13 Feb 2010 7:55:34 UTC

Topic 194771

(moderation:

http://www.fileden.com/files/2006/9/12/214557//theUniverse.jpg

As far as I know, dark matter is needed because galaxies don't have enough mass to stick together. Suppose the universe wraps upon itself. From the picture above, neither galaxy A or B has enough mass to stay together. However, gravity is not bound to our spatial dimensions, and so galaxies A and B are attracted to each other through other dimensions. If this were true, then I see no need for dark matter. The mass of galaxy A would warp space-time, and the attraction to galaxy B would warp space-time just enough more as to keep both galaxies together.

The other thing about this shape for the universe, is that it also explains why the universe's rate of expansion is accelerating. It is only because the universe is in ellipses, similar to the way the earth speeds up approaching the sun, and slows down moving away from the sun.

This brings up a unnerving question. Assuming this to be true, what happens to galaxies at the point of greatest acceleration of space? I would imagine that any small galaxy would be flung apart, due to the fact that any galaxy on the opposing side of the universe is so far away. Also, if the shape of the universe were a much more exaggerated ellipses, could the point of fastest expansion be considered a big bang?

I have asked here before if anyone thought if the universe wrapped upon itself, and the general answer was no. I ask again because I realized tonight that if true, it may explain dark matter and the big bang. Please feel free to tell me what you think of my idea.

Please note that in the picture, the ellipses labeled the entire universe is only the ellipses itself, not the are in the middle. Galaxies A and B are bulges in spacetime due to the matter present at those locations. That matter exists in spacetime, not inside of the ellipses itself. The area inside the ellipses labeled the entire universe is unreachable for us.

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## Shape of the universe negates the need for dark matter

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I made the picture clickable. I didn't use [img] because the picture is rather big.

GruÃŸ,

Gundolf

Computer sind nicht alles im Leben. (Kleiner Scherz)

## Are there any opinions on my

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Are there any opinions on my idea?

## Well the overall shape of the

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Well the overall shape of the Universe is a tricky one for sure. Mainly because :

- we're in it. We can't pop out and have a look from the 'outside'

- it changes with time

- we only 'know' about the bits that light travels from to us

- it could well have more dimensions than readily visualised by humans

What you're proposing, I think, could be described as a 'finite unbounded manifold'.

- it's finite because it is not infinite. So you keep walking in any direction then eventually you'll come back to the same spot. This is the 'wrap around' bit.

- it's unbounded because it has no boundary. So there isn't an area, or edge, or point which could be said to be the frontier - with the Universe on one side and Nothing on the other.

- it's a manifold because that's the mathematical name for regions/volumes that have certain 'reasonable' properties like smoothness ( no jumps or gaps ) and such like.

A circle would be a one dimensional unbounded finite manifold. It's one dimensional because ( even though it exists in a higher dimensional space ) I can describe positions on the circle by one number only - how far around from some given starting point, say. It's finite as any two points can only be at most one half circumference away - 'the long way around is the short way home'. It's unbounded because there is no particular point which separates the 'inside' of the manifold from the 'outside'. There's no gaps, and no jumps. A 'jump' would be if I travel around the circle NOT always by moving to adjacent points : so I 'disappear' from one place and 're-appear' some distance away.

A square in the plane is a two dimensional, bounded, finite manifold. To locate any point I use two numbers, referring to distance along two axes ( up/down and across/back ). I can't have two points further apart than the diagonal length between opposite corners. It is bounded because the edges ( that's why we call them edges ) have a direction/sense separating 'inside' from the 'outside'.

So if the Universe was an infinite, unbounded manifold - of three dimensions - then it would just keep on going, forever, never ending etc ..... what people generally mean if we say 'infinite space'. This is more or less what is usually implied when we draw up a set of 3 mutually perpendicular axes ( x, y and z ). We mark the origin where we denote the zero for each axis, but put an arrow on the axis ends to say 'this just keeps on going, and going, and .... '.

I personally like the finite unbounded manifold idea. It's like a room - say cubically shaped for this discussion - but when you go out through the left wall you come back in via the right. Ditto for floor/roof and front/back. There's no boundary so I can never leave the room, and if there was just two people in it you could only be one half a room away at most. I can reach the other guy by traversing the room space OR by passing through a wall. Whichever is the shortest, say. Now the weird thing is that there doesn't have to be self evident walls, floors or roofs. Travel along a given axis could be just like a circle, as there's no real 'mid point' anywhere along the arc of the circle and no real 'end' to traverse and come back to the 'start'. ( I might choose to mark the zero of my axis somewhere, but that's my arbitrary choice. Any other choice is equivalent. )

What I think your diagram is showing is that galaxy A is really quite nearby galaxy B when we assume some wrap-around, and but not close if we just think in terms of going across the middle ?

Is what you are also showing is different rates of expansion in different 'corners', the effect being for us as perceiving a Big Bang emerging from one of them?

Do tell .... :-)

Cheers, Mike.

