What is seen from the farthest star?

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Discussion Overview

The discussion explores the nature of the universe as perceived from the farthest stars and galaxies, questioning concepts such as the edge of the universe, the implications of general relativity, and the possibility of a multiverse. Participants engage in thought experiments regarding the visibility of galaxies and the structure of the universe, including the implications of the Big Bang and cosmic expansion.

Discussion Character

  • Exploratory
  • Debate/contested
  • Conceptual clarification
  • Mathematical reasoning

Main Points Raised

  • Some participants suggest that from a distant planet, the sky could be divided between blackness and galaxies, questioning if a star could exist at the "edge" of the universe.
  • Others argue that general relativity implies there is no edge to the universe and that it appears similar regardless of location.
  • One participant proposes that if the universe is homogeneous, the Big Bang could be one of many, potentially nested within older bubbles from previous Big Bangs.
  • Another participant challenges this idea, asking for clarification on why the original premise would lead to such a conclusion.
  • Some theories suggest our observable universe might be part of a larger multiverse, though this remains speculative and lacks hard evidence.
  • A participant explains that the expansion of space means objects not bound to each other will move away over time, impacting visibility as one changes location in the universe.
  • There is a suggestion that the observable universe's edge might coincide with the universe's actual edge, but this remains uncertain.
  • One participant notes that the Big Bang did not occur at a single point, but rather throughout the universe simultaneously.
  • Another participant mentions that observations have been made to support the idea of an infinite universe or one much larger than what is observable.

Areas of Agreement / Disagreement

Participants express multiple competing views regarding the nature of the universe, the implications of general relativity, and the concept of the Big Bang. The discussion remains unresolved, with no consensus on the existence of an edge to the universe or the nature of cosmic expansion.

Contextual Notes

Participants acknowledge limitations in their understanding of the universe's structure, including the potential for a closed universe and the implications of cosmic expansion on visibility and observation.

  • #31
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.
 
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  • #32
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.
 
  • #33
IGBY International said:
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?
 
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  • #34
Grinkle said:
There is no edge.
I was using the term "edge" a little bit loosely.
Grinkle said:
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.
Grinkle said:
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.
 
  • #35
stoomart said:
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.
 
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  • #36
Comeback City said:
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.
 
  • #37
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.
 
  • #38
IGBY International said:
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:

IGBY International said:
Light circulates within creating a multitude of past "Light" objects that are observed as further and further away. Reflections, duplicates of our past existence.
 
  • #39
lifeonmercury said:
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?
 
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  • #40
IGBY International said:
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.
IGBY International said:
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?
 
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  • #41
Jason R Carrico said:
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.
 
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  • #42
Algr said:
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?
 
  • #43
Sounds like an infinite stack of turtles to me.
 
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  • #44
Grinkle said:
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.
 
  • #45
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.
 
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  • #46
@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.
 
  • #47
@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
 
  • #48
Thanks, but I got a 404 error code.
 
  • #49
No 404 for me, it may have been a temporary server outage.
 
  • #50
Oh well, it just won't open for my phone then I guess. I will try to hunt it down some other way
 
  • #51
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  • #52
Thank you so much. I've got it now
 
  • #53
I am not convinced that I have not got it yet, but it is fun trying,.
 
Last edited:
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  • #54
diogenesNY said:
@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

That article makes it very easy to understand 'universal expansion'
thanks
 
  • #55
in my not-so-humble opinion, if we could see a person looking thru a telescope in our direction, that person could not see us, but how our galaxy looked 13-14 billion years ago. since that person was alive at the 'beginning of the universe' the visible universe may have been that one galaxy. it wouldn't actually be the only galaxy, just the only one to shed enough light to see. light from other galaxies hasn't reached the viewer yet, so darkness in all directions would be seen.
 
  • #56
fencewalker said:
in my not-so-humble opinion, if we could see a person looking thru a telescope in our direction, that person could not see us, but how our galaxy looked 13-14 billion years ago.

Let's replace "person" with "observer", since we commonly use the latter term when discussing how things look in the universe. This observer would be constrained by the time it takes light to travel to their location, yes, but so would we. So this observer would have had to exist 13 billion years ago and would be long, loooong dead. They wouldn't have been able to see us, or rather our area of the universe, because at this time the light from our area of space had not yet had time to reach them.

fencewalker said:
since that person was alive at the 'beginning of the universe' the visible universe may have been that one galaxy. it wouldn't actually be the only galaxy, just the only one to shed enough light to see. light from other galaxies hasn't reached the viewer yet, so darkness in all directions would be seen.

Pretty much. At this time, the visible universe for this observer would have been a very small area of space that contained matter in the early stages of galaxy formation.
 

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