The Cosmology Thread

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Re: The Cosmology Thread

Post by UncleBob » Thu Oct 09, 2014 8:14 am

OldWorldSwine wrote:
UncleBob wrote:Billions of Galaxies are Missing from the Cosmos

I struggled whether to post this here or in the "Shenanigans of Jocose" thread.
Could not finish the article, as it is behind their registration wall. It is kind of amusing, though, to think in terms of "missing" galaxies, rather than maybe allowing that we may have made a big mistake in our calculations somewhere. But that's just semantics. It's when things don't add up that you know the science is about to get interesting.
In many ways, we are living in the golden age of observational astronomy. For instance, the moon is moving away from the earth and yet it is at the perfect distance that we can see the sun's corona during a solar eclipse. In the future, with cosmic expansion, it is possible that we will not be able to observe any stars beyond our galaxy. The cosmic Event Horizon is already shrinking in that it is likely that we see fewer galaxies each century or so. Wouldn't it be interesting if we already cannot observe 1/3, 1/2, or more of the universe?
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Re: The Cosmology Thread

Post by OldWorldSwine » Thu Oct 09, 2014 8:39 am

UncleBob wrote:
OldWorldSwine wrote:
UncleBob wrote:Billions of Galaxies are Missing from the Cosmos

I struggled whether to post this here or in the "Shenanigans of Jocose" thread.
Could not finish the article, as it is behind their registration wall. It is kind of amusing, though, to think in terms of "missing" galaxies, rather than maybe allowing that we may have made a big mistake in our calculations somewhere. But that's just semantics. It's when things don't add up that you know the science is about to get interesting.
In many ways, we are living in the golden age of observational astronomy. For instance, the moon is moving away from the earth and yet it is at the perfect distance that we can see the sun's corona during a solar eclipse. In the future, with cosmic expansion, it is possible that we will not be able to observe any stars beyond our galaxy. The cosmic Event Horizon is already shrinking in that it is likely that we see fewer galaxies each century or so. Wouldn't it be interesting if we already cannot observe 1/3, 1/2, or more of the universe?
Yeah. Objects at opposite ends of the visible universe are moving away from one another faster than the speed of light, are they not?

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Re: The Cosmology Thread

Post by Rusty » Thu Oct 09, 2014 9:15 am

OldWorldSwine wrote:
UncleBob wrote:
OldWorldSwine wrote:
UncleBob wrote:Billions of Galaxies are Missing from the Cosmos

I struggled whether to post this here or in the "Shenanigans of Jocose" thread.
Could not finish the article, as it is behind their registration wall. It is kind of amusing, though, to think in terms of "missing" galaxies, rather than maybe allowing that we may have made a big mistake in our calculations somewhere. But that's just semantics. It's when things don't add up that you know the science is about to get interesting.
In many ways, we are living in the golden age of observational astronomy. For instance, the moon is moving away from the earth and yet it is at the perfect distance that we can see the sun's corona during a solar eclipse. In the future, with cosmic expansion, it is possible that we will not be able to observe any stars beyond our galaxy. The cosmic Event Horizon is already shrinking in that it is likely that we see fewer galaxies each century or so. Wouldn't it be interesting if we already cannot observe 1/3, 1/2, or more of the universe?
Yeah. Objects at opposite ends of the visible universe are moving away from one another faster than the speed of light, are they not?
I think the universe's size depends upon what ones assumes about the universe. These are not facts that are known. So all of the answers presume different models. For example if the universe is finite but unbounded then the universe may be smaller than the observable universe ie distant images of galaxies may be early images of much more nearby galaxies. That's one possibility, and AFAIK I haven't seen anything that excludes that. Another is that the universe is actually much much larger than the observable universe. According to Alan Guth it could be on order of 10^23 times as large. And there are other models that find that the universe is bigger than the observable universe but only by a factor of a few hundred. So take your pick. It's not known.

Due to cosmic expansion the light from distant things that are visible now may not be visible in the future ie the light from those objects for events closer to us in time may never reach us. I think this is what Bob may mean by objects vanishing. But the cosmic horizon isn't shrinking. It should remain fairly constant at about 16 B LYs. It's space expanding and faster as the distance to us increases. So we should see more distant objects rather than fewer initially. Where initially should be taken as the next billion years or so. But none of this 'vanishing' applies to objects to which our Galaxy is gravitationally bound. Clearly they cannot be beyond the horizon or they wouldn't be gravitationally bound. Andromeda isn't going to vanish. It's going to merge with the Milky Way in a few billion years. It's blue-shifted. And there will be many others to which we remain bound eg the entire Virgo supercluster. Being gravitationally bound means it remains within our horizon. Cosmic expansion really only matters at distances beyond approx. 300M LYs. There is a LOT of stuff within that distance that will continue to be visible for a very long time. So I really doubt that we'll detect fewer things 100 years from now, hypothetically because some vanish beyond the horizon in the meantime. Those events ie vanishing beyond the horizon are still way off in the future.
Last edited by Rusty on Thu Oct 09, 2014 9:27 am, edited 2 times in total.
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Re: The Cosmology Thread

