Earth is flat with portals all the way along so you think it's curved! Very clever really. It was invented by the dinosaur scientists who were dominant around 50,000 days ago. They came from Mars on a skateboard. They died out when a 10" pizza hit the earth at 92% the speed of light, causing catastrophic cheese damage, to the earth's inner parts, which is why we have stuffed crusts on pizza, because they almost stuffed our crust entirely!