Esplorando la gravità quantistica: i fisici si sintonizzano sull'anello cosmico dei buchi neri

Di Whitney Clavin, Caltech, 29 maggio 2023

Gli studi condotti dal Caltech propongono nuovi e rigorosi test per la teoria generale della relatività di Einstein, cercando segni di gravità quantistica nelle increspature dello spaziotempo generate dalle collisioni dei buchi neri. Uno studio presenta un’equazione per il comportamento del buco nero all’interno delle teorie della gravità quantistica, basandosi sul lavoro precedente, mentre il secondo suggerisce un metodo per applicare questa equazione ai dati di LIGO, un osservatorio di onde gravitazionali, per rilevare potenziali deviazioni dalla relatività generale.

New methods will allow for better tests of Einstein's general theory of relativity using LIGOThe Laser Interferometer Gravitational-Wave Observatory (LIGO) is a large-scale physics experiment and observatory supported by the National Science Foundation and operated by Caltech and MIT. It's designed to detect cosmic gravitational waves and to develop gravitational-wave observations as an astronomical tool. It's multi-kilometer-scale gravitational wave detectors use laser interferometry to measure the minute ripples in space-time caused by passing gravitational waves. It consists of two widely separated interferometers within the United States—one in Hanford, Washington and the other in Livingston, Louisiana." data-gt-translate-attributes="[{"attribute":"data-cmtooltip", "format":"html"}]">LIGO data.

La teoria generale della relatività di Albert Einstein descrive come il tessuto dello spazio e del tempo, o spaziotempo, è curvo in risposta alla massa. Il nostro sole, ad esempio, deforma lo spazio intorno a noi in modo tale che il pianeta Terra rotola attorno al sole come una biglia lanciata in un imbuto (la Terra non cade nel sole a causa dello slancio laterale della Terra).

La teoria, rivoluzionaria al momento in cui fu proposta nel 1915, riformulava la gravità come una curvatura dello spaziotempo. Per quanto questa teoria sia fondamentale per la natura stessa dello spazio che ci circonda, i fisici dicono che potrebbe non essere la fine della storia. Sostengono invece che le teorie della gravità quantistica, che tentano di unificare la relatività generale con la fisica quantistica, nascondono segreti su come funziona il nostro universo ai livelli più profondi.

L'equazione di Dongjun Li e dei suoi collaboratori descrive come risuonerebbero i buchi neri nel regime oltre la relatività generale. Credito: Caltech

One place to search for signatures of quantum gravity is in the mighty collisions between black holes, where gravity is at its most extreme. Black holes are the densest objects in the universe—their gravity is so strong that they squeeze objects falling into them into spaghetti-like noodles. When two black holes collide and merge into one larger body, they roil space-time around them, sending ripples called gravitational wavesGravitational waves are distortions or ripples in the fabric of space and time. They were first detected in 2015 by the Advanced LIGO detectors and are produced by catastrophic events such as colliding black holes, supernovae, or merging neutron stars." data-gt-translate-attributes="[{"attribute":"data-cmtooltip", "format":"html"}]">onde gravitazionali verso l'esterno in tutte le direzioni.

Dongjun Li. Credito: Caltech

The National Science Foundation-funded LIGO, managed by Caltech and MIT, has been routinely detecting gravitational waves generated by black holeA black hole is a place in space where the gravitational field is so strong that not even light can escape it. Astronomers classify black holes into three categories by size: miniature, stellar, and supermassive black holes. Miniature black holes could have a mass smaller than our Sun and supermassive black holes could have a mass equivalent to billions of our Sun." data-gt-translate-attributes="[{"attribute":"data-cmtooltip", "format":"html"}]"> fusioni di buchi neri dal 2015 (i suoi osservatori partner, Virgo e KAGRA, si sono uniti alla caccia rispettivamente nel 2017 e nel 2020). Finora, tuttavia, la teoria generale della relatività ha superato test su test senza alcun segno di cedimento.

Now, two new Caltech-led papers, in Physical Review X and Physical Review LettersPhysical Review Letters (PRL) is a peer-reviewed scientific journal published by the American Physical Society. It is one of the most prestigious and influential journals in physics, with a high impact factor and a reputation for publishing groundbreaking research in all areas of physics, from particle physics to condensed matter physics and beyond. PRL is known for its rigorous standards and short article format, with a maximum length of four pages, making it an important venue for rapid communication of new findings and ideas in the physics community." data-gt-translate-attributes="[{"attribute":"data-cmtooltip", "format":"html"}]"Physical Review Letters, describe new methods for putting general relativity to even more stringent tests. By looking more closely at the structures of black holes, and the ripples in space-time they produce, the scientists are seeking signs of small deviations from general relativity that would hint at the presence of quantum gravity./p>

The first study, titled "Perturbations of spinning black holes beyond General Relativity: Modified Teukolsky equation," was funded by the Simons Foundation, the Brinson Foundation, and the National Science Foundation (NSF). Other authors include Nicolás Yunes of the University of Illinois at Urbana-Champaign. The second study, titled "Black Hole Spectroscopy by Mode Cleaning," was funded by the Brinson Foundation, the Simons Foundation, NSF, and the Australian Research Council Center of Excellence for Gravitational Wave Discovery (OzGrav). Ling Sun of the Australian National UniversityFounded in 1946, the Australian National University (ANU) is a national research university located in Canberra, the capital of Australia. Its main campus in Acton encompasses seven teaching and research colleges, in addition to several national academies and institutes." data-gt-translate-attributes="[{"attribute":"data-cmtooltip", "format":"html"}]"Australian National University is also a co-author./p>New methods will allow for better tests of Einstein's general theory of relativity using LIGOThe Laser Interferometer Gravitational-Wave Observatory (LIGO) is a large-scale physics experiment and observatory supported by the National Science Foundation and operated by Caltech and MIT. It's designed to detect cosmic gravitational waves and to develop gravitational-wave observations as an astronomical tool. It's multi-kilometer-scale gravitational wave detectors use laser interferometry to measure the minute ripples in space-time caused by passing gravitational waves. It consists of two widely separated interferometers within the United States—one in Hanford, Washington and the other in Livingston, Louisiana." data-gt-translate-attributes="[{"attribute":"data-cmtooltip", "format":"html"}]"LIGO data./strong>