If all of the galaxies we see rotate the same way, are we “looking down” from a pole and seeing only those with the same rotation we have, as opposed to a more equatorial view that would be evenly split.
This along blows my mind: I picture this bin bang and everything expanding from that point and... that everything is now a sphere. In my mind. But it isn't? Yes, I know next to nothing but love thinking about all of this.
It is often presented this way because models generally mix up the observable universe and the universe. One key notion is that we are at the center of the universe. Not the Milky Way, not the Sun, Earth is. Yet we know that Earth isn't at the center, so what is that? Because it is defined as our ability to travel from where we are at. Each of us could be considered at the center of our own observable universes, but this is a distinction we don't make because they overlap so closely that we don't have tools with the precision to tell them apart. I would guess that even aliens on the other side of Milky Way have an observable universe that overlaps so closely with our that they are equal to whatever level of precisions our tools allow for. Once you get to someone in a different galaxy, especially one that is moving away from us and not closer, then they have a different observable universe.
But then, what is the universe? One way to think of it is to imagine that every galaxy has at least one intelligent species with their own observable universe. The universe is the sum of all observable universes. The very nature of how to sum them together, what it means to combine multiple sets of thing which include items that don't exist relative to other items in the set, is a question we can't really answer yet. Because of this, even a question like the size of the universe is unknown, and even the question of if more of the universe exists outside of the observable universe isn't simple to answer and gets into the nature of what it means to exist. If someone exists in the universe, but not in the observable universe, it becomes an instance of Russell's Teapot.
Yes, 1d. But it's easier to go from a strip to a sheet to a block than trying to imagine an infinite block from scratch.
The important part is that at any given point on the elastic strip, both sides are getting further away. Everything else is getting further away.
You might think if A-B-C-D are points on the tape and A-B are expanding and C-D are expanding, then B and C must be squished together, but the distance between them is also expanding. You have infinite elastic, but you also have infinite room to stretch it (even along the direction it already occupies). You now have A--B--C--D.
It's tempting to think about that stretch from the point of view of the floor/table beneath the elastic, in which case some parts of the elastic move faster than others as they stretch, but if you always think from a point on the elastic, then the speed of the rest of the elastic depends on how far away it is. Stuff twice as far away moves away twice as fast. Stuff infinitely far away moves away infinitely fast. That's true for every point on the elastic. No bunching up.
The observable universe is an illusory artifact of being an observer traveling at less than the speed of light. A constant distance in every direction is a sphere. That tells us nothing about the actual structure of the universe.
In other words, your observable universe is different than mine and that's both spheres we're in the middle of. That suggests the universe itself probably isn't a sphere.
Is it an illusory artifact or is it all that exists? If it can't be observed, it can't be tested, it can't be verified in any way or ever interacted with, then isn't it just an instances of Russell's Teapot and thus does not exist? What does it mean for science if existence isn't a binary property or one that we set as a truth yet is entirely untestable?
We definitely have reason to believe that there’s universe outside the observable universe. The CMB uniformity suggests that that’s the case as do our theoretical models. The mere fact that two observers have different observable universes indicates it is indeed an illusory artifact.
Just because something is untestable today doesn’t mean it will be for all time. However, the untestability problem has started to creep much more deeply into cosmology and high particle physics in particular - our technology and models aren’t staying enough ahead to provide a lot of fertile testable ground.
>Just because something is untestable today doesn’t mean it will be for all time.
This is generally true, but such ideas are kept outside the realm of science until they are. In this case specifically, all our knowledge points to this remaining untestable as it would require FTL travel which is on par with violating conservation of energy or time travel. It even allows solving the halting problem (Turing machine in timeloop until it halts, you outside of the timeloop can then check if the Turing machine in the timeloop ever left it).
It is entirely possible that there are things which are true which science cannot verify because of the underlying philosophy by which science operates. Things that exist outside of the observable universe, if FTL travel is truly impossible, would fall outside the realm of science.
>The mere fact that two observers have different observable universes indicates it is indeed an illusory artifact.
Do they? The nature of the observable universe is that, if you can communicate with someone else, any information they can receive and pass on to you is part of your observable universe as all information travels at the speed of light or slower. If they can receive information and cannot pass it on to you, they are not part of your observable universe any longer and no longer exist (exception if FTL interactions are discovered). Thus the only observers that exist in a way you can interact with, can make any testable hypothesis concerning, and thus can be considered by science, are observers in your observable universe.
Because measurements confirm a homogeneous and isotopic universe. A spherical universe would imply a special point, the center, which would go against these cosmological principals.
Could be a universe that folds in on itself in multidimensional space so that every point looks like the center. But it almost certainly isn’t a 3d sphere.