Scientists Are Getting Closer to Finding Evidence of the Fifth Force

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Here’s what you’ll learn when you read this story:

Some physicists believe that a fifth fundamental force could be the cause of some observational anomalies.
A study is investigating ways to closely examine the trajectories of well-documented asteroids to hopefully detect anomalies that could provide evidence of such a force.
Although the study shows no fifth force anomaly present in the asteroid Bennu, future explorations of the asteroid Apophis could provide an even better chance to find this elusive force—if it exists at all.

According to the current Standard Model, four fundamental forces underpin all known physics: electromagnetism, gravity, and the strong and weak nuclear forces. However, since the mid-1980s, physicists have wondered if a fifth fundamental force could exist, which would help to explain some observational anomalies. And since then, many studies have boldly claimed discovery of this elusive force.

In 1986, for example, scientists at MIT thought that antigravity could maybe could be a fifth force, and in 2000, another group named the force “quintessence” as a way to explain dark energy. In 2015, a study by the Hungarian Academy of Sciences discovered a particle 30 times heavier than an electron that could form the basis of a fifth force, and the U.S.-based Fermilab stated boldly that they were on the cusp of discovering this mysterious force in 2023.

And, of course, there’s a strong contingent of physicists who think a fifth force doesn’t exist at all.

One proposed way of examining if such a force could exist is by closely monitoring asteroid trajectories, and few near-Earth asteroids are as well observed as Bennu. A study by an international team of scientists analyzes Bennu to try and placing constraints on a possible fifth fundamental force in the search of ultralight dark matter.

Bennu, one of the most dangerous near-Earth objects, has been meticulously tracked by optical and radar astrometric data since it was discovered in 1999. As the destination for the OSIRIS-REx asteroid retrieval mission, additional X-band radiometric and optical navigation tracking data added even more trajectory precision.

The idea is that any deviation in the expected trajectory of the asteroid could be the result of an unknown fifth force at work. The results of the study were published in the journal Nature Communications Physics.

“Interpreting the data we see from tracking Bennu has the potential to add to our understanding of the theoretical underpinnings of the universe, potentially revamping our understanding of the Standard Model of physics, gravity and dark matter,” Yu-Dai Tsai, the lead author on the paper, said in a press statement. “The trajectories of objects often feature anomalies that can be useful in discovering new physics.”

The trajectories of heavenly objects have yielded incredible discoveries before. Neptune, for example, was first “discovered” not through a telescope, but by the meticulous calculations of Uranus’ orbit and discovery of gravitational anomalies therein. However, such a technique isn’t foolproof, as some scientists also believed that a planet named Vulcan existed between the Sun and Mercury. This, obviously, turned out to be false.

“These results highlight the potential for asteroid tracking as a valuable tool in the search for ultralight bosons, dark matter, and several well-motivated extensions of the Standard Model,” Sunny Vagnozzi, assistant professor at the University of Trento in Italy and study co-author, said in a press statement.

While this study didn’t find “evidence in the data for the presence of a fifth force affecting the motion of Bennu,” the ORSIRIS-REx’s sequel, OSIRIS-APEX, could provide even more data as the mission zooms onward toward the asteroid Apophis. Because this asteroid will zoom by Earth in 2029, a detailed study of its trajectory will deliver even further restrictions on the fifth force than what Bennu could provide.

So, while the ongoing exploration of the fifth force continues in accelerator labs around the world, some scientists are turning toward space to answer the deepest mysteries of physics.

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