The concept of the universe being infinite or having an edge can be a bit challenging to understand, but I'll try to explain it as best I can.
When we talk about the universe being infinite, we are usually referring to the idea that it has no boundaries or edges in the traditional sense. This means that it does not exist within any larger space and does not have a specific "center." Instead, it is often described as being homogeneous and isotropic, meaning that it looks the same on a large scale no matter where you are within it.
The Big Bang theory suggests that the universe as we know it began from a singularity, an extremely dense and hot point, around 13.8 billion years ago. However, it's important to note that the singularity was not a point in physical space as we understand it. It was a point of infinite density and temperature, where our current understanding of physics breaks down.
After the initial singularity, the universe rapidly expanded in an event called cosmic inflation. This expansion happened at an incredibly fast rate, causing the universe to become much larger than the observable universe we can see today. Since then, the universe has continued to expand, although at a slower rate.
While we can observe a portion of the universe known as the observable universe, which is limited by the distance that light has had time to reach us since the Big Bang, we cannot say with certainty what lies beyond our observable universe. It is possible that the universe extends far beyond what we can observe, and if it does, it could be infinite in size.
One way to think about the universe's expansion without needing to envision an "edge" is the balloon analogy you mentioned. Imagine a balloon being inflated. As the balloon expands, the surface of the balloon stretches in all directions. There is no specific point on the balloon that represents the "center" of the expansion, nor is there an edge to the balloon's surface. Similarly, the universe can be thought of as expanding in a similar way, with no central point or boundary.
It's important to remember that our understanding of the universe is based on scientific theories and observations, and our knowledge is continually evolving as new discoveries are made. The question of whether the universe is truly infinite or has any form of boundary is still an area of active scientific research and debate.