What is meant by the term "elements of physical reality" used by EPR paper? I was thinking about the phenomenon of quantum entanglement. The widely accepted view of nature of reality is that of copenhagen interpretation(please correct me if I am wrong!) while Einstein pointed out that this picture lacks something called "Elements of Physical reality"
I didn't understand what EPR intended by that term. Can anyone explain it to me? Or is there any way to better understand the phenomenon of quantum entanglement?
 A: 
The widely accepted view of nature of reality is that of copenhagen interpretation(please correct me if I am wrong!)

I am not sure whether it is "widely accepted" today. Bohr and company tried to persuade everyone there is nothing to worry about in the EPR paper, and that was quite successful, but then later John Bell and others have shown them wrong (Bell's inequalities), and after that we have many people and papers studying quantum theory interpretations. So I think the Copenhagen philosophy is not as widely accepted today as it was while Bohr lived.
I recommend reading the EPR paper. Regarding elements of reality, EPR explain what they mean in there:

A comprehensive definition of reality is, however, unnecessary for our purpose. We shall be satisfied with the following criterion, which we regard as reasonable. If, without in any way disturbing a system, we can predict with certainty (i.e., with probability equal to unity) the value of a physical quantity, then there exists an element of physical reality corresponding to this physical quantity.

A: The original article by Einstein, Podolsky and Rosen includes the following paragraph:

The elements of the physical reality cannot be determined by a priori philosophical considerations, but must be found by an appeal to results of experiments and measurements. A comprehensive definition of reality is, however, unnecessary for our purpose. We shall be satisfied with the following criterion, which we regard as reasonable. If, without in any way disturbing a system, we can predict with certainty (i.e., with probability equal to unity) the value of a physical quantity, then there exists an element of physical reality corresponding to this physical quantity. It seems to us that this criterion, while far from exhausting all possible ways of recognizing a physical reality, at least provides us with one such way, whenever the conditions set down in it occur. Regarded not as a necessary, but merely as a sufficient, condition of reality, this criterion is in agreement with classical as well as quantum-mechanical ideas of reality.

EPR didn't provide a complete definition of an element of reality, but they thought it must include being able to make predictions about it with probability 1. Since quantum mechanics doesn't always allow this EPR thought there must be some other description that improves on quantum mechanics and allows such descriptions. Later physicists figured out that any such description consistent with the predictions of quantum mechanics would have to be non-local.
AFAICT the Copenhagen interpretation gives no account of what is happening in reality to produce the outcomes of the EPR experiment, and denies that any such explanation is possible or desirable. But since there can be no such thing as checking whether an experiment has been done correctly unless there is an account of what is supposed to happen in reality in that experiment this philosophy would, if taken seriously, require abandoning physics. And furthermore, since every experiment involves physics it would undermine all of science. This is not very satisfactory.
There is an account of what is happening in reality in experiments involving entanglement. The short version is that in entanglement experiments quantum information is carried in decoherent quantum systems in such a way that the expectation values of those systems aren't dependent on that information - this is called locally inaccessible information:
https://arxiv.org/abs/quant-ph/9906007
https://arxiv.org/abs/1109.6223
A: Every particle has “elements of physical reality”. We couldn’t detect them if they didn’t. These elements, also known as variables could be as simple as mass, velocity, direction, angular momentum/Polarization, oscillation/frequency, coherency/timing/linear dependence.
EPR discusses perfectly correlating two particles, and as many of these   “Elements of Physical Reality” as possible. Then sending them in different directions to be measured later. IF everyone of these unhidden variables are not perfectly correlated, then the results can be skewed.
