B What is seen from the farthest star?

[bubal]

Imagine someone in a planet at the farthest star of the farthest galaxy from ours. From that planet would the sky be a half black and the other half full of galaxies? Could a star be at the "edge" of the universe or general relativity contradicts that?

 

[russ_watters]

Imagine someone in a planet at the farthest star of the farthest galaxy from ours. From that planet would the sky be a half black and the other half full of galaxies? Could a star be at the "edge" of the universe or general relativity contradicts that?

General Relativity contradicts that; the universe looks basically the same no matter where you are. There is no edge.

 

[Jason R Carrico]

If that is true, then wouldn't that mean that the big bang that created our universe is one of many or could be inside of another bubble created by an older big bang that could be inside an even older big bang, so on and so on?

 

[Comeback City]

If that is true, then wouldn't that mean that the big bang that created our universe is one of many or could be inside of another bubble created by an older big bang that could be inside an even older big bang, so on and so on?

Why would it mean that?

 

[rootone]

There are some theories suggesting that our observable universe could be part of a larger 'multiverse'.
However that is not necessarily true and there is no hard evidence of it.

 

[Jason R Carrico]

Why would it mean that?

If the answer to the original question is that no matter where I stand in the expanding bubble of matter and energy created by the big bang, I see the same thing, stars galaxies and whatever, even on the very edge of that bubble, then what I look out onto beyond the bubble must have been created by a different big bang, right?

 

[Jason R Carrico]

That is assuming there is something outside the bubble to look out onto.

 

[Algr]

Imagine someone in a planet at the farthest star of the farthest galaxy from ours. From that planet would the sky be a half black and the other half full of galaxies? Could a star be at the "edge" of the universe or general relativity contradicts that?

Imagine you tried this with your position on a globe of the Earth. There is a "farthest point" from you, but there is nothing special about it. And you are at the farthest point from that point: Any direction you walk in would bring you closer to that point.

 

[bubal]

Let's perform a thought experiment. Imagine that the Universe was smaller, only Laniakea, or even smaller, only the Local group. In this case you could be at the far edge of Andromeda and see the dark emptiness, unless you saw the Milky way on both sides. (In case that the Universe is closed, something that I don't know if is proven). It would be great if someday a telescope could see a pattern of let's see the southern universe looking at the northern universe.

 

[Simon Peach]

infinite, seem to sum this question up

 

[lifeonmercury]

It's possible the edge of the observable universe is actually the edge of the entire universe. We can't see any further than 46 billion light years in any direction and really don't know for sure what's behind this horizon. However, the consensus is that we wouldn't find anything special out there.

 

[Drakkith]

If the answer to the original question is that no matter where I stand in the expanding bubble of matter and energy created by the big bang, I see the same thing, stars galaxies and whatever, even on the very edge of that bubble, then what I look out onto beyond the bubble must have been created by a different big bang, right?

There is no expanding bubble. The expansion of space means that the distance between all unbound objects increases over time. Stop and think about that for a moment. Any object without a sufficient attractive force will, over time, move away from you. If you instantly moved 1 billion light years away you will still see objects moving directly away from you, including the location you used to be at. After moving to this new location, you lose sight of some objects that you used to be able to see in your previous location (because you've moved and their light has not had time to reach your new location yet) but you will find that new objects have now been brought into your field of view. These new objects couldn't be seen in your previous location, again because their light hadn't had time to reach that location yet.

No matter where you go you will find the above holds true. Objects not bound to you will always be moving directly away from you and you will always find new objects entering your view as you move around the universe. This is, of course, only true if the universe is infinite in size. If not, then you may eventually come back around to your previous location (despite having moved directly away from it the whole time) or something else may happen. Current observations rule out a finite universe smaller than a certain size, with that size being some amount much larger than the observable universe. I confess I don't have a number for you.

Additionally, please note that the big bang did not occur at a single point in space. The singularity (if it ever actually existed) existed throughout the entire universe at the same time.

