71–80 of 120 posts
Earlier quoted context omitted.
Wouldn't the center be the Big Bang and the 3D Universe at the current time (if Relativity lets me write about a current time) be the 3D surface of the 4D sphere (or spheroid) that the Big Bang is creating by keeping to expand?
the big bang happened everywhere
Rotation relative to what?
Rotation is absolute. Unlike linear motion, you can tell if you're sitting in a rotating frame of reference or not. Experiments such as the Coriolis force, and Foucault's pendulum, are demonstrations of this principle.
In fact, a historical oddity is that when this idea was nailed down by both theory and experiment, the Catholic Church dropped its ban on heliocentrism. (Not that it mattered, the horse had already left the barn).
Universe is called universe because it is the only one. Everything that exists should be part of the universe. When we say the universe rotates, what does it mean? Rotate relative to what? Does it mean that there's a larger "universe" that contains ours?
Oops, it turns out we used the name too soon.
When people say "universe" these days they mean the "visible universe" (or maybe the visible universe plus the stuff we're sure is there, but that falls outside our light cone now) - and not the original definition of the word anymore.
(Not that we have "found" anything else yet.)
Rotation relative to what?
I consider this to be a good question, but with a reasonably familiar answer: Rotation is absolute. Unlike linear motion, you can tell if you're sitting in a rotating frame of reference or not. Experiments such as the Coriolis force, and Foucault's pendulum, are demonstrations of this principle. In fact, a historical oddity is that when this idea was nailed down by both theory and experiment, the Catholic Church drop…
Earlier quoted context omitted.
Wouldn't the center be the Big Bang and the 3D Universe at the current time (if Relativity lets me write about a current time) be the 3D surface of the 4D sphere (or spheroid) that the Big Bang is creating by keeping to expand?
the big bang happened everywhere
There's really no way to know if there was something in existence before the big bang however. We just lack evidence of such a thing.
Earlier quoted context omitted.
Why is that? I've heard this before but don't understand what it actually implies. Like, why can't 2 things meaningfully be half a Planck distance apart?
Imagine that at some small distance, space itself is quantum, so quantized. I.e. at the bottom, space is a discrete graph with incredibly small edges. Possibly very tangled and not even layed out in obvious dimensions over short distances. We don’t know if that is the case. That is only one possibility. But it seems very clear that whatever happens at the Planck distance or lower isn’t simple smooth space as we model…
Earlier quoted context omitted.
Why is that? I've heard this before but don't understand what it actually implies. Like, why can't 2 things meaningfully be half a Planck distance apart?
Imagine the universe is made out of graph paper, with only the points of intersection of the lines being actually "real". That is, space is actually discrete. If that is true, then you cannot meaningfully talk about things being "half a square" apart. People (some people) think that the universe really is that way, at the Planck distance. Actual experimental confirmation is somewhat lacking at this time...
> All objects within our universe rotate, including planets, stars, solar systems, galaxies, and galaxy clusters. Moreover, black holes, spherically symmetric objects with horizons, display near maximal rotation as presented by Daly (2019). The idea that everything revolves [...] naturally extends to the whole universe, as hinted by recent claims of anisotropic Hubble expansion in X-ray observations by Migkas et al.…
And also from the abstract:
> Curiously, this is close to the maximal rotation, avoiding closed time-like loops with a tangential velocity less than the speed of light at the horizon.
That's weird considering that in lambda CDM the universe's accelerating expansion implies that stuff falls out of our observable universe, which implies that there is more stuff beyond the edge of the observable universe, and anyways there is no center of the universe and we are only at the center of our observable universe, which also further implies that there is stuff beyond the observable universe. Are they saying that our observable universe has a rate of rotation such that the tangential velocity at the edge is about the speed of light? What about the stuff beyond the edge? And as u/BigParm wonders, doesn't having the whole universe rotate imply a center? Surely we can't be at that center. But maybe there can be an illusion that we are at the center of rotation.