What Are Quasars? Explained by Hubble Telescope

[Alan McDougal]

Hi, people,

Just to bump myself into the forum could someone address this question about Quasars The Hubble space telescope picks up light from these unimaginably distant energy sources called quasars, which came into being some1 billion years after the big bang or, about some 10/11 billion years ago.

The Earth came into existence some 5 billion years ago, so these distant objects might no longer exist and if they still do, they must be far out toward the edge of the known universe.

Now my question might seem simplistic but say these objects only transmitted energy into the universe for say 1 billion years, how the heck! are we still receiving light from them or how did we come to be separated from, them given that the Earth is only 5 billion years old

I hope this does not come over too convoluted

Regards

Alan

 

[Kurdt]

Quasars are of course very very far away so the light has been traveling for a long time to reach us since it only has a limited speed.

Welcome to PF by the way!

 

[tiny-tim]

Welcome to PF!

Hi Alan! Welcome to PF!

Where were we 10 billion years ago?

Just dust 'n' stuff,

And it was the dust 'n' stuff that was moving away … and so fast that the light has only just caught up!

 

[Alan McDougal]

Quasars

Kudt

You said

Quasars are of course very very far away so the light has been traveling for a long time to reach us since it only has a limited speed

I know this basic fact light 186 000 miles per second. But light from these quasars left them say 11 billion years age, and if these objects only existed for 2 billion and our Earth came into being some five billion years later we would not receive light from them at present.

As I see it, the quasars from which we still obtain light must have existed as quasars for longer than the life span of planet earth. Of course, we are seeing these remote objects as they were in the distant past and they might not even exist now.

However, the explainaton just given the position of the finite speed of light does not make total sense to me.

Looking at the whole history of the universe on a smaller time scale say in minutes Minute 0) creations happens, 2) quasars exist, light begins to spew out into the universe for 4) minutes (and quasar dies), minute 6) the Earth exists. How do we account for the separation between the quasars and Earth given that the Earth came into being 4 minutes after said quasar

Taking the time scale back up to billions. Creation happens, year 1 billion quasars is born, and year 4 billion Earth's is born (all relative to light speed). We must, therefore be at year 9 billion at present. However, that tell us how the separation is 11 billion light years or years happened, since the astronomers say we picking up light from an object that has only reached us now up as photon on its mirror from the unbeleable past and distance of 11 billion years or light years if you like

Give it a go and tackle the enigma please

Alan

 

[Wallace]

At any instant the Universe is the same everywhere. The objects in the Universe at any given time give off light. The expansion of the Universe leads to the light we see from an object today being 'redshifted' by comparison to when it was emitted. Redshift is a shift in the wavelengths of the spectrum of light.

Now, imagine looking at just one area in the sky. If we look with a good enough telescope we will see a whole heap of objects that have different redshifts. The greater the redshift the further that object is away, but more importantly for your question, the light we see was emitted by the object at an older time. Just say for arguments sake that we look at a quasar that appears to have a redshift of 2 (this means that the wavelength of the light is twice as long as we see it compared to when it was emitted). Now if we run our cosmological equations we might work out that redshift 2 was say 10 billion years ago. That is to say that if we see an object with a redshift of 2 then the light we are seeing was emitted by it 10 billion years ago (remember these are just arbitrary numbers, we can work out the exact numbers easily enough).

Now, the key things to realize is that if we looked at this region of the sky a long time later, say several billion years we might find that the quasar we saw before was no longer there. It has ceased to give of much light. However, what we notice is that there are now some other quasars that have appeared that we didn't see before. They have a higher redshift, say 3 or 4. What has happened? The 'new' quasars existed at the same time as the first, however they existed further away from us, so the light has taken longer to get here. Since the whole universe is now older (and larger), the light appears now to us even more redshifted, even though it was the same as the light from the first quasar when emitted from the quasar.

We could continue this process for as long as we want. We will always see more and more distant quasars as the light from quasars that were ever more distant from us when they existed finally reaches us.

Does that make sense?

