Imagine you somehow came out of the universe, what would the shape you looking at? Will that be a bubble, a huge box or flat plate. This was a mind boggling question to scientists for centuries of years. But based on new observations they have come to a conclusion. What is the shape of the universe?
According to the General relativity space itself can be curved and wrap. On top of that scientist figure out the shape of the universe determined by how dense the mass spread across the space.
Based on some critical density, scientist figured out there can be 3 shapes. Those are open, close and flat. Measurements indicate that the universe is flat, suggesting that it is also infinite in size. You can find more details in above video.