Busting the Chameleon: Scientists Find No Evidence for a Fifth Fundamental Force

The hunt for dark energy, the mysterious force accelerating the expansion of the universe, has led scientists down many intriguing paths. One promising candidate was the “chameleon force,” a hypothetical fifth fundamental force whose strength would vary depending on the density of matter. This chameleon-like behavior made it incredibly difficult to detect.

Now, a groundbreaking experiment led by He Jian-hua at Nanjing University in China has delivered the strongest evidence yet against the existence of the chameleon force, at least in its basic form. He and his team employed a highly sensitive apparatus: a magnetically levitated graphite strip and a test mass, shielded within a Faraday cage to eliminate interfering electric fields. The setup allowed them to probe energy scales previously inaccessible, filling a crucial gap in earlier research.

The experiment’s precision was remarkable. By using incredibly thin masses, the team minimized the influence of gravity, ensuring that any detected movement would be attributable to the chameleon force, if it existed. Using an optical microscope and laser system, they meticulously searched for any displacement between the masses – a telltale sign of the chameleon force at work. The result? Nothing.

“If dark energy really exists and operates through the chameleon force, we should have detected it,” says He. “Our highly sensitive sensor found nothing.”

While this doesn’t entirely rule out the possibility of a chameleon force operating at different energy scales or unrelated to dark energy, it significantly weakens the leading model. Experts like Jeremy Sakstein at the University of Hawai’i at Manoa agree that this research narrows the search parameters. Adrienne Erickcek at the University of North Carolina adds that while the link between the chameleon force and dark energy is less likely, the possibility of a different type of chameleon force remains open.

Undeterred, the team plans to refine their experiment by cooling it to extremely low temperatures. This will allow them to explore even smaller energy scales and test other dark energy candidates, such as symmetron theory, another potential fifth force.

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