The Universe May Be Shaped Like a Doughnut

NewbieV writes "The NY Times (reg., etc.) is reporting that data from the Wilkinson Microwave Anisotropy Probe may suggest that the universe might be shaped like a doughnut or a cylinder: it might be possible, like in the old video game Spacewar, to drift off one 'side' of the Universe and reappear on the other."

Comments

Observations

[TWX_the_Linux_Zealot]

Then in theory, we'd be able to see the same part of space from two vantage points, assuming that they're not farther away from us than the distance that light could have travelled since the universe came into being, assuming that one believes in the big bang theory.

So, would this mean that if we can't see one point from two directions now, that if we suddenly can, we've reached the halfway point of the life of the universe? Would we lose the redshift in favour of a green shift?

mmm....donuts...

[bravehamster]

I had a math teacher at the Naval Academy that specialized in donut-shaped mathematics. I bet he's calling up all his math friends right now and yelling at them "See! I told you I wasn't wasting my time!" He did have a really cool poster of the earth if it were shaped like a donut and he spent several class periods describing what the gravity and climate would be like on such a world.

dimensions

[planckscale]

A popular theory is that our universe is but a bubble (or doughnut) in a sea of other universe bubbles (or doughnuts); contained and wrapped up into about 10 dimensions. But looking at our universe from another dimension, it may have the appearance of an O or just some contorted blob of goo. This is depending on the relative point and dimension of the observer.

What is outside of the donut?

[CresentCityRon]

Coffee? Void? Dark Matter? Does that question even make sense? I'm not up on this and would be most interested in getting a better understanding of this.

Re:Silly students

[Anonymous Coward]

Nope, they're claiming full 3-torus status for the Universe.

Kind of disappointing, because 3-projective planes are much more fun! Go far enough in any direction and the universe comes back as its mirror image!

Space War Analogy is bad

[crumley]

The Space War anlaogy for a curved universe doesn't really fit. The behavior in Spae War is discontinuous. You start out on one edge of the screen and after going past the edge of the screen, you are magically transported to the other side.

In certain types curved universe the behavior would be quite different. If you start out going in one direction and continue going long enough, you may end up where you started. There would be nothing discontinuous about this motion though. A "straight" path in a curved universe isn't really what we would think of as straight. As you go along your "straight" path the stars that appear to be ahead of you would impercibly change as time wore on. Eventually you could end up back where you started, but considering the likely size of the Universe, it might take you longer than the age of the Universe to do it.

Anyway, curved space is weird to think about, but not as weird as Space War.

Dr. Tegmark's original paper on the web

[LinuxParanoid]

There's also a BBC story on the same topic, or you can go straight to Dr. Tegmark's webpage version of his paper (with cool pics).

I've admired Dr. Tegmark's home page since he was a grad student, not so much for the design skills (ha!) but as an exemplar of mixing serious and non-serious publications for other colleauges and onlookers to enjoy, explore, and learn from. Tegmark gets the web. As for the science, some of it I can actually understand.

I would also commend to the curious Slashdot reader a couple items I found facinating from the 'non-serious' section of his website:

a very cool diagram of "Relationships between various basic mathematical structures" from his Theory of Everything paper

and another paper addressing the question: Why does the universe have 3 spatial and 1 time dimension?

--LP

A Thought...

[solarlux]

Interesting... let's assume for a moment that the universe's expansion was frozen.

Now, if I threw a baseball in a straight line from point x,y,z in the universe, at some point, that baseball would again pass through one of the planes of its starting location? (I'm neglecting all interferences, including gravity)

3-d space curving ... hmmmmm... I'm having trouble picturing what this 3-d curvature would look like. Anyone have a helpful mental image of this?

Re:The shape of a doughnut?

[Nihilanth]

the donut analogy is a bit of a gloss. The interior space of the torus dosen't represent the three dimentional space we inhabit, rather, the path you take around the inside of the torus is supposed to represent all three dimentions, simplified as a vector in the torus...so, picture being inside the torus, and travelling all the way around the interiour of it and coming back to where you started...well..there's no way to visualize this situation for all three dimentions, but the torus is as clear as you can make it. Don't think about what happens if you travel to the inner or outer wall, that would be equivilant to "leaving" space in this simplified abstraction.

Black hole from the inside.

[Ungrounded Lightning]

Remember the rubber-sheet/morning glory shaped deformation model of gravity? Some time back I recall a description of a black hole as dropping such a BIG marble on the rubber sheet that it keeps going down, stretching the "rubber sheet" forever, at least as fast as the speed of light. Think a "taffy sheet", or a "stem" of the "morning glory" stretching like a stream of honey.

