Imagine an impossible journal

You mean 'isotropic'? I thought this was a near-requirement of most cosmological theories, especially those invoking inflation.

Isn't this an issue of geometry, quite distinct from the above isotropy?

 

Completely out of my depth here, but anyway: I recall watching a show on astronomy, and there was comment about there being an anomaly in the appearance of spiral galaxies. When they consider the galaxy's theoretical speed of rotation, it seems the spirals don't appear as they "should", they should be smearing out more, but look like a slower rotation is occurring. They went on to say that so far, they're not sure why.

Maybe some local warping of space? Just looking at a few pics, I got thinking: if the center of the galaxy was somehow "receding", like you're looking down a tunnel, would that explain the spiral shape anomaly?? do not know, back to sleep, lol.

 

why would they arrive back on earth, instead of continuously moving away from it?

 

hard to picture. i have thought this since childhood. what's outside?

 

If the universe is a spherical shape, or if when you drop off one edge you appear at the other like a 1980s era video game

 

that's what i mean. you're saying there is nothing when you go beyond the screen?

 

Who knows. Some think there are whole other universes there, possibly an infinite number. But many of the theories say even though other universes exist we have no way to leave ours (part of where the closed universe idea comes from). I am not an expert on it but I have always found it really interesting.

Here's one question I have. It's always said the edge of observable universe is about 13.6 billion light years away, and that the light from that area was emitted 13.6 billion years ago. And the same for all things we look at, just at smaller distances. But since the universe is expanding, weren't those things closer to earth when the light we see was emitted? So shouldn't the light actually be somewhat younger than that? Maybe I am thinking of it wrong

 

Do note that the most distinct arm structure appears in blue light, which is dominated by the largest and hottest and brightest stars, which also have very short lifetimes. Most of them won't live for a full orbit around the core, so don't drift far from the cosmic shock waves and violence that spawn them. When viewed in red light, the color of the smaller and cooler and dimmer stars that live many billions of years, the arm structure is far less distinct. Those stars live for many many orbits, and they do 'smear' a lot more.

If I recall correctly, the elliptical galaxies (no arm structure) tend to have mostly older red stars, with a significant shortage of the blue stars. By cosmological standards, the bright hot blue stars are always very young, burning out rapidly.

Some young-earth proponents don't make this distinction, and use the lack of 'arm smearing' of the bright blue stars as evidence that the universe cannot be old.

Open vs closed, bounded vs unbounded, Euclidean vs Reimann vs spherical, I thought that those were still TBD. Though cosmological inflation does push strongly for near-Euclidean geometry, and observations remain consistent with that, with no evidence of non-Euclidean variants yet appearing.

Flip your viewpoint -- those were the distances when that light was emitted. They are farther away now.

'The edge of observable universe' is merely the edge of what we can see today. As time progresses, that boundary keeps pushing back. It does not mean there is any true 'edge of the actual universe' anywhere near there, the universe likely extends far beyond, out of view. Though there are some pretty wild theories of what might be.

 

Yeah, just the limit of our "headlights".