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vincentm
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I'm having trouble wrapping my head around this, can someone explain this to me?
Thank you,
Vincent
Thank you,
Vincent
Read a book.vincentm said:I'm having trouble wrapping my head around this, can someone explain this to me?
Thank you,
Vincent
A little brusque maybe?DaveC426913 said:Read a book.
It wasn't an admonishment, it was responding in kind to his query.Garth said:A little brusque maybe?
Wow, thanks for being rude. For your information the book's section on this is a little hard to grasp, i was hoping for an explanation from here, if everyone was to follow this advice of yours then why would this site continue to exist? Remind me never to ask for your help, by the way thanks Garth!DaveC426913 said:Read a book.
(What? You wanted a better answer? How about asking a better question. )
Touche' i could have formulated my question better, my apologies as well.DaveC426913 said:OK, I guess it came across as a little harsh. It wasn't intended to be harsh, so much as it was intended to be tutorial. My curt response was a not-so-subtle way of saying "I'll put as much effort into this as you do."
See, this forum has a policy of encouraging guidance - helping people through things, rather than doing the work for them. A very common phrase on this board is: "Show your work!"
If your question explained what you DO know about Olber's paradox and where it goes wrong for you, it would be far more likely to elicit all sorts of helpful responses.
Anyway, since Garth covered it fairly well, there's nothing for me to add.
That argument is just as valid and approaches the geometry from a different direction. Take any thin shell around the Earth containing typical stars. The luminosity of each star L ~ [itex]\frac{1}{r^2}[/itex] but the surface area of the shell, and hence the typical number of stars within it, A ~ [itex]r^2[/itex] so the total luminosity from each shell, of whatever radius r is the same. Now add each shell out to inifinity and no matter how small the luminosity from each shell is, the total diverges to infinity. It isn't exactly true because what hasn't been taken into account is the light that is blocked by stars in the foreground, which is why it is easier to do the calculation my first way round.vincentm said:Anyways the way its explained to me in the book I'm reading is an example of a spherical shell surrounding the earth, and as this shell grew in radius then the total luminosity of the stars would increase because more stars are incased in the "shell, but this isn't exactly true, right?
Good point, though I would replace the word 'mooted' with the word 'mitigated'. A starscape lit so would still be nigh-infinitely bright.turbo-1 said:Even in an infinite (spacially and temporally) universe, Olber's paradox is mooted by redshift. The more distant an object is, the more redshifted its light. Light from objects sufficiently distant from us will be redshifted into undetectibility.
turbo-1 said:Even in an infinite (spacially and temporally) universe, Olber's paradox is mooted by redshift. The more distant an object is, the more redshifted its light. Light from objects sufficiently distant from us will be redshifted into undetectibility.
matt.o said:That is why Garth specified a static universe.
Yes -that is why it was a paradox to Olbers and the others back then, today with an expanding universe there is no paradox - the sky is dark at night!vincentm said:But doesn't a static universe say that it is not expanding?
Garth said:Yes -that is why it was a paradox to Olbers and the others back then, today with an expanding universe there is no paradox - the sky is dark at night!
garth
Only in that as a Big Bang universe is not infinite AND eternal AND static it is not surprising that in such the sky is dark at night.vincentm said:Ok, stupid question time:
How does Olber's Paradox play into supporting evidence for the big bang?
Well, we already need to start delving into the infrared regions to see much of anything beyond what Hubble has shown us, and more distant objects will be redshifted still more.DaveC426913 said:Good point, though I would replace the word 'mooted' with the word 'mitigated'. A starscape lit so would still be nigh-infinitely bright.
True, but that's because most of us are under the assumption that redshift is caused by cosmological expansion. When Hubble and his team established the relationship between redshift and distance, he did not embrace this view. He was working within the confines of a steady-state model. Even in Hubble's steady-state model, Olbers paradox would be laid low by the distance/redshift relationship, even for a temporally and spacially infinite universe.matt.o said:That is why Garth specified a static universe.
What metric do you have in mind that is more predictive than the FRW model?turbo-1 said:True, but that's because most of us are under the assumption that redshift is caused by cosmological expansion. When Hubble and his team established the relationship between redshift and distance, he did not embrace this view. He was working within the confines of a steady-state model. Even in Hubble's steady-state model, Olbers paradox would be laid low by the distance/redshift relationship, even for a temporally and spacially infinite universe.
I am proposing no metric in that post, merely pointing out that if distant objects are more redshifted than closer objects, sufficiently distant objects will be redshifted out of obvservability, regardless of the mechanism responsible for the redshift, mooting Olber's Paradox.Chronos said:What metric do you have in mind that is more predictive than the FRW model?
That is not a stupid question . . . . In fact it is one of the best questions you can ask. What it means, logically, is the universe cannot be both infinitely old and spacious at the same time.vincentm said:Ok, stupid question time:
How does Olber's Paradox play into supporting evidence for the big bang?
Chronos said:That is not a stupid question . . . . In fact it is one of the best questions you can ask. What it means, logically, is the universe cannot be both infinitely old and spacious at the same time.
But the sky would only be 'burning bright at night' if the universe were infinite & eternal & static.Chronos said:I contest the claim the universe need be static. In an infinitely spacious, infinitely old universe that contains an infinite number of stars, we should see an infinite number of photons bombarding us from every direction. Unless those photons are somehow redshifted out of existence by new physics [i.e., replacing the ever popular laws of thermodynamics], The night sky should as bright as the surface of the sun.
You would need pretty big eyes to see mag 29!sunblock said:Wouldn't it be more logical to say that the sky isn't dark at night. It looks dark to us because person nature evolved us with eyes that detected the highest level possible without looking directly at the sun and our eyes just arn't sensitive enough to see the avaliable light at night. If they were we would be blind in the daytime unless we had really thick sunglasses.
I don't entirely disagree, just wonder what number you derive assuming an upper limit of z = 1100?Garth said:But the sky would only be 'burning bright at night' if the universe were infinite & eternal & static.
If it were not static but expanding then the temperature of the sky would be attentuated by the red shift,
[itex]F \propto \frac{1}{(1 + z)^2}[/tex]
there would be similar attentuations for a finite size, depending on the circumference, or a finite age, depending on the distance 'out' to either event horizon, or back to the epoch of 'first light'.
As the universe is both cosmologically red shifted (however that is interpreted), and limited in both age, and (as it is thought) distance out to the particle horizon, the combined attentuations result in the very faint sky background luminosity (down to about mag 29 I believe).
The CMB provides an example of one form of radiation (the whole sky) that was not covered by Olber's paradox, which has been attenuated from ~ 30000K to ~ 30K.
Garth
Try 2.760K .Chronos said:I don't entirely disagree, just wonder what number you derive assuming an upper limit of z = 1100?
Chronos said:That is not a stupid question . . . . In fact it is one of the best questions you can ask. What it means, logically, is the universe cannot be both infinitely old and spacious at the same time.
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