{"id":35300,"date":"2023-10-21T04:45:00","date_gmt":"2023-10-21T04:45:00","guid":{"rendered":"https:\/\/www.lifeandnews.com\/articles\/?p=35300"},"modified":"2023-10-31T13:37:01","modified_gmt":"2023-10-31T13:37:01","slug":"why-is-space-so-dark-even-though-the-universe-is-filled-with-stars","status":"publish","type":"post","link":"https:\/\/www.lifeandnews.com\/articles\/why-is-space-so-dark-even-though-the-universe-is-filled-with-stars\/","title":{"rendered":"Why is space so dark even though the universe is filled with\u00a0stars?"},"content":{"rendered":"\n

Brian Jackson<\/a>, Boise State University<\/a><\/em><\/p>\n\n\n\n

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Curious Kids<\/a> is a series for children of all ages. If you have a question you\u2019d like an expert to answer, send it to curiouskidsus@theconversation.com<\/a>.<\/em><\/p>\n\n\n\n

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Why is space so dark despite all of the stars in the universe? \u2013 Nikhil, age 15, New Delhi<\/strong><\/p><\/blockquote>\n\n\n\n

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People have been asking why space is dark despite being filled with stars for so long that this question has a special name \u2013 Olbers\u2019 paradox<\/a>.<\/p>\n\n\n\n

Astronomers estimate that there are about 200 billion trillion stars<\/a> in the observable universe. And many of those stars are as bright or even brighter than our sun. So, why isn\u2019t space filled with dazzling light?<\/p>\n\n\n\n

I am an astronomer<\/a> who studies stars and planets \u2013 including those outside our solar system \u2013 and their motion in space. The study of distant stars and planets helps astronomers like me<\/a> understand why space is so dark.<\/p>\n\n\n\n

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https:\/\/embed-player.newsoveraudio.com\/v4?key=x84olp&id=https:\/\/theconversation.com\/why-is-space-so-dark-even-though-the-universe-is-filled-with-stars-205810&bgColor=F5F5F5&color=D8352A&playColor=D8352A<\/p>\n\n\n\n

You can listen to more articles from The Conversation, narrated by Noa, here<\/a>.<\/em><\/p>\n\n\n\n

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You might guess it\u2019s because a lot of the stars in the universe are very far away from Earth. Of course, it is true that the farther away a star is, the less bright it looks \u2013 a star 10 times farther away looks 100 times dimmer<\/a>. But it turns out this isn\u2019t the whole answer.<\/p>\n\n\n\n

Imagine a bubble<\/h2>\n\n\n\n

Pretend, for a moment, that the universe is so old that the light from even the farthest stars has had time to reach Earth. In this imaginary scenario, all of the stars in the universe are not moving at all.<\/p>\n\n\n\n

Picture a large bubble with Earth at the center. If the bubble were about 10 light years<\/a> across, it would contain about a dozen stars<\/a>. Of course, at several light years away, many of those stars would look pretty dim from Earth.<\/p>\n\n\n\n

If you keep enlarging the bubble to 1,000 light years across, then to 1 million light years, and then 1 billion light years, the farthest stars in the bubble will look even more faint. But there would also be more and more stars inside the bigger and bigger bubble, all of them contributing light. Even though the farthest stars look dimmer and dimmer, there would be a lot more of them, and the whole night sky should look very bright.<\/p>\n\n\n\n

It seems I\u2019m back where I started, but I\u2019m actually a little closer to the answer.<\/p>\n\n\n\n

Age matters<\/h2>\n\n\n\n

In the imaginary bubble illustration, I asked you to imagine that the stars are not moving and that the universe is very old. But the universe is only about 13 billion years old<\/a>.<\/p>\n\n\n\n

\"Image<\/a>
Galaxies as they appeared approximately 13.1 billion years ago, taken by the James Webb Space Telescope. NASA\/ESA\/CSA\/STScI\/Handout from Xinhua News Agency via Getty Images<\/a><\/figcaption><\/figure>\n\n\n\n

Even though that\u2019s an amazingly long time in human terms, it\u2019s short in astronomical terms. It\u2019s short enough that the light from stars more distant than about 13 billion light years hasn\u2019t actually reached Earth yet. And so the actual bubble around Earth that contains all the stars we can see only extends out to about 13 billion light years from Earth<\/a>.<\/p>\n\n\n\n

