Question:
Did you know that if the Sun switched suddenly off, neutrinos would tell us in 8 minutes, while we would have sunlight for a million years more?
Answer:
<p>This is another consequence of neutrinos' elusivity: both photons and neutrinos are produced by the nuclear reactions taking place in the core of the Sun. Afterwards, they need to reach the surface of the star before being able to travel in the empty space towards us., which, as you probably know, takes about 8 minutes to light, and almost the same to neutrinos. It is exactly the journey from the nucleus to the surface that makes all the difference: for neutrinos, the Sun is transparent, so it is very fast for them. Photons, instead, participate to the electromagnetic interaction, and therefore they have a much higher probability to interact with the electrons and nuclei that compose the solar plasma. This means that they have to walk a very very tortuous path through continuous absorptions, scatterings and re-emissions, until they slowly cross, one after the other, all the outer layers of the Sun. This takes on average millions years! So, what would happen if the Sun switched off in this instant? The huge amount of photons that are already on their way to the Sun's surface will just go on in their journey, and sunlight would be granted for some other million years. However, the absence of neutrino flux would be noticed by all the neutrinos detectors we have on Earth in less than 10 minutes. </p>
<p><img alt="" src="/sites/default/files/images/nu_vs_light_sun.gif" style="width: 391px; height: 343px;" /></p>