What is physics?

As the present time, there are three main frontiers of fundamental science.First, the world of the
extremely large, the universe itself, Radio telescopes now gather information from the far side of
universe and have recently detected, as radio waves, the (firelight) of a big bang which probably
started off the expanding universe nearly 20 billions years ago.

 Second, the world of the extremely small, that of the particles such as ,electrons,protons,neutrons
,mesons and others.the third frontier is the world of complex matter .it is also the world of (middle-sized) things, from molecules at one extreme to the earth at the other.this is all fundamental physics,which is the
heart of science.
But what is physics?
 according to definition,physics deals with the study of matter and energy and the relationship 
between them.the study of physics involves investigating such things as the laws of  motion, the 
structure of space and time, the nature and type of forces that hold different materials together, 
the interaction between different particles, the interaction of electromagnetic radiation with matter 
and so on.