Edge of the Universe

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dangineer

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I'm also not too terribly familiar with current research in cosmology; what is the evidence that the universes is not closed? Is the flatness of space as observed by the CMB experiments an indication of this?

I would think that if the edge of the universe had some net mass, it might help explain dark energy. The expansion of space may not be accelerating, but all the mass inside the universe could be accelerating towards the edge.

Maybe this idea is a little too far out there...
 
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KickLaBuka

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if the edge of the universe had some net mass, it might help explain dark energy. The expansion of space may not be accelerating
You're close. Very close.
 
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SpeedFreek

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dangineer":6qf7sil4 said:
I'm also not too terribly familiar with current research in cosmology; what is the evidence that the universes is not closed? Is the flatness of space as observed by the CMB experiments an indication of this?
Yes. As far as we can tell, the universe is within 2% of being flat. So the universe may be flat, or it might be curved but the scale of that curvature would be so large that the radius would be far larger than our observable universe.

dangineer":6qf7sil4 said:
I would think that if the edge of the universe had some net mass, it might help explain dark energy. The expansion of space may not be accelerating, but all the mass inside the universe could be accelerating towards the edge.

Maybe this idea is a little too far out there...
It is the acceleration of objects that are closer to us than the objects at the edge of the universe that tells us the universe is accelerating. At the cosmological scale, the closer the object we look at, the further away that object is from where it should be if the expansion were still decelerating. We think the expansion has only been accelerating for the past 5 billion years or so, which means that light which has been travelling for less than 5 billion years will have always been travelling through a universe where the expansion is accelerating. We see the objects at the edge of the universe as they were 13 billion years ago, when the rate of expansion was decelerating - their light will have been affected by the acceleration for less than half of the time it has been travelling towards us.

The light-curves of Type 1a supernovae last longer than predicted in a decelerating universe, the closer we look to home. This tells us the rate of expansion must have accelerated relatively recently, progressively "stretching" that light more and more as the rate of expansion continues to accelerate.
 
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dangineer

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My last statement about the egde of the universe having mass was probably incorrect due to the gravitational shell effect (gravitational forces on an object in a shell of mass tend to cancel due to symmetry). Although I still think that if certain things are assmed at the boundary of space, we may get interesting results. I'll have to ponder this for a while to come up with a possible scenario.
 
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ramparts

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dangineer":unkknlnh said:
My last statement about the egde of the universe having mass was probably incorrect due to the gravitational shell effect (gravitational forces on an object in a shell of mass tend to cancel due to symmetry). Although I still think that if certain things are assmed at the boundary of space, we may get interesting results. I'll have to ponder this for a while to come up with a possible scenario.
I'll give you a helpful hand, if you promise to remember that this is all purely speculative and likely has no basis in reality ;) Yes, there is a shell effect - if the shell is uniform in mass and density. But if there's more mass in one part of the shell than in the others, and you're inside the shell, you'll move towards the more massive end. Hopefully, of course, this will put an end to your theory-mongering though! Perhaps you can see why.
 
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dangineer

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Well, the mass assumption doesn't work out in any way. If there were an asymmetrical mass distribution, either everything would accelerate in one direction, wheras we wouldn't notice it, or we would see everything moving in one direction, which goes against observations.
 
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ramparts

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dangineer":934z679t said:
Well, the mass assumption doesn't work out in any way. If there were an asymmetrical mass distribution, either everything would accelerate in one direction, wheras we wouldn't notice it, or we would see everything moving in one direction, which goes against observations.
Exactly :) This would go against isotropy (that the universe is roughly the same in all directions), which is fairly well observed.
 
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dryson

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Since travel faster than the speed of light is prohibited in our universe, this does indeed belong in The Unexplained.
Even the most powerful scope imaginable cannot exceed that basic limit.

However, since this is the Unexplained, you can make up any kind of unrealistic physics you wish :)

Since it's impossible, you have no limits!
Who said that going faster then the speed of light was impossible? You are trying to say that going faster then the speed of light is against some law. There is no prohibition saying that we cannot travel faster then the speed of light, and don't start running off at the mouth about how Einstein said that it wasn't possible. Humanity has just begun to understand only a small area of space that is within it's spaced based and planetary based equipment.

