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The border of the universe?

Akoto said:
If gravity could be strong enough to overcome expansion and maintain our supercluster, why not hold superclusters together?

Wouldnt there ever be a point where every particle is equaly spaced apart and unable to interact with eachother?
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(See: Quantum Mechanics)
 
^^^


yeh, i don't think its expanding fast enough for humans to observe such an event as to be completely isolated from the universe. also, from what i understand, gravity comes at us at a very different "angle" than other forces that we know of. ( like say magnatism is coming from behind and ahead (2D, gravity is coming in 3D?) ofcourse i don't mean literally 2 or 3 deminsions.

can somebody explain that better, sorry.
 
mr_p, you shouldn't call it a cell, the higher reality would not be able to interact with this one or they'd be the same reality. I call it a pixel, but it would be the smallest possible amount of light. For our reality that is.
 
you think its possible that the universe is like a bubble, next to a bunch of other bubbles pushing on each other. they force eachother into very small spaces. when the tension is great enough, from all the bubbles pushing one together the bubble starts expanding back on the other bubbles.

i dont really know how to expand it better
 
gugglebum said:
We have all heard the theory that the universe is expanding - which has always made me think: Expanding into what?

If the universe is supposedly all there is, how could it be expanding? Something without a border can't really expand, can it?

Also, if it's expanding, into what is it expanding? There must be something on the other side into which the universe is expanding.

Sorry I know this isn't very scientific and probably very misinformed but I've always wondered what the latest research and theories on this are? Anyone care to enlighten me? In layman's terms if possible, I'm not much of a scientist!
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The confusion comes from two different definitions of the word 'expanding.'

Usually when you think of something 'expanding,' you think of looking at something and seeing it growing larger. Obviously this definition only works for finite objects which you can imagine being 'outside' of. By definition you can't be outside the universe, and it may not even be finite.

The proper way to define 'expanding' here is to mean that distances between things are getting bigger. This is what scientists mean when we say the universe is expanding. Pick any two galaxies, and they're moving further apart. And the greater the distance between them now, the faster they're moving apart. It's sort of like the picture below:

cphotons.gif


You can see how this picture could extend forever.


akoto said:
If gravity could be strong enough to overcome expansion and maintain our supercluster, why not hold superclusters together?
Click to expand...
Excellent question! There's a short answer and a long answer. The short answer is: Because gravity is stronger at smaller distances. Imagine a universe filled with clumps of matter flying apart; whether or not the universe sticks together depends on how far apart the clumps are. But whether or not each clump stays in one piece just depends on its size & mass. So make each clump small enough and it'll hold itself together, but spread the clumps out far enough apart, and their mutual attraction is too weak to hold them together.

The long answer: Well, if you start with a perfectly homogenous expanding universe -- that is, a universe which is exactly the same everywhere, kind of a uniform fluid or plasma -- then yes, in fact, either everything will stick together, or everything will get pulled apart. The only way you can get things like clusters which individually hold together but separate from each other is if you have some kind of unevenness. I mean, some kind of perturbation which makes this part of universe slightly more dense than that part of the universe. Our universe had such tiny, tiny perturbations within the first fraction of a second after the Big Bang.

If you use Einstein's theory of gravity (general relativity, a.k.a. GR) to figure out what would happen to such a perturbation, you find the following: For a given environment (the density of the universe, the speed of sound in it, its rate of expansion, etc) there is a length called the Jeans length. If a region smaller than the Jeans length is slightly more dense than its surroundings, it will undergo a chain reaction: since it has more mass than the surrounding part of the universe, its gravitational pull is slightly stronger. Since its gravitational pull is stronger, it pulls more mass towards it, making it even more dense and its mass even greater, thus increasing its gravitiational pull even more.... You get the idea. This process is what causes the collapse of matter into things like clusters, galaxies, stars, and planets.

