The size of the observable universe is determined by the distance light has had time to travel since the Big Bang, given the current age of the universe and the speed of light. the estimated radius of the observable universe is about 46.5 billion light-years. However, it's important to note that the observable universe is not a fixed sphere centered on us; rather, it's a region around us from which light has had time to reach us since the beginning of the universe.
The concept of "outside" the observable universe is a bit challenging to grasp since, by definition, it refers to regions that are beyond our observational reach. We cannot directly observe or interact with anything beyond the observable universe because the light from those regions has not had enough time to reach us. Therefore, we have limited knowledge about what lies beyond our observable universe.
Regarding where the universe ends, our current understanding of the universe's structure suggests that it may be infinite in extent. In other words, there may not be a specific boundary or edge beyond which the universe ends. Instead, the universe could extend indefinitely in all directions, without a well-defined outer boundary. However, it's important to note that our understanding of the universe is continually evolving as scientific research progresses, so future discoveries may provide new insights into its size and structure.