One of the most famous experiments in physics is the double slit experiment and why is it famous?
According to Richard Feynman, the Nobel Prize-winning Physicst who made remarkable contributions to quantum physics “Double slit experiment is a phenomenon which is impossible to explain in a classical way and which has in it the heart of quantum mechanics.
Let’s break down what Richard Feynman meant when he said — impossible to explain in a classical way.
We are not going to discuss the in depth physics of the experiment which is beyond the scope of this article.
To start off, imagine a wall with two slits in it. Imagine throwing tennis balls at the wall. Some will bounce off the wall, but some will travel through the slits. If there’s another wall behind the first, the tennis balls that have travelled through the slits will hit it. If you mark all the spots where a ball has hit the second wall, what do you expect to see? That’s right. Two strips of marks roughly the same shape as the slits
In the image below, the first wall is shown from the top, and the second wall is shown from the front.
We observe the above pattern in our classical world. We know everything in our classical world is made up of atoms, so our each tennis ball is also made up with billions of atoms. According to the quantum world, if we conduct the same experiment with the atoms of these tennis balls with smaller slits and a screen behind the slits, we don’t observe the same above pattern but instead we get a interference pattern as shown in the image below
This made Physicsts curious so they decided to detect the path of atoms. They placed a detector between the split and screen, then something weird happened the inference pattern changed back to the particle pattern like the one we observed with the tennis balls. Same thing happened even when they placed the detector before the split. No matter where they placed the detector the moment they tried to detect the path of the atom, the inference pattern changed to particle pattern and with the detector off it changed back to inference pattern.
This is spooky and no one in the Physics world has the explanation for this behaviour and no one has ever seen anything like this in the classical world
Now let’s try to understand the spookiness in the experiment with another system in the Classical world. Every system in the Universe has granularity and these granular level particles or items have their own distinct characteristics.
In double slit mass is the system with atoms at the granular level. For our thought experiment we are cosidering the Humans as a system. Just like each tennis ball is made up of billions of atoms at their granular level each human system is made up of billions of people
Imagine each of our human system is made of shy people, introverts, extroverts, non vegetarians and animal haters and some other people with unidentified character and each system has equal number of people with equal number of these characteristics
Imagine there are two doors just like the slits and behind the slits there are multiple rooms which are completely unique and they just allow people only with unique characteristics(There is one room for shy people, one for introverts, one for extroverts, one for non vegetarians and one for animal hater) and there are two special rooms right behind the doors where anyone can enter irrespective of their character
If we start sending each human system through these doors and asked them to occupy a room. we will find everyone in those two special rooms which are right infornt of the two doors because these human systems are mix of different characters so they can’t occupy other rooms because they can’t distinguish themselves from other human systems
Now lets break each human system just like we broke the tennis ball into atoms in the double slit experiment. The granular level of each human system is each indiviudal with unique character (the person can be shy, introvert, animal hater or person with unidentified character)
If we start sending each individual through these doors you don’t see all the people in just two special rooms like before. Instead you see all the rooms being occupied because each individual has a unique character, you see a different pattern just like the interference pattern. Now if I stand at the door to record which room each individual is occupying then again I may find all the people in the two special rooms right behind the doors because people doesn’t want to reveal their real character so the pattern returns just like we observed in the double slit when we placed a detector
It is not weird and spooky and we can observe this in every system if we can break the system into its granularity. The behaviour of the granular particle doesn’t have to match up with the behaviour of the system. The behaviour of the tennis ball doesn’t have to match up with the behaviour of its atoms and maybe the behaviour of galaxies doesn’t have to match up with the behaviour of planets. The behaviour at granular level depends on the characteristics of granular particles that make up the system
This might not be the problem of Classical world or Quantum world, the behaviour emerges at the granularity of the system