NASA Scientists Probe Dark Energy – Time To Rework Albert Einstein’s Theory of Gravity?

NASA Scientists Probe Dark Energy – Time To Rework Albert Einstein’s Theory of Gravity?

Illustration de l’énergie sombre. Crédit : Frank Summers Visualization, Space Telescope Science Institute. Simulation par Martin White, UC Berkeley et Lars Hernquist, Harvard University

L’une des plus grandes énigmes de l’astrophysique pourrait-elle être résolue en retravaillant la théorie de la gravité d’Albert Einstein ? Pas encore, selon une nouvelle étude co-écrite par

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The universe is expanding at an accelerating rate, and physicists don’t know why. This phenomenon seems to contradict everything scientists understand about gravity’s effect on the cosmos: It’s as if you threw an apple in the air and instead of coming back down, it continued upward, faster and faster. The cause of the cosmic acceleration, dubbed dark energy, remains a mystery.

A new study marks the latest effort to determine whether this is all simply a misunderstanding: that expectations for how gravity works at the scale of the entire universe are flawed or incomplete. This potential misunderstanding might help researchers explain dark energy. However, the study – one of the most precise tests yet of Albert Einstein’s theory of gravity at cosmic scales – finds that the current understanding still appears to be correct. The study was from the international Dark Energy Survey, using the Victor M. Blanco 4-meter Telescope in Chile.

The results, authored by a group of scientists that includes some from NASA’s Jet Propulsion Laboratory (Webb SMACS 0723

This image – the first released from NASA’s James Webb Space Telescope – shows the galaxy cluster SMACS 0723. Some of the galaxies appear smeared or stretched due to a phenomenon called gravitational lensing. This effect can help scientists map the presence of dark matter in the universe. Credit: NASA, ESA, CSA, and STScI

More than a century ago, Albert Einstein developed his Theory of General Relativity to describe gravity. Thus far it has accurately predicted everything from the orbit of Mercury to the existence of black holes. But some scientists have argued that if this theory can’t explain dark energy, then maybe they need to modify some of its equations or add new components.

To find out if that’s the case, members of the Dark Energy Survey looked for evidence that gravity’s strength has varied throughout the universe’s history or over cosmic distances. A positive finding would indicate that Einstein’s theory is incomplete, which might help explain the universe’s accelerating expansion. They also examined data from other telescopes in addition to Blanco, including the ESA (European Space Agency) Planck satellite, and reached the same conclusion.

Einstein’s theory still works, according to the study. So no there’s no explanation for dark energy yet. However, this research will feed into two upcoming missions: ESA’s Euclid mission, slated for launch no earlier than 2023, which has contributions from NASA; and NASA’s Nancy Grace Roman Space Telescope, targeted for launch no later than May 2027. Both telescopes will search for changes in the strength of gravity over time or distance.

Blurred Vision

How do scientists know what happened in the universe’s past? By looking at distant objects. A light-year is a measure of the distance light can travel in a year (about 6 trillion miles, or about 9.5 trillion kilometers). That means an object one light-year away appears to us as it was one year ago, when the light first left the object. And galaxies billions of light-years away appear to us as they did billions of years ago. The new study looked at galaxies stretching back about 5 billion years in the past. Euclid will peer 8 billion years into the past, and Roman will look back 11 billion years.

The galaxies themselves don’t reveal the strength of gravity, but how they look when viewed from Earth does. Most matter in our universe is dark matter, which does not emit, reflect, or otherwise interact with light. While physicists don’t know what it’s made of, they know it’s there, because its gravity gives it away: Large reservoirs of dark matter in our universe warp space itself. As light travels through space, it encounters these portions of warped space, causing images of distant galaxies to appear curved or smeared. This was on display in one of first images released from NASA’s James Webb Space Telescope.

Cette vidéo explique le phénomène appelé lentille gravitationnelle, qui peut faire apparaître des images de galaxies déformées ou tachées. Cette distorsion est causée par la gravité, et les scientifiques peuvent utiliser cet effet pour détecter la matière noire, qui n’émet ni ne réfléchit la lumière. Crédit : Centre de vol spatial Goddard de la NASA

Les scientifiques du Dark Energy Survey recherchent dans les images de galaxies des distorsions plus subtiles dues à la flexion spatiale de la matière noire, un effet appelé lentille gravitationnelle faible. La force de la gravité détermine la taille et la distribution des structures de matière noire, et la taille et la distribution, à leur tour, déterminent à quel point ces galaxies nous apparaissent déformées. C’est ainsi que les images peuvent révéler la force de la gravité à différentes distances de la Terre et à des époques lointaines tout au long de l’histoire de l’univers. Le groupe a maintenant mesuré les formes de plus de 100 millions de galaxies, et jusqu’à présent, les observations correspondent à ce qui a été prédit par la théorie d’Einstein.

