The fundamental difference between Newtonian mechanic and quantum mechanics lies in the fact that Newtonian mechanics is covered with the motion of a particle under the influence of applied force and it taken for granted that such quantities as the particles position, mass, velocity and acceleration can be measured simultaneously, whereas Quantum mechanics is concerned with the motion of a particle taking into account the facts of Heisenberg uncertainty principle according to which the position and momentum of a particle can’t be measured simultaneously with accuracy.



The quantities whose relationship quantum mechanics explores are the probabilities. For example the radius of electrons orbit in ground state hydrogen atom is always exactly 5.3 * 10-11 according to Newtonian mechanics but quantum mechanics states that this is the most probable radius. Hence Newtonian mechanics is nothing but an approximate version of quantum mechanics. So for the microscope universe, the quantum mechanics represents out best efforts to data in formulating it.



The exact position and momentum of electron is not be possible. to know about this statement let's study about uncertainty principle.



To understand the physical concept of uncertainty principle, first we need to know the position of an object is determined. Now for determination of the position of an object, we must to able to see the object. And we know this can be done only by the help of light of suitable wavelength.



When a beam of light falls on any object, the photons of the incident light are scattered at the surface of the object and the reflected light, which is reflected by the cause of reflection, is enters our eyes.



Now, if the object is large, the position and velocity of the object will not change by the impact of the striking photons of incident light. Then we found that it will be possible to determine both the position and velocity of the object simultaneously.



But, at microscopic level, means to say in case of microscopic objects, such as electrons, the interaction of the striking photons of incident light with the particle will cause appreciable displacement of the particle from its normal or original path. And this considerable change in the path of the electron is the proof of uncertainty.





As a result of this, there is the considerable change in its path and velocity due to the impact of a single photon used to observe it. Thus, the very act of measuring the position of the microscopic particle causes a change in its momentum. The collision of photons of the incident light with the electron sends it in an unpredictable direction.



So according to the Heisenberg uncertainty principle it is not possible to determine simultaneously the exact position and momentum of electron or other microscopic objects