A precise definition of macroscopic and microscopic objects What are the formal definitions of "macroscopic object" and "microscopic object". How can one differentiate between them? I mean, is there any fixed condition by which we can distinguish between them?
 A: I suspect this will be closed as "opinion based". I don't believe there is a canonical answer. Usually microscopic scale relates to phenomena that occur on a level much smaller than the system under consideration (atoms in a crystal when you are thinking about the crystal, for example).
There is an analogy with micro- and macro-economics. Micro-economics describes how individuals make economic decisions (spend, save, etc). Macro-economics describes how the system ("the economy" of a city, country, world) evolves as a result of the micro behavior.
They are almost always related - with one being the aggregate of the other. And they may require a different level of effort to observe - although I would not say it's necessarily "naked eye vs aided eye". 
For example, when you consider the evolution of a galaxy, the motion of the moons around the planets in the solar systems may be considered "microscopic" - "small compared to the scale of the system under consideration". This means it may not be possible to set an absolute limit on the size where "microscopic" becomes "macroscopic".
A: Mesoscopic physics is a branch of science which is in between microscopic and macroscopic physics. In this branch, objects of sizes in between 100  to 10000 nm is taken into consideration(from the size of a virus to a bacterium). However, this is not defined precisely. This new branch of physics, evolved about 10 years ago, is now an exciting field of research in physics. It has many scopes------nano fabrication, mesoscopic brain dynamics,etc.
