Asked by Dj
If nuclear fusion in the sun's core suddenly stopped today, would the sky be dark in the daytime tomorrow? why
Answers
Answered by
Count Iblis
No, it would take millions of years before we noticed an effect. The reason is that the photons produced by nuclear reaction in the Sun's interor scatter very often. They travel only a very short distance inbetween collisions with the ions. After a collision they travel in some pretty much random direction compared to the direction before the collision. This is known as a random walk.
If the photons travel a distance d on average betwen collisions, then after N collisions they'll have travelled on average a distance of sqrt(N) d
(not N d)
d is about 10^(-6) meters. The radius of the Sun is of order 10^8 meters, so the number of collisions N needed for a photon to escape is of order 10^28. The total distance the photons will have travelled inbetween all the collsions is thus 10^22 meters, which is about a million lightyears.
If the photons travel a distance d on average betwen collisions, then after N collisions they'll have travelled on average a distance of sqrt(N) d
(not N d)
d is about 10^(-6) meters. The radius of the Sun is of order 10^8 meters, so the number of collisions N needed for a photon to escape is of order 10^28. The total distance the photons will have travelled inbetween all the collsions is thus 10^22 meters, which is about a million lightyears.
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