Smoking-gun evidence for modified gravity at low acceleration

A new study reports conclusive evidence for the breakdown of standard gravity in the low acceleration limit.


A new study has challenged Einstein and Newton’s theories of gravity: It presented conclusive evidence for the breakdown of standard gravity in the low acceleration limit.

Scientists observed the orbital behaviors of wide binary stars from data collected by the European Space Agency’s Gaia space telescope. The Sejong University in Seoul, Korea, conducted the study.

Scientists used up to 26,500 wide binaries within 650 light years (LY). They mainly focused on calculating gravitational accelerations experienced by binary stars as a function of their separation or the orbital period by a Monte Carlo deprojection of observed sky-projected motions to the three-dimensional space.

Kyu-Hyun Chae, professor of physics and astronomy at Sejong University in Seoul, said, “From the start, it seemed clear to me that gravity could be most directly and efficiently tested by calculating accelerations because the gravitational field itself is an acceleration. My recent research experiences with galactic rotation curves led me to this idea. Galactic disks and wide binaries are similar in their orbits, though wide binaries follow highly elongated orbits while hydrogen gas particles in a galactic disk follow nearly circular orbits.”

According to the study, general relativity and Newton’s universal law of gravitation both predict that an orbit around two stars will vary from one another when the accelerations are less than one millimeter per second squared. The observed acceleration is about 30 to 40% higher than the Newton-Einstein prediction for accelerations lower than 0.1 nanometers per second squared.

The significance is quite high and satisfies the traditional standard for scientific discovery, 5 sigma. Two separate acceleration bins in a sample of 20,000 broad binaries with a distance limit of 650 LY each exhibit variances with > 5 sigma significance in the same direction.

The reported rise of accelerations at lower accelerations is a puzzle because the observed accelerations stronger than around 10 nanometers per second squared corresponds well with the Newton-Einstein prediction from the same research. Intriguingly, this breakdown of the Newton-Einstein theory at accelerations weaker than approximately one nanometer per second squared was proposed 40 years ago by theoretical physicist Mordehai Milgrom at the Weizmann Institute in Israel in a new theoretical framework known as modified Newtonian dynamics (MOND) or Milgromian dynamics in current usage.

Additionally, the Milgrom and the late physicist Jacob Bekenstein’s AQUAL MOND-type Lagrangian theory of gravity accurately predicts the boost factor of roughly 1.4. Interestingly, the correct boost factor necessitates the Milky Way galaxy’s external field effect, a singular prediction of MOND-type modified gravity. As a result, the vast binary data reveal the breakdown of Newtonian dynamics and the manifestation of modified gravity’s external field effect.

Chae says, “It seems impossible that a conspiracy or unknown systematic can cause this acceleration-dependent breakdown of the standard gravity in agreement with AQUAL. I have examined all possible systematics as described in the rather long paper. The results are genuine. I foresee that the results will be confirmed and refined with better and larger data in the future. I have also released all my codes for transparency and to serve any interested researchers.”

Wide binary dynamics cannot be influenced by dark matter, even if it existed, unlike galaxy rotation curves where the observed boosted accelerations can, in theory, be attributed to it in the Newton-Einstein standard gravity. According to the MOND framework, the weak acceleration limit is where the standard gravity fails.

Despite Newton’s gravity’s triumphs, general relativity is required to explain relativistic gravitational phenomena like gravitational waves and black holes. Similarly, despite all of the general relativity’s achievements, a new theory is required to explain MOND events in the weak acceleration limit. The ultraviolet disaster of classical electrodynamics, which gave rise to quantum physics, may share some similarities with the weak-acceleration catastrophe of gravity.

Wide binary anomalies are a catastrophe for conventional gravity and cosmology, which rely on the ideas of dark matter and dark energy. There is no longer a requirement for a significant amount of dark matter in galaxies or even the universe because gravity follows MOND.

Theoretical physicist, Mordehai Milgrom, at the Weizmann Institute in Israel, said, “A new revolution in physics seems now underway. On the present results and the prospects. This finding results from a very involved analysis of cutting-edge data, which was performed meticulously and carefully.”

“But for such a far-reaching finding — and it is indeed very far-reaching — we require confirmation by independent analyses, preferably with better future data. If this anomaly is confirmed as a breakdown of Newtonian dynamics, and especially if it indeed agrees with the most straightforward predictions of MOND, it will have enormous implications for astrophysics, cosmology, and fundamental physics at large.”

Xavier Hernandez, a professor at UNAM in Mexico who first suggested wide binary tests of gravity a decade ago, says, “It is exciting that the departure from Newtonian gravity that my group has claimed for some time has now been independently confirmed, and impressive that this departure has for the first time been correctly identified as accurately corresponding to a detailed MOND model. The unprecedented accuracy of the Gaia satellite, the large and meticulously selected sample Chae uses, and his detailed analysis make his results sufficiently robust to qualify as a discovery.”

Pavel Kroupa, professor at Bonn University and Charles University in Prague, said, “With this test on wide binaries as well as our tests on open star clusters nearby the Sun, the data now compellingly imply that gravitation is Milgromian rather than Newtonian. The implications for all of astrophysics are immense.”

Journal Reference:

  1. Kyu-Hyun Chae. Breakdown of the Newton–Einstein Standard Gravity at Low Acceleration in Internal Dynamics of Wide Binary Stars. The Astrophysical Journal. DOI 10.3847/1538-4357/ace101
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