size of the universe

[Auri-El]

I have a science question and I'm not quite sure where to put it, so if this is the wrong spot I apologize.
The universe is about 14 billion years old, so it can't possibly be more than 14 billion light years across, I thought. I went to verify this, and found this source that says we can see stuff that's 46 billion lightyears away. How is that possible? The article mentions space expanding, but how can it travel faster than light? If the speed of light is really the cosmic speed limit, and I trust Hawking when he says it is, then how can space have expanded quickly enough to be over 40 billion light years across? This science stuff is so confusing.

[m52nickerson]

When you are talking about objects and the fact that they can't go faster than the speed of light you are talking about that object moving away from, or towards a fixed point.  The universe is expanding in all directions at the same time, so the rate of expansion between and to objects is the sum of their velocities.

Say you have two space ships that take off in opposite directions, each travailing at the sped of light or C.  The rate at which they are moving away from each other would be 2C.

Also the speed of light is a limitation found within our universe.  As the edges of the universe expand into the nothingness around them they may not be constrained to that limitation.

http://curious.astro.cornell.edu/question.php?number=575

http://en.wikipedia.org/wiki/Faster-than-light#Universal_expansion

[Star Cluster]

To be honest, this is something that not even most astronomers fully comprehend, and I don;t pretend to understand it completely myself.  But I'll try to muddle through an explanation as best as I can.

Imagine you and I were to start in opposite directions from a single starting point and you had a gun capable of firing a bullet that would travel at a constant speed until it hit something.  And let's say we both starting traveling at the same time and could instantly travel at a speed just 1/2 the speed of the bullet the gun you had would fire.  Let's also say that we both traveled for one hour before you fired the gun in my direction and then dropped the gun at that point but you continued to travel at the same rate.  But since we are both traveling away from the point where the gun was fired, by the time the bullet caught up with me, we would both be a much greater distance from each other than when you fired the gun. 

What you have to keep in mind is that the speed of light is constant, but it is constant from it's place of origin.  While light may be traveling at you at 186,000 mps, if you are traveling at away from the source of the light, it will take longer to get to you than if you were standing still.  And the universe is not only still expanding, but evidence indicates the expansion is actually speeding up. 

I know this is probably not the best explanation, but I hope it helps.

[Auri-El]

That...sort of makes sense. Only, the Cornell link said the event horizon seems to be about 16 billion light years. How can we see further than that? Is that like, we see a galaxy 16 billion light years off, redshifted by 5, and we can figure out how far the object would be now if we could still see its light?

[MadCatTLX]

I have a science question and I'm not quite sure where to put it, so if this is the wrong spot I apologize.
The universe is about 14 billion years old, so it can't possibly be more than 14 billion light years across, I thought. I went to verify this, and found this source that says we can see stuff that's 46 billion lightyears away. How is that possible? The article mentions space expanding, but how can it travel faster than light? If the speed of light is really the cosmic speed limit, and I trust Hawking when he says it is, then how can space have expanded quickly enough to be over 40 billion light years across? This science stuff is so confusing.

Do we know where the center of the universe is? If not, then for all we know Earth could be relatively close close to the edge of the universe.

[Auri-El]

I realize that, but that's not really what I was asking. My logic (which is incorrect, as shown by the links m52nickerson provided): The Big Bang happened 14 billion years ago, and all the matter in the universe has been expanding ever since. Matter cannot travel faster than 99.99% the speed of light. Therefore, the universe cannot be more than 14 billion light years in radius, or more than 28 billion light years in diameter, because then matter would be travelling faster than the speed of light. So when the article I linked in the original post says we can see objects 46 billion light years away, it doesn't make sense because we shouldn't be able to see more than 28 billion light years away, depending on where we are in the universe.

[Star Cluster]

Who are you responding to, Kali, me or MadCat?  Did you see my explanation?  M52 posted his answer while I was typing mine, so I don't know if you've seen it or not.  If you haven't, maybe it will help you understand it a little better.

[Auri-El]

Oh, I was replying to MadCat, sorry. I think I understand it a bit better, thanks.   Just one thing I'm still wondering:

the Cornell link said the event horizon seems to be about 16 billion light years. How can we see further than that? Is that like, we see a galaxy 16 billion light years off, redshifted by 5, and we can figure out how far the object would be now if we could still see its light?

