expansion of universe vs looking direction

[1of6Billion]

I'm not sure how to formulate this, but I'll give it a try.
(also, if this is the n-th time this question is asked, forgive me)
The Big Bang is currently the best accepted theory on how the universe started. Right?
Following on the Big Bang there is an ongoing period of expansion. Right?
So, if we look at a photo Hubble made of a galaxy some 13,8 billion light years away, we look at a much smaller universe than our current. Right?

If we point Hubble in the opposite direction of the first snapshot, what doe we see? :?: :?: :?:

Is it the same galaxy? Is the sky littered with repeating patches of ancient universe? :ugeek:
Or is the ancient universe somehow stretched all over the sky? If so, how's that possible?? :shock:

 

[origin]

I'm not sure how to formulate this, but I'll give it a try.
(also, if this is the n-th time this question is asked, forgive me)
The Big Bang is currently the best accepted theory on how the universe started. Right?

Yes

Following on the Big Bang there is an ongoing period of expansion. Right?

Yes

So, if we look at a photo Hubble made of a galaxy some 13,8 billion light years away, we look at a much smaller universe than our current. Right?

Yes, if you are saying that the source of the light that took13.8 billion years to reach us was much closer 13.8 billion years ago.

If we point Hubble in the opposite direction of the first snapshot, what doe we see? :?: :?: :?:

The 'other side' of the universe.

Is it the same galaxy?

No, why would it be the same galaxy?

Is the sky littered with repeating patches of ancient universe? :ugeek:

No, we are in a universe that has 3 spacial directions, why would we see a repeating patch? - I don't quite see why you would think that.

Or is the ancient universe somehow stretched all over the sky? If so, how's that possible?? :shock:

I am really confused by your confusion! Lets look at the universe as a very simple model of a big bubble. The universe and we are in the bubble. The bubble is expanding which means each point inside the bubble is moving away from each other point, so in any direction you look the everything is receding from you. This is a very simplistic model that is just presented to show that when viewed from one point; in every direction a different part of the universe is seen and the other points are moving away from us. Does this make sense to you?

 

[ramparts]

Exactly - it's a common misconception (and I believe it's yours) that the Big Bang started at a point and everything moved outward from there. Space itself was compressed and then expanded, so all points moved apart from each other. The universe, then, looks the same in every direction.

 

[FlatEarth]

Is it the same galaxy? Is the sky littered with repeating patches of ancient universe?

Actually, this has been studied by astronomers. There was a theory that the universe is like a hall of mirrors, and is not nearly as large as it appears. A search was done to look for repeating clusters and patterns which would be an indication that this is the case. It isn't. No repeating patterns were discovered.

 

[yevaud]

That's correct. That idea was dispelled by Kurt Godel many, many decades ago. It's along the same idea that if one were to keep heading for the "edge" of the universe, one would end up on the other side of the universe, which, as we know today, is absurd.

 

[ramparts]

Actually, the idea of the universe having a closed topology isn't absurd, even though we know if it's true, it can only be on scales much larger than the size of the observable universe. What do you mean that Gödel disproved it? I was unaware of any result like that from him.

 

[yevaud]

Pertains to the understanding that we are in a "no boundary" state, and that the universe isn't rotating. Godel showed that to do so would allow an entire raft of physical violations, such as time travel, etc.

 

[weeman]

Speedfreek...calling Speedfreek! Your assistance is needed in the Cosmic Expansion Dept. :mrgreen:

I think we just need a sign that we shine into the sky whenever we need Speedfreek, like Batman.

 

[1of6Billion]

Are we not in the middle of our observable universe? :?:
Let's take it a bit further... If we where, somehow, able to peek even further than 13,8B lightyears away. Let's say to the moment that the universe was the size of a galaxy.... :geek:

How could it be visible in all directions???

 

[origin]

Are we not in the middle of our observable universe? :?:

No we are not in the middle of the observable universe. There is no middle there is no edge. I know this stuff is confusing, the problem is that it is outside of our normal experiences. So we make models to help explain what is going on, but they are just models that have there limitations.

If we look at the expansion of the universe as a movie and run in the movie in reverse then we see that all the galaxies would be much closer. If we continue to run it backwards the galaxies will be on top of each other. Lets go even further back in time and now the universe is the size of a grapefruit. Now this is important - this is just a model so that we can visualize it, it is not really the size of a grapefruit, because there still is no edge of the universe for anything in the universe. Further, there is nothing, I mean nothing outside of the universe so in reality you cannot measure the size of the universe because you would have to be outside of the universe with a ruler and that just is not possible.

