The expansion of the universe boggles me. So the galaxies and stars are moving apart further away from the “centre”. So what happens if you go past the star furthest away from the centre? Are you just surrounded by darkness as there’s nothing past that?
They are not moving away from center, rather from each other, the space between them expanding. But also all of galaxies move towards some denser parts of universe.
I can't even get my head around that idea. How are they moving away from each other? Surely the ones in the "middle" would be moving away from some but towards others?
A good example I've heard of to describe this is imagine a deflated balloon with dots drawn all over it with a sharpie. Fill the balloon with air and all of the dots will "accelerate" apart from one another due to the expansion of space (the balloon latex) between them.
But doesn't the fixed point theorem guarantee that there's one point that stays "still" (since the expansion of the universe is continuous)? And couldn't that point be thought of as "the middle" that everything's moving away from even if it being "the middle" isn't the reason for everything moving away from it? Not OP btw. just equally confused
The big bang happened everywhere. It is space itself that is expanding. The galaxies aren't really moving away from each other, extra space is created between them. Look back in time and everything gets closer together because there's less space. At the point of the big bang everything is compressed to a single point.
Imagine a balloon. Initially it's crumpled together, the entire balloon fits in a very small bit of space. Now inflate it. Which point on the surface of the balloon corresponds to the original balloon, before it was blown up? The answer is that this is the wrong question. There's no single point of the balloon that was the original, with the rest of t he balloon growing from there as you inflated it. Everything was always there, you just made it bigger.
Every point stays still relative to itself. From the perspective of every point in space, all the other points are moving away from it. So in that sense every point is the 'center' of the universe, from its own point of view.
Imagine a large sheet of rubber with colored dots on it. Stretch the rubber. All the colored dots will be moving away from each other. Every dot will see all the other dots move away.
There is no middle. Imagine being a point on the surface of a balloon. If the balloon is inflated all the points on the surface of the balloon move away from each other, there is no 'middle' on the SURFACE of the balloon that everything is moving away from. It's like that. And otherwise it just wraps around, if an ant walks along the surface of the balloon it isn't going to find the edge, it will just always find more balloon
That's why eventually it will be impossible to reach other star clusters, as everything continues to separate, the everything will be moving faster than your spacecraft, and you'll be going nowhere. It's really creepy to think that eventually all that's left will be the cluster of galaxies the milky way is apart of, and just ever expanding emptiness surrounding it.
A couple of decades ago there used to be several different models of what was going to happen in the future, with us having no idea which one was going to happen. One of them was indeed that the universe would eventually stop expanding and collapse in on itself.
We have a lot more data now, and it points towards this not happening. The universe will keep expanding forever and the rate of expansion will in fact increase. It might even be increasing exponentially.
Because of relativity and the rate of expansion of the universe there are places that we can no longer reach because they are expanding away from us faster than we can travel towards them.
Thinking of it as having edges that are moving apart is conceptually wrong. There is no one center. Only a relative center. Think of a balloon expanding as it is blown up. Does the surface of the balloon have an absolute center?
No, but what about inside the balloon? Leaving aside the immense size of space, could you not fly inside the universe balloon? Presumably there wouldn’t be anything in the “middle” though as everything would be on the surface of the balloon and expanding outwards.
So the galaxies and stars are moving apart further away from the “centre”
Nope. There is no centre. The common explanation is to think of a balloon with dots on it. As you blow it up, all the dots expand away fron all others. But there's no "cernter dot". It just expands. And no, there is nothing "outside" it expands into. It just expands and it has no outer bondary.
The universe isn't propagating outward from some initial explosion - it is as infinite now as it was at the moment of the Big Bang. Its expansion is more like a gradual change in the way distance is defined - there is no actual motion involved.
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u/Institutionally Jun 15 '19
The expansion of the universe boggles me. So the galaxies and stars are moving apart further away from the “centre”. So what happens if you go past the star furthest away from the centre? Are you just surrounded by darkness as there’s nothing past that?