Interference fringes are now clearly visible.
Isn't that incredible? So each time you fire shot, you don't
know where it's going to land at all. It looks totally random to you, I believe.
But after a while, you see a pattern emerging.
And that pattern is something we physicists can predict.
So it's not totally random, there is certain regularity to it.
But each time you can predict.
So in that sense, physics is indeed uncertain.
You don't know exactly what's going to happen for one experiment.
But if you keep doing millions of experiments,
you can predict the pattern of the outcome.
So that's what a microscopic world actually does.
And to describe this kind of strange
situation we need something called quantum mechanics.
And that is the laws of physics that govern the microscopic world.
So, even though each electron is a particle, when you shoot
it, it lands at a very particular place because it's a point.
But when you see this pattern that emerged towards the end of the day,
it looks like actually waves, and this is an experiment that you can do.
So, if you have a hose, you shot water into the pond,
it lands here and there's another guy doing the same thing over there.
And each water shot into the pond will creat a ripple of waves.
It does it from here. It does it from over there.
But when the two waves overlap with each other,
and this is where you see these fringe pattern.
And this is called interference of waves.
And the word interference doesn't sound very positive, but what you
see is the regular variation in the depth of the wave.
And that is the effect of interference.
So what we, we saw in the case of the experiment on a previous slide
is that well, we think electron is a particle.
But by doing this experiment, we saw a pattern
emerging that shows the electron is actually a wave.
On the other hand, we always use the thing that the
light is a wave, but it also behaves like a particle too.
So a particle is a wave, a wave is
a particle, and that's what quantum mechanics is telling us.
And strangely
enough, when you remember the previous slide, then electron can
actually go through two different holes at the same time.
If there were only one hole, then electron knows which hole to
go through, then there was no possibility of this interesting fringe pattern.
So, when you throw an electron into that wall, one electron
actually passes through two wall, two holes at the same time.
Very counter-intuitive,
that, but that's exactly what this experiment has demonstrated.