The best I can do is offer another model. We will use the earth - if I ask you to walk to the edge of the earth you would rightly say there is no edge. Add one more dimension and you have the universe you cannot get to the edge of the universe because there is no edge.

My brain hurts now so I am going to have a cup of coffee and vegetate.

 

[ramparts]

Though everything origin said is right, I'd like to add that by definition we are in the center of our observable universe. But the universe extends far beyond that, so it's kind of a meaningless statement. But yes, that is true.

Pertains to the understanding that we are in a "no boundary" state, and that the universe isn't rotating. Godel showed that to do so would allow an entire raft of physical violations, such as time travel, etc.

Well, Gödel universes and closed timelike curves certainly don't violate any known physics, just our common sense. It's been conjectured, but never proven, that they're unphysical.

And I'm still not getting what you mean by the "no boundary state" business. Why would a universe with a closed topology necessarily be rotating (if that's what you're saying)? Even if so, why would that entail an unphysical Gödel universe?

 

[FlatEarth]

Are we not in the middle of our observable universe? :?:

The truth is no one really knows the answer to your question. The answers are educated guesses, but that's as good as we can do. So understanding that, there can be a center to the universe, and we may be at the center. When I say there may be a center, I mean there may be a geometric center, not a gravitational center like a galaxy. Both are possible, both are unproven, as are all other explanations. We are at the center of the observable universe.

Let's take it a bit further... If we where, somehow, able to peek even further than 13,8B lightyears away. Let's say to the moment that the universe was the size of a galaxy.... :geek:

How could it be visible in all directions???

I used to think that if we could look back far enough we could see matter in the past that we are now made from. WRONG! The best way to visualize it is to remember that matter in our region of space never really moved that far from its original position. We can only look from our point of view inside the universe, which never really changed throughout time. Therefore, if the entire universe were the size of the galaxy, we would still look out and see it all around us.

 

[origin]

Though everything origin said is right, I'd like to add that by definition we are in the center of our observable universe. But the universe extends far beyond that, so it's kind of a meaningless statement. But yes, that is true.

This statement present a problem, to my way of thinking (which may very well be wrong). If we truly are the center of our observable universe then we are at the center of a sphere which, is the observable universe. So then if we were to go to the edge of that sphere then we would have another sphere of observable universe in which we were the center, this could go on infinitum. The other possibility is that at some point you approach the 'edge' of the universe in which case the observable universe would not appear spherical or identical in every direction, which would lead you to be able to point towards the 'center' of the universe. I don't believe either of these cases is accurate.

It seems to me that observable universe only appears spherical. To illustrate my point lets assume that there was a tralfamadorian that was outside the universe and could see the universe as a whole it could be that the tralfamadorian would see that the earth is about 137 miles from edge of the universe; but we would see the universe as a shpere because of the curvature of space.

I may be comlpletely misunderstanding what you are saying and be going off the deep end, but I get nervous when there is any talk of a center regarding of the universe because people tend to latch on to that and get the wrong idea about the nature of the universe

 

[ramparts]

Though everything origin said is right, I'd like to add that by definition we are in the center of our observable universe. But the universe extends far beyond that, so it's kind of a meaningless statement. But yes, that is true.

This statement present a problem, to my way of thinking (which may very well be wrong). If we truly are the center of our observable universe then we are at the center of a sphere which, is the observable universe. So then if we were to go to the edge of that sphere then we would have another sphere of observable universe in which we were the center, this could go on infinitum. The other possibility is that at some point you approach the 'edge' of the universe in which case the observable universe would not appear spherical or identical in every direction, which would lead you to be able to point towards the 'center' of the universe. I don't believe either of these cases is accurate.

That's exactly right. Whether or not there is an edge to the universe (which, you correctly point out, would imply a center - kind of) is irrelevant here, though. The observable universe is simply the stuff we can see. Given that on the scale of billions of light years, the universe is homogeneous and (key word here) isotropic, that is, it's the same in all directions, the edge of what we can see is the same distance in all directions. So yes, you can talk about our observable universe as a sphere with us at the center. The thing is that it's not physically meaningful, and an alien race in another galaxy certainly wouldn't call us the center of the universe.

