Page 353 - Blog Posts v1

E64 - How long does it take a new photon to reach us from its creation in the sun?
All of the sun's photons are generated through nuclear reactions within it. If a photon is generated at the centre of the sun it can take anywhere between 2 days and 200,000 years to escape the body of the sun.
That's because the path of the photon is purely probabilistic. At the centre of the sun the pressure and temperature are enormous. The density of hydrogen atoms is also enormous. Consequently, every photon encounters many, many trillions of hydrogen atoms before finally escaping.
Each time it interacts with a hydrogen atom its path is deflected. And so it 'bounces' along inside the sun until its path leads to the door out (this is called 'scattering').
The speed of light, in free space, is approx 299,792.458 km/s (which is about 186,282 miles per second in old money!). However, at the sun's centre this can be as slow as a few centimetres per second, due to the huge densities in there.
As the photon moves towards the sun's surface the density reduces markedly. Its speed increases but it still scatters off many hydrogen atoms. Finally, it will scatter off its last hydrogen atom and escape from the sun's atmosphere into free space, where it will reach the speed of light.
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