When light arrives at the end of space, what happens?

[Jinsuk Kim]

Mr, Drakkith,
You said that "We don't know. It is an open problem in cosmology."
I respect you. This word is not a joke. Really.
I would like to express my respect to all participants in this post. Especially, if he seems to be good.
But the others who answered me also think like you?
I remember that many persons answered me the (present) universe is infinite.
First, I can't agree with you.
Let's wait the others' replies about question No.26.

 

[stefan r]

You said that "There's nothing different between 1 minute and 1 million years except for scale. If the universe is currently infinite in size, then it was also infinite 1 minute after the big bang, 1 year after the big bang, or a million years after the big bang."
I agree with you and that is the reason why I say "1 minute".
Then can you answer me about the question "1 minute after big bang, its size is finite or infinite?"

Right now, without using anyone else's data prove that the surface of Earth is spherical and finite. It is not as simple as some people make it out to be. Eratosthenes was the first person we know of who measured Earth's circumference. He needed measurements at 2 locations that were separated by 900 km. Of course you could get in an airplane and fly around the world but that only works because we have the ability to fly that distance.

I can measure my back yard. Based on those measurements I can easily prove that Earth's circumference must be much larger than my back yard. The overall shape of Earth is not clear. I can use a bubble level to show that it is fairly flat. I can use plum lines to show gravity is basically going in one direction. Those measurements would not indicate much useful information about Earth's overall shape. The sphere is large enough that the plumb lines look nearly parallel. The deviation from parallel is much less than the width of the string.

Receiving data from an alien civilization located a few billion light years away could clarify some cosmology issues. If that data stream exists we have not found it yet. We might get some constraints by watching distant galaxies drop over the event horizon over the next few million years. Astronomy only has measurements taken from one solar system and distant galaxies have only been observed for a few decades.

 

[davenn]

First, I can't agree with you.

Well that is your problem, not ours ... you have been given very good answers based on today's knowledge of cosmology

Let's wait the others' replies about question No.26.

I seriously doubt that you will get anything different to what you have already been told

If you cannot accept it, then go and do some serious study and you will see that what you have been told here aligns with current theories of cosmology

 

[phinds]

First, I can't agree with you.
Let's wait the others' replies about question No.26.

@Jinsuk Kim I find this very odd. You have joined a forum on science where people know what they are talking about, for the purpose of finding the answers to some questions. You have been given answers which are correct to the extent that science currently knows the answers. THEN you decide that the people on the forum do NOT know what they are talking about because you don't like the answers and you decide to ignore the repeated and consistent answers that you have been given. Very odd.

 

[Klystron]

...I highly recommend looking into some basics about topology if you want to understand this material. Thing will make MUCH more sense then.

I also recommend Steven Weinberg's excellent book "The First Three Minutes". Prof. Weinberg presents a detailed perspective on current theory -- last time I read this book was revision 6 including data and observations since original publication.

 

[phinds]

@Jinsuk Kim I also recommend the link in my signature

 

[diogenesNY]

@Jinsuk Kim , why not have a look at the following paper:

http://www.mso.anu.edu.au/~charley/papers/LineweaverDavisSciAm.pdf

This is a very readable and lucid paper by Charles Lineweaver and Tamara Davis that was published as an article in Scientific American in 2005. Your question(s) are fairly answerable in terms of what we understand about the universe (more or less) but sometimes the explaining gets a bit confusing.

This article should shed a bit of light on your inquiries, and answer a bunch more questions that I suspect you may have (or soon will).

Highly recommended, and highly credible.

diogenesNY

 

[Jinsuk Kim]

It has not been discussed at all about “What happens to the light that arrives at the end of space?” I raised this question to feel and understand about the concept and meaning of space. This cannot be discussed because most people answered “infinite.” So I will not touch on this question anymore.

I am not an expert in astrophysics but I am not unfamiliar in the big bang theory. In this post, it seems that “the size of the univere is infinite” is the mainstream. “finite” seems to be the non-mainstream. But at No.24 Mr. russ_watters said “It is not necessarily true that the universe is infinite”. I suppose he is an expert. I know that “finite” is not non-mainstream. Then why many people insist “infinite”?

My final question in this post is why the theories that insist “the size of the universe is infinite” has been established?

1. Because the newly observed results suggest it.

2. There is no observed result suggesting it. But because theoretically it is correct.

Will you answer me? If you don’t mind, please explain it easily and simply, not in detail.

