Just before I get my coffee... :D

I've been asking myself where's the edge of the universe.
Are we in the edge of the universe? Are we in the centre? Are we somewhere in between?

If the universe exapands like a circle, is the edge of the circle the past, and the centre the present? Or that is just how we would see it!?!? :eek:

Now, excuse me... I'm going to get that coffee... :D

The universe is finite in size but has no 'edge'. Sounds like a paradox at first but u could travel infinitely far in any direction but never ever come to an 'end' of the universe. It is possible to arrive back where u started though!

The further u look into the depth of the universe the older is the light that reaches your eyes so its like looking through time. This is merely from our vantage point however so whats going on over there now is invisible to us for some time.

The universe is finite in size but has no 'edge'. Sounds like a paradox at first but u could travel infinitely far in any direction but never ever come to an 'end' of the universe. It is possible to arrive back where u started though!
Wouldn't that implie that the universe is actually a sphere? Cause here on earth, the same thing applies... whatever direction you go, you end up in the same place... :eek:

The further u look into the depth of the universe the older is the light that reaches your eyes so its like looking through time. This is merely from our vantage point however so whats going on over there now is invisible to us for some time.
So the present and the past is everywhere...?? :D

One way of thinking about it could be that the Edge of the universe is where our past light cone meets the Big Bang - in other words, the surface of a sphere 26 billion light years across, with Earth at the center.

Singularities in GR spacetime (black holes and the Big Bang) could also be considered to be edges to spacetime.

Actually, since the Edge of the Universe must be a edge of spacetime, rather than an edge of space, then the first paragraph in my previous post is probably the best suggestion - that the Big Bang is the Edge of the Universe.

One way of thinking about it could be that the Edge of the universe is where our past light cone meets the Big Bang - in other words, the surface of a sphere 26 billion light years across, with Earth at the center.


But its not the edge of the universe as u could still travel beyond that light cone (if given sufficient means!). It doesn't mean that nothing exists beyond our light cone. Thats just self-centered :)

Wouldn't that implie that the universe is actually a sphere? Cause here on earth, the same thing applies... whatever direction you go, you end up in the same place... :eek:


So the present and the past is everywhere...?? :D

No, the universe is not like a sphere because a sphere has an edge. It is however like the earths surface as u say. The reason we cannot find an edge to the surface of the earth is because gravity confines us to live on a 2D surface on a 3D sphere. Now we all know that the universe is £D at least to our senes so try to imagine (although impossible to conceptualise) a 3D surface on a 4D sphere. That would be 'a' model structure of the universe.

The galaxies in the Hubble Ultra Deep Field are already effectively beyond the edge of our universe; if we had a spcaceship that could go at light speed or just a bit slower we could set off toward those galaxies and never get there;

don't forget that those galaxies have been travelling away from us for 13.2 billion years as well.
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John Connellan: Pete did not say that the edge of the universe was outside our light cone. He suggested that it is where our past light cone intersects with the big bang. That seems to be a reasonable view. Note that the light cone is a 3D cone, not a 2D cone. A 2D cone is a model that drops one spatial dimension.

Thinking about these concepts is a bit mind boggling because you must think of the 4D continuum.

If the Big Bang model is valid (seems likely), the initial universe can be though of as a point, or at most a very tiny volume. From our current view, that point is the surface of a sphere billions of light years in diameter.

BTW: The following remark in an article about cosmology boggled my mind.. . . researchers can determine the distance CMB photons have traveled before reaching Earth: About 45 billion light years. The photons have traveled for about 14 billion years. The expansion of the universe has elongated their route.The article did not elaborate on the above remark, which was only vaguely related to the main concepts of the article.

From the above, it seems that our personal universe is a sphere centered on us and about 90 billion light years in diameter. Our descendants are not likely to get a view of the current edge of our universe.

Our intuitive notions suggest that time and space are infinite, which might not be a correct view of reality. Many ask what was happening before the Big Bang. Perhaps there is no before. They also ask what is beyond our universe. Perhaps there is no beyond.

It seems reasonable to claim that matter and energy cannot exist without space and time. The converse might also be valid. Can space and time exist without matter and energy? The Big Bang model at least suggests that time started with the Big Bang, and perhaps space started then also.

I believe asking the question "where is the edge of the universe?" is akin to asking "where is the top of this sphere?". It's not really quite right. I don't think the universe really has an "edge" per se.

No, the universe is not like a sphere because a sphere has an edge. It is however like the earths surface as u say. The reason we cannot find an edge to the surface of the earth is because gravity confines us to live on a 2D surface on a 3D sphere. Now we all know that the universe is £D at least to our senes so try to imagine (although impossible to conceptualise) a 3D surface on a 4D sphere. That would be 'a' model structure of the universe.
Yes, sure. I understand that. That' what I wa thinking about when I talked about the earth. My problem is that I can't picture such thing... :D

I believe asking the question "where is the edge of the universe?" is akin to asking "where is the top of this sphere?". It's not really quite right. I don't think the universe really has an "edge" per se.
How can a definite space have no edge? If the universe is expainding, than it has to have and edge, because it is the edge that is expanding in the first place!

