Basically the title – I have a degree in Aerospace Engineering, but I still can’t answer this question posed by my girlfriend. An infinitely expanding universe implies that there’s a “container” the universe is expanding into, kind of like how you can pour a pancake into a pan & it’ll expand to the limits of the pan. But then that also implies that said container existed before the universe / big bang, which is…wild. Anyway, please ELI5!
In: Physics
I think the main response I would have to this is, why does there have to be an “into”?
Honestly even posing that as a requirement brings about a whole shitload of logical issues, because there would always need to be a larger container.
Usually to make things further apart, you move them apart. But space is making more space between the things. So the things are getting further away, but because they’re getting more space put between them.
The short answer is we don’t know
Why does the universe have to expand into anything though? Space as we know it only exists within our universe so there isn’t necessarily anything outside the universe.
One working theory is that the universe is not unlike a bubble in some kind of universal fabric that has numerous other bubble universes in it.
At this point it’s nothing but speculation as we have no way to test or observe any of this.
It’s counterintuitive, but the universe is not expanding “into” anything. The universe is not some volume of space inside a larger container, and it’s not a thing that’s expanding from some central location like an explosion. When we say the universe is expanding, what we mean is that everything in the universe is moving away from everything else. This is happening everywhere in the universe.
First, we don’t actually know. Second, there’s no reason to believe that it’s expanding INTO anything. Physics is under no obligation to be intuitive to us. It could be that the universe itself is the container and that container is simply getting bigger.
Measuring the universe will blow your mind. The easiest ELi5 is we don’t know.
We know that it is expanding, but we have no idea on the actual size or what “space” its trying to occupy. The best measurements we have actually suggest the universe is flat. But it’s flat in the way of trying to measure the curvature of the earth and literally not having enough measurable space to actually see the curve take place. Think about those guys that try to measure by putting 9 ft high holes a certain amount of distance away to see the light, there is enough literal space on earth to have the holes far enough apart to actually measure the curve. With space it measures as just ‘flat’, we literally cannot see 2 points far enough away from each other to measure any sort of curve. So we literally cannot see far enough to know whats beyond the “space” the universe occupies.
It’s easiest to understand if you use this definition of ‘nothing’ – the absence of all **magnitude** or **quantity**.
The universe is expanding into the dearth of magnitude and quantity.
Oh man, we’re never gonna figure this out, are we?
It actually does not imply that. It’s perfectly valid to imagine a world in which space is expanding from the perspective of being in that world without the space having to expand “into” something. I mean, if everything was actually shrinking, thats equivalent. but speaking in terms of physics theory there does not need to be such a “container” If there did, wouldn’t that container need a container? most do not believe it is turtles all the way down
Imagine a balloon. Blow up the balloon about 1/2 away and draw a few dots on it.
The universe is like the 2 dimensional surface of the balloon (It is really important that we are only talking about the 2d surface, do not think about this as a 3d problem)
The entire surface of the balloon is a 2D space that has a certain volume. This volume represents the entire universe. Everything that exists in this 2D world is there. Then, you blow up the balloon further, the dots move apart from each other.
From the 2D perspective, the universe has gotten larger, but even when it was small, someone could map the entire thing and know every point. When it is blown up, all the points are just further away from each other.
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