this post was submitted on 25 Sep 2024
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If we are considering "the universe" to mean the spacetime that we exist in, there could be an "outside," but we just don't know, and there's no indication of such an outside, or anything about what it would be like.
By way of infinite spacetime, yes, there is only a part of spacetime that we can observe, because the farthest part is moving away from us faster than the speed of light. I seem to recall there having been some estimations of how large all of spacetime is, observable and unobservable, and that it has a finite size.
That said, there does not appear to be a limit to the size of spacetime. Based on what is currently known, spacetime is expanding, the expansion is accelerating, and there is no limit to the expansion.
Honest question: if “nothing is faster than the speed of light,” then how could the universe be expanding faster than the fastest thing?
So all space is expanding. Locally, that's "just a teeny tiny bit," and the force of gravity is plenty strong enough to keep things up to about the size of galaxies (maybe galaxy clusters) gravitationally bound. Andromeda, for example, is the only galaxy that is heading towards us.
But all of space is quite big. Over the vast distances of space, all of the "teeny tiny" local expansions add up. This means that the galaxies which are furthest away from us are also receding from us most quickly. This is not because those galaxies are moving through space; it's because of all the expanding space in between them and us.
The speed of light (in a vacuum) is the fastest anything can move through space.
Would a fair, albeit crude, analogy be like when I fart and the gas forces my butt cheeks apart (the expansion between two objects)? (_|_)💨
Crude, yes. Fair, no.
Consider a balloon. Uninflated, make a mark on opposite sides, and then make a third mark right next to one of those. When you inflate that balloon, the two points on opposite sides of it become farther apart because of the stretching of the whole balloon, but the two marks right next to each other don't become nearly as far apart, because they are only experiencing "local" expansion.
I wanted to make a fart joke.
But I like your balloon explanation. That makes sense to me.
We must sometimes succumb to our basest instincts.
Don’t you mean our basic stinks?
Ok I’ll stop.
Fill the balloon with a fart
Just fill the balloon with farts.
Wait until you hear about relativity.
And also we don't know that C is the limit entirely, but it is so far. Also, we don't know if there are more dimensions in our reality or not because we cannot observe them. And no, I don't have much of a better answer.
Basically, we still know we don't know a lot, and we probably don't know a ton of what we don't know that we don't know. Also magic.
It took my awhile to get it until somebody put it this way. The objects aren't exactly "moving" apart from each other, rather space in between them is expanding. So instead of thinking of it like a bunch of objects in a line being pulled away from each other, instead imagine it like a bunch of vector based objects random placed on an infinite canvas - now rather than moving the objects at all, try to imagine instead reducing the scale of all of the objects equally. Now of course this isn't perfect, as really what is happening is kind of the opposite, as the objects remain the same but the space between increases, but the relationship is the same here. So nothing is exactly "moving" in relative space, but everything is still expanding. Thus this expansion can happen infinitely without anything breaking the speed of light.
ELI5: If I'm moving away from you at 50 KPH and you're moving away from me in the opposite direction at 50 KPH then after 1 hour we will be 100 kilometers away from each other even though the speed limit is 75 and neither of us broke it.
That's an extreme reduction but gets the general idea across.
That isnt how it works. The speed of light is the speed of causality; it doesn't have anything to do with light. Its just the fastest speed at which things can happen. Light, being massless, happens to travel at that speed.
In your scenario, the light beam would just be stretched along its length and the 2D interface on the surface of the moon would just "lag behind" from your POV. But it would lag at the speed of light.