How can a definite space have no edge? If the universe is expainding, than it has to have and edge, because it is the edge that is expanding in the first place!

what you're missing is that the expansion is creating space...

what you're missing is that the expansion is creating space...
So... where is the space expanding? What is beyond space? Are you saying there is no "space" beyond our universe? If so, than what exists beyond our universe? It cannot be vacuum, because vacuum needs space. What is it than?

So... where is the space expanding?

LOL. Well see, that's the whole thing then isn't it? You can guess but since it isn't space you can hardly go there eh?

What is beyond space?
I don't know. I would guess "nothing", not even space. That's kind of hard to imagine though. I think to a human "nothing" seems like "empty space" so it's hard to switch up to "not even space". *shrug*

Are you saying there is no "space" beyond our universe?

Not really, but I am saying that it probably isn't "space" as we know it since it wouldn't be the edge of the universe if it were eh? I mean if it were just more space then why wouldn't it be part of the universe?

If so, than what exists beyond our universe?

I don't believe the concept of "existence" as we know it, could really apply to conditions outside of the universe. Perhaps in another universe like ours, but.. hell I don't really know. Just giving you my understanding.

It cannot be vacuum, because vacuum needs space. What is it than?

I dunno. I can only say "not space-time" because it if were, then it would be and then it would be part of the universe so you wouldn't be outside of the universe eh?

I've never seen you not knowing so many things... :D

LOL. Well see, that's the whole thing then isn't it? You can guess but since it isn't space you can hardly go there eh?
:D I presume it may be another "kind" of space... Or maybe another "universe"...

I don't know. I would guess "nothing", not even space. That's kind of hard to imagine though. I think to a human "nothing" seems like "empty space" so it's hard to switch up to "not even space". *shrug*
Can "nothing" exist?

Not really, but I am saying that it probably isn't "space" as we know it since it wouldn't be the edge of the universe if it were eh? I mean if it were just more space then why wouldn't it be part of the universe?
Maybe our universe is inside another universe? Maybe the boundaries of our universe is like the boudaries of a black hole, in another universe?

I don't believe the concept of "existence" as we know it, could really apply to conditions outside of the universe. Perhaps in another universe like ours, but.. hell I don't really know. Just giving you my understanding.
Maybe the truth is out there... :D

I dunno. I can only say "not space-time" because it if were, then it would be and then it would be part of the universe so you wouldn't be outside of the universe eh?
Again, an universe inside another universe...?

I guess we don't know enough to really know where is the edge of the universe? What can be out there?

Maybe the truth is out there sure, but maybe it's literally beyond our comprehension?

I mean that in the most literal sense. Try to imagine a cube in 28384 dimensions and you might know what I'm talking about. It simply doesn't fit in your head.

Maybe the truth is out there sure, but maybe it's literally beyond our comprehension?

I mean that in the most literal sense. Try to imagine a cube in 28384 dimensions and you might know what I'm talking about. It simply doesn't fit in your head.
There was a time when we thought that the earth was plane. We used to think in 2D. Than, there was a time that we found out that it is actually all 3D. Not long time ago, we found out that it is actually 4D. The world around us is still 4D, but the difference is irrelevant. If we talk about the universe, the fourth dimension becomes relevant. As we get farther away from ourselves we encounter things that are harder to understand. That doesn't mean that we will never be able to understand them, it just means that we are not ready to understand them yet. ;)

http://hubblesite.org/newscenter/newsdesk/archive/releases/2004/07/

Furthest images yet of space

AS has been said "The Truth Is Out There" - just because we do not know the answer yet, does not mean its a lie!

Modern inflationary theory imagines that space as a whole is greater than infinite, in the sense that it's always expanding much faster than the speed of light, and so could never be crossed. Our Universe would be a coherent bubble which "froze out" of the chaotic eternal inflation and settled down to a stable, specific dimensionality - and the energy inherent in the vacuum, which would otherwise continue to drive inflation, was transformed into our familiar types of energy and matter.

Still, even that coherent bubble is at least 10 quadrillion times wider than our OBSERVABLE Universe, which started out as a tiny quantum-scale region within it before the last instant of inflation. That's why the background temperature of space is virtually the same wherever we look: regions of different temperature are out there, but far beyond our observable horizon.

Yes, sure. I understand that. That' what I wa thinking about when I talked about the earth. My problem is that I can't picture such thing... :D

Its ok, u don't have to. We, as humans cannot !

Everyone else: Beyond space is nothing as u all say but why are u trying to define nothing? Nothing is nothing. There is no point thinking of what it would be like to be where there is nothing because it is impossible to get there or be there!

Big Bang theory indicates that our universe is larger than the observable part of it. At some distance from us, the recession velocity exceeds the speed of light. That distance defines our observable universe, yet there are galaxies beyond that distance still fleeing from us.

If the current theory about accelerating expansion is valid, our observable universe is getting smaller.

There are those who claim that time and space do not exist in the absence of matter and energy. For those, space and time do not exist beyond the farthest galaxies. They might be correct. The notion of a finite universe seems counterintuitive. On the other hand, singularities and infinities also seem counterintuitive.