 

[Andrea Panza]

Hi Jinsuk,
I am afraid that we cannot really answer to your question "What happens to the light that arrives at the end of space", because it is made with the incorrect assumption that the universe has a boundary (an edge of some sort), but our current understanding suggests that the universe has no edges.
If we compare your light beam with an ant walking on the surface of a sphere the ant can go on and move forever, even if the sphere is not infinite.
And the universe does not need to be a sphere or a an hypersphere, it is enough that the universe has some kind of closed geometry so that it loops back on itself (with looping back I mean that if you proceed in a straight line for long enough you will find yourself at the starting point).
If the universe does not loop back it is probably infinite so, again the light will not reach the edge because there is no edge, as there is no upper bound the the series of integers, your light beam will go on and on across the space and the space will be always filled with stars and galaxies as all the universe as we know it started with the big bang and the big bang happened everywhere at the same time.
Since the light speed has a finite value and the universe is expanding at a certain point the light will reach the limit of the observable universe with respect of the initial starting position: this means that we cannot see what is beyond a given distance from us because the space is expanding and the distance every second increases more than the distance the light can travel in a given second (it is like trying to run up on an escalator that is going in the opposite direction with a speed faster than your running speed). Please note that this horizon, this limit of the observable universe (the point where the 'escalator'-space expansion becomes faster than light) is not an hard edge, but is just an observer dependent phenomenon, every point in the universe has an horizon and two places even just few millimeters apart on the surface of Earth will have very similar but slightly different horizons.
So as per our understanding there is no real edge in the universe.
I hope it helps,
regards.

 

[phinds]

It has not been discussed at all about “What happens to the light that arrives at the end of space?” I raised this question to feel and understand about the concept and meaning of space. This cannot be discussed because most people answered “infinite.” So I will not touch on this question anymore.

You continue to refuse to listen to what you are being told. It is NOT true that your question is meaningless because space may be infinite or not. It is meaningless because there is no "end" to space whether or it is infinite or not, as you have been told repeatedly

 

[phinds]

My final question in this post is why the theories that insist “the size of the universe is infinite” has been established?

AGAIN, you continue to not listen to what you are being told. It is NOT established that the universe is infinite. That seems to be most likely with our current understanding but it is NOT established fact, and you have been told that repeatedly.

 

[Andrea Panza]

My final question in this post is why the theories that insist “the size of the universe is infinite” has been established

As others already pointed out, is not that easy to determine if something is infinite for real or just way bigger than the detection limit of your tools:

If I draw some circles on a piece of paper and I ask you to calculate the curvature (or at least find the approximate center) the task is not difficult if the size of the circles is smaller than the dimensions of the piece of paper. It is still doable even if the circle is bigger than the piece of paper (so you can only see a portion of the circle), if the curvature is marked enough, but will you be able to find the center of the circle if what I give you looks exactly as a straight line?

The current scientific observations suggest that the universe is either finite but way bigger than what we can observe or really infinite.

I might add that the universe is not only defined by the 3 spatial dimensions but there is also a time dimension and at least for what I understand the flow of time is already considered to be infinite in the direction of the future (in the sense that the universe will slowly cool and things will spread and decay, but it does not look like that there will be a 'final second' before everything shuts down).

I hope it helps

 

[CWatters]

Perhaps the OP should google "what is the universe expanding into".

If the universe was one dimensional everything would be "on one line", the concept of something being "off the line" would be meaningless.

If the universe was two dimensional everything would be "on one plane", the concept is something being "off the plane" would be meaningless.

If the universe was three dimensional everything would be "in a volume". The concept of something being " outside that volume" would be meaningless.

 

[Jinsuk Kim]

As others already pointed out, is not that easy to determine if something is infinite for real or just way bigger than the detection limit of your tools:

If I draw some circles on a piece of paper and I ask you to calculate the curvature (or at least find the approximate center) the task is not difficult if the size of the circles is smaller than the dimensions of the piece of paper. It is still doable even if the circle is bigger than the piece of paper (so you can only see a portion of the circle), if the curvature is marked enough, but will you be able to find the center of the circle if what I give you looks exactly as a straight line?

The current scientific observations suggest that the universe is either finite but way bigger than what we can observe or really infinite.

I might add that the universe is not only defined by the 3 spatial dimensions but there is also a time dimension and at least for what I understand the flow of time is already considered to be infinite in the direction of the future (in the sense that the universe will slowly cool and things will spread and decay, but it does not look like that there will be a 'final second' before everything shuts down).

I hope it helps

Thank you for your kindness. You are very gentle. I will read your comments once again.

 

[PeterDonis]

There is no "end of space", so the question being asked in this thread is based on a misconception. Either the universe is spatially infinite, or it is spatially finite without a boundary (a hypersphere). Either way there is no "end of space".

Thread closed.