Questions

[Nazgûl Killer]

I have just seen 3 science shows in a row about space (I love the subject and I know some about it), about the death of the sun, the end of the universe and about our galaxy (About how it was formed/how it will be destroyed/how it will merge with the Andromeda galaxy) and I have a big question:

Since these shows offered the query of "Are there multiple universes?" - And some answered positively (Scientists) and some answered negatively, I was wondering: How is it possible that our universe is expanding into infinity, if there are MULTIPLE universes? I mean, that would mean (If, for example, there were only 5) that there are 5 infinities out there, as far as my logic can conceive, this is impossible.
So, I want to ask: What do you think? Is it possible? How?

[Alba gu Brath]

The multi-verse theory, if I'm not mistaken says that, material swallowed up by a black hole, is released out of the other end of the black hole and creates another "big bang". If this theory is true, it would seem like the universes are structured like layers in a cake, one on top of the other. So within their layer, they can expand to whatever length they want.

[eisenkopf]

I think it's entirely possible. Or not.

If you try to picture or imagine the whole thing before your mental eye, you'll end up nowhere. It's no good, our perception, cognition and mental capacities are evolved to deal with 3+1 dimensions (such as tracking and extrapolating the trajectory of, say, potential food).

The whole astrophyical research can only be understood with mathematics, where it does not matter how many dimensions you have to deal with. Metaphors such as "layers of a cake" or "behind the black hole" etc. are of very limited use, and may actually add to the confusion. As long as you are not able and/or willing to grasp the underlying mathematics (as I am not), you have to believe what the nutters in the labs and observatories tell you.

[Nazgûl Killer]

I think it's entirely possible. Or not.

If you try to picture or imagine the whole thing before your mental eye, you'll end up nowhere. It's no good, our perception, cognition and mental capacities are evolved to deal with 3+1 dimensions (such as tracking and extrapolating the trajectory of, say, potential food).

The whole astrophyical research can only be understood with mathematics, where it does not matter how many dimensions you have to deal with. Metaphors such as "layers of a cake" or "behind the black hole" etc. are of very limited use, and may actually add to the confusion. As long as you are not able and/or willing to grasp the underlying mathematics (as I am not), you have to believe what the nutters in the labs and observatories tell you.

No offense, but this is exactly the response I was expecting to see, and the one I didn't want to see. Anyone can come up with the reason of "We're not smart enough to understand" or "They are right, end of story", I want a true explanation behind it.

I assure you, I can understand whatever you try to explain to me, whether I read it once, twice or research it, so that explanation doesn't it it. (Again, no offense)

The multi-verse theory, if I'm not mistaken says that, material swallowed up by a black hole, is released out of the other end of the black hole and creates another "big bang". If this theory is true, it would seem like the universes are structured like layers in a cake, one on top of the other. So within their layer, they can expand to whatever length they want.

Actually, if that theory is true, that means that we will eventually run out of 'universe' - I mean, I can go all the length and never reach the end, sure, but if I start travelling the width of the universe? I'd reach the end eventually, wouldn't I? - Most scientists believe the universe has no end, meaning it expands in every possible direction... That is my question, how can infinity exist twice? Let alone more?

[Alba gu Brath]

Actually, if that theory is true, that means that we will eventually run out of 'universe' - I mean, I can go all the length and never reach the end, sure, but if I start travelling the width of the universe? I'd reach the end eventually, wouldn't I? - Most scientists believe the universe has no end, meaning it expands in every possible direction... That is my question, how can infinity exist twice? Let alone more?

Oh yea, I see what you mean. It would be possible to expand the width of the universe but not vertically.

[PurPul]

Oh yea, I see what you mean. It would be possible to expand the width of the universe but not vertically.

Why wouldn't it be possible? The "layers of a cake" is mearly a theory.Nobody could accuratly tell how many universes there are if we can't even tell what our univers is like.

[Copperknickers II]

I have just seen 3 science shows in a row about space (I love the subject and I know some about it), about the death of the sun, the end of the universe and about our galaxy (About how it was formed/how it will be destroyed/how it will merge with the Andromeda galaxy) and I have a big question:

Since these shows offered the query of "Are there multiple universes?" - And some answered positively (Scientists) and some answered negatively, I was wondering: How is it possible that our universe is expanding into infinity, if there are MULTIPLE universes? I mean, that would mean (If, for example, there were only 5) that there are 5 infinities out there, as far as my logic can conceive, this is impossible.
So, I want to ask: What do you think? Is it possible? How?

If there are other universes, they are in other dimensions. Only in this dimension (spacetime, call it 4 dimensions if you will) does the universe exist.

