However, this theory says it mirrors. So, it is more like a computer monitor that either A) reflects the mouse pointer, turning it 180 degrees and as you keep moving up and hit the edge, you start coming back down, even though you keep moving up, and so on. Things just bounce around forever in perfect Newtonian laws. Or B) you can set your monitor up to "wormhole" the mouse from the top to the bottom. When you hit the top edge, the mouse reappears at the bottom and keeps going up again. It's analogous to (B), in fact.
So you are perfectly correct. Outside the universe is undefined. However, if this theory is correct, it still must exist. No. A space defined by topological "mirroring" does not have to have an "outside".
Otherwise, we come to this conclusion:
We find in the future that the distance between the "mirrors" is X lightyears. Why that size and not another? You can ask the same question of any universe, not just a "mirrored" universe. And the question has nothing to do with whether the universe has an "outside".
If it fluxuates at all, it is expanding "into" something or contracting "from" something. A universe can expand without there being something "outside" the universe into which it expands. The expansion of space can be defined purely intrinsic to that space, without reference to any exterior embedding space.
It is possible for our universe to be embedded in a larger, "outside" space, but it is not necessary.
I thought they didn't and rather thought that the universe was about 180 billion ly large and that we were somewhere in there, not being able to tell where exactly since we can only see about 13.8 billion ly away. Astronomers think the universe is about 13.8 billion years old. They think the observable universe (the part we can see) extends about 50 billion lightyears in any direction. The entire universe is often believed to be infinite within the context of inflationary cosmology.
And don't tell me that we/they are supposed to think that there's something (even if it's only vaccum) out of this huge 180 billion ly large ball because we couldn't get there even if we were on the edge of the universe (I wonder what we'd see tho) There is no edge of the universe, as far as we know. The universe is either believed to be infinite or finite but unbounded; in either case, there is no edge.
And by the way, why do we care about the background microwave radiation to determine the shape of the universe? I mean what does it have to do with it, besides to give information about the early universe? We care for the reason you state: it gives information about the early universe. If the universe is finite and multiply-connected, as suggested in this story, it's possible for light to circumnavigate the universe and reappear somewhere else, giving multiple images of the same source. Light emitted recently won't have had time to travel that far, but light emitted long ago (such as the CMBR) may have.
If you were in a spaceship hovering just above the event horizon of a black hole (accelerating away from is just sufficiently to keep that distance) - and neglecting for the moment that you couldn't biologically survive that sort of acceleration - then looking out to your left or right, toward the "horizon" of the sphere contained within the event horizon, you would see in the distance your own self, however many light-seconds in the past it takes for light to travel around the black hole, correct?
Only if you're at the "photon sphere" (1.5 times the Schwarzschild radius); that is the location at which light can circularly orbit a black hole. Outside the photon sphere light will spiral outwards from the black hole, and inside it it will spiral inwards, and in either case will not return to you where you are hovering.
For some visualizations of what it looks like to hover near a black hole, see Greg Egan's applet and summary.
So my question is, under high acceleration in open space, such that you have this "acceleration black hole" behind you, would you see the same sort of effects? Look left or right or up or down (here saying the black hole is "behind" you rather than "below" you as above) or anywhere along the circle perpendicular to your line of motion, and you'd see the image of your own spaceship? If so, how does that work? And if not, why not?
This "acceleration horizon" (the Rindler horizon) is not a sphere, so light cannot orbit it. It's more like a "wall".
Basically, it boils down to if the universe is finite, it therefore has shape and bounds right?
It has a shape (regardless of whether or not it is finite), but it doesn't have to have bounds (even if finite). A spherical surface is finite, but unbounded.
In this particular case, we are comparing it to a soccer ball.
Actually, we're comparing it to a soccer ball (well, not really) with some of its faces topologically identified. If you take a square and topologically identify opposite edges, you get a finite and unbounded torus. The topology discussed here is more complicated.
But if it has bounds, then what is beyond those bounds? Is our "universe" inside a larger finite shape? or is what contains our universe infinite?
The universe is not believed to have bounds or to be contained inside any higher-dimensional space, except in certain speculative "braneworld" scenarios. Thus, in standard cosmology, there is no such thing as "outside of our universe".
Slashdot Mirror
We find in the future that the distance between the "mirrors" is X lightyears. Why that size and not another? You can ask the same question of any universe, not just a "mirrored" universe. And the question has nothing to do with whether the universe has an "outside". If it fluxuates at all, it is expanding "into" something or contracting "from" something. A universe can expand without there being something "outside" the universe into which it expands. The expansion of space can be defined purely intrinsic to that space, without reference to any exterior embedding space.
It is possible for our universe to be embedded in a larger, "outside" space, but it is not necessary.
Tangential question here:
No pun intended?
If you were in a spaceship hovering just above the event horizon of a black hole (accelerating away from is just sufficiently to keep that distance) - and neglecting for the moment that you couldn't biologically survive that sort of acceleration - then looking out to your left or right, toward the "horizon" of the sphere contained within the event horizon, you would see in the distance your own self, however many light-seconds in the past it takes for light to travel around the black hole, correct?
Only if you're at the "photon sphere" (1.5 times the Schwarzschild radius); that is the location at which light can circularly orbit a black hole. Outside the photon sphere light will spiral outwards from the black hole, and inside it it will spiral inwards, and in either case will not return to you where you are hovering.
For some visualizations of what it looks like to hover near a black hole, see Greg Egan's applet and summary.
So my question is, under high acceleration in open space, such that you have this "acceleration black hole" behind you, would you see the same sort of effects? Look left or right or up or down (here saying the black hole is "behind" you rather than "below" you as above) or anywhere along the circle perpendicular to your line of motion, and you'd see the image of your own spaceship? If so, how does that work? And if not, why not?
This "acceleration horizon" (the Rindler horizon) is not a sphere, so light cannot orbit it. It's more like a "wall".
Basically, it boils down to if the universe is finite, it therefore has shape and bounds right?
It has a shape (regardless of whether or not it is finite), but it doesn't have to have bounds (even if finite). A spherical surface is finite, but unbounded.
In this particular case, we are comparing it to a soccer ball.
Actually, we're comparing it to a soccer ball (well, not really) with some of its faces topologically identified. If you take a square and topologically identify opposite edges, you get a finite and unbounded torus. The topology discussed here is more complicated.
But if it has bounds, then what is beyond those bounds? Is our "universe" inside a larger finite shape? or is what contains our universe infinite?
The universe is not believed to have bounds or to be contained inside any higher-dimensional space, except in certain speculative "braneworld" scenarios. Thus, in standard cosmology, there is no such thing as "outside of our universe".