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Craville Studies >>
Physics >> Quantum Physics
Timeline
Quantum Physics Timeline
This timeline traces the developments in
quantum physics from 1900 to around 1930.
The period
from 1900 to 1930 was the period during which quantum physics was
born. Throughout that time, there were many scientists who
contributed to our current understanding of quantum mechanics.
To view a
particular scientist's contribution, click their name. To view a
more detailed explanation of their discovery, click the discovery
link.
Scientists:
Main Contributors:
Johannes Rydberg
Ernest Rutherford
Albert Einstein
Niels Bohr
James Chadwick
Louis de Broglie
Wolfgang Pauli
Werner Heisenberg
Enrico Fermi
Clinton Davisson
Lester Germer
Other Contributors:
JJ Thomson, Max Planck, Hans Geiger, Ernest Marsden, James Franck,
Gustav Hertz, E.S. Bieler, Satyenda Nath Bose, Max Born, Pascual
Jordan, Erwin
Schrödinger, Paul Dirac and
George Paget Thomson.
Timeline:
Individual
Discoveries:
Discovery of the Electron:
1897 -
Joseph John Thomson, a knighted British physicist, investigated
cathode rays and identified that they were made up of a stream of
negatively charged particles. These become known as electrons. He
also measured an electron's mass to be around 1000 times smaller
than that of a hydrogen ion. Without first having knowledge of
electrons, future developments and models would not have been
possible.
The "Plum Pudding" Model:
1898 -
J.J. Thomson continued on from his work with electrons to
develop a model of the atom. This model became known as the "plum
pudding" model. In the model, he described electrons as negative
plums embedded in a pudding of positive matter.
Hydrogen Line Spectrums:
1900 -
Johannes Rydberg, a Swedish Physicist, refined the expression
for observed hydrogen line spectrums. However, at this time the
phenomenon was still unexplainable. What Rydberg was witnessing was
the Balmer series of hydrogen. The Balmer series was the spectra of
lines consisting of visible light with transitions to the first
excited state (n=2).
Black Body Radiation & the Birth of Quantum Theory:
1900 -
American physicist Max Planck explains black body radiation in
terms of an emission of quantized energy packets. He postulated that
energy is radiated in small units. He called these units quanta. A
black body is an object that absorbs all radiation that falls on it.
Planck's law states that the spectral intensity of electromagnetic
radiation from a black body at a certain temperature is given by an
expression.
Planck would
eventually receive the Nobel prize for this work and without this
law, Einstein would not have been able to produce his report five
years later on special relativity.
Planck did
run in to one problem with his work. When Planck derived the black
body radiation equation he made an assumption that energy was
quantized. He had no way to prove this and so assumed that it was
just a mathematical trick.
Planck's Constant & the Publication of Quantum Theory:
1901 -
Max Planck calculated the value to Planck's constant to be
6.6260693 x 10-34 J s. He also
published his quantum theory.
Alpha Particle Nature:
1903 -
Ernest Rutherford, a New Zealand physicist, establishes the fact
that alpha particles have a positive charge. This allowed for later
scientists to establish alpha particles as helium nuclei.
Einstein's Theory
of Special Relativity:
1905 -
German born, Swiss/American physicist Albert Einstein released
his theory of special relativity. Prior to this, the photoelectric
effect required explaining. The photoelectric effect is the emission
of electrons from matter upon the absorption of electromagnetic
radiation. Einstein explained this by proposing that light consisted
of discrete quantized bundles of energy. These were later called
photons.
He also
determined the mass-energy equivalence formula, and this became one
of the most well known equations of all time.
E = mc2
He also
stated that the speed of light was constant for all observers and
that it was independent of its source.
The year of
1905 was later regarded as his "wonderful" year as it was the year
he began to unravel more mysteries of physics than any other
scientist.
The Geiger Counter:
1908 -
Hans Geiger develops the Geiger counter, a device capable of
detecting radiation. The device proved exceedingly useful for later
experiments conducted using radioactive sources.
