There's a lot of different theories floating around.

The most obvious one is nothingness, there is no 'outside of the Universe' because the Universe is all that exists.
Proponents of this theory think that if you got to the edge of the Universe and stuck your hand out, it would re-enter the Universe on the other side, but that's assuming that the Universe is round, or has any kind of shape to it.

Another theory is that there is a Multiverse. Essentially, there is an unlimited amount of Universes, like a never ending foam of bubbles.

Another is called the 'Ekpyrotic' Universe theory, this suggests that there are two membranes which constantly reverberate off one another, injecting matter into each other.
Think of it like holding up 2 pieces of paper side by side and hitting them against one another, matter exchanges occur on the subatomic level.
Essentially, there is supposed to be another Universe out there, adjacent to ours.

In short, no one really knows.

I'm going to say there is nothing outside of the universe. The universe is everything. We are the universe. We are one.

I think you mean to ask "What's outside of the galaxy"
Our galaxy is the milky way. The universe contains the milky way and many other galaxies.

Edit:
I wanna say that the universe is never-ending, it just keeps expanding. I think there are millions of galaxies, like ours, that can support life that are all contained within this one universe. But hey, who knows. It's just one of those things that you ponder

Nobody knows but there are a few theories.

1) There is no end. It's infinite.
2) Once you think you've gone far enough you just end up at the original spot.
3) Infinite bubbles of what we call a Universe. So it's not a universe. More of a multiverse.

Unfortunately our technology hasn't advanced that far to even see what is past a few planets.

Maybe bedrock is at the end of the Universe so we can't mine out of it :trollin:

YunoGasai wrote Unfortunately our technology hasn't advanced that far to even see what is past a few planets.

Care to explain this?

Every one of those is an entire galaxy.

I imagine it to be like mario so you just run off the screen and come through on the other side, so you would just keep on going round lol

You could say that it's simply more stars, galaxies and so fourth. The observable universe is ever expanding as light we previously could not see becomes visible.

Jeeves wrote There's a lot of different theories floating around.

The most obvious one is nothingness, there is no 'outside of the Universe' because the Universe is all that exists.
Proponents of this theory think that if you got to the edge of the Universe and stuck your hand out, it would re-enter the Universe on the other side, but that's assuming that the Universe is round, or has any kind of shape to it.

Another theory is that there is a Multiverse. Essentially, there is an unlimited amount of Universes, like a never ending foam of bubbles.

Another is called the 'Ekpyrotic' Universe theory, this suggests that there are two membranes which constantly reverberate off one another, injecting matter into each other.
Think of it like holding up 2 pieces of paper side by side and hitting them against one another, matter exchanges occur on the subatomic level.
Essentially, there is supposed to be another Universe out there, adjacent to ours.

In short, no one really knows.

This is the best answer ive seen, weel done and plus rep for you

Thats easy itll be More universe