Post by UncleBob » Thu Oct 09, 2014 9:23 am

Rusty wrote:
OldWorldSwine wrote:
UncleBob wrote:
OldWorldSwine wrote:
UncleBob wrote:Billions of Galaxies are Missing from the Cosmos

I struggled whether to post this here or in the "Shenanigans of Jocose" thread.
Could not finish the article, as it is behind their registration wall. It is kind of amusing, though, to think in terms of "missing" galaxies, rather than maybe allowing that we may have made a big mistake in our calculations somewhere. But that's just semantics. It's when things don't add up that you know the science is about to get interesting.
In many ways, we are living in the golden age of observational astronomy. For instance, the moon is moving away from the earth and yet it is at the perfect distance that we can see the sun's corona during a solar eclipse. In the future, with cosmic expansion, it is possible that we will not be able to observe any stars beyond our galaxy. The cosmic Event Horizon is already shrinking in that it is likely that we see fewer galaxies each century or so. Wouldn't it be interesting if we already cannot observe 1/3, 1/2, or more of the universe?
Yeah. Objects at opposite ends of the visible universe are moving away from one another faster than the speed of light, are they not?
I think the universe's size depends upon what ones assumes about the universe. These are not facts that are known. So all of the answers presume different models. For example if the universe is finite but unbounded then the universe may be smaller than the observable universe ie distant images of galaxies may be early images of much more nearby galaxies. That's one possibility, and AFAIK I haven't seen anything that excludes that. Another is that the universe is actually much much larger than the observable universe. According to Alan Guth it could be on order of 10^23 times as large. And there are other models that find that the universe is bigger than the observable universe but only by a factor of a few hundred. So take your pick. It's not known.

Due to cosmic expansion the light from distant things that are visible now may not be visible in the future ie the light from events closer to us in time may never reach us. I think this is what Bob may mean by objects vanishing. But the cosmic horizon isn't shrinking. It should remain fairly constant at about 16 B LYs. So we should see more distant objects rather than fewer initially. Where initially should be taken as the next billion years or so. But none of this 'vanishing' applies to objects to which our Galaxy is gravitationally bound. Clearly they cannot be beyond the horizon or they wouldn't be gravitationally bound. Andromeda isn't going to vanish. It's going to merge with the Milky Way in a few billion years. And there will be many others to which we remain bound eg the entire Virgo supercluster. Cosmic expansion really only matters at distances beyond approx. 300M LYs. There is a LOT of stuff within that distance that will continue to be visible for a very long time. So I really doubt that we'll detect fewer things 100 years from now, hypothetically because some vanish beyond the horizon in the meantime. Those events ie vanishing beyond the horizon are still way off in the future.
Yes, this all assumes an expanding universe and, yes, they should be observable for millions of years. Also, when I said "our galaxy" I meant that most all of that matter should have collected into a galaxy by then, or at least in that process.

http://en.wikipedia.org/wiki/Cosmological_horizon
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Re: The Cosmology Thread

Post by Rusty » Thu Oct 09, 2014 9:42 am

UncleBob wrote:
Rusty wrote:
OldWorldSwine wrote:
UncleBob wrote:
OldWorldSwine wrote:
UncleBob wrote:Billions of Galaxies are Missing from the Cosmos

I struggled whether to post this here or in the "Shenanigans of Jocose" thread.
Could not finish the article, as it is behind their registration wall. It is kind of amusing, though, to think in terms of "missing" galaxies, rather than maybe allowing that we may have made a big mistake in our calculations somewhere. But that's just semantics. It's when things don't add up that you know the science is about to get interesting.
In many ways, we are living in the golden age of observational astronomy. For instance, the moon is moving away from the earth and yet it is at the perfect distance that we can see the sun's corona during a solar eclipse. In the future, with cosmic expansion, it is possible that we will not be able to observe any stars beyond our galaxy. The cosmic Event Horizon is already shrinking in that it is likely that we see fewer galaxies each century or so. Wouldn't it be interesting if we already cannot observe 1/3, 1/2, or more of the universe?
Yeah. Objects at opposite ends of the visible universe are moving away from one another faster than the speed of light, are they not?
I think the universe's size depends upon what ones assumes about the universe. These are not facts that are known. So all of the answers presume different models. For example if the universe is finite but unbounded then the universe may be smaller than the observable universe ie distant images of galaxies may be early images of much more nearby galaxies. That's one possibility, and AFAIK I haven't seen anything that excludes that. Another is that the universe is actually much much larger than the observable universe. According to Alan Guth it could be on order of 10^23 times as large. And there are other models that find that the universe is bigger than the observable universe but only by a factor of a few hundred. So take your pick. It's not known.

