Intuition is something all of us heavily rely on in our day to day life, mostly without being aware about it. So what’s intuition? Intuition is nothing but subconscious decisions we make, which need not be logical or rational. These decisions are based on our model of “reality”, accumulated from normal life experiences. For instance, if there is a kid sitting in a car holding a helium balloon tied to a string, it is simply intuition which would tell you that if you accelerate the car in the forward direction, the balloon should tilt backwards. (In reality, it actually tilts forward as its lighter than air !)

Intuition is what makes us believe that if we blow air between two strips of paper held parallel to each other, both the strips should move apart.

It is again intuition, which would tell you that the friction on a rectangular block kept on a rough surface would be more if it is laid on the surface horizontally rather than kept standing vertically, such that surface area of contact is more in the first case (Intuition betrays once again ! Friction would actually be the same in both the cases, as friction is independent of surface area of contact). Intuition is so overwhelmingly convincing that it leads ancient Greek philosophers to believe that the Earth is flat for embarrassingly many centuries.

In 1927, experimental physicists Clinton Levisson and Lester Germer performed an experiment of paramount importance, so much so that it ignited the initial flames of a whole new revolution in physics, known as quantum mechanics, which govern how subatomic particles behave. This experiment, popularly known as the double slit experiment involved a barrier having two slits or gaps, an electron gun capable of firing electrons towards the barrier and a screen parallel and beyond the barrier to detect and count the emergent electrons.

When the first slit was closed and electrons were fired at the barrier at a constant rate, some x electrons hit a particular region A of screen, passing through the second slit. When the second slit was closed and the same thing was repeated, again x electrons hit a particular region B of the screen, passing through the first slit. So if we were to open both the slits and fire electrons again, there should be 2x electrons(x electrons each in region A and B) hitting the screen right ? Surprisingly, the actual outcome was way different.

Results of the Double Slit Experiment when firing electrons

When both slits were open, there were regions in the screen that were abundantly hit by electrons alternatively along with regions whereas no electrons hit at all, creating alternating dark and light bands respectively. Some dark bands (where electrons hit) were outside region A or B while some light bands(where no electrons hit) were in region A or B, which completely defied logic and intuition of how particles should behave.

The most peculiar thing was this pattern that had formed on the screen was exactly the same as the characteristic pattern of interfering waves which also produced alternating dark and light regions owing to constructive and destructive interference of waves respectively.

Double Slit Interference of Sunlight

This could mean only one thing : electrons behaved as a particle when one slit was closed, with the other open, while the electrons behaved as waves when both the slits were open ! With this, we arrived at the wave/particle duality, every particle is a wave and every wave is a particle too. Another strange thing is that this behavior is only exhibited in particles upto a certain size, the maximum one observed till now being molecules that each comprised of 810 atoms.

The double slit experiment formed a base that lead to even stranger theories. For example, it was found that if only one electron is passed through either of the slits, both being open, the interference pattern of alternating bands was observed on the screen. This was unexpected because a wave cannot interfere with itself. Hence, this pattern could mean only one thing — that one electron passed through both the slits simultaneously. Quantum superposition was hence discovered, i.e. a particle can occupy different positions at the same instant of time. Consequent experiments and theoretical advances in this newly discovered sub atomic realm lead to even more bizarre theories in quantum mechanics — such as the mere act observing the outcome of an event might alter its past, also implying nothing exists until it is observed; pair of quantities, such as position and velocity of a particle cannot be simultaneously measured with complete accuracy, no matter how precise instruments become (Heisenberg’s Uncertainty Principle) and so on.

If you feel baffled, lost and simply think quantum mechanics doesn’t make any sense, you are not alone. Albert Einstein, despite being the founding pillar of quantum mechanics was later extremely apprehensive of it — the probabilistic nature of quantum mechanics as well as the presence of a fundamental uncertainty was completely indigestible to him. Despite all the opposition it had faced initially, each and every experiment has agreed with the results of quantum mechanics and has confirmed its validity. Quantum mechanics today finds it’s applications in practically every field of modern science and technology : be it study of the atomic structure, microbiology and genetics, electronics and integrated circuits, and so much more.

Lord Kelvin, one of the greatest physicists of the 19th century, who deservingly earned his first name because of his insurmountable contributions to numerous branches of physics, especially thermodynamics, had once famously said in 1900, “There is nothing new to be discovered in physics” while the head of the U.S Patent Office is said to have recommended the government to close the patent office and save the expense because he believed “Everything that can be invented, has been invented” Little did they know about the irony in their words, when merely 5 years later, the greatest revolution in physics took place with the discovery of special and later general relativity as well as the beginning of quantum mechanics, something that entirely shook the very foundation of science. For me, this is the best part about science: it is an ever evolving and dynamic study. Change is literally the only constant in science. Nothing is absolute and permanent, as Einstein had rightly told, “No amount of experimentation can prove me right but a single experiment can prove me wrong”.

It is quite strange that we can very accurately tell the chemical composition of the core of planets and stars hundreds and thousands light years away from Earth using complex methods such as spectral analysis, but we hardly know anything about the internal composition of our very own Earth as well as the cause of the Earth’s magnetic field. We went from strongly debating whether molecules and atoms exist or not to designing and producing molecular machines, i.e. molecules whose movements can be controlled by us and hence be used to perform tasks when energy is supplied (for which the Nobel Prize in Chemistry (2016) was awarded). Heck, we can synthesize artificial elements and create exotic particles in particle colliders now. We have come to such a level in genetics that we can create test tube babies as well as genetically modify characteristics, but we still aren’t sure how our brain works and neither have we gained much lead in curing cancer and viral diseases. We may be knowing so much, but yet we know so less. This, I would say is the beauty of science. This urge for knowing and understanding is what drives us forward. This quest for finding the beauty in science, is what advances mankind.