There just are not enough stars in the bubble to fill every line of sight. Of course, if you look in some directions in the sky, you can see stars. If you look at other bits of the sky, you can\u2019t see any stars. And that\u2019s because, in those dark spots, the stars that could block your line of sight are so far away their light hasn\u2019t reached Earth yet. As time passes, light from these more and more distant stars will have time to reach us.<\/p>\n\n\n\n

The Doppler shift<\/h2>\n\n\n\n

You might ask whether the night sky will eventually light up completely. But that brings me back to the other thing I told you to imagine: that all of the stars are not moving. The universe is actually expanding, with the most distant galaxies moving away from Earth at nearly the speed of light<\/a>.<\/p>\n\n\n\n

Because the galaxies are moving away so fast, the light from their stars is pushed into colors the human eye can\u2019t see. This effect is called the Doppler shift<\/a>. So, even if it had enough time to reach you, you still couldn\u2019t see<\/a> the light from the most distant stars with your eyes. And the night sky would not be completely lit up. https:\/\/www.youtube.com\/embed\/ikgRZt1BSyk?wmode=transparent&start=0 The Doppler shift, also known as the redshift, is a phenomenon in which light from objects that are moving away from an observer appears more toward the red end of the spectrum.<\/p>\n\n\n\n

If you wait even longer, eventually the stars will all burn out \u2013 stars like the sun last only about 10 billion years<\/a>. Astronomers hypothesize that in the distant future \u2013 a thousand trillion years from now \u2013 the universe will go dark, inhabited by only stellar remnants<\/a> like white dwarfs and black holes.<\/p>\n\n\n\n

Even though our night sky isn\u2019t completely filled with stars, we live in a very special time in the universe\u2019s life, when we\u2019re lucky enough to enjoy a rich and complex night sky, filled with light and dark.<\/p>\n\n\n\n

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Hello, curious kids! Do you have a question you\u2019d like an expert to answer? Ask an adult to send your question to CuriousKidsUS@theconversation.com<\/a>. Please tell us your name, age and the city where you live.<\/em><\/p>\n\n\n\n

And since curiosity has no age limit \u2013 adults, let us know what you\u2019re wondering, too. We won\u2019t be able to answer every question, but we will do our best.<\/em><\/p>\n\n\n\n

Brian Jackson<\/a>, Associate Professor of Astronomy, Boise State University<\/a><\/em><\/p>\n\n\n\n

This article is republished from The Conversation<\/a> under a Creative Commons license. Read the original article<\/a>.<\/p>\n","protected":false},"excerpt":{"rendered":"

Brian Jackson, Boise State University Curious Kids is a series for children of all ages. If you have a question you\u2019d like an expert to answer, send it to curiouskidsus@theconversation.com. Why is space so dark despite all of the stars in the universe? \u2013 Nikhil, age 15, New Delhi People have been asking why space […]<\/p>\n","protected":false},"author":44,"featured_media":35301,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":[],"categories":[3410,8],"tags":[218,12590,14731,14729,3834,5615,10224,14730,187,10042,8133],"_links":{"self":[{"href":"https:\/\/www.lifeandnews.com\/articles\/wp-json\/wp\/v2\/posts\/35300"}],"collection":[{"href":"https:\/\/www.lifeandnews.com\/articles\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.lifeandnews.com\/articles\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.lifeandnews.com\/articles\/wp-json\/wp\/v2\/users\/44"}],"replies":[{"embeddable":true,"href":"https:\/\/www.lifeandnews.com\/articles\/wp-json\/wp\/v2\/comments?post=35300"}],"version-history":[{"count":2,"href":"https:\/\/www.lifeandnews.com\/articles\/wp-json\/wp\/v2\/posts\/35300\/revisions"}],"predecessor-version":[{"id":35385,"href":"https:\/\/www.lifeandnews.com\/articles\/wp-json\/wp\/v2\/posts\/35300\/revisions\/35385"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.lifeandnews.com\/articles\/wp-json\/wp\/v2\/media\/35301"}],"wp:attachment":[{"href":"https:\/\/www.lifeandnews.com\/articles\/wp-json\/wp\/v2\/media?parent=35300"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.lifeandnews.com\/articles\/wp-json\/wp\/v2\/categories?post=35300"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.lifeandnews.com\/articles\/wp-json\/wp\/v2\/tags?post=35300"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}