Date |
Person |
Contribution |
1900 |
Max Planck |
To explain black body
radiation (1862), he suggested that electromagnetic energy
could only be emitted in quantized form, i.e. the energy could only
be a multiple of an elementary unit E = hν, where
h is Planck's constant
and ν is the frequency of the radiation. |
1901 |
Frederick Soddy and Ernest Rutherford |
Discovered nuclear
transmutation when they found that radioactive thorium was
converting itself into radium through a process of nuclear decay. |
1902 |
Gilbert N. Lewis |
To explain the octet rule (1893), he
developed the “cubical atom” theory in
which electrons in the form of dots were positioned at the corner
of a cube and suggested that single, double, or triple “bonds” result when two atoms are held together
by multiple pairs of electrons (one pair for each bond) located
between the two atoms (1916). |
1904 |
Richard Abegg |
Noted the pattern that the numerical difference between the
maximum positive valence, such as +6 for
H_{2}SO_{4}, and the maximum negative
valence, such as -2 for H_{2}S, of an element
tends to be eight (Abegg's rule). |
1905 |
Albert Einstein |
Determines the equivalence of matter and
energy. |
1905 |
Albert Einstein |
First to explain the effects of Brownian motion as caused by the kinetic energy (i.e., movement) of atoms,
which was subsequently, experimentally verified by Jean Baptiste Perrin, thereby settling
the century-long dispute about the validity of John Dalton's atomic
theory. |
1905 |
Albert Einstein |
Publishes his Special
Theory of Relativity. |
1905 |
Albert Einstein |
Explained the photoelectric
effect (1839), i.e. that shining light on certain materials can
function to eject electrons from the material, he postulated, as
based on Planck’s quantum hypothesis (1900), that light itself consists of individual quantum particles
(photons). |
1907 |
Ernest Rutherford |
To test the plum pudding model (1904), he fired,
positively-charged, alpha particles
at gold foil and noticed that some bounced back thus showing that
an atom has a small-sized positively charged atomic nucleus at its center. |
1909 |
Geoffrey Ingram
Taylor |
Demonstrated that interference patters of light were generated
even when the light energy introduced consisted of only one photon.
This discovery of the wave-particle duality of matter and
energy was fundamental to the later development of quantum field theory. |
1909 and 1916 |
Albert Einstein |
Showed that, if Planck's law of black-body
radiation is accepted, the energy quanta must also carry
momentum p = h / λ, making them
full-fledged particles. |
1911 |
Lise Meitner and Otto Hahn |
Performed an experiment that showed that the energies of
electrons emitted by beta decay had a continuous rather than discrete
spectrum. This was in apparent contradiction to the law of
conservation of energy, as it appeared that energy was lost in the
beta decay process. A second problem was that the spin of the
Nitrogen-14 atom was 1, in contradiction
to the Rutherford prediction of ½. These anomalies were later
explained by the discoveries of the neutrino and the neutron. |
1912 |
Victor Hess |
Discovers the existence of cosmic
radiation. |
1912 |
Henri Poincaré |
Published an influential mathematical argument in support of
the essential nature of energy quanta. |
1913 |
Robert Andrews
Millikan |
Publishes the results of his "oil drop" experiment, in which he
precisely determines the electric
charge of the electron. Determination of the fundamental unit
of electric charge made it possible to calculate the Avogadro constant (which is the number of
atoms or molecules in one mole of any
substance) and thereby to determine the atomic weight of the atoms of each element. |
1913 |
Johannes Stark and Antonino Lo Surdo |
Independently discovered the shifting and splitting of the
spectral lines of atoms and molecules due to the presence of the
light source in an external static electric field. |
1913 |
Niels Bohr |
To explain the Rydberg formula
(1888), which correctly modeled the light emission spectra of
atomic hydrogen, Bohr hypothesized that negatively charged
electrons revolve around a positively charged nucleus at certain
fixed “quantum” distances and that each of these “spherical orbits”
has a specific energy associated with it such that electron
movements between orbits requires “quantum” emissions or
absorptions of energy. |
1915 |
Albert Einstein |
First presents to the Prussian Academy of Science what
are now known as the Einstein
field equations. These equations specify how the geometry of
space and time is influenced by whatever matter is present, and
form the core of Einstein's General Theory of Relativity.
