Conclusion

We repeat the same experiment by using a sound detector and a detector similar to the previous one (it detects the energy of the waves). The results are fascinating. See why.

Each time a photon reaches the end (both detectors) we hear a sound, because of the sound detector. We know that a photon is a particle, we also know that the sound detector reacts to a falling particle, so we are ensured that a photon has reached it. We also expect to see a curve similar to N₁₂ (light as particles). Instead what we see is a curve similar to Ι₁₂, which comes from the second part of the experiment (light as waves)! In other words we "hear the particles" but we "see the waves".

If we repeat the experiment by having only the one slit open we take a curve similar to the Ν₁ or the Ν₂. Why photons act like particles and waves at the same time? We cannot answer to this question. This is the mystery about light. However the same happen when we repeat the experiment with electrons instead of photons.

Going through

Assumption 1: A photon passes through the slit No1 or the slit No2.

Correct? Let us see. If Assumption 1 is correct then the number of photons should be equal to the sum of the photons passed thorugh the slits No1 and No2. But we did not see this, instead we saw the curve Ι₁₂

If we were to monitor a photon we would need a detector, a camera, whatever it could observe it. Still we would come to nothing because the Heisenberg uncertainty principle states that one cannot assign, with full precision, values for certain pairs of observable variables, including the position and momentum, of a single particle at the same.

At this point we reach the end of the two-slits experiment. It became impossible to know everything about light. The nature proved to be wiser than man or just like Heraclitus said "she likes to be hidden". However this journey was captivating and full of surprises.