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iron4
2006-Apr-01, 06:49 AM
Consider a closed Robertson-Walker Universe (thus with finite volume). Can somebody give me an estimate of the volume of this universe (the whole Universe, not only the observable Universe)?

GOURDHEAD
2006-Apr-01, 12:53 PM
If they did, I doubt it would be credible. We know too little about the Hubble parameter, its rate of change over time, exactly when the inflation epoch ended, and how big the universe was at the end of the inflation epoch.

kzb
2006-Apr-03, 05:52 PM
Well according to this

http://www.astro.ucla.edu/~wright/cosmology_faq.html#MX

if I've interpreted in correctly, the volume of the total universe (not just the "observable universe") is infinite. Don't pretend to understand it myself, mind.

kzb
2006-Apr-03, 05:54 PM
Slight correction, from that website:

Is the Universe really infinite or just really big?
We have observations that say that the radius of curvature of the Universe is bigger than 70 billion light years. But the observations allow for either a positive or negative curvature, and this range includes the flat Universe with infinite radius of curvature. The negatively curved space is also infinite in volume even though it is curved. So we know empirically that the Universe is bigger than several times the observable Universe. Since we can only look at small piece of an object that has a large radius of curvature, it looks flat. The simplest mathematical model for computing the observed properties of the Universe is then flat Euclidean space. This model is infinite, but what we know about the Universe is that it is really big.

iron4
2006-Apr-03, 09:59 PM
Well according to this

http://www.astro.ucla.edu/~wright/cosmology_faq.html#MX

if I've interpreted in correctly, the volume of the total universe (not just the "observable universe") is infinite. Don't pretend to understand it myself, mind.

RW universes that are closed have finite volume. RW universes that are flat can have finite or infinite volume. RW Universes that are open have infinite volume. The consensus is that the Universe is flat, though I tend to think that is closed

Unknown User
2006-Apr-23, 09:37 AM
Wouldn't it be possible to measure some of the volume of the invisible universe using satelites with atomic clocks? If you put an atomic clock on a plane relative to one left on the ground the time on the one on the plane will pass slower than the one on the ground because time is moving slower. For example the earth travels around the sun at a certain speed and our solar system travels around our galaxy at a certain speed. If we look at the visible universe I am guessing we also know which direction our galaxy is headed and at some approximate speed.

So what if you send many satelites into space all with atomic clocks and all in different directions. Lets say our galaxy is moving to the right in our visible universe. Now lets say one satelite is also sent of to the right and another to the left. Shouldn't the satelite headed in the same direction our galaxy is heading slow down more than the satelite headed in the other direction because the satelite headed in the same direction as our galaxy is moving through space faster than the satelite that is headed to the left?

Now lets say the clock on the satelite traveling to the left says that time is passing slower for it than the one headed to the right when from what we can observe the satelite that is headed to the right is moving faster relative to our galaxy in the universe.

Wouldn't that suggest that part of the invisible universe that is beyond what we can see is moving our visible universe to the left at a greater speed than we appear to be moving to the right? Than we would know that there must be an area of universe beyond what we can see, sorta like spokes on a wheel, that is moving what we can see of our universe faster in one direction than the other? I have no idea if that is the way it works. Did that make any sense? :)

antoniseb
2006-Apr-23, 01:37 PM
...I have no idea if that is the way it works. Did that make any sense? :)
Your explanation made sense, in that it told us what you thought could test it, and why you thought it would work. However, it won't work. Just for starters, you would need to get the Satellites back to compare the clocks. Second, there is no universal frame of reference.

afterburner
2006-Apr-23, 08:24 PM
Second, there is no universal frame of reference.

Could we not approximate the "center" of our universe one day, and send an atomic clock there (which would beam the "real" time back to us)? How would that not be a reasonable place for a universal frame of reference? Or we could always just make sure that this one clock is not moving with respect to a large enough area, that it would make a difference for us humans.

Dragon Star
2006-Apr-23, 08:31 PM
Could we not approximate the "center" of our universe one day, and send an atomic clock there (which would beam the "real" time back to us)? How would that not be a reasonable place for a universal frame of reference? Or we could always just make sure that this one clock is not moving with respect to a large enough area, that it would make a difference for us humans.

http://en.wikipedia.org/wiki/Reference_frames

Unknown User
2006-Apr-23, 08:43 PM
Your explanation made sense, in that it told us what you thought could test it, and why you thought it would work. However, it won't work. Just for starters, you would need to get the Satellites back to compare the clocks. Second, there is no universal frame of reference.

Ok I somewhat understand what you are saying I think. What you are saying is time is relevant to a fixed point in the universe, the center of the universe or something like that? And that we need to know that point before we could make calculations? I am not sure because I don't understand exactly how this all works.

From what I understand the faster you travel the more time slows and the clocks we use to measure this change have no idea what a universal frame of reference is yet they record a difference in time. So it is as if they have no choice but to know because measuring time gives us that answer. Argh this is so hard to try and explain. As for the satelites, they could just transmit the data back to us.


http://en.wikipedia.org/wiki/Reference_frames

Interesting read but I am still confused :)

antoniseb
2006-Apr-23, 09:58 PM
...As for the satelites, they could just transmit the data back to us.

How would you know how far away they transmitted from accurately enough to know if there was a difference in their clocks?

