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Shri.S.Ramakrishnan, Inspector of Customs, Trichy is the author of this article.
The world of atoms and the particles smaller than the size of atom is completely different from the world which we see. The world of atoms and particles smaller than atom is governed by ‘Quantum Mechanics’. The behaviour of atoms and sub-atomic particles defies our common sense and poses so many interesting and complex questions.
Dual Nature of Light:
For example, you can ask this very simple question. What is light? Is it a wave? Is it made up of particles? The answer is ‘yes’ to both the questions.
Light exhibits the properties of wave as well as of particle. Light may be easily construed as wave from the properties of reflection, refraction, interference etc., But, it is also known to be made up of tiny particles called ‘photons’. A ray of light may have millions of photons in it. This is what makes it interesting. How? A wave is something which transmits energy and it has got certain characteristics. Particles are matter that occupies some space. They don’t have the characters of waves. The light behaves both as wave and particle.
‘Double-Slit Experiment’ is a famous experiment that shows this dual nature of light. The experimental set-up is something like the one mentioned here.
This is how bullets (particles) behave:
Take two card boards. Place one cardboard behind the other i.e., both the card boards stand parallel to each other. Now make a hole in the first cardboard. Take a gun and shoot continuously at the hole of the first cardboard. What will happen? All the bullets that cross the hole of the first cardboard hit the second cardboard and a cluster of bullets will appear in the second cardboard.
Make one more hole below the first hole of the first cardboard. Now shoot continuously at both the holes of the first cardboard. The second cardboard will now have two clusters of bullets in line with the two holes of the first cardboard. It is obvious that this happens.
Behaviour of Light as particle in Double-Slit Experiment:
Assume that you have photons (the particle that constitutes light) with you. Repeat the experiment.
First time there is only one hole in the first cardboard. You throw the photons that you have at the hole of the first cardboard. What will happen? Like bullets, the photons that crossed the first cardboard form a cluster in the second cardboard like the bullets you fired. The photons exhibit the property of ‘particles’.
Behaviour of Light as waves in Double-Slit Experiment:
Now you make the second hole below the first hole of the first cardboard. Throw the photons at both the holes. Will there be two clusters of photons in the second cardboard? No. There will be an interference pattern in the second cardboard. When the photons are thrown at two holes they don’t form two clusters. Instead they form an interference pattern which is the character of wave. Now the photon exhibits the property of wave.
What could be made out of Double-Slit Experiment?
When there is only one hole at the first cardboard the photons simply formed a cluster as like the bullets. But when there are two holes the photons form interference pattern like a wave. So, dual property of light is proved here. So what is interesting? The story does not end here. The interesting part of Double-Slit Experiment starts here.
Light defies Logic on further Double-Slit Experiment:
To test this further, instead of throwing photons at both the holes simultaneously, we throw only one photon at a time continuously. The photons can go through only one of the holes and there is no possibility of interference between photons and there is no chance for forming wave pattern as in the in earlier case, in which wave pattern was formed when more number of photons were thrown through a single hole.
So, they must form only two clusters on the second cardboard now. This is only our assumption. But on the contrary, our assumption fails as Light starts to defy logic. Even when you throw only one photon at a time, still the second cardboard has interference pattern which is the property of wave.
This is most intriguing about the behaviour of photons. Even when there is nothing to interfere with even then they form interference pattern by exhibiting the property of wave. How this is possible?
Double-Slit Experiment by closely observing the slits:
[Result: Light says “when you mount a watch on me I will behave like a particle, when I am not watched I will act as Wave!”]
Perplexed by the behaviour of photons, Scientists made an arrangement to observe how this is possible. They placed a photon detector near both of the holes to watch, through which hole the photons pass and repeated the experiment (i.e., throwing only one photon at a time continuously). To confuse the scientists more, the photons started behaving like bullets i.e., they formed two clusters on the second cardboard and not an interference pattern (wave property). The scientists took the next step. They removed photon detector from one of the holes and repeated the experiment. Even now the photons did not make any interference pattern but only two clusters in the second cardboard.
The following video would give you crystal-clear explanation of Double Slit Experiment.
So from the last leg of Double-Slit Experiment, it could be observed by scientists that
Light display both the properties of particle and wave.
They know that whether there is one hole or two holes in the cardboard.
They change their behaviour when they are being observed.
They not only know whether there is a photon observer near the hole through which they pass but also whether there is a photon observer near the other hole.
Are particles of lesser size Conscious?
It is interesting to note that not only photons but also atoms and all the particles of size lesser than atom behave exactly in the same manner as the photons did. Are atoms and particles of lesser size conscious? If not, how do they know that they are being observed? Why do they change their behaviour once they are being observed? So, what is real? Is it the behaviour of these particles when they are not being observed? Or is it the behaviour of them when they are being observed?
God does not throw Dice:
Is it true that the world (ultimately composed of atoms and other small particles) exists only when we observe? What happens to world when we stop observing (through any of our senses)? We can’t for sure prove that the world still continues to exist when we are not observing !
Einstein could not accept the proposition that something exists only because it is being observed. Because it removes certainty from the world as anything in the world changes its behaviour depending upon whether they are being observed or not.
God, as far as Einstein was concerned, has not made anything uncertain in this world. Hence, Einstein tried to prove “Quantum Mechanics” wrong and he also famously remarked,
“God does not play dice”.
The views expressed in this article are those of the guest author and are not intended to represent the views of GConnect.