A tale of Two slits

Say you are a human with a basic understanding of how the world works, i.e., you understand classical mechanics.

You decide to conduct this experiment: take a laser and shine it through a barrier with two slits. You’d expect the resulting pattern would appear something like this:


But this is not what happens! Instead, you notice this weird band pattern.


                            PC: artemiawatson on Tumblr

How could a light source behave like that? So you call upon your friend Dr. Tonomura (actual physicist) to conduct this experiment with photons or electrons in his laboratory to see if this behavior is consistent.

He decides to conduct it with electrons and invites you to watch. And to your astonishment, as electrons start hitting the screen you get a pattern similar to the one you got at home. 


Results of a double-slit-experiment performed by showing the build-up of an interference pattern of single electrons.

Numbers of electrons are a) 11, b) 200, c) 6000, d) 40000, and e) 140000.

The pattern( known as an interference pattern ) is mysterious but similar to ones you’d seen before.

The other day when you were at the Arboretum you noticed that ripples caused by rocks thrown in the pond behave in the same way and produced the same pattern.


So what is going on?

This double slit experiment supports the idea that light is a wave since in the classical sense that you would never see such a behavior from a particle.

But then you also have experiments like the photoelectric effect which is predicated on the particle view.


                                      PC: Germain Salvato-Vallverdu

So are electrons and photons behaving like a wave or a particle? Well… it’s both!

Albert Einstein wrote:

It seems as though we must use sometimes the one theory and sometimes the other, while at times we may use either. We are faced with a new kind of difficulty. We have two contradictory pictures of reality; separately neither of them fully explains the phenomena of light, but together they do.

The interference pattern that we saw earlier was first observed by Thomas Young in the early 1800s.  When physicists continued to study the results of the double slit, its variants and other experiments, it lead them to a bizarre new world underlying everyday reality – The quantum world. (A story for another day)


                               Source; Tout Est Quantique 

Now is it possible to replicate the same bizarre behavior that we have discussed on a macroscopic scale (say with bouncing droplets)

For this, check out the latest FYFD post on hydrodynamic double slit experiment and stay tuned for the next post in this series

In case you had missed out, here are the previous posts on this collaborative series on Pilot wave Hydrodynamics with FYFD : 1) Introduction; 2) Chladni patterns; 3) Faraday instability, 4) Bouncing droplets ,5) Complex Lattice systems