 

[Vanadium 50]

The age of the Earth doesn't enter into it. (Think about it - we see a QSO with a radio telescope, and that's only a few years old) The fact that we are riding on a 5 billion year old planet as opposed to one that's some other age isn't relevant.

 

[Alan McDougal]

Thank you Wallace,

I overlooked the fact that space is stretching , this would explain the separation mentioned and what would have been a 9 billion sparation if the universe did the impossible and was static. The 9 billion in my argument was stretched out by the expansion of space time and became 11 billion?

Am I correct?

Thanks a lot

Alan

 

[Kurdt]

I know this basic fact light 186 000 miles per second. But light from these quasars left them say 11 billion years age, and if these objects only existed for 2 billion and our Earth came into being some five billion years later we would not receive light from them at present.

This isn't quite true. I'm assuming you're thinking all the light should have already reached us and so we shouldn't see them any more. It is entirely possible to see the light from quasars now since the universe underwent a period of rapid expansion in the past. This means the quasars would be far enough away to be still receiving their light today. So if you take inflation into account then all your problems would appear to be solved.

 

[Alan McDougal]

Hi Vanadium,

You said
""The age of the Earth doesn't enter into it. (Think about it - we see a QSO with a radio telescope, and that's only a few years old) The fact that we are riding on a 5 billion year old planet as opposed to one that's some other age isn't relevant.""

Respectfully it does matter if our world came into being 1000 billion years into the future this light source would never reach us as the universe would have reached and accelerated to the point of almost infinity by then.

Regards

Alan

 

[Alan McDougal]

Kurdt,

Of course you are correct and I posted the same conclusion, just before your post came in.

Alan

 

[Wallace]

Hi Alan, issues about the 'stretching of space' are I think a red-herring to this discussion. Vanadium is correct in suggesting the age of our planet is irrelevant as well.

Lets just ignore the expansion of the Universe for a moment. Imagine we live in an infinitely large universe that is static but does evolve in the sense that there is a period of time where there are a lot of quasars banging away and then they all turn off. Let's simplify this further to say that each quasar simply sends a single flash of light towards us.

The quasars are all at different distances from us, but the light from each travels at the same speed. Would we expect then to see a single flash, representing the quasar epoch and then darkness? No, we instead would continue to see flashes from quasars for the rest of time, since as time goes on we see the flash from ever more distant sources.

Hopefully this makes it clear then that because we live in a homogeneous universe that is either infinite or so big that for all intents and purposes we may consider it to be infinite, that we will always see light from every epoch in the history of the Universe at all times. The same argument applies to the cosmic microwave background. This is the light emitted by every bit of material in the universe 13ish Billion years ago, however we have always been able to see this light and will always be able to see it in the future. We are not seeing the light from the same region all the time, as time goes on we see the light that was emitted by ever more distant regions.

When we consider that the universe is expanding and everything else that that entails it does not change the principle of this, just the details. It is important to realize that homogeneity and a finite speed of light are the only things required to answer your original question. Expansion etc just confuse the issue and change the numerical details.

 

[Alan McDougal]

Hi, Wallace

You said

Lets just ignore the expansion of the Universe for a moment. Imagine we live in an infinitely large universe that is static but does evolve in the sense that there is a period of time where there are a lot of quasars banging away and then they all turn off. Let's simplify this further to say that each quasar simply sends a single flash of light towards us.

The quasars are all at different distances from us, but the light from each travels at the same speed. Would we expect then to see a single flash, representing the quasar epoch and then darkness? No, we instead would continue to see flashes from quasars for the rest of time, since as time goes on we see the flash from ever more

distant sources.

Maybe I am a bit slow, but how about simplifying it even further. Assume there is only one quasar in your infinity huge steady state Fred Hoyl universe and only one other object namely earth. Separated by 9 billion light years. Said quasar gives off only one flash towards us. Therefore, it is logical that our telescope would register this flash 9 billion years later due to light finite speed.

Relate the argument to looking at someone turning a flashlight (quasars) in a dark forest at night (space) on and then off only once in the dark of night. would see a brief flash and then darkness.

I see your point that even with only one quasar but in reality the flash would in actuality last much longer.