 

[Jason R Carrico]

It's possible the edge of the observable universe is actually the edge of the entire universe. We can't see any further than 46 billion light years in any direction and really don't know for sure what's behind this horizon. However, the consensus is that we wouldn't find anything special out there.

I agree that it is possible that what we can see is all that there is to see. It's also just as possible that it's not. I thought roughly 14 billion light years was as far as we could currently see.

 

[Drakkith]

Let's perform a thought experiment. Imagine that the Universe was smaller, only Laniakea, or even smaller, only the Local group. In this case you could be at the far edge of Andromeda and see the dark emptiness, unless you saw the Milky way on both sides. (In case that the Universe is closed, something that I don't know if is proven). It would be great if someday a telescope could see a pattern of let's see the southern universe looking at the northern universe.

Such observations are already being done. So far we haven't seen the back of our own heads.

But seriously, these observations have yielded results supporting the idea that the universe is either infinite or much larger than the observable universe.

 

[russ_watters]

If the answer to the original question is that no matter where I stand in the expanding bubble of matter and energy created by the big bang, I see the same thing, stars galaxies and whatever, even on the very edge of that bubble, then what I look out onto beyond the bubble must have been created by a different big bang, right?

You missed the last sentence of my post.

 

[Jason R Carrico]

There is no expanding bubble. The expansion of space means that the distance between all unbound objects increases over time. Stop and think about that for a moment. Any object without a sufficient attractive force will, over time, move away from you. If you instantly moved 1 billion light years away you will still see objects moving directly away from you, including the location you used to be at. After moving to this new location, you lose sight of some objects that you used to be able to see in your previous location (because you've moved and their light has not had time to reach your new location yet) but you will find that new objects have now been brought into your field of view. These new objects couldn't be seen in your previous location, again because their light hadn't had time to reach that location yet.

No matter where you go you will find the above holds true. Objects not bound to you will always be moving directly away from you and you will always find new objects entering your view as you move around the universe. This is, of course, only true if the universe is infinite in size. If not, then you may eventually come back around to your previous location (despite having moved directly away from it the whole time) or something else may happen. Current observations rule out a finite universe smaller than a certain size, with that size being some amount much larger than the observable universe. I confess I don't have a number for you.

Additionally, please note that the big bang did not occur at a single point in space. The singularity (if it ever actually existed) existed throughout the entire universe at the same time.

Can you elaborate on that last statement? It seems to contradict most of what I have read, or maybe I didn't understand what I was reading. Either way, please explain.

 

[Drakkith]

Can you elaborate on that last statement? It seems to contradict most of what I have read, or maybe I didn't understand what I was reading. Either way, please explain.

Yes, it is often stated that the big bang was an explosion from a single point. But according to my understanding this is not true. If we wind back time in our model of the universe, we will find that at t=0 the density of matter goes to infinity at every point in universe (which is still infinite in size). So the singularity, if it actually existed, would occur everywhere and essentially be infinite in size.

I wish I could elaborate further, but I know very little about the details.

 

[Jason R Carrico]

I've never heard that before. I'd like to read about it. Can you give me a link?

 

[Drakkith]

I've never heard that before. I'd like to read about it. Can you give me a link?

If I can find the thread(s) where I've seen this, I'll be sure to post a link.

 

[Comeback City]

If the answer to the original question is that no matter where I stand in the expanding bubble of matter and energy created by the big bang, I see the same thing, stars galaxies and whatever, even on the very edge of that bubble, then what I look out onto beyond the bubble must have been created by a different big bang, right?

@Drakkith nailed it pretty well. Just because you are at the edge of the observable universe, which is relative to us on Earth, that doesn't mean you won't be able to see other matter in all directions. It is likely that the edge of the observable universe has its own observable universe that is relative to it, as @Drakkith stated that the universe is likely to be either infinite or much larger than our observable universe. As for the multiverse theory, if it did stand true, I'm not sure if you could see outside your own universe and into another. That seems beyond my current understanding of the universe.

