Einstein Couldn’t Solve Quantum Gravity’s Code. Scientists Just Got One Step Closer.
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Although three of the four fundamental forces of nature can be found in the quantum realm, gravity remains the lone outsider.
A new experiment conducted by an international team of European scientists recorded the smallest measurement of gravity ever at just 30 attoNewtons (aN).
Measuring a particle weighing only 0.43 mg, future measurements could traipse into the quantum realm and discover the ever-elusive quantum gravity.
The theory of… well, everything… in physics is mostly governed by two big ideas—general relativity and quantum field theory. Einstein’s general relativity helped re-contextualize our understanding of how massive bodies throughout the universe interact with and influence the fabric of space-time, and quantum field theory defines the atomic world.
While these two theories work well to describe their respective worlds (though there’s always room for improvement), they don’t play nice with each other, which is a pretty big problem if you want to unify the physics of the cosmos under one set of rules. Where the physical world contains evidence of the four fundamental forces—electromagnetism, weak nuclear force, strong nuclear force, and gravity—the quantum world only exhibits the first three. That’s why physicists have been searching for any kind of evidence related to quantum gravity for nearly a century.
This search for quantum gravity has baffled the greatest minds—including Einstein himself who said in his General Theory of Relativity that there was no experiment to prove quantum gravity. Though Einstein was one of the most gifted physicists who’s ever lived, his predictions didn’t always come true. Einstein once thought it’d likely be impossible to ever detect gravitational waves, and now LIGO has a growing list of them. So, could Einstein be wrong about quantum gravity experiments?
Well, an international team of scientists—from U.K.’s University of Southampton, Leiden University in the Netherlands, and Italy’s Institute of Photonic and Nanotechnologies—is eager to find out. In a new study published in the journal Science Advances, the team details an innovative process through which they were able to detect the smallest amount of gravity ever recorded. The gravity was captured from a tiny particle, only 0.43mg in size. It’s not quite in the quantum realm, but it’s so tiny that it’s nearly adjacent.
“For a century, scientists have tried and failed to understand how gravity and quantum mechanics work together,” University of Southampton’s Tim Fuchs, a lead author on the study, said in a press statement. “Now we have successfully measured gravitational signals at the smallest mass ever recorded, it means we are one step closer to finally realizing how it works in tandem. From here we will start scaling the source down using this technique until we reach the quantum world on both sides.”
Like most breakthroughs in the quantum world, this set-up requires extra-cold temperatures—just one-hundredth of degree above absolute zero. This low temp combined with superconducting devices, called traps, levitated the sample. With “advanced vibration isolation’ in place, according to the press release, sensitive instruments were able to detect a weak pull of just 30 attoNewtons (aN), which is a billionth of a billionth of a Newton (much like an attosecond is a billionth of a billionth of a second). If scientists can keep pushing forward on how small gravitational measurements can be, they could soon traipse into the quantum realm.
“Our new technique that uses extremely cold temperatures and devices to isolate vibration of the particle will likely prove the way forward for measuring quantum gravity,” University of Southampton’s Hendrik Ulbricht, a co-author on the study, said in a press statement. “Unraveling these mysteries will help us unlock more secrets about the universe's very fabric, from the tiniest particles to the grandest cosmic structures.”
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