Although this theory is not directly applicable to quantum
mechanics, theorists of quantum
gravity seek to reconcile them. |
1916 |
Arnold Sommerfeld |
To account for the Zeeman effect
(1896), i.e. that atomic absorption or emission spectral lines
change when the light source is subjected to a magnetic field, he
suggested there might be “elliptical orbits” in atoms in addition
to spherical orbits. |
1918 |
Ernest Rutherford |
Noticed that, when alpha
particles were shot into nitrogen
gas, his scintillation
detectors showed the signatures of hydrogen nuclei. Rutherford determined that the
only place this hydrogen could have come from was the nitrogen, and
therefore nitrogen must contain hydrogen nuclei. He thus suggested
that the hydrogen nucleus, which was known to have an atomic number of 1, was an elementary particle, which he decided
must be the protons hypothesized by Eugen Goldstein. |
1919 |
Irving Langmuir |
Building on the work of Lewis (1916), he coined the term
"covalence" and postulated that coordinate covalent bonds occur
when two electrons of a pair of atoms come from both atoms and are
equally shared by them, thus explaining the fundamental nature of
chemical bonding and molecular chemistry. |
1922 |
Arthur Compton |
Found that X-ray wavelengths increase due to scattering of the
radiant energy by "free electrons". The scattered quanta have less energy than the quanta of the
original ray. This discovery, known as the "Compton effect," or
"Compton scattering" demonstrates
the "particle" concept of
electromagnetic
radiation. |
1922 |
Otto Stern and Walther Gerlach |
Stern-Gerlach
experiment detects discrete values of angular momentum for
atoms in the ground state passing through an inhomogeneous magnetic
field leading to the discovery of the spin of the electron. |
1923 |
Louis De Broglie |
Postulated that electrons in motion are associated with waves
the lengths of which are given by Planck’s constant h
divided by the momentum of the mv =
p of the electron: λ = h / mv = h
/ p. |
1924 |
Satyendra Nath Bose |
His work on quantum mechanics
provides the foundation for Bose-Einstein statistics, the
theory of the Bose-Einstein
condensate, and the discovery of the boson. |
1925 |
Friedrich Hund |
Outlined the “rule of maximum
multiplicity” which states that when electrons are added
successively to an atom as many levels or orbits are singly
occupied as possible before any pairing of electrons with opposite
spin occurs and made the distinction that the inner electrons in
molecules remained in atomic orbitals
and only the valence electrons
needed to be in molecular orbitals
involving both nuclei. |
1925 |
Werner Heisenberg |
Developed the matrix mechanics
formulation of Quantum Mechanics. |
1925 |
Wolfgang Pauli |
Outlined the “Pauli
exclusion principle” which states that no two identical
fermions may occupy the same quantum state
simultaneously. |
1926 |
Gilbert Lewis |
Coined the term photon, which he derived
from the Greek word for light, φως (transliterated phôs). |
1926 |
Erwin Schrödinger |
Used De Broglie’s electron wave postulate (1924) to develop a
“wave equation” that
represents mathematically the distribution of a charge of an
electron distributed through space, being spherically symmetric or
prominent in certain directions, i.e. directed valence bonds, which gave the correct
values for spectral lines of the hydrogen atom. |
1927 |
Charles Drummond Ellis
(along with James Chadwick and
colleagues) |
Finally established clearly that the beta decay spectrum is in
fact continuous and not discrete, posing a problem that would later
by solved by theorizing (and later discovering) the existence of
the neutrino. |
1927 |
Walter Heitler |
Used Schrödinger’s wave equation (1926) to show how two
hydrogen atom wavefunctions join
together, with plus, minus, and exchange terms, to form a covalent bond. |
1927 |
Robert Mulliken |
In 1927 Mulliken worked, in coordination with Hund, to develop