However, if a region bigger than the Jeans length becomes slightly-more-dense than its surroundings, nothing happens -- the expansion (and pressure) of the universe is too large and overpowers the slightly bigger gravitiational pull of the region, smoothing things out. So there's a maximum size of the bodies that collapse -- no objects bigger than the Jeans mass can form in a perpetually-expanding universe. That's why all superclusters are destined to pull apart forever (or at least as long as the universe continues expanding).
 
doesntmatter said:
yeh, i don't think its expanding fast enough for humans to observe such an event as to be completely isolated from the universe. also, from what i understand, gravity comes at us at a very different "angle" than other forces that we know of. ( like say magnatism is coming from behind and ahead (2D, gravity is coming in 3D?) ofcourse i don't mean literally 2 or 3 deminsions.

can somebody explain that better, sorry.
Click to expand...
I'd try and explain it better, but I've no idea what you're referring to :o
 
Excellent question! There's a short answer and a long answer. The short answer is: Because gravity is stronger at smaller distances. Imagine a universe filled with clumps of matter flying apart; whether or not the universe sticks together depends on how far apart the clumps are. But whether or not each clump stays in one piece just depends on its size & mass. So make each clump small enough and it'll hold itself together, but spread the clumps out far enough apart, and their mutual attraction is too weak to hold them together.

The long answer: Well, if you start with a perfectly homogenous expanding universe -- that is, a universe which is exactly the same everywhere, kind of a uniform fluid or plasma -- then yes, in fact, either everything will stick together, or everything will get pulled apart. The only way you can get things like clusters which individually hold together but separate from each other is if you have some kind of unevenness. I mean, some kind of perturbation which makes this part of universe slightly more dense than that part of the universe. Our universe had such tiny, tiny perturbations within the first fraction of a second after the Big Bang.

If you use Einstein's theory of gravity (general relativity, a.k.a. GR) to figure out what would happen to such a perturbation, you find the following: For a given environment (the density of the universe, the speed of sound in it, its rate of expansion, etc) there is a length called the Jeans length. If a region smaller than the Jeans length is slightly more dense than its surroundings, it will undergo a chain reaction: since it has more mass than the surrounding part of the universe, its gravitational pull is slightly stronger. Since its gravitational pull is stronger, it pulls more mass towards it, making it even more dense and its mass even greater, thus increasing its gravitiational pull even more.... You get the idea. This process is what causes the collapse of matter into things like clusters, galaxies, stars, and planets.

However, if a region bigger than the Jeans length becomes slightly-more-dense than its surroundings, nothing happens -- the expansion (and pressure) of the universe is too large and overpowers the slightly bigger gravitiational pull of the region, smoothing things out. So there's a maximum size of the bodies that collapse -- no objects bigger than the Jeans mass can form in a perpetually-expanding universe. That's why all superclusters are destined to pull apart forever (or at least as long as the universe continues expanding).
Click to expand...

Thanks, I think I get it. But if you take a star for example which explodes, is'nt it more likely that one or more particles get thrown outside Jeans length, thus producing an overal entropic Universe?

Like wouldnt thoes perturbations keep getting magnifyed due to random collisions and instability, eventualy (and thats a very long eventualy) resulting in every clump of matter being broken up untill there is'nt anything left to break?

I remember learning something about the heat death of Universe that states that all reactions are inherantly entropic and will eventualy creat useless heat. Is that related?
 
Akoto said:
Thanks, I think I get it. But if you take a star for example which explodes, is'nt it more likely that one or more particles get thrown outside Jeans length, thus producing an overal entropic Universe?

Like wouldnt thoes perturbations keep getting magnifyed due to random collisions and instability, eventualy (and thats a very long eventualy) resulting in every clump of matter being broken up untill there is'nt anything left to break?

I remember learning something about the heat death of Universe that states that all reactions are inherantly entropic and will eventualy creat useless heat. Is that related?
Click to expand...
Well, above I was talking about the initial formation of structure in the universe. The question of what will happen to it eventually is a different one.

Basically, yes, assuming continued expansion, eventually particles should get broken apart. Mostly -- protons will never break up into quarks, for example, though they may decay into other types of particles. This is on an extremely long timescale, though.... for all practical purposes, cold, dark lumps of matter (like brown dwarfs, neutron stars, etc) can stick around nearly forever.
 