The Paschen Series:
1908 -
The Paschen series of hydrogen was discovered. These were lines
consisting of infra-red radiation with transitions to the second
excited states (n=3).
Alpha Particles:
1909 -
Ernest Rutherford and Thomas Royds demonstrated that alpha
particles are doubly ionized helium atoms. This discovery would not
have been made possible except for Rutherford's 1903 work on the
nature of an alpha particle.
Geiger-Marsden Experiment:
1909 -
From Rutherford's above work, Hans Geiger and Ernest Marsden
undertook the Geiger-Marsden experiment whereby different metal
foils were bombarded with alpha particles.
According to
the prevailing "Plum pudding" model of the time, all the alpha
particles should have been deflected off but only some were
reflected.
This result
meant that the "plum pudding" model of the atom was incorrect but it
wasn't until 1911 that this result was explained.
Rutherford's Model of the
Atom:
1911 -
Following the disproven "plum pudding" model, Rutherford set out
to propose his own model of the atom. Based on the results of the
Geiger-Marsden experiment, he postulated that since only some alpha
particles were deflected, the atom must be mainly empty space.
He concluded
that most of the atom's mass was located in a tiny centre, the
nucleus, and electrons were held in orbits surrounding this nucleus
by electrostatic attraction.
But his new
model was not fool proof. The main problem surrounding his model was
that based on his predictions, electrons should radiate
electromagnetic energy and rapidly spiral into the nucleus.
However,
despite its obvious problems, the model provided the base for Bohr's
work a few years later.
Bohr's Model of the Atom:
1913 -
Following on from the model developed by Ernest Rutherford,
Danish physicist Niels Bohr developed his own model of the atom. He
followed on from Rutherford's idea that electrons orbited the
nucleus but also stated that the chemical properties of an element
were largely due to its electron configuration.
Bohr also
introduced the idea that an electron could drop from a higher energy
orbit to a lower one, emitting a photon of discrete energy. This was
the main reason for its success, the fact that it could explain the
spectral lines of hydrogen observed by Rydberg in 1900.
Bohr's model
would not have been made possible without Rutherford's model before
him and knowledge of the hydrogen spectrum.
A success of
Bohr's model was that an equation was developed that could predict
the wavelengths of hydrogen spectrum lines:
The model
also correctly predicted the ionisation energy for hydrogen and
predicted the existence of other series in the spectrum (even though
they had not yet been discovered).
However,
there was still limitations with the model. These included:
· The Bohr model of the
atom was only able to be exclusively applied to hydrogen. It failed
to explain the behaviour of any atoms that contained more than one
electron.
·
The Bohr model was
unable to explain the observed trend that some spectral lines were
more intense than others in the spectrum of hydrogen. In other
words, it failed to explain why the hydrogen spectrum was
inconsistent.
· When the individual
spectral lines were examined closely it was found that they were not
solid lines of emitted light or a narrow range of frequencies
emitted from the atom, but that they were in fact made up of a
number of hyperfine spectral lines. This could not be explained by
the Bohr model of the atom.
· The Bohr model failed
to explain the observation why a discharge tube, when placed in a
magnetic field, caused the spectral lines to be split into several
finely separated but individual lines. This became known as the
Zeeman Effect. This implied the energy levels were split which was
unacceptable to the concept of metastable orbits or energy levels in
the Bohr model.
· The model
itself is a mixture of classical physics and quantum physics and
this is a problem in itself.
Stationary States:
1914 -
James Franck and Gustav Ludwig Hertz worked together to validate
the Bohr model of the atom. Their experiment became known as the
Franck-Hertz experiment and by performing an electron scattering
experiment they were able to confirm the existence of stationary
states.
Protons in the Nucleus:
1914 -
Ernest Rutherford proposed that the nucleus, which was known to
be positively charged, contained protons.
Continuous Primary Beta
Spectrum:
1914 -
Sir James Chadwick, and English physicist, showed that the
primary beta spectrum is continuous but contains an energy anomaly.
The Lyman Series
1916 -
The Lyman series of hydrogen was discovered. These were lines
with ultraviolet radiation that had transitions to the ground state
(n=1).
