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NASA Scientists Help Probe Dark Energy by Testing Gravity

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

A new study from the international Dark Energy Survey, using the Victor M. Blanco 4-meter Telescope in Chile, 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 scientists explain dark energy. But 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 results, authored by a group of scientists that includes some from NASA’s Jet Propulsion Laboratory, were presented Wednesday, Aug. 23, at the International Conference on Particle Physics and Cosmology (COSMO’22) in Rio de Janeiro. The work helps set the stage for two upcoming space telescopes that will probe our understanding of gravity with even higher precision than the new study and perhaps finally solve the mystery.

More than a century ago, Albert Einstein developed his Theory of General Relativity to describe gravity, and so far it has accurately predicted everything from the orbit of Mercury to the existence of black holes. But if this theory can’t explain dark energy, some scientists have argued, 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 satelliteand reached the same conclusion.

The study finds Einstein’s theory still works. So no explanation for dark energy yet. But 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 Telescopetargeted for launch no later than May 2027. Both telescopes will search for changes in the strength of gravity over time or distance.

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