# Question about the Age of the Universe

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#### duncanbmcg

##### Guest
I was hoping someone could answer this for me:

Facts:

1) The universe is around 13.8 billion years old... I'm not sure how they get this number, this is what I'll dive into later.

2) In terms of objects we can see - the furthest galaxy is about 13.5 billion light years away.

3)When we look at galaxies that are 13.5 billion light years away, we are viewing them as they looked 13.5 billion years ago.

4) Light is the fastest thing in the universe.

5) The Big Bang started in a single location, one giant boom.

___________________________________________________________________

My question is: From Earth's standpoint - we can look back and see galaxies that are 13.5 billion light years away. Imagine I was on a planet, circling a star, in that same galaxy - would I not also be able to see objects 13.5 billion light years away in any direction? Couldn't this go on to infinity?

My point is - if light is the fastest thing in the universe - then by our current timeline of the universe, light has had 13.8 billion years to travel in any direction after the big bang. But if you consider this in context to my above statement - the new age of the universe would be infinite.

Can anyone explain this to me?

:geek:

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#### Gravity_Ray

##### Guest
There are many people on these boards that are a magnitude smarter than me. But Let me take a stab at this and since we are both amatures then my limited answer may make some sense to you.

Don’t think of the big bang as an explosion IN space. Think of it as the explosion OF space. So think of any one point in the universe (anywhere) as a fly stuck in a cube of jello. As the cube of jello is expanding the fly "appears" to be moving outwards, but in reality the jello is moving outwards, not the fly. Well now that I think about this is kind of gross, so maybe think of it as a dot in a balloon, so as the balloon is being blown up the dots appear to be moving away from each other from their perspective.

So everyplace in the universe was one place at one time. The place itself expands and the things in it appear to be moving away from each other, but it’s relative. The universe itself was/is traveling faster than light. It’s called inflation. So even if you happen to be at the edge of the universe all you will see looking in all directions is the universe.

Not sure if I made things worse or better or if I even answer the question you were asking rightly or wrongly.

Phew, I need a cup of coffee.

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#### ramparts

##### Guest
duncanbmcg":s2oowtma said:
My question is: From Earth's standpoint - we can look back and see galaxies that are 13.5 billion light years away. Imagine I was on a planet, circling a star, in that same galaxy - would I not also be able to see objects 13.5 billion light years away in any direction? Couldn't this go on to infinity?

All indications point to the fact that, if the universe is finite (which seems reasonable), then it is MUCH bigger than our observable universe - that is, much larger than 13.7 billion light years in any direction from us. So pretty much any galaxy we could see almost certainly would see what we do - 13ish billion light years' worth of stuff in all directions.

My point is - if light is the fastest thing in the universe - then by our current timeline of the universe, light has had 13.8 billion years to travel in any direction after the big bang. But if you consider this in context to my above statement - the new age of the universe would be infinite.

I'm not entirely sure what you mean by saying the age of the universe would be infinite. Gravity_Ray's point is a good one and very true, that the Big Bang was an explosion of space, not of stuff within space. So we can't go find the place "where" the Big Bang happened - everywhere was condensed down into whatever went "bang". Maybe that answers your question?

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#### weeman

##### Guest
Hi Duncan. Welcome to SDC!

The biggest thing to take into consideration is the fact that the universe is expanding. So, with such incredible distances, it makes things very deceiving. Since space is so vast, and light has a limited speed limit, it creates a visible boundry that seperates the observable universe (the universe as we see it today) from the material universe (the universe as it would actually exist today). This means that the radius of OUR observable universe is 13.5 billion lightyears while the ACTUAL radius of the universe (from our point of view) is more like 48 billion lightyears.

To answer your question about infinity, no matter where you are in the universe, your visible sphere will always be 13.5 billion lightyears; but it does not mean that the universe is itself infinite. It's best to think of the 13.5 billion lightyear mark not so much as a measurement of distance, but more of a measurement of time. The 13.5 billion lightyear limit means that it has taken nearly the entire age of the universe for light from distant galaxies to reach us. It's impossible (at this point in time) for us to see galaxies that are 15 or 20 billion lightyears away because that would put them at an age that is older than the universe itself.

Here is a link that describes basic measurments for distance. Keep in mind that there's FOUR different distance scales that astronomers take into consideration:

http://www.atlasoftheuniverse.com/redshift.html

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#### SpeedFreek

##### Guest
duncanbmcg":3fevz4gp said:
My question is: From Earth's standpoint - we can look back and see galaxies that are 13.5 billion light years away. Imagine I was on a planet, circling a star, in that same galaxy - would I not also be able to see objects 13.5 billion light years away in any direction? Couldn't this go on to infinity?
Yes, it is assumed that any observer, wherever they are in the universe, would be able to see light coming from all directions that has been travelling for 13.7 billion years, and this applies to observers currently at the edge of our observable universe. Yes, it could go on to infinity.

duncanbmcg":3fevz4gp said:
My point is - if light is the fastest thing in the universe - then by our current timeline of the universe, light has had 13.8 billion years to travel in any direction after the big bang. But if you consider this in context to my above statement - the new age of the universe would be infinite.