The quasar flashes maybe 9 billion years and our Hubble telescope some 13 billion years later looks for light where the object should have been found. They would see nothing. The duration of the flash 9 billion years or one pico second makes no difference, it is gone before we can observe its light on our telescope. The duration of the light source from the quasar has ended 9 billion years ago while we only looked at this part of space 4 billion years after the quasar has ceased to exist. The light flash is gone!

But nevertheless we do see the quasar in our telescope, because of the “Fact” that the universe is not infinite or static and has expanded say by 3 billion light years further out, since the brief flashing hypothetical single quasar became into being and flashed its light.

So we are further out sort of racing ahead like a baseball player running ahead (expanding universe) to catch a ball (light flash) if he did not run to ahead catch the ball he would miss it (static universe)

Space stretches or expands but the speed of light remains the same and, therefore, must travel 3 billion light-years futher, in my argument, and this gives us the opportunity or time to note it on our telescope. In a static universe, the quasar will remain 9 billion light years from Earth and in an expanding universe; it would recede a further 3 billion light years out from us.

What I am trying to get over is that in a static universe the quasar object reamain at 9 billion light years away and would recede out 12 billion light years in an expanding universe like ours. Indicating that we indeed can observe things from a more remote past than would be the case in a static universe.

Forgive me if I mentioned elementary facts, as I am sure you are aware of, but I just restated them for the purpose of my argument

Alan

 

[Wallace]

What I am trying to get over is that in a static universe the quasar object reamain at 9 billion light years away and would recede out 12 billion light years in an expanding universe like ours. Indicating that we indeed can observe things from a more remote past than would be the case in a static universe.

This is true but irrelevant to your original question. As I said, the expansion of the universe changes the numerical details, so that we don't for instance the light emmitting from some distance object say 10 Billion years ago when it is 10 Billion light years away. Yes, the expansion of the universe makes these two number unequal. However as I said this just confuses the issue in regards to your original question, it really is a red herring.

In your example of the single quasar and us in the Universe then regardless of whether or not the Universe is expanding we might still miss the flash of light, or we might be lucky. It depends on when the quasar flashed, how far away it is and when we happen to look.

However this is not the case for the Universe. The important fact is that 10 Billion years ago the Universe was full of quasars. If we imagine that they all flash their light for a short period then for many of those quasars we will miss seeing the flash. This is indeed what we find, we don't see quasar near to us even though we do see the galaxies that the quasars were in when they were 'on'. This is because the light went past us billions of years ago when we weren't watching.

However, we do see the light coming from quasars that were far enough away from us when they were 'on'. Go into the future though and we won't see those specific quasars, since the light will have past us. However we will then see different quasars that were even further away from us when they released their light.

The times you gave in the original post (i.e. quasars form 11 billion years ago, shine for 1 billion years but the Earth is only 5 billion years old) are completely irrelevant. You could change all of those numbers to any value and we would still see quasars, well as long as there are quasars in the Universe before we exist anyway.

I worry about this thing you said

But nevertheless we do see the quasar in our telescope, because of the “Fact” that the universe is not infinite or static and has expanded say by 3 billion light years further out, since the brief flashing hypothetical single quasar became into being and flashed its light.

You say it is a 'Fact' that the universe is not infinite but this is not true. It is fundamental to understanding your question to realize that the Universe really is infinite for all intents and purposes relating to this question, and may indeed by truly infinite. It is so big that even if it was finite it essentially looks to us the same as if it was infinite. The second thing to realize is that the universe is the same everywhere at a given point in time. These two facts alone will answer your question.

Are you perhaps thinking that the Big Bang happened at some point in space and everything in the Universe moved away from the point after the Big Bang, such that at some point in time everything in the Universe was at the same place?? If so this may be your problem. This is a very common misconception about the Big Bang and may be what is leading you astray.

Again, I suggest you think about the Cosmic Microwave Background. This is light emitted from a time even earlier than the light from quasars, which really did get released in a single flash from every region of the Universe. If you can understand why it is that we can still see it, and will continue to be able to see it forever then you will understand your quasar question. Again this doesn't rely on the Universe expanding and if you need to invoke 'the expansion of space' to understand this then I don't think you have understood it.

