If space is infinite, why is it black?

Why is space black?

11 Answers

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  • Anonymous
    10 years ago
    Favorite Answer

    You are not the first person in history to ask what is actually a profound question.

    The name given to this question is "Olber's Paradox".

    Basically stated, if we assume that the universe is infinite, then looking at the sky in

    any direction, we should expect our line of sight to eventually encounter a star. If our

    eye encounters a star in every direction at every point in the sky, then the night sky

    should be brightly lit and full of light, rather than mostly dark.

    The commonly accepted explanation relies on the fact that our universe is both

    expanding and has a finite age:

    In order to explain Olbers' paradox, one would need to account for the relatively low brightness of the night sky in relation to the circle of our sun. The universe, according to the mainstream theory of the universe, called the Big Bang Theory, is only finitely old; stars have existed only for part of that time. So, as Poe suggested, the Earth receives no starlight from beyond a certain distance, corresponding to the age of the oldest stars. Space is sufficiently rarefied that most lines from the Earth do not touch any star within this distance of Earth. They will proceed all the way to the Big Bang itself.

    However, the Big Bang theory introduces a new paradox: it states that the sky was much brighter in the past, especially at the end of the recombination era, when it first became transparent. All points of the local sky at that era were brighter than the circle of the sun, due to the high temperature of the universe in that prehistoric era; and we have seen that most light rays will terminate not in a star but in the relic of the Big Bang.

    This paradox is explained by the fact that the Big Bang Theory also involves the expansion of the "fabric" of space itself (not just the distance of objects in that space) that can cause the energy of emitted light to be reduced via redshift. More specifically, the extreme levels of radiation from the Big Bang have been redshifted to microwave wavelengths (1100 times lower than its original wavelength) as a result of the cosmic expansion, and thus form the cosmic microwave background radiation. This explains the relatively low light densities present in most of our sky despite the assumed bright nature of the Big Bang. The redshift also affects light from distant stars and quasars, but the diminution is only an order of magnitude or so, since the most distant galaxies and quasars have redshifts of only around 5. Thus, the mainstream explanation of Olbers' paradox requires a universe that is both finitely old and expanding.

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  • eri
    Lv 7
    10 years ago

    Space isn't infinite, it's just really big. But people have brought up this point before - since there are so many stars and galaxies out there, why is space black instead of light? It's called Olber's paradox. There's a link to a good explanation below, but the basic idea is that most stars are so far away that your eyes don't process the few photons you get from then so you can see them. That's why we need telescopes with cameras.

    http://en.wikipedia.org/wiki/Olbers%27_paradox#The...

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  • 10 years ago

    Space is not infinite. Steady State has been put to bed. And space is black to our eyes because we see a very limited amount of the spectrum. Could we see radiation that would fill up a great amount of what we see. It is our own human limitations that reveal nothing but for black in all but the brightest regions of the universe.

    B

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  • Tom S
    Lv 7
    10 years ago

    Space is not infinite in time or volume, and it is expanding. Those are the reasons for it being dark (black).

    Source(s): Olber's paradox
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  • 10 years ago

    Because it doesn't have air like our atmosphere does. Aside from the stars and nebulae, it is black because it can't reflect starlight.

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  • Anonymous
    10 years ago

    Because there is no air in space - nothing to scatter light (like our atmosphere does).

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  • 10 years ago

    What color would you expect it to be? It's a huge void so of course its going to be black. no colors,aside from stars and galaxies.

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  • Leon
    Lv 4
    10 years ago

    To be honest I don't know why but I wish it was red or something cause that would look awesome at night

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  • 10 years ago

    Because there's mostly nothing in it. There's nothing to reflect light back.

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  • 10 years ago

    What color would you want it to be?

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