The concept of the expansion of the universe can be a bit counterintuitive, but I'll try to explain it as best as we currently understand it based on scientific theories and observations.
When we say that the universe is expanding, we mean that the distances between galaxies and other cosmic structures are increasing over time. This expansion is not a motion of galaxies through space but rather an expansion of space itself. It's important to note that the expansion is happening everywhere, not just at the edges or boundaries of the universe.
The analogy often used to explain this is to imagine the universe as the surface of a balloon. As you inflate the balloon, all points on its surface move away from each other. The surface itself is expanding, and there is no need for an "outside" space for this expansion to occur. Similarly, in the case of the universe, it is expanding from within itself, and there is no known boundary or edge.
It's crucial to understand that the concept of "outside" the universe may not be well-defined or applicable in the context of our current understanding of the universe. The universe, as we know it, includes all of space, time, matter, and energy. Asking what is outside the universe is somewhat akin to asking what is north of the North Pole or what came before the Big Bang—it may not be a meaningful question within our current understanding of the universe.
It's worth mentioning that cosmologists are actively studying and exploring these questions through theoretical models and observations. However, the nature of the universe beyond what we can observe directly remains a subject of scientific inquiry and speculation.