 

[Alan McDougal]

Wallace

Also, the universe can expand at a greater rate than light speed and take an object with it at that rate. Matter, energy and information cannot exceed light speed , but objects can recede at greater than the speed of light from each other.

The expansion of the universe could thus make it appear older than it really is. Of course this is not the case with the universe at present. But the far future??

alan

 

[Wallace]

Hi Alan. I am aware of the nature of the expanding Universe and the tricks that it can play. However I re-iterate that the expansion of the Universe is not the solution to your original question.

Let me know if you are still confused about this and I can try and explain it some more.

 

[Alan McDougal]

Wallace I m a persistent old geezer and don't think I am lead astray.

"Thank you for your infinite patience".

You say it is a 'Fact' that the universe is not infinite but this is not true. It is fundamental to understanding your question to realize that the Universe really is infinite for all intents and purposes relating to this question, and may indeed by truly infinite. It is so big that even if it was finite it essentially looks to us the same as if it was infinite. The second thing to realize is that the universe is the same everywhere at a given point in time. These two facts alone will answer your question.

Are you perhaps thinking that the Big Bang happened at some point in space and everything in the Universe moved away from the point after the Big Bang, such that at some point in time everything in the Universe was at the same place?? If so this may be your problem. This is a very common misconception about the Big Bang and may be what is leading you astray.

Again, I suggest you think about the Cosmic Microwave Background. This is light emitted from a time even earlier than the light from quasars, which really did get released in a single flash from every region of the Universe. If you can understand why it is that we can still see it, and will continue to be able to see it forever then you will understand your quasar question. Again this doesn't rely on the Universe expanding and if you need to invoke 'the expansion of space' to understand this then I don't think you have understood it.

I know the universe has no central point and it is more like a loaf of bread with galaxies representing as chocolate chips in the expanding loaf. "No central point there"

The Cosmic Microwave Background is somewhere out toward the edge of the expanding universe, even if it has no central point as per bread loaf.

The Cosmic Background must be getting more remote from every other object in the universe, because the univere "IS" expanding at a colossal rate.

If the universe were infinite as you suggest then into what is it expanding?

Also why did Alan Guths universe expand and then obediently stopped a moment later and then deciding to expand to allow for clumping and creation of galaxies.

Space has no mass so it can exceed the speed of light out into infinity and on this bases your infinite universe might be true.



Simplify my point down to one single photon and one photosensitive plate. If they were separated by 9 billion light years in a static universe, the plate would reflect it exactly 9 billion years after it was emmited . In the case of an expanding universe like ours, the photo sensor might only show the photon on its plate 30 billion years later, depending on the rate of expansion of the universe at the moment.

I reflect my problem with the oxymoron of the untrue impossible/ fact that infinity must be true, but it can't be true? In a rather poetic manner where I take the part of "god" below:...

""In my imagination I got trapped on an infinity road, No beginning no end. So on my endless ceaseless journey I constructed barriers like walls to end my journey, but the barriers just then also extended out into infinite forever. So to overcome the boredom of my ceaseless travel, I made a paradise to rest in for as long as I like and then countless different paradises and just or fun burning "hells" to make my lonely everlasting journey some fun""

By God maybe?

Even God can't be Infinite although he must push on towards it forever!

Alan

 

[Alan McDougal]

Wallace I m a persistent old geezer and don't think I am lead astray.

"Thank you for your infinite patience".


You say it is a 'Fact' that the universe is not infinite but this is not true. It is fundamental to understanding your question to realize that the Universe really is infinite for all intents and purposes relating to this question, and may indeed by truly infinite. It is so big that even if it was finite it essentially looks to us the same as if it was infinite. The second thing to realize is that the universe is the same everywhere at a given point in time. These two facts alone will answer your question.

Are you perhaps thinking that the Big Bang happened at some point in space and everything in the Universe moved away from the point after the Big Bang, such that at some point in time everything in the Universe was at the same place?? If so this may be your problem. This is a very common misconception about the Big Bang and may be what is leading you astray.

