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Weirdness & The Beauty of Quantum Mechanics

(Last Updated On: October 15, 2019)

Quantum Mechanics

As mathematical machinery that can capture the essence of the micro world, the formalism of quantum mechanics is an indubitable success. However, the attempts to realize the inner workings of the micro world in terms of our long-cherished classical notions of reality are doomed to fail. Physicists began to comprehend that the universe is constructed quite differently from how they had supposed.

With any theory at a certain point, you can’t help asking ‘so why things behave this way? where do these rules come from?’ Unlike other areas in science where experiments could be done systematically and conclusions could be drawn through proper observations and measurements, for quantum mechanics, things are not so simple. We never could say that quantum mechanics is a theory that one could test by observation and measurement but rather it’s a theory about what it means to ‘observe and measure’.

Also Read: Quantum Fields (Real or Not)

From now on my attention goes a little deeper to the paradoxes and puzzles of quantum mechanics. We will see the weirdness & beauty of quantum mechanics. Starting with the most famous of them all the ‘Schrodinger’s Cat’.

Schrodinger’s Cat

For a normal person, a cat kept inside a box is nothing much to think about. But for a physicist like Erwin Schrodinger, this scenario seems to be a quantum puzzle that woke him up at night.

Schrodinger imagined a cat together with a decaying radioactive source kept inside an opaque box. There is a chance of 50 percent for the decay to happen and it causes the breaking of a cyanide bottle and the cat to be killed. With a classical approach each time the box is opened and it’s verified whether the cat is dead or alive. One finds that it is dead half the times and alive in the other half. Now suppose that quantum mechanics is applied to the cat and a quantum state | alive ) or | dead ) is given to it, one could expect mysterious results.

Prior to the measurement that is before anyone opens the box and checks the condition of the cat it is represented by a superposition of states |alive) or |dead) given as

|ψ) = 1 √2 { |alive) + |dead) }

I have no further intention to add any equations as I remember the words of Professor Stephen Hawking who once said: “with each equation included in a book it would halve the sales”. Now going back to the expression representing the state of the cat anyone with basic knowledge in math could figure out that there is an equal probability of 1,2 each for the cat to be both alive and dead before measurement.

Now the question arises as to what is so special about measurement?

The involvement of a conscious observer who measures the state of the system forces the system to enter into any of its eigenstates or in other words the wave function collapses by the act of measuring the state. This is why in this case as soon as we open the box we are left with a cat either dead or alive and not a superposed state.

There are many interpretations in quantum mechanics, the one about the superposition of states before observing the system is the famous Copenhagen interpretation. That means the act of measuring affects the system, causing the set of probabilities to reduce to any one of the possible values immediately after the measurement. Here the involvement of a conscious observer for carrying out measurement is a subject of debate even today. Philosophers and scientists are yet to find a proper meaning for the word ‘conscious observer’. For time being let’s focus our attention on a famous paradox put forward by Einstein and hence leave the Schrodinger’s cat in its superposed state.

EPR Paradox (Einstein, Podolski & Rosen )

Einstein, as we know is the most prominent theoretical physicist to have walked the earth. Einstein’s viewpoint of reality was in disagreement with that of quantum theory. He started to doubt the completeness aspect of quantum mechanics. For this, he analyzed the description of many-particle systems in quantum mechanics and argued that either quantum mechanics is an incomplete theory or else one needs to give up the long-cherished notion of locality.

Einstein along with Boris Podolsky and Nathan Rosen arrived at these conclusions in their groundbreaking 1935 paper-usually called the EPR paradox. The main focus of that paper was the entangled electron spin states. Let’s suppose that there are 2 electrons with each pointing either up or down giving it spin up or spin down state respectively. Now that imagine these 2 electrons are correlated or entangled and somehow their properties are interwind. These entangled electrons are now sent to two different places A and B. If a scientist at A measures the spin of that electron he might find that it is spin up. Immediately he could conclude that the one at B is spin down.

Danish physicist Niels Bohr said that quantum properties like the spin exist only when we observe it. Until that point, they don’t have any particular value. As soon as the spin of the electron at location A is measured and found to be spin up the one at B turns out to be spin down. This ‘instantaneous communication’ was the core of the EPR paper.

But that’s impossible because Einstein’s theory of special relativity prohibits any signal to travel faster than light. If Bohr’s intuition was right that quantum particles do not have the properties at all until they are measured, then the EPR experiment contains a magical effect that Einstein called ‘spooky action at a distance’. Einstein found the situation unsatisfactory. He refused to believe that at the fundamental level nature is statistical. ‘God does not play dice’ was his famous quote showing his disagreement with the foundations of quantum mechanics.

The quantum puzzles described above are just two among a lot of other mindblowing quantum phenomena. If we dig deep enough into the scientific and philosophical implications of entanglement one could realize that at the beginning of time every atom, electron, quark and all other elementary particles were situated in a space so tiny that their wavefunctions overlapped. So during the initial stages of the big bang, everything was together or we could say things were in an entangled state and even with the evolution of space and time all the species share some common traits because of the initial entanglement we all had way back in time.

Maybe one day scientists would discover the role entanglement in developing emotional connections we feel towards other creatures. With that being said it could be summarised by indebting the words of the famous Physicist Max Born who once said,

I’m now convinced that Theoretical Physics is actual Philosophy.

Read Also: The Nature of Quantum Fluctuations