Yes the idea of a universe that is finite and unbounded is a bit hard to grasp. Its kind of like this. Look out in any direction, any direction at all, the view is exactly the same. We appear to be right smack dab in the middle of it all. Which we are. Always. Everyone everywhere is right smack dab in the middle. Dudes on some star way over in Andromeda? Yeah those dudes too.
We have a hard time drawing this, and its even harder to visualize, I sure never can, but its kind of like this. Mass curves space time. Not a lot. Takes a lot of mass. Even so you have to be pretty close. But Einstein math'd it out and some years later when they observed the orbit of Mercury with great enough precision sure enough, the planet was exactly as much slower as relativistic physics said it should be. So math curves space time.
Another way it has been observed to do this is with very distant galaxies. Yeah here ya go https://www.universetoday.com/wp-content/uploads/2014/11/Gravitational-lensing-galaxyApril12_2010.jp...
So now notice how the massive galaxy cluster curved space time around it? The light actually travels a straight line. Its the straight line that's curved. Well it only looks curved because of our frame of reference. Hey don't blame me! I didn't make the rules! Just telling it like it is. To the extent of our current understanding anyway.
So obviously (its obvious, right?) the whole mass of the whole universe is doing exactly the same thing. Curving space-time. Curving it so much it wraps around on itself like a ball.
Only it can only appear that way from outside. Same as the Earth can only appear spherical by leaving the surface and going out into space. Perspective. From here on Earth it appears quite flat. Or at any rate two dimensional. So it is with our finite, unbounded, universe.
We have a hard time drawing this, and its even harder to visualize, I sure never can, but its kind of like this. Mass curves space time. Not a lot. Takes a lot of mass. Even so you have to be pretty close. But Einstein math'd it out and some years later when they observed the orbit of Mercury with great enough precision sure enough, the planet was exactly as much slower as relativistic physics said it should be. So math curves space time.
Another way it has been observed to do this is with very distant galaxies. Yeah here ya go https://www.universetoday.com/wp-content/uploads/2014/11/Gravitational-lensing-galaxyApril12_2010.jp...
So now notice how the massive galaxy cluster curved space time around it? The light actually travels a straight line. Its the straight line that's curved. Well it only looks curved because of our frame of reference. Hey don't blame me! I didn't make the rules! Just telling it like it is. To the extent of our current understanding anyway.
So obviously (its obvious, right?) the whole mass of the whole universe is doing exactly the same thing. Curving space-time. Curving it so much it wraps around on itself like a ball.
Only it can only appear that way from outside. Same as the Earth can only appear spherical by leaving the surface and going out into space. Perspective. From here on Earth it appears quite flat. Or at any rate two dimensional. So it is with our finite, unbounded, universe.