A lengthy journey from core to surface
Photons are generated in the Sun’s core during nuclear fusion. However, they do not instantly escape into space. Instead, they undergo an extremely inefficient random walk through the dense plasma, scattering countless times before emerging.
Travel time of a single photon
Because of repeated interactions with electrons and ions, the average time a photon spends traveling from its birth to the photosphere is estimated at about 100 000 years. During this period the photon loses energy, is repeatedly absorbed and re‑emitted, and finally breaks through the Sun’s visible layer.
Why today’s daylight predates humanity
The solar radiation we receive today originated in a process that began long before the first civilizations. In other words, the light reaching Earth is a “hundred‑thousand‑year‑old” signal from the Sun’s interior.
Implications of a hypothetical solar shutdown
If the Sun were to cease producing energy, the light already present in the outer layers would continue to shine for a few minutes, while the deep‑seated photon reservoir would be depleted over millennia. The slow transport mechanism means that the observable effects of a shutdown would not become apparent for tens of thousands of years.
Key points
- Photons require roughly 100 000 years to travel from the Sun’s core to its surface.
- Their journey is a random walk through dense plasma.
- Current sunlight is significantly older than human civilization.