Again, I suggest you think about the Cosmic Microwave Background. This is light emitted from a time even earlier than the light from quasars, which really did get released in a single flash from every region of the Universe. If you can understand why it is that we can still see it, and will continue to be able to see it forever then you will understand your quasar question. Again this doesn't rely on the Universe expanding and if you need to invoke 'the expansion of space' to understand this then I don't think you have understood it.

I know the universe has no central point and it is more like a loaf of bread with galaxies representing as chocolate chips in the expanding loaf. "No central point there"

The Cosmic Microwave Background is somewhere out toward the edge of the expanding universe, even if it has no central point as per bread loaf.

The Cosmic Background must be getting more remote from every other object in the universe, because the univere "IS" expanding at a colossal rate.

If the universe were infinite as you suggest then into what is it expanding?

Also why did Alan Guths universe expand and then obediently stopped a moment later and then deciding to expand to allow for clumping and creation of galaxies.

Space has no mass so it can exceed the speed of light out into infinity and on this bases your infinite universe might be true.



Simplify my point down to one single photon and one photosensitive plate. If they were separated by 9 billion light years in a static universe, the plate would reflect it exactly 9 billion years after it was emmited . In the case of an expanding universe like ours, the photo sensor might only show the photon on its plate 30 billion years later, depending on the rate of expansion of the universe at the moment.

I reflect my problem with the oxymoron of the untrue impossible/ fact that infinity must be true, but it can't be true? In a rather poetic manner where I take the part of "god" below:...

""In my imagination I got trapped on an infinity road, No beginning no end. So on my endless ceaseless journey I constructed barriers like walls to end my journey, but the barriers just then also extended out into infinite forever. So to overcome the boredom of my ceaseless travel, I made a paradise to rest in for as long as I like and then countless different paradises and just or fun burning "hells" to make my lonely everlasting journey some fun""

By God maybe?

Even God can't be Infinite although he must push on towards it forever!

Alan

 

[Wallace]

The Cosmic Microwave Background is somewhere out toward the edge of the expanding universe, even if it has no central point as per bread loaf.

No, the CMB is everywhere it is light that was emitted by every region of the Universe around 13 Billion years ago. The CMB we see at any given moment originated from a spherical shell surrounding us. As time goes on the radius of the shell increases, i.e. as time goes on we see the CMB photons that came from a region further and further away. We are not seeing the same region continually as it moves away, we are seeing different regions.

The Cosmic Background must be getting more remote from every other object in the universe, because the univere "IS" expanding at a colossal rate.

Again, the CMB is a sea of light that is everywhere in the Universe. It is not moving away from anywhere.

If the universe were infinite as you suggest then into what is it expanding?

Nothing! Again this is a common question, but is a big misconception. The expansion of the Universe is not the Universe getting bigger in some absolute sense, just the distance between everything increasing. Imagine an infinite line of points all separated by one metre. This line can expand such that each point is now two metres apart. The total length of the line remains infinite, the line hasn't extended to anywhere it wasn't before, but everything on the line has been stretched.

Also why did Alan Guths universe expand and then obediently stopped a moment later and then deciding to expand to allow for clumping and creation of galaxies.

This is a whole question in itself. Maybe you should ask that in a separate thread to avoid confusing this one. Just remember that this has no relevance to your question! (but is a good question in its own right)

Space has no mass so it can exceed the speed of light out into infinity and on this bases your infinite universe might be true.

It's not my infinite universe, I'm just conveying the current theory. There are a lot of interesting questions here and I encourage you to read some of the older threads on this (there are many) or ask about this in a new thread. Again, the expansion of the Universe has nothing to do with the original question you asked in this thread.

Simplify my point down to one single photon and one photosensitive plate. If they were separated by 9 billion light years in a static universe, the plate would reflect it exactly 9 billion years after it was emmited . In the case of an expanding universe like ours, the photo sensor might only show the photon on its plate 30 billion years later, depending on the rate of expansion of the universe at the moment.

Yes this is true, but again is not the solution to your question! The reason we see the CMB at all times, and see quasars at all times is precisely because there is not a single object. Think of the CMB as a infinite series of emitters that fired off photons. As time goes on we see the photons from the emitters that were further and further away when they fired the light. The same goes for quasars.

