Classical to Quantum transition

 

We are build up by the classical intuitions. Newton, Maxwell, Einstein, they were and still are the pioneers of classical physics. Newton's law of gravity was perhaps one of the greatest breakthrough in the history of humankind. His apple and gravity story has been more and more pervasive since the time when he thrusted us into the world of calculus and mechanics. Maxwell's theory of electromagnetism became very famous and still forms the foundation of today's electromagnetism. Einstein, who is famous for his energy mass equivalence principle is still regarded as one of the greatest minds that ever lived. His complicated equations of General Relativity still forms the basis of how we geometrize gravity and the dynamical nature of space time. From photoelectric effect to special relativity, his contribution to physics is just astounding. For a certain time period people thought that this was the complete and correct description of the world we live in. But as we went to smaller scale there seemed an urge for another theory because at tiniest of scale the classical mechanics was just not quite right. A famous experiment, the double slit experiment made us realize that there was a need of a theory that would fundamentally alter the way we look and understand the world. This sudden urge led us to the world of Quantum Mechanics.

                                                        Quantum mechanics is a tool, a very important mathematical tool which has a reputation of being weird and counterintuitive. But it turns out that quantum theory is not very difficult. It is a linear theory and linear theories are simpler, for example Maxwell's equations are very linear but Einstein's field equations are very non linear so it is very complicated. The equations of QM were written by Schrodinger and Heisenberg in 1925 but the foundations were set earlier by person like Max Planck. It is a theory that governs the subatomic world but it is not limited to small sacle. People make mistake by thinking that QM applies only for tiny objects but it turns out that it is not only confined to microscopic domain. It applies to us and everything. The fact is just that the manifestation of it is greater at the microscopic domain

-The Double slit Experiment

In this experiment we have a gun say that fires bullets towards a plate that has two slits. Behind the slits is a screen  for the detection of bullets. Now we fire bullets towards the slits and some of the bullets go through the slit and land on the screen and some bullets do not go through. The bullets can go through either of the slit but not both. Let us say the bullet that went through the left slit will land just behind the slit on the screen and same for the bullet that goes through right slit. At the end what we get is two bands of bullets separated form each other and that is completely obvious. The bullet through right slit landed on right part of screen and left bullets on left part of screen giving us two distinct bands.

        Double slit experiment with bullets

                         

Now if we replace the bullets with electrons then do we get any difference? Our classical intuition says that what happened with bullets, the same will happen with electrons. We will get two distinct bands. But when the experiment is done, the result is surprising. Instead of getting two bands, we get many alternate bright and dark bands, just like a wave. The beam of electrons went through both slits and  interfered to produce this wave like phenomena. So are electrons wave? 

             At this time it may not be that mysterious because a beam of electrons can be wave and it is not too surprising. But, what happens when we fire single electron at a time and see the results? Ok now we fire a single electron, wait for 5 minutes and then fire another electron. Surprisingly we get the same alternate bright and dark bands. If you cover one slit, this effect completely fades away. It is only when both slits are open at the same time, we see this interference effect. So the electron  has to go through both slits at the same time to produce this interference effect but when we measure it we find it always in a single definite location which gives rise to so called 'The measurement problem of Quantum Mechanics'. A single electron somehow goes through both the slit and interferes with itself to produce the effect. It is unbelievable. So not only beam of electron behaves like wave, a single electron too behaves as a wave. And this cannot be understood by our classical intuition which treats electron like a particle. 

The experiment showed that there is something missing fundamentally in how we look at the world. So people thought what could be that wave nature and Born came up with an idea. He said that the wave associated with that particle is probability wave which describes the probability of finding that particle. The greater the hump, the greater is the probability of finding the particle. But it can be anywhere, the particle can be at the place where the wave doesn't even have a bump. This enigmatic phenomenon of particle being at multiple place at the same time is in technical language called superposition. 

Schrodinger quickly wrote down the equation for that wave. So from classical deterministic world we were then thrown into the fuzzy world of probability. 

                    The thing that was so striking was that if you encountered probability in the Classical calculation, your calculations were considered simply wrong or incomplete or there were some mistakes during  calculations . The picture of the world was absolutely deterministic and certain, nothing probabilistic there. Then QM comes along and says 'There's nothing deterministic, we only deal probabilities here'. For a person who grew with strong classical intuition, this must hurt badly. In classic mechanics probabilistic outcome were termed incomplete and then there comes a theory which had it's central idea based on probability. That is why many people had their issues with QM. Einstein famously coined the phrase "God doesn't play dice". (There are a lot of Einstein's quote out there and sometimes i doubt that he really said all of those or not, Jokes apart). But as time elapsed, people accepted this new way of thinking. And it's amazing that it only took people much of 20-30 years to accept a radically new way of thinking. So the time of QM emergence was in some sense intimidating and disheartening because all the previous theories would be replaced but at the same time very intriguing, exciting and fascinating for scientists around the globe for having a more correct description of the physical world.

You can contact me at :- kafleashesh24@gmail.com

For further information :- https://www.instagram.com/_anti_histamine/

                       

https://learnwithashesh.blogspot.com/