Enigmatic Electrons

The Quantum world is very different from the classical world. We all know that Quantum mechanics works well in practice, providing a highly precise means of interpreting the behaviour of subatomic particles, something that classical physics — the physics deduced by Sir Isaac Newton and others, fails to do so. Initially electrons were believed to be particles. But then there was evidence that they behaved like waves in phenomena such as electron diffraction. And so there was a growing confusion about the nature of subatomic particles. Were they wave like or particle like? And this confusion did not get resolved until the mid '20s when the laws of quantum mechanics were discovered, which actually showed that atomic particles are neither waves nor particles. They behave in their own strange quantum mechanical way.

But the Quantum Physics is really hard to comprehend and it has some of its own mysteries. A good example of this is the behaviour of electrons in the Double-slit Experiment. 

When macroscale objects such as bullets are shot at a barrier with two slits, with a wall behind the slits, the objects travel straight through the slits and hit the wall in one particular area. But when electrons(or light consisting of photons) are fired instead of macroscale objects, they do not hit the wall at one particular area , but hit the wall at a number of different points at the same time with different strength causing an interference pattern of many lines. The really amazing part is that unlike sound waves or water waves, the interference pattern is still produced when electrons are fired one at a time. Because the interference pattern remains even when the electrons are shot one at a time, the experiment seems to suggest that each electron somehow travels through both slits at the same time and interferes with itself. Mind-boggling? Yet true!

The second unusual part of the Double-slit experiment is that the electrons stop creating an interference pattern when scientists set up a detector near one of the slits to determine which slit(s) an electron is passing through. Under these circumstances, the electrons simply create two straight lines, the same as classical particles, as if they know everything that is going around.

Scientists ran the same experiment with polarising filters in front of each of the two slits. Any photon going one way would become "labelled" with left-handed circular polarization, while any photon going through the other slit is labelled with right-handed circular polarization. In this version of the experiment, it is possible in principle to tell which slit any particular photon arriving at the second screen went through. Surprising enough, the interference pattern vanishes -- even though nobody ever actually looks to see which photon went through which slit.

Now came a new trick -- the eraser. A third polarising filter was placed between the two slits and the second screen, to scramble up (or erase) the information about which photon went through which hole. Now, once again, it is impossible to tell which path any particular photon arriving at the second screen took through the experiment. Now, the interference pattern reappears.

The strange thing is that interference depends on "single photons" going through both slits "at once", but undetected. So how does a single photon arriving at the first screen know how it ought to behave in order to match the presence or absence of the erasing filter on the other side of the slits?

So how  does the electron come to know that it is being detected? There was a substantial chance that the electron was detected at this particular point. So now we would say to ourselves, if the electron went through slit 1, how could it possibly matter to it whether slit 2 was open or not? And if it did not matter to it, how could it be that the probability of detection of that electron went down from a substantial value to being very close to zero?

I rummaged the internet about the reason for such behaviour of electrons, I found certain theories explaining this but full of paradox and internal contradictions. In reality it has been baffling physicists and is still inexplicable.

Nobel Prize winner Physicist Richard Feynman also said, "i can safely say that nobody understands quantum mechanics. Do not keep saying to yourself, if you can possibly avoid it, ‘But how can it possibly be like that?’ because you will go down the drain into a blind alley from which nobody has yet escaped. Nobody knows how it can be like that." (The Character of Physical Law, BBC Publications, 1965).

“If we want to describe what happens in an atomic event, we have to realize that the word “happens” can only apply to the observation, not to the state of affairs between two observations.”

Heisenberg