I reflect my problem with the oxymoron of the untrue impossible/ fact that infinity must be true, but it can't be true? In a rather poetic manner where I take the part of "god" below:...

""In my imagination I got trapped on an infinity road, No beginning no end. So on my endless ceaseless journey I constructed barriers like walls to end my journey, but the barriers just then also extended out into infinite forever. So to overcome the boredom of my ceaseless travel, I made a paradise to rest in for as long as I like and then countless different paradises and just or fun burning "hells" to make my lonely everlasting journey some fun""

By God maybe?

Even God can't be Infinite although he must push on towards it forever!

Alan

Even if you can't accept philosophically that the Universe is infinite, the observational fact is that it is so big that we can't tell the difference between it being infinite or just really really big. We can assume it is infinite and this model works.

Again, please read over my previous posts and try and come to grips with this. Think about what you would see in a static inifinite universe. If you can understand in that model why you will always see the CMB and always see quasars then you will have understood this problem. The expansion of the Universe is an interesting discussion topic, but it is not the solution to the problem here and is only confusing the issue.

 

[Kurdt]

This is probably my fault since I thought inflation would cure the misconception that the universe is expanding from a small point in a kind of linear fashion which seemed to be present at the beginning of the thread.

 

[Alan McDougal]

Wallace,

At last, I get it!

Quasar is an object from the very early universe, when it was still young, in the young universe. (I knew this). However, it must be also extremely old now. Too see how long it continues to exist, we would have to do the impossible, for us, and track its light flow via our vantage point from earth, for maybe billions of years until entropy takes over in its old age and the quasar descends into the eternal chaotic state and vanishes.

Of course it the universe was static we would have no real idea how remote this object would be.

We know by the red shift, however, that is very remote indeed,” but this fact is not relevant to my question”.

"Earth is simple separated from quasars and this is a fact". I through all my other unnecessary elements out of my baby cot.

By the way you said the universe expands into nothing. There is no such thing as nothing. Everything that exists has always existed in one form or the other, nothing new can come out of non-existence.

Unexisting nothingness is a frightening mind-bending, brain twisting concept incomprehensibly even to the most lofty intellect.

I leave it at that as I know this forum is not about the philosophical I think!

Thank you for taking the time and effort to make me think for myself!

Regards

Alan

 

[Alan McDougal]

I wrongly said I "through" all unnecessary elements out of my baby cot

in my previous post instead of

I "threw" all unnecessary elements out of my baby cot."

I don't see a method to modify.edit mistakes please help

Alan

 

[tiny-tim]

I don't see a method to modify.edit mistakes please help

Hi Alan!

There is an edit button … but it only works for 30 minutes.

 

[rubecuber]

basic quasar info:
Quasar is a huge space object that is reeeeeealy bright anbd emits a looooooooot of radiation. i think that if you were to wikipedia it or read a brief history of time or spaceship neutrino, you'd get a getter understanding of it. Hazaaaaaaaaaaaaaaaaaaaaaaaaaa

 

[Alan McDougal]

ruecuber,

There is no such thing as "basic quasar info"

You comments are not helpful and come over childish,

For the others perhaps you should consider the fact that so called highly intelligent people are not good at thinking. None of you gave an answer to my question in this thread. or instance by saying back ground cosmic microwave radiation is not somewhere but everywhere. For goodness sake, how can something that exists in the background also be everywhere?

Using a static universe to solve the argument gets us absolutely nowhere, all it does it tell us the Earth and quasar are separated. Not by how far (no red shift)

For instance if we receive light from a remote sources such as quasar 12 billion years light years from Earth in our expanding universe, this object would have to moved out to a distance of 24 light years by now which is more than the proposed age of the universe. Therefore, does it still exist?

The assumption that one is ignorant and a patronizing attitude is not helpful, I am an amateur astronomer and know what I am talking about.

