The Universe Is Expanding...
 

Ok I've read many things stating that the size of the Universe is in fact expanding. This concept has has generated a few problems for me to grasp.

First if we start out stating that the Universe is all that exists (including space) how could this increase or decrease in size? I understand that we can sa ythe matter is getting spread out further from a conceptual center (being the point of the big bang in theory).

Now since Space itself is the complete lack of matter, it seems to me that having this included in a definition of the universe makes it impossible for it to expeand or retract, but rather just items in it to move within it's boundries (which are by definition limitless). Thus wouldn't the so called Universe always be the same size and the real issue just be matter moving within it?

Also could we make the arguement that infinity exists in the lack of existence of things in space. Since there is no limit to the amount of nothingness that would be in the Universe? (though I think I've read somewhere about a natural curve to the Universe, which would mean it has boundries, and thus something (even if that something is "Nothing") must exist outside it.

If I haven't confused you yet, as i'm sure i've had difficulty explaining what I mean, please give me your thoughts on the subject.

There's your main problem. Space is not by definition limitless.


The image which is most often used to imagine the expanding universe is a balloon being inflated. The surface (and only the surface) is used to represent space (the ballons surface is only two dimensional, where as space is really three dimensional).
When the balloon is only slightly inflated a line drawn around its 'equator' is quite a short distance. As you inflate the baloon, any two points on the surface will move away from each other (every galaxy is receeding from every other one) and the 'equator' of the ballon gets much bigger (space is expanding).

I'd point at this part of your statement - space (and time) is not just lack of matter, it is the framework in which matter can exist. You simply can't have matter unless there's some 'space' for it to exist in - likewise, you can't have space without there being any matter - the two are inter-dependent - and potentially equivalent.

The universe has boundaries but it's a little more complicated than it sounds. The idea of the universe expanding like an explosion with everything moving away from a central point is a common misconception, The universe is actually expanding from every point in all directions, this means the centre of the expansion is not in our three dimensions. Imagine drawing points on a balloon and then blowing it up - as the ballon got bigger the points would all move away from each other, the centre of this expansion is in the middle of the ballon not on it's surface where the points are, I think this may make things a bit more confusing - sorry

Good analogy!

The universe can be infinite because space/time is curved. Picture a tiny bug walking on the inner surface of a basketball. It can go forever and never reach the end - as far as the bug is concerned, his basketball universe is infinite.

And the universe isn't necessarilly all that exists. Many scientists hypothesize that there are many universes, and we're just in one of them. Again with the bug, all he could see was his basketball - he'd never know that his basketball was on a rack next to 20 others.

You might want to read "Coming of Age in the Milky Way" by Tim Ferris. It explains a lot of things in ways normal people like me can understand.

Thanks for the suggestion! I'll have to go find it once I get through my history books for this semester

Just something related I thought I would interject:
Using our balloon example we understand that without the two dots actually moving, more space is appearing between them. The result is that they are moving farther apart. In addition the farther apart they are the faster they move apart. Eventually the points can become so far apart that the distance between them is increasing at the speed of light, or even faster! (This is ok because they are not really moving, there is just new space between them. Funky.) Nothing can exceed the speed of light so it is possible that the universe does not wrap like a balloon at all, but rather is like a flat sheet of rubber with the edge being stretched away so quickly that someone standing on the sheet would never be able to catch or even see it.

Also, something I don't think the others have said yet, is that there is no truly empty space, there is still energy there (or so it is theorized.)

PS I think this should probably be in Tilted Knowledge.

I wonder what the nothingness is that the universe (balloon or flat sheet) is expanding into? Is the universe filled space and the nothingness empty space? Are there other universes out there in the nothingness? This infinity stuff is enough to make a sane person crazy.

It is not expanding into any empty space, that would be part of the universe. The stuff that is outside the universe is not stuff, it is not even space, it is nothing... it is not even empty, it does not exist! It is sometimes difficult to grasp but you cannot think of outside the universe being a place.

But using that analogy your not accounting for the fact that every point in universe is expanding and moving away at the same rate, using the sheet of rubber analogy two points both perpendicular to the stretch direction would not appear to be moving apart, you need the form of the ballon to shift the centre of the expansion off the sheet itself

I did not explain it well, but the arrangement I was thinking of has each of the sheet's edges being pulled away from the center of the sheet simultaneously. Of course a 2D analogy will never explain the 3D concept perfectly.

thats what i thought you meant, even in that situation the centre of the expansion is on the sheet itself. A 2d analogy will never explain the 3d perfectly but stripping away a dimension makes it possible for us to comprehend possiblilities such as centres of expansion not existing within our 3d framework.