“Il y a encore de la place pour contester la théorie de la gravité d’Einstein, car les mesures deviennent de plus en plus précises”, a déclaré la co-auteure de l’étude Agnès Ferté, qui a mené la recherche en tant que chercheuse postdoctorale au JPL. « Mais nous avons encore beaucoup à faire avant d’être prêts pour Euclid et Roman. Par conséquent, il est essentiel que nous continuions à collaborer avec des scientifiques du monde entier sur ce problème, comme nous l’avons fait avec le Dark Energy Survey.

Référence : « Dark Energy Survey Year 3 Results: Constraints on extensions to ΛCDM with low lensing and galaxy clustering » par DES Collaboration : TMC Abbott, M. Aguena, A. Alarcon, O. Alves, A. Amon, J. Annis, S Ávila, D. Bacon, E. Baxter, K. Bechtol, MR Becker, GM Bernstein, S. Birrer, J. Blazek, S. Bocquet, A. Brandao-Souza, SL Bridle, D. Brooks, DL Burke, H Camacho , A. Campos, A. Carnero Rosell, M. Carrasco Kind, J. Carretero, FJ Castander, R. Cawthon, C. Chang, A. Chen, R. Chen, A. Choi, C. Conselice, J. Cordero, M. Costanzi, M. Crocce, LN da Costa, MO Pereira, C. Davis, TM Davis, J. DeRose, S. Desai, E. Di Valentino, HT Diehl, S. Dodelson, P. Doel, C. Doux, A. Drlica-Wagner, K. Eckert, TF Eifler, F. Elsner, J. Elvin-Poole, S. Everett, X. Fang, A. Farahi, I. Ferrero, A. Ferté, B. Flaugher, P Fosalba, D. Friedel, O. Friedrich, J. Frieman, J. García-Bellido, M. Gatti, L. Giani, T. Giannantonio, G. Giannini, D. Gruen, RA Gruendl, J. Gschwend, G. Gutiérrez, N Hamaus, I. Harrison, W.G. Hartley, K. Herner, SR Hinton, DL Hollowood, K. Honscheid, H. Huang, EM Huff, D. Huterer, B. Jain, DJ James, M. Jarvis, N. Jeffrey, T. Jeltema, A. Kovacs, E. Krause, K. Kuehn, N. Kuropatkin, O. Lahav, S. Lee, P.-F. Leget, P. Lemos, CD Leonard, AR Liddle, M. Lima, H. Lin, N. MacCrann, JL Marshall, J. McCullough, J. Mena-Fernández, F. Menanteau, R. Miquel, V. Miranda, JJ Mohr, J. Muir, J. Myles, S. Nadathur, A. Navarro-Alsina, RC Nichol, RLC Ogando, Y. Omori, A. Palmese, S. Pandey, Y. Park, M. Paterno, F. Paz- Chinchón, WJ Percival, A. Pieres, AA Plazas Malagón, A. Porredon, J. Prat, M. Raveri, M. Rodriguez-Monroy, P. Rogozenski, RP Rollins, AK Romer, A. Roodman, R. Rosenfeld, AJ Ross, ES Rykoff, S. Samuroff, C. Sanchez, E. Sanchez, J. Sanchez, D. Sanchez Cid, V. Scarpine, D. Scolnic, LF Secco, I. Sevilla-Noarbe, E. Sheldon, T. Shin , M. Smith, M. Soares-Santos, E. Suchyta, M. Tabbutt, G. Tarle, D. Thomas, C. A, A. Troja, MA Troxel, I. Tutusaus, TN Varga, M. Vincenzi, AR Walker, N. Weaverdyck, RH Wechsler, J. Weller, B. Yanny, B. Yin, Y. Zhang et J. Zuntz, 12 juillet 2022, Astrophysique > Cosmologie et astrophysique non galactique.
arXiv:2207.05766

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