[Star Cluster]

Oh, I was replying to MadCat, sorry. I think I understand it a bit better, thanks.   Just one thing I'm still wondering:

the Cornell link said the event horizon seems to be about 16 billion light years. How can we see further than that? Is that like, we see a galaxy 16 billion light years off, redshifted by 5, and we can figure out how far the object would be now if we could still see its light?

Pretty much, yeah.   13.6 billion years is about as far out as we have actually ever seen.  However, the object that we see can be much further than that now.  The light doesn't care where that object is currently nor does it matter.  We are seeing it where it was at the time the light left it. 

Like I said earlier, I'm certainly no expert on this and it confuses even seasoned astronomers.  But this is the way I understand it.  It appears to me  what you were referring to in your OP may have just been a case of bad wording on the authors part.

[Old Viking]

When I am asked to describe accurately the size of the universe, I hold my arms out horizontally from my shoulders and say, "Bigger than this."

[MadCatTLX]

I realize that, but that's not really what I was asking. My logic (which is incorrect, as shown by the links m52nickerson provided): The Big Bang happened 14 billion years ago, and all the matter in the universe has been expanding ever since. Matter cannot travel faster than 99.99% the speed of light. Therefore, the universe cannot be more than 14 billion light years in radius, or more than 28 billion light years in diameter, because then matter would be travelling faster than the speed of light. So when the article I linked in the original post says we can see objects 46 billion light years away, it doesn't make sense because we shouldn't be able to see more than 28 billion light years away, depending on where we are in the universe.

I know that's not what your asking, I was just asking a related question and making a statement about it. Since you seem to have been doing research on this do you happen to know if we know where the center of the universe is? And if so, do we know what,if anything, is located there.

[Auri-El]

Oh, I wasn't doing research, not really. I just was watching Sagan's Cosmos and it made me wonder about the size of the universe. I decided to do a quick Google search to see if my guess was correct, and what I found confused me. That was when I decided to ask for help here. I don't know anything about what's at the center of the universe, or where the Milky Way is, relative to the rest of the universe.

[Star Cluster]

Our location in the universe is rather difficult impossible to answer.  As far as we're concerned, relative to what we can see, we are at the center of the observable universe.   We can see objects as far away as we can possibly see in whichever direction we look. 

But we also know which direction the universe is expanding relative to our position due to whether the light from an object has a red shift or blue shift.  Objects moving towards us will have a blue shift while objects moving away will have a red shift.  This means the ones with a blue shift would be in the direction of the location of the big bang. 

So, no, we do not know how far we are from either the center or the edge of the universe.  All we know is that the universe is one big-ass place and we're in there somewhere.

[Yla]

Say you have two space ships that take off in opposite directions, each travailing at the sped of light or C.  The rate at which they are moving away from each other would be 2C.

Actually, that's wrong. They distance they move apart from each other would be 1C, not 2C. Galileian laws of motion are no longer applicable at relativisitic speeds.
The only way they can beat C is by universal expansion, i.e. they move at C, and due to the expansion of space itself, the distance between them increases. Relation between distance traveled and time needed can rise above C this way.

That's the explanation for the super-far-away galaxies. They do not travel at superluminal speeds, neither to an absolute frame of reference(which doesn't exist), nor to us observing. But the space itself is expanding between us and them, increasing the distance.

The reason we can see them is because at the time the light was sent out, the distance was still smaller (I'm not talking about the galaxy moving. Assume it's stationary at the edge of observable space for now). While the photons are covering that distance, the distance increases, Doppler-shifting them, but they still reach us despite the point of origin now being further away than they could have covered at C in the time since the Big Bang.

[m52nickerson]

Say you have two space ships that take off in opposite directions, each travailing at the sped of light or C.  The rate at which they are moving away from each other would be 2C.

Actually, that's wrong. They distance they move apart from each other would be 1C, not 2C. Galileian laws of motion are no longer applicable at relativisitic speeds.
The only way they can beat C is by universal expansion, i.e. they move at C, and due to the expansion of space itself, the distance between them increases. Relation between distance traveled and time needed can rise above C this way.

Neither ship would be traveling at greater than C. You have to remember that C is calculated from a fixed point.  When we are looking at the rate at which the two ships are moving apart we no longer have a fixed point.

Think about it.  If the ships both traveled in opposite directions at C for on light year they would each be one light year away from the starting point, and thus two light years from each other.  Meaning that they where traveling apart at 2C.