Originally posted by adam warlock Yes. On your case the balloon geometry is embebbed on a 3-d space but on the case of the Universe it isn't imbebbed in anything else. It is all that is. Kinda like being in the balloon and not being aware of an extra dimension (cause there isn't any in this case).
Yes, you'd have to embed the Universe in a fourth dimension, which could be expanding with the Universe. So I suppose there would be an 'edge' in that sense, but not one that we have access to.
Originally posted by PinkFloyd Since the universe is expanding, there must be a point at which one could call the Edge of the Universe, right? Granted, that boundry would change every moment (since it's always expanding at a fantastic rate), but still, at a given point in time, one should be able to say "Right here IS the edge of the universe." My question is what is on the other side ...[text shortened]... answer I've heard is some sort of parallel opposite universe. Anyone have a conjecture?
Imagine an ant on an the surface of an expanding balloon. The ant can go on forever in circles, thinking it is infinite. The analogy is not very good, but it's purpose is to make you realize there are mathematical abstractions for the way the Universe works that make your reasoning comparable to the ant's. We simply don't have the ability to visualize the whole.
Originally posted by mtthw Yes, you'd have to embed the Universe in a fourth dimension, which could be expanding with the Universe. So I suppose there would be an 'edge' in that sense, but not one that we have access to.
I'm not sure that you have to embed anything in a higher dimension.
Let's compare with the surface of the earth. It is a two dimensional surface, yet no edge within these two dimensions. Any point of the surface needs two coordinates to be fully qualified, two is enough. Therefore is the surface of the Earth only two-dimensional.
The space itself has three dimensions (Perhaps I should say three big spatial dimensions, so the string theory's 11 dimensions doesn't disturb this reasoning.) Every point in the universe can be qualified with only three coordinates. There is no need for the fourth one.
In three spatial dimensions there is no edge anywhere. There is no inside universe, and no outside either, it is just - universe.
Originally posted by FabianFnas I'm not sure that you have to embed anything in a higher dimension.
Let's compare with the surface of the earth. It is a two dimensional surface, yet no edge within these two dimensions. Any point of the surface needs two coordinates to be fully qualified, two is enough. Therefore is the surface of the Earth only two-dimensional.
The space itself ha ...[text shortened]... no edge anywhere. There is no inside universe, and no outside either, it is just - universe.
My reasoning is like this. The surface of the Earth is 2D, but it needs to be curved in a third dimension to give it the necessary geometry - so the Earth is 3D.
Now we're thinking about the Universe. It's three dimensional. But we can get the same geometric effect by allowing it to curve in a fourth dimension. The universe itself may only have three dimensions, but you still need the fourth.
As I said, this is only one possible interpretation.
Originally posted by mtthw My reasoning is like this. The surface of the Earth is 2D, but it needs to be curved in a third dimension to give it the necessary geometry - so the Earth is 3D.
Now we're thinking about the Universe. It's three dimensional. But we can get the same geometric effect by allowing it to curve in a fourth dimension. The universe itself may only have three di ...[text shortened]... nsions, but you still need the fourth.
As I said, this is only one possible interpretation.
Well, the surface, where we walk and live, is only a surface of two dimensions. But this surface is closed in a spere. If you want to se what's inside, then you go into the third dimension.
Universe is a three dimensional space that is closed. You can't get out of it, you can't go into it (like the surface of the Earth), it isn't closed into a hypersphere. There is no inside of this round three-dim surface. The fourth dimension is not needed.
Originally posted by FabianFnas Well, the surface, where we walk and live, is only a surface of two dimensions. But this surface is closed in a spere. If you want to se what's inside, then you go into the third dimension.
Universe is a three dimensional space that is closed. You can't get out of it, you can't go into it (like the surface of the Earth), it isn't closed into a hypersph ...[text shortened]... de of this round three-dim surface. The fourth dimension is not needed.
...as I see it...
You need the metric of your space (how far from each other are two different points in your surface or hyper-surface). In a sphere it is easy, but in real world, general relativity says we need to include the dynamical variable time to describe that same metric. And that it is dependent on things like mass, that can be assigned positions in that 4 dimensional space.
Things might get even more complex...
But the problem is a lot more complex then saying "there's an extra dimension, we only see 3", and make analogy with surfaces-volumes".
When you see expansion of the Universe, the universe is not really expanding into something. It's simple the metric that is being changed.
Originally posted by FabianFnas Let's not go off topic.
It's only a linguistic term.
Wasn't trying to go off topic nor offend...I mean we have somewhat scientific proof that the universe is 14.5 billion years old and it still expanding...but we also know that our galaxy is slowly eating itself...so my whole wonderment is the fact although expanding there are still attractions and I think eventually it will all come back together.
Of course that is so many billions of years away it won't make a difference to me...lol.
Originally posted by nmdavidb Wasn't trying to go off topic nor offend...I mean we have somewhat scientific proof that the universe is 14.5 billion years old and it still expanding...but we also know that our galaxy is slowly eating itself...so my whole wonderment is the fact although expanding there are still attractions and I think eventually it will all come back together.
Of course that is so many billions of years away it won't make a difference to me...lol.
Dave
I just didn't understnad your question. Both you and me know what 'something' is and it has nothing to do with the expansion of the universe.
