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TOMKEEN
2010-Jul-20, 12:13 AM
Quasers which we see as being very far back in time. Presumably these quaser galaxies have aged to be more mature galaxies such as our own. An astronomer who now lives on those would look to our galaxy would see it maybe a quaser galaxy very far back in time when it was very young.

My question is what would that astronomer see if he look in exactly the opposite direction as our galaxy? Would he see a completely different galaxies as the ones we can see or would it be our near by galaxies. If it is a different set of galaxies it would mean our universe is limitless otherwise the universe is a kind of four dimension sphere or am i being stupid?

antoniseb
2010-Jul-20, 10:58 AM
Welcome to the BAUT forum TOMKEEN.

Let me paraphrase your question, so it's clear what I think I'm answering. If we see a galaxy hosting a quasar as it was say 8 billion years ago (taking an example age from a range of possible values), what would an astronomer in that galaxy now (or 8 billion years later, so as to avoid relativity issues with the word 'now') see if they look on the same direction (away from us)?

The answer is that they would see scenes similar to what we see now, with mature galaxies without quasars close by, and young galaxies, some with quasars in the far distance. We typically can see galaxies beyond the quasars, so we know a little about what is there. To answer something you seem to be asking, the universe is presumed not to be infinite, but probably much larger than the limits of our ability to see it, so it is unlikely that astronomers in galaxies we can detect (when they were young) could see around the the other way and see our backs as it were. We don't have a good clue how big the universe is in that sense, but it is almost certainly much bigger than twice what we can see.

Messier Tidy Upper
2010-Jul-26, 04:43 PM
What would an astronomer *what* if they were on a quaser galaxy as it is now? That's what we need to know before we can answer your question TOMKEEN! ;-)

What would they see - looking at their own quasar or out into space?

What would they experience? What would they do?

Given quasars formed particularly at a really early stage in the cosmos it is unlikely an astronomer could exist at all because planetary systems probably hadn't formed and if they had life probably hadn't yet arisen on them.

Which is why your'e talking *now* I suppose - but then a quasar *now* isn't a *quasar* anymore now and in fact could well be a galaxy like our own - the Milky Way too may have been a quasar early in its life! Many quasars might also now be elliptical galaxies or other varieties too. I don't think many quasars - if any at all - are active these days and I'm not sur eif we can tell whethjer agiven galaxy was aquasar once or not.

Still, I will note this quote which may be helpful or interesting for you hopefully :


“Quasars are so luminous that if one was in action in a local group galaxy its brilliance would rival that of the Sun.”
- P.284, Ferris, ‘Seeing in the Dark’, Simon & Schuster, 2002.

Now I'm not sure exactly how it look - its an interesting excercise in imagination but you'd see a brilliant source of light - perhaps discernible (with the right filters or projection as sunspost and prominences are perhaps?) as a jet as bright as our Sun and perhaps even with the surrounding galaxy - of which the quasar is the active core visible. Of course, there's also the possibility of dust clouds obscuring the glowing heart of the quasar to be taken into account ..

.. and the fact that the radiation from the quasar may (& I'm not sure here but may) make life a lot harder to exist so nearby. Which means its probably a good thing this question remains a hypothetical and not a practical one. ;)

PS. I presume you've seen teh Wikipedia page for quasars here : http://en.wikipedia.org/wiki/Quasar right?

caveman1917
2010-Jul-26, 05:00 PM
If i'm getting your question right, what would an astronomer see if he were on one of those quasar galaxies now? With 'now' meaning he will think the universe as 13.7 billion years old, ie like we are now (emerged in the same CMB as we are).

Then the question is simple to answer, he will see the same thing we are seeing. 'Normal' galaxies near by, and quasars further away. He will (probably) see our milky way as being a quasar.
This answer really rests on an assumption we make, called the cosmological principle.

You might want to check the wiki article on the cosmological principle here (http://en.wikipedia.org/wiki/Cosmological_principle).

caveman1917
2010-Jul-26, 05:19 PM
I see you're also asking about wether that astronomer would see 'round the corner' and see our backs.

With current understanding of expansion and the size of the universe this isn't possible. You cannot send a light signal one way, and then wait for it to come back from the other direction. It will never arrive. Which would be the equivalent of your question. Expansion would make the distance that light signal has to travel bigger in a faster way than light can cross it.

mugaliens
2010-Jul-27, 03:39 PM
I suppose we could use any verb, but as Tomkeen restated the question in his second paragraph with "see," then the only logical conclusion is that "see" is the verb to use.

As for the 'round the corner' approach, I read nothing in Tomkeen's post which claims this at all. He's merely asking what we'd see if we were at a quasar galaxy and looking back towards Earth. He's asking if we'd see a younger version of our Milky way and the others in our cluster, or if we'd be seeing different galaxies altogether. My take on his question is that he's asking if galaxies can "recycle." The answer to that is "somewhat," though its not limitless, and further recyclings of stellar material result in stars which use versions of fusion involving heavier elements. Indeed, the heavier elements were created in such stars, but they're relatively sparse compared to hydrogen and helium.

caveman1917
2010-Jul-27, 03:47 PM
As for the 'round the corner' approach, I read nothing in Tomkeen's post which claims this at all.

My question is what would that astronomer see if he look in exactly the opposite direction as our galaxy? Would he see a completely different galaxies as the ones we can see or would it be our near by galaxies. If it is a different set of galaxies it would mean our universe is limitless otherwise the universe is a kind of four dimension sphere or am i being stupid?
(my bold)

I had interpreted this as meaning wether looking away from us, he would see 'round the corner' (see our galaxies) or not.

mugaliens
2010-Jul-28, 01:51 AM
(my bold)

I had interpreted this as meaning wether looking away from us, he would see 'round the corner' (see our galaxies) or not.

Re-reading it, I can see how one might see that in what he wrote. I gave him the benefit of the doubt and assumed since he mentioned looking at quasar galaxies as the were, he'd be thinking along the same lines if he were there and looking here. In other words, would it be much like what's around us today, or would it be very different i.e. changed over time?

caveman1917
2010-Jul-29, 12:30 AM
Well, it was especially that last sentence in the part i quoted above that made me think he was asking about that. "If they see the same galaxies, the universe is a sphere; if they don't, the universe is infinite".

It seemed a two-fold question to me, the first part being what you made of it, the latter part being what i made of it.

Either way, he's got both answers now :)