AlphaNumeric said:
I'd try and explain it better, but I've no idea what you're referring to :o
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well say that gravity moves in a different way. like not necessarily bound by what we can see and touch..etc.

from what i understand gravity can move throughout the universe freely. like from outside of the 3 demensions that we can see and the "demension" of time which hold all of the stars and planets and such. it takes an effect on things differently that say electromagnestism, which is seems to be more confined to our demension.

like i said i'm not really familiar, it was a long time ago that i saw something related to string theory that showed what we can see of the force that is gravity as being able to flow through all of the "slices of the loaf" as NOVA put it.
 
doesntmatter said:
well say that gravity moves in a different way. like not necessarily bound by what we can see and touch..etc.

from what i understand gravity can move throughout the universe freely. like from outside of the 3 demensions that we can see and the "demension" of time which hold all of the stars and planets and such. it takes an effect on things differently that say electromagnestism, which is seems to be more confined to our demension.

like i said i'm not really familiar, it was a long time ago that i saw something related to string theory that showed what we can see of the force that is gravity as being able to flow through all of the "slices of the loaf" as NOVA put it.
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You're thinking of 'brane-world' models of gravity. These postulate that the universe as we know it is actually just a small 3-d 'slice' inside a higher-dimensional space. Much like a drawing on a sheet of paper is a 2-d image confined to a thin, virtually 2-d piece of paper inside a 3-d world. In brane-world models, the electromagnetic and strong and weak nuclear forces are confined to our thin 3-d brane, just as ordinary matter is; but gravity can escape the brane and propagate throughout all dimension of space. This is meant to explain, among other things, why gravity is so, so, SO much weaker than other forces.

But brane-world models are currently just a guess. Like string theory, there's no hard evidence yet that the brane-world idea is correct. It's an interesting and clever guess, yes, but right now we have no idea whether or not it's true.
 
if you think about animals, each animal or "being" can only understand so much. like:
a dog understands that cars make people go away and come back
fish understand that people outside the tank feed them
but..
a dog cant understnad how an engine works
and a fish cant understand that its food was bought in a store
THEY JUST CANT
and nothing will ever ever ever ever change that.
i mean a dog could stare at an engine all day, watch you take it apart and put it back together, but it will not effect its understanding of anything.
the bottom line is no matter how smart we get, or how much we learn, there is going to be a point where seeing somthing is not enough to understand it. fish see water all day, animals breath air all day but they still dont know those things exist.
the question is: what are you not seeing that is in front of your face all day long?

to put a non-scientific, uninformed, terrible spelling, spin on this :)
 
and nothing will ever ever ever ever change that.
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and what about evolution?
humans haven't either always been able to understand how an engine works
we don't know what dogs (nor humans) will be able to do in a few thousand years
 
complexPHILOSOPHY said:
http://en.wikipedia.org/wiki/Gravity

I am just going to post this reference so we have a common definition of gravity to go off of because you are losing me, doesntmatter.

Using this reference can you still postulate your question or does the reference contradict your conceptualization?

If it doesn't contradict it, could you try to explain it better using this reference?
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i haven't checked back on this thread in awhile, but zorn described it as well as and better than i know it.

i was kinda just getting at the "everything will eventually pull apart" subject and what different theories or guesses have to say about it.

i'd love to see a "string theory for dummies" thread brought up by the more knowledgable of us to talk about the many branches it has and feasable directions it could go regarding things we know now to be true (not just talking about the theory itself, but the impact of the different directions its going would have on science.)

that was off topic.. sorry.
 
If something on the 'edge' of the universe is expanding away from us at the speed of light, and the image is always coming at us at the speed of light, wouldnt anything we're observing always stay the same looking?

Also, what are some theory's as to what started the expansion aka the two green dots to explode?
 
