Outside the universe?

I have a lot of questions about the universe. If you were to, defying all probability and speed required to live long enough to make it there, step outside the boundary of universe, what would happen? If you were outside our universe, the place that contains matter, and boundaries are only limited by when this matter, stuff, or atoms cease being, what would happen to your body? Would you simply not exist? Would you simply expand the universe with every step, flap, stroke, WHATEVER YOU WOULD DO OUT THERE, and bring the atoms along? I mean, when you die in the universe, your body is decomposed and recycled, all thanks to energy and atoms. But outside the universe, such things JUST DONT EXIST! You cant just disappear either, I mean, where would everything go? Could you have caused the destruction of our very own universe? Any real theories, nothing about how this will never happen, or that the universe is infinite, because it is not. I want a hypothetical but explainable idea.