Due to cosmic expansion the light from distant things that are visible now may not be visible in the future ie the light from events closer to us in time may never reach us. I think this is what Bob may mean by objects vanishing. But the cosmic horizon isn't shrinking. It should remain fairly constant at about 16 B LYs. So we should see more distant objects rather than fewer initially. Where initially should be taken as the next billion years or so. But none of this 'vanishing' applies to objects to which our Galaxy is gravitationally bound. Clearly they cannot be beyond the horizon or they wouldn't be gravitationally bound. Andromeda isn't going to vanish. It's going to merge with the Milky Way in a few billion years. And there will be many others to which we remain bound eg the entire Virgo supercluster. Cosmic expansion really only matters at distances beyond approx. 300M LYs. There is a LOT of stuff within that distance that will continue to be visible for a very long time. So I really doubt that we'll detect fewer things 100 years from now, hypothetically because some vanish beyond the horizon in the meantime. Those events ie vanishing beyond the horizon are still way off in the future.
Yes, this all assumes an expanding universe and, yes, they should be observable for millions of years. Also, when I said "our galaxy" I meant that most all of that matter should have collected into a galaxy by then, or at least in that process.

http://en.wikipedia.org/wiki/Cosmological_horizon
Millions? It's Billions. By 'our galaxy' do you mean the merged Andromeda-Milky Way? A merged galaxy is at least 5 B years out. The tidal effects of the galaxies passing through each for the first time won't be for about 2-3 billion years. So our sun is very likely in old age and a in a nova state and has expanded beyond the Earth's orbit so the Earth is gone by the time the merge is done. The local group is still bound to the Virgo supercluster and there are plenty of other things bound to it as well. Try and explain why they would go away if they remain gravitationally bound. They're well within 300M LYs. The wiki article appears to have a cosmic event horizon of 46 B LYs. But they're qualifying it as comoving distance ie indep. of space expansion. So their limit is much further out than the number I mentioned. We get no signal from any object at those distances today.
Last edited by Rusty on Thu Oct 09, 2014 9:54 am, edited 1 time in total.
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Re: The Cosmology Thread

Post by UncleBob » Thu Oct 09, 2014 9:48 am

Rusty wrote: Millions? It's Billions. By 'our galaxy' do you mean the merged Andromeda-Milky Way? A merged galaxy is at least 5 B years out. The tidal effects of the galaxies passing through each for the first time won't be for about 2-3 billion years. So our sun is very likely in old age and a in a nova state and has expanded beyond the Earth's orbit so the Earth is gone by the time the merge is done. The local group is still bound to the Virgo supercluster and there are plenty of other things bound to it as well. Try and explain why they would go away if they remain gravitationally bound. They're well within 300M LYs.
Yes. Millions make up billions. Yes, our galaxy will be eventually merged with Andromeda and the other dwarf galaxies and assorted matter. Yes, our solar system will be gone or extinct but that does not mean that humanity will be, though it is likely humanity will be bound to the galaxy.
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Re: The Cosmology Thread

Post by Rusty » Thu Oct 09, 2014 9:59 am

UncleBob wrote:
Rusty wrote: Millions? It's Billions. By 'our galaxy' do you mean the merged Andromeda-Milky Way? A merged galaxy is at least 5 B years out. The tidal effects of the galaxies passing through each for the first time won't be for about 2-3 billion years. So our sun is very likely in old age and a in a nova state and has expanded beyond the Earth's orbit so the Earth is gone by the time the merge is done. The local group is still bound to the Virgo supercluster and there are plenty of other things bound to it as well. Try and explain why they would go away if they remain gravitationally bound. They're well within 300M LYs.
Yes. Millions make up billions. Yes, our galaxy will be eventually merged with Andromeda and the other dwarf galaxies and assorted matter. Yes, our solar system will be gone or extinct but that does not mean that humanity will be, though it is likely humanity will be bound to the galaxy.
:egor: Ok but I still don't see any argument that says objects we see now are going to vanish within 100 years or so. I'll be generous, make it a million years instead of a hundred. What is going to vanish? We should see more objects.