Think of it as a pile of tortoises going out in all directions. One or two of those directions are the physical universe which we experience, the rest are other universes in other dimensions. Infinity is all of those universes and everything else besides.

[Nazgûl Killer]

So, basically what I see here is that people do agree that there are multiple universes but in several theories.

Think of it as a pile of tortoises going out in all directions. One or two of those directions are the physical universe which we experience, the rest are other universes in other dimensions. Infinity is all of those universes and everything else besides.

I like that theory, I wonder if there could be a 'second universe' with more than 3D/4D... Something like 11D.
That would be insane.


Are there any other theories aside the multi-dimensional one and the cake layers?

[Baron von Sky Hat]

The is very very little agreement on which, if any, of the multiple universe theories are valid. They're highly speculative, and to the best of my knowledge, no one has come up with any sort of experiment to prove/disprove any of them.

I think you're linking too much the idea of our three dimensional space (or 4D space-time, whichever really) in our universe, as something that's fundamental, and onto which the universe fits.
Rather, it's a property of our universe. Say you draw a `map' of a 2D universe on a piece of paper, then you draw another one on a different piece of paper. They can't overlap, their geometry and dimensions are specific to their piece of paper. You could stack up dozens of these `universes' on top of one another without them overlapping (or even necessarily interacting).
They would simply be entirely different existances, with their geometries, dimensions and properties independant and concurrent.
You can either think of it as an extra dimension, in the paper analogy, the extra dimension is the third, in which you're stacking them. For a 4D space-time universe or somesuch it could be a fifth dimension.

It's difficult to cover the concept, both because some of them are mathematically complicated, and also because there isn't one concept to cover, several different theories which are basically `multiple universe' based have different concepts on to which they're built.

Many of them suppose that the other universes would have the same physical rules (so 3 `physical' dimensions, time, etc), I think some are along the lines of different breaking of symmetries within physical rules, such that the effective physical rules and constants would be different in other universes.

I don't really know much about them, I've never been that interested in the specifics because they seem so speculative (I kind of feel the same about string theory, if I'm honest, it's not really testable at the moment, so it's all a bit up-in-the-air).

Nevertheless, the concept in general, relating to the nature of reality, is a massive question, clearly. That's pretty much the extent of my limited knowledge on them, hope that it might provide something useful.

The idea in general is difficult to approach, since we know a limited amount about the extent of our own universe. It's generally thought that our universe's geometry is approximately flat, and that the entire universe is expanding (whether it is expanding at a constant rate, slowing rate or accelerating rate has some mixed opinions). However, since the universe is definitely expanding, there is an absolute `horizon' to what we can see.

Everything is moving away from everything else, the further away the thing is, the faster it appears to be moving away (this is what causes red shift of distant objects). At a certain distance the things would seem to be moving away from us at the speed of light (due to space expanding, rather than it physically moving like that), so light from beyond that point will never reach us. We can never observationally determine what is beyond that distance. In fact I think that depending on the manner in which the universe is expanding, we can't interact with that region at all, as I presume it would violate various causality conditions of relativity (since it's effective speed appears to be faster than light)? I don't really deal with this subject, possibly someone with a better understanding of cosmological maths may have more to add?

[Nazgûl Killer]

The is very very little agreement on which, if any, of the multiple universe theories are valid. They're highly speculative, and to the best of my knowledge, no one has come up with any sort of experiment to prove/disprove any of them.

I think you're linking too much the idea of our three dimensional space (or 4D space-time, whichever really) in our universe, as something that's fundamental, and onto which the universe fits.
Rather, it's a property of our universe. Say you draw a `map' of a 2D universe on a piece of paper, then you draw another one on a different piece of paper. They can't overlap, their geometry and dimensions are specific to their piece of paper. You could stack up dozens of these `universes' on top of one another without them overlapping (or even necessarily interacting).
They would simply be entirely different existances, with their geometries, dimensions and properties independant and concurrent.
You can either think of it as an extra dimension, in the paper analogy, the extra dimension is the third, in which you're stacking them. For a 4D space-time universe or somesuch it could be a fifth dimension.

It's difficult to cover the concept, both because some of them are mathematically complicated, and also because there isn't one concept to cover, several different theories which are basically `multiple universe' based have different concepts on to which they're built.

Many of them suppose that the other universes would have the same physical rules (so 3 `physical' dimensions, time, etc), I think some are along the lines of different breaking of symmetries within physical rules, such that the effective physical rules and constants would be different in other universes.

I don't really know much about them, I've never been that interested in the specifics because they seem so speculative (I kind of feel the same about string theory, if I'm honest, it's not really testable at the moment, so it's all a bit up-in-the-air).

