Will the night sky eventually end up completely black because the universe is expanding?
No, the night sky will not eventually end up completely black. It is true that the universe is expanding, which causes many stars to be farther and farther away from earth, and therefore causes them to be dimmer. But the expansion of the universe only affects the distance between galaxy groups. It does not affect the distance between stars inside a galaxy, or even the distance between galaxies in a group. On galaxy group scales and smaller, local gravity overpowers the universe's expansion. The stars in our Milky Way galaxy and in nearby galaxies are not increasing in their distance from the earth, despite the expansion of the universe. As a result, the stars in our galaxy and in nearby galaxies are not growing dimmer over time. Interestingly, almost all of the stars that you can see in the night sky with your naked eye are in our galaxy. This means that the expansion of the universe will have essentially no effect on the appearance of the night sky to the naked eye, no matter how long we wait. The night sky will not go completely dark because of the expansion of the universe.
However, powerful telescopes can see other galaxies outside of our group. If we wait long enough, the expansion of the universe will cause there to be fewer galaxies for powerful telescopes to look at. As a galaxy's distance from earth significantly increases, its light is spread over a greater area before reaching us, and is therefore dimmer. As time goes on, more and more galaxies will become simply too far away for powerful telescopes to see. Increasing the sensitivity of our telescopes can help, but it can only do so much. The light from receding galaxies is not only dimmer, it is also redshifted. This means that all the different colors in the light are Doppler shifted to lower frequencies because of the receding motion of the galaxy. As time goes on, the speed at which a certain galaxy outside our group is receding increases because of the universe's expansion, and therefore its light gets more and more redshifted. Light that used to be green or red ends up as radio waves. Eventually, the redshift gets so extreme that the light is effectively redshifted down to nothing. No amount of technological progress will enable telescopes to see light that is not there. As a result, in the very distant future, the universe will have expanded so much that the light from all of the stars and galaxies outside of our galaxy group will never reach earth. Astronomers in the distance future will have to be content with studying only our local group of galaxies. But, again, the night sky will still look the same to the naked eye.
References:
Wikipedia
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Comments (11)
20 Nov 2019
I am not saying that any of this factual information is incorrect, but if I were you I would be more cautious about how trustworthy your sources are. Wikipedia is a very untrustworthy source to get information from, as it can be edited by anyone and everyone. If you do find anything you find interesting on Wikipedia, I would advise you to get at least two trustworthy sources that agree with the information before accepting it as truth. Still, I think you did a great job on this post and I learnt a lot.
20 Nov 2019
Thank you genius_flute, I take that in mind when I do my next post.
21 Nov 2019
Eventually the sky will become completely black due to suns' (stars) becoming completely cut out of light and destroyed, the night sky will probably not become black for the next trillion years or something, so we don't have to worry about this. And anyway, if the night sky didn't become completely black, then we would still have our sun go out at some point or fall inside itself due to gravity.
21 Nov 2019
my opinion is that if humans put to many lights or space crafts in space it will become to difficult to see up to the stars but i am pretty sure that the moon unless it explodes will always be there
21 Nov 2019
In away it could!
What if all the stars in the sky collect to much gas from the atmosphere and explode ?!?!?!?
21 Nov 2019
I might just disappear altogether maybe because of the fact that the stars could or either they could explode because they can have been in the world for a long time!
28 Nov 2019
i agree and disagree with your post as the universe is expanding. i disagree because i don't think the universe will become black.
28 Nov 2019
i agree with you because the universe is expanding
28 Nov 2019
I think that the night sky will not turn black as the sun still has a few billion years left until it explodes. When then the night sky turns back the earth might erode.
Cheerful_photograph wikipedia is not reliable.
28 Nov 2019
It might stop expanding Cheerful_photograph.I disagree because world might be big but there might be 10% for me to think that world is going to stop expanding.People might disagree
28 Nov 2019
I disagree with you because the world is expanding but not everything on the internet is true.
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