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
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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