There is no edge of the Universe, what would happen if you come to the edge of space which is the Universe? Would you fall off into more space? If this is how your think then perhaps you should read up on history alittle bit about a guy named Christopher Columbus would discovered that the world was round or at least oblong and spherical. The world is not flat and those that think that it is, you should really think about what you post and who you talk to./
 
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MeteorWayne

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As I said "However, since this is the Unexplained, you can make up any kind of unrealistic physics you wish" :) :)
 
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dryson

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As I said "However, since this is the Unexplained, you can make up any kind of unrealistic physics you wish"
There is no such thing as unrealistic physics, if this is true then unrealistic physics built the airplane, shuttle, nuclear reactor's, satellite's, CERN, NIF........It should instead be called undiscovered physics as in reality unrealistic notions are what religions are based off of.
 
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MeteorWayne

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You are wrong. All those things are based on real physics. That's why they work.
 
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ramparts

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dryson":2is4ihyk said:
Who said that going faster then the speed of light was impossible? You are trying to say that going faster then the speed of light is against some law. There is no prohibition saying that we cannot travel faster then the speed of light, and don't start running off at the mouth about how Einstein said that it wasn't possible. Humanity has just begun to understand only a small area of space that is within it's spaced based and planetary based equipment.
Please, please, read up on special relativity. There are very good reasons that travel faster than the speed of light is prohibited by very well-established laws of physics, and while it's possible we might find that not to be true, it's also possible we'll discover rainbow unicorns. No one is going to sit around explaining basic physics to you when you routinely ignore our attempts to do so, and fail to do any reading yourself.

There is no edge of the Universe, what would happen if you come to the edge of space which is the Universe? Would you fall off into more space? If this is how your think then perhaps you should read up on history alittle bit about a guy named Christopher Columbus would discovered that the world was round or at least oblong and spherical. The world is not flat and those that think that it is, you should really think about what you post and who you talk to./
Just because the Earth's surface is curved doesn't mean the universe's has to be, too. A scientific argument would be to show evidence that such a thing is true. An unscientific argument would be to say "read up on Christopher Columbus, n00bs". As you may be aware, the local geometry of the universe is found to be flat within about 2%. It's possible that globally, on larger scales, there is an overall curvature, like the Earth's, but we have absolutely no evidence for that at the moment.

dryson":2is4ihyk said:
There is no such thing as unrealistic physics, if this is true then unrealistic physics built the airplane, shuttle, nuclear reactor's, satellite's, CERN, NIF........It should instead be called undiscovered physics as in reality unrealistic notions are what religions are based off of.
As MeteroWayne said above, there is definitely such a thing as unrealistic physics. Like, physics that's not based in reality. You know, physics that says that gravity falls off as 1/r, or that like charges attract, etc.
 
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dangineer

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I would really like to see more discussion and less arguing in these forums, please.

Dryson, I think the problem we are all having is that you make claims that seem to contrdict most people's understanding about physics. If you really feel that they do not, then that is fine, but please for our sake, could you support your ideas in a clear and concise manner? Since you say that basic mathematics needs to be understood before learning physics, then I presume you have a good handle on mathematics and can use it. Maybe we could start with the quote below:

"Who said that going faster then the speed of light was impossible? You are trying to say that going faster then the speed of light is against some law. There is no prohibition saying that we cannot travel faster then the speed of light, and don't start running off at the mouth about how Einstein said that it wasn't possible."

So you seem to disagree with Einstein's theory of special relativity. If you can prove his theory wrong mathematically using an air tight argument, then I'm sure people in this forum wouldn't try to discount your ideas as much. You suggest that you know more than many of us do, so I'm confident that you can do this.
 
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Mars_Unit

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Back in 1976 I wanted to use large telescopes to evaluate Uranium to get a reading of the age of the Universe.

It was to be my thesis at college. A few years later another used Thorium to date the Universe at 4.7 Billion years old.

At the time I accepted this value, but now I realize it is wrong. That is the age of the oldest rocks, not Galaxies.

We can only see in a sphere 13.7 Billion years ago and the late Professor Philip Morrison believed we would see a huge wall of Hydrogen gas forming into Galaxies, but I never seen it.

Back in the 70's I believed in the Supergalaxy Theory that all Galaxies must form an even greater Galaxy, but all we see is some kind of Cosmic Foam with our scan of the Galaxies.
 
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kelvinzero

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ramparts":13jwqgk2 said:
That makes two of us :lol: So my second question essentially asked: we can't get there from here, but "there" should still exist, no? Imagine that we were in a galaxy 13.7 or so billion light years from us (the farthest we can see) at the present day, measured in their time. They imagine the same thing for yet further distant galaxies, etc. Eventually we'd expect one would arrive at an "edge".
By the way, Although the universe is meant to be about 13.7 billion years old, it is believed to be much wider than 13.7 light years in radius.

http://en.wikipedia.org/wiki/Observable_universe
"The edge of the observable universe is now located about 46.5 billion light-years away."

