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Old 01-22-2019, 01:56 PM
 
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A goodly number of scientists also write poetry. But a poet - especially one of Edgar Allen Poe's genre) - writing science is a turnaround His book "Eureka" seems to be his only surviving work in this field. In it, he predicted quite a few scientific discoveries to come which did indeed come - and a few that are still to come like how the universe will end. Today, I just learned something new about Edgar with this bit from The Physics of the Universe web site. https://www.physicsoftheuniverse.com/



"..... Olbers (who definitively stated the problem in 1823, although several others, dating back to the time of Newton, had previously posed similar ideas in various ways) asked why, if the universe was studded with billions upon billions of stars, the night sky was not completely lit up with the light from all these stars. The answer (first pointed out, interestingly enough, by the author Edgar Allen Poe in 1848 .... )



I'll bet someone here knows the answer. For me it is just another laurel for Edgar Allen Poe who had such a tragic life.
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Old 01-22-2019, 11:20 PM
 
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Originally Posted by Hazel W View Post
A goodly number of scientists also write poetry. But a poet - especially one of Edgar Allen Poe's genre) - writing science is a turnaround His book "Eureka" seems to be his only surviving work in this field. In it, he predicted quite a few scientific discoveries to come which did indeed come - and a few that are still to come like how the universe will end. Today, I just learned something new about Edgar with this bit from The Physics of the Universe web site. https://www.physicsoftheuniverse.com/



"..... Olbers (who definitively stated the problem in 1823, although several others, dating back to the time of Newton, had previously posed similar ideas in various ways) asked why, if the universe was studded with billions upon billions of stars, the night sky was not completely lit up with the light from all these stars. The answer (first pointed out, interestingly enough, by the author Edgar Allen Poe in 1848 .... )



I'll bet someone here knows the answer. For me it is just another laurel for Edgar Allen Poe who had such a tragic life.
Hi Hazel. Yes. There are far more stars in the Universe than there are in our observable Universe. Since light can only travel at 186,000 mile per second, and since the Universe is only some 13.7 billion years old, the light from stars beyond the sphere of our observable Universe hasn't had time to reach us. And the light from the stars that are within the observable Universe isn't enough to light up the night sky any more than they do.

Also, since the Universe is expanding, light from objects that are moving away from us gets red shifted. Light can eventually get red shifted out of the visible light part of the spectrum and into the microwave end of the spectrum. Thus, the cosmic microwave background radiation. And more than that, the further away galaxies are from each other, the faster the rate of expansion. While the speed limit within the Universe is the speed of light, space itself can expand faster than light. This means that the light from galaxies that are far enough away will never reach us because the expansion of space is carrying those galaxies away from us faster than the light from them can travel toward us. Given enough time all non-gravitationally bound galaxies will move beyond the sphere of our observable Universe and the only stars in the night sky will be from the stars in our own galaxy and from the galaxies that are gravitationally bound to our own galaxy such as the Andromeda galaxy which is actually on a collision course with us.

Thanks for posting that web site.
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Old 01-23-2019, 06:29 AM
 
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Originally Posted by Mike555 View Post
Hi Hazel. Yes. There are far more stars in the Universe than there are in our observable Universe. Since light can only travel at 186,000 mile per second, and since the Universe is only some 13.7 billion years old, the light from stars beyond the sphere of our observable Universe hasn't had time to reach us. And the light from the stars that are within the observable Universe isn't enough to light up the night sky any more than they do.

Also, since the Universe is expanding, light from objects that are moving away from us gets red shifted. Light can eventually get red shifted out of the visible light part of the spectrum and into the microwave end of the spectrum. Thus, the cosmic microwave background radiation. And more than that, the further away galaxies are from each other, the faster the rate of expansion. While the speed limit within the Universe is the speed of light, space itself can expand faster than light. This means that the light from galaxies that are far enough away will never reach us because the expansion of space is carrying those galaxies away from us faster than the light from them can travel toward us. Given enough time all non-gravitationally bound galaxies will move beyond the sphere of our observable Universe and the only stars in the night sky will be from the stars in our own galaxy and from the galaxies that are gravitationally bound to our own galaxy such as the Andromeda galaxy which is actually on a collision course with us.

Thanks for posting that web site.



Thank you, Mike. I wish I'd remembered that last night when a friend asked "What happens to light once it passes us by?" Some of it is never going to reach, let alone pass us. Edgar Allen Poe had an answer to that, also. He believed the expansion would go only so far and then --- is the word "collapse"? --- back to almost a point. Almost. But Poe went another direction with his conclusion. Another topic.
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Old 01-23-2019, 11:23 AM
 
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Originally Posted by Hazel W View Post
Thank you, Mike. I wish I'd remembered that last night when a friend asked "What happens to light once it passes us by?" Some of it is never going to reach, let alone pass us. Edgar Allen Poe had an answer to that, also. He believed the expansion would go only so far and then --- is the word "collapse"? --- back to almost a point. Almost. But Poe went another direction with his conclusion. Another topic.
Collapse or contract are both correct terms. However, the view today is that there is not sufficient mass in the Universe to stop the expansion of the Universe and that 'dark energy' is causing the expansion of the Universe to actually accelerate. But, and I have to modify what I said in my other post, that doesn't necessarily mean that it will continue to do so as stated in the link below.
Update by Christopher Springob: Astronomers' understanding of this problem has changed dramatically since we first answered this question in January 1999. There's now convincing evidence that the expansion of the universe is actually accelerating, not decelerating. This cannot be due to gravity. It must be due to "dark energy", a repulsive force of empty space that counteracts gravity on large scales. (You can read more about this here.)