BTW: For an observer (if any) in another galaxy, the observable universe is different than ours.

The universe is finite in size but has no 'edge'. Sounds like a paradox at first but u could travel infinitely far in any direction but never ever come to an 'end' of the universe. It is possible to arrive back where u started though!

The further u look into the depth of the universe the older is the light that reaches your eyes so its like looking through time. This is merely from our vantage point however so whats going on over there now is invisible to us for some time.

Sorry,but it doesn't make sense,universe has limits,because its expanding therefore universe has boundaries,it expands like an balloon,and that expanding shows that there is a limit of the universe.

Big Bang theory indicates that our universe is larger than the observable part of it. At some distance from us, the recession velocity exceeds the speed of light. That distance defines our observable universe, yet there are galaxies beyond that distance still fleeing from us.

If the current theory about accelerating expansion is valid, our observable universe is getting smaller.

There are those who claim that time and space do not exist in the absence of matter and energy. For those, space and time do not exist beyond the farthest galaxies. They might be correct. The notion of a finite universe seems counterintuitive. On the other hand, singularities and infinities also seem counterintuitive.

BTW: For an observer (if any) in another galaxy, the observable universe is different than ours.

The only problem is there couldn't be the absence of the energy.There could be the absence of the matter,but not energy.If there was no energy,the whole Big Bang thing and the laws of physics wouldn't occur at all.With the Big bang energy started to transform in matter,as well creating the laws of physics.

How does energy transform into matter? Is it just cooling down so that matter is energy that is less energetic?

Sorry,but it doesn't make sense,universe has limits,because its expanding therefore universe has boundaries,it expands like an balloon,and that expanding shows that there is a limit of the universe.

I didn't say it didn't have limits! U ARE right that it doesn't make sense though.....to u that is, and I warned u by saying it sounds like a paradox at first. When I used the term finite, I meant there are limits to our universe.

Sorry,but it doesn't make sense,universe has limits,because its expanding therefore universe has boundaries,it expands like an balloon,and that expanding shows that there is a limit of the universe.

Hi Gravage,
Here's some things to think about.

Since we can't see the limits, how do we know that the Universe is expanding?
What does "expanding" really mean in this context?
Does it mean "getting bigger? Or something else?
What is actually observed?

I have seen the bold part of the following many times, but it is only valid for certain geometries. The universe is finite in size but has no 'edge'. Sounds like a paradox at first but u could travel infinitely far in any direction but never ever come to an 'end' of the universe. It is possible to arrive back where u started though!I think that the 3D surface of a 4D hyper-sphere has that property. The 2D surface of a 3D sphere obviously has that property. No Euclidean space has that property.

Our 4D space-time continuum does not have that property. It would imply time travel back to an event in the life of the traveler.

In the past, it might have been possible to travel to the edge of the expanding universe. I have no idea how fast the universe was expanding when it was only a few light years or less in diameter. If the Big Bang theory is valid (there is little reason to assume otherwise), it is certainly not possible to do so today. The extreme edge is receding faster than the speed of light relative to us. A traveler starting here on Earth could never catch the edge.

Pondering the situation at the edge of the universe might belong to the realm of philosophy rather than physics.

There is surely a galaxy near or at the edge of our observable universe. Such a galaxy does not seem to be in any peculiar circumstance. An observer in such a galaxy would view our galaxy as being at the edge of his/her observable universe. Of course, our observable universe is much smaller than the entire universe.

Our observable universe seems spherically symmetric in its gross properties. Is there a galaxy whose observable universe is not spherically symmetric? If so, such a galaxy would be much nearer to the edge than we are, implying an observable edge. Would an observer near the edge notice a gravitational force directed away from the edge due to all the matter in that direction?

Might a region near the edge be similar in gravitational properties to regions inside of and near to the Event Horizon of a Black Hole? When Big Bang cosmology allowed the possibility of gravity overcoming the expansion, there was speculation about the possibility that our universe was inside the Event Horizon of a really big Black Hole. Note that inside the Event Horizon of a large Black Hole, the average density need not be high. A process such as the Big Bang expansion inside an Event Horizon could fight the inevitable collapse for a while.

Note that inside a spherical shell, there is no net gravitational force due to the shell. If the matter in the Black Hole were not all concentrated in a singularity, there would be a point in the very center with no net gravitational force. There is no net force at the center of the Earth (pressure would be intense, but no gravitational force). Is some process fought the collapse, there could temporarily be regions with low or zero gravitational force inside the Event Horizon.

The "world" is as big as your imagination and as small as you can see.


Very interesting posts I might add, it kept me from studying my microbiology :). I also viewed the picture from the Hubble and saw such a huge similarity with micros I viewed in class...

How does energy transform into matter? Is it just cooling down so that matter is energy that is less energetic?

No,it's not energetic,it's simply less usable...

Its quite usable in nuclear power plants :)

I suppose matter/antimatter annihilation would be the most efficient way of converting mass to energy. Problem is, getting hold of any significant quantity of antimatter...

Yes that is actually 100% efficient isn't it?! Still, nuclear power generation is very efficient too.

There is no "100%". I learnt that in Statistics... :D