 

[Jason R Carrico]

@Drakkith nailed it pretty well. Just because you are at the edge of the observable universe, which is relative to us on Earth, that doesn't mean you won't be able to see other matter in all directions. It is likely that the edge of the observable universe has its own observable universe that is relative to it, as @Drakkith stated that the universe is likely to be either infinite or much larger than our observable universe. As for the multiverse theory, if it did stand true, I'm not sure if you could see outside your own universe and into another. That seems beyond my current understanding of the universe.

I completely understand that if I move to the edge of what we currently see I will have a new observable universe. That was never the question. Everything I've ever seen or read about the big bang explains it as a rapid expansion of energy from a singularity. From the size of an atom to a basketball in a Planck second, expanding faster than the speed of light, because the expansion of space-time has no speed limit. The analogy of drawing stars on a balloon and blowing it up makes all the stars on it move away from each other, cool. If I'm on the surface e of the balloon and look up, what do I see?

 

[Grinkle]

It is likely that the edge of the observable universe has its own observable universe that is relative to it,

There is no edge. The universe looks the same no matter your position in-the-large. There are galaxies after galaxies, forever. There are not multiple finite big-bangs that over lap each other. That picture of multiple big bangs implies that there is a superstructure of infinite space-time that is populated by big bangs that sprout galaxies and stars all co-populating the same space time fabric. This is not what the expansion theory says. At one point the universe was simultaneously infinitely dense and infinitely large. It expanded and its density became less than infinity. If you find that hard to grasp, it comforts me because I find it hard to grasp. But I can grasp that expansion of an infinite universe predicts that no matter where I am in an infinite universe, I see galaxies in all directions.

Multiverse theories postulate completely separate space-times that, if they co-exist in some over-arching fabric, that fabric is not space-time. The picture of multiple big-bangs does not reconcile the different views in this thread.

 

[rootone]

The singularity is not a physical object, it represents where math breaks down and produces nonsense, (like infinite density).
We don't actually know what happened at t=0, and the big bang theory doesn't propose an answer.
It merely states that very shortly after whatever it is that happened the Universe must have been in a very hot dense state,
and since then it has expanded and cooled.

 

[Jason R Carrico]

So the big bang did not originate from a single point, but instead originated everywhere, simultaneously, and has no edge because it is infinite. Is that the current theory?

 

[Grinkle]

Is that the current theory?

I don't know how many on this forum would agree that is the current theory. My own understanding has always been along these lines -

The extent of the universe (finite vs infinite) has not changed over time. If it is infinite in extent now, then it has always been infinite in extent.

The expansion theory says that at time zero the universe was infinitely dense. IMO this leads some to describe the early universe as infinitely small, which description I disagree with.

So the big bang did not originate from a single point, but instead originated everywhere, simultaneously, and has no edge

I interpret expansion / big bang to be saying this, yes.

 

[rootone]

Yes, the big bang happened to the entire Universe, not in some part of it.
Whether or not it is infinite, the jury is still out.
Some things can be finite, yet still are endless, like a journey around the Eath's equator.
You can keep heading west (or east) as long as the Earth exists, although the size of Earth is finite.

 

[Jason R Carrico]

Can someone point me to some articles or books that can help me further understand that?

 

[stoomart]

Can someone point me to some articles or books that can help me further understand that?

This Wikipedia article is a good start. If the universe is infinite in size (relative to density), it seems logical that it has been expanding for infinite time (relative to any reference frame), and will continue to do so.

 

[Jason R Carrico]

This Wikipedia article is a good start. If the universe is infinite in size (relative to density), it seems logical that it has been expanding for infinite time (relative to any reference frame), and will continue to do so.

Thank you. Great answer with tons of links to keep me entertained for days I'm sure. Again, thanks.

 

[Jason R Carrico]

Thanks to everybody actually. This has been a very enlightening conversation.