a molecular orbital theory where electrons are assigned to states
that extend over an entire molecule and, in 1932, introduced many
new molecular orbital terminologies, such as σ bond, π bond, and
δ bond. |
1928 |
Paul Dirac |
In the Dirac equations, Paul Dirac integrated the principal of
special relativity with quantum electrodynamics and hypothesized
the existence of the positron. |
1928 |
Linus Pauling |
Outlined the nature of the chemical
bond in which he used Heitler’s quantum mechanical covalent
bond model (1927) to outline the quantum mechanical basis for all types of
molecular structure and bonding and suggested that different types
of bonds in molecules can become equalized by rapid shifting of
electrons, a process called “resonance” (1931), such that resonance
hybrids contain contributions from the different possible
electronic configurations. |
1929 |
John Lennard-Jones |
Introduced the linear combination of
atomic orbitals approximation for the calculation of molecular orbitals. |
1930 |
Wolfgang Pauli |
In a famous letter, Pauli suggested that, in addition to
electrons and protons, atoms also contained an extremely light
neutral particle which he called the "neutron." He suggested that
this "neutron" was also emitted during beta decay and had simply
not yet been observed. Later it was determined that this particle
was actually the almost massless neutrino. |
1931 |
Walther Bothe and Herbert Becker |
Found that if the very energetic alpha particles emitted from polonium fell on certain light elements,
specifically beryllium, boron, or lithium, an unusually
penetrating radiation was produced. At first this radiation was
thought to be gamma radiation,
although it was more penetrating than any gamma rays known, and the
details of experimental results were very difficult to interpret on
this basis. Some scientists began to hypothesize the possible
existence of another fundamental, atomic particle. |
1931 |
Enrico Fermi |
Renamed Pauli's "neutron" to neutrino
in order to distinguish it from the then-hypothetical possibility
of a much more massive neutron. |
1932 |
Irène Joliot-Curie and
Frédéric Joliot |
Showed that if the unknown radiation generated by alpha particles fell on paraffin or any
other hydrogen-containing compound, it ejected protons of very high energy. This was not in itself
inconsistent with the proposed gamma ray
nature of the new radiation, but detailed quantitative analysis of
the data became increasingly difficult to reconcile with such a
hypothesis. |
1932 |
James Chadwick |
Performed a series of experiments showing that the gamma ray
hypothesis for the unknown radiation produced by alpha particles was untenable, and that the
new particles must be the neutrons
hypothesized by Enrico Fermi. Chadwick
suggested that, in fact, the new radiation consisted of uncharged
particles of approximately the same mass as the proton, and he
performed a series of experiments verifying his suggestion. |
1932 |
Werner Heisenberg |
Applied perturbation theory
to the two-electron problem and showed how resonance arising from electron
exchange could explain exchange
forces. |
1932 |
Mark Oliphant |
Building upon the nuclear transmutation experiments of Ernest Rutherford done a few years
earlier, fusion of light nuclei (hydrogen isotopes) was first
observed by Oliphant in 1932. The steps of the main cycle of
nuclear fusion in stars were subsequently worked out by Hans Bethe
throughout the remainder of that decade. |
1932 |
Carl D. Anderson |
Experimentally proves the existence of the positron. |
1933 |
Leó Szilárd |
First theorized the concept of a nuclear chain reaction. He
filed a patent for his idea of a simple nuclear reactor the
following year. |
1934 |
Enrico Fermi |
Published a very successful model of beta decay in which neutrinos were produced. |
1934 |
Enrico Fermi |
Studies the effects of bombarding uranium isotopes with neutrons. |
1934 |
N.N.Semyonov |
Develops the total quantitative chain chemical reaction theory.
