Four Realms of Physics

Today we introduce four realms of Physical laws that govern the
universe:
(i) Classical Mechanics
(ii) Relativistic Mechanics
(iii) Quantum Mechanics
(iii) Quantum Field Theory

Let us start with our everyday life. Things are going very slow
here. ...Yes. Even on freeways in and around Boston or Los
Angeles! Those crazy drivers who are having the fun of their twisted
mind by cruising at 90 miles per hour are really too slow to catch up
with the speed of light which is about 186,282 miles per second or
about 3 hundred thousand Kilometer per second.

Things that happen in this world - the interaction of forces and
bodies - can be fully described by Newton's three laws which are
introduced in high school Physics courses. Using these equations,
we know, for example, how exactly a projectile traverses its path
in the air, how to determine the slope of a bending freeway so that
at least reasonable drivers do not topple their cars while negotiating
the curve at normal speed, etc and etc ....

In the 16th Century Newton introduced these concepts and
equations and some great Mathematical tools like Calculus to solve
and understand many such problems and mysteries of life.
In general, that is the realm of Classical Mechanics. These equations
were tested and successfully used so many times in so many cases
and situations that at the end of the nineteenth century, some
Physicists came to believe that Physics was coming to an end
... Nothing more to know or understand about Physical laws.

Twentieth century changed all that when scientists tried to look
at microscopic objects and their motion and in 1905 a clerk of
a patent office at Bern, named Albert Einstein, explained what
happens when something approaches the speed of light ...

...And we got into new arenas of Physics - Relativity and Quantum
Mechanics .. and then Quantum Field Theory....