 

[Chronos]

While it is possible to detect if the universe is finite, it is impossible to even know [much less prove] if it is infinite. The are symptoms of a finite universe [e.g., see circles in the sky] that could be evident. No such symptoms have been detected to date and our models works just fine for an infinite universe, so it is the model of choice among the great majority of cosmologists. The most notable exception was, interestingly enough, probably Einstein, who struggled with the notion because his field equations behaved badly at infinity. Besides, a finite universe conflicts with the very concept of a universe [implies something beyond all that ever has or ever will exist] and many people have a difficult time wrapping their head around that idea. 'Turtles all the way down' [more universes] is not a particularly appealing explanation.

 

[IGBY International]

According to the general theory or relativity light bends. A universe is a closed system nothing gets out, nothing comes in. Light circulates within creating a multitude of past "Light" objects that are observed as further and further away. Reflections, duplicates of our past existence.

 

[stoomart]

According to the general theory or relativity light bends. A universe is a closed system nothing gets out, nothing comes in. Light circulates within creating a multitude of past "Light" objects that are observed as further and further away. Reflections, duplicates of our past existence.

My understanding is that spacetime is cosidered to be flat, in which light does not bend unless influenced by gravity. Do you have a reference that explains what you are saying in technical terms?

 

[Comeback City]

There is no edge.

I was using the term "edge" a little bit loosely.

The universe looks the same no matter your position in-the-large. There are galaxies after galaxies, forever. There are not multiple finite big-bangs that over lap each other. That picture of multiple big bangs implies that there is a superstructure of infinite space-time that is populated by big bangs that sprout galaxies and stars all co-populating the same space time fabric. This is not what the expansion theory says. At one point the universe was simultaneously infinitely dense and infinitely large. It expanded and its density became less than infinity. If you find that hard to grasp, it comforts me because I find it hard to grasp. But I can grasp that expansion of an infinite universe predicts that no matter where I am in an infinite universe, I see galaxies in all directions.

I understand how the big bang works. And I also understand that you will see galaxies everywhere in an infinite universe. The only discrepancy occurs if the universe is finite, which I believe is what the OP was mainly asking about: as in, what do you see at the edge (again loosely) of a finite universe. I believe the answer to this would lie within GR but not entirely certain. Also, not sure where the multiple overlapping big bangs thing got here.

Multiverse theories postulate completely separate space-times that, if they co-exist in some over-arching fabric, that fabric is not space-time. The picture of multiple big-bangs does not reconcile the different views in this thread.

Indeed I will research the multiverse theory(ies) more.

 

[Drakkith]

My understanding is that spacetime is cosidered to be flat, in which light does not bend unless influenced by gravity. Do you have a reference that explains what you are saying in technical terms?

Here's a good place to start: https://en.wikipedia.org/wiki/Shape_of_the_universe

Specifically, see the section on Global Universe Structure.

 

[PhanthomJay]

As for the multiverse theory, if it did stand true, I'm not sure if you could see outside your own universe and into another. That seems beyond my current understanding of the universe. ?:)

IF there were a multiverse, it is my understanding that light could not penetrate through the 'bubble'...it is forever confined to our own universe. There had been some speculation, however, a while back by Hawking and M-Theory gurus, that perhaps high frequency gravity waves could penetrate the small higher order dimensions of spacetime, via black holes as i recall, and this is just speculation and not a theory, but the M-theorists are here to stay for a long time in the never ending quest to unlock the Universe's most hidden secrets. Unfortunately, the theories may be untestable, unable to be falsified, and thus, not a theory. As I understand it, I am not the expert on these matters.

 

[IGBY International]

Excuse me for my ignorance. I have been referring to implications of Gravity's Rainbow which is a recently added experiment at CERN.
If you are not familiar with it then of course you would not understand my posts.

 

[stoomart]

Excuse me for my ignorance. I have been referring to implications of Gravity's Rainbow which is a recently added experiment at CERN.
If you are not familiar with it then of course you would not understand my posts.