Assuming astronomers' interpretations of the data are correct, and the universe is indeed accelerating at an ever-faster rate, we still don't know what the ultimate fate of the universe is going to be because we don't know if the dark energy will always be repulsive. There are some models that allow for it to become attractive in the future, which would cause the universe to ultimately recontract. But if dark energy is real, then the density of matter will no longer have much impact on the final fate of the universe, because dark energy tends to win out over gravity in the long run.

How do we know if the universe will keep expanding forever? (Intermediate) - Curious About Astronomy? Ask an Astronomer
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Old 01-23-2019, 12:00 PM
 
2,714 posts, read 3,003,760 times
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Originally Posted by Mike555 View Post
Collapse or contract are both correct terms. However, the view today is that there is not sufficient mass in the Universe to stop the expansion of the Universe and that 'dark energy' is causing the expansion of the Universe to actually accelerate. But, and I have to modify what I said in my other post, that doesn't necessarily mean that it will continue to do so as stated in the link below.
Update by Christopher Springob: Astronomers' understanding of this problem has changed dramatically since we first answered this question in January 1999. There's now convincing evidence that the expansion of the universe is actually accelerating, not decelerating. This cannot be due to gravity. It must be due to "dark energy", a repulsive force of empty space that counteracts gravity on large scales. (You can read more about this here.)

Assuming astronomers' interpretations of the data are correct, and the universe is indeed accelerating at an ever-faster rate, we still don't know what the ultimate fate of the universe is going to be because we don't know if the dark energy will always be repulsive. There are some models that allow for it to become attractive in the future, which would cause the universe to ultimately recontract. But if dark energy is real, then the density of matter will no longer have much impact on the final fate of the universe, because dark energy tends to win out over gravity in the long run.

How do we know if the universe will keep expanding forever? (Intermediate) - Curious About Astronomy? Ask an Astronomer

Do you know the old song "I'll never say never again again?" "It will never happen." A constant refrain.


About the dark energy story, is there a link that should get me there? Thanks.
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Old 01-23-2019, 12:48 PM
 
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Originally Posted by Hazel W View Post
Do you know the old song "I'll never say never again again?" "It will never happen." A constant refrain.



https://www.youtube.com/watch?v=YghFAHhU2OI


Quote:
About the dark energy story, is there a link that should get me there? Thanks.
This article addresses the question of what dark energy is.

https://www.space.com/20929-dark-energy.html

But I like this YouTube video by PBS Space Time Digital Studios. Astrophysicist Matt O’Dowd writes and hosts the PBS Space Time video series and does a great job of explaining things.

Anti-gravity and the True Nature of Dark Energy | Space Time | PBS Digital Studios


https://www.youtube.com/watch?v=UwYSWAlAewc
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Old 01-23-2019, 01:53 PM
 
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Oh, all right. I have grown quite used to people turning a link into the word "here". Sorry. :-)


It's a busy day here. I'd better move on. Thanks for your help.
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Old 01-23-2019, 02:14 PM
 
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Originally Posted by Hazel W View Post
Oh, all right. I have grown quite used to people turning a link into the word "here". Sorry. :-)


It's a busy day here. I'd better move on. Thanks for your help.
I don't understand.
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Old 01-23-2019, 02:45 PM
 
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Originally Posted by Mike555 View Post
I don't understand.

Oh, I was just enjoying the chats so much that I feared I'd be taking up too much time. Sometimes I get going and never stop. Meanwhile my desk is piled with things that await doing. I'll be back to learn more. Much more fun that reconciling bank statements and filling in tax papers.


Or, did you mean you didn't understand about the link? I do not know how it is done but some people can leave off a link and type the word "here" which actually takes you to that page. Fascinating what can be done on a computer that can't be done with a typewriter.
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Old 01-23-2019, 02:54 PM
 
22,789 posts, read 17,263,699 times
Reputation: 9502
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Originally Posted by Hazel W View Post
Oh, I was just enjoying the chats so much that I feared I'd be taking up too much time. Sometimes I get going and never stop. Meanwhile my desk is piled with things that await doing. I'll be back to learn more. Much more fun that reconciling bank statements and filling in tax papers.


Or, did you mean you didn't understand about the link? I do not know how it is done but some people can leave off a link and type the word "here" which actually takes you to that page. Fascinating what can be done on a computer that can't be done with a typewriter.
I don't understand why you said ''Oh, all right. I have grown quite used to people turning a link into the word "here". Sorry. :-)'' And then saying you were sorry about it.
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