I have made this letter longer than usual because I lack the time to make it shorter. Blaise Pascal

## RE: What I think your

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I am proposing that the universe is shaped like a football (an American football!). Matter as we know it is bound to the surface area. Gravity is not bound to the surface area and can travel through the middle of the universe (where the air is in a football). This is why galaxies that should fly apart do not, because of the little extra tug from galaxies on the opposite side of the universe. We will never actually see these other galaxies, because they are quite far away since we are bound to the surface.

Yes!

## RE: I am proposing that the

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Ah, branes and gravity reaching off the brane. We only directly know the aspect of gravity acting on the brane, but because of effects travelling through the 'volume' then we'll see non-inverse-square characteristics at sufficiently large scales. Lisa Randall has had quite a lot to say about this. Apparently there is some hope of LHC being helpful on this one, if I have read rightly, but I couldn't quote the reasoning.

Cheers, Mike.

I have made this letter longer than usual because I lack the time to make it shorter. Blaise Pascal

## Now I am Worried ! This

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Now I am Worried !

This means the â€˜Doomsday Machineâ€™ on Star Trek ,that came

from Andromeda, could be closer than we thought !

## RE: Now I am Worried

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Speaking of Andromeda, Rod posted some absolutely spectacular imagery indeed of that galaxy from the new WISE on the APOD thread. Some dusty places in the universe :)

I think dark matter was introduced to explain the reason why a galaxy's expected rotation curve is different from what is actually observed. Galaxy's appear to have more mass than can be seen with light (electromagnetic interactions), but regardless of what dark matter is made of, it interacts with the force of gravity like normal matter.

Wouldn't that mean that half the universe would be expanding while the other half is on the slow side of the ellipse? Yet the sky looks pretty much the same in all directions beyond our galaxy, which is to say that for all the galaxies beyond our local group, they all appear to be receding from us, equally in all directions and the farther away a galaxy is, the faster it appears to be receding.

The geometry of the universe appears to be flat (with about 98% certainty), as opposed to the shape of a closed sphere (am guessing elliptical shape would be in this category) or an open saddle shape. What would the distribution of microwave background radiation look like if the universe was elliptical in shape? How does that compare with the results from the WMAP?

I think all ideas have some validity with regard to the perceptions upon which they're based. Good to keep asking/searching :)

I'm not very knowledgeable of all the differences between strings, loops, membranes and holography. And if the universe was spherical (or elliptical), but had an infinite radius (not sure how the minor axis of an ellipse could be infinite and still be called 'minor' though), wouldn't that mean that the surface of the sphere is perfectly flat?

Mike, interesting comments on geometries (here and in Rod's New look at gravity thread). Got me to thinking a lot about cubes â€“ not for particles but for spacetime. For a cube, dV/ds = Â½A, right? If spacetime is discrete, tightly packed spheres don't fill all of the volume. I guess a quantum of spacetime could be spherical and overlapping with neighboring spheres, thus filling the entire volume ... but the cube is one of the simplest space-filling shapes, and the inherent orthogonality between all the vertices seems like the natural way that symmetry and rigid connectedness (spacetime warps as a whole implying connections spanning the quanta)coexist ... for a 4-cube (accommodating space and time), there are 8 three-dimensional cubes â€“ home of the 'Eightfold Way' ?

Martin, thanks for the comments on the force already being there, really helps with trying to visualize why calculations have to be done 'instantaneously' with the models & sims :)

## RE: For a cube, dV/ds =

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Yup, for 'normal' 3D shapes dV/ds = SomeNumber * A. The SomeNumber is shape dependent. But this behaviour is simply a reflection of what we mean by 3D anyway : a volume being an area swept along some ( orthogonal ) direction - so the distance along that direction factors into the SomeNumber. If you really want to fry your brain with the possible geometries of space(time) then check out Calabi-Yau spaces/manifolds.

Cheers, Mike.

I have made this letter longer than usual because I lack the time to make it shorter. Blaise Pascal

## RE: Wouldn't that mean

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Yes.

If the universe is extremely large, we won't be able to see any evidence of curvature. So for us, it would all look the same.

The geometry of the OBSERVABLE universe is flat. If you take a picture of the ground from an inch off the ground, you won't be able to see the curvature of the earth. Why would we expect different when looking at the sky? If you were to take a step back you would see that over a period of distances too large for us to see, the universe does have curvature. Also, there is the following quote from http://collidinguniverses.blogspot.com/2009/05/universe-arguments-against-flatness.html

## RE: If you really want to

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Indeed â€“ an arrangement of Calabi-Yau spaces in a space-time-filling array of 4-cubes :)

You're right, HG, that the local geometry can be different than the global geometry. But if the global geometry of the universe is an ellipsoid then that means it's finite â€“ which to me implies an infinite amount of remaining spacetime that more than dwarfs the universe nearly unto insignificance, and so what might such an excess be filled with? I suppose it could be a type of Multiverse ...

To me, the nature of the interaction between light and matter, on the smallest scales observable, implies a stranger and singular (invariant) solution that is 'already there' in infinite extent. Not so much things like entanglement, but more what happens to time and distance when velocity equals the speed of light â€“ things are connected on levels (or dimensions?) for photons in ways that allow for taking all possible paths - as if distance and time weren't there somehow ...