Can anyone explain this to me?

:geek:
The universe might have been infinite in extent when it began, 13.7 billion years ago. Or, the universe might act like a 3 dimensional surface that "wraps around" on itself (something like the surface of a sphere, but raised a dimension) so that if you were able to travel far enough and could beat the rate of expansion (which is impossible) you might find yourself back where you started.

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#### erak

##### Guest
This stuff can confuse me....is it like this???....I am the center point of my universe(here on Earth)....it would take me 13.7 billion years to reach the farthest points in my universe(that I can see with the technology of today)....but i am expanding out with the universe,so, myself and these points that I can see today stay the same distance apart. But, is all of the universe(no matter which point you are at) expanding out at the same rate???? Or are there variations in expansion? IDK....I'm confused...lol

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#### duncanbmcg

##### Guest
Hey thanks for all your replies. Weeman - you speak my language - thanks for that link. That makes more sense now... although it's still confusing.

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#### weeman

##### Guest
erak":3nn1z873 said:
This stuff can confuse me....is it like this???....I am the center point of my universe(here on Earth)....it would take me 13.7 billion years to reach the farthest points in my universe(that I can see with the technology of today)....but i am expanding out with the universe,so, myself and these points that I can see today stay the same distance apart. But, is all of the universe(no matter which point you are at) expanding out at the same rate???? Or are there variations in expansion? IDK....I'm confused...lol

It would take much longer than 13.7 billion years to reach those distant objects, because they are much farther today. And like you say, you will have to fight against the expansion to reach those distant objects.

As for your question about the rate of expansion, the answer is : Yes - Space expands out at the same rate to every observer in the universe. Since expansion causes every point of space to expand away from every other point of space, each observable point in space becomes the center of its own observable universe. What astronomers found about expansion is that the rate of expansion is proportional to distance. If a galaxy that's 1 billion lightyears away is expanding at a rate of X, then galaxies that are twice as far away will expand twice as fast, galaxies that are three times as far away will expand three times as fast, and so on. Eventually the expansion reaches a velocity that is equal to or greater than the speed of light.

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#### killium

##### Guest
When you look far away, you look back in time. What you see is young. The planet with an observer that you see at 13.5 billion light-years distance exists in a universe that is 13.5 billion years younger than ours. So from what you can see of him, his universe is much smaller and younger than our's and he can't look away at 13.5 billion light years in all directions.

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#### erak

##### Guest
So, the galaxies that are further from me are actually moving faster away from me than those that are closer. But, what causes this??? is it similar to gravity?

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#### rocketmonkey

##### Guest
Your question is a good one, with an answer only people that focus really well at space know. The reason that we can see only things 13.5 billion light years away and the the universe is 13.8 billion years old is because light actually isn't the fastest thing in the universe. The fastest thing is the rate the universe itself expands.

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#### rocketmonkey

##### Guest
erak":2spyuqvp said:
So, the galaxies that are further from me are actually moving faster away from me than those that are closer. But, what causes this??? is it similar to gravity?

You were so close to the right answer that its funny. It actually is gravity. :lol:

killium":2spyuqvp said:
When you look far away, you look back in time. What you see is young. The planet with an observer that you see at 13.5 billion light-years distance exists in a universe that is 13.5 billion years younger than ours. So from what you can see of him, his universe is much smaller and younger than our's and he can't look away at 13.5 billion light years in all directions.

It has actually evolved 13.5 billion years over there than what we see over here. :geek:

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#### erak

##### Guest
k...that makes sense. Is it possible that the reason the outer points of our universe are expanding more quickly than the inner points is due to our universe being pulled by other universes around us? Creating some kind of a balance between everything?

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#### SpeedFreek

##### Guest
erak":ida394v3 said:
Is it possible that the reason the outer points of our universe are expanding more quickly than the inner points is due to our universe being pulled by other universes around us?

Everywhere (at the large scales) is expanding at roughly the same speed, at any given time.

Imagine points 1 unit apart in all directions. Now expand the distance between each point until it is 10 times its original size, moving all the points apart from each other.

Originally, whatever point you chose as your viewpoint, if you looked in any direction, there were points 1, 2, 3, 4, 5... units away. After the expansion those points are now 10, 20, 30, 40, 50... units away. So the closest point moved from 1 to 10 units away, so it moved 9 units. The next point moved from 2 to 20 units away, so it moved 18 units in the same length of time. The 5th point moved from 5 to 50 units, so it moved 45 units in the same time the first point moved 9 units! The further you look, the faster a point receded! But it doesn't matter which point you are on, the view of increasing speed with distance would always be the same. Every point can consider themselves to be at rest and everything else to be receding from them in all directions.

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#### ramparts

##### Guest
Whoaaaa whoa whoa. Hold your horses there, rocket monkey. Gravity does play a role in the expansion of the universe, but it would slow it down, not explain the expansion itself.

Erak, the reason faraway galaxies seem to be moving from us faster than nearby galaxies is simple - the universe is expanding, so every galaxy, everywhere, sees that phenomenon. Imagine you put a bunch of dots on a balloon and blew it up; each dot would expand away from each other dot, and if you think about it, each of those dots would see the same phenomenon. The further away some other dot was, the faster it would be moving away. What the universe is doing is similar to that; it's expanding, and this phenomenon, this proportionality of speed with distance, is an illusion created by that.

Why is the universe expanding? Well, the simple answer is that there was a Big Bang that got it started expanding, and it hasn't stopped yet. There are plenty of complications to that story, but that's the idea

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#### rocketmonkey

##### Guest
He asked why galaxies closer to us are moving slower than the ones farther away, and that is what I said the ones closer to us are more affected by our gravity than ones farther away, thus making their expansion slower.

erak":9bg5ttwv said:
k...that makes sense. Is it possible that the reason the outer points of our universe are expanding more quickly than the inner points is due to our universe being pulled by other universes around us? Creating some kind of a balance between everything?

I see how you would think that, but there is no gravity between universes. Some universes don't even have gravity as a law of physics. We do have a universe that is practically sticking to ours, but it isn't because of gravity. Picture the universes as bubbles formed by a bubble artist. Bubbles can form inside other bubbles, connected to other bubbles, by themselves, and in several various shapes and forms. Each one has different laws of physics. So between universes, there are no rules, hence no gravity.

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#### FlatEarth

##### Guest
rocketmonkey":3ihhbabg said:
He asked why galaxies closer to us are moving slower than the ones farther away, and that is what I said the ones closer to us are more affected by our gravity than ones farther away, thus making their expansion slower.
That's not correct, RM. The rate that space is expanding is the same everywhere in the universe. Therefore, with more distance (more space) the speed objects move away from each other is greater. Gravity has nothing to do with it.

rocketmonkey":3ihhbabg said:
erak":3ihhbabg said:
k...that makes sense. Is it possible that the reason the outer points of our universe are expanding more quickly than the inner points is due to our universe being pulled by other universes around us? Creating some kind of a balance between everything?

I see how you would think that, but there is no gravity between universes. Some universes don't even have gravity as a law of physics. We do have a universe that is practically sticking to ours, but it isn't because of gravity. Picture the universes as bubbles formed by a bubble artist. Bubbles can form inside other bubbles, connected to other bubbles, by themselves, and in several various shapes and forms. Each one has different laws of physics. So between universes, there are no rules, hence no gravity.
This also is not correct. There are no other universes that we know of. The idea of other universes is really science fantasy.

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#### ramparts

##### Guest
rocketmonkey":15mkf7ff said:
He asked why galaxies closer to us are moving slower than the ones farther away, and that is what I said the ones closer to us are more affected by our gravity than ones farther away, thus making their expansion slower.

Sure, except that's not true. As FlatEarth said, it's only an illusion that closer galaxies are moving away from us more slowly than faraway galaxies. Think about it; why would our galaxy be the only one whose gravity determined how fast the entire universe was expanding?

erak":15mkf7ff said:
k...that makes sense. Is it possible that the reason the outer points of our universe are expanding more quickly than the inner points is due to our universe being pulled by other universes around us? Creating some kind of a balance between everything?

I see how you would think that, but there is no gravity between universes. Some universes don't even have gravity as a law of physics. We do have a universe that is practically sticking to ours, but it isn't because of gravity. Picture the universes as bubbles formed by a bubble artist. Bubbles can form inside other bubbles, connected to other bubbles, by themselves, and in several various shapes and forms. Each one has different laws of physics. So between universes, there are no rules, hence no gravity.

Once again FlatEarth got to it before me There may be other universes, but we certainly have no evidence of their existence and, if they do exist, we have no idea what their physics are.

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#### rocketmonkey

##### Guest
ramparts":29207p33 said:
Once again FlatEarth got to it before me There may be other universes, but we certainly have no evidence of their existence and, if they do exist, we have no idea what their physics are.

That's what I said. If they do exist, they would have different physics.

He asked about the universes so I answered in the thought that there are. I am neutral in the multiverse theory, so when people ask about a topic I am neutral on I answer in their point of view.

I think I said my answer with the galaxy's gravity the wrong way. The speed of the galaxies slow down, not the rate of space-time expansion for them. And that only happens if we are closer to the big bang center of the universe.

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#### ramparts

##### Guest
That's just not true - or at least, it's a far more complicated explanation than the currently accepted one Think about it, your explanation involves us being near the center of the universe. The mainstream explanation - that we don't need to be anywhere special, and it's spacetime itself that expands - fits the data beautifully and is extraordinarily simpler. It also doesn't require us to be in the center of the universe which, if you think about it, is a huge claim.

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#### Woggles

##### Guest
weeman":2o5m34s4 said:

Thanks for the link the Comoving Distance - DC helped me get my head around some of this stuff. I always wondered about the actual size (distances)

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