“theory of everything”

http://www.world-science.net/othernews/090707_string

A “theory of everything” is said to solve its first real-world problem

July 8, 2009
Courtesy University of Leiden
and World Science staff

For the first time, re­search­ers say they have solved a real-world prob­lem us­ing a very ab­stract “the­ory of ever­ything” that of­ten has been crit­i­cized as un­test­a­ble.

Now, the sci­en­tists claim, the crit­ics may have to re­think their po­si­tion.

The sci­en­tists at­tempted to use the con­tro­ver­sial doc­trine, known as string the­o­ry, to ex­plain an as­pect of super-conducti­vity—a phe­nom­e­non in which elec­tric cur­rent zooms through an ob­ject with­out meet­ing any of the nor­mal re­sist­ance.



‘AdS/CFT’ cor­resp­ond­ence that relates a gra­vity-de­ter­mined world in a higher dimension to 'quan­tum-cri­ti­cal' worlds formed, for ex­am­ple, by elec­trons in a lower-dim­en­sion­al world on the 'out­side' of the first world. (Cour­tesy Sci­ence)


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String the­o­ry is a bid to re­solve al­most all the mys­ter­ies of phys­ics at a b­low by bridg­ing the gap be­tween the two most suc­cess­ful the­o­ries of the 20th cen­tu­ry, gen­er­al rel­a­ti­vity and quan­tum me­chan­ics. Each has been suc­cess­ful at ex­plaining how the un­iverse be­haves over vast dis­tances and in ti­ny spaces, re­spec­tive­ly. But they con­flict in some ways; both can’t be right.

String the­o­ry claims all the par­t­i­cles of na­ture are ac­tu­ally dif­fer­ent vibra­t­ions of un­seen, ti­ny loops called “strings.” The the­o­ry math­e­mat­ic­ally fixes the ma­jor in­con­sis­ten­cies be­tween the oth­er two. In the pro­cess, if it’s cor­rect, it would show the un­der­ly­ing un­ity of na­ture’s forc­es.

But it only works if the strings have sev­er­al ex­tra di­men­sions in which to vi­brate be­yond the di­men­sions we see. Dif­fer­ent ver­sions of string the­o­ry pro­pose 10 or 26 di­men­sions, some of which are in­vis­i­ble be­cause they are rolled up in­to ti­ny balls.

Sci­en­tists at the Un­ivers­ity of Lei­den in the Neth­er­lands used the math­e­mat­ics of string the­o­ry to un­der­stand so-called high-tem­per­a­ture su­per­con­duc­tiv­ity. The ef­fort­less shoot­ing of cur­rent through “su­per­con­duct­ing” ma­te­ri­als was once be­lieved to oc­cur only at tem­per­a­tures so ab­surdly cold as to make prac­ti­cal ap­plica­t­ions of the phe­nom­e­non un­like­ly. But more and more ex­am­ples are com­ing up where it al­so oc­curs at high­er tem­per­a­tures, ac­cord­ing to the Lei­den phys­i­cists.

Elec­trons, the sub­a­tom­ic par­t­i­cles that car­ry elec­tric cur­rent, can form a spe­cial kind of state, a so-called quan­tum crit­i­cal state, that plays a role in this high-tem­per­a­ture super-conducti­vity.

“It has al­ways been as­sumed that once you un­der­stand this quan­tum-crit­i­cal state, you can al­so un­der­stand high tem­per­a­ture super-conducti­vity. But, al­though the ex­pe­ri­ments pro­duced a lot of in­forma­t­ion, we had­n’t the faintest idea of how to de­scribe this phe­nom­e­non,” said Lei­den phys­i­cist Jan Za­a­nen.

String the­o­ry now of­fers a so­lu­tion, he added. “This is su­perb. I have nev­er ex­perienced such eu­pho­ria,” he re­marked, ex­plaining that the num­bers fit so pre­cisely that he was as­ton­ished. The find­ing is re­ported this week in the re­search jour­nal Sci­ence.

Za­a­nen de­scribes the quan­tum-crit­i­cal state as a “quan­tum soup,” where­by the elec­trons form a col­lec­tive in­de­pend­ent of dis­tances, and show the same be­hav­iour at tiny scales or at the roughly hu­man scale.

Be­cause of Za­a­nen’s in­ter­est in string the­o­ry, he and string the­o­reti­cist Koen­raad Schalm be­came ac­quaint­ed af­ter Schalm’s ar­ri­val at Lei­den Un­ivers­ity. Za­a­nen had an un­solved prob­lem and Schalm was an ex­pert in the field of string the­o­ry. Their com­mon in­ter­est brought them to­geth­er, and they de­cid­ed to work jointly.

The pair used the as­pect of string the­o­ry known as Ad­S/CFT cor­re­spond­ence. This al­lows situa­t­ions in a large, so-called rel­a­tivistic, world to be trans­lated in­to a de­scrip­tion at mi­nus­cule, so-called quan­tum phys­ics lev­el. This cor­re­spond­ence bridg­es the gap be­tween these two dif­fer­ent worlds. By ap­ply­ing the cor­re­spond­ence to the the­o­ret­i­cal situa­t­ion where a black hole vi­brates when an elec­tron falls in­to it, they ar­rived at a de­scrip­tion of elec­trons that move in and out of a quan­tum-crit­i­cal state.

This is the first time a cal­cula­t­ion based on string the­o­ry has been pub­lished in Sci­ence, even though the the­o­ry is widely known, Za­a­nen said.

“There have al­ways been a lot of ex­pecta­t­ions sur­round­ing string the­o­ry,” Za­a­nen ex­plained, hav­ing him­self stud­ied the the­o­ry to sat­is­fy his own cu­ri­os­ity. “String the­o­ry is of­ten seen as a child of Ein­stein that aims to de­vise a rev­o­lu­tion­ary and com­pre­hen­sive the­o­ry, a kind of ‘the­o­ry of ever­ything.’ Ten years ago, re­search­ers even said: ‘Give us two weeks and we’ll be able to tell you where the Big Bang came from.’ The prob­lem of string the­o­ry was that, in spite of its ex­cel­lent maths, it was nev­er able to make a con­crete link with the phys­i­cal real­ity—the world around us.”

“Ad­S/CFT cor­re­spond­ence now ex­plains things that col­leagues who have been bea­ver­ing away for ages were un­able to re­solve, in spite of their enor­mous ef­forts,” he went on. “There are a lot of things that can be done with it. We don’t fully un­der­stand it yet, but I see it as a gate­way to much more.”