Gravitons, the particles thought to carry gravity, have never been seen in space – but something very similar has been detected in a semiconductor
By Karmela Padavic-Callaghan
27 March 2024
Have we spotted hints of gravitons?
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Physicists have been searching for gravitons, the hypothetical particles thought to carry gravity, for decades. These have never been detected in space, but graviton-like particles have now been seen in a semiconductor. Using these to understand gravitons’ behaviour could help unite the general theory of relativity and quantum mechanics, which have long been at odds.
“This is a needle in a haystack [finding]. And the paper that started this whole thing is from way back in 1993,” says Loren Pfeiffer at Princeton University. He wrote that paper with several colleagues including Aron Pinczuk, who passed away in 2022 before they could find hints of the elusive particles.
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Pinczuk’s students and collaborators, including Pfeiffer, have now completed the experiment the two began discussing 30 years ago. They focused on electrons within a flat piece of the semiconductor gallium arsenide, which they placed in a powerful refrigerator and exposed to a strong magnetic field. Under these conditions, quantum effects make the electrons behave strangely – they strongly interact with each other and form an unusual incompressible liquid.
This liquid is not calm but features collective motions where all the electrons move in concert, which can give rise to particle-like excitations. To examine those excitations, the team shined a carefully tuned laser on the semiconductor and analysed the light that scattered off it.
This revealed that the excitation had a kind of quantum spin that has only ever been theorised to exist in gravitons. Though this isn’t a graviton per se, it is the closest thing we have seen.