We should actually be able to calculate this. It's the distance at which space is moving away (with objects) at the speed of light. Anything at that distance today is not visible anymore. This is from Hubble's law. Since the expansion is accelerating we would need to evaluate an integral for the future. But we can't yet see those objects. They're either always beyond any propagation time or they're in the future for us. As time passes we will see some of them because their light emitted long ago will finally reach us.
Last edited by Rusty on Thu Oct 09, 2014 10:10 am, edited 1 time in total.
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Re: The Cosmology Thread

Post by UncleBob » Thu Oct 09, 2014 10:06 am

Rusty wrote:
UncleBob wrote:
Rusty wrote: Millions? It's Billions. By 'our galaxy' do you mean the merged Andromeda-Milky Way? A merged galaxy is at least 5 B years out. The tidal effects of the galaxies passing through each for the first time won't be for about 2-3 billion years. So our sun is very likely in old age and a in a nova state and has expanded beyond the Earth's orbit so the Earth is gone by the time the merge is done. The local group is still bound to the Virgo supercluster and there are plenty of other things bound to it as well. Try and explain why they would go away if they remain gravitationally bound. They're well within 300M LYs.
Yes. Millions make up billions. Yes, our galaxy will be eventually merged with Andromeda and the other dwarf galaxies and assorted matter. Yes, our solar system will be gone or extinct but that does not mean that humanity will be, though it is likely humanity will be bound to the galaxy.
:egor: Ok but I still don't see any argument that says objects we see now are going to vanish within 100 years or so. I'll be generous, make it a million years instead of a hundred. What is going to vanish? We should see more objects.
Well, we don't know. We don't know what we can't see. The new telescopes continue to discover areas that we didn't know existed or couldn't see before but we are approaching the limit of what we can see. We have technology that has increased our observable universe but, with expansion, there may be areas we can never see. We don't know. Eventually we will reach the limits of technology and certain objects may start disappearing. In any case, if the universe is expanding at an accelerated rate and if the universe is larger than our ability to observe it then we will observe less in a century than we can now.
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Re: The Cosmology Thread

Post by Rusty » Thu Oct 09, 2014 10:31 am

UncleBob wrote:
Rusty wrote:
UncleBob wrote:
Rusty wrote: Millions? It's Billions. By 'our galaxy' do you mean the merged Andromeda-Milky Way? A merged galaxy is at least 5 B years out. The tidal effects of the galaxies passing through each for the first time won't be for about 2-3 billion years. So our sun is very likely in old age and a in a nova state and has expanded beyond the Earth's orbit so the Earth is gone by the time the merge is done. The local group is still bound to the Virgo supercluster and there are plenty of other things bound to it as well. Try and explain why they would go away if they remain gravitationally bound. They're well within 300M LYs.
Yes. Millions make up billions. Yes, our galaxy will be eventually merged with Andromeda and the other dwarf galaxies and assorted matter. Yes, our solar system will be gone or extinct but that does not mean that humanity will be, though it is likely humanity will be bound to the galaxy.
:egor: Ok but I still don't see any argument that says objects we see now are going to vanish within 100 years or so. I'll be generous, make it a million years instead of a hundred. What is going to vanish? We should see more objects.
Well, we don't know. We don't know what we can't see. The new telescopes continue to discover areas that we didn't know existed or couldn't see before but we are approaching the limit of what we can see.
What is the nature of that limit? If it is expansion of space ie Hubble expansion then we can calculate it. And we can place an upper bound on that distance limit today and also it's event origin time because of propagation time. The thing that complicates it is that there may have been Guth's early inflation. If so then there are objects that never were within any signal time ie their signal will never reach us. This is independent of how far back we go. Those objects and events were always outside our light cone.
UncleBob wrote:We have technology that has increased our observable universe but, with expansion, there may be areas we can never see. We don't know. Eventually we will reach the limits of technology and certain objects may start disappearing. In any case, if the universe is expanding at an accelerated rate and if the universe is larger than our ability to observe it then we will observe less in a century than we can now.
What is the oldest and most distant EM signal we know? It's the CBR, that occurred approx. 400K years after the event. This is long after Guth's inflation. And that emission occurred before any stars or galaxies were created. So what has to happen to the cbr? It's now red-shifted to 2.7 K. But we can still detect it. And it's uniform in the sky except for our motion ie doppler effects of the receiver's motion. We're inside the big bang's leading edge as the CBR signal. No EM signal propagated further than that.
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Re: The Cosmology Thread