And that is just the observable bit.
 
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SpeedFreek

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ramparts":19433crq said:
Just because the Earth's surface is curved doesn't mean the universe's has to be, too. A scientific argument would be to show evidence that such a thing is true. An unscientific argument would be to say "read up on Christopher Columbus, n00bs". As you may be aware, the local geometry of the universe is found to be flat within about 2%. It's possible that globally, on larger scales, there is an overall curvature, like the Earth's, but we have absolutely no evidence for that at the moment.
And we have absolutely no evidence against it either. :) The question is open.

But there is a subtler aspect to all this. Even if the universe is totally flat, it might have no edge.

You can take the concept of circumnavingating the surface of a 3-Sphere (a closed universe), but use a torus instead. This is a 3-torus of course, whose surface has 3 dimensions (it is a 4 dimensional shape, just like the 3-Sphere).

If the universe was "wrapped" onto the surface of a 3-Torus, it would look flat to any observer within it (all parallel lines stay parallel) - but there are directions where those lines form closed loops.

Is the universe finite or infinite? - Joseph Silk
Is the universe finite or infinite? - Joseph Silk
(I put links to both google.com and google.co.uk as I have heard people in different countries get different preview pages)

Extending the WMAP bound on the Size of the Universe
 
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ramparts

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Yes, the topology of the universe is an open question (although perhaps not open itself!). Thanks for your insightful post :)
 
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mental_avenger

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There is really no reason to make the answer to this question any more complicated than it needs to be. The answer is probably very simple. The Universe is an infinite void. It is not necessary for it to contain anything in order for it to exist and be infinite in size. Somewhere in that infinite void a very compact singularity violently exploded, something we call the Big Bang. All the material that was released from the BB began expanding into the void of the Universe. Currently that material exists as a finite amount of matter expanding outward from its origin. What we call space is merely the local region of the Universe.

It is possible that there are or have been other areas of expanding matter elsewhere in the infinite Universe, but there will probably never be any way to find out.

Time is merely a natural consequence of existence.

Bottom line, although we cannot find the edge of the Universe, since there isn’t one, we might someday be able to find the edge of the mass of expanding matter from the BB.

Meanwhile, we have all we can do trying to analyze the Observable Universe. Since the further away an object is the faster it is moving away, the edge of the Observable Universe is that distance from us at which everything is moving away at c relative to us.
 
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SpeedFreek

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Wow MA, I don't know where to begin... :shock:

Lets start with your statement - "the edge of the Observable Universe is that distance from us at which everything is moving away at c relative to us".

Firstly, do you mean "is moving away at c" right now, or was moving away at c when the light we see was emitted? Do you mean the Hubble distance "then", or the Hubble distance "now"?

The Hubble distance was 5.7 billion light-years when the light we see was emitted from galaxies that were receding at c and that light has a redshift of a little over z=1.4, which means those regions have receded to around 14 billion light-years away by now, due to the expansion of the universe. But that light was only emitted a little over 9 billion years ago.

We have seen light that has been travelling for much longer than that, and thus has covered a greater distance. Photons from more distant galaxies were just passing those galaxies at the edge of our Hubble sphere 9 billion years ago!

We have seen galaxies at redshift z=7, whose light has been travelling for nearly 13 billion years. Their light was travelling for around 4 billion years before it overtook those galaxies at z=1.4 and crossed into our Hubble sphere. From our point of view, the light from those z=7 galaxies was receding from us for 4 billion years, as the space it was travelling through was receding from here superluminally. As the rate of expansion decelerated, that light eventually found itself in regions of space that were receding from here at less than the speed of light, as it passed into our Hubble sphere, 9 billion years ago.

We have seen the light from galaxies that were receding at multiples of c when that light was emitted, so how can the distance where an object did, or does, recede at c, be considered the edge of our observable universe?

It's late now, I'll leave the part about the infinite void till tomorrow. :)
 
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ramparts

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mental_avenger":vj8gb2zy said:
There is really no reason to make the answer to this question any more complicated than it needs to be. The answer is probably very simple.
Indeed! Why complicate things by talking about "data" and "theories" when we can just assert something very simple without worrying about whether or not it agrees with reality?

Is that what mental_avenger is going to do?

