Knowledge Horizon

in medieval world, people believe earth is flat. because they lack of knowledge. 

lets make an analogy between earth and knowledge.

on earth, it has surface. some filled wih lands, some filled with water. human, may like to divid the land by boundary, and call each area in term of nation. A more natural division may be the heritages, like ice land, tropical, dessert, etc.

on knowledge, it has a lot of subjects, like physics, arts, Psychology, politics, biology, etc. but these are the man made boundaries. in reality, we can see the boundary of different subjects is hard to distinguish, just like the boundary of tropical and dessert. 

if our understanding of knowledge reached certain level, we can see our knowledge system form a globe. there is one and only 1 knowledge, but different aspects of it. 

that's why, when we study at some level. we will entitled Doctor of Philosophy. because there is only 1 knowledge.

and human is now working on the discovery of different landscape of the knowledge globe.