Reality of duality

I hope you all went through last article and plunge into Schrodinger’s thought experiment and feel some glimpse of Quantum Physics and its weirdness. Before taking our journey towards the physics of lights, eventually at Theory of Relativity, let’s see one more practical experiment of Quantum physics. It is more uncanny and mystical experiment ever done in the respective field. The experiment first performed by Thomas Young, known as “Double Slit Experiment”. Some of you might have been heard about this(perhaps in recent time).

To start off, imagine a wall with two slits in it. Imagine you are throwing a tennis ball at the wall. Some will bounce off the wall but some will travel through the slits. Now let’s consider there’s another wall behind the first, the ball that traveled through the slits of first wall will hit on it. If you mark the spots where a ball has hit the second wall, what do you expect to see? Obviously right. Two strips of marks roughly the same shape as the slits. Following image shows the first wall with slits from top and the second wall is from the front.

Now, instead of tennis ball, we are using a shining light of single color and of a single wavelength. Imagine shining such light at the wall of two slits. What do you expecting in this condition? The light traveling through slits only gets hit on second wall and pattern that will form on the second wall is of two slits. But now you are wrong here, this doesn’t happen. As the light wave passes through both slits, it essentially splits into two new waves, each spreading out from one of the slit. This two waves then interferes with each other and they reinforce each other. And when these waves of lights hits on the second wall place behind the first, you will see the stripes like pattern, called an Interference pattern. That bright stripes come from the waves reinforcing each other. Photons pass at one time through wall containing two slits. If either path of photon is monitored, it seemingly passes through one slit or the other without showing interference pattern. Conversely, if neither is checked, photon will appear to have passed through both slits simultaneously before interfering with itself, acting like a wave. Strange!!!! The wave-particle duality of photon. In the following image, you can see the actual interference pattern when passes through two slits.Actual image of interference pattern of lightArtistic representation of Dual slit experiment with light

Now imagine firing electrons at our wall of two slits but if you close the one slit among two, you will see only one rectangular strip (through which that electrons has passed) on the second wall. Just as tennis ball would: the spots arrive in the form of strip roughly the same shape of slit. But when you keep both slits open, the pattern is interference i.e. more stripes than two.

How could this happen? This might be because electron interfere with each other. But how can an electron pass through both slits at a time? There could be possibility that electron somehow splits, then passes through slits once, interfere with itself and then recombines to meet the second screen as a single.

To find this out, you have to put detector by the slits to see which slit an electron passes through. The scientists actually did this and they are stunned after seeing the results. Pattern on the detector screen turns into the particle pattern of two strips, as seen in the situation of tennis ball. The interference pattern disappeared. As if that electrons knew that someone is observing us and they changed their nature. As if they were being spied and decided not to be caught in act of performing weird quantum secret. You can see following, the actual double slit experiment with electrons. Individual picture show the pattern you get as more and more electrons fired.

Our act of looking, measuring, observing a quantum system has profound effect on the system. Simply, our observation affecting the reality. This is how quantum realm behaves. If you have any question, please put it in the comment, I’ll try my best to answer the respective question. Till then, stay in your duality until you’re being observed.