There isn't an edge, there can't be cos the universe is everything and therefore it cannot have an edge. The imagination is limitless so there is nothing we cannot imagine and the universe is limitless so there is no limit. It defines the limits and therefore has to be outside the limits. Physicists say there is no edge for rather complex, maths reasons but from a philosophical point of view systems go from the smallest to the biggest, the smallest has no lowrer edge and the biggest has no upper edge. the universe is the biggest system so it cannot have an upper edge, otherwise something could theoretically be bigger by excedding that limit. Now that's some ancient Greek Style Logic right there. Not sure if they actually came up with that though, i just thought it now.