Post by UncleBob » Thu Oct 09, 2014 6:19 pm

Rusty wrote:
UncleBob wrote:
Rusty wrote:
UncleBob wrote:
Rusty wrote: Millions? It's Billions. By 'our galaxy' do you mean the merged Andromeda-Milky Way? A merged galaxy is at least 5 B years out. The tidal effects of the galaxies passing through each for the first time won't be for about 2-3 billion years. So our sun is very likely in old age and a in a nova state and has expanded beyond the Earth's orbit so the Earth is gone by the time the merge is done. The local group is still bound to the Virgo supercluster and there are plenty of other things bound to it as well. Try and explain why they would go away if they remain gravitationally bound. They're well within 300M LYs.
Yes. Millions make up billions. Yes, our galaxy will be eventually merged with Andromeda and the other dwarf galaxies and assorted matter. Yes, our solar system will be gone or extinct but that does not mean that humanity will be, though it is likely humanity will be bound to the galaxy.
:egor: Ok but I still don't see any argument that says objects we see now are going to vanish within 100 years or so. I'll be generous, make it a million years instead of a hundred. What is going to vanish? We should see more objects.
Well, we don't know. We don't know what we can't see. The new telescopes continue to discover areas that we didn't know existed or couldn't see before but we are approaching the limit of what we can see.
What is the nature of that limit? If it is expansion of space ie Hubble expansion then we can calculate it. And we can place an upper bound on that distance limit today and also it's event origin time because of propagation time. The thing that complicates it is that there may have been Guth's early inflation. If so then there are objects that never were within any signal time ie their signal will never reach us. This is independent of how far back we go. Those objects and events were always outside our light cone.
UncleBob wrote:We have technology that has increased our observable universe but, with expansion, there may be areas we can never see. We don't know. Eventually we will reach the limits of technology and certain objects may start disappearing. In any case, if the universe is expanding at an accelerated rate and if the universe is larger than our ability to observe it then we will observe less in a century than we can now.
What is the oldest and most distant EM signal we know? It's the CBR, that occurred approx. 400K years after the event. This is long after Guth's inflation. And that emission occurred before any stars or galaxies were created. So what has to happen to the cbr? It's now red-shifted to 2.7 K. But we can still detect it. And it's uniform in the sky except for our motion ie doppler effects of the receiver's motion. We're inside the big bang's leading edge as the CBR signal. No EM signal propagated further than that.
I remember reading about the effect some time ago. I may have mis-remembered the time scales.

As the universe ages, expands, future cosmologists will know less
So why is the past the best time to observe the universe? There are actually two competing stages to study the cosmos. During the young universe the cosmic horizon is closer to you and as the universe gets older you can see more of it due to light having more time to travel. As time goes by, however, matter collapses. This stage “muddies the water” of the cosmic sea because you misplace reminiscence of original conditions of minute scales.
In the end, the first grows better as the second becomes worse.

The best time for observers to research the cosmos was about half a billion years following the Big Bang because the formation of galaxies and stars began. However, it’s not too late for astronomers.

“21-centimeter surveys are our best hope," said Loeb. "By observing hydrogen at large distances, we can map how matter was distributed at the early times of interest.

Eventually, in approximately 10 and 100 times the universe’s current age, researchers will not be able to study the stars because of the expansion; galaxies are moving beyond our horizon and the light that leaves the distant galaxies will never reach us in the future.
Top astronomer says universe will eventually disappear

I'm not saying we will have a dark universe in 100 years but we will be able to see less than today. This effect may not be as noticeable until much later.
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Re: The Cosmology Thread

Post by UncleBob » Thu Oct 09, 2014 6:29 pm

Oh, and as for disappearing objects and technology limitations:

A Galactic Scale Disappearing Act: Lyman Break Galaxies at z ~ 8 ~ 9
Their study also reveals that the candidates with z ~ 8 – 9 do not provide enough ionizing flux to re-ionize the Universe; however, they mention that fainter galaxies falling below their detection limit likely account for a significant UV contribution. If this is the case, then more faint galaxies are needed to account for the needed flux than predicted by a faint end slope of a Salpeter Initial Mass Function. These findings may have to wait for confirmation from observations made by the James Webb Space Telescope.
So we may have very faint objects that we can't see providing UV pollution--we don't know. It may be possible to circumvent that with future technology. It is possible that, if we had our current technology 100, 500, 1000, or more years ago, we could have seen these objects (if they are there).
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Re: The Cosmology Thread

Post by A_Morley » Thu Oct 09, 2014 6:35 pm

The last word should go to the late Sir Patrick Moore.
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Re: The Cosmology Thread

