Anonymous
Anonymous asked in Science & MathematicsAstronomy & Space · 1 decade ago

# Astronomy question!?

Olders paradox seeks the explanation for why the night sky is dark. True or flase?

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True, it seeks it, but by definition, a paradox performs an explanation, but by explaining, seems to contradict itself.

You might be thinking, the more distant stars are fainter than nearby stars because of the inverse square law. But the farther you look into space, the larger the volume you will see, and thus the two effects cancel out. Every spot on the sky must be occupied by a star, and the night sky should be dark. Now we know that stars are grouped into galaxies, but the paradox remains: our line of sight will eventually intersect a galaxy.

The brightnesses of stars does decrease with greater distance (remember the inverse square law) BUT there are more stars further out. The number of stars within a spherical shell around us will increase by the same amount as their brightness decreases. Therefore, each shell of stars will have the same overall luminosity and because there are a lot of ever bigger shells in an infinite universe, there is going to be a lot of light!

Olbers concluded that the night sky was dark because intervening clouds of dust and gas absorbed the starlight from distant sources. However, these same clouds would heat up from the collection of light energy and glow brightly. Any intervening material absorbing the starlight would eventually heat up and radiate as much energy as it absorbed, so the problem remains even if you try these 'shields'. Of course, stars are not points. They do have a definite size, so they can block light from other stars. The total brightness of the universe will not be infinite, but only as bright as the surface of a star (!). You can substitute 'galaxy' for 'star' in the preceding paragraphs if you want to update Olbers' Paradox for modern times.

Have fun!

True. The paradox basically states that if stars are evenly spaced in space (sorry) then the light from the farthest ones (which are more numerous) will equal the light from the nearest ones and hence the sky should be dazzlingly bright. Clearly it is not, and that is the paradox.

Olbers paradox did not (could not) take into account the presence of galaxies with few or no stars in between, and dust and gas in our own galaxy.

• Anonymous