There once were 2 bugs inside an inflated balloon. The balloon was slowly being inflated and one bug asked the other "I wonder what's outside the balloon?"
Mathmatically, space and time need each other to exist. Outside the universe, there is no time, therefore, we can probably assume there's no space either. There's nothing. We have to rethink the definition of nothing to even get close to understanding the kind of nothing that exists (or doesn't exist actually) outside the universe.
We often think of nothing as a lack of anything. Well actually that's completely true. But what about deep space? (inside the universe) Isn't that nothing also? It's dark, void, no air, no light, no matter, so isn't it nothing? No, it still has time and space at that spot. Those are 2 things. Now subtract those 2 things, that's true nothing. That's what's outside the universe.
So does that mean if we got in a spaceship and sped into the edge of the universe, would he slam into the nothing and bounce off? If we did, wouldn't that be something, like a wall? More likely, we would simply cease to exist as we moved into the nothing. Or maybe the ship would simply push against the edge of space and not move forward any faster than the speed of the universe's expansion.
Doesn't make sense does it? It should, but it doesn't. Why doesn't it make sense? Why can't the universe be inifintely large? Why does it have limits? Is there a sign at the edge of the universe that says "This area under construction - God" ? A logical deduction could be that the reason why these bizarre paradoxical limits exist, is because it's just not real. It's, we, the galaxies, space, and time, are just data inside an inconceivabley advanced computer running a simulation. But the computer has limitations and cannot simulate a true infinite universe. So it's math stops at the edge. And beyond that, are points where no more data can exist (until it gets upgraded).