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Sunlight is older than you think — much older
💡 Sunlight's 8-minute trip to Earth is trivial compared to the tens of thousands of years its energy spent bouncing its way out of the Sun's dense interior.
You've probably heard that sunlight takes about 8 minutes to reach Earth. True — but that's only the last leg of an astonishingly long journey. The energy in that light was created in the Sun's core, and getting out of the Sun took far, far longer than crossing the 150 million kilometres of space to your window.
Deep in the core, nuclear fusion produces high-energy photons. But the Sun's interior is so dense that a photon can travel only a tiny distance before slamming into a particle, being absorbed, and re-emitted in a random new direction. This zig-zagging is called a random walk — the photon staggers around like a drunk, making almost no net progress outward. Each step is minuscule, and there are an unimaginable number of them.
Estimates for how long this takes vary widely — commonly cited figures range from around 10,000 to 170,000 years — because it depends on hard-to-pin-down assumptions about the Sun's density and opacity. Either way, the light warming your face today began as energy released when mammoths might still have roamed the Earth. Only after finally escaping the surface does it make the quick 8-minute sprint to us.