Young's experiment, wave-nature of light (English)

2-1: Young's Experiment, the Wave Nature of Electrons

[The Double-Nature of Light]

First, let us review

on the duality briefly.

As explained on the pages,

3-8: Summary of Part 3

and

Epilogue : Opening to Quantum Mechanics,

in the previous Seminar,

the wave nature of light was

confirmed by Young's double-slit experiment.

The photograph of the interference fringes

in Young's experiment

shown below

is, so to speak,

the result of

a cooperative work of

the particle nature

and the wave nature of light.

You should keep this in mind.

On the other hand,

the particle nature

of light was established by

Einstein's hypothesis of photon

based on Planck's energy quantum

and its experimental confirmation.

Young's experiment

A monochromatic light

from a point source

passes through the two thin slits,

S₁

and

S₂,

and makes an interference fringes

on the screen.

An example of

the interference fringes

in Young's experiment

is shown in the following

picture,

where

(A)

represents the picture

of the pattern on the screen

when only one of the slits is open,

and

(B)

shows the picture

of the striped pattern

on the screen

when both the slits are open.

[The Wave Nature of Electrons]

Since the discovery of electron

by J. J. Thomson,

nobody had doubted

that an electron

is a very small and

very light particle

seemed as almost one point,

whereas it has been

clarified after

the proposal of matter wave

by de Broglie

that

electrons possess

not only particle nature

but also wave nature.

It has been confirmed that

other substance particles

as well as electrons

have the duality of particle nature and wave nature.

[Abandon the Idea of Choice between Two Alternatives]

At the beginning

of the 20th century,

physicists in the world

came up against

the serious contradiction

between the particle nature

and the wave nature.

Is this a true contradiction?

We think that light

or an electron

must be a particle

or a wave, exclusively.

Is this the reason

why we feel the particle-wave duality

as a contradiction?

The idea that we have

to choose between

two alternatives,

"particle" or "wave"

might be a classical

thinking way.

Isn't it possible

to consider that the duality

might be an essential

quality of matter?

It was discussed that

the photograph

of the interference fringes

in Young's experiment

shown above

is

a cooperative work

of the particle-wave

double natures of light.

The photograph cannot exist

without any of the two natures.

This thoroughly deny

the above-mentioned idea of

choice between

two alternatives.

As learned on the page,

1-5: The Meaning of the Wave Function,

we know that

the wave function

represents the

probability that the

particle will be found;

precisely speaking,

the square of the absolute

value of

the wave function

represents the probability.

You may be enough

wise to notice that

we can unify

the particle nature

and the wave nature

within quantum mechanics

by introducing the concept

of probability

without adopting

the idea to choose

between the

two alternatives.

Let us discuss this

in further detail

on the following pages.

Go back to the top page of Part 2.

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