's in the papers"
January 27, 2015


Scientists testing theory that there are multiple universes

Aug. 4, 2011
Courtesy of University College London
and World Science staff

A group of phys­i­cists claims to be con­duct­ing the first test of a the­o­ry that holds our uni­verse is just one of many.

Their re­sults? Poss­ible evi­dence in sup­port of the the­ory has been found, but more da­ta re­mains to be ex­am­ined, they re­port.

They’re look­ing for disk-like pat­terns in the cos­mic mi­cro­wave back­ground radia­t­ion—a type of heat radia­t­ion that per­me­ates the skies and is be­lieved to be left over from the Big Bang, an ex­plo­sive event that gave birth to our uni­verse. These pat­terns could pro­vide tell-tale ev­i­dence of col­li­sions be­tween oth­er uni­verses and our own, the re­search­ers ex­plain.

The re­search is de­scribed in pa­pers pub­lished in the jour­nals Phys­i­cal Re­view Let­ters and Phys­i­cal Re­view D

An in­i­tial pro­pos­al de­scrib­ing the idea be­hind such tests was pub­lished in the lat­ter jour­nal in 2007. Many mod­ern the­o­ries of fun­da­men­tal phys­ics pre­dict that our uni­verse is in a bub­ble, and that there are oth­er bub­bles con­tain­ing oth­er uni­verses, per­haps with dif­fer­ent laws of na­ture. The search for disk-like pat­terns is based on the no­tion that uni­verses might knock to­geth­er. These bumps could then leave round “bruis­es” on the sur­face of each col­lid­ing uni­verse, like two pears that have been smacked to­geth­er. These marks would al­so be re­flected in the mi­cro­wave back­ground—specifically, in the maps that astron­om­ers have put to­geth­er show­ing temp­er­ature vari­a­tions in this ra­dia­tion at diff­erent points ac­ross the sky.

One prob­lem was that be­fore now, it was hard to search for the disk-like pat­terns be­cause they could be any­where in the sky—and have any size. Phys­i­cists al­so needed to be able to test wheth­er any pat­terns they de­tected were really the re­sult of col­li­sions or just flukes in the da­ta. “It’s a very hard sta­tis­ti­cal and com­puta­t­ional prob­lem,” said Hiran­ya Peiris of Uni­vers­ity Col­lege Lon­don, co-author of the re­search. “But that’s what pricked my cu­ri­os­ity.”

Peiris and col­leagues from Im­pe­ri­al Col­lege Lon­don and the Pe­rim­e­ter In­sti­tute for The­o­ret­i­cal Phys­ics in Wa­ter­loo, On­tar­i­o, ran sim­ula­t­ions of what the sky would look like with and with­out col­li­sions. The find­ings al­so pro­vided an up­per lim­it on how many such bub­ble col­li­sion signa­tures there could be, the sci­en­tists said.

“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 Uni­vers­ity Col­lege Lon­don doc­tor­al stu­dent Ste­phen Feeney, a col­la­bo­ra­tor on the re­search. Feeney cre­at­ed a for­mu­la to de­ter­mine wheth­er a mod­el with or with­out col­li­sions would bet­ter fit a wealth of cos­mic mi­cro­wave back­ground da­ta from NASA’s Wilkin­son Mi­cro­wave An­i­sot­ro­py Probe space­craft.

One of dilem­mas fac­ing phys­i­cists is that hu­mans are very good at no­tic­ing pat­terns that may be there only by co­in­ci­dence. But the new for­mu­la is de­signed to be very hard to fool, im­pos­ing very strict rules on wheth­er the da­ta fits a pat­tern or wheth­er the pat­tern is down to chance. “It’s all too easy to over-interpret in­ter­est­ing pat­terns in ran­dom da­ta, like the ‘face on Mars’ that, when viewed more close­ly, turned out to just a nor­mal moun­tain,” not­ed Im­pe­ri­al Col­lege’s Dan­iel Mort­lock, a co-author of the re­search.

The search based on da­ta from the NASA probe has turned up four candidate areas in the micro­wave back­ground that could be the sig­nature of a col­lision, ac­cord­ing to the re­search­ers. But noise in the data makes a definitive conclusion impossible, they added; new da­ta cur­rently com­ing in from the Eu­ro­pe­an Space Agen­cy’s Planck sat­el­lite should help solve the puz­zle.

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A group of physicists claims to be conducting the first test of a theory that holds our universe is just one of many. Their results? Inconclusive so far, but more data remains to be examined, they report. They’re looking for disk-like patterns in the cosmic microwave background radiation—a type of heat radiation that permeates the skies and is believed to be left over from the Big Bang, an explosive event that gave birth to our universe. These patterns could provide tell-tale evidence of collisions between other universes and our own, the researchers explain. The research is described in papers published in the journals Physical Review Letters and Physical Review D. An initial proposal describing the idea behind such tests was published in the latter journal in 2007. Many modern theories of fundamental physics predict that our universe is in a bubble, and that there are other bubbles containing other universes, perhaps with different laws of nature. The search for disk-like patterns is based on the notion that universes might knock together. They could then leave round “bruises” on the surface of each colliding universe, like two pears that have been smacked together. These marks would also be reflected in the microwave background. One problem was that before now, it was hard to search for the disk-like patterns because they could be anywhere in the sky—and have any size. Physicists also needed to be able to test whether any patterns they detected were really the result of collisions or just flukes in the data. “It’s a very hard statistical and computational problem,” said Hiranya Peiris of University College London, co-author of the research. “But that’s what pricked my curiosity.” Peiris and colleagues from Imperial College London and the Perimeter Institute for Theoretical Physics in Waterloo, Ontario, ran simulations of what the sky would look like with and without collisions. The findings also provided an upper limit on how many such bubble collision signatures there could be, the scientists said. “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 University College London doctoral student Stephen Feeney, a collaborator on the research. Feeney created a formula to determine whether a model with or without collisions would better fit a wealth of cosmic microwave background data from NASA’s Wilkinson Microwave Anisotropy Probe spacecraft. One of dilemmas facing physicists is that humans are very good at noticing patterns that may be there only by coincidence. But the new formula is designed to be very hard to fool, imposing very strict rules on whether the data fits a pattern or whether the pattern is down to chance. “It’s all too easy to over-interpret interesting patterns in random data, like the ‘face on Mars’ that, when viewed more closely, turned out to just a normal mountain,” noted Imperial College’s Daniel Mortlock, a co-author of the research. The search based on data from the NASA probe has been inconclusive, the team added, but new data currently coming in from the European Space Agency’s Planck satellite should help solve the puzzle.