From New Scientist via StumbleUpon comes a finding that may be just weird enough to be true.

It's long been thought that the Universe could be finite, though expanding. A good analogy is to imagine a flatland in 2 dimensions. Rather than this 2D universe being flat like a piece of paper of infinite size, it's more like the surface of a slowly expanding balloon. So if a flatland spaceship travelled in its 2D space in a straight line, it would eventually arrive back where it started. The inhabitants would deduce that their 2D space must be curved in some higher dimension they can't perceive, only deduce.

So what would be the effect of a higher dimensional curvature on our own 3D space? With a powerful enough telescope, we could look in certain directions, and see an image of things at the edge of perception. We'd expect to look in the opposite direction, and see the same thing. Except that doesn't work too well, as we'd expect to see the same sort of thing no matter which way we look, and that's not compatible with a sphere, the Universe would have to be faceted, one of the regular solids - a tetrahedron, a cube, an octahedron, a dodecahedron, or an icosahedron.

It would be likely that each facet would appoximate a disk - and the closest approximation is each pentagonal side of a dodecahedron.

The idea of a balled-up universe was first proposed in 2003 by Jean-Pierre Luminet at the Paris Observatory, France, as a way to explain some odd patterns in the cosmic microwave background - the afterglow of the big bang. The CMB contains warmer and cooler splotches, which reflect the density variations of the universe in its youth. This fits nicely with cosmological models, except that if you blur the microwave map into big enough pixels, the splotches disappear and the map looks less random than you'd expect - and nobody can explain why.

Luminet and his colleagues suggested that this might be because the universe is finite, but is wrapped around on itself. This means that if a spaceship could cross the universe and "exit" through one side, it would still be in the same region of space but would "re-enter" from the opposite side of the universe. Because of this wrap-around effect, images of everything in the universe would appear to be repeated in the CMB. The best way to explain the data was if the universe is like a dodecahedron - a ball-like shape with a surface of 12 identical pentagons.

Boudewijn Roukema, an astronomer at the Nicolaus Copernicus University in Poland, and his colleagues have reached another conclusion: the team "cut" rings from a version of the WMAP data taken from opposite sides of the sky, twisted the cut-out rings relative to each other and looked for matches. They also considered variations in the orientation of the entire dodecahedron over the sky to ensure that some of their pairs of rings were cut from opposite flat sides of the dodecahedron instead of from its corners or edges.

They found that those rings were a close match if one ring was rotated by about 36 degrees around their perpendicular axis (see Diagram). Importantly, calculations for a dodecahedral universe predict that this is the angle you would see.

So how big is the Universe? Quite small, really. From the original 2003 New Scientist article, before the 36 degree twist was found:

If confirmed, they would indeed be stunning. They would mean that the Universe is relatively small, something like 70 billion light years across. What's more, we could in theory see the entire cosmos and check that there are no hidden corners where the laws of physics are different.Like many hypotheses in Science, it may not even be in the right ballpark (so to speak). But the evidence is getting stronger that this may indeed be the case.

For instance, it would rule out exotic ideas such as chaotic inflation, which suggests our local Universe is just one of myriad expanding bubbles beyond eyeshot, each with slightly different physical laws.

It would also banish the philosophical paradoxes of an infinite Universe, such as the idea that every person on Earth has an infinite number of alien doubles leading parallel lives. "If we could prove that the Universe was finite and small, that would be earth-shattering," says David Spergel of Princeton University in New Jersey. "It would really change our view of the Universe."

## 5 comments:

As any Trekker knows: "The universe is a spheroid region, 705 meters in diameter."

At least, that's one of my favourite quotes from ST:TNG :)

First off, we're not seeing all the way back to the beginning; that was even long ago than we have seen. Besides which, we haven't seen all that big a piece of the universe 14 giga years ago.

I was thinking 40 billion light years across BTW. Figure 20 billion light years to the starting time, then double that to get the diameter as opposed to the radius.

One question I've always had is how can the universe be larger than it is older, given the limitations of the speed of light?

Even taking into consideration E=mc^2, and given the amount of energy presumably given off by the big bang, how much faster than the speed of light would the original expansion (say within the first few hours or days) have to be moving to ensure that it is as large as it is today, and how much energy would it have consumed? My calculus and diff. equations aren't up to snuff yet, and I haven't been able to figure it out on my own.

I've been devouring the available physics books in my local bookstores, but no one, not even Smolin or Feinman (sp? I don't have a book in front of me) gives a clear answer about this. It's been nagging at me for almost a year now, since I got back into the study of theoretical physics, and not being able to find an answer is driving me nuts.

So now we know what dice God uses. But how many D12s is It rolling?

How interesting

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