The idea of the chain reaction, developed by Semyonov, is the basis
of various high technologies using the incineration of gas
mixtures. The idea was also used for the description of the nuclear
reaction. |
1935 |
Hideki Yukawa |
Published his hypothesis of the Yukawa Potential and predicted
the existence of the pion, stating that such a potential arises
from the exchange of a massive scalar field, such as would be found
in the field of the pion. Prior to Yukawa's paper, it was believed
that the scalar fields of the fundamental forces necessitated
massless particles. |
1936 |
Carl D. Anderson |
Discovered muons while he studied cosmic
radiation. |
1937 |
Carl Anderson |
Experimentally proves the existence of the pion. |
1938 |
Charles Coulson |
Made the first accurate calculation of a molecular orbital wavefunction with the hydrogen molecule. |
1938 |
Otto Hahn, Fritz Strassmann, Lise Meitner, and Otto Robert Frisch |
Hahn and Strassmann sent a manuscript to Naturwissenschaften
reporting they had detected the element barium after bombarding
uranium with neutrons. Simultaneously, they communicated these
results to Meitner. Meitner, and her nephew Frisch, correctly
interpreted these results as being nuclear fission. Frisch
confirmed this experimentally on 13 January 1939. |
1939 |
Leó Szilárd and Enrico Fermi |
Discovered neutron multiplication in uranium, proving that a
chain reaction was indeed possible. |
1942 |
Kan-Chang Wang |
First proposed the use of beta
capture to experimentally detect neutrinos. |
1942 |
Enrico Fermi |
Created the first artificial self-sustaining nuclear chain
reaction, called Chicago Pile-1 (CP-1), in a racquets court below
the bleachers of Stagg Field at the University of Chicago on
December 2, 1942. |
1945 |
Manhattan Project |
First nuclear fission explosion. |
1947 |
G. D. Rochester
and C. C.
Butler |
Published two cloud chamber photographs of cosmic ray-induced
events, one showing what appeared to be a neutral particle decaying
into two charged pions, and one which appeared to be a charged
particle decaying into a charged pion and something neutral. The
estimated mass of the new particles was very rough, about half a
proton's mass. More examples of these "V-particles" were slow in
coming, and they were soon given the name kaons. |
1948 |
Sin-Itiro Tomonaga and
Julian Schwinger |
Independently introduced perturbative renormalization as a method of
correcting the original Lagrangian of a
quantum field theory so as to
eliminate an infinite series of counterterms that would otherwise
result. |
1948 |
Richard Feynman |
Stated the path integral
formulation of quantum mechanics. |
1949 |
Freeman Dyson |
Determined the equivalence of the formulations of quantum electrodynamics that existed
by that time — Richard Feynman's
diagrammatic path integral
formulation and the operator method developed by Julian Schwinger and Sin-Itiro Tomonaga. A by-product of that
demonstration was the invention of the Dyson series. |
1951 |
Clemens C. J. Roothaan and George G. Hall |
Derived the Roothaan-Hall
equations, putting rigorous molecular orbital methods on a firm
basis. |
1952 |
Manhattan Project |
First explosion of a thermonuclear bomb. |
1954 |
Chen Ning Yang and Robert Mills |
Derived a gauge theory for nonabelian groups, leading to the
successful formulation of both electroweak unification and quantum chromodynamics. |
1955 and 1956 |
Murray Gell-Mann and Kazuhiko Nishijima |
Independently derived the Gell-Mann–Nishijima
formula, which relates the baryon
number B, the strangeness
S, and the isospin
I_{z} of hadrons to the
charge Q, eventually leading to the systematic
categorization of hadrons and, ultimately, the Quark Model of hadron composition. |
1956 |
P. Kuroda |
Predicted that self-sustaining nuclear chain reactions should
occur in natural uranium deposits. |
1956 |
Clyde L. Cowan and Frederick Reines |
Experimentally proved the existence of the neutrino. |
1957 |
William Alfred Fowler,
Margaret Burbidge, Geoffrey Burbidge, and Fred Hoyle |
