Reach the End of Universe: Is There a Wall?

[david90]

If u reach the end of the universe, do u think there's a wall? All thing must have an end right?

 

[Chronos]

Not at all. Even if the universe is finite, it wraps around on itself like a donut. Everywhere it always appears just the same as anywhere else.

 

[A_I_]

you can answer yourself, just imagine the following situation:

Suppose you are at what u were calling "the edge of the Universe"
isn't there anything beyond?

 

[moving finger]

If u reach the end of the universe, do u think there's a wall? All thing must have an end right?

You are assuming the universe is finite and flat. This is what some early humans may have thought when considering the flat Earth :

If u reach the end of the earth, do u think there's a wall? All thing must have an end right? (it's another version of Chronos' answer)

 

[RoboSapien]

Even if there was a wall, what did U think was it made up of.

In a way I believe there is a wall, its made of space. It goes farther as you try to touch it. but I also believe that it is going farther at speed of light as the first light from the big bang must be still going farther.

Chronos
{
But if universe is as U say it is then we should be able to see echos of big bang, shouldn't we ?
}
This is my view only , please don't delete it.

 

[Garth]

Chronos
{
But if universe is as U say it is then we should be able to see echos of big bang, shouldn't we ?
}

That depends on how large the circumference was.
Looking for "echos of big bang", actually 'circles in the sky', is one way of constraining cosmological theory that is an active area of research.


Garth

 

[moose]

One way to think of it is as one of those old mario games, or pacman, when you get to the side, and go through, you just end up on the other side...

 

[meteor]

actually is believed that the Universe is flat, that is has a curvature k=0, but it doesn't constraint the topology to one possibility, a flat universe can have different topologies (infinite, an hypertorus,...) A topology of an hypertorus means that the universe is finite, but this doesn't mean that the universe has a "wall" indicating its ending. Similarly, if the universe is not flat (there are two other possibilities: that is spherical or that is hyperbolic), each of these two possibilities admits more than one topology

 

[ray b]

past the edge is the
NOT YET

but as the edge is moving at light speed or faster with inflatesion/expansion

BUT YOU CAN'T GET THERE FROM HERE

so why worry

 

[Chronos]

Even if there was a wall, what did U think was it made up of.

In a way I believe there is a wall, its made of space. It goes farther as you try to touch it. but I also believe that it is going farther at speed of light as the first light from the big bang must be still going farther.

Chronos
{
But if universe is as U say it is then we should be able to see echos of big bang, shouldn't we ?
}
This is my view only , please don't delete it.

I won't delete it, I can't, and I would not if I could. My interest is in asking you to think again. Let's talk about the evidence and what it might mean.

 

[Phobos]

If u reach the end of the earth, do u think there's a wall? All thing must have an end right? (it's another version of Chronos' answer)

Good analogy. People may envision an end of the Earth (like how ancient sailors were afraid of sailing off the end of the Earth) when they put themselves at the center (the beginning point). But those ancient sailors were not at the beginning point of the Earth's surface...they were just at some point on the surface. Like that, the universe has no beginning or end in ordinary 3D space. It may curve back on itself like a globe or it may be infinite in extent. We must be careful not to apply the geocentric view to our place in the universe.

 

[Rev Prez]

Good analogy. People may envision an end of the Earth (like how ancient sailors were afraid of sailing off the end of the Earth) when they put themselves at the center (the beginning point). But those ancient sailors were not at the beginning point of the Earth's surface...they were just at some point on the surface. Like that, the universe has no beginning or end in ordinary 3D space. It may curve back on itself like a globe or it may be infinite in extent. We must be careful not to apply the geocentric view to our place in the universe.

The analogy still needs one more refinement to address intuition that a manifold need be embedded in higher dimensional space. And unfortunately I can't think of a way to do that without resorting to Flatland examples.

 

[RoboSapien]

I won't delete it, I can't, and I would not if I could. My interest is in asking you to think again. Let's talk about the evidence and what it might mean.

Ok , but U did not mention any observable evidence in this CASE ? did I miss something ?

What do U wana me 2 thinkbout ?

 

[david90]

Good analogy. People may envision an end of the Earth (like how ancient sailors were afraid of sailing off the end of the Earth) when they put themselves at the center (the beginning point). But those ancient sailors were not at the beginning point of the Earth's surface...they were just at some point on the surface. Like that, the universe has no beginning or end in ordinary 3D space. It may curve back on itself like a globe or it may be infinite in extent. We must be careful not to apply the geocentric view to our place in the universe.

I had this dream a while ago where I was zooming thru the univerise and reached its end. The wall was solid and black and I touched it with my hand.

Isn't the Earth's ground the "end" of the earth?

 

[oldunion]

There is something deceptively incorrect about a universe being finite or progressing incessently into the unknown. However, it is what we call home now that is the infinite* universe.

The tangible universe is the reflection of our intellect. It will expand or contract according to our subconscious whims. it is whatever or wherever we believe it to be.

The infinite universe is thought, the center of anyone's universe is their mind-expanding anywhere.

 

[Phobos]

Isn't the Earth's ground the "end" of the earth?

This is the "flatland" problem that Rev Prez mentioned.

As an analogy, traveling the surface of the Earth falls short of visualizing curved space. This is because you need to limit your reality to just the 2D surface of the Earth (there is no up/down...no "ground"). But of course our common sense knows the Earth is 3D and we immediately visualize the 2D surface curving into 3D space.

For curved 3D space, you may be tempted to visualize a 4th dimension of space that it curves into, but we know of no such dimension. (we do however, have the 4th dimension of time to work with)

 

[X-43D]

That's a very good question: They teach us that space and time began with the big bang (before that there was no space and time) and that space itself is expanding (the distance between the galaxies). If so, what is outside this space-time?