Alan

 

[Wallace]

For the others perhaps you should consider the fact that so called highly intelligent people are not good at thinking. None of you gave an answer to my question in this thread. or instance by saying back ground cosmic microwave radiation is not somewhere but everywhere. For goodness sake, how can something that exists in the background also be everywhere?

Anywhere that you go in the Universe you will see CMB photons coming at you from all directions. I'd say that's a pretty good definition of something being 'everywhere'. In addition, every point in the Universe 13 Billion years ago gave of the light that forms the CMB. Somewhere out there are aliens that are currently seeing the CMB photons that were emitted by the hydrogen atoms that now make up the water in our oceans. The same is true for every region of the Universe. The CMB was produced by every part of the Universe and can currently be observed in every part of the Universe to be coming from every direction. Again I'd say that's a pretty good definition of something being 'everywhere'.

I'm not sure what you mean by the CMB being 'in the background'? Maybe if you explain a little more what you mean by that we can clear up this confusion.

Using a static universe to solve the argument gets us absolutely nowhere, all it does it tell us the Earth and quasar are separated. Not by how far (no red shift)

The point is that it doesn't matter how far we are separated from anyone particular quasar. Yes, if we properly consider an expanding universe we find that quasars are most commonly found between a redshift of 1 and 2. If we existed further in the future, we would still see quasars, but now we would see them at a different redshift, say between 4 and 5. They wouldn't be the exact same quasars we see now, since there light will have already passed us. They will be different quasars, ones that were further away from us when they were 'on' such that their light took longer to reach us.

For instance if we receive light from a remote sources such as quasar 12 billion years light years from Earth in our expanding universe, this object would have to moved out to a distance of 24 light years by now which is more than the proposed age of the universe. Therefore, does it still exist?

I'm not sure where you are getting those exact numbers from, but yes the quasar still exists. In an expanding universe the distance in light years to a distant object today is not the same number as the amount of time the light has been traveling, but I can't fathom how that makes something stop existing?

Remember also that saying something is '20 Billion lights years away' is actually a very loose terminology. Cosmologists don't measure distance like this precisely because it is bad practice. What that distance means is this:

'If you hit pause on the Universe such that time and motion frooze and measured the distance to that distant object with a ruler that is how far away the object is'

Clearly this is an impossible distance to measure, but we can calculate what it would be if it was somehow possible. Remember that we are seeing the light from the object, not actually seeing the object today.

Better measures of distance are redshift, angular diameter distance, luminosity distance etc. Don't get too hung up on distances stated in billions of light years since this is an inherently unphysical definition of distance.

Again I re-iterate that all of this just clouds the understanding of your original question, which was why can we see quasars given that they only exist for a short time. I will say again that the expansion of the Universe only needs to be considered if we want to know whether we can see one particular quasar at some particular distance. For a particular quasar there will be one single period of time that we see it. However, due to the fact that the Universe is very large (and possibly infinite) we know that regardless of the specifics of the expansion, or indeed whether the Universe is expanding at all, that we will always be able to see quasars regardless of the current age of the Universe or any other number. This is purely a result of the Universe being Homogeneous, large and light traveling at a finite speed.

The assumption that one is ignorant and a patronizing attitude is not helpful, I am an amateur astronomer and know what I am talking about.

Alan

No one is assuming anything (as far as I can tell) and no one has patronised you, again as far as I can tell. I've been trying to help to understand this, since you asked the question. If you knew all about this already you wouldn't have needed to ask the question in the first place. If you don't want help I can stop giving it, but then I wonder why you bothered asking the question in the first place?

 

[Alan McDougal]

Walter,

I'm not sure where you are getting those exact numbers from, but yes the quasar still exists. In an expanding universe the distance in light years to a distant object today is not the same number as the amount of time the light has been traveling, but I can't fathom how that makes something stop existing?

My point about the possibility of the quasar “no longer existing” is that we get a snap shot of it when it was still a child some 13 billion years ago. Maybe the life span of an intense energy source such as a quasar might be only “1 billion years”, so it might be dead or just a dark cinder of its previously glorious self.

