Light Gets Even Lighter: A New Upper Limit for the Photon’s Mass ⚡ экспресс
Testing the masslessness of the photon is a fundamental challenge in physics. Fast radio bursts (FRBs) with known dispersion measures provide a unique opportunity to constrain the photon's rest mass. An improved distribution of the extragalactic gas contribution to dispersion is proposed, in good agreement with model data. Using this, constraints on the photon mass are obtained within three cosmological models: ΛCDM, wCDM, and w₀wₐCDM (the latter favored by DESI data). The upper limits at 1σ: 4.83×10⁻⁵¹ kg, 4.71×10⁻⁵¹ kg, and 4.86×10⁻⁵¹ kg — the most stringent from FRBs to date. The weak model dependence confirms the reliability of FRBs as a tool and indicates the masslessness of the photon.
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.