|History of Physics:
Since antiquity people have been writing about their attempts to understand the
behavior of matter and energy. The philosophers and physicists of old did not
understand how or why objects fall to the ground, how fires burn, how sounds
propagate through gasses, how light propagates through a vacuum, how plants grow,
why objects seem solid, how the earth and the moon travel around the sun, why stars
shine, or how people transferred genetic information to their children.
Many of the early proposed theories wrongly attempted to explain physical
phenomena in terms of concepts unrelated to science. Many early scientists across
the globe couched their theories in philosophical or religious pretext and never
attempted to explain their theories in terms of systematic, experimental testing.
There were many exceptions though. Archimedes (287-212 B.C.) for example
derived many correct quantitative relationships and was one of the first to develop
accurate laws describing mechanics and hydrostatics.
Galileo (1564-1642) was one of the first to use experimental data in order to
construct physical theories. His utilization of a rough form of the scientific method
allowed him to predict and validate certain observations related to optics, motion and
dynamics including an understanding of inertia, gravity, lenses and planetary motion.
Galileo proved, before Newton, that two bodies of similar weight will fall at the same
speed (in a vacuum). He also used the newly invented telescope to observe some of
the irregularities and imperfections of planetary bodies (sunspots, mountains on the
moon…). His findings helped to support the heliocentric (sun centered) view of our
solar system as he used the telescope to discover moons orbiting Jupiter (this
proved that everything in the universe did not orbit around the earth). He also
proposed the revolutionary idea that the Milky way was composed of stars similar to
our sun. His correct ideas threatened the preexisting explanation of physical law at
the time… the doctrine of physical uniformity of physics and the heavens which was
established by the church.
In 1687, Newton published the Principia Mathematica and created the foundation for
modern physics. The book detailed two comprehensive and successful physical
theories: Newton’s laws of motion (now referred to as “classical” mechanics) and
Newton’s law of gravitation. The laws of motion explained how objects move and it
proved that an understanding of the physical conditions before an event can allow
one to extrapolate and often correctly predict the outcome after the event (cause and
effect). The law of gravitation brought about the science of astrophysics which
explains planetary and celestial movement using our fundamental understanding of
the physics of gravity. These theories were industriously extended by the efforts of
Lagrange, Hamilton and others who helped to concretely establish classical physics.
The laws of classical physics showed that matter (in the form of physical objects) and
energy (in the form of motion and gravity) could be qualitatively related and thus
Boyle, Young and many others helped to develop and expand upon thermodynamics
in the 18th century. In 1733 Bernoulli used statistical results to substantiate
thermodynamic theories thus initiating the field of statistical mechanics. In 1798
Thompson equated two previously distinct forms of energy by offering a formulaic
explanation of the conversion of motion into heat. In 1847, Joule explained that
energy is always conserved in mechanical processes. He showed that energy is
never lost within a system, that it can simply take different forms.
Thermodynamics allows scientists to understand the energy of heat exchange within
closed systems. Because our universe is a closed system, the laws and formulas
derived from thermodynamics have been more recently applied to further our
understanding of how our universe was formed and why it looks the way that it does.
In the nineteenth century Faraday and Ohm began to develop an understanding for
the behavior of electricity, and magnetism. In 1855, James Clark Maxwell used
equations to unify electricity and magnetism. This celebrated discovery had
profound implications on technology and on our understanding of light as an
The study of the emission of electromagnetic waves by certain (unstable) atoms is
know as radioactivity. The phenomenon was discovered by Henri Becquerel