Once upon a time, a British gentleman called Thomas Young did a nice little experiment involving light. He wanted to prove that light propagated in the form of waves.

As it was 1801 it was needed to "prove" that little fact about light.
The experiment was quite simple. Young made coherent light travel through two very narrow slits on a wall at the same time. Beyond the wall he kept a screen to check the final incidence pattern of light.

The setup was something like this:
The single slit was a desperate attempt at getting coherent light. It was 1801. Laser was many years away.

What Young got was an interference pattern on the screen which can only happen if light propagated as wave.
The single slit pattern has been provided as reference.

You get a brightest band when two peaks coincided. When a peak met a trough they canceled out each other and produced a dark band. Other bands of varying brightness lay between those two extremes.

Light became seriously controversial again in 1921, when none other than Albert Einstein received the Nobel Prize for discovering that light consists of tiny sub-atomic particles, which later came to be known as photons.

So, it seemed, light could exist both as particle as well as wave. This strange phenomenon was labeled "wave-particle duality". It was subsequently discovered, thorough different experiments, that all subatomic particles had that property. This raised serious questions about our understanding of reality. Because it allowed the fundamental building blocks of universe to exist in an ambiguous state. A particle is very different from a wave. While the former is concentrated mass, the latter in distributed energy.

Quantum physics got a big boost when an electron gun was invented which could fire one electron at a time. Until then we always had to deal with a group of electrons. Group behaviour always differs from individual behaviour in some way or the other.

Anyway scientists performed the double slit experiment again with one electron at a time. The sole electron has two choices now:
  1. Go through any one of the slits
  2. Collide with the wall and die.

The choice of going through both the slits simultaneously and subsequently interfering with itself did not exist. With thousands of electrons flying around at the speed of light, that was always a possibility however distant.
After a few million rounds of firing, scientists got the same old band pattern. This time the pattern is not visually appealing as electrons are used.

So the most obvious conclusion was that each electron became a wave and passed through both the slits simultaneously. But that would be an irreversible process which did not quite agree with the phenomenon of wave - particle duality, which demanded that both the natures be present at the same time . It entirely depended on the apparatus used. An instrument designed to measure a particle should see a particle. The same apples to wave also.

I know it is confusing and demanding at the same time. To understand it better one may consider an amphibian vehicle as an example.
The strange contraption is a boat and a car at the same time. We need to take it to an appropriate terrain to test its particular ability.

Coming back to the experiment, scientists wanted to see through which of the two slits did an electron travel through. So they placed a detector after each slit.
The presence of the detector changed the way the elections behaved. They suddenly started behaving like particles. The pattern on the screen changed completely to suit the particle like behavior.

The beautiful interference pattern collapsed just because of the presence of a detector. In quantum physics lingo this is called the observer effect.

Observer effect is the central mystery, and as per Richard Feynman the only mystery, of quantum physics. The quantum world behaves differently in the presence of an observer. It is possible that it becomes too self- conscious. We, civilised humans, do that all the time. After going through the wide range of mind-boggling, imagination-stretching, sanity-testing interpretations listed in Wikipedia, I feel encouraged to come up with my own interpretation.

I propose, rather preposterously, that every quantum particle has a ghost inside it. Furthermore, I also postulate that a particle has an identity preserving aspect which a wave singularly lacks. It is too easy to merge and split waves.

The ghost owns the particle assigned it. It is little possessive about the right of space assigned to it through the particle. It is also quite skeptical about humans. Their limitless hunger for resources have left every square inch of land owned by someone.

The ghost, under normal circumstances, likes to relax by spreading out the particle as a wave. But whenever a human agent came looking for a particle the ghost promptly collapsed the wave and presented a particle.

I know that the reader may see a high alcohol level in blood behind the hypothesis. But trust me there is competition for that unenviable label too! One of the popular interpretations want is to believe in the existence of multiple, totally segregated worlds.

In the next part of this article I will discuss about some other equally spooky quantum phenomenon and apply my ghost theory to explain them.