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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."
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More images from probe homepage
Did anyone here actually *read* A Brief History of Time? Hawking described how the gravity of the universe may be so intense that it causes the universe to wrap around into a spherical shape. Of course this was just a theory back when he wrote the book.
Actually....in the episode where the Mensa society runs Springfield, Stephen Hawking shows up, and at the end says: "Homer, your idea of a doughnut-shaped universe is intriguing. I must steal it for my next book."
I'm out of my mind right now, but feel free to leave a message.....
Actually, no, they didn't. n-dimensional universes -- if they are compact -- are shaped like n-tori, not n-spheres. The question is quether they have genus one (and are thus flat) or have genus 2+ (are have negative curvature.)
We're talking about a Torus, not a spherical universe. If true, the universe is still 'flat', there's no 'wrapping' as you put it, it just repeats in all directions.
I am a science fantasy fan
The article says that an experiment is going on that could find this out, but it is only possible to measure up to 28 billion light years which is most likely too small, even if the universe is finite.
Though I could be wrong, I think the opposite of redshift is blueshift, not greenshift.
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Yes we could see "the half way" point, however there red shift would NOT become green shift (there is no such thing) or blue shift (which does exist) because each point of view would still see things in that direction as getting further away. Think of the donught getting larger....just becuase you know where the oppisites side is doesn't mean taht things getting further from the right get closer to the left. In fact it wouldn't even effect the amount of redshift.
Well, firstly, it has long been thought that the universe was closed. This is just suggesting that the universe might be topologically equivalent to the equivalent of the hypersurface of a hypertoroid, rather than the hypersurface of a hypersphere, as previously assumed.
Secondly, the opposite of a red-shift is a blue-shift. The complementary nature of red and green is a property of human eyes, not of the light itself. Red light is lower in energy; blue light is higher. Things rushing away from us as space expands would leave light from distant objects moving more slowly relative to us if not for special relativistic effects. With the effects, the energy of the light is reduced. However, you're right... when an object is approaching you, light from it is blue-shifted, and that would be what we should expect when the universe starts collapsing.
The question is assumed to not make sense. The surface of a torus has topological properties similar to that of the universe (according to the article). It's just a statement about what happens when you move a long way in one direction and how points in the universe can be reached from one another, not an assertion that the universe is sitting in some hyperdimensional 'space' outside the universe.
Hawking described how the gravity of the universe may be so intense that it causes the universe to wrap around into a spherical shape.
IIRC, Hawking was talking about the shape of spacetime in that section. And in fact, the results from WMAP indicate that the universe will expand forever, contradicting that particular model of spacetime.
When these people say that the universe may be shaped like a donut or like a cylinder, they are supposing that spacetime can be expressed as the product of a space part and a time part, and that the space part is shaped like a donut (or whatever).
In this model the space part would be the 3-torus T^3, the time part would be an open interval I, and spacetime would be IxT^3. Good luck on visualising that!
oops..i got it backwards.
imagine travelling across the SURFACE of the torus.
whoops!
Even if the hypertori topology of the universe is correct it doesn't imply that the universe has any particular curvature, it's still possible that it has positive, negative or flat intrinsic curvature.
You have to remember that the curvature of a torus embeded in 'flat' 3 space is purely an artifact of that embeding and not intrinsic in the topology of the torus. More specifically, there exist mappings from the embeded (intrinsicly curved) surface of the three dimensionally embeded torus to topologically identicle spaces that have everywhere flat intrinsic curvature.
As a thought experiment, consider a cube where the faces are portals to their oposites. Internally, this construct has the topology of a hypertorus but an everywhere flat topology.
For some nice diagrams and comentary that explain curvature (of the important, intrinisic kind) rather well, take a look at this, just skip over any of the math thats beyond your abilities, it's not really needed to understand the concepts.
Realities just a bunch of bits.
Imagine space as a rubber sheet with a grid of dots (atoms/particles/etc) on it; as space expands ( you stretch the sheet in all directions) all of the dots get farther from each other. My understanding is that matter itself isn't really flying outward, but space itself is stretching so that everything seems to be growing farther apart (so no matter where you're looking from, light gets redshifted). Recent studies lead to the conclusion that eventually the rubber sheet of space will be stretched so much that the dots (atoms/particles/etc) will be so far apart that the attractive forces cannot bind them any longer; at that point the universe undergoes the "Big Rip" and everything disintegrates into nothingness....
Why do we even assume a simple symmetrical shape? For example, what is to stop universe from being Klein bottle shaped? Or perhaps the universe is a hypersphere, but has dimples like a golf ball. I'm really curious.
If the universe began as a point object (planck-scale sized) and was extremely uniform to begin with, then this uniformity would be reflected in its shape later in life.
OTOH, some of the newer ideas about scalar fields and self-replicating universes would give a contorted, infinitely complex shape on a large scale (imbalances would magnify themselves).
The simplest answer is "because it makes the math easier" (cue mathematician/physicist/engineer jokes...).
A different dimension. Maybe another alternate universe. Our donut may be one of many other donuts. As far as 4th-dimensional creatures like us our concerned, if you could look from 'outside' our universe, everything could look like a big blob within a dark void
As the donut (or sphere or what-have-you) represents space itself, the concept of something "outside" it doesn't really work. Only relationships between different parts of the universe are defined. Treating the universe as the surface of some object is just a trick to make it easier to visualize (otherwise it would just be a set of functions defining relationships between points).
Some of the inflationary models put the universe we can interact with within a larger space, but that just gives us disjoint parts of one larger universe. Much like the event horizon of a black hole, the interface between them would represent a boundary across which interaction and information flow is restricted, and different space/time coordinate systems would be used inside and outside them. (The inflationary bubble looks like an infinite space from the inside and an expanding bubble from the outside; all points on the boundary look like they're at the beginning of time from the inside.)
So, no Voyager-esque bright expanding shell or external vantage point in the simplest scenario, and something a bit different from what you're probably envisioning in the various inflationary models that posit bubbles within larger spaces.
Black holes, like quantum mechanics, are not something you can reason about using your newtonian-evolved intuition. So don't feel too bad.
The manifold within an event horizon has significantly different properties than without. Outside the event horizion, the manifold is "timelike", meaning you are free to move in space but limited in time. Inside, the manifold is "spacelike", meaning you are free to move in time, but your direction in space is limited. At this point, analogies become difficult.
You can generate multiple event horizons around a black hole. You can get one from mass, and another one from angular momentum. If you pass through both of them, I think you go back into a timelike region. But don't ask me what things are like in there, I gave up on physics and switched majors to comp sci.
If you know anything about topology, you'd know that coffee cups are doughnuts.