It's easy to see why enough gravity keeps light ORBITING the gravity from spiraling out and away. But this also explains why light going STRAIGHT AWAY from the center of the hole never gets out - space is being stretched at least as fast as it moves (or maybe even faster), so it never makes it out of the hole.

Well, this got me thinking: "What does a black hole look like from the INSIDE? What would one see from the viewpoint of the matter that was already there when the event horizon formed?"

And the answer seemed to be: "An expanding universe, starting from a very small but finite volume and expanding indefinitely, containing a large-but-finite amount of matter, which was initially compressed into an EXTREMELY dense lump - perhaps a quark fluid or denser."

In other words, something like the current universe. Perhaps with the moment of the formation of the event horizon corresponding to the end of the big-bang model's "inflationary period", but eliminating the need for a faster-than-light inflationary period.

Cosmic background becomes the layer of matter and energy just below the event horizon, which is just getting here now. Cosmic background structure represents the matter distribution at that level at that time - a fossil of the orbital dynamics of the accretion cloud. (I don't think you get to see an "inside view" of the infalling half of the Hawking radiation.)

You can go in any direction at up to the speed of light and never reach "the edge", which is (from your viewpoint) receeding at lightspeed.

Not being a professional physicist, at this point I haven't attempted any mathematical models or resolutions with any of the current cosmological models. So I have no idea if I'm just spinning a yarn or if this can be pounded int shape for testing against the real universe. But it might be interesting to try some time.

(The concept of gravity indefinitely stretching the coordinate system also leads to another possibility: Can gravity be modeled as masses constantly "sucking up" the coordinate system, which stretches between them meanwhile?)

Re:Black hole from the inside.

[Anonymous Coward]

Why? The more it stretches, the more of it there is to stretch. You're constantly creating more coordinate system.

There's no such thing as "creating more coordinate system".

No quantum limit on the INSIDE at all.

As the curvature grows, quantum effects take over and space can no longer be described as a smooth sheet.

Nope. That large-but-finite mass being smeared out into a seemingly infinite volume of space is the sea of quarks (or whatever) that started out as the matter forming the initial black hole.

Actually, all that mass collapses to a point in a finite time --- from its own perspective.

The stretching of space is what lets it escape its mutual gravatation sufficiently to thin out, cool down, become atoms, stars, supernovae, solar systems, and eventually evolve observers like you and me.

That doesn't actually happen in a black hole. If, say, a 10-solar mass star collapsed into a black hole, then an observer standing on the surface of the star would see the star underneath him, and himself, be crushed down to zero volume in less than 150 microseconds (according to his own watch and meter stick).

Space does not expand inside a black hole. This is true regardless of who the observer is.

Seems to me that beneath the horizon you'd see an infinite space (or at least as much of it as light leaving at the "big bang"/"horizon forming" moment could have reached), filled with the matter that was inside the event horizon at the moment it formed.

You'd see a whole lot of nothing, because the original collapsing star would be long gone, as would its light. (Unless you fell in as the star collapsed; then you could watch its surface collapse underneath you.) There certainly won't be any matter further out from you, if it fell in before you.

Look far enough in ANY direction and you're looking at the event horizon

No. You can look in directions that don't end at the event horizon.

I've always been uncomfortable with a faster-than-light "inflation" phase. That seems like a kludge to rescue the extrapolation of an expanding universe backward to a point.

Inflationary theory has nothing to do with the universe's origin as a singularity. It was not introduced to be compatible or incompatible with that.

This way you never GET back to a point - because you never came from one. The closest you get to a point is the center of mass of the matter trapped in (and forming) the new black hole.

It still doesn't look like an expanding universe from the inside. It looks like lots of things collapsing inward, and it all ends very quickly.

Re:The WMAP site says otherwise

[Dynedain]

except that there are theories that other 'insides' exist in the 'outside'....complicated as that may seem

The Universe is Flat, not Doughnut shaped.

[itistoday]

From their site:

"The Inflationary Theory, an extension of the Big Bang theory, predicts that density is very close to the critical density, producing a flat universe, like a sheet of paper. WMAP has determined, within the limits of instrument error, that the universe is flat"

Last I heard doughnuts aren't flat.

Re:Going around it in different directions.

[Anonymous Coward]

Does this really work with the idea that in space, there is no privileged point of view? This would essentially give space a directional system where we're used to thinking of it as going on and on without a standard up or down, center or edge.

In a toroidal universe, there are indeed privileged directions. (This does not violate the relativity principle, however. That only requires space to be locally isotropic -- that you can't determine a preferred direction by doing experiments within a small closed box. If you made the box the size of the universe, it would be a different story.)