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October 25, 2007

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Cosmic anomaly could point to ultimate realities

Oct. 25, 2007
Special to World Science  

An en­ig­mat­ic “cold spot” thought to have marked the in­fant un­iverse—and ac­cord­ing to one stu­dy, as­so­ci­at­ed with a giant void to­day—may re­sult from an ex­ot­ic, long-sought struc­ture called a cos­mic de­fect, a team of sci­en­tists say.

If so, this could be a mo­men­tous find­ing, be­cause such a de­fect is be­lieved to re­flect the way the var­i­ous types of forc­es in na­ture emerged from what once was a sin­gle, un­der­ly­ing force.

De­fect stru­ctures can be beau­ti­ful, as il­lus­tra­ted by this mag­ni­fi­ca­tion of such struc­tures in a li­quid crys­tal—a type of flu­id, used in app­li­ca­tions such as flat-panel dis­plays, marked by re­la­tive­ly or­der­ly ar­range­ment of its mo­le­cules. The "knots" arise from the way crys­tals in the sub­s­tance are ori­ent­ed dif­fer­ently in dif­fer­ent areas. Cos­mo­lo­gists the­o­r­ize that some­thing an­alo­gous may have oc­curred on a cos­mic scale. (Image cour­te­sy Ol­eg D. La­v­ren­to­vich, Kent State Uni­ver­si­ty).

A cos­mic de­fect is like a cloudy spot in an ice cu­be. This arises be­cause wa­ter, so­lid­i­fy­ing, crys­tal­lizes dif­fer­ently in dif­fer­ent ar­eas. Si­m­i­lar forma­t­ions, known as crys­tal de­fects, oc­cur in many sub­stances dur­ing so­lidifica­t­ion, due to im­pur­i­ties and oth­er causes. The pro­cess is al­so called “sym­me­try break­ing,” be­cause the sub­stance loses its orig­i­nal qual­ity of be­ing bas­ic­ally the same in eve­ry di­rec­tion.

Cos­mol­o­gists spec­u­late that a grander ver­sion of such a de­fect—a cos­mic de­fect—could have aris­en when atoms first co­a­lesced out of the amor­phous soup the un­iverse once was. Such a tran­si­tion is, like so­lidifica­t­ion, called a phase change, be­cause it in­volves a switch be­tween two states of mat­ter.

But in the cos­mic case, the “sym­me­try break­ing” would in­volve a separa­t­ion of two or more forc­es out of what orig­i­nally was one. Cos­mol­o­gists have been the­o­riz­ing for dec­ades on how na­ture’s forc­es—four types are ac­knowl­edged—could have aris­en from a pri­mor­di­al one. This quest is driv­en largely by a deep-seat­ed feel­ing that sim­ple ex­plana­t­ions of real­ity are just more like­ly, and pleas­ing, than messy, mul­ti­fac­et­ed ones.

So now, re­search­ers say they’ve iden­ti­fied a pos­si­ble cos­mic de­fect.

"It will be very in­ter­est­ing to see wheth­er this ten­ta­tive ob­serva­t­ion firms up in com­ing years. If it does, the im­plica­t­ions will be ex­tra­or­di­nary,” said Neil Tur­ok of the Un­ivers­ity of Cam­bridge in the U.K., one of the re­search­ers. The de­fect’s prop­er­ties would “pro­vide an ab­so­lutely un­ique win­dow” on­to the ul­ti­mate na­ture of mat­ter and the forc­es gov­ern­ing it, he added. The find­ings ap­pear on­line Oct. 25 in the re­search jour­nal Sci­ence.

A cos­mic de­fect would have formed when the un­iverse was vastly hot­ter than to­day. But sci­en­tists can’t rec­re­ate such high tem­per­a­tures in the lab­o­r­a­to­ry, and this has be­dev­iled ef­forts to test the var­i­ous the­o­ries of this “u­nifica­t­ion” of forc­es. The char­ac­ter­is­tics of a de­fect could shed much light on this, Turok ex­plained.