Conservation of
energy-momentum:
1916 -
Albert Einstein develops the theory for the conservation of
momentum-energy for general relativity. He stated that momentum and
energy are intertwined just as space and time are.
From this it
follows that mass, energy and momentum will cause the space-time
continuum to be curved.
Stimulated Radiation
Emission:
1917 -
Albert Einstein introduces the idea of stimulated radiation
emission. This idea had implications in science for the future as
stimulated radiation emission is what makes lasers possible.
Prediction of the Neutron:
1920 -
Due to the fact that there was a mass difference in what an atom
should weigh and its actual mass, Ernest Rutherford concluded that
the nucleus of a atom contained some particle that had mass but no
charge. He theoretically predicted the existence of the neutron.
This
prediction later led to James Chadwick's confirmation of the
existence of neutrons in 1932.
Strong Nuclear Interaction:
1921 -
Due to the fact that the gravitational attraction of particles
in the nucleus was not sufficient enough to hold a nucleus together
and the fact that based on what was known at the time, a nucleus
should fly apart, James Chadwick and E.S. Bieler conclude that some
strong force holds a nucleus together. They called this force
'strong nuclear interaction.'
Brackett Series of Hydrogen:
1922 -
The Brackett series of hydrogen was discovered. These were lines
with infra-red radiation that had transitions to the third excited
state (n=4).
Wave-Particle Duality:
1923 -
French nobleman and physicist, Louis de Broglie, concluded that
because no-one had successfully proven light was a wave or a
particle, all particles must have some wave-like properties and vice
versa.
His greatest
achievement was to take this idea and development it mathematically
into a formula. The de Broglie wavelength of a particle could be
expressed by:
However, de
Broglie had no experimental results to back up his conclusions and
so it was not readily accepted.
Discovery of the Pfund
Series:
1924 - The Pfund series of hydrogen , consisting of infra red
lines with transitions to the fourth excited state (n=5), is
discovered.
Bose-Einstein Statistics:
1924 - Satyenda Nath Bose and Albert Einstein combined
together to find a new way to count quantum particles. This later
became known as Bose-Einstein statistics. They also predicted that
extremely cold atoms should condense into a single quantum state.
This later became known as the Bose-Einstein condensate.
Quantum Exclusion
Principle:
1925 - Wolfgang Pauli, an Austrian physicist, is most noted
for his work on the quantum exclusion principle. He also explained
the previously unexplainable Zeeman effect.
Pauli stated
that electrons, known as fermions in his principle, are unable to
occupy the same quantum state. As a result of this electrons 'pile
on top' of one another and this can produces phenomena such as the
Zeeman effect.
Pauli used Bohr's model of the atom that electrons were contained in
shells and realised that by adding a fourth quantum number to where
there was only three before, he could explain the maximum number of
electrons in each shell.
The exclusion principle provided the reason as to why electrons were
arranged in shells of 2, 8, 18, etc.
Matrix Mechanics:
1925 - German physicists Werner Heisenberg, Max Born and
Pascual Jordan successfully developed matrix mechanics. Matrix
mechanics was the first version of quantum mechanics and lead to the
development of quantum field theory. They built a 'coherent
mathematical framework' to which quantum physics could be applied.
From this, Wolfgang Pauli applied matrix mechanics to the hydrogen
atom and successfully derived Balmer's equation and Rydberg's
constant.
Fermi-Dirac Statistics:
1926 - Enrico Fermi and Paul Dirac find a second method to
count quantum particles. The became known as Fermi-Dirac statistics
and opened the way for solid-state physics. Through this, Fermi
discovers the spin-statistics connection.
Wave Mechanics:
1926 - Erwin
Schrödinger
develops a second description of quantum mechanics. He calls his
description wave mechanics and is based more on physical, continuous
wave motions whereas Heisenberg's was based on a mathematical
approach. Schrödinger's definition included the famous Schrödinger
equation:
Heisenberg
did not like
Schrödinger's more practical approach but later in the year
Schrödinger proved that the two descriptions were equal. He showed
that Heisenberg's matrices could be developed in his own theory and
that his own theory could be derived from Heisenberg's matrices.
