LIGHTNING 鈥渟prites鈥� that dance on top of electrical storm clouds are helping to check whether photons are truly massless.
Theory predicts that photons don鈥檛 have any mass, but it has been a struggle to prove this experimentally. A new approach discovered by Martin F眉llekrug at the Goethe University in Frankfurt, Germany, could help.
In a paper to be published in Physical Review Letters, F眉llekrug describes measuring the ultra-low-frequency radio waves that sprites emit. He tested the method in Antarctica, using copper coils to detect the magnetic field of the radio waves, from which he deduced their speed. This was used to estimate the photon鈥檚 mass. His results show that each must have a mass smaller than 4 脳 10鈭�52 kg. This is not the strictest limit ever set, but his technique has the potential to push measurements closer to zero than ever before.
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