In a breakthrough that could redefine our understanding of gravity and the universe, scientists have designed an experiment able to detect a gravitational force equal to one-quintillionth of a Newton on a minuscule particle. This trailblazing research from scientists in the U.K., Netherlands, and Italy, published in Science Advances, signifies a monumental step toward unraveling the enigma of quantum gravity.
Gravity permeates our daily existence, influencing everything from the moon’s orbit to the simple act of dropping an apple. Yet, despite its omnipresence, gravity’s impact is almost negligible at the quantum level. Reconciling the effects of gravity on both the classical and quantum scales has remained one of physics’ most elusive goals for decades. The quest for a unified theory has led to speculative frameworks like string theory and loop quantum gravity, but tangible measurements have been scarce—until now.
The recent study by Tjerk Oosterkamp, Ph.D., and his colleagues aimed to measure gravitational forces on a particle weighing just 0.43 milligrams with unprecedented precision. �Although this development does not yet demonstrate quantum gravity, it lays critical groundwork for future experiments. Oosterkamp, a professor at Leiden University, stresses, ”What we’re saying is that this is a step on the way towards measuring quantum gravity effects."
Understanding gravitational effects at such a minuscule scale requires ultra-sensitive detection methods that filter out background noise, akin to distinguishing a whisper in a noisy room. The team utilized a range of sophisticated tools for their experiment, including a dilution refrigerator to minimize thermal noise, a mass-spring system to absorb environmental vibrations, and a superconducting trap to levitate the particle. Placing a 2.4-kilogram source mass nearby created the necessary gravitational interaction for measurement.
Operating under near absolute zero conditions, the team achieved an astonishing feat: measuring a 30-attoNewton gravitational force on the tiny particle. Yasunori Nomura, Ph.D., a theoretical physics professor at UC Berkeley, acknowledges the significance of this development but also highlights the challenges ahead. “This measurement is a step toward directly observing gravitational forces in a truly quantum regime," Nomura states, noting that existing techniques may still fall short of reaching scales where quantum gravity becomes pronounced.
Despite these limitations, Oosterkamp envisions broader applications for their setup. He aspires to enhance the sensitivity of gravitational wave detectors, such as LIGO and VIRGO, which observe ripples in spacetime caused by cosmic events like black hole collisions. Oosterkamp aims to contribute to the development of the Einstein Telescope, a next-generation detector planned for Europe in the 2030s. The temperature control techniques from his research could significantly advance this field.
Rana Adhikari, Ph.D., a CalTech physicist and LIGO contributor, emphasizes the potential impact of ultra-low temperature operations. “Future gravitational wave detectors will need to build on this work's foundation. Operating at such low temperatures would eliminate nearly all thermodynamic noise sources," Adhikari remarks. He views Oosterkamp’s work as a vital piece of the larger puzzle of quantum gravity. �
The quest to measure quantum gravity is undoubtedly long and complex. Still, each step, like the one taken by Oosterkamp’s team, brings us closer to a profound understanding of the universe’s most fundamental forces. As Adhikari eloquently puts it, “This [work] is a great example of how experimental ingenuity can lead to making measurements of the universe in a new way. The road towards quantum gravity will be decorated with experiments of ever-increasing sensitivity."
