There are likely to be infinite, or at least countless universes out there. We haven't seen them because any signs of their existence, such as wavelengths along the EMS, may very well take trillions of years go get here, and also may very well be too faint to detect from the astronomical (excuse the pun) distances away. From a historical standpoint, most cultures believed that they were the center of the earth, i.e., the mediterranean was once believed to be all that was. Then it was earth with the heavens around it, then our solar system, our galaxy, etc. Based on cultural logic, we are, more than likely, incorrect about assuming that ours is the only universe, that aliens don't exist, and that socks disappear into a 'sock abyss'.