This is how the universe evolved according to the standard big bang model:

http://www.nasa.gov/images/content/56200main_dark_expansion-lg.jpg

 

[Chronos]

There is no 'outside', at least not any possible to observe.

 

[Scinan Heorte]

The answer is simple... no, there is no wall.
You will fall off the edge, and land upon the back of the great turtle whose strength supports the pillars upon which the cosmos is held in balance.

 

[Phobos]

You will fall off the edge, and land upon the back of the great turtle whose strength supports the pillars upon which the cosmos is held in balance.

Funny, but probably not helpful for david90.

 

[Mike2]

Funny, but probably not helpful for david90.

Is there an entropy associated with the cosmological event horizon just as there is for a black hole event horizon? Does the entropy of the cosmological event horizon constrain the information/entropy inside it just as with a BH? What then are the consequences of an accelerating universe in which the cosmological event horizon is getting smaller? Would this cause a corresponding decrease in entropy inside the cosmo event horizon? I find it interesting that life on Earth seems to have appeared at about the same time that the universe started accelerating about 4-5 billion years ago.

 

[RoboSapien]

... Does the entropy of the cosmological event horizon constrain the information/entropy inside it just as with a BH? ...

U mean the wall is the even horizon ?

 

[Mike2]

U mean the wall is the even horizon ?

Not a physical barrier, but the situation is similar to a BH event horizon. Objects that approach either horizon redshifts and freezes as it approaches it. So for the same reasons I suppose that an entropy must be associated with the cosmological event horizon as it does for a black hole event horizon - entropy of the universe would decrease if material with entropy disappeared behind it. If so, then the question becomes how does this restrict the entropy within the cosmological event horizon. And if it is restricted, then the question is how does a shrinking cosmological event horizon effect events inside.

 

[RoboSapien]

... Objects that approach either horizon redshifts and freezes as it approaches it. So for the same reasons I suppose that an entropy must be associated with the cosmological event horizon as it does for a black hole event horizon ...

So is the universe shrinking or expanding ?

 

[misskitty]

I think most physicists would agree the universe is expanding in one way or another. Although I could be wrong.

 

[misskitty]

The answer is simple... no, there is no wall.
You will fall off the edge, and land upon the back of the great turtle whose strength supports the pillars upon which the cosmos is held in balance.

Interesting you should mention this. My sister, who is well versed in Asian culture and customs and history, was telling me about this one day. Does anyone know how this theory was started?

 

[misskitty]

Edit: I forgot to ask: how do we know there is no wall if we don't know where the end of the universe is? I agree there probably is no wall, but how do we know it doesn't expand with the universe?

 

[selfAdjoint]

Edit: I forgot to ask: how do we know there is no wall if we don't know where the end of the universe is? I agree there probably is no wall, but how do we know it doesn't expand with the universe?

On the "Strings, Branes, and LQG" forum we are discussing a couple of papers that suggest our observable universe is in the interior of a huge bubble, the expanded result of some fluctuation when the whole universe was small, and that is why we have a nearly flat universe (omega ~ 1), but our mass and dark matter together only come up to an omega of 0.27. The missing .73 has been attributed to "dark energy", but these papers suggest that in the bubble interior, our matter is depleted, only 27% of what it is on the average in the whole universe, so both the omega ~ 1 and our 27% are explained as a special case without positing any dark energy.

So in this picture there would be an expanding "wall", the surface of the bubble, but what it would separate us form is just the rest of the universe.

 

[Mike2]

So is the universe shrinking or expanding ?

If space expands, then the accumulative effect is that the farther away you get, the faster space is receding away from you. At some distance, then, space will be receding so fast that we will never see photos emitted by galaxies from that distance; this is called the cosmological event horizon.

OK, if that be true, then if space is accelerating in its expansion, then the distance at which objects recede so fast that we will never see them again, the cosmological event horizon, will get even closer to us than if there was no acceleration. Thus accelerated expansion causes a shrinking of the cosmological event horizon. This is not a physical barrier; it's an observational barrier. Every galaxy has a different cosmologial event horizon with the center at that galaxy.

All right, so consider my previous argument:
If the cosmological event horizon has entropy associated with it since otherwise the entropy of the universe would decrease as objects with entropy disappeared behind it, then what does it mean that the cosmological event horizon is shrinking so that its entropy is decreasing?

 

[RoboSapien]

Imagine this : if everything is shrinking then its obvious that the residents will think that the universe is expanding.

 

[misskitty]

On the "Strings, Branes, and LQG" forum we are discussing a couple of papers that suggest our observable universe is in the interior of a huge bubble, the expanded result of some fluctuation when the whole universe was small, and that is why we have a nearly flat universe (omega ~ 1), but our mass and dark matter together only come up to an omega of 0.27. The missing .73 has been attributed to "dark energy", but these papers suggest that in the bubble interior, our matter is depleted, only 27% of what it is on the average in the whole universe, so both the omega ~ 1 and our 27% are explained as a special case without positing any dark energy.

So in this picture there would be an expanding "wall", the surface of the bubble, but what it would separate us form is just the rest of the universe.

Interior of a bubble huh? Ok, I can see that (kinda have to when it comes to physics and the universe ). Where did the bubble theory come from. My computer is very tempramental when it comes to links. So I didn't ge to see the papers you were talking about.

Not to be a pain or anything, but could someone please explain the Dark Matter concept? Someone, I don't remember who, tried to explain it, but unfortunatly I didn't comprehend it as well as I previously though. Sorry.