Mak­ing gi­ant strides

Arab News - - OPINION -

of GW150914, the length changed by less than one-thou­sandth of the size of a pro­ton.

The chal­lenges in de­tect­ing such a small change were enor­mous, given the var­i­ous types of noise that could in­flu­ence the mea­sure­ment and de­stroy its in­tegrity. LIGO dug the tiny, short chirp out from the om­nipresent chaos of space by com­par­ing the mea­sure­ments of the two in­ter­fer­om­e­ters. The noise at one is not cor­re­lated with the noise at the other —un­like the sig­nal from a pass­ing grav­i­ta­tional wave, which would oc­cur first at one lo­ca­tion and then the other. The sig­nal from GW150914 co­in­cided with such im­pres­sive ac­cu­racy that any pos­si­bil­ity of it be­ing a spu­ri­ous chance event was ex­cluded.

LIGO’s success is not only a tri­umph of tech­nol­ogy; it is also — and more im­por­tantly — the re­sult of a cen­tury of work by the­o­rists on math­e­mat­i­cal de­scrip­tions of grav­i­ta­tional waves — not just Ein­stein, but also Leopold In­feld, Joshua Gold­berg, Richard Feyn­man, Felix Pi­rani, Ivor Robin­son, Her­mann Bondi, and An­dré Lich­nerow­icz.

LIGO’s dis­cov­ery, specif­i­cally, was made pos­si­ble by the Pol­ish physi­cist An­drzej Traut­man, who pro­vided grav­i­ta­tional wave the­ory with sharp math­e­mat­i­cal rigor, and the French physi­cist Thibault Damour, who de­vel­oped prac­ti­cal math­e­mat­i­cal tools for us­ing ob­served wave fronts to de­ci­pher in­for­ma­tion about the waves’ sources. Their work es­tab­lished the solid math­e­mat­i­cal base of the the­ory that made the success of LIGO pos­si­ble.

Ein­stein’s The­ory of Gen­eral Rel­a­tiv­ity is mankind’s great­est in­tel­lec­tual achieve­ment. And yet no­body has re­ceived a No­bel Prize for de­vel­op­ing its math­e­mat­i­cal foun­da­tions. The prize has been given to ex­per­i­men­tal physi­cists who made ob­ser­va­tional con­fir­ma­tions of some of the the­ory’s im­por­tant pre­dic­tions. And it has been given to quan­tum physi­cists for purely math­e­mat­i­cal works. But it has never been awarded to a pure the­o­rist re­search­ing rel­a­tiv­ity.

Mea­sure­ments of grav­i­ta­tional waves will not only pro­vide insights into phe­nom­ena that un­til now were com­pletely out of reach. The The­ory of Gen­eral Rel­a­tiv­ity de­scribes large-scale phys­i­cal phe­nom­ena: Hu­mans, rocks, plan­ets, stars, gal­ax­ies, the en­tire uni­verse. Quan­tum Me­chan­ics, on the other hand, is equally suc­cess­ful at de­scrib­ing the uni­verse at the small­est scales: Quarks, elec­trons, atoms and mol­e­cules.

Many physi­cists are con­vinced that these prob­lems in­di­cate a miss­ing in­gre­di­ent in our un­der­stand­ing of the fun­da­men­tal prin­ci­ples of na­ture. In des­per­a­tion, of­ten mixed with ar­ro­gance, some are sug­gest­ing com­pletely crazy quan­tum-grav­ity con­cepts, in­clud­ing bizarre al­ter­na­tives for stan­dard Ein­steinian black holes — with no ex­per­i­men­tal foun­da­tion.

As a re­sult, for many physi­cists to­day, the gen­uinely fun­da­men­tal prob­lem of rec­on­cil­ing the two the­o­ries has de­gen­er­ated into pompous, mean­ing­less hum­bug. What is needed are solid ex­per­i­men­tal facts to sweep away all this non­sense and per­haps even in­spire a so­lu­tion to the dilemma. And that is ex­actly what fu­ture mea­sure­ments of grav­i­ta­tional waves could pro­vide. The writer is pro­fes­sor of The­o­ret­i­cal Physics at Gote­borg Univer­sity, Swe­den. Project Syndicate

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