Heisenberg's
Uncertainty Principle:
1927 - Werner Heisenberg develops his uncertainty principle.
Heisenberg showed that uncertainty is an inherent property of
quantum mechanics. He reasoned that there were pairs of quantities
that could not be determined simultaneously. He stated that if a
particle's exact position is known, its momentum cannot be known
accurately and vice versa.
This is represented by Heisenberg's Uncertainty Principle where
∆x and
∆p are inherent uncertainties in position and momentum:
Principle of
Complementarity:
1927 - Niels Bohr was not entirely happy with Heisenberg's
Uncertainty Principle. It was based on wave-particle duality and the
fact that an observation of an atomic system would disturb the
system. Bohr preferred the description put forward in his principle
of complemetarity in that when you observe a wave-like property of
something, it still has a particle-like nature but you do not see it
during the observation. This rule also holds true for the inverse.
Wave-like Nature of
Electrons:
1927 - Clinton Davisson and Lester Germer confirmed the wavelike nature of an electron
independently of George Paget Thomson, who did likewise. They did this
by verifying the electron diffraction of a crystal.
Davisson & Germer were actually trying to study the reflection of
electrons from a nickel surface. However, there was a crack in the
vacuum tube they were using and as a result the nickel surface
oxidised. They attempted to remove the oxidisation by heating, but
this recrystallised the surface. When they fired electrons at it
now, the electrons were diffracting. Since diffraction is a wave
property they had almost inadvertently proven de Broglie's theory.
The Dirac Equation:
1928 - Paul Dirac presented a relativistic theory of an
electron. This included the Dirac Equation which could correctly
predict the spin of electrons. He also predicted the existence of a
particle similar to an electron but one that had a positive charge.
An anti-electron, or positron, was observed by Carl Anderson in
1932.
The Zitterbewegung Motion:
1930 - Erwin
Schrödinger proposed his concept of zitterbewegung motion. The
motion is a theoretical circular motion formula for elementary
particles, in particular electrons. This motion is responsible for
producing their spin and magnetic moment.
Discovery of the Neutron:
1932 - James Chadwick
discovered the neutron. After years of predicted existence since
being put forward in 1920 by Ernest Rutherford, the final frontier
in terms of atomic understanding was complete and this discovery
marked the end of the development of quantum physics but the
beginning of its wider reach.
The
Future:
Following Chadwick’s discovery, a
new and exciting world became possible through quantum physics.
Over the ensuing years quantum
mechanics had a big impact on developments in technology. These
included:
- The ability to explain
and control properties in metals, insulators, semiconductors and superconductors.
· The invention of the
transistor. This invention led to more developments in the areas of
computing and micro chipping. It also led a revolution in
communication and information technology.
· The invention of
lasers and masers.
· The ability to explain
the structure of the atom nucleus.
· The ability to explain
the mechanical and thermal properties of solids.
· It gave chemistry a
firm base and explained chemical bonding. Molecular biology and
genetic engineering have also been made possible.
· Processes in
astrophysics such as the physics of stars can be explained using
quantum mechanics.
· Theories surrounding
black holes can be explained using quantum mechanics.
In terms of what the future has in
store for quantum physics, there are many possible directions.
Superconductors and genetic engineering will certainly play a big
role in society in the future as well as the area of
telecommunications.
But quantum mechanics also has some
more far reaching consequences. One such application of quantum
physics is in quantum teleportation. Whilst scientists believe that
human teleportation is around a century away yet, super fast quantum
computers will begin to appear on the shelves over the next decade.
Despite all the possible
applications of quantum physics, there is still much work to be done
to get some of the above mentioned applications part of mainstream
society.
Scientist by Scientist:
Johannes Rydberg:
Hydrogen Line Spectrums:
1900 -
Johannes Rydberg, a Swedish Physicist, refined the expression
for observed hydrogen line spectrums. However, at this time the
phenomenon was still unexplainable. What Rydberg was witnessing was
the Balmer series of hydrogen. The Balmer series was the spectra of
lines consisting of visible light with transitions to the first
excited state (n=2).
