Light Gets Even Lighter: A New Upper Limit for the Photon’s Mass ⚡ экспресс
Fast radio bursts (FRBs) are cosmic pulses whose dispersion in the intergalactic medium depends on frequency. By improving the model of dispersion distribution from gas, scientists set a record upper limit on the photon mass: about 4.9×10⁻⁵¹ kg (for ΛCDM, wCDM, and w₀wₐCDM models). These are the tightest constraints obtained from FRBs, and they depend weakly on the choice of cosmological model. The result robustly confirms the masslessness of light. Curiously, even such a tiny mass would show up in the delay of radio signals traveling for billions of years.
Fast radio bursts are bright cosmic flashes that, like a starting signal, launch a race of radio waves across the Universe. Astronomers used them to check whether the photon – the particle of light – has mass. If mass existed, the speed of light would depend on its color: blue rays, like heavier runners, would lag behind red ones. But observations show that any delay is fully explained by the drag of intergalactic hydrogen – a sparse gas that only slightly slows the waves.
Scientists considered various scenarios of Universe’s expansion, including the influence of dark energy, and set a new mass limit: the photon is lighter than 5×10⁻⁵¹ kg. This is billions of times less than the mass of the lightest known particle. The precision is astonishing: distant blue light would lead red by only a second – and that tiny shift would already have been noticed, but it’s not there.
The result strengthens the foundation of physics laid by Albert Einstein: light remains the fastest and massless racer.
🎯 If the photon had such mass, then over the distance to the Andromeda Galaxy, the blue ray would be late to the finish by a trillionth of a second.