In their 1957 paper Synthesis of the Elements in
Stars, they explained how the abundances of essentially all
but the lightest chemical elements could be explained by the
process of nucleosynthesis in
stars. |
1961 |
Clauss Jönsson |
Performed Young's
double-slit experiment (1909)
for the first time with a particle other than photons by using
electrons and with similar results, confirming that massive
particles also behaved according to the wave-particle duality that is a
fundamental principal of quantum
field theory. |
1961 |
Sheldon Lee Glashow |
Extended the electroweak unification models developed by
Julian Schwinger by including a
short range neutral current, the Z0. The resulting symmetry
structure that Glashow proposed, SU(2) X U(1), formed the basis of
the accepted theory of the electroweak interactions. |
1962 |
Leon M. Lederman, Melvin
Schwartz and Jack
Steinberger |
Showed that more than one type of neutrino exists by detecting interactions of the
muon neutrino (already hypothesised with the
name "neutretto") |
1962 |
Murray Gell-Mann and Yuval Ne'eman |
Independently classified the hadrons according to a system that
Gell-Mann called the "Eightfold
Way," and which ultimately led to the quark model (1964) of hadron composition. |
1962 |
Jeffrey Goldstone, Yoichiro Nambu, Abdus
Salam, and Steven Weinberg |
Developed what is now known as Goldstone's Theorem, in which it was proved
that, if there is continuous symmetry transformation under which
the Lagrangian is invariant, then either the vacuum state is also
invariant under the transformation, or there must exist spinless
particles of zero mass, thereafter called Nambu-Goldstone bosons. |
1963 |
Nicola Cabibbo |
Developed the mathematical matrix by which the first two (and
ultimately three) generations of quarks could be predicted. |
1964 |
Murray Gell-Mann and George Zweig |
Independently proposed the quark model of
hadrons, predicting the arbitrarily named up, down, and strange quarks. Gell-Mann is credited with
coining the term "quark," which he found in James Joyce's book Finnegans Wake. |
1964 |
François Englert, Robert Brout, Peter
Higgs, Gerald Guralnik, C. R. Hagen, and Tom
Kibble |
Postulated that a fundamental quantum field, now called the
Higgs field, permeates space and, by way
of the Higgs mechanism, provides
mass to all the elementary subatomic particles that interact with
it. While the Higgs field is postulated to confer mass on quarks
and leptons, it represents only a tiny portion of the masses of
other subatomic particles, such as protons and neutrons. In these,
gluons that bind quarks together confer most of the particle mass.
The Higgs mechanism, which gives mass to vector bosons, was
theorized in 1964 by François Englert and Robert Brout. In October
of the same year, Peter Higgs, working from the ideas of Philip
Anderson reached the same conclusions; and, independently, by
Gerald Guralnik, C. R. Hagen, and Tom Kibble, who worked out the
results by the spring of 1963. |
1964 |
Sheldon Lee Glashow and
James Bjorken |
Predicted the existence of the charm
quark. The addition was proposed because it allowed for a
better description of the weak
interaction (the mechanism that allows quarks and other
particles to decay), equalized the number of known quarks with the number of known leptons, and implied a mass formula that correctly
reproduced the masses of the known mesons. |
1967 |
Steven Weinberg and Abdus Salam |
Published a paper in which he described Yang-Mills Theory using the SU(2) X U(1)
supersymmetry group, thereby yielding
a mass for the W particle of the Weak
Interaction via spontaneous symmetry
breaking. |
1968 |
Stanford University |
Deep
inelastic scattering experiments at the Stanford Linear
Accelerator Center (SLAC) showed that the proton
contained much smaller, point-like objects and was therefore not an
elementary particle. Physicists at the time were reluctant
to identify these objects with quarks,
instead calling them "partons" — a term coined by Richard Feynman.
