Why is the Universe Black?Date: 04/11/2001 at 08:25:31 From: Shane Kenyon Subject: Light in the universe and black hole I was wondering...why is the universe black? I also wanted to know if there is a such thing as a black hole that sucks everything into it including light. If there is, wouldn't space be void? Koron Date: 04/11/2001 at 09:02:14 From: Doctor Mitteldorf Subject: Re: Light in the universe and black hole Dear Koron, The first question you ask has a history dating back to 1744, when Jean Philippe Olber first posed "Olber's paradox." I've done a Web search on that topic, and here are a few places you can read about it. One short explanation is that it is the stars very, very far from us that would make the night sky bright as a star; but the expansion of the universe weakens the light that comes from these stars, so that the total amount of light from them ends up being quite small. Olber's Paradox: Why is the Night Sky Dark? - Cornell University Astronomy http://astrosun.tn.cornell.edu/courses/astro201/olbers_paradox.htm Olber's Paradox - Creation Moments http://pages.prodigy.net/jessieann/Space/olbrpara.html Olber's Paradox - National Schools' Observatory, U.K. http://www.schoolsobservatory.org.uk/study/sci/cosmo/internal/olbers.htm Olber's Paradox - Eric Weisstein, Astronomy http://scienceworld.wolfram.com/astronomy/OlbersParadox.html Your second question is about black holes. Many people misunderstand these objects and think of them as "sucking up" everything around them. One thing to remember about a black hole is that from far away they have the same gravity as anything else. For example: the Earth revolves around the sun, pulled by its gravity. If at this very moment the sun suddenly implodes and becomes a black hole, with the same mass that it had before it imploded, then the earth would continue around in exactly the same orbit that it's in now. The thing that makes black holes special is just their tiny size. Take the sun again: now, you can't get within 100,000 miles of the sun because you'd be inside it. Even if you were inside it, you wouldn't be pulled by the sun's whole gravity, because some of the sun would be "outside of you." This keeps the sun's gravity from ever getting really, really strong. But if the sun collapsed into a black hole, it would be less than 10 miles across. All that mass, concentrated in a tiny space! Now you could get really close to it, and the gravity would be terrifically strong, so strong it could "suck up" light. But you see that in a sense the gravity didn't get stronger, only more concentrated. The strange properties of black holes come from the fact that they're small, so you can get close in. - Doctor Mitteldorf, The Math Forum http://mathforum.org/dr.math/ |
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