A friend of mine asked me why we don't fall off the earth if it a sphere? It was so easy to answer that but then it hit me, if gravity makes us to stay on the sphere,then it means up and down is just an illusion. If you stand straight at both the poles of the earth, gravity pulls down your body towards the earth. Meaning, both of you will have two different kinds of up and down. My up is your down and your down is my up.