The Hubble deep field photos and the edge of the universe

  • #1
Sophrosyne
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TL;DR Summary
Does the very embryonic appearance of the farthest galaxies in the visible universe suggest the "real" edge can't be too far beyond?
The Hubble telescope was able to capture images of the edges of our visible universe in its deep space photos. These were among its most breathtaking pictures. They show galaxies from about 14 billion light years away, as well as in the past, from the very beginning of time and space in our universe. What they show are very embryonic, primitive galaxies just in the process of formation- the very first galaxies after the big bang. But due to cosmic inflation, we believe that the actual universe actually extends even beyond this visible portion. We just can't see it because right after the big bang, space expanded faster than light, and so these parts of the universe grew beyond our perception.

But what we are seeing couldn't have been too much after the big bang, speaking in terms of relativistic invariance of our own time/space frame of reference.

Also, our ability to see the fair homogeneity of the cosmic background radiation, which also seems to be an event which developed fairly early on after the big bang, suggests that the actual edge in space-time can't be too far beyond these things that we do see. Wherever that edge is, these things that we do see should be covering something like ~99% of the whole thing.

Right?

Is there something wrong with this line of reasoning?
 

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  • #2
phinds
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Summary: Does the very embryonic appearance of the farthest galaxies in the visible universe suggest the "real" edge can't be too far beyond?
There IS NO "edge" to the universe, so the rest of your post is moot.

I recommend the link in my signature
 
  • #3
Sophrosyne
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There IS NO "edge" to the universe, so the rest of your post is moot.

I recommend the link in my signature

I understand. But let me ask the question another way: is what we are seeing in our visible universe likely covering most of it? If the universe is 14 billion years old, and many of these galaxies are close to that age, isn't that most of the universe, both space and time-wise, within our visible universe?

IOW, the balloon may have no "edge". But can't we tell anyway whether we are seeing MOST of it?
 
  • #4
phinds
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I understand. But let me ask the question another way: is what we are seeing in our visible universe likely covering most of it? If the universe is 14 billion years old, and many of these galaxies are close to that age, isn't that most of the universe, both space and time-wise, within our visible universe?
HIGHLY unlikely. Estimates of the size of the universe make our Observable Universe a percentage of the whole ranging from utterly trivial down to nothing more than a rounding error in the 500th decimal place.
 
  • #5
Sophrosyne
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HIGHLY unlikely. Estimates of the size of the universe make our Observable Universe a percentage of the whole ranging from utterly trivial down to nothing more than a rounding error in the 500th decimal place.

Would you reconsider if these galaxies we were seeing were fully mature looking, rather than the very primitive shapes we see now?
 
  • #6
phinds
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Would you reconsider if these galaxies we were seeing were fully mature looking, rather than the very primitive shapes we see now?
That would be impossible. Those galaxies were formed very early in the life of the universe so could not possibly be mature when they emitted the light that we see.

I really suggest that you read some basic cosmology, as you are misunderstanding some VERY basic concepts.
 
  • #7
Sophrosyne
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That would be impossible. Those galaxies were formed very early in the life of the universe so could not possibly be mature when they emitted the light that we see.

I really suggest that you read some basic cosmology, as you are misunderstanding some VERY basic concepts.

OK. It just seems to me that if the visible universe was only a very small part of the whole, even the furthest galaxies we saw would be fairly mature ones, as everything else would have been pushed out by cosmic inflation beyond our visible range.

But I will take your advice and try to figure this out a little bit more on my own.
 
  • #8
Bandersnatch
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It just seems to me that if the visible universe was only a very small part of the whole, even the furthest galaxies we saw would be fairly mature ones, as everything else would have been pushed out by cosmic inflation beyond our visible range.
I'm not sure how exactly you're imagining it, since it doesn't follow. You'd observe the youngest galaxies as being the furthest away even if the universe were not expanding (whether spatially infinite or not). That is just a consequence of it taking time for light to travel. Can you see how this works in the static case?

In expanding universe you don't lose the youngest light from sight, leaving just the more recent one - you just see the youngest light coming from different distances than it would in the static case. That is, the light carrying the images of the young galaxies that was emitted closer, and which without expansion would have long passed you by.

Note: it's probably best to focus on the run-of-the-mill expansion and forget about inflation for now, since it's a period before light could travel freely (or existed) and has little bearing on the confusion at hand.
 