The Universe is an infinite void. It is not necessary for it to contain anything in order for it to exist and be infinite in size. Somewhere in that infinite void a very compact singularity violently exploded, something we call the Big Bang. All the material that was released from the BB began expanding into the void of the Universe. Currently that material exists as a finite amount of matter expanding outward from its origin. What we call space is merely the local region of the Universe.
Yep.
 
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mental_avenger

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SpeedFreek":372dn5e8 said:
Firstly, do you mean "is moving away at c" right now, or was moving away at c when the light we see was emitted? Do you mean the Hubble distance "then", or the Hubble distance "now"?
Since the term used was “observable”, any object, the light from which we can observe at a given moment would be within the Observable Universe. That would mean any object that was moving away from us a some amount less than c at the time the object emitted the light. Of course that changes from moment to moment. BTW, that was one of Isaac Asimov’s terms.
 
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mental_avenger

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ramparts":1fhj18hu said:
Indeed! Why complicate things by talking about "data" and "theories" when we can just assert something very simple without worrying about whether or not it agrees with reality?
IMO, my observations appear to agree with reality rather well. Some people seem to have a problem with the concept of infinity, so they formulate all sorts of complex systems in an attempt to avoid infinity. The problem is, that usually only moves the problem with infinity to the next level, but it is still there.

The main problem with current theories is that they are all necessarily based upon incomplete data. That is, there are still a great number of things that we can observe, but cannot explain. There are also a great number of things we cannot observe at all. What we observe about those things is the effects they have on something observable, or what we think is effecting something observable. Having a reproducible set of observations about the effects on an observable phenomenon does not necessarily mean that we understand the mechanisms that cause those effects. A good example of that is light; is it a wave or is it a particle? Maybe it is neither, but rather something for which we have no macro analogy.
 
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SpeedFreek

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mental_avenger":2uygwyza said:
SpeedFreek":2uygwyza said:
Firstly, do you mean "is moving away at c" right now, or was moving away at c when the light we see was emitted? Do you mean the Hubble distance "then", or the Hubble distance "now"?
Since the term used was “observable”, any object, the light from which we can observe at a given moment would be within the Observable Universe. That would mean any object that was moving away from us a some amount less than c at the time the object emitted the light. Of course that changes from moment to moment. BTW, that was one of Isaac Asimov’s terms.
So what about the objects we have seen, that were moving away from us faster than light at the time those objects emitted that light? Everything from around redshift z~1.6 upwards, to z=1090 (all light emitted between 9 and 13.7 billion years ago)?

Are those objects not part of our observable universe?
 
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mental_avenger

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SpeedFreek":3967xkag said:
So what about the objects we have seen, that were moving away from us faster than light at the time those objects emitted that light? Everything from around redshift z~1.6 upwards, to z=1090 (all light emitted between 9 and 13.7 billion years ago)?

Are those objects not part of our observable universe?
Light emitted from any object that is actually moving away from us at greater than c will never reach us, so the object will not be observable by us. There are some situations where an object appears to be moving at greater than c relative to us, but that is an illusion. Bottom line, any object, the light from which we can see at any given moment, is part of our Observable Universe at that given moment. (as the name implies)

http://www.universetoday.com/2008/04/22 ... -of-light/
 
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ramparts

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mental_avenger":10sm3oqm said:
ramparts":10sm3oqm said:
Indeed! Why complicate things by talking about "data" and "theories" when we can just assert something very simple without worrying about whether or not it agrees with reality?
IMO, my observations appear to agree with reality rather well. Some people seem to have a problem with the concept of infinity, so they formulate all sorts of complex systems in an attempt to avoid infinity. The problem is, that usually only moves the problem with infinity to the next level, but it is still there.
I agree with what you're saying about infinity, but that's not a scientific argument, and shouldn't be used as a conversation-stopper. There are many possible geometries for the universe that are currently consistent with the data, and to say "let's not complicate things, and just say the universe is infinite" is very, very unscientific.

The main problem with current theories is that they are all necessarily based upon incomplete data. That is, there are still a great number of things that we can observe, but cannot explain. There are also a great number of things we cannot observe at all. What we observe about those things is the effects they have on something observable, or what we think is effecting something observable. Having a reproducible set of observations about the effects on an observable phenomenon does not necessarily mean that we understand the mechanisms that cause those effects. A good example of that is light; is it a wave or is it a particle? Maybe it is neither, but rather something for which we have no macro analogy.
I'm sorry, but what are "complete" data? What you've just described applies to every theory of science. Is this a "problem?" I think you're just taking a feature to be a bug.
 
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