@gorillapaws “So if I were in an imaginary spaceship and pointed at where the core would have been, and went forward as a very fast speed, what happens?”
What’s going to happen is you’re not going to be able to point yourself in that direction in the first place. Like @gasman said, the balloon analogy might have been more confusing than helpful. Many times in discussing the universe, we have to think about the concept of fourth (or higher) dimensions, which as far as I know are impossible to imagine visually. The best way to discuss these concepts is to extrapolate from lower dimensions. So to conceptualize a four dimensional hypercube, you first think about a three dimensional cube (has 2 dimensional square faces) and extrapolate – and you can conclude that a hypercube would have cubes as its faces. Don’t try to picture it, it’ll make it worse.
My point being that the balloon analogy is just another such tool and it doesn’t apply directly. The universe isn’t truly a shell expanding in a spherical shape. In the case of the balloon, that would be a universe in which the creatures living in it were two dimensional. They could travel around on the surface of the balloon but not in. To them, the only existing directions are forward, backward, left, and right, there is no up or down and so they couldn’t point themselves “downward” towards the center of the balloon in order to try and reach it.
So you have to do some extrapolation in order to apply the balloon model to the real universe. Instead of a two dimensional shell expanding spherically, we are a three dimensional shell expanding hyperspherically. Again…...don’t try to picture it. And we can point ourselves forward, backward, left, right, up, or down, but the “center” of the “balloon” would be in a direction other than all of those.
Disclaimer: This is all my (very amateurish) understanding of how things work and I definitely might have some misconceptions; do point them out if you spot them.