A half-sky map of slight tem­per­a­ture vari­a­tions in the cos­mic mi­cro­wave back­ground ra­di­a­tion, thought to map struc­tures in the very ear­ly uni­verse. Blue stands for colder ar­eas; red for hot­ter re­gions, where it's be­lieved mat­ter was dens­er. These dense re­gions are thought to have lat­er be­come ga­laxy-rich zones. The boxed ar­ea marks an un­u­su­al "cold spot" re­search­ers rec­og­nize in the da­ta. (Im­age cour­te­sy WMAP Sci­ence Team, NA­SA)

The team de­vel­oped its pro­pos­al af­ter stu­dying a strik­ing “cold spot” in the so-called cos­mic mi­cro­wave back­ground, a faint back­ground glow that per­me­ates the un­iverse. 

The mi­cro­wave back­ground is thought to come from the sur­face of what could be called the fire­ball of the Big Bang, a sort of ex­plo­sion that as­tro­no­mers believe gave birth to the universe. 

This surface re­mains vis­i­ble be­cause some of its light waves are just reach­ing us now. The sur­face also rep­re­sents the tran­si­tion from when the un­iverse was a fog­gy, amor­phous soup to when it cooled down and atoms co­a­lesced out of the mix, clear­ing up the view. The mi­cro­wave back­ground is thus con­sid­ered our ear­li­est ba­by pic­ture of the un­iverse, at about 300,000 years of age. 

The radia­t­ion varies faintly in tem­per­a­ture from point to point. These fluctua­t­ions are thought to re­flect dif­fer­ences in the dens­ity of mat­ter: it was hot­ter in more com­pact ar­eas, chil­li­er in spars­er zones. The dens­er ones are be­lieved to have lat­er co­a­lesced in­to ga­lax­ies, where­as a large cold zone could be­come a rel­a­tively emp­ty space.

In­deed, one study has found that the “cold spot,” in the di­rec­tion of the con­stella­t­ion Erid­a­nus, cor­re­sponds to a vast, anom­a­lous “su­per­void” be­reft of ga­lax­ies to­day. But Tur­ok said ques­tions have aris­en about wheth­er there is really an un­usu­ally large def­i­cit of ga­lax­ies there.

In any case, re­search on the cold spot is now in­ter­sect­ing with the­o­ret­i­cal work done since the 1970s on what could have tran­spired at the cos­mic tran­si­tion when atoms formed. Par­t­i­cle phys­i­cists de­ter­mined that var­i­ous sorts of de­fects should have de­vel­oped as dif­fer­ent par­t­i­cles sep­a­rat­ed from the hot soup, or plas­ma, Tur­ok said.

One such de­fect, known as a tex­ture, is “a three-di­men­sion­ ob­ject like a blob of en­er­gy. But with­in the blob the en­er­gy fields mak­ing up the tex­ture are twisted up,” ac­cord­ing to Turok. Tex­tures and oth­er de­fects should be de­tect­a­ble as tem­per­a­ture varia­t­ions in the cos­mic mi­cro­wave back­ground, he went on.

If the cold spot is a tex­ture, “it would al­low us to dis­crim­i­nate among dif­fer­ent the­o­ries” pro­posed for how the un­iverse evolved, said Mar­cos Cruz of the In­sti­tuto de Fi­sica de Can­ta­bria, in San­tan­der, Spain, a mem­ber of the re­search team. Cruz and his col­leagues had been puz­zling over the cold spot’s pos­si­ble ori­gins and brought the prob­lem to Turok when they found the prob­lem de­fied all ex­plana­t­ions oth­er than a de­fect. Turok agreed the spot had the prop­er­ties that would be ex­pected if a tex­ture had caused it.

Some anomaly in the cos­mic mi­cro­wave back­ground has al­so been pro­posed to pos­sibly re­sult from a col­li­sion with anoth­er un­iverse. But that pos­sibil­ity is con­sid­ered more spec­u­la­tive, and its pro­po­nents have de­clined to spe­cif­ic­ally im­plicate the cold spot.

"We're not cer­tain this is a tex­ture by any means,” ei­ther, said Tur­ok. One pos­sibil­ity is that it’s simply a ran­dom, es­sen­tially mean­ing­less fluctua­t­ion in the mi­cro­wave back­ground, he not­ed, but the chance of a ran­dom one be­ing so large is only about one per­cent. “There are a num­ber of fol­low-up checks which can now be done. So the tex­ture hy­poth­e­sis is ac­tu­ally very testable," said Turok.