I hate to be a pest, but are we describing an expanding universe that creates it's own space as it expands and any area/nothingness/space outside of it does not exist, because there is "no outside of it"?

Right, the universe is not only what exists but also the area in which things have the capacity to exist. It seems that we are getting more of the space in which things can exist, but it does not make any sense to talk about that space coming from anywhere.

This sounds somewhat questionable. So the universe is expanding, though there are no boundaries and there is nothing it is expanding into. I am assuming you are leaving out the elasticity of the balloon and explaining the universe as an equal amount of matter and energy expressed in a given area. Also how can we be sure of the nothingess beyond our universe and at that the confines of our universe. Is this predicted from creation theories or expansion and interaction of bodies of mass? Also are you attempting to define hyperbolic geometry?

If the expanding universe is elastic, everyone remembers ether, then it has very odd "elastic" properties since studies show that the universe is not only expanding, but something is accelerating the galaxies further and further away from each other.
An we can be sure that whatever exists on the opposite side of our universe's light boundary, we will never see since we would have to go faster than light to ever reach it, which Einstein proved we can't do in normal space or with conventional travel.

The universe is that area in which things can take place; we say there is nothing outside the universe simply because it flies in the face of the definition.

This is not predicted from creation theories, expansion or interaction of mass, or anything else so needlessly complicated. It also does not involve "hyperbolic geometry" or any other buzzword. Nothing exists outside the universe because all of reality is the definition of the universe; byt virtue of existing it would fall under the term.

space is defined in hyperbolic geometry it is not a buzz word it is an area of mathematics and physics. Also if the universe is the area where all things can take place, then how do we know where matter and anti-matter are created. I may be a little rusty, but last I knew we didn't know what caused this reaction to create the two and then anhilate themselves. Also, it seems like a loose definiton of universe and therefore there could not be a multiverse theory. I think that that is a false definition.

I think i can explain it in a way that *may* make some sense (the universe expanding that is).

Say for example you have a Mirror. Now this mirror is flat, Imagine it is 2 dimensional. Now when you look in the mirror you dont just see a non-moving, inactive, surface.. there is movement and depth. You can appear to peer deeply into the mirror yet the mirror is flat, it can appear that there is more space inside the mirror yet if you were to look on the other side of it there would be nothing.. discontinuance. If you were to peer into the mirror and move it toward/away from you, you'd be able to see more of the "universe" inside it, it would seem to expand and contract depending on how you shifted it around. The surface area of the mirror stayed the same, yet there appeared to be "more" space "inside" it.

I'm not quite sure that came out exactly the way i would have wanted it, but there you go.

Not sure how that relates to an expanding universe?
I think as an analogy it may need a few more reference points, what does the mirror represent, what is the significance of it bieng 2d whilst apparently showing 3d.
It sounds interesting but think it needs expounding on

Yea, its all rather difficult to put into words hehe. A better example may be a hologram, but that would be even more taxing to explain, and i wouldn't even know where to begin on that one right now (have been up all night). There's a few theories flying around that the universe *is* actually a type of hologram of sorts.

In fact.. i did a quick google search right now and look what i found :)
http://www.tfproject.org/tfp/archive...p/t-23447.html
which was from:
http://twm.co.nz/hologram.html

The TFP post took two posts to get it all in, i don't want to quote something so huge into this thread. I think everyone will trust a link to another TFP post :p

Edit: WARNING: Only read the link if you are prepared to have your brain both implode and explode at the same time in the attempt to fully grasp everything that it is trying to explain. :crazy:

It gets even trickier when you consider the possibility that there is more than one universe out there, beyond the edges of our own. I personally think it's quite likely. It might help explain accelerating galaxy separation.

I want to know about the entire universe. How big it is, and where does it go to?

Taking the balloon analogy further, I thought of how far the balloon has expanded as the lapse of time. If you think of a mass on the surface of the ballon, it bends both space and time. I was wondering if this was along the correct line of thought?

hmmm, hadn't thought of that but spacetime is meant to be curved so I think that's a plausible line to follow, might be interesting

CSFilm/d*d, while there can be a closed universe, this isn't guaranteed.

You can have a limitless, boundless universe, that expands.

