naive question; If we can see a developing situation before the final product, 13 billion years into the past, could it be that we are looking back into time in two opposing directions?, and this one was the long one around, past the halfway mark? --move to appropriate forum?
ALMA sees old galaxies before they merged. two ways to look back into the past?
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Xelasnave.1947
Valued Senior Member
I don't know what you are asking could you expand upon your opening post.
Alex
Alex
Write4U
Valued Senior Member
I think I understand the question.
IMO , when we look back in time we're always looking toward the BB, from any direction. You cannot look past the BB for space expanding on the other side of the BB.
We're always looking toward the center, i.e the BB. Moreover, all galaxies were formed after the BB.
Does that answer your question?
http://earthsky.org/space/is-our-universe-ringing-like-a-crystal-glass
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NotEinstein
Valued Senior Member
You might want to rephrase that: the BB is not a center of anything (at least not in mainstream cosmology). It's the starting point of our universe, but it can't be called a center in any meaningful way, to the best of my knowledge.
Write4U
Valued Senior Member
Yes I thought of that after I posted.
But then it becomes a question if the BB expandad in all 3 D directions. The illustration seems to contradict that. It looks you can actually slice 2 D time surfaces , i.e . what was present at any given moment in time.
Which sounds reasonable, else how could we look back in time at all.
NotEinstein
Valued Senior Member
Yes, it did. Just check the maths for yourself: https://en.wikipedia.org/wiki/Friedmann–Lemaître–Robertson–Walker_metric
That's because:
1) It's a 2D picture
2) It's just an illustration
I don't understand how that first sentence connects to the latter?
Write4U
Valued Senior Member
Look at the accompanying texts which indicate the sliced time frames of the evolution of the a wavelike expanding cone.
The illustration is looking at the universe from a side view. Now that might be incorrect, but that how it is depicted in wiki.
NotEinstein
Valued Senior Member
Unless that picture is 5 dimensional (3 space and 1 time, and 1 extra space dimension to look at it from a side view), it is not depicting reality correctly.
Write4U
Valued Senior Member
It seems obvious were are looking at the universe from an observation point outside the universe. So yes, but that does not necessarily assume 5 dimensions. It is an abstract POV.
NotEinstein
Valued Senior Member
In other words, it's not an accurate depiction of the universe, as such an observation point cannot exist (i.e. how can the concept of positions be well-defined outside of spacetime?).
So even if that picture suggests the BB started at some center (it actually doesn't), that's just the inaccuracy of the picture, and not a proper representation of the universe. Just search on the internet if the BB was at the center of the universe, if you don't understand the maths in the Friedmann–Lemaître–Robertson–Walker metric Wiki article.
Write4U
Valued Senior Member
I did not make that claim. It was illustrative in context of the question in post # 1, as I understood it.
True it started at the point of the BB and its evolution over time and it is true we can look across the universe along a slice of time which gives us the approximation of the current size of the universe, but that's not looking back in time to the beginning (BB)[/QUOTE]
If you mean the center of a sphere you are correct. I was speaking of the center of a plane a slice of time.
Of course this does not take an manifolds into account, but it illustrate a pair of opposite wave functions. Hence the article heading ; Is the Universe ringing?
The illustration shows 7 opposite cycles of peaks and troughs.
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NotEinstein
Valued Senior Member
Yes you did, in your post #9:
For there to be an observation point outside of the universe, there must be a position outside the universe for that observation point to take.
And if you were talking about it being an accurate depiction of the universe, your post #5:
is clearly deriving properties of the univetruth from that picture, indicating you take the picture
Correction: visible universe, at best. We have no idea how large the universe is, or if it's even finite in size.
Actually, it is. The further you look away, the more into the past you are looking.
A plane does not have a center, so that's incoherent.
Write4U
Valued Senior Member
Are you comparing the sun to the BB.? i.e. as a spherical expansion from a singularity? that would give the universe a center just like the sun is the center of our solar system.
Is the unverse spherical with the BB at its center? But the diameter of the universe is 93 billion lightyears across in this slice of time and that would place the BB at 46.5 billion light years away and not 14.7 billion (light) years at the half-way point which would be the BB and I believe this is what the original poster asked.
Can you answer the question better? Please help me out.
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Seattle
Valued Senior Member
No, I'm not comparing the Sun to the BB. Why would you think that? I'm just talking about the concept of looking back in time.
The BB isn't the "center". The universe is the universe. It is all expanding , not expanding from a center outward.
There is no "half-way" point as you are describing. As was pointed out above in another post, there is the concept of the visible universe and what's beyond that. The visible universe is just the portion of the universe that light can get to from here in 14 billion years so it's twice 14 billion plus expansion. Any expansion beyond the speed of light will never be accessible from here.
My last paragraph is undoubtedly full of mistakes and is totally up for correction by anyone more knowledgeable on this subject.
Write4U
Valued Senior Member
Fundamentally I agree with all of that.No, I'm not comparing the Sun to the BB. Why would you think that? I'm just talking about the concept of looking back in time.
The BB isn't the "center". The universe is the universe. It is all expanding , not expanding from a center outward.
There is no "half-way" point as you are describing. As was pointed out above in another post, there is the concept of the visible universe and what's beyond that. The visible universe is just the portion of the universe that light can get to from here in 14 billion years so it's twice 14 billion plus expansion. Any expansion beyond the speed of light will never be accessible from here.
My last paragraph is undoubtedly full of mistakes and is totally up for correction by anyone more knowledgeable on this subject.
However we have been able to approximate when the BB happened by it's remaining background noise and apparently we are still riding the wave created by the BB.
Alex, to use the "sun" illustration in some of the replies. when looking back in time, the incoming radiation really, ---how is it that we can see an earlier image of it and also, or not, the 8 minute old (present).
The News item said it showed the old galaxies in the process of merging, but they have merged since, so, where is that younger image? has it moved, shrunk? past us by?
The one dimensional time representation post 3 are difficult I think, for we look back into time to the beginning, no matter where we look, an expanding sphere, looking along the surface helps me more.
I always like to look at fellow surfers, I like sharing a wave. so: how come , looking along that break, I can see event of those galaxies merging? where is the image of the united entity along the wave in my line of sight??
That is an interesting wave of energy we are riding. it's crest length curves right back into the smaller and smaller space. Us pointing the board into the future.
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Seattle
Valued Senior Member
Nebel, I'm not sure what you aren't clear about so if my answer isn't applicable, just ignore it.
The old galaxy that we are just now seeing will have changed but we can't see that because it's so far away that not enough time has passed for us to see those changes.
We can see how galaxies closer to us have evolved and we can guess that that's the way the old galaxy will evolve.
The benefits here is just finding the oldest possible galaxies to give us a window into the earliest times in our universe. We aren't seeing both old and new images of the oldest galaxy and that seems to be your confusion.
The old galaxy that we are just now seeing will have changed but we can't see that because it's so far away that not enough time has passed for us to see those changes.
We can see how galaxies closer to us have evolved and we can guess that that's the way the old galaxy will evolve.
The benefits here is just finding the oldest possible galaxies to give us a window into the earliest times in our universe. We aren't seeing both old and new images of the oldest galaxy and that seems to be your confusion.
NotEinstein
Valued Senior Member
It's due to the finite speed of light. Light emitted by the sun takes about 8 minutes to reach us, so when we look at the sun (not directly! dangerous!) we see the sun as it was 8 minutes ago.
Same deal; the light of these old galaxies to a long time to reach us. We are seeing the galaxies as they were a long time ago. The merger has already taken place, but the information (light) of that event is still underway and hasn't reached us yet.
(Not sure what you mean by this?)