Post by Rusty » Thu Oct 09, 2014 7:13 pm

UncleBob wrote:
Rusty wrote:
UncleBob wrote:
Rusty wrote:
UncleBob wrote:
Rusty wrote: Millions? It's Billions. By 'our galaxy' do you mean the merged Andromeda-Milky Way? A merged galaxy is at least 5 B years out. The tidal effects of the galaxies passing through each for the first time won't be for about 2-3 billion years. So our sun is very likely in old age and a in a nova state and has expanded beyond the Earth's orbit so the Earth is gone by the time the merge is done. The local group is still bound to the Virgo supercluster and there are plenty of other things bound to it as well. Try and explain why they would go away if they remain gravitationally bound. They're well within 300M LYs.
Yes. Millions make up billions. Yes, our galaxy will be eventually merged with Andromeda and the other dwarf galaxies and assorted matter. Yes, our solar system will be gone or extinct but that does not mean that humanity will be, though it is likely humanity will be bound to the galaxy.
:egor: Ok but I still don't see any argument that says objects we see now are going to vanish within 100 years or so. I'll be generous, make it a million years instead of a hundred. What is going to vanish? We should see more objects.
Well, we don't know. We don't know what we can't see. The new telescopes continue to discover areas that we didn't know existed or couldn't see before but we are approaching the limit of what we can see.
What is the nature of that limit? If it is expansion of space ie Hubble expansion then we can calculate it. And we can place an upper bound on that distance limit today and also it's event origin time because of propagation time. The thing that complicates it is that there may have been Guth's early inflation. If so then there are objects that never were within any signal time ie their signal will never reach us. This is independent of how far back we go. Those objects and events were always outside our light cone.
UncleBob wrote:We have technology that has increased our observable universe but, with expansion, there may be areas we can never see. We don't know. Eventually we will reach the limits of technology and certain objects may start disappearing. In any case, if the universe is expanding at an accelerated rate and if the universe is larger than our ability to observe it then we will observe less in a century than we can now.
What is the oldest and most distant EM signal we know? It's the CBR, that occurred approx. 400K years after the event. This is long after Guth's inflation. And that emission occurred before any stars or galaxies were created. So what has to happen to the cbr? It's now red-shifted to 2.7 K. But we can still detect it. And it's uniform in the sky except for our motion ie doppler effects of the receiver's motion. We're inside the big bang's leading edge as the CBR signal. No EM signal propagated further than that.
I remember reading about the effect some time ago. I may have mis-remembered the time scales.

As the universe ages, expands, future cosmologists will know less
So why is the past the best time to observe the universe? There are actually two competing stages to study the cosmos. During the young universe the cosmic horizon is closer to you and as the universe gets older you can see more of it due to light having more time to travel. As time goes by, however, matter collapses. This stage “muddies the water” of the cosmic sea because you misplace reminiscence of original conditions of minute scales.
In the end, the first grows better as the second becomes worse.

The best time for observers to research the cosmos was about half a billion years following the Big Bang because the formation of galaxies and stars began. However, it’s not too late for astronomers.

“21-centimeter surveys are our best hope," said Loeb. "By observing hydrogen at large distances, we can map how matter was distributed at the early times of interest.

Eventually, in approximately 10 and 100 times the universe’s current age, researchers will not be able to study the stars because of the expansion; galaxies are moving beyond our horizon and the light that leaves the distant galaxies will never reach us in the future.
Top astronomer says universe will eventually disappear

I'm not saying we will have a dark universe in 100 years but we will be able to see less than today. This effect may not be as noticeable until much later.
Those guys have been reading their own marketing literature and are so full of sh*t that their eyes are brown. 8O

If we look at Hubbles law and specifically the value of H, it's approx. 70 km/sec at a distance of a megaparsec ie 326 million light years. So the expansion speed increases with distance. Ok, so here's a skill testing question... How far away does an object have to be so that it is receding from us at 300,000 km/sec? It's something like 4300 megaparsecs ie roughly 14,000 Million Light years. Does that last number look familiar or is it just me that sees the age of the universe? We cannot see back that far. Nothing is going to vanish anytime soon. Instead there is still light enroute from distant objects that hasn't reached us yet ie there will be new objects.

Also 326 M LYs is huge. And many things within that radius are gravitationally bound. Things that are gravitationally bound to our local galaxies are not going to vanish over the horizon. They can't. So what is going to vanish, exactly?

Far off in the unimaginably distant future we will never receive light from very distant objects near the horizon now. That's hardly a dark universe. Somebody hand them some exlax.

