Transcript The History of Quantum Mechanics

The History of Quantum Mechanics
J P SINGH
ASSOCIATE PROFESSOR PHYSICS
PGGC-11
This
Timeline has much Entropy.
1922:
1905:
•Neils Bohr
won Nobel
Prize in
physics
1925:
•Heisenberg
developed the
Heisenberg
Uncertainty
principle
1940:
Pauli proves
Spin-Statistic
Theorem
•Albert Einstein wrote
the paper, "On a
Heuristic Viewpoint
•SternPublishes
Concerning the
•Wolfgang
Gerlach
paper on
Production and
•Werner
Pauli
Experiment
Wave
Transformation of
developed the Heisenberg
Light“; proposed the •Max Planck won (Verified the fourth quantum won Nobel Mechanics
Nobel prize in
space
and
idea of energy
Prize in
number- the
physics
quantization
Schrödinger's
quanta dealing with
physics
spin number
theory)
Equation
the photoelectric
effect.
1918:
1900:
1913:
1921:
•Won the Nobel
Prize in Physics
•Max Planck
•Neils Bohr
for his discovery
proposed theory proposed
and
about blackatomic
body radiation structure theory explanation of
the law of the
photoelectric
effect.
1924:
1932:
1936:
1929: 1933:
•Louis De Broglie
Louis De
•Otto Stern
published his
doctoral thesis, Broglie won measures the
magnetic
“Recherches sur la the Nobel
Prize in
moment of the
théorie des
Physics
for
proton
quanta”, which
introduced his hypothesis. •Schrodinger
wins Nobel
theory of electron
prize
for his
waves.
Schrodinger
Equation
1944:
•Wolfgang
Pauli won
Nobel Prize in
physics
1943:
•Otto Stern
receives Nobel
prize in Physics
Erwin Schrödinger
• In 1926, at the University of Zurich,
published a series of 4 papers
– Wave Mechanics & Schrodinger’s Equation
– Solved Quantum Harmonic Oscillation, the
Rigid rotor, diatomic molecules and rederived
his equation
– Compared his approaches to Heisenerg
– Showed how to work with time
Schrödinger’s Equation
• While this appears to be a rather complicated
equation, it is.
•
means at time t
• i is the square root of –1
•
Planck’s constant divided by 2π
•
Derivative with respect to time
• ψ(t) = Wave Function
• H(t) = Quantum Hamiltonian
Erwin Schrödinger
• First paper has been
universally celebrated as
one of the most important
achievements of the
twentieth century, and
created a revolution in
quantum mechanics, and
indeed of all physics and
chemistry
• Nobel Prize 1933
• Schrödinger’s Cat Thought
Experiment - 1935
Schrödinger’s Cat
• Decay of gas kills cat
• 50% chance of decay
• 50% dead cat?
Otto Stern & Walter Gerlach
• Otto Stern and Walter Gerlach are famous for
their Stern-Gerlach experiment, in which they
shot a beam of silver atoms through a nonuniform magnetic field, showing that the
atoms split up into only 2 bands
• This verified the space quantization theory,
and tested whether particles had intrinsic
angular momentum
Stern-Gerlach Experiment
More on Otto Stern
• Developed Molecular Ray
Method
• Demonstrated the wave
nature of atoms and
molecules
• Measured atomic magnetic
moments
• Corrected the proton’s
magnetic moment
• Nobel Prize in Physics in
1943
Werner Heisenberg
• Won Nobel Prize in 1932 in Physics "for the creation of
quantum mechanics, the application of which has, inter alia,
led to the discovery of the allotropic forms of hydrogen".
• Heisenberg pointed out that it is impossible to know both the
exact position and the exact momentum of an object at the
same time. Applying this concept to the electron we realize
that in order to get a fix on an electron's position at any time,
we would alter its momentum. Any attempt to study the
velocity of an electron will alter its position. This concept,
called the Heisenberg Uncertainty principle, effectively
destroys the idea of electrons traveling around in neat
orbits. Any electron that is subjected to photons will have its
momentum and position affected.
More on Heisenberg
• Invented Matrix
Mechanics
• Formulated the
Copenhagen
Interpretation of
Quantum Mechanics
with Bohr
• Proposed ProtonNeutron model of
atomic nucleus
Heisenberg's Experiment
Wolfgang Ernst Pauli
• Nobel Prize in Physics in 1945
• The exclusion principle (No two electrons may exist in the same
quantum state) provided the reason for electrons in atoms being
arranged in shells with the maximum number of electrons being 2,
8, 18, 32… etc, from the first to the nth shell.