Take your baloon. Now make it flat.

Flatter than that. Expand it out until it is a limitless plane.

Now, draw on that plane a grid, with the grid lines 1 cm apart.

Next, imagine the entire plane getting stretched, so the grid lines are 2 cm apart.

Notice that this plane didn't expand into anything. All of this action happened within the plane itself. Which points out flstf's error. =)

The universe isn't the contents of the balloon. It is the surface of the balloon.

The real trick is to now imagine this in 3 dimensions. Draw a scaffolding over reality. Now imagine the distance between the scaffolds getting larger, and everything moving with it.

We now have a limitless space (infinite in scope), that expanded by a factor of 2.

The 'space is expanding' claim basically comes from the cosmological observations that the further something is away from us, the faster it is moving away from us -- and, there seems to be evidence that a medium-long time ago, every bit of reality we can see was right next to each other (because it was the same tempurature). The rest, as far as I can tell, is syntatic sugar and mathimatical magic to make sense of these observations.

true - it could be an open universe where it keeps expanding and never contracts, if the force of gravity is not enough to overcome the force of the expansion.

That renders the ballon analogy useless

The problem with this analogy is that there is a centre to the expansion described, this is not the case with the universe.

How so?

Take a balloon. Make it larger and larger.

Notice how the surface gets more and more flat. You can see this yourself by drawing larger and larger circles, then looking at a small piece of the edge -- as the circle gets larger, 1 cm of the circle's edge gets flatter and flatter.

After you make it really large and nearly flat at any one point, you can still expand it. And, if you are standing on the balloon, the expansion just makes things move away from each other -- it gets to the point where you can't tell the balloon is curved, and all you can see is a locally flat area 'expanding'.

Now imagine it was so flat, it extended off to infinity in all directions. Perfectly flat, not just 'close to flat'. Locally, a really really big balloon and a infinitely flat plane look identical, so locally everything looks the same.

A flat plane is the surface of a balloon grown to infinite size. =)

There is a center? Well, there is where you are looking at the plane.

If you are at a point, you see the grid expanding away from you. So you think "oh, I must be at the centre".

Now, lets say you move somewhere else. Surprisingly, you see exactly the same thing -- everything moves twice as far away from you, and it looks like you are at the centre!

No matter where you are on the infinite plane, when it expands by a factor of two, it looks like you are at the centre of the plane.

This is just like how the universe looks like to us. When we look out into space, we see everything expanding away from us. In reality, everything is just moving away from everything, so there is no centre. The same thing happens on the infinite plane with a grid drawn on it.

There is no frame of reference other than the grid. All perception is anchored at a point on this grid -- as far as someone can tell, wherever they are on the grid looks stationary, everything else is what is moving.

You can't just chuck infinity in, the models of the universe described only work for finite universes, this is the way the big bang theory works to explain the nature of our universe - I ain't saying it's definately case but it works better than just supposing the universe is infinate because it's so big

First, the universe can be both flat and finite. The only flat, boundryless surface embedable in 3 dimensional space is the infinite plane -- so it is a good example to use to describe what is going on. I guess I could say "the universe is like a sheet of paper with opposite sides identified" (mmm, donut), but that seems overly complex. One doesn't need topology to understand this concept.

If you can understand how an infinite plane can expand by a factor of two, without any centre, and without expanding "into" anything, it might help you understand how the universe could do the same thing. Even if the universe doesn't look like an infinite plane, the image is still useful.

Secondly, as far as I am aware, there is no reason to believe the universe isn't infinite in size. Attempts to determine the diameter of the universe using microwave background radiation came up with "bigger than what we can see".

You can have a 'big bang' that starts with an infinite sized universe, involves space stretching rapidly, and ends up with an infinite sized universe which is 'bigger' than the original universe in a local way. It looks just like ours does, as a bonus.

I don't believe in infinity as a real-world phenomanon, and as such, can't accept the idea of an infinite universe. I'm happy to allow for things to be bigger than we can ever see beyond - but I can't accept infinity as being anything other than an often usefull, but otherwise abstract concept, nothing more.

Is finite space somehow less abstract?

yes, finite space is tangible and far more comprehensible. Infinity is a concept, an abstraction that does not exist except as a mathematical tool.