The other thing is that we live in the era of stars in this universe. The stars won't last forever and there is probably a limit to the creation of new ones at some point. So if the universe goes dark it seems more likely that it's because the age of stars has ended and all stars have cooled to cinders.
Last edited by Rusty on Thu Oct 09, 2014 7:44 pm, edited 1 time in total.
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Re: The Cosmology Thread

Post by OldWorldSwine » Thu Oct 09, 2014 7:38 pm

A_Morley wrote:The last word should go to the late Sir Patrick Moore.
That made me ridiculously happy.
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Re: The Cosmology Thread

Post by Thunktank » Thu Oct 09, 2014 8:35 pm

Rusty wrote:
UncleBob wrote:
Rusty wrote:
UncleBob wrote:
Rusty wrote:
UncleBob wrote:
Rusty wrote: Millions? It's Billions. By 'our galaxy' do you mean the merged Andromeda-Milky Way? A merged galaxy is at least 5 B years out. The tidal effects of the galaxies passing through each for the first time won't be for about 2-3 billion years. So our sun is very likely in old age and a in a nova state and has expanded beyond the Earth's orbit so the Earth is gone by the time the merge is done. The local group is still bound to the Virgo supercluster and there are plenty of other things bound to it as well. Try and explain why they would go away if they remain gravitationally bound. They're well within 300M LYs.
Yes. Millions make up billions. Yes, our galaxy will be eventually merged with Andromeda and the other dwarf galaxies and assorted matter. Yes, our solar system will be gone or extinct but that does not mean that humanity will be, though it is likely humanity will be bound to the galaxy.
:egor: Ok but I still don't see any argument that says objects we see now are going to vanish within 100 years or so. I'll be generous, make it a million years instead of a hundred. What is going to vanish? We should see more objects.
Well, we don't know. We don't know what we can't see. The new telescopes continue to discover areas that we didn't know existed or couldn't see before but we are approaching the limit of what we can see.
What is the nature of that limit? If it is expansion of space ie Hubble expansion then we can calculate it. And we can place an upper bound on that distance limit today and also it's event origin time because of propagation time. The thing that complicates it is that there may have been Guth's early inflation. If so then there are objects that never were within any signal time ie their signal will never reach us. This is independent of how far back we go. Those objects and events were always outside our light cone.
UncleBob wrote:We have technology that has increased our observable universe but, with expansion, there may be areas we can never see. We don't know. Eventually we will reach the limits of technology and certain objects may start disappearing. In any case, if the universe is expanding at an accelerated rate and if the universe is larger than our ability to observe it then we will observe less in a century than we can now.
What is the oldest and most distant EM signal we know? It's the CBR, that occurred approx. 400K years after the event. This is long after Guth's inflation. And that emission occurred before any stars or galaxies were created. So what has to happen to the cbr? It's now red-shifted to 2.7 K. But we can still detect it. And it's uniform in the sky except for our motion ie doppler effects of the receiver's motion. We're inside the big bang's leading edge as the CBR signal. No EM signal propagated further than that.
I remember reading about the effect some time ago. I may have mis-remembered the time scales.

As the universe ages, expands, future cosmologists will know less
So why is the past the best time to observe the universe? There are actually two competing stages to study the cosmos. During the young universe the cosmic horizon is closer to you and as the universe gets older you can see more of it due to light having more time to travel. As time goes by, however, matter collapses. This stage “muddies the water” of the cosmic sea because you misplace reminiscence of original conditions of minute scales.
In the end, the first grows better as the second becomes worse.

The best time for observers to research the cosmos was about half a billion years following the Big Bang because the formation of galaxies and stars began. However, it’s not too late for astronomers.

“21-centimeter surveys are our best hope," said Loeb. "By observing hydrogen at large distances, we can map how matter was distributed at the early times of interest.

Eventually, in approximately 10 and 100 times the universe’s current age, researchers will not be able to study the stars because of the expansion; galaxies are moving beyond our horizon and the light that leaves the distant galaxies will never reach us in the future.
Top astronomer says universe will eventually disappear

I'm not saying we will have a dark universe in 100 years but we will be able to see less than today. This effect may not be as noticeable until much later.
Those guys have been reading their own marketing literature and are so full of sh*t that their eyes are brown. 8O

If we look at Hubbles law and specifically the value of H, it's approx. 70 km/sec at a distance of a megaparsec ie 326 million light years. So the expansion speed increases with distance. Ok, so here's a skill testing question... How far away does an object have to be so that it is receding from us at 300,000 km/sec? It's something like 4300 megaparsecs ie roughly 14,000 Million Light years. Does that last number look familiar or is it just me that sees the age of the universe? We cannot see back that far. Nothing is going to vanish anytime soon. Instead there is still light enroute from distant objects that hasn't reached us yet ie there will be new objects.

Also 326 M LYs is huge. And many things within that radius are gravitationally bound. Things that are gravitationally bound to our local galaxies are not going to vanish over the horizon. They can't. So what is going to vanish, exactly?

Far off in the unimaginably distant future we will never receive light from very distant objects near the horizon now. That's hardly a dark universe. Somebody hand them some exlax.

