Expert: Jayendra Upadhye - 8/21/2006

Question
hello, it is a rare privilge to have some one who is always ready to answer ones questions. I am not a science student or researcher,i am just interested in science as a hobby.
My question is why is space dark? considering the heat/light the sun generates and the light the moon too contributes, all the stars, how come space is still dark?

Answer
Hello Ibrahim,
This question was first asked / taken up in a scientefic inquiry by Heinrich Wilhelm Olbers.
It is called Olbers paradox after his name.

ref:-
http://en.wikipedia.org/wiki/Olbers'_paradox

The explanation has two components.
1 - Technically, the farther away a star is, the more red shifted it appears.
This is due to the expansion of the universe. (look up hubbles constant and the red shift on wikipedia).
Hence, one reason why the sky looks dark is that in the dark regions, the stars in any particular direction are so far away that its light has got red shifted to below visible regions...may be to below radio freq. regions. And hence is "unobservable".

2 - The other component also from the Big bang is the immeasurably intense blast itself!
The "terrible & Blinding flash" of the bang is preserved as a "fossilised" echo that we now see as the COSMIC BACKGROUND RADIATION, corresponding to radio emission of hydrogen at about 3 degrees kelvin. No point in space is cooler than that anywhere in the universe. It is the actual temperature of absolute space "everywhere".
This has happened because the universe has cooled to that level since the bang.

Both components are invisible to the naked eyes, and so space is dark!
Main reason being the Bang, and the expanding universe.

Hope that suffices.
Jayen