Someone asked me:
Q. Why does there are two different “theories” of Mechanics for macro object such as yourself and micro such as electron when the macro is essentially a formation of micro?
I replied Quantum Mechanics covers both.
Please write a Physics answer.

Manmohan Dash

There are no different laws. Earlier we had no experience of the micro as they were beyond our ability. Gradually they threw exceptions towards the laws we understand for the macroscopic entities. we were forced to study them. we see that the macro laws need to be modified such that the micro is also explained. turns out that the laws that explain micro are responsible for giving precise explanations for macro as well. So there is no two laws and the understanding that macro consists of micro, also came with such exceptions and the new laws, or we would have tried to formulate laws that already explained the constituents.

The macro comes in two types: waves and particles. particles are localized or well defined space-time objects. Waves are well defined but extend across indefinite space in a patterned way. In macroscopic laws called classical mechanics: there were two types of laws therefore, wave laws and particle laws. These laws are basically differential equation. SO we had a wave equation of motion and a particle equation of motion, each of which are differential equations.

When microscopic entities and phenomena were understood we see that there is a mixing of these two kinds of laws or differential equation: the waves and the particles merge to give us a new type of equation of motion or differential equation called the Schrodinger equation. This Schrodinger equation called quantum mechanics, splits into either particle explanation or wave explanation.

It turns out that macroscopic phenomena and objects are rather a mixation of waves and particles at the microscopic level which are explained by a combo-differential-equation instead of particles and waves as separate differential equation. So there are two things: waves and particles at the macro level are actually mixing of waves and particles at the micro level. Now we have one law: Quantum Mechanics. {waves+particles at micro is 1 law, earlier waves and particles at macro were two laws, this reduction from 2 to 1 is called reductionism, a consequence of unification, like father and mother is reduced to parents and ex-girl friends are reduced into strangers.}

But since macroscopic studies were performed for 100s of years there is a legacy way of dealing with such rather than changing everything to fit the micro laws. (quantum laws) But there is a robust understanding how they all fit together: called a correspondence principle at times because quantum or micro laws transpire/correspond into macro laws.

*BZ* thinks there are two laws, one for small and one for big, hence he will believe in God rather. Not that any amount of explanation is sufficient for such rashes. But let me give it a shot. BZ was shut up by some earlier answers of mine and some think-able people.

Quantum laws pervade everywhere. The diffraction of prism or windows, the little stars that sparkle on your window pane are all quantum mechanical effects brought into the fore of our sight. We gaze at it from our convenience, but they are produced at the minion and carried forth without prejudice to yet another scale, the scale of ours. The electro-magnetic effects from stars that are received by us is an example of how quantum effects have been carried to the grand scale of planets and stars. Classical mechanics would not have explained because they are not produced classically, just like the shoes do not explain bacteria. But bacteria causes bloodshed in our posterior. They came from within, they are not outside demons of bible. Bible explains things that do not exist. But Quantum Mechanical laws explains things that exist, those that are suitable for our growth and sustenance and those that cause us blood and bad health.

Manmohan Dash

some commentaries:

  • (SK) A comprehensive study of Micro and Macro State is in Statistical Mechanics.
  • (MD) Although thats slightly advanced than mechanics in terms of wave particles. There everything is treated as given, quantum and classical formalism, statistics methods and techniques, complexity, empiricism, chemistry.
  • (MD) SK; and here the question was a bit elemental in terms of micro and macro. I mean in quantum texts they would use different terminology, like “elementary particles” and “large objects”, “planetary objects” or something !!
  • (SK) We are also in a micro state with reference of the universe.
  • (MD) well we are in a relative-micro scale. But since scale can be defined without bringing in Physics advance concepts, it suffices to be in an absolute scale, where we have string theoretic, atomic, nano, micro, everyday-scale, atmospheric, planetary, cosmological, extent of universe.

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