Great question! Unfortunately it’s quite hard to tell! If the Big Bang created the Universe, and everything is travelling out from a certain point since it happened, then it must ‘end’ at some point as the planets, stars, galaxies and the like can only travel at a certain speed.
So some people reckon the Universe is 93 billion light years across! That’s even more than millions and millions of km (a LOT more!). So what is beyond it? That’s the good question. As the Universe is probably still expanding, then there must be something for it to expand in to. I don’t know what that would be, but I imagine it would be empty space. But who’s to say there isn’t another Universe that started from another Big Bang which is also out there expanding?
What do you think? I think it’s a fascinating and mind boggling question, and concept! but I love it!