`We are en­rich­ing our knowl­edge of the cos­mos'

Down to Earth - - SPECIAL REPORT -

We now have a dif­fer­ent chan­nel to un­der­stand the uni­verse. Grav­i­ta­tional waves (GWs) are not elec­tro­mag­netic (EM) waves, so we can­not "see" them though our eyes or with tele­scopes. But this is the first time ever we have seen black holes of this mass (about 30 times heav­ier than the sun), and we have seen them col­lide.

We were "blind" to cer­tain aspects of the uni­verse, but now we will be able to study them as LIGO de­tects more such events. It is also the only way we can test Ein­stein's gen­eral the­ory of rel­a­tiv­ity in the "strong grav­ity" regime. De­tec­tion of GWs was one of the fi­nal re­main­ing ev­i­dence of Ein­stein's the­ory of rel­a­tiv­ity. Th­ese waves gen­er­ate a "strain"—a frac­tional change in length of any­thing that they travel through. Mea­sur­ing this small change in length re­quired one of the most sen­si­tive in­stru­ments ever built with the best lasers, vac­uum and other tech­ni­cal ap­pa­ra­tus.

Dur­ing the early stages of LIGO, we demon­strated tech­nol­ogy, learnt lessons and adapted them to the next gen­er­a­tion of in­stru­ments. Af­ter LIGO's first run, we im­ple­mented sev­eral tweaks at all lev­els—from hard­ware up­grades to bet­ter sig­nal pro­cess­ing—to make de­tec­tions pos­si­ble.

The de­tec­tion of GWs is a long-awaited con­fir­ma­tion of Ein­stein's pre­dic­tions. How­ever, it does not deal with, say, the quan­tum na­ture of mat­ter. This dis­cov­ery im­proves our un­der­stand­ing of grav­ity, but does not give us a grand uni­fied the­ory just yet.

Fur­ther data from the GW de­tec­tors will tell us more about black holes, cer­tain types of bi­nary neu­tron stars and neu­tron star bi­nar­ies. This will fur­ther our un­der­stand­ing about the for­ma­tion and death of stars, and en­rich our knowl­edge of our cos­mic neigh­bour­hood.

(As told to Down­ToEarth) VARUN BHALERAO In­ter-Univer­sity Cen­tre for As­tron­omy and Astro­physics (IUCAA), Pune. He is work­ing with the LIGO pro­ject

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