What is the modern understanding about Four Great Elements and Reality?
Modern Understating

There are infinite number of Buddhas in the past (though only few are recorded), and they preached the same Dhamma. With respect to Science this is always in constant evolution in terms of the understanding and body of knowledge. Though Science generally may not refute Buddhism drawing parallels may not be useful. 

Understanding the 4 Elements

Understanding of the 4 elements should be at the experiential level or at the level that is felt. Conceptual understanding falls into the sphere of Perception, through this is also essential, but as stepping stone to the next item which is putting into practice with a view to experience it for one self.