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


Particle smasher might also act as time machine, scientists say

March 30, 2005
Courtesy of David Salisbury/Vanderbilt University
and World Science staff

The world’s larg­est par­t­i­cle col­lider may al­so be the first ma­chine that can make things trav­el back­wards in time, two sci­en­tists say. 

“Our the­o­ry is a long shot,” ad­mits Tom Weiler, a phys­i­cist at Van­der­bilt Un­ivers­ity in Nash­ville, Tenn., “but it does­n’t vi­o­late any laws of phys­ics or ex­pe­ri­men­tal con­straints.”

A composite illustration of the Large Had­ron Col­li­der, the world's most power­ful par­ticle ac­ce­ler­ator. Shown in the back­ground is the land­scape on the French-Swiss border where the ac­celer­at­or lies un­der­ground. (Courtesy CERN)

Par­t­i­cle col­liders are de­signed to smash atoms or sub­a­tom­ic par­t­i­cles to find out what com­po­nents make them up. The world’s larg­est such de­vice, the Switzerland-based Large Had­ron Col­lider, went in­to opera­t­ion in 2009 and is al­so in­tend­ed to pos­sibly re­veal the ex­ist­ence of a sub­a­tom­ic par­t­i­cle called the Higgs bos­on. This is an ent­ity that phys­i­cists in­voke to ex­plain why oth­er com­po­nents of atoms have mass, or in plainer terms, weight.

If the col­lider suc­ceeds in pro­duc­ing the Higgs bos­on, some sci­en­tists pre­dict it will al­so cre­ate a sec­ond par­t­i­cle, called the Higgs sin­glet. Weiler and col­league Chu Ma­n Ho, al­so of Van­der­bilt, the­o­rize that these sin­glets should be able to jump in­to an ex­tra, fifth di­men­sion where they can move ei­ther for­ward or back­ward in time and re­ap­pear in the fu­ture or past.

The the­o­ry “avoids all the big para­dox­es” that nor­mally come up with time trav­el, Weiler said. “Be­cause time trav­el is lim­it­ed to these spe­cial par­t­i­cles, it is not pos­sible for a man to trav­el back in time and mur­der one of his par­ents be­fore he him­self is born, for ex­am­ple. How­ev­er, if sci­en­tists could con­trol the pro­duc­tion of Higgs sin­glets, they might be able to send mes­sages to the past or fu­ture.”

The test of the re­search­ers’ the­o­ry will be wheth­er the phys­i­cists mon­i­tor­ing the col­lider beg­in see­ing Higgs sin­glet par­t­i­cles ap­pear­ing spon­ta­ne­ously along with prod­ucts of their own de­cay, or break­down. If they do, Weiler and Ho be­lieve that they will have been pro­duced by par­t­i­cles that trav­el back in time to ap­pear be­fore the col­li­sions that pro­duced them.

Weiler and Ho’s the­o­ry is based on a so-called “the­o­ry of ev­ery­thing” called M-the­o­ry. A small ca­dre of the­o­ret­i­cal phys­i­cists have de­vel­oped M-the­o­ry to the point that it can ac­com­mo­date the prop­er­ties of all the known sub­a­tom­ic par­t­i­cles and forc­es, in­clud­ing gra­vity, but it re­quires 10 or 11 di­men­sions in­stead of our fa­mil­iar four. This has led to the sug­ges­tion that our un­iverse may be like a four-di­men­sional mem­brane, called a “brane” float­ing in a mul­ti­-di­men­sional space-time called the “bulk.”

Ac­cord­ing to this view, the bas­ic build­ing blocks of our un­iverse are perma­nently stuck to the brane and so can­not trav­el in oth­er di­men­sions. There are some ex­cep­tions, how­ev­er. Some ar­gue that gra­vity, for ex­am­ple, is weaker than oth­er fun­da­men­tal forc­es be­cause it spreads out in­to oth­er di­men­sions. Anoth­er pos­sible ex­cep­tion is the pro­posed Higgs sin­glet, which re­sponds to gra­vity but not to any of the oth­er bas­ic forc­es.

Weiler be­gan look­ing at time trav­el six years ago to ex­plain anoma­lies seen in sev­er­al ex­pe­ri­ments with neu­tri­nos. Neu­tri­nos are nick­named ghost par­t­i­cles be­cause they re­act rarely with or­di­nary mat­ter: Tril­lions of neu­tri­nos hit our bod­ies eve­ry sec­ond, yet we don’t no­tice them be­cause they zip through with­out af­fect­ing us.