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  • #9
russ_watters
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HIGHLY unlikely. Estimates of the size of the universe make our Observable Universe a percentage of the whole ranging from utterly trivial down to nothing more than a rounding error in the 500th decimal place.
Or to put it another way, I believe the prevailing opinion is that the universe is spatially infinite.
 
  • #10
russ_watters
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Would you reconsider if these galaxies we were seeing were fully mature looking, rather than the very primitive shapes we see now?
They can't simultaneously be old and far away, so I'm not clear what your logic is here.

It just seems to me that if the visible universe was only a very small part of the whole, even the furthest galaxies we saw would be fairly mature ones, as everything else would have been pushed out by cosmic inflation beyond our visible range.
But how can a galaxy be mature yet have formed just after the big bang?
 
  • #11
phinds
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Or to put it another way, I believe the prevailing opinion is that the universe is spatially infinite.
Right. I thought of that after I posted and and had left the computer and was thinking of editing my post just now to let him know that, so I'm glad you pointed it out.
 
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  • #12
phinds
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OK. It just seems to me that if the visible universe was only a very small part of the whole, even the furthest galaxies we saw would be fairly mature ones, as everything else would have been pushed out by cosmic inflation beyond our visible range.
As has already been pointed out while I was gone, that is totally faulty logic.

But I will take your advice and try to figure this out a little bit more on my own.
Good idea.
 
  • #13
Sophrosyne
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They can't simultaneously be old and far away, so I'm not clear what your logic is here.

OK, I don’t want to look like I’m being stubborn here. But this sentence really puzzles me. I impression was that in astronomy, The further you look out, the further “back in time” you look.
I'm not sure how exactly you're imagining it, since it doesn't follow. You'd observe the youngest galaxies as being the furthest away even if the universe were not expanding (whether spatially infinite or not). That is just a consequence of it taking time for light to travel. Can you see how this works in the static case?

In expanding universe you don't lose the youngest light from sight, leaving just the more recent one - you just see the youngest light coming from different distances than it would in the static case. That is, the light carrying the images of the young galaxies that was emitted closer, and which without expansion would have long passed you by.

Note: it's probably best to focus on the run-of-the-mill expansion and forget about inflation for now, since it's a period before light could travel freely (or existed) and has little bearing on the confusion at hand.

OK, what clears this up for me a little bit is "it's probably best to focus on the run-of-the-mill expansion and forget about inflation for now, since it's a period before light could travel freely (or existed) and has little bearing on the confusion at hand".

I was picturing inflation having occurred first AFTER light could travel freely.

Thanks.
 
  • #14
phinds
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OK, I don’t want to look like I’m being stubborn here. But this sentence really puzzles me. I impression was that in astronomy, The further you look out, the further “back in time” you look.
EXACTLY. So when you look at something far away you are seeing it as it was a LONG time ago, when it was young. Thus what you see can't be both far away and old. Reread post #6.
 
  • #15
Sophrosyne
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EXACTLY. So when you look at something far away you are seeing it as it was a LONG time ago, when it was young. Thus what you see can't be both far away and old. Reread post #6.

OK. I see. I was using the word "old" as in "long time ago", not as age.

I think where my confusion was happening was in thinking that light started traveling BEFORE cosmic inflation. Now, however, the presence of the cosmic background radiation makes more sense.
 
  • #16
phinds
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OK. I see. I was using the word "old" as in "long time ago", not as age.

I think where my confusion was happening was in thinking that light started traveling BEFORE cosmic inflation. Now, however, the presence of the cosmic background radiation makes more sense.
Nothing we can see goes back anywhere NEAR as far as the end of inflation. Again, all of this is cosmology 101, or even a pre-requisite for it, so I suggest some basic reading.

This is fascinating stuff but trying to learn it by random questions on an internet forum is NOT the way to go about it.
 
  • #17
Bandersnatch
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This is fascinating stuff but trying to learn it by random questions on an internet forum is NOT the way to go about it.
Why not?
 
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  • #18
russ_watters
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OK, I don’t want to look like I’m being stubborn here. But this sentence really puzzles me. I impression was that in astronomy, The further you look out, the further “back in time” you look.
Right, so if we are looking at an old and distant galaxy, to us it will look young and distant. The universe is almost 15 billion years old, so if we look at a galaxy 13 billion light years away, that is 14 billion years old it will look 14-13= 1 billion years old.

[edit] And similarly if you are hoping to see a galaxy that is "now" 1 billion years old, but 14 billion light years away it will look 1-14= -13 billion years old...in other words, not yet formed when the light that reaches us today was sent.
 
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