Nevertheless, the concept in general, relating to the nature of reality, is a massive question, clearly. That's pretty much the extent of my limited knowledge on them, hope that it might provide something useful.

The idea in general is difficult to approach, since we know a limited amount about the extent of our own universe. It's generally thought that our universe's geometry is approximately flat, and that the entire universe is expanding (whether it is expanding at a constant rate, slowing rate or accelerating rate has some mixed opinions). However, since the universe is definitely expanding, there is an absolute `horizon' to what we can see.

Everything is moving away from everything else, the further away the thing is, the faster it appears to be moving away (this is what causes red shift of distant objects). At a certain distance the things would seem to be moving away from us at the speed of light (due to space expanding, rather than it physically moving like that), so light from beyond that point will never reach us. We can never observationally determine what is beyond that distance. In fact I think that depending on the manner in which the universe is expanding, we can't interact with that region at all, as I presume it would violate various causality conditions of relativity (since it's effective speed appears to be faster than light)? I don't really deal with this subject, possibly someone with a better understanding of cosmological maths may have more to add?

Well, first, thank you, that cleared up most things and pretty much ended this subject...
Second... Even in an expanding universe, anything affected by gravity (Mars/Moon/Earth/Venus or other planets in solar systems/duo stars or stuff like that) don't move away from each-other, celestial powers who are NOT affected by gravity, do. That's just a little something I know because I read a lot of the subject.

Anyways - I consider this closed, thank you everyone, you've been a great help - If any moderators roam this little thread, you can close it if you will, unless anyone else wants to debate here.

[Baron von Sky Hat]

Well, first, thank you, that cleared up most things and pretty much ended this subject...
Second... Even in an expanding universe, anything affected by gravity (Mars/Moon/Earth/Venus or other planets in solar systems/duo stars or stuff like that) don't move away from each-other, celestial powers who are NOT affected by gravity, do. That's just a little something I know because I read a lot of the subject.

Anyways - I consider this closed, thank you everyone, you've been a great help - If any moderators roam this little thread, you can close it if you will, unless anyone else wants to debate here.

There's no need for it to be an end to the discussion, and what I've contributed certainly isn't the entirity of the matter.

Although I have to disagree on your second point. Technically, everything is affected by the gravity of everything else, even if it's small amounts. Our Sun orbits the galactic center through gravity, and our galaxy interacts with other nearby galaxies through gravity. You need gravity, even in the small amounts, to work over such large distances to get matter clumping together with eventually forms galaxies in the first place.

The expansion of the universe is the expansion of space itself, even things interacting by gravity move away from one another. Over a distance such as the Earth to the Sun such movement is practically undetectable, but it still occurs. Because every little `bit' of space is expanding, the further away an object, the more `bits' of space inbetween, so the faster away it appears to be expanding.

[Nazgûl Killer]

There's no need for it to be an end to the discussion, and what I've contributed certainly isn't the entirity of the matter.

Although I have to disagree on your second point. Technically, everything is affected by the gravity of everything else, even if it's small amounts. Our Sun orbits the galactic center through gravity, and our galaxy interacts with other nearby galaxies through gravity. You need gravity, even in the small amounts, to work over such large distances to get matter clumping together with eventually forms galaxies in the first place.

The expansion of the universe is the expansion of space itself, even things interacting by gravity move away from one another. Over a distance such as the Earth to the Sun such movement is practically undetectable, but it still occurs. Because every little `bit' of space is expanding, the further away an object, the more `bits' of space inbetween, so the faster away it appears to be expanding.

To be honest, my second point is not something I decided, it's something scientists agree on.
They simply say that the 'strength' of the expanding universe is weaker than the 'strength' of the sun's gravity, for that matter.
They showed some sort of proof... But that's about the only part I do not remember vividly from that show, all I do remember is that they said that objects in our solar system, or, in a solar system, or, affected by some sort of celestial power's gravitational pull are simply unaffected by the Universe's expansion.

This is a quote from a physics forum I usually roam:

The concept of expansion of universe, everything moving away from everything, doesn't make sense on such small scales as Earth-Moon (or for that matter, neither on the Earth-Sun scale, or even between Sun and nearby star scale). These systems are bound by gravitational relationships, making the effect of cosmological expansion negligible.

The real reason for the radial expansion is gravitational pull between Earth and moon and such.

Add : And obviously, hubble constant appears in cosmological expansion.

People there usually know what they talk about, so I find it easy to rely on what they say.

Thread - http://www.physicsforums.com/showthread.php?p=2284049