Weiler and col­leagues Hein­rich Päs and Sandip Pak­vasa at the Un­ivers­ity of Ha­waii de­vised an ex­plana­t­ion of the anoma­lies based on the ex­ist­ence of a hy­po­thet­i­c par­t­i­cle called the ster­ile neu­tri­no. In the­o­ry, ster­ile neu­tri­nos are even less detecta­ble than reg­u­lar neu­tri­nos be­cause they in­ter­act only with gravita­t­ional force. As a re­sult, ster­ile neu­tri­nos are anoth­er par­t­i­cle un­bound to the brane and thus the­o­ret­ic­ally capa­ble of trav­eling through ex­tra di­men­sions.

Weiler, Päs and Pak­vasa pro­posed that ster­ile neu­tri­nos trav­el faster than light by tak­ing short­cuts through ex­tra di­men­sions. Ac­cord­ing to Ein­stein’s gen­er­al the­o­ry of rel­a­ti­vity, there are cer­tain con­di­tions in which trav­eling faster than the speed of light is equiv­a­lent to trav­eling back­ward in time.

Weiler and Ho de­scribed their new re­search in a pa­per posted March 7 on the re­search web­site arX­

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The world’s largest particle collider may also be the first machine that can make things travel backwards in time, two scientists say. “Our theory is a long shot,” admits Tom Weiler, a physicist at Vanderbilt University in Nashville, Tenn., “but it doesn’t violate any laws of physics or experimental constraints.” Particle colliders are designed to smash atoms or subatomic particles to find out what components make them up. The world’s largest such device, the Switzerland-based Large Hadron Collider, went into operation last year and is also intended to possibly reveal the existence of a subatomic particle called the Higgs boson. This is an entity that physicists invoke to explain why other components of atoms have mass, or in plainer terms, weight. If the collider succeeds in producing the Higgs boson, some scientists predict it will also create a second particle, called the Higgs singlet. Weiler and colleague Chu Man Ho, also of Vanderbilt, theorize that these singlets should be able to jump into an extra, fifth dimension where they can move either forward or backward in time and reappear in the future or past. The theory “avoids all the big paradoxes” that normally come up with time travel, Weiler said. “Because time travel is limited to these special particles, it is not possible for a man to travel back in time and murder one of his parents before he himself is born, for example. However, if scientists could control the production of Higgs singlets, they might be able to send messages to the past or future.” The test of the researchers’ theory will be whether the physicists monitoring the collider begin seeing Higgs singlet particles appearing spontaneously along with products of their own decay, or breakdown. If they do, Weiler and Ho believe that they will have been produced by particles that travel back in time to appear before the collisions that produced them. Weiler and Ho’s theory is based on a so-called “theory of everything” called M-theory. A small cadre of theoretical physicists have developed M-theory to the point that it can accommodate the properties of all the known subatomic particles and forces, including gravity, but it requires 10 or 11 dimensions instead of our familiar four. This has led to the suggestion that our universe may be like a four-dimensional membrane, called a “brane” floating in a multi-dimensional space-time called the “bulk.” According to this view, the basic building blocks of our universe are permanently stuck to the brane and so cannot travel in other dimensions. There are some exceptions, however. Some argue that gravity, for example, is weaker than other fundamental forces because it spreads out into other dimensions. Another possible exception is the proposed Higgs singlet, which responds to gravity but not to any of the other basic forces. Weiler began looking at time travel six years ago to explain anomalies seen in several experiments with neutrinos. Neutrinos are nicknamed ghost particles because they react rarely with ordinary matter: Trillions of neutrinos hit our bodies every second, yet we don’t notice them because they zip through without affecting us. Weiler and colleagues Heinrich Päs and Sandip Pakvasa at the University of Hawaii devised an explanation of the anomalies based on the existence of a hypothetical particle called the sterile neutrino. In theory, sterile neutrinos are even less detectable than regular neutrinos because they interact only with gravitational force. As a result, sterile neutrinos are another particle unbound to the brane and thus theoretically capable of traveling through extra dimensions. Weiler, Päs and Pakvasa proposed that sterile neutrinos travel faster than light by taking shortcuts through extra dimensions. According to Einstein’s general theory of relativity, there are certain conditions in which traveling faster than the speed of light is equivalent to traveling backward in time. Weiler and Ho described their new research in a paper posted March 7 on the research website