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Transcript
You Gotta Know These 20th-Century Physicists
1.
Niels Bohr (1885–1962) Bohr reconciled Rutherford’s results from the gold foil experiment
with Planck’s quantum theory to create a model of the atom in which electrons resided in
specific energy levels at specific stable radii. This model was the basis for Balmer’s work with
spectroscopy and Rydberg’s energy formula, which explicitly stated the frequency of light that an
electron would emit if it went from a higher energy to a lower energy. Bohr and his son fled to
the US in World War II under the pseudonym Baker and contributed to the Manhattan Project.
2. Louis de Broglie (1892–1987) de Broglie’s work quantifying the wave-particle duality of
quantum mechanics earned him the 1929 Nobel Prize in Physics. His doctoral thesis, which
proposed that all particles have a characteristic wavelength dependent on their momentum, was
so groundbreaking that the reviewers passed it directly to Einstein, who endorsed it. In
opposition to the probabilistic interpretation of quantum mechanics, de Broglie later worked to
define a purely causal interpretation, but his work remained unfinished until David Bohm
refined it in the 1950s. His last name is pronounced approximately [duh BROY].
3. Albert Einstein (1879–1955) In one year — 1905, called his annus mirabilis, or miracle year —
Albert Einstein authored four papers that revolutionized modern physics. The first explained
the photoelectric effect in terms of discretized electromagnetic radiation. The second formed the
foundation for modern statistical physics by explaining the seemingly-random motion of
particles in a fluid, a behavior called Brownian motion. The third reconciled Maxwellian
electrodynamics with classical mechanics by positing a finite, constant speed of light. This is now
known as special relativity. The fourth paper contained his statement that the energy of a body is
equal to its mass times the speed of light squared. Ten years later, in 1915, Einstein published his
theory of general relativity, which generalized special relativity to account for gravitational
fields.
4. Enrico Fermi (1901–1954) Fermi is best known to the public as a main contributor to the
Manhattan Project, his work with statistical physics laid the groundwork for modern electronics
and solid-state technologies. He applied the Pauli exclusion principle to subatomic particles to
create Fermi-Dirac statistics, which accurately predicted the low-temperature behavior of
electrons. Particles which obey Fermi-Dirac statistics are called fermions in his honor. Fermi
also suggested the existence of the neutrino in order to balance nuclear beta-decay chains.
5.
Richard Feynman (1918–1988). Feynman developed a mathematical formalism called the
path integral formulation of quantum theory that utilized the “sum over histories,” taking into
account all possible paths a particle could take. This constituted the creation of quantum
electrodynamics and earned him the 1965 Nobel Prize in Physics. He also used the sum over
histories in developing Feynman diagrams, which illustrate the interaction of subatomic
particles. Aside from being a prolific physicist, Feynman was also an accomplished bongo player
and sketch artist.
6. George Gamow (1904–1968) Gamow was one of the first to explain the implications of the Big
Bang theory of cosmology. He correctly predicted the abundance of hydrogen and helium in the
early universe, nicknamed Alpher-Bethe-Gamow theory (an intentional pun on the first three
letters of the Greek alphabet, alpha, beta, and gamma, for which the otherwise unrelated
physicist Hans Bethe was included), and also theorized that the the heat from the Big Bang
would still be visible as the cosmic microwave background radiation. Although Gamow received
no Nobel for this prediction, the CMB’s discoverers, Arno Penzias and Robert Wilson, as well as
two later observers, John Mather and George Smoot, did receive Nobels.
7.
Werner Heisenberg (1901–1976) Heisenberg is most known for his matrix interpretation of
quantum theory, which constructs observable quantities as operators, which act on a system. His
famous uncertainty principle (better translated, however, as “indeterminacy principle”) states
that the more accurately an object’s position can be observed, the less accurately its momentum
can. This is because shorter wavelengths of light (use as a sort of measuring-stick) have higher
energies, and disrupt a particle’s momentum more strongly. Heisenberg earned the 1932 Nobel
Prize in Physics for discovering the allotropic forms of hydrogen.
8. Max Planck (1858–1947) Planck allowed quantum theory to move forward in the early 20th
century by correctly modeling how an object radiates heat, solving the ultraviolet catastrophe,
which was a predicted unbounded increase in the amount of radiation emitted at high
frequencies. Planck’s Law of Radiation superseded the Rayleigh-Jeans Law, which was used
until that point. He suggested that electromagnetic energy could only be emitted in specific
packages, called quanta (singular quantum, from the Latin for “how much”), positing that the
energy of this photon was equal to its frequency times a fixed value h, now known as Planck’s
constant.
9. Ernest Rutherford (1871–1937) Rutherford’s gold foil experiment provided the first evidence
that the atom was made up of a large, positively-charged nucleus, surrounded by a cloud of
negatively-charged electrons. Rutherford won the 1908 Nobel Prize in Chemistry for this work.
Rutherford was also an early leader in nuclear fission techniques, having discovered the decay of
carbon-14 and providing the impetus for modern carbon dating. As part of this research, he
discovered the proton and neutron, the latter in cooperation with James Chadwick. He is also
the only native New Zealander with an element named after him (Rutherfordium, atomic
number 104).
10. Erwin Schrödinger (1887–1961) Schrödinger contributed to the early formulations of
quantum theory as a foil to Heisenberg, Bohr, and Dirac, criticizing their Copenhagen
interpretationwith thought experiments like his famous Schrödinger’s Cat argument. He
formulated both the time-independent and time-dependent Schrödinger equations, partial
differential equations which described how quantum systems behaved. Schrödinger’s work was
the basis for Heisenberg’s matrix formalism, Feynman’s path integral formalism, and quantum
mechanical perturbation theory, which considers the effects of a small disturbance to a quantum
system.
Honorable mentions:
11. Marie (1867–1945) and Pierre (1859–1906) Curie rigorously isolated and experimented on
radioactive materials, forming the basis for early nuclear and particle physics.
12. Paul Dirac (1902–1984) was one of the first to attempt a generalization of quantum theory to
relativistic speeds, the result of which was the Dirac equation.
13. Murray Gell-Mann (born 1929) predicted the existence of quarks, which compose protons,
neutrons, and other, heavier particles.
14. Robert Millikan (1868–1953; not to be confused with Robert Mullikan, a chemist) determined
the charge of the electron by meticulously observing oil droplets in an electric field and noting
the time it took them to fall a certain distance.
15. J. Robert Oppenheimer (1904–1967) oversaw much of the Manhattan project, but was later
stripped of his security clearance during the McCarthy-era Red Scare, as a result of his
acquaintance with communists and his enmity with Edward Teller.
16. Wolfgang Pauli’s (1900–1958) namesake exclusion principle prohibits most types of particles
from occupying the same state, and forms the basis for chemical bonds.