Contribution:
Rydberg was the one who gave us the first glimpse into the hydrogen
spectrum. Without it, the rest of the spectrum may not have been
discovered till a much later date.
Back to Top
Ernest Rutherford
Alpha Particle Nature:
1903 -
Ernest Rutherford, a New Zealand physicist, establishes the fact
that alpha particles have a positive charge. This allowed for later
scientists to establish alpha particles as helium nuclei.
Alpha
Particles:
1909 -
Ernest Rutherford and Thomas Royds demonstrated that alpha
particles are doubly ionized helium atoms. This discovery would not
have been made possible except for Rutherford's 1903 work on the
nature of an alpha particle.
Geiger-Marsden Experiment:
1909 -
From Rutherford's above work, Hans Geiger and Ernest Marsden
undertook the Geiger-Marsden experiment whereby different metal
foils were bombarded with alpha particles.
According to
the prevailing "Plum pudding" model of the time, all the alpha
particles should have been deflected off but only some were
reflected.
This result
meant that the "plum pudding" model of the atom was incorrect but it
wasn't until 1911 that this result was explained.
Rutherford's Model of the Atom:
1911 -
Following the disproven "plum pudding" model, Rutherford set out
to propose his own model of the atom. Based on the results of the
Geiger-Marsden experiment, he postulated that since only some alpha
particles were deflected, the atom must be mainly empty space.
He concluded
that most of the atom's mass was located in a tiny centre, the
nucleus, and electrons were held in orbits surrounding this nucleus
by electrostatic attraction.
But his new
model was not fool proof. The main problem surrounding his model was
that based on his predictions, electrons should radiate
electromagnetic energy and rapidly spiral into the nucleus.
However,
despite its obvious problems, the model provided the base for Bohr's
work a few years later.
Protons
in the Nucleus:
1914 -
Ernest Rutherford proposed that the nucleus, which was known to
be positively charged, contained protons.
Prediction of the Neutron:
1920 -
Due to the fact that there was a mass difference in what an atom
should weigh and its actual mass, Ernest Rutherford concluded that
the nucleus of a atom contained some particle that had mass but no
charge. He theoretically predicted the existence of the neutron.
This
prediction later led to James Chadwick's confirmation of the
existence of neutrons in 1932.
Contribution:
Rutherford's
main contributions to physics was in the development of the model of
an atom. He also worked with beta decay and produced his own model
of the atom in 1911. He was also the one who predicted the existence
of neutrons.
Back to Top
Albert Einstein
Einstein's Theory of Special Relativity:
1905 -
German born, Swiss/American physicist Albert Einstein released
his theory of special relativity. Prior to this, the photoelectric
effect required explaining. The photoelectric effect is the emission
of electrons from matter upon the absorption of electromagnetic
radiation. Einstein explained this by proposing that light consisted
of discrete quantized bundles of energy. These were later called
photons.
He also
determined the mass-energy equivalence formula, and this became one
of the most well known equations of all time.
E = mc2
He also
stated that the speed of light was constant for all observers and
that it was independent of its source.
The year of
1905 was later regarded as his "wonderful" year as it was the year
he began to unravel more mysteries of physics than any other
scientist.
Conservation of energy-momentum:
1916 -
Albert Einstein develops the theory for the conservation of
momentum-energy for general relativity. He stated that momentum and
energy are intertwined just as space and time are.
From this it
follows that mass, energy and momentum will cause the space-time
continuum to be curved.
Stimulated Radiation Emission:
1917 -
Albert Einstein introduces the idea of stimulated radiation
emission. This idea had implications in science for the future as
stimulated radiation emission is what makes lasers possible.
Bose-Einstein Statistics:
1924 - Satyenda Nath Bose and Albert Einstein combined
together to find a new way to count quantum particles. This later
became known as Bose-Einstein statistics. They also predicted that
extremely cold atoms should condense into a single quantum state.
