I just can’t fathom what’s on the other side of the universe, and would love if you guys could help!
In: Physics
The best metaphor for this is to imagine the universe is 2D, not 3D, so it’s basically on a plane, like stars are painted on a sheet of paper. Now imagine it’s not a sheet of paper but the rubber surface of a ballon. Now imagine the ballon is inflating. More and more space (the surface) is created, it is expanding, but it’s not like it is expanding “over” empty space: the space itself is expanding.
(This metaphor creates some misunderstanding as well, but works well for your question. Here is where it fails: it leads you to think you need some “3D” space outside/inside that 2D “universe”; you don’t actually need that to explain our universe).
When we say the universe is expanding what we mean is that space itself is expanding. And space itself is not expanding into more space but rather there is just more and more space in among all the other space. So the new places that the univers expands into is evenly distributed thorughout the universe and is brand new. The places that the universe expands into did not exist before. If you were to measure the distance between two far away galaxies very accuratly an then repeat the measurement some time later you will find that there are now more space between the galaxies even if they have not moved in relation to each other. There are just more space, more places that have popped into existance between the galaxies.
There may be nothing beyond the edge of expanding spacetime.
What really might make you think is that the universe will likely expand until all time and motion stops. All heat ceases. And then… something very special may occur – a reversal of entropy only possible as the end state of the universe becomes mathematically equivalent to the beginning.
The universe already exists everywhere, it’s just stretching. So the gaps between things are growing bigger.
I’m a little late, but I think I can add a good analogy as to how space can expand when it is infinite and there’s nothing outside of it. Imagine a number line. You’re sitting at 1, and I’m sitting at 2. Now, we “expand” our number line by multiplying every number by 2. So you’re now sitting at 2, and I’m sitting at 4. The distance between us has increased, but we haven’t “moved.” Space itself is expanding beneath us!
But as to what space is expanding “into” it’s expanding into itself. Where did 5 go? It expanded to 10. Where did 100 go to? It went to 200. Where did 9,825,651,057,241 go to? Well, you get the idea. Because there’s no limit to infinity, you never “run out” of space to expand “into” and there’s no edge that needs to push some boundry. Where things were, well, they’re farther apart now.
So what parts are *not* expanding? If everything were expanding at the same rate, we wouldn’t notice, right? So the radius of the earth is not expanding… the radius of the solar system is not, galaxy is not? Where is that line/gradient, or how does that work?
Does that mean that the longer we wait the further we will have to travel to reach another planet ?
Nothing that you should concern yourself with. Who told you you could snoop around anyway?
Apparently, it’s not even known whether the entire universe (as opposed to just the observable universe) is finite or infinite ([Wikipedia](https://en.wikipedia.org/wiki/Universe#Size_and_regions)). This doesn’t directly affect your question, since either way the expansion is just things in the universe getting further apart, but it’s interesting to think that there might not even be “places the universe hasn’t reached” at all.
I would like to propose that science simply does not know the answer to this, as it contains multiple unknown elements:
1) What is space-time “made out of”? We only understand about 10% of it (thanks to our ongoing effort o understand dark energy and dark matter).
2) How fast is space expanding? We have recently discovered it is variable, but ultimately we don’t know.
3) Why or how does space expand. We don’t know.
4) What existed before this universe? We don’t know.
5) The concept of OP that there is something “outside” our Universe is another example of something we don’t know.
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