 This principle is significant for the fact that it explains why matter
occupies space exclusively for itself and does not allow other
material objects to pass through it, at the same time allowing lights
and radiations to pass. It states that no two identical fermions may
occupy the same quantum state simultaneously. A more rigorous
statement of this principle is that for two identical fermions, the total
wave function is anti-symmetric
More on Pauli
• Derived observed
spectrum of H2,
supporting Heisenberg
• Proved Spin-Statistics
Theorem
• First named Neutrinos
Max Planck and
Black Body Radiation
• Emission of light from hot objects (objects appear
black before heating)
• How does the intensity of the electromagnetic
radiation emitted by a black body depend on
the frequency of the radiation and the
temperature of the body?
• Interpolated between the laws of Wien and
Rayleigh-Jeans
• Assumed that energy exists in individual units
(discrete bundles)
• First proposed in a meeting on October 19, 1900
Planck’s Contributions
• Formula predicts the spectral intensity of
electromagnetic radiation at all
wavelengths from a black body at
temperature T
•h is Planck’s constant which is measured in J.s
•6.63x 10-34
•Energy is always emitted or absorbed as a whole
number multiple of h (2hv, 3hv…)
Walk the
Planck
• Later simplified this to E=hv in which E is
energy, h is Planck’s constant, and v is
frequency
More stuff on Planck
• Basically states that energy is always emitted
or absorbed in discrete units, called quanta
(quantized)
• Gave the name “quantum”, which means
“fixed amount,” to the smallest quantity of
energy that can be emitted/absorbed as
electromagnetic radiation
• Awarded Nobel Prize in Physics in 1918 for this
• *No major flaws or errors
• This is regarded as the start of quantum
physics
Neils Bohr
• Introduced his concepts by borrowing ideas
from quantum physics (Max Planck) in 1913
• Presented a model of atomic structure that still
stands true today
• Started by assuming that electrons move in
circular orbits around the nucleus
• Determined that chemical properties of an
element are determined by the number of
electrons in its outer shell
More Bohring Information
• Idea that an electron can drop
from a higher-energy level to a
lower one, emitting a photon
• Also determined that:
– Electron exists a certain
distance from the nucleus
– Electrons have circular orbits
– No energy is given off if an
electron stays in one location
• Received Nobel prize in 1922
for physics
Flaws
• His assumptions
about the energy
given off when an
electron drops to a
lower-energy level
only stands true for
hydrogen (other
elements are too
large)
• Problem with
describing an
electron merely as
a small particle
circling the nucleus
Prince Louis-Victor de Broglie
• Won the Nobel Prize in Physics
in 1929
• Professor at the Faculty of
Sciences at Paris University
• Elected a member of the
Academy of Sciences of the
French Institute in 1933
• Broglie stated that all matter
has a wave-like nature
• States that any moving particle
or object had an associated
wave
• Created a new field in physics,
called wave mechanics, uniting
the physics of light and matter
Broglie’s Equation
λ= the particle's wavelength
h= Planck's constant
p= the particle's momentum
m= the particle's rest mass
v= the particle's velocity
c= the speed of light in a
vacuum
More on de Broglie
• Equation used to describe the wave properties of
matter, specifically, the wave nature of the electron
• The de Broglie relation shows that the wavelength is
inversely proportional to the momentum of a particle
and that the frequency is directly proportional to the
kinetic energy of the particle
Albert Einstein
• Won the Nobel Prize in Physics in
1921 for his discovery and
explanation of the law of the
photoelectric effect
• Widely regarded as one of the
greatest physicists of all time
• Formulated the theory of
relativity and made significant
contributions to quantum
mechanics and statistical
mechanics
• Also famous for formulating E =
mc2
The Photoelectric Effect
• The photoelectric effect is the emission of
electrons from matter upon the absorption of
electromagnetic radiation, such as ultraviolet
radiation or x-rays
The Photoelectric Effect
• When light shines on a metal surface, the surface
emits electrons
• A polished, negatively charged piece of metal such as
zinc will lose its charge if it is exposed to ultraviolet light.
This phenomenon is called the photoelectric effect
The Photoelectric Effect
• The photoelectric effect can be
modeled by the equation:
Ekin = h f – W
Ekin = maximal kinetic energy of an emitted electron
h = Planck constant (6.626 x 10-34 Js)
f = frequency
W = work function (the energy required to free an electron
from the material)
The Photoelectric Effect
• In 1905, Einstein's work predicted that the
energy of the ejected electrons would
increase linearly with the frequency of the
light
• At this time his idea could not be proven but,
in 1915, it was found to be accurate when
Robert Andrews Millikan experimentally
determined the relationship to be linear
Summary
• All of these men are interrelated in their
discoveries; some proved the discoveries of
others, others borrowed ideas and concepts