Joe McNally/Getty Images

Terminer ce qu'Einstein avait commencé

GÖTEBORG – Il y a longtemps dans une galaxie lointaine, très lointaine, deux énormes trous noirs (chacun ayant une masse à peu près 30 fois supérieure à celle du soleil), sont entrés en collision, ont fusionné en émettant une explosion brève et puissante d'ondes gravitationnelles. L'énergie de cette explosion s'est propagée dans l'univers à la vitesse de la lumière, en diluant sa puissance à travers l'immensité de l'espace.

Plus d'1 milliard années plus tard, l'énergie de l'explosion a atteint la Terre sous la forme d'un signal incroyablement faible, d'une durée d'environ un dixième de seconde. Le 14 septembre 2015, les scientifiques de l'Observatoire à interféromètre laser d'ondes gravitationnelles (LIGO)aux États-Unis ont détecté des ondes gravitationnelles ayant la force d'un gazouillis sur leurs instruments et ont ainsi fourni la première confirmation d'une prédiction faite par Albert Einstein 100 ans auparavant.

LIGO, qui fonctionne sous la direction de la Fondation nationale pour la science (NSF) des États-Unis, utilise deux interféromètres perfectionnés. Ces merveilles de haute technologie, situées aux extrémités opposées du pays et mises en service peu avant la mesure réussie de l'onde gravitationnelle (appelée GW150914), fonctionnent selon le principe de l'interférence lumineuse. Ces appareils détectent les contraintes exercées sur la géométrie de l'espace/temps induites par les ondes gravitationnelles, par la mesure des altérations dans la longueur des bras des interféromètres. Dans le cas de GW150914, sa longueur a varié du millième de la taille d'un proton en moins.

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