Sorry Yakk I don't mean to keep contradicting you, but the big bang model only works with a finite universe. The big bang model suggests that all matter which is in the universe, the universe itself was contained in a very very small space - which was unstable and exploded, the tricky thing to try to appreciate is that it was not an explosion as we percieve one, as it's centre was not within the universe which resulted - what my original balloon analogy attempts to show. since the explosion and resluting universe had boundaries, it was not infinite and so could never become infinate.

From what I understand boundaries are as hard to find as infinate space. The best we can do is aproximate where one thing ends and another one starts. It also seem that we never actually seen an end of things alltogether. One seems to follow the other and another.

For myself to say finite space is tangible, is to say that a poket of space is tangible, but it's pretty damn hard to imagine an end to the world now isn't it.

The problem with every analogy given is that they require space to expand into something.

The ballon example:

- we got two points.
- the two points move away from each other creating space.
- but in order to create that space I had to displace the air around the baloon.

All that was to simply say: I don't get it :p

This Thread belongs in the knowledge section

the Tshirt does not shrink when you wash it.
the cotton does, and takes the Tshirt with it.

I often confuse the vacuum of space with the E=MC squared of the mathematical universe we are debating here.

1. Space is a vacuum and in that vacuum there is matter and electromagnetic radiation and time dimensions etc. Our universe is in this "space". Space may be infinite, and it likely goes beyond our universe.

2, Assuming you already know about matter and electromagnetic radiation: Time is a dimension that has properties. It can be bent like light and is affected by the gravity effect etc.

3.When all matter was together in a singular place (singularity) electromagnetic radiation and time were bent to the point that they all turned back in on the singularity. (who knows what the actual shape was... I prefer a ball for simplicity)

4. When point 3 was the case our universe was small, all atomic activity had stopped... the small singularity resided inside of an infinitely large vacuum we call space.

5. The Big bang occurred a billionth of a second later and ..kabloom....and the expanding universe began. Matter, radiation, etc started it's journey outward, into the vacuum. Because of it's speed , time was/is affected.

6. When scientists debate over the shape of space and time and our universe they are talking about the space-time dimensions of our universe. There is nothing to say that there are not other universes outside of our own, in space.

Did I get it wrong?

Please advise

Not exactly. What many people call "space" is anything outside the atmosphere of the Earth, but in the terms of the universe it is an area in which things can exist. This space can be occupied by matter or other forms of energy, or it can be completely empty. Our universe is all the matter and energy that exist, and also all the empty space in which matter and energy can exist. We do not know if space is infinite or not because we have not found an edge, but it does seem to be getting larger. (I will talk about time later down.)

This is a good way to think of it in a general sense, but it is much more complex. Lets just say that the rate at which time passes is variable and relative to the observer.

Try to imagine a point rather than a 3 dimensional object. A point has no length, width, or depth at all. Think of a map grid; point (32,57) is infinitely small.

Negative on the last half of number 4; space itself was a single point. Length, width, and depth were meaningless because everything including the capacity to exist was all in the same place (all places were one). I cannot really comment about if atomic activity was stopped or not because pretty much all of our understanding of the universe today make no sense in that context.

Matter and energy did extend out, but space extended as well. Suddenly things could exist apart from each other. This can also be considered to be the start of time.

Scientists are talking about not only the matter and energy but also the capacity to exist that makes up our universe. There might be other universes "outside" our own but it would be a peculiar concept indeed.

I would like to make a simple analogy to better explain the concept of "space", as you seem to be thinking of it as merely a vacuum. Remember that a vacuum is "A space empty of matter".

Lets imagine a piece of paper, which for our example will be completely 2 dimensional (no thickness). On this paper we will draw a stick figure and let him explore the area. Soon enough he will come to an edge of the paper. Beyond the edge of the paper the capacity for drawn things to exist ceases. You are probably thinking of this piece of paper floating in the air somewhere or sitting on a table; you are still stuck thinking in a 3 dimensional context. Remember in our example I only defined the sheet of paper and outside the sheet of paper is truly nothing.

If you can begin to think in the terms of 2 dimensions then you can understand how hard it would be to add an unknown type of dimension to our 3D view. Scientists cannot disprove the possibility of other universes but they would be separated from us by an indescribable void and located in a manner which hurts my brain to think about.

It seems to me that is space was infinite, and we trace it back to the big bang, then it must have been infinite then, just incredibly dense. You can't shrink infinity into a point, or expand a point into infinity.

If space was at one time a singularity, it must now be finite. I guess.

