A photon is like a soap bubble: weightless, swift, indestructible. It can cross the universe unchanged. But in the far reaches of space, where the speed of light might fluctuate slightly, the bubble suddenly gets heavy. And then, as if under its own weight, it pops into two even lighter bubbles — neutrinos. These ghostly twins pass through planets like a knife through butter.

Recent calculations combining the laws of electricity and magnetism with quantum field theory have shown: super-energetic cosmic rays from the Crab Nebula challenge the Standard Model of physics, as described by Einstein and Sunyaev. If a photon acquires a tiny mass, it can transform into two neutrinos.

The decay is extremely rare and takes a thousand years — a cosmic blink. But future observatories, sensitive to both light and neutrinos, will be able to detect the sudden disappearance of photons using methods of ultra-precise light measurement. A dip in the gamma-ray glow would be the first signal: the universe is more complex than we thought.