The objects that were observed at SLAC would later be identified as
up and down
quarks. Nevertheless, "parton" remains in use as a collective term
for the constituents of hadrons (quarks,
antiquarks, and gluons). The strange
quark's existence was indirectly validated by the SLAC's
scattering experiments: not only was it a necessary component of
Gell-Mann and Zweig's three-quark model, but it provided an
explanation for the kaon (K) and pion (π) hadrons discovered in cosmic rays in
1947. |
1970 |
Sheldon Lee Glashow,
John Iliopoulos and Luciano Maiani |
Presented further reasoning for the existence of the as-yet
undiscovered charm quark. |
1971 |
Martinus J. G. Veltman and Gerardus 't Hooft |
Showed that, if the symmetries of Yang-Mills Theory were to be broken
according to the method suggested by Peter
Higgs, then Yang-Mills theory can be renormalized. The
renormalization of Yang-Mills Theory predicted the existence of a
massless particle, called the gluon, which
could explain the nuclear Strong Force.
It also explained how the particles of the Weak Interaction, the W and Z bosons, obtained their mass via
spontaneous symmetry
breaking and the Yukawa
interaction. |
1972 |
Francis Perrin |
Discovered the existence of "natural nuclear
fission reactors" in uranium deposits in Oklo, Gabon, where
analysis of isotope ratios demonstrated that self-sustaining,
nuclear chain reactions had occurred. The conditions under
which a natural nuclear reactor could exist were predicted in 1956
by P. Kuroda. |
1973 |
Makoto Kobayashi
and Toshihide Maskawa |
Noted that the experimental observation of CP violation could be explained if an
additional pair of quarks existed. The two
new quarks were eventually named top and
bottom. |
1974 |
Pier Giorgio Merli |
Performed Young's
double-slit experiment (1909)
using a single electron with similar results, confirming the
existence of quantum fields for
massive particles. |
1974 |
Burton Richter and Samuel Ting |
Charm quarks were
produced almost simultaneously by two teams in November 1974 (see November
Revolution) — one at SLAC under Burton
Richter, and one at Brookhaven National Laboratory under Samuel Ting. The charm quarks were
observed bound with charm antiquarks in
mesons. The two discovering parties had
independently assigned the discovered meson two different symbols,
J and ψ; thus, it became formally known as the J/ψ meson. The discovery finally convinced
the physics community of the quark model's validity. |
1975 |
Martin Lewis Perl |
With
his colleagues at the SLAC–LBL group, he detected the tauon
in a series of experiments between 1974 and 1977. |
1977 |
Leon Lederman |
Observed the bottom
quark with his team at Fermilab. This
discovery was a strong indicator of the top
quark's existence: without the top quark, the bottom quark
would have been without a partner that was required by the
mathematics of the theory. |
1983 |
Carlo Rubbia and Simon van der Meer |
Unambiguous signals of W particles were seen in January 1983 during a
series of experiments conducted by Carlo Rubbia and Simon van der
Meer at the Super Proton Synchrotron. The actual experiments were called UA1 (led by Rubbia) and UA2 (led by Peter
Jenni), and were the collaborative effort of many people.
Simon van der Meer was the
driving force on the use of the accelerator. UA1 and UA2 found the
Z particle a few months later, in May
1983. |
1995 |
Fermilab |
The top quark was finally observed by
a team at Fermilab. It had a mass much greater than had been
previously expected — almost as great as a gold atom. |
1995 |
Eric Cornell, Carl Wieman and Wolfgang Ketterle |
The first "pure" Bose–Einstein condensate was created by Eric
Cornell, Carl Wieman, and co-workers at JILA.
They did this by cooling a dilute vapor consisting of approximately
two thousand rubidium-87 atoms to below 170 nK using a combination
of laser cooling and magnetic evaporative cooling. About four months
later, an independent effort led by Wolfgang Ketterle at MIT created a
condensate made of sodium-23. Ketterle's condensate had
about a hundred times more atoms, allowing him to obtain several
important results such as the observation of quantum mechanical
interference between two different condensates. |
2000 |
CERN |
CERN scientists publish experimental results in which they
claim to have observed indirect evidence of the existence of a
quark-gluon plasma, which they
call a "new state of matter." |