RE: Deciphering the monsters of our universe, aka black holes
Hello @lemouth
First, one starts from the fact that the universe is a flat surface to a very good approximation. This does not come from nowhere. We have very strong measurements (i.e. data) pointing to this conclusion.
You're definitely right here, it sounds weird. I don't know much or anything about General relativity. But I was thinking since the universe was made of space and time, how is it a flat surface (where does the depth comes from, if it was a surface?).
Thoughts like; are we (our planets and stars) on the universe just like we (humans) are on earth.
What defines the universe? I mean if the universe was some surface, it should be contained in some other material that has a volume, since space itself is a quantity that has volume.
All these thoughts are just coming to my mind.
I'm not as smart as my username 😢.
Some hints below that maybe will help you (otherwise please come back to me).
Everything likes in the definition of flatness (and of surface by the way). As I said in the post, a cylinder is a flat surface. It is all a matter of shooting parallel lasers and have them never crossing each other.
We have the observable universe that is well defined. For the rest, we can speculate anything as it is impossible to test it and verify it.