This later became known as the Bose-Einstein condensate.
Contribution:
Often
regarded as the greatest physicist of all time, Albert Einstein's
theory of special relativity laid the foundation for the space-time
continuum to be understood. He was the one who began to realise the
deeper implications of what was occurring on a molecular level.
Back to Top
Niels Bohr
Bohr's Model of the Atom:
1913 -
Following on from the model developed by Ernest Rutherford,
Danish physicist Niels Bohr developed his own model of the atom. He
followed on from Rutherford's idea that electrons orbited the
nucleus but also stated that the chemical properties of an element
were largely due to its electron configuration.
Bohr also
introduced the idea that an electron could drop from a higher energy
orbit to a lower one, emitting a photon of discrete energy. This was
the main reason for its success, the fact that it could explain the
spectral lines of hydrogen observed by Rydberg in 1900.
Bohr's model
would not have been made possible without Rutherford's model before
him and knowledge of the hydrogen spectrum.
A success of
Bohr's model was that an equation was developed that could predict
the wavelengths of hydrogen spectrum lines:
The model
also correctly predicted the ionisation energy for hydrogen and
predicted the existence of other series in the spectrum (even though
they had not yet been discovered).
However,
there was still limitations with the model. These included:
-
·
The Bohr model of the
atom was only able to be exclusively applied to hydrogen. It failed
to explain the behaviour of any atoms that contained more than one
electron.
-
·
The Bohr model was
unable to explain the observed trend that some spectral lines were
more intense than others in the spectrum of hydrogen. In other
words, it failed to explain why the hydrogen spectrum was
inconsistent.
-
·
When the individual
spectral lines were examined closely it was found that they were not
solid lines of emitted light or a narrow range of frequencies
emitted from the atom, but that they were in fact made up of a
number of hyperfine spectral lines. This could not be explained by
the Bohr model of the atom.
-
·
The Bohr model failed
to explain the observation why a discharge tube, when placed in a
magnetic field, caused the spectral lines to be split into several
finely separated but individual lines. This became known as the
Zeeman Effect. This implied the energy levels were split which was
unacceptable to the concept of metastable orbits or energy levels in
the Bohr model.
-
·
The model
itself is a mixture of classical physics and quantum physics and
this is a problem in itself.
Contribution:
Bohr is regarded as the one who first began to understand the
spectrum of hydrogen during his development of his model of the
atom. He also helped confirm the wave-particle duality.
Back to Top
James Chadwick
Continuous Primary Beta Spectrum:
1914 -
Sir James Chadwick, and English physicist, showed that the
primary beta spectrum is continuous but contains an energy anomaly.
Strong
Nuclear Interaction:
1921 -
Due to the fact that the gravitational attraction of particles
in the nucleus was not sufficient enough to hold a nucleus together
and the fact that based on what was known at the time, a nucleus
should fly apart, James Chadwick and E.S. Bieler conclude that some
strong force holds a nucleus together. They called this force
'strong nuclear interaction.'
Discovery of the Neutron:
1932 - James Chadwick
discovered the neutron. After years of predicted existence since
being put forward in 1920 by Ernest Rutherford, the final frontier
in terms of atomic understanding was complete and this discovery
marked the end of the development of quantum physics but the
beginning of its wider reach.
Contribution:
He was the one who proposed the
strong nuclear force and also is credited with the discovery of the
nucleus. Chadwick is regarded as the person who ended the
development of quantum physics and started its wider impact.
Back to Top
Louis de Broglie
Wave-Particle Duality:
1923 -
French nobleman and physicist, Louis de Broglie, concluded that
because no-one had successfully proven light was a wave or a
particle, all particles must have some wave-like properties and vice
versa.
His greatest
achievement was to take this idea and development it mathematically
into a formula. The de Broglie wavelength of a particle could be
expressed by:
However, de
Broglie had no experimental results to back up his conclusions and
so it was not readily accepted.
Contribution:
He was the
one who converted a qualitative theory of the dual nature of light
into a mathematical expression.
