Transition from quantum to classical

It is often wondered, by many people, why the “obvious” notions of classical mechanics are not applicable at microscopic world (incorrectly identified as quantum domain). One then develops a feeling that classical laws break at “quantum” level which is inundated with “strange” notions. Classical mechanics is considered as the true mechanics of nature. Then it is thought that one can get quantum results by considering certain unspecified “forces” or “interactions”.

If anything, it is the other way round. Quantum mechanics is our best understanding of nature (yet) and it is to be believed that nature follows quantum mechanics. The notions of this mechanics like uncertainty principle, tunnelling and quantization should be considered “obvious” (resulting from the postulates) albeit less commonly observed at our length scale (by common people). It can be shown that classical notions emerge when one considers appropriate interactions (using quantum mechanics). Quantum mechanics is valid at our length scales too (not only limited to microscopic levels). It is the de-coherence which is responsible for emergence of classical results which are, by default, fed in out intuitions. Whole universe comes under quantum domain!

W. H. Zurek is one of the pioneers studying this emergence of classicality from quantumness. My talk was based on an article published by Prof. Zurek in Physics Today.