Universe is expanding universally, but locally we don't feel anything of it. Inside our galaxy the effect of universe expansion has near to no meaning, even in our local galaxy cluster it has much effect.
The Andromeda galaxy is on collision course to our Milky Way. Only random movement, nothing more.
Originally posted by FabianFnas The Andromeda galaxy is on collision course to our Milky Way. Only random movement, nothing more.
Not random movement, a victory for gravity. Theories are just that but the most accepted suggests that gravity's victory will be final.
The orignal topic, as mentioned, the universe is boundless (but not infinite!) hence no "edge" for anything to exist beyond. Philosphically this answer is very unpleasing. It is just a theory though, just happens to fit best with the little we know.
Originally posted by Caba Not random movement, a victory for gravity. Theories are just that but the most accepted suggests that gravity's victory will be final.
The orignal topic, as mentioned, the universe is boundless (but not infinite!) hence no "edge" for anything to exist beyond. Philosphically this answer is very unpleasing. It is just a theory though, just happens to fit best with the little we know.
The question if Andromeda and Milky Way are going to collide because of gravitation, I think the answer is no. We were at collision course even before we had any significant gravitational effect of eachother. These movements are random and the collisions are random at beforehand. However, the gravitional effects are considerable when it happens.
Gravity rules? No, not on universe as a whole. Gravitation is not (as we now know) halt the expansion and pull everything together again into a Big Crunch. But gravitation rules locally.
I don't know for sure about the Big Crunch...like i said...just a thought...but gravity will play a huge role due to mass.
We all know Kepler's 3rd law P2=A3
But when you take what Newton did with (m1 + m2 )P2=A3 then we can also measure the attraction of an object to another.
I know this is mainly used for distance but I think there is one more formula I think that if used with this then you can calculate the attraction rate.
Can't remember...shouldn't have slept so much during physics clas..lol
Originally posted by FabianFnas The question if Andromeda and Milky Way are going to collide because of gravitation, I think the answer is no. We were at collision course even before we had any significant gravitational effect of eachother. These movements are random and the collisions are random at beforehand. However, the gravitional effects are considerable when it happens.
I disagree, without the effects of gravity we would not hit Andromeda. Gravity over billions of years has shaped individual (infact all mass) galaxies and how they interact. It's no coincidence or random set of events that the two largest galaxies in our local cluster are on a collision course.
The boss of our part of the universe is the large cluster of galaxies in Virgo and we can see the effect of it's gravity causing our local group to accelerate towards it and also the movement of the thousands of galaxies in the cluster.
Gravity's reach is huge. It's the weakest force but given enough mass it will win (black holes). Wether there is enough for it to stop the expansion of the universe and indeed reverse it, well, that remains to be seen. What we do know though is it is fudamental in the interaction of mass in the universe. Withou gravity you won't even have galaxies form never mind collide.
Originally posted by Caba I disagree, without the effects of gravity we would not hit Andromeda. Gravity over billions of years has shaped individual (infact all mass) galaxies and how they interact. It's no coincidence or random set of events that the two largest galaxies in our local cluster are on a collision course.
The boss of our part of the universe is the large cluster of galax ...[text shortened]... mass in the universe. Withou gravity you won't even have galaxies form never mind collide.
Of course you are right that gravitation is a strong force with this kind of masses we are talking about despite the distance btween the galaxies. But not so strong that all galaxies in our local cluster takes find eachother in the shortest period of time. Most of the galaxies are actually missing eachother. Andromeda and Milky Way just happen to be in a collision course towards one another.
But you are right, without gravity, the universe would be totally different from what it is now, on that we agree.
Originally posted by mtthw My reasoning is like this. The surface of the Earth is 2D, but it needs to be curved in a third dimension to give it the necessary geometry - so the Earth is 3D.
Now we're thinking about the Universe. It's three dimensional. But we can get the same geometric effect by allowing it to curve in a fourth dimension. The universe itself may only have three di ...[text shortened]... nsions, but you still need the fourth.
As I said, this is only one possible interpretation.
Actually you don't need a fourth spacial dimension for the Universe to bend on itself. I don't how much do you know about differential geometry and manifolds and such but an understanding of those notions is really needed to explain things propperly. I won't pretend that I can explain that in a good way but I think that serigado has already given a very good response. The metric of the space-time continuum in general relativity changes and that is why some people say space-time is curved even though I think that that is a bad-picture and an lead to incorrect reasonings
Originally posted by adam warlock Actually you don't need a fourth spacial dimension for the Universe to bend on itself. I don't how much do you know about differential geometry and manifolds and such but an understanding of those notions is really needed to explain things propperly. I won't pretend that I can explain that in a good way but I think that serigado has already given a very ...[text shortened]... is curved even though I think that that is a bad-picture and an lead to incorrect reasonings
The more we probe into space, the more it seems to me and a lot of cosmologists that there was something before the big bang, and that something more and more seems to be the inside of a black hole, our universe being the 'white hole'. There doesn't seem to be any way around that. I think more and more evidence will be gleaned making that conclusion inescapable. It will cause a lot of rethinking about embedded dimensions and such. Just because we can show mathematically other dimensions are not needed for relativity to work does not mean there are no other dimensions.
beyond the expanding universe
07 Mar '08 14:07
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