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An enigmatic “cold spot” thought to have marked the infant universe—and according to one study, associated with a huge void in today’s cosmos—may result from an exotic, long-sought structure called a cosmic defect, a team of scientists say. If so, this could be a momentous finding, because such a defect is believed to reflect the way the various types of forces in nature emerged from what once was a single, underlying force. A cosmic defect is like a cloudy spot in an ice cube. This arises because water, solidifying, crystallizes differently in different areas. Similar formations, known as crystal defects, occur in many substances during solidification, due to impurities and other causes. The process is also called “symmetry breaking,” because the substance loses its original quality of being basically the same in every direction. Cosmologists speculate that a grander version of such a defect—a cosmic defect—could have arisen when atoms first coalesced out of the amorphous soup the universe once was. Such a transition is, like solidification, called a phase change, because it involves a switch between two states of matter. But in the cosmic case, the “symmetry breaking” would involve a separation of two or more forces out of what originally was one. Cosmologists have been theorizing for decades on how nature’s forces—four types are acknowledged—could have arisen from a primordial one. That quest is driven largely by a deep-seated feeling that simple explanations of reality are just more likely, and pleasing, than messy, multifaceted ones. So now, researchers say they’ve identified a possible cosmic defect. "It will be very interesting to see whether this tentative observation firms up in coming years. If it does, the implications will be extraordinary,” said Neil Turok of the University of Cambridge in the U.K., one of the researchers. The defect’s properties would “provide an absolutely unique window” onto the ultimate nature of matter and the forces governing it, he added. The findings appear online Oct. 25 in the research journal Science. A cosmic defect would have formed when the universe was vastly hotter than today. But scientists can’t recreate such high temperatures in the laboratory, and this has bedeviled efforts to test the various theories of this “unification” of forces. The characteristics of a defect could shed much light on this, Turok explained. The team developed its proposal after studying a striking “cold spot” in the so-called cosmic microwave background, a faint background glow that permeates the universe. The microwave background is thought to come from the surface of what could be called the Big Bang fireball, which remains visible because some of its light waves are just reaching us now. That surface represents the transition from when the universe was a foggy, amorphous soup to when it cooled down and atoms coalesced out of the mix, clearing up the view. The microwave background is thus considered our earliest baby picture of the universe, at about 300,000 years of age. The radiation varies faintly in temperature from point to point. These fluctuations are thought to reflect differences in the density of matter: it was hotter in more compact areas, chillier in sparser zones. The denser ones are believed to have later coalesced into galaxies, whereas a large cold zone could become a relatively empty space. Indeed, one study has found that the “cold spot,” in the direction of the constellation Eridanus, corresponds to a vast, anomalous “supervoid” bereft of galaxies today. But Turok said questions have arisen about whether there is really an unusually large deficit in galaxies there. In any case, research on the cold spot is now intersecting with theoretical work done since the 1970s on what could have transpired at the cosmic transition time when atoms formed. Particle physicists determined that various sorts of defects should have developed as different particles separated from the hot plasma of the infant universe, Turok said. One such defect, known as a texture, is “a three-dimensional object like a blob of energy. But within the blob the energy fields making up the texture are twisted up,” according to Turok. Textures and other defects should be detectable as temperature variations in the cosmic microwave background, he went on. If the cold spot is a texture, “it would allow us to discriminate among different theories that have been proposed for how the universe evolved,” said Marcos Cruz of the Instituto de Fisica de Cantabria, in Santander, Spain, a member of the research team. Cruz and his colleagues had been puzzling over the cold spot’s possible origins and brought the problem to Turok when they found the problem defied all explanations other than a defect. Turok agreed that spot had the properties that would be expected if a texture had caused it. Some anomaly in the cosmic microwave background has also been proposed to possibly result from a collision with another universe. But that possibility is considered more speculative, and its proponents have declined to specifically implicate the cold spot. "We're not certain this is a texture by any means,” either, said Turok. One possibility is that it’s simply a random, essentially meaningless fluctuation in the microwave background, he noted, but the chance of a random one being so large is only about one percent. “There are a number of follow-up checks which can now be done. So the texture hypothesis is actually very testable," said Turok.