In the vast expanse of our universe, four fundamental forces—gravity, electromagnetism, and the strong and weak nuclear forces—are widely accepted as the pillars of physics. However, for nearly four decades, a growing number of scientists have speculated about the possibility of a fifth force that could address unresolved questions within our understanding of the cosmos. Recent research published in Nature Communications Physics propels this inquiry forward, focusing particularly on the peculiar movements of asteroids in space.
Asteroids, with their rocky forms drifting through the solar system, serve as ideal subjects for studying cosmic forces. Once researchers establish an asteroid’s shape, spin, and distance from the Sun, they can predict its trajectory with remarkable precision. Any deviation from this predicted path might suggest the influence of an unknown force at play. This idea hinges on the notion that if we understand how an asteroid should behave under the known forces, any anomalies could provide critical insights into new physics.
The research team has zeroed in on Bennu, a near-Earth asteroid roughly the height of the Empire State Building. NASA’s OSIRIS-REx mission has equipped scientists with an unprecedented dataset about Bennu, allowing for meticulous tracking of its orbit. Lead author Yu-Dai Tsai and his team employed radio, radar, and optical methods to detect subtle “wiggles” in Bennu’s trajectory. These small deviations could indicate the presence of a fifth force if they cannot be accounted for by known physical phenomena like sunlight pressure or gravitational forces.
Up to this point, Bennu has not revealed any mysterious shifts in its path. While this finding may seem like a setback for the fifth-force hypothesis, it doesn’t eliminate the possibility; rather, it suggests that Bennu alone may not be the key to unlocking this mystery. Scientists are now eager for new targets and advanced tools to continue their investigation.
The next significant opportunity comes in April 2029, when Apophis, another near-Earth asteroid, will pass closer to our planet than many satellites. This close encounter presents an ideal chance for astronomers to monitor Apophis’s movement with unprecedented accuracy, down to a few meters. NASA’s OSIRIS-APEX mission aims to capitalize on this event by gathering comprehensive data on Apophis’s position, rotation, and surface characteristics. Co-author Sunny Vagnozzi emphasizes that Apophis may offer crucial insights into ultralight bosons, dark matter, and other theoretical extensions of the Standard Model. If Apophis shows any unexplained deviations, it could provide vital clues to the existence of novel particles or forces.
The quest for a fifth force is not a new endeavor; hints have emerged sporadically since the mid-1980s. For instance, in 1986, researchers at MIT proposed that “antigravity” effects might arise from an unknown force. The term “quintessence” was introduced in 2000 to describe a potential fifth force linked to dark energy. More recently, in 2015, scientists at the Hungarian Academy of Sciences reported encountering a heavy “X-boson,” a particle that could carry this elusive force. In 2023, Fermilab scientists claimed they were on the cusp of confirming new physics tied to an additional force. Each of these claims sparked excitement, but none provided conclusive evidence.
Understanding whether a fifth force exists carries monumental implications for science. A confirmed fifth force could necessitate a revision of the Standard Model, the foundational framework describing particle interactions. It could also enhance our comprehension of dark matter, the mysterious substance constituting a significant portion of the universe’s mass. Furthermore, refining our grasp of all forces acting on spacecraft would enable engineers to calculate more accurate flight paths for probes and satellites, ultimately improving space exploration efficiency.
As scientists await the close approach of Apophis in 2029, the stakes are high. Should its trajectory align precisely with predictions, the fifth-force hypothesis will face another challenge. Conversely, any unexplained deviations could signify that we are on the brink of discovering new dimensions of physical reality. Whether Bennu remains a “no sign yet” or Apophis presents us with groundbreaking revelations, this ongoing investigation into the forces shaping our universe continues to capture the imagination.
The quest for understanding the universe is a journey that combines the art of observation with the rigor of scientific inquiry. As we look up at the night sky, we remain hopeful that the answer to one of physics’ most intriguing mysteries may soon be revealed, potentially reshaping our understanding of the cosmos and our place within it.
