**Introduction**

At the smallest level inside an atom, the world behaves differently than what is observed with the naked eyes. In our fast paced lives, where we are concerned with the concrete nature of things – its definiteness, it was difficult to accept that the universe at the quantum level is no different than a coin toss, and relies on probability of events , rather than a fixed set of well-defined equations governing its behavior. Einstein and Bohr, two of the greatest physicists debated on various theories of quantum physics.Albert Einstein didn’t really believe in quantum mechanics, as more than often it was self-contradictory and often violated its own logical conclusions. Needless to say, quantum theory, even after decades of study, is still in its infancy and has a long way to go in order to be established as something concrete. As a result of which, several interpretations and versions of it was established in order to explain its bizarre nature.

**Interpretations of Quantum Physics**

*1. Copenhagen Interpretation(Schrodinger’s cat)*

Neils Bohr and Werner Heisenberg’s interpretation of the situation, alongwith Heisenberg’s uncertainty principle is known as the Copenhagen interpretation of quantum physics, which strives to assert the subjective-ness of the observer, whose act of observation/measurement is what forces the system of particle to select one definite state. In essence, the configuration of a system depends on the observer and through the very act of observation, the observer is interacting with the system causing it to change. Prior to the act of observation, the system is considered a probabilistic superposition of all possible states the quantum particle. This was clearly stated through a thought experiment by Schrodinger that involves the famous, “Schrodinger’s cat”.

*This thought experiment, consists of a cat inside a closed box with a radioactive/poisonous source that could be triggered by the cat. The box, in question is soundproof and perfectly sealed ,i.e. there is no way of determining whether the cat has triggered the mechanism and killed itself. The only way of knowing its state (dead or alive), is therefore by opening it. Schrodinger, therefore, concluded that the cat must have been both dead and alive simultaneously (exists as quantum superposition of both the states – dead and alive) , prior to opening the box when it forces itself to take only one .*

The above theorem is applicable to all real life scenarios that involves uncertainty, such as a practical coin toss. While in the air, the coin is a quantum superposition of heads and tails. A layman would interprets this spinning coin above the palm to be of neither heads, nor tails, but according to Bohr-Schrodinger’s theory, the coin can be interpreted as both heads and tails.

*2. Everett Interpretation/ Many-world Theory*

The many word-theory strives to assert the objective nature of reality and opposed to the previously mentioned Copenhagen Interpretation. This states that all possible that could have occurred in the past, has occurred in some other universe(multi-verse).It says that the universe is therefore, a tree that branches out every time a quantum state of any particle of that universe is determined. The observer, therefore, only experiences one such state in his present universe and experience a different outcome in another.

In the context of Schrodinger’s cat experiment, Everett’s interpretation suggests that at the precise moment when the box is opened, the universe splits into two branches , where the cat is dead is one and alive in another.But, the observer who notes only one such reading continues his existence in only one branch.

**3. Bohm’s Interpretation/De Broglie- Bohm Theory**

This states the existence of the quantum configuration, determined by a wavefunction which also asserts the objective nature of reality. However, it removes the role of the observer for it in be in one state. That is the configuration exists even when it is not observed.

If we ask the question, does the moon exist when we close our eyes? Copenhagen Interpretation would suggest that it doesnt, but according to Bohm Theory it continues to exists irrespective of the observer’s presence.

*4. Quantum decoherence*

It states that the act of observation causes the wavefunction to “collapse” into one of the either state, i.e. the act of measurement causes the quantum system to convert itself to a classical system(which is characterized by its definiteness ). In a quantum system, a particle can exist simultaneously in more than one points in space(this is what is happening inside the probability space of an electron orbiting around a nucleus) Quantum decoherence theory is quite similar to copenhagen interpretation and complements it, instead of contradicting it. This “wavefunction collapse” is similar to “quantum leap” proposed by Bohr and is in fact a different way of explaining things. The postulate of quantum decoherence theory in correct in its explanation of this jumping from one state to another, but fails to explain the dynamics/process of how it actually happens. To explain such a thing at a much more fundamental level, we still make detours from concrete scientific theories towards spirituality and consciousness, and the role of awareness in the actual process of manifestation/observation.

**Quantum Entanglement**

Two particles are said to be entangled when the act of measurement of one, affects the other instantaneously even at extremely large separation. An experiment was conducted with two particles one kept on earth and the other on the moon, and the speed of transmission of information was no different (distances where even light would take around 1.3 seconds). Information from one particle is sent to another with a speed faster than light, the moment its state is determined/measured. This phenomenon was known as “quantum entanglement”.

Einstein called this “spooky action at a distance”, due to its inexplicable nature and violation of theory of relativity.

**EPR paradox**

Named after three scientists Einstein, Podolsky and Rosen, the EPR paradox asserts the incomplete nature of quantum theory. It also states that particles can interact in a way such that it is possible to determine both its position and momentum more accurately than Heisenberg’s uncertainty principle, unless the act of measuring one particle instantaneously affects the other i.e. the particles are entangled. This quantum entanglement was therefore a blow to the existing scientific theories of the time. It also said that if the system of two entangled particles was considered as a whole, then we can determine the relation of one particle with respect to another. But, if particles are isolated, then it is impossible to determine its absolute state.