Professor Dave here, let's talk about the
double slit experiment.
In learning about the first few discoveries
that led to the development of quantum
mechanics, we discussed wave-particle
duality, so we understand that both light
and matter behave as both particles and
waves. But we glossed over some of the
technical details, so let's zoom in for a
moment. In 1801, Thomas Young performed
experiments where light was passed
through a plane with two slits in it,
striking a screen beyond. The diffraction
and interference patterns that resulted
clearly supported the wave model of
light, with the brighter bands
representing constructive interference
and the darker bands representing
destructive interference, with the width
of the bands being a function of the
frequency of the light. Later in the
century, Maxwell showed that light is a
wave of oscillating electric and
magnetic fields, so it seemed as though
the case was closed on the declaration
of light as waves. But as we said, in 1905
Einstein solved the problem of the
photoelectric effect by assigning
particle nature to light, thus wave
particle duality was born. Later, de
Broglie proposed that particles must
therefore also display wave-like
behavior, and this was shown to be true
in an experiment just like Young's more
than 100 years prior. This modern version
is what we are typically referring to
when we talk about the double-slit
experiment. From this it was shown that a
beam of electrons exhibits diffraction
and interference patterns just like
light does. This demonstrates the
wave-like properties of electrons and by
extension matter in general. Later, low
intensity experiments showed that even
an individual electron when passing
through biprisms or slits will
interfere with itself, making the wave-like
nature of the electron undeniable.
So it was shown that electrons act as both
particles and waves, but not just
electrons, neutrons were also shown to
exhibit diffraction patterns. It must be
understood that since all particles are
also waves, literally any object could
hypothetically exhibit a diffraction
pattern, so long as the object passes
through an aperture roughly the size of
the objects wavelength. But remember that
massive objects have incredibly tiny
wavelengths, so for something like a
human being to diffract, they would have
to pass through an aperture around 10 to
the negative 36 meters wide, which is a
trillionth of a trillionth of a
trillionth of a meter, so this will be
pretty tough no matter how much you diet.
In this way, we begin to see how
Newtonian mechanics is not the
fundamental descriptor of motion, but
rather that it emerges from quantum
mechanics as objects become large enough
that their wavelengths are negligible, so
don't worry, everything you learned in
classical physics will still work just
fine for any object you can see with
your eyes. But along with these waves of
matter came the wave function and the
quest to describe it mathematically.
This would be impossible without the creation
of quantum mechanics, which was achieved
by a host of brilliant minds, but we will
focus on two people in particular: Erwin
Schrodinger and Werner Heisenberg.
Let's move forward and see what they had to
say on the subject.
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