I don't see how the rainbow gravity theory would affect light geodesics on cosmological scales (maybe to a minor degree close to massive objects), especially to this extent:

Light circulates within creating a multitude of past "Light" objects that are observed as further and further away. Reflections, duplicates of our past existence.

 

[Simon Peach]

It's possible the edge of the observable universe is actually the edge of the entire universe. We can't see any further than 46 billion light years in any direction and really don't know for sure what's behind this horizon. However, the consensus is that we wouldn't find anything special out there.

Why would the edge of the seeable universe be the edge of the whole universe? Is the horizon the edge of the earth?

 

[Comeback City]

According to the general theory or relativity light bends. A universe is a closed system nothing gets out, nothing comes in. Light circulates within creating a multitude of past "Light" objects that are observed as further and further away. Reflections, duplicates of our past existence.

Excuse me for my ignorance. I have been referring to implications of Gravity's Rainbow which is a recently added experiment at CERN.
If you are not familiar with it then of course you would not understand my posts.

How does the gravity rainbow theory state that light circulates and gives us "duplicates of our past existence"? From my understanding, gravity rainbow theory states that gravity has different effects on different wavelengths of light and that the Big Bang never actually happened. What is the relation?

 

[Algr]

If I'm on the surface e of the balloon and look up, what do I see?

Under the balloon analogy you can't look up because you are a two dimensional being on a universe expanding into the 3rd dimension. The real universe is expanding into a fourth spatial dimension (not time) that you can't see because you are three dimensional.

 

[Grinkle]

Under the balloon analogy you can't look up because you are a two dimensional being on a universe expanding into the 3rd dimension. The real universe is expanding into a fourth spatial dimension (not time) that you can't see because you are three dimensional.

Hmmm. It never occurred to me before that expansion might imply a 3d surface embedded in a 4d space. Does expansion imply a 4th spatial dimension, or is that carrying the balloon analogy further than is meaningful?

 

[rootone]

Sounds like an infinite stack of turtles to me.

 

[Drakkith]

Hmmm. It never occurred to me before that expansion might imply a 3d surface embedded in a 4d space. Does expansion imply a 4th spatial dimension, or is that carrying the balloon analogy further than is meaningful?

It only implies that our universe may behave in a manner similar to as it would act if it were embedded in a higher dimensional space. Whether it is embedded or not is unknown and probably can't be known since we have no way of interacting in a hypothetical 4th spatial dimension.

 

[Chronos]

Keep in mind if you traveled to the most distant known galaxy the universe would be many billions of years older than it is at this moment - simply because nothing can travel faster than c and the universe would continue to age and expand during the journey. Were you at one of these distant places this very moment, the universe would be billions of years younger than it currently is because you had to already have been there when the light we currently observe here was emitted from there - for the same reason. No matter where or when you are in the universe you are always at the center of your observable universe. The long and short of it is - the 'edge' of the observable universe is like a rainbow: an illusion that never actually exists anywhere at any time irrespective of whether it is finite or not.

 

[Grinkle]

@Chronos Thanks for the reminder. Its very easy for me to fall into thought experiments that ignore c or other constraints and then spend lots of time trying to make sense of things.

 

[diogenesNY]

@Jason R Carrico, Grinkle, et al:

Have a look at the following article by Charles Lineweaver and Tamara Davis. "Misconceptions about the Big Bang." This was published in the March 2005 edition of Scientific American. It deals fairly directly with most of what is being kicked about here.

Here is a link to a copy of the article:
http://www.mso.anu.edu.au/~charley/papers/LineweaverDavisSciAm.pdf

Highly recommended.

diogenesNY

 

[Jason R Carrico]

Thanks, but I got a 404 error code.

 

[rootone]

No 404 for me, it may have been a temporary server outage.

 

[Jason R Carrico]

Oh well, it just won't open for my phone then I guess. I will try to hunt it down some other way