Keep in mind that just because we cannot find an edge does not indicate that something is infinite, therefore any declarations of space being infinite in size are only speculation. With space "stretching" it is quite possible that if there is an edge it would be impossible to observe or reach because space is being created faster than the speed of light.

Then again, the current workings of the universe may not conform to current logic and we need to reorder our ways of thinking to understand it.

Phage, there is no need for the "finite sized universe" hypothesis.

All experiments attempting to find the width of the universe have failed.

If this was true, space was never a point.

On the other hand, there are models that seem to indicate a phenomina like our visible universe could inflate out of a 20-lb concentration of a particular strange field in a hot medium. If this was the case, then the visible universe would just be an inflated bubble within something else, much much larger than our cosmic horizon. We would be like underwater animals, living at a hot spring on the bottom of the ocean. A seemingly infinite universe to them is just some small corner of the 'real' universe.

Secondly, below Plank-distance and Plank-time, modern physics is silent. In the early parts of the big bang, the equations of physics keep spewing out infinities and nonsense: cosmologists have pushed back the model of the universe to fractions of a second after "time 0", but the last little bit is not understood.

The fact is, alot of these things are still up in the air. So making definite statements about things like this isn't honest.

There are many models which explain why the visible universe seems like it is. One of the strongest involves a 'space inflation field' in a very hot early universe -- that model explains everything from the baseline universal ratio of helium to hydrogen to the clustering of galaxies to the tempurature and tempurature variation of interstellar space, to redshift from far galaxies and stars. The "hot inflation" model of the universe is called "the big bang". But even in that one model, there are many details that are not ironed out, and there are competing theories that explain what we can see but make different predictions about things we can't yet detect. (Example: gravity wave predictions differ between the "big bang" model and the "brane collision" model)

My point was that it is not possible to prove that the universe is infinite in size, you can only prove it is finite. Your statement at the top about space never being a point needs clarification; if we view space-time as being created in the Big Bang then space could certainly have been a point. With the observed expansion of space-time there is no indication that it is expanding "into" anything at all.

Too true, and as our understanding of the universe increases we may come across truths which defy our current logic.

Suppose you had a theory that indicates that space is infinite, and has other corroborating things it also indicates. That is pretty strong evidence.

Remember, science 'facts' are statements that are disprovable and have proven hard to disprove. No statement in science (unless you include mathematics in science) are "proved" in the strict sense. Trial by fire is the rule: if the statement survives tough challenges, you gain confidence in it.

Eventually, you end up with as much confidence in a statement as you should have when using Newton's laws to work out the path of a baseball.

Why could it not have come into being infinite in 4 dimensions (space x 3 and time x 1)? If the current extent of space is indeed infinite, then no amount of inflation could have inflated a point to infinite space.

Alot of current theories claim that space-time is infinite in at least one dimension (time), it doesn't seem that much of a stretch to assume that it is infinite in 4, especially with the current knowledge that the universe is not folded up within the observable radius.

My point is simply that saying "space started as a point that defined all that is" is overly strong. That is one of the theories.

Others include spacetime being an inflation of a relatively small area (from plank-area to something as huge as an atom or even more), the brane-collision model, just something that happens within blackholes, or many other quite decent theories.

I can understand why some theories would say that time is infinite in the dimension of time, but what corroborates that? We already know that there was a start, and just because we have not come to an end does not mean that there will not be one. Sure, we cannot come up with a good reason for it to end (but then we don't really have a good reason for it to start anyway).

I take issue with your statement that nothing except mathematics in science is proven. For instance, anyone can go out and determine the boiling point of water at standard pressure. This is an observable phenomenon. Stating that the universe is infinite in size is not an observable phenomenon and cannot be proved correct, only disproved.

As you said, if theories are hard to disprove then your confidence in them becomes greater. However this only applies if it is reasonable that tests can be performed that would disprove the theory if it was wrong. An example of this in action: I propose that the center of the star Alpha Centauri A suddenly formed little green men last Tuesday. It is very difficult (impossible we presume) to disprove such a theory but it does not make any sense for us to gain confidence in it because of that.

Now look at the theory "Space is infinite in size." Is it within our capacity to disprove this theory? No, but it is also unreasonable to assume that it is within our capability at this time to disprove it were it false.

In any case, your point is well taken. Our discussion is based on current theories and views of the structure of the universe and are very likely to change as we progress. One day we may be looked back at in the same way we look back at those who believed that the world was flat.