The other thing is that we live in the era of stars in this universe. The stars won't last forever and there is probably a limit to the creation of new ones at some point. So if the universe goes dark it seems more likely that it's because the age of stars has ended and all stars have cooled to cinders.
Why am I imagining the human race far, far into the future moving about the universe in great artificial worlds? They travel about creating man made stars to replace dying stars in a dying universe. A new universe made by man gods! 8O

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Re: The Cosmology Thread

Post by Rusty » Thu Oct 09, 2014 8:41 pm

UncleBob wrote:Oh, and as for disappearing objects and technology limitations:

A Galactic Scale Disappearing Act: Lyman Break Galaxies at z ~ 8 ~ 9
Their study also reveals that the candidates with z ~ 8 – 9 do not provide enough ionizing flux to re-ionize the Universe; however, they mention that fainter galaxies falling below their detection limit likely account for a significant UV contribution. If this is the case, then more faint galaxies are needed to account for the needed flux than predicted by a faint end slope of a Salpeter Initial Mass Function. These findings may have to wait for confirmation from observations made by the James Webb Space Telescope.
So we may have very faint objects that we can't see providing UV pollution--we don't know. It may be possible to circumvent that with future technology. It is possible that, if we had our current technology 100, 500, 1000, or more years ago, we could have seen these objects (if they are there).
This is different issue than objects going over the cosmic horizon. They are well within the cosmic horizon but there are other challenges including technology issues with detector sensitivity. Also this isn't uv pollution but the medium between galaxies etc absorbing some wavelengths but not all so they find other ways to detect them. There is an outstanding question concerning when & how the universe 'reionized' so that the dark age ended and the age of stars began.
Look at the the z for the CBR, 1100. And it hasn't vanished. The z for cosmologically redshifted objects tells us something about the FRW scaling factor in the universe at the time the radiation left the object. All they can do is probe the past. It's detective work looking for the evidence that clinches or rejects a theory about what happened. It's arguing about the history.

The accelerating expansion poses two real questions. Is the Hubble coefficient increasing over time? Or is the acceleration modest so that it takes a very long duration for distant (not gravitationally bound) objects to move with expanding space far enough away from each other that they are over the horizon? Either the Hubble coefficient increases so that it overcomes gravity within intergalactic distances of a million light years; or there is a very long time for objects to diffuse enough and become much more distant so that they approach the cosmic horizon from each other. In either case it's possibly many times the age of the universe away in time. Which is what your article "As the universe ages, expands, future cosmologists will know less" says too. It's not a practical problem.
Eventually, in approximately 10 and 100 times the universe’s current age, researchers will not be able to study the stars because of the expansion; galaxies are moving beyond our horizon and the light that leaves the distant galaxies will never reach us in the future
For the mathematically challenged & convenience... a nomograph relating redshift Z to age and distance.
Image

z — redshift;
H — current value of the Hubble constant, km/s/Mpc;
r comov — comoving distance, Mpc;
dm — distance modulus;
age — age of the Universe, Gyr;
time — lookback time, Gyr;
size 1” — physical size of an object which is seen as an 1” arc on the sky, kpc;
angle 1kpc — angular size of a rod with physical size 1 kpc, arcsec

technical reference so you understand the meanings of the headings
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Re: The Cosmology Thread

Post by UncleBob » Wed Oct 29, 2014 8:13 am

"One man's theology is another man's belly laugh." - Robert A. Heinlein

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Re: The Cosmology Thread

Post by UncleBob » Thu Oct 30, 2014 9:17 am

"One man's theology is another man's belly laugh." - Robert A. Heinlein

"Many of the points here, taken to their logical conclusions, don't hold up to logic; they're simply Godded-up ways of saying "I don't like that." - Skip

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Re: The Cosmology Thread

Post by UncleBob » Thu Oct 30, 2014 9:23 am

"One man's theology is another man's belly laugh." - Robert A. Heinlein

"Many of the points here, taken to their logical conclusions, don't hold up to logic; they're simply Godded-up ways of saying "I don't like that." - Skip

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Re: The Cosmology Thread

Post by Rusty » Thu Oct 30, 2014 10:20 am

Where to start?

1) One post could have contained these meandering, poorly reported, vague, and generally misleading articles. And why are they here?
OK I have to ask you to please NEVER bring another IBT article here. First, they mislead the reader but even worse they have determined little videos that natter at the reader about something else. I hate their pages. OK?

The evidence is not yet convincing and that's an important part of the story. A better article is the SA one - http://www.scientificamerican.com/artic ... -way-core/

2) What is this?
The article seems peripheral to the question. The author never answers the question. It seems more like a general wiki article about interpreting stellar age.

3) And this one doesn't actually deal with the Bubble that is featured in it's title. I'm happy for her that she discovered her father is bright. BUT WHY DIDN'T EDITOR SEND HER BACK TO COMPLETE THE ARTICLE?
So which bubble were they talking about?
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