Double Slit Experiment
Double slit experiment is one of the most famous and intriguing experiment in quantum mechanics. It describes about the superposition of a particle and explains how weird it gets when we observe somethings. It is also the basic experiment that somehow relates Schrodinger Cat experiment and generalize some ideas. So, what is double slit experiment and how does it work and what does observing mean??
Double slit experiment was performed by Thomas Young. It demonstrated the separation of waves and particles performed. To understand, we need to know some properties of wave and particle.
We all know that wave is a
disturbance created in a medium. Wave has
different factors/parts called crests, troughs, amplitude, node, antinode and
so on.
This is a figure of a normal wave
vibrating on a medium. Crests are the highest point whereas troughs are the
lowest point.
Interference is the property when two progressive waves superpose with each other and the crests of the first wave collides with the crests of the other and trough of the first wave collides with trough of the other wave and forms wave with maximum amplitude.
There are two types of interference pattern on wave:
1.Constructive interference:
When two
waves collides and the crests of one wave collides with the crests of the other
and similarly, when the trough of one waves collide with other it forms a resultant
wave with maximum crests, troughs and amplitude this wave or pattern is constructive
interference.
2. Destructive interference
When two waves collide with each other and the crests of one wave collides with troughs of the other wave and similarly, the troughs of one wave collides with crests of the other the crests cancel's the troughs and vice versa forming a resultant wave with 0 crests and troughs and 0 amplitude that is destructive interference.
Now, that we know some functions of wave, we can somehow understand the double slit experiment.
Many years ago, scientists had a debate about if light is a wave or a particle? There were many experiments performed like Einstein proved that light is a particle as it consists energy in packet form called photons in photoelectric effect whereas many other scientists proved that light is a wave like Huygens in Huygens Principle and wave theory of light. But then came Young’s double slit experiment which completely showed that light is a wave and proved it with wave properties. However, some very fascinating and kind of weird results were also shown after this experiment which basically supported some of the quantum theories.
First let’s discuss about young’s double slit experiment
which proved that light is a wave.
The above figure is an experimental figure of the young’s double
slit experiment. The monochromatic wave/ laser light is called a source which
produces light. Since, there is a screen with two slits the light as a wave
diffracts through it and again interferes with each other. As we mentioned
before that light is a wave and when it interferes with each other constructive
and destructive interference are formed. This showed that light is a wave since
it is diffracted and constructed. We can check the results from the optical
screen where the dark paths are called dark fringe and white paths are white
fringe produced by light wave.
Similarly, if we repeat this same experiment with an electron
we get different results. Let’s say that we replace the source from laser light
to a gun that shoots electron repeatedly then we know that electron is a particle
and when it enters through a slit it gives regular pattern unlike wave.
Fig: particle (electron) through double slit experiment
Electron will divide into following patterns through the slit
and can be viewed from the optical screen. This happens when we observe the
process and what do I mean from observing? Well, it gets so weird when we don’t
observe this process and directly see the result. If we repeat the same process
but we don’t observe it, the electrons would literally create the pattern just
like the wave did which is the interference pattern.
Fig: electron in double slit experiment
when not observed.
This happens when we don’t observe the process. Hence, electron
acts as wave when not observed but acts as a particle when observed. This is
the main core of quantum mechanics. We can see the interference pattern on the
screen which is identical to the wave pattern. It has no explanations of why
particles are different when observed and what does observing really means? All
we know is it happens with all particles. Many scientists have their own
theories that observing collapses wave function and others but it is not
proved. So every particle is a wave and follows wave property but when we
observe it, it becomes particle and changes its property too.