Back to Top
Wolfgang Pauli
Quantum Exclusion Principle:
1925 - Wolfgang Pauli, an Austrian physicist, is most noted
for his work on the quantum exclusion principle. He also explained
the previously unexplainable Zeeman effect.
Pauli stated
that electrons, known as fermions in his principle, are unable to
occupy the same quantum state. As a result of this electrons 'pile
on top' of one another and this can produces phenomena such as the
Zeeman effect.
Pauli used Bohr's model of the atom that electrons were contained in
shells and realised that by adding a fourth quantum number to where
there was only three before, he could explain the maximum number of
electrons in each shell.
The exclusion principle provided the reason as to why electrons were
arranged in shells of 2, 8, 18, etc.
Contribution:
Pauli's work on the exclusion principle helped us to understand the
Zeeman effect and also aided chemistry by explaining why the shell
configurations are 2, 8, 18, etc.
Back to Top
Werner Heisenberg
Matrix Mechanics:
1925 - German physicists Werner Heisenberg, Max Born and
Pascual Jordan successfully developed matrix mechanics. Matrix
mechanics was the first version of quantum mechanics and lead to the
development of quantum field theory. They built a 'coherent
mathematical framework' to which quantum physics could be applied.
From this, Wolfgang Pauli applied matrix mechanics to the hydrogen
atom and successfully derived Balmer's equation and Rydberg's
constant.
Heisenberg's Uncertainty Principle:
1927 - Werner Heisenberg develops his uncertainty principle.
Heisenberg showed that uncertainty is an inherent property of
quantum mechanics. He reasoned that there were pairs of quantities
that could not be determined simultaneously. He stated that if a
particle's exact position is known, its momentum cannot be known
accurately and vice versa.
This is represented by Heisenberg's Uncertainty Principle where
∆x and
∆p are inherent uncertainties in position and momentum:
Contribution:
Heisenberg's greatest achievement was his matrix mechanics, which
allowed a mathematical approach to quantum physics, and his
uncertainty principle, which allowed us to get a better
understanding of the relationship between position and momentum.
Back to Top
Enrico Fermi
Fermi-Dirac Statistics:
1926 - Enrico Fermi and Paul Dirac find a second method to
count quantum particles. The became known as Fermi-Dirac statistics
and opened the way for solid-state physics. Through this, Fermi
discovers the spin-statistics connection.
Contribution:
Fermi's contribution may seem small but without his efforts, solid
state physics may not have been possible.
Back to Top
Clinton Davisson
Wave-like Nature of
Electrons:
1927 - Clinton Davisson and Lester Germer confirmed the wavelike nature of an electron
independently of George Paget Thomson, who did likewise. They did this
by verifying the electron diffraction of a crystal.
Davisson & Germer were actually trying to study the reflection of
electrons from a nickel surface. However, there was a crack in the
vacuum tube they were using and as a result the nickel surface
oxidised. They attempted to remove the oxidisation by heating, but
this recrystallised the surface. When they fired electrons at it
now, the electrons were diffracting. Since diffraction is a wave
property they had almost inadvertently proven de Broglie's theory.
Contribution:
Davisson finally confirmed what had been theorised, that electrons
acted as both a wave and a particle. This helped further understand
the hydrogen spectrum.
Back to Top
Lester Germer
Wave-like Nature of
Electrons:
1927 - Clinton Davisson and Lester Germer confirmed the wavelike nature of an electron
independently of George Paget Thomson, who did likewise. They did this
by verifying the electron diffraction of a crystal.
Davisson & Germer were actually trying to study the reflection of
electrons from a nickel surface. However, there was a crack in the
vacuum tube they were using and as a result the nickel surface
oxidised. They attempted to remove the oxidisation by heating, but
this recrystallised the surface. When they fired electrons at it
now, the electrons were diffracting. Since diffraction is a wave
property they had almost inadvertently proven de Broglie's theory.
Contribution:
Davisson finally confirmed what had been theorised, that electrons
acted as both a wave and a particle. This helped further understand
the hydrogen spectrum.
Back to Top
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