Answer:
To see objects smaller than microscopic limits
Step-by-step explanation:
The theory of Relativistic Quantum mechanics can be applied to particles that are massive and propagates at all velocities even those which are comparable to the speed of light and is capable to accommodate particles that are mass less. This theory find its application in atomic physics, high energy physics, etc.
It is necessary to use relativistic quantum mechanics when it is desired to see the objects that are too small to be seen with the help of microscope.