What I mean in other words is say; Assuming I lived long long ago and by the fastest transport method of those days it would take a 100 years to send a picture of my newborn baby to another village far off. The life span then of a person is only say 80 years, by the time the picture of how my baby looked, would be incorrect and indeed he would have aged become extremely old and reached his inevitable demise ,just as a distant quasar also might have.

This is what I meant about a distant quasar You see it as “it was” , not “as it is” and indeed it might not even exists just like the baby in the above analogy



Assuming the Doppler red shift is accurate for a 13 billion light year distant quasar, then you are correct the distance must be 13 billion light years and if we had an hypothetical caliper or protractor and opened it up to a gap of 13 billion light years we would find the object there. The red shift we know is accurate at fairly near distances on cosmoligical scale but do not know for absolute surety on the huge scale of the most distant objects in the universe.

The comment about patronizing me was not directed at you Walter!

Alan

 

[Wallace]

Walter,



My point about the possibility of the quasar “no longer existing” is that we get a snap shot of it when it was still a child some 13 billion years ago. Maybe the life span of an intense energy source such as a quasar might be only “1 billion years”, so it might be dead or just a dark cinder of its previously glorious self.

What I mean in other words is say; Assuming I lived long long ago and by the fastest transport method of those days it would take a 100 years to send a picture of my newborn baby to another village far off. The life span then of a person is only say 80 years, by the time the picture of how my baby looked, would be incorrect and indeed he would have aged become extremely old and reached his inevitable demise ,just as a distant quasar also might have.

This is what I meant about a distant quasar You see it as “it was” , not “as it is” and indeed it might not even exists just like the baby in the above analogy

Yes, absolutely. You look back in time as you look at greater distances so yes, the quasars we see today are no longer 'on', though they still would exist as black holes at the centre of a galaxy, just not pumping out all the light they used to.

 

[Alan McDougal]

If the Universe is only 14 billion years old, how can we see objects that are now 47 billion light years away?

When talking about the distance of a moving object, we mean the spatial separation NOW, with the positions of both objects specified at the current time. In an expanding Universe this distance NOW is larger than the speed of light times the light travel time due to the increase of separations between objects as the Universe expands. This is not due to any change in the units of space and time, but just caused by things being farther apart now than they used to be.

What is the distance NOW to the most distant thing we can see? Let's take the age of the Universe to be 14 billion years. In that time light travels 14 billion light years, and some people stop here. But the distance has grown since the light traveled. The average time when the light was traveling was 7 billion years ago. For the critical density case, the scale factor for the Universe goes like the 2/3 power of the time since the Big Bang, so the Universe has grown by a factor of 22/3 = 1.59 since the midpoint of the light's trip. But the size of the Universe changes continuously, so we should divide the light's trip into short intervals. First take two intervals: 7 billion years at an average time 10.5 billion years after the Big Bang, which gives 7 billion light years that have grown by a factor of 1/(0.75)2/3 = 1.21, plus another 7 billion light years at an average time 3.5 billion years after the Big Bang, which has grown by a factor of 42/3 = 2.52. Thus with 1 interval we got 1.59*14 = 22.3 billion light years, while with two intervals we get 7*(1.21+2.52) = 26.1 billion light years. With 8192 intervals we get 41 billion light years. In the limit of very many time intervals we get 42 billion light years. With calculus this whole paragraph reduces to this.

Another way of seeing this is to consider a photon and a galaxy 42 billion light years away from us now, 14 billion years after the Big Bang. The distance of this photon satisfies D = 3ct. If we wait for 0.1 billion years, the Universe will grow by a factor of (14.1/14)2/3 = 1.0048, so the galaxy will be 1.0048*42 = 42.2 billion light years away. But the light will have traveled 0.1 billion light years further than the galaxy because it moves at the speed of light relative to the matter in its vicinity and will thus be at D = 42.3 billion light years, so D = 3ct is still satisfied.

If the Universe does not have the critical density then the distance is different, and for the low densities that are more likely the distance NOW to the most distant object we can see is bigger than 3 times the speed of light times the age of the Universe. The current best fit model which has an accelerating expansion gives a maximum distance we can see of 47 billion light year

source:http://www.astro.ucla.edu/~wright/cosmology_faq.html#DN