The quantum amusements

Quantum mechanics started as an attempt to concoct a discretized model of nature. Einstein's explanation of photo electric effect by using Plank's quanta model of light provided the ignition quantum mechanics needed to rock the scientific community. When the whole scientific world was busy celebrating the success of Einstein's General relativity and Special relativity, the few other scientists very busy creating their share of history. The success of Einstein's General relativity had huge impact on how physics and in general science had to studied and discovered. The rules were simple and elegant, define some properties for any physical object and try to concoct a theory on how these properties and variables were going to evolve with time. Einstein's General relativity dealt with position, velocity and acceleration as these variables. Somehow, some other great scientists such as Bohr, Schroedinger, Heisenberg did not get the memo of these rules. They themselves devised a theory which questioned the very existence of these variables and their values. Einstein's universe was purely a deterministic universe. If state of the universe at any particular moment is known, then there exists physical laws which will determine universe's state at any time of future and past. Here by "State", we mean the values of these "Properties" or variables(position, velocity, acceleration , spin etc.) for every particle of this universe. Einsteins idea was simple, even if we don't know the values of these variables in current state and we also don't know the physical laws according to which these variables evolve, there are some values of these properties which are there and also are laws according to which these variables evolve. Einstein's deterministic universe left no space for any free will which we feel. Einstein used to call "free will" as an illusion of human prejudices. Then came Heisenberg's uncertainty principle which said that natures itself introduces randomness to values of these variables. Heisenberg uncertainty principle asserts that it's not merely practical limitation on some value's calculation, in fact that it's meaningless to ask for the value of that variable before the measurement has been made. Basically, it says that there is no reality evolving with time unless you make a measurement. And what value we will get on measurement, is purely random. We can only know the probabilities. Bohr was ardent supporter of this idea. Einstein was totally against this idea. "God doesn't play dice with universe", He Said. He proposed that toss of dice also looks probabilistic from the first glance, but if we exactly know all the variables(velocity, spin , air friction etc) at the time of toss, we can exactly predict which number we are going to get with the toss. He asserted that such variables should also exists for quantum mechanics which will predict the outcome of quantum measurements correctly in each case rather than just assigning probabilities. In 1927 Solvay conference, Einstein came up with several thought experiments which tried to show shortcomings of Heisenberg Uncertainty principle. For every thought experiment, Bohr had answer. Interestingly, in one of the answers, Bohr used Einstein's General relativity to controvert the Einstein's thought experiment. Einstein's continued his quest to prove that quantum mechanics did not provide complete picture of nature's mechanism. In 1935, He published a paper known as EPR paradox. I will not go into the details, but paper basically demonstrated a thought experiment which showed that reality exists even before you measure it. For once it seemed that Einstein had controverted quantum mechanics. This time even great Bohr had no answer. Einstein died thinking that quantum mechanics was an incomplete theory. In 1964, Bell came with an inequality which has to hold for any theory which is local in nature(all effects are local) and which assumes some real values of variables even before measurement. It was found that Quantum mechanics violates that inequality. So indirectly it was proved that no one could concoct a theory in agreement with quantum mechanics which predicts the variables before measurement and which is also local in nature. Einstein's dream died with this theorem. We constantly talk about reality, but it does not even exists before we measure it. Reality or locality, make a choice!!