The classical mechanics (and it's relativistic enlargements) describes macroscopic objects. This objects consist of a very large number of particles, normally atoms. The properties of the mechanical objects can be exactly defined (mass, speed, position in space) and reproduce.
Differently the particles. It is virtually impossible to measure the properties of a single particle exactly. To describe particles in thermodynamics we already operate with probability. All particles have different speed and positions, this means different energies (and also relativistic masses). Furthermore particles can change their energies continuous. You can say that all particles have variable internal energy. Scientists like Pauli and Heisenberg apply the mechanics to the particles. How reliable can be mechanics in this case?
Quantum mechanics surely has it's limitations. For example it is based on the principle of action at a distance. Quantum field theory rectifies this by using force carrier fields such as, photon, W+, W-gauge bosons. Such a field theory again has its own limitations. When we fix an interaction vertex, the uncertainty in momentum becomes very large. The scattering cross sections and decay rates involve integration over all possible momenta. Therefore we face infinities. We often say that the scattering cross section is blowing up. This problem is again fixed in a string theory, which again has it's own problems. Primary problem is that to test predictions of string theory one has to build colliders of super large energies, which are beyond our current technical abilities. Therefore, viewing in proper perspective, we should not think that quantum mechanics is an ultimate and final theory. We should rather appreciate the partial success of this theory in explaining microscopic phenomenon.
The theories of quantum mechanics are based on the Copenhagen interpretation according to which basic postulates of single particle quantum system are,
we therefore see that (historically) even in the early days of the formulation of quantum mechanics scientists were aware of many of it's limitations.
Thank you for the answers!
But I'm just in a hurry so I can't reply.
Hans: I have no idea why I have received a down-vote. My point is the most simple: Every known theory in Physics has its own limitations.
Dear Biswajoy!
I don't know either.
What do you mean with "Every known theory in Physics"?
In my opinion: it exist only reality and no theory. If a theory has limitations, the theory is consequently wrong. This theory approach to reality, but a better theory will be found. We have some theories to describe the world of particles. No theory is congruent with reality and here lies the problem.
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