Unknown User
2006-Apr-23, 10:28 PM
How would you know how far away they transmitted from accurately enough to know if there was a difference in their clocks?

Ok I am trying to figure out how to explain what I mean. Lets say we have satelite A and B. Satelite A is traveling the same direction through our visible universe as our galaxy. And from what we can see we conclude that our galaxy is traveling to the right from our point of view at the theoretical speed of 100,000 kps in our universe. Now if we were to launch a satelite in the same direction our galaxy is heading in the universe and the satelite accelerates so that it is traveling slightly faster than our galaxy is we can then compare the time of its clock with Satelite B which is heading to the left in our universe.

Now Satelite A and B are both using the same propulsion and are traveling at the same speed from their propulsion but because satelite A is moving in the same direction as our galaxy through the universe doesn't that mean it is traveling slightly faster than satelite B? I am not sure if this is how it works.

So now we are at the point where from what we can see satelite A is traveling through space faster then satelite B which are both carrying atomic clocks. The clock on satelite A is going to count time slower then the clock on satelite B because satelite B is traveling slower. We would not have to have an accurate distance between the satelites because the only information the satelites are transmitting back to us is what time their clock displays. Well it's not that we do not need an accurate distance of the satelites from us. We would have to have an exact distance otherwise we would not known when they transmitted that data back to us. But shouldn't we be able to calculate that if they are both launched at the same time and are travelling at the same speed?

Satelite A would transmit that it clock says. 10:15 PM and satelite B would transmit that its clock says 10:14 PM. We see that satelite A's clock is counting time faster because it isn't moving through space as fast as satelite B even though from our perspective satelite A should be moving faster. The reason time is passing slower on satelite B is because it is traveling through space faster then A because our arm of the universe is only a small part of many larger arms of the universe.

Both satelites left earth at the exact same time and exact same speed. I am not sure if time works that way but if it does than couldn't we use that to have a rough idea of the size of some of the invisible universe.
Because from our point of view our galaxy that is moving to the right in our visible universe is traveling at such and such a speed. What we can't see is that our visible universe, which is just an arm extending out of a much larger universe is not travelling to the right as we observe but is actually travelling to the left at a great speed because in the greater picture of the universe most of the matter and energy we can not see is actually moving faster to the left not the right. My brain hurts :)

antoniseb
2006-Apr-23, 11:15 PM
Now Satelite A and B are both using the same propulsion and are traveling at the same speed from their propulsion but because satelite A is moving in the same direction as our galaxy through the universe doesn't that mean it is traveling slightly faster than satelite B? I am not sure if this is how it works.

It's time to find a nice website that will teach you about special relativity at your level of math and science understanding. What you are suggesting cannot be understood without it. It's well explained in a lot of places, and it would be a lot of reinventing the wheel for us to figure out how best to explain it to you. I am not trying to shoo you away. Please participate in other threads while you learn this stuff, and feel free to ask us specific questions in the Q&A section.

Unknown User
2006-Apr-23, 11:27 PM
It's time to find a nice website that will teach you about special relativity at your level of math and science understanding. What you are suggesting cannot be understood without it. It's well explained in a lot of places, and it would be a lot of reinventing the wheel for us to figure out how best to explain it to you. I am not trying to shoo you away. Please participate in other threads while you learn this stuff, and feel free to ask us specific questions in the Q&A section.

I am not sure if I will ever understand it. Which is why I posted my ideas here to see what others had to say. From what I have learnt in documentaries, some very interesting stuff by Stephen Hawking, Michu Kaku and programs like Nova. Like many other people I am sure I find it hard to sleep trying to understand why things are the way they are. I didn't think I was breaking any rules and I have been very friendly and polite and thought that is what this forum was about :)

antoniseb
2006-Apr-23, 11:40 PM
I didn't think I was breaking any rules and I have been very friendly and polite

You aren't breaking any rules. You have been friendly. Almost a model citizen. Glad to have you here. I'm giving you advice about how to go forward. You can learn enough about special relativity in a few hours to go forward. We look forward to having you here, and participate, but you'll be happier thinking about the things you're thinking about if you understand special relativity better. Depending on your goals, you do not need to study the math of it. But there are things we'll have trouble explaining and questions you'll have trouble asking until you learn a little more about this subject... especially frames of reference.

Unknown User
2006-Apr-23, 11:50 PM
You aren't breaking any rules. You have been friendly. Almost a model citizen. Glad to have you here. I'm giving you advice about how to go forward. You can learn enough about special relativity in a few hours to go forward. We look forward to having you here, and participate, but you'll be happier thinking about the things you're thinking about if you understand special relativity better. Depending on your goals, you do not need to study the math of it. But there are things we'll have trouble explaining and questions you'll have trouble asking until you learn a little more about this subject... especially frames of reference.

Yes I see what you are saying and understand that. I will look around and see what I can learn about such things.

Dragon Star
2006-Apr-23, 11:53 PM
Learning hard concepts takes time, I have been here for months and still know very little about Astronomy, but I still find it a lot of fun!

neilzero
2006-May-08, 01:30 AM
If the Total Universe were a cube 10E11 = 100 billion lightyears on each edge the volume is 10E33 = 1000 decillion cubic light years. A cube is very unlikely, but 10E33 is likely as good as any other guess. Neil