 

[1of6Billion]

Is it possible visualise it somehow? :?:

 

[Woggles]

Wow what a great topic. And great explanations.

I was always wondering something about the deep field Hubble discovered. Was it just lucky to have guess that that point in the space may have being (how to word it hummm ) the being of the universe? (seeing that Hubble is peering back 13 plus billion years) What if the team doing the deep field study had pointed Hubble in completely different direction, would we be seeing the (almost being of the universe,) or as close to? Sorry folk not sure if I am wording myself correctly here, just hope the point is getting across!!


Paul

 

[ramparts]

No, no, and no The main point of this thread is that looking direction doesn't matter. In fact, one of the great discoveries of the 20th century is that on large scales, the universe is isotropic - that is, it looks the same in all directions. The beautiful thing about the Hubble Deep Field was that they were able to point to a really bland, normal patch of sky that didn't even have all that many galaxies, and still saw all the richness they did. You would see something very similar if you repeated the observation in any direction on the sky.

 

[Mee_n_Mac]

Wow what a great topic. And great explanations.

I was always wondering something about the deep field Hubble discovered. Was it just lucky to have guess that that point in the space may have being (how to word it hummm ) the being of the universe? (seeing that Hubble is peering back 13 plus billion years) What if the team doing the deep field study had pointed Hubble in completely different direction, would we be seeing the (almost being of the universe,) or as close to? Sorry folk not sure if I am wording myself correctly here, just hope the point is getting across!!


Paul

Just to add to ramparts answer above ... it's not so much luck as good planning. You have to avoid nearby stars and galaxies and dust and etc that would block (or compete with) the light coming from more distant places in the universe. One you've done that then the spots selected needed to be where the Hubble could point for long enough to get the exposure. Those conditions satisfied then, as said, it doesn't much matter where you look. There was the original Hubble Deep Field with was followed up by the HDF-South. They were different directions and saw the same general "stuff". The Hubble Ultra Deep Field was yet another different portion of the sky and again confirmed that the universe looks pretty much the same no matter where you look. And of course WMAP gave a real good measurement of the "sameness" of the CMBR. The Planck spacecraft will add to these measurements.

 

[Woggles]

Oh ok I get it now. Well I think I do lol. Basically no matter where we look we are always looking back in time, the beginning in a way. So here the next question then. If it doesn't matter where we look, and it was possible to detect the "Big Bang” Then we would "see it" in any (Detect it) in any direction? I understand the cosmic background radiation is from the Big Bang.

 

[MeteorWayne]

Just one point, IIRC, the Hubble Ultra Deep field used the same view as the original deep field, just with longer exposure.
I could be wrong, but I think thats what I remember.
MW

 

[ramparts]

Oh ok I get it now. Well I think I do lol. Basically no matter where we look we are always looking back in time, the beginning in a way.

Exactly!

So here the next question then. If it doesn't matter where we look, and it was possible to detect the "Big Bang” Then we would "see it" in any (Detect it) in any direction? I understand the cosmic background radiation is from the Big Bang.

Sure thing. Again, the Big Bang didn't happen at a certain point which everything is moving away from. Everywhere in space was compressed and the Big Bang was the expansion of that - so in a sense, it happened everywhere.

 

[Woggles]

Thanks ramparts


Wow this stuff just blows my mind!!!! Love it!! lol

 

[orienteer]

Imagine a infinitely large 3D blank canvas. Imagine a ball of paint exploding any where on that canvas and no resistance to stop the movement of the paint. From one of those dots of paint, you would be able to see all of the dots in all directions, but you can not see the edge of the canvas, because there is no edge. Do not mix up the idea that we can see the paint (Matter) but not the canvas (The Universe) Maybe there is a planet that only has stars out during the summer, but it would not stop them from heading the other way.

 

[Mee_n_Mac]

Just one point, IIRC, the Hubble Ultra Deep field used the same view as the original deep field, just with longer exposure.
I could be wrong, but I think thats what I remember.
MW

I recalled that the HDF was in some portion of Ursa Major and the HUDF was ... well ... someplace else. :roll: So I checked wiki (should be good enough for this) and it says the HUDF was in Fornax, which is a decidely different portion of the sky than that where Ursa Major resides.

FWIW the HDF-S was a portion in Tucana, another southern constellation I've never seen.

 

[MeteorWayne]

OK, thanx. It was just from memory. I'm on a backup computer today, so am limited in time and capability. MW