^^^ Hi,

Well, there isn't any 'edge' to the universe as a whole. But for things at the edge of the visible part of the universe, you're correct. The closer something is to the visible edge, the slower it will seem to change to us. Something exactly at the visible edge wouldn't change at all; it would seem frozen in time. (Of course we couldn't actually see such an object, because the light from it would be so weak.)

There's no real idea as to what caused the Big Bang. There's some vague speculation -- for example, in the theory of chaotic inflation, there is a much much larger universe which is mostly unstable, so that tiny quantum fluctuations can cause little pieces of it to blow up into universes of there own. But no one has any idea whether any of this speculation is true or not.
 
vegan said:
and what about evolution?
humans haven't either always been able to understand how an engine works
we don't know what dogs (nor humans) will be able to do in a few thousand years
Click to expand...
well maybe I should have said it another way. I just mean that the way things stand at this time. its impossible. just the fact that the universe "seems" endless to us now tells me that the answers to these questions are beyond human comprehension.
would a grasshopper not describe earth as endless?
I dont even claim to know that im right, because i think the human mind cant grasp the universe in full anyway.
it just bothers me when people say they know the unknown.
you dont know if the universe is endless cause you havent seen all of it.
and i dont know if god exists because i have not met him.
and pls dont make fun of my spelling as an attempt to make me seem stupid. this is just my opinion
 
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^^^

i agree with you to a certain point.

you're saying that we if we can't see the entire universe that we can't judge it as a whole. that makes sense but as vegan said, we may someday have the ability to do so, and would then know whether or not the universe is infact infinite.

i see the point you were trying to make though.

say we find start to be able to see smaller and smaller objects through technology. what point can we get to that we say "this is the basic material, there is nothing making this up." its kinda the opposite of trying to understand the "very big", but its still the same point. just because we could eventually see the whole universe, would that then mean that we actually have seen "the whole thing." what if we only thought we were seeing it all and thus quit trying. where do you draw the line?
 
To address some of the original questions:

If the universe is supposedly all there is, how could it be expanding? Something without a border can't really expand, can it?
Click to expand...

Why can't it? Who says it can't get bigger then it allready is? I understand the whole mind fuck is that it can get bigger and yet remain the same size at the same time. I think the reason why we dont get it is because we have nothing to compare to. Everything we know has a beginning, an end, or a set size. I dont think infinity should even be considered a size.

Infinity is not something that you can count up to or reach. Its not like the universe grew to an infinite size. Size no longer matters when compared to infinity. You can say that solar systems when compared to planets are larger in size, but what happens when you compare each to something of infinite size? Is one still bigger then the other? Why is it?

Think about it. Take the number 1 and the number 1,000,000. How much do you need to add to 1 to get infinity? How much do you need to add to 1,000,000 to get to infinity? Isn't it the same value that you need to add to each? Doesn't this mean that anything when compared to infinity is really the same size?

Its a mind fucker but I think that just because it doesn't make sense doesn't mean that its impossible for infinity to get bigger or smaller as its past the point of actually being a set size. Its just makes us retarded to try to imagine it.

Also, there is a theory that states that universe is actually finite but boundless. Meaning it doesn't actually have an edge that you can cross but it's still a finite size. The way it works is that no matter which direction you travel into you eventually wind up back where you started so long as you keep your heading in a straight line. There are video games like this. Where you get to one side of the map and automatically pop out the other side so you can never actually determine where the edge is. Seems whacky but supposedly there is evidence to support this and if you think about it, no matter how retarded it may seem for the universe to be floating around in a bunch of nothing its certainly a possibility. I mean what do we know? Right?

Also, if it's expanding, into what is it expanding? There must be something on the other side into which the universe is expanding.
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Why must there be something? Because that is what makes sense? Why can't it be something which doesn't make sense according to what we see? You gotta figure that if our laws of physics or pretty everything we know no longer apply on a sub-atomic level, why should they apply once you reach supra-cosmic level. Why can't it just be a whole bunch of nothing out there? I know its hard to think about it .. but is it impossible? Certainly not.. I mean, how could we know?
 
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