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


Fed “string theory,” computer reportedly explains our 3D space

Dec. 24, 2011
Courtesy of 
and World Science staff

A long-controversial but pop­u­lar the­o­ry of the uni­verse has en­a­bled a su­per­com­puter to ex­plain why space ap­pears three-di­men­sion­al, some phys­i­cists say.

The hu­man brain can’t really con­ceive of a space with more than three di­men­sions, of­ten called height, width and length. But sci­en­tists say there is no math­e­mat­i­cal rea­son there can’t be more such di­rec­tions. In­deed, a the­o­ry of the uni­verse called su­per­string the­o­ry in­sists there are. What out­weighs this in­con­ven­ience, in the minds of its many pro­po­nents, is that this mod­el man­ages to of­fer a un­ified ex­plana­t­ion for na­ture’s oth­er­wise dis­par­ate build­ing blocks and phys­i­cal forc­es.

Su­per­string the­o­ry vi­su­al­izes the el­e­men­ta­ry par­t­i­cles of na­ture as ti­ny loops that vi­brate like strings. When they move through time, they trace out struc­tures known as world­sheets. The art­ist's con­cep­tion above is de­signed to help il­lus­trate the over­all idea. (Im­age cour­te­sy Flavio Rob­les/L Berke­ley Nat'l Lab)

Su­per­string the­o­ry—which is ac­tu­ally one ver­sion of a group of the­o­ries col­lec­tively called string the­o­ry—asserts that na­ture’s com­po­nent par­t­i­cles can all be rep­re­sented as the dif­fer­ent ways that ti­ny strings can vi­brate in these many di­men­sions. These vibra­t­ional pos­si­bil­i­ties are anal­o­gous to the pos­si­ble notes of a gui­tar or vi­o­lin string.

A fre­quent ob­jec­tion to string the­o­ry is that it’s un­test­a­ble, a crit­i­cism its pro­po­nents of­ten dis­pute, though it has not passed any real-world tests with wide agree­ment.

One thing most phys­i­cists do agree on is that the uni­verse orig­i­nat­ed in an ex­plo­sion from an in­visibly ti­ny point. Var­i­ous ob­serva­t­ions, in­clud­ing that the uni­verse is still ex­pand­ing in a con­tinua­t­ion of this pri­mal burst, sup­port this idea. How­ev­er, sci­en­tists haven’t been able to clar­i­fy how this “Big Bang” hap­pened in de­tail.

In su­per­string the­o­ry, one of the al­lowed string vibra­t­ions cor­re­sponds to a par­t­i­cle that car­ries the force of gra­vity. Su­per­string ad­vo­cates say this fea­ture leads to an­oth­er ad­van­tage: it brings el­e­men­ta­ry par­t­i­cles as a group un­der the reach of Ein­stein’s gen­er­al the­o­ry of rel­a­ti­vity—an ex­tremely pow­er­ful mod­el of the uni­verse, but one that chiefly de­scribes gra­vity and has dif­fi­cul­ty il­lu­mi­nat­ing the world of sub­a­tom­ic par­t­i­cles. By ex­tend­ing its reach in­to that realm, re­search­ers be­lieve they can al­so probe more deeply in­to the na­ture of the Big Bang. 

A re­main­ing stum­bling block has been that cal­cula­t­ions have been un­able to ac­count for com­plica­t­ions re­sult­ing from in­ter­ac­tions among strings them­selves.

In the new stu­dy, phys­i­cists with the High En­er­gy Ac­cel­er­a­tor Re­search Or­gan­iz­a­tion, Shi­zu­o­ka Uni­vers­ity and Osa­ka Uni­vers­ity, all in Ja­pan, said they de­vel­oped a math­e­mat­i­cal meth­od to over­come this last prob­lem. With that, they man­aged to sim­u­late the birth of the uni­verse as though it had started with nine spa­tial di­men­sions, as claimed by su­per­string the­o­ry. 

As the sim­ula­t­ion went on, three of these di­men­sions turned out to un­dergo an ex­pan­sion that would al­low them to be­come vis­i­ble to­day, con­sist­ent with real­ity, the sci­en­tists re­ported. The rest of the di­men­sions re­mained hid­den. String the­o­rists hold that un­seen ex­tra spa­tial di­men­sions are curled up so that they be­come rel­e­vant only at mi­nus­cule scales.

The new find­ings sup­port su­per­string the­o­ry, and are to be pub­lished in the jour­nal Phys­i­cal Re­view Let­ters, said the in­ves­ti­ga­tors, who per­formed work on the su­per­com­puter Hi­tachi SR16000 at Kyo­to Uni­vers­ity. The re­search might al­so be ex­tend­ed to help ex­plain ad­di­tion­al mys­ter­ies, such as why the uni­verse is ex­pand­ing at an ever-growing rate, they added.

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A long-controversial but popular theory of the universe has enabled a supercomputer to explain why space appears three-dimensional, some physicists say. The human brain can’t really conceive of a space with more than three dimensions, often called height, width and length. But scientists say there is no mathematical reason there can’t be more such directions. Indeed, a theory of the universe called superstring theory insists there are. What outweighs this inconvenience, in the minds of its many proponents, is that this model manages to offer a unified explanation for nature’s otherwise disparate building blocks and physical forces. Superstring theory—which is actually one version of a group of theories collectively called string theory—asserts that nature’s component particles can all be represented as the different ways that tiny strings can vibrate in these many dimensions. These vibrational possibilities are analogous to the possible notes of a guitar or violin string. A frequent objection to string theory is that it’s untestable, a criticism its proponents often dispute, though it has not passed any real-world tests with wide agreement. One thing most physicists do agree on is that the universe originated in an explosion from an invisibly tiny point. Various observations, including that the universe is still expanding in a continuation of this primal burst, support this idea. However, scientists haven’t been able to clarify how this “Big Bang” happened in detail. In superstring theory, one of the allowed string vibrations corresponds to a particle that carries the force of gravity. Superstring advocates say this feature leads to another advantage: it brings elementary particles as a group under the reach of Einstein’s general theory of relativity—an extremely powerful model of the universe, but one that chiefly describes gravity and has difficulty illuminating the world of subatomic particles. By extending its reach into that realm, researchers believe they can also probe more deeply into the nature of the Big Bang. A remaining stumbling block has been that calculations have been unable to account for complications resulting from interactions among strings themselves. In the new study, physicists with the High Energy Accelerator Research Organization, Shizuoka University and Osaka University, all in Japan, said they developed a mathematical method to overcome this last problem. With that, they managed to simulate the birth of the universe as though it had started with nine spatial dimensions, as claimed by superstring theory. As the simulation went on, three of these dimensions turned out to undergo an expansion that would allow them to become visible today, consistent with reality, the scientists reported. The rest of the dimensions remained hidden. String theorists hold that unseen extra spatial dimensions are curled up so that they become relevant only at minuscule scales. The new findings support superstring theory, and are to be published in the journal Physical Review Letters, said the investigators, who performed the simulation on the supercomputer Hitachi SR16000 at Kyoto University. The work could also be extended to help explain additional mysteries, such as why the universe is expanding at an ever-growing rate, they added.