The universe is a big balloon and we live on the skin…
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So if you go far enough in a straight line, you end up where you started? 
Sort of. If you could travel at infinite speed, yes. But you cannot travel at infinite speed. As mere matter, you can only travel, at maximum, close to the speed of light. For very large distances, the universe is expanding, effectively, faster than the speed of light. So you can never “circumnavigate” the universe. An anaogly is a bug crawling on the surface of a balloon, trying to get from point A to point B on the surface of the balloon. If someone is blowing up the balloon, causing point A and point B to move away from each other (the surface area of the balloon itself is getting bigger), and the two points are moving away from each other faster than the bug can crawl, no he will never get to point B.So if you go far enough in a straight line, you end up where you started?
ljwilley
I’m pretty sure it will work…
Have you ever thought about seeing stars in the sky this way: What you are seeing up there is years premature! The stars are lightyears away therefore you are seeing what they looked like that many years ago! Some of the stars you see may not exist anymore in real time.
Here is a good website explaining how the universe can expand faster than the speed of light.
https://www.skyatnightmagazine.com/space-science/does-universe-expand-faster-than-light
The speed of light is as fast as matter and energy can travel through the universe, that is, through the space of the universe. But space itself is expanding, carrying objects with it, and, effectively, making the objects move “away” from each other. The expansion rate of space itself is not limited by the speed of light. Space is stretching at a rate of about .007 percent every million years. If two objects are close together, like our Sun and Alpha Centauri (4.3 light years apart at present), .007 percent of 4.3 light years over a million years is not very fast effective movement. But if two objects are already far away from each other, 20 billion light years, for example, then .007 percent of 20 billion light years every million years is fast “effective” movement due to the ecpansion of space itself. In fact from the perspective of someone in one of those galaxies, the other galaxy is receding away from the person’s galaxy at faster than the speed of light.
https://www.skyatnightmagazine.com/space-science/does-universe-expand-faster-than-light
The speed of light is as fast as matter and energy can travel through the universe, that is, through the space of the universe. But space itself is expanding, carrying objects with it, and, effectively, making the objects move “away” from each other. The expansion rate of space itself is not limited by the speed of light. Space is stretching at a rate of about .007 percent every million years. If two objects are close together, like our Sun and Alpha Centauri (4.3 light years apart at present), .007 percent of 4.3 light years over a million years is not very fast effective movement. But if two objects are already far away from each other, 20 billion light years, for example, then .007 percent of 20 billion light years every million years is fast “effective” movement due to the ecpansion of space itself. In fact from the perspective of someone in one of those galaxies, the other galaxy is receding away from the person’s galaxy at faster than the speed of light.
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Too much to comprehend.
Check out the “loaf of raisin bread” analogy in the article. That’s a very intuitive example of how the universe expands. Say there are two raisins in some raisin bread dough. Say they are one inch apart. When you bake the raisin bread, the entire loaf expands. The two raisins are carried along with the expanding bread, moving away from each other until they are two inches apart. You can think of the raisins as galaxies and the bread as the universe - space itself.
So to continue that thought - all the stars I see at one glance in the night sky are all at different times lengths (and distance) away from me. I see one star as it was 1 billion years ago, another star I see is as it was 2 billion years ago.
Trying to imagine that graphed out, or on a spreadsheet - it would be very spikey/noisey indeed!
That's actually an open question. The best current measurements say the "space" part of spacetime is very flat, so it's less like a spherical balloon inflating and more like a big flat sheet of rubber stretching itself out in all directions.So if you go far enough in a straight line, you end up where you started?
But "very flat" isn't the same as "exactly flat" so there could be a small positive curvature that eventually makes space wrap around into a sphere. There's also the possibility of a small negative curvature, which forms shapes that are hard to explain because they don't have nice two-dimensional surface-in-three-dimensional-space analogies. Some of these are finite and some of them aren't. And also there are solutions for flat space that still manage to wrap around onto themselves to become finite.
That's something that I've pondered... We are standing on a sphere, and the further we look out in any direction, the "surface" is actually that of a smaller universe.
Like a hetamap - only use female colors (3.2 million), not male colors (16)! 
https://en.wikipedia.org/wiki/Cosmic_microwave_background
https://en.wikipedia.org/wiki/Cosmic_microwave_background
We're TRAPPED in the middle of the bubble! Here comes multiple dimensions, I can just feel it...!
NateB
Well-Known Member
So if you go far enough in a straight line, you end up where you started?
I have a theory that someone has written song lyrics for every situation.
3rd Planet by Modest Mouse
"For the Universe is shaped exactly like the Earth, if you go straight long enough, you'll end up where you were."
/tangent
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