Size v Age of the Universe

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nethrus

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In the latest edition of Space.com newsletter it states that the currently accepted age of the universe is 13.7 billion years old and its width is 156 billion light years. Assuming that the big bang happened at what is now the centre of the current universe and that matter (or even radiation) cannot travel faster than the speed of light, how is the universe so big? Surely its width could not be more than 27.4 billion light years? Or am I missing something here?
 
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harmonicaman

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Think of it as a train going from Big Bang, NY to Present Day, CA. The trip takes you 13.7 billion years.<br /><br />Unfortunately, the train track is a rubber band which is continuously stretching longer and longer over time; so even though the trip only took you 13.7 billion years, you covered 78 billion light years in actual distance traveled.<br /><br />Since we observe ourselves to be located at the center of this infinitely expanding bubble of space and time, we double this distance to 156 billion light years and define this as the distance from one side of the universe to the other.
 
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drwayne

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Nethrus,<br /><br />Did you register under a different name?<br /><br />If not, there is another poster asking a very similar question, in which case this sounds like a homework question.<br /><br />Wayne <div class="Discussion_UserSignature"> <p>"1) Give no quarter; 2) Take no prisoners; 3) Sink everything."  Admiral Jackie Fisher</p> </div>
 
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kmarinas86

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<font color="yellow">In the latest edition of Space.com newsletter it states that the currently accepted age of the universe is 13.7 billion years old and its width is 156 billion light years. Assuming that the big bang happened at what is now the centre of the current universe and that matter (or even radiation) cannot travel faster than the speed of light, how is the universe so big? Surely its width could not be more than 27.4 billion light years? Or am I missing something here?</font><br /><br />Yes. Space expands at an acceleration of c*H, the speed of light times the hubble constant, and this is without the objects having relative motion. If you factor in the relative (actually peculiar) motion, which averages out to 0, you are left with an outward acceleration of c*H. The acceleration doesn't stop, and space expands faster than c at distances greater than 13.7 billion light years.
 
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billunsworth

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Hi I guess the answers to this thread explain why as we look at objects further and further away they seem to be accelerating away from us. If the size of the Universe equalled the age then further away things would be getting closer together and at the limit we would be able to see the big bang itself!
 
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alkalin

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Hears one problem as I see it with what you said. If everything was expanding and if I were walking across my room and let’s say it was about twenty feet, the size of my steps would not change in relation to the room. I would get to the other side with exactly the same number of steps. Even though the size of the room got larger, I did also, so the number of steps were the same. Am I missing something?
 
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nethrus

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Thanks guys. Thinks I'll shut myself in a dark room to ponder those replies.<br /><br />Basically, what I think your saying is that the universe itsself or the space within it (whatever that is) is expanding and that the velocity of anything moving within that space is increased by a factor proportional to its distance from any other point in space. That factor being, presumable, the Hubble Constant.<br /><br />So am I right in saying that anything further away than 13.7 light years must be moving away from us at more than the speed of light and would therefore be invisible. So how can we be sure its actually there?<br /><br />I tend to think of space as a vacuum, although I realise it must be filled with all types of radiation and possibly other things as yet undiscovered such as gravity waves. Nonetheless the expansion of a vacuum seems a bit of a paradox to me, but I'm probably thinking far too linear.<br /><br />Thanks anyway. You've all been a great help. And no, it's not a college project, just curious.
 
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harmonicaman

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<b>Nethrus -</b><br /><br /><i>"So am I right in saying that anything further away than 13.7 light years must be moving away from us at more than the speed of light and would therefore be invisible. So how can we be sure its actually there?"</i><br /><br />You're correct! But don't think of it as the light itself which is moving faster; the very space itself is expanding and carrying the light along with it.<br /><br />And we believe the origin of the universe is really there, beyond what we can observe, in the same way that you believe a fog shrouded bridge is really connected to land on the other side, even though you can't see it. <br /><br />We can observe the universe expanding and deduce that it must have been much smaller in the past; go back far enough in time and you should end up at the singularity; or at least that's the theory... <img src="/images/icons/rolleyes.gif" />
 
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alokmohan

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(SPACE.com) -- A project aiming to create an easier way to measure cosmic distances has instead turned up surprising evidence that our large and ancient universe may be even bigger and older than previously thought.<br /><br />If accurate, the finding would be difficult to mesh with current thinking about how the universe evolved, one scientist said.<br /><br />A research team led by Alceste Bonanos at the Carnegie Institution of Washington has found that the Triangulum galaxy, also known as M33, is about 15 percent farther away from our own Milky<br />
 
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supernova65

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The way I understand it, not everything expands. The Hubble expansion only applies to gravitationally unbound objects in the universe, so that you don't expand, neither does your room, nor for earth, nor the solar system, nor the Milky Way, etc... because gravity keeps all that together, well in a matter of speaking, dark matter is needed for the Milky Way in addition to gravity, but that's another topic. The expansion happens on a much larger scale than our own backyard I'm afraid.
 
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alokmohan

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What is gravitationally unbound objects?Are there two types of object?
 
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derekmcd

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I believe what he is referring to is the Virgo supercluster that we are a part of. The local group is gravitionally bound and may be headed towards something referred to as the Great Attractor. The galaxies in our local group are not expanding away from each other. More distant galaxies and clusters that are, in fact, expanding away from our own local group are considered gravitationally unbound in reference to our own local group. <div class="Discussion_UserSignature"> <div> </div><br /><div><span style="color:#0000ff" class="Apple-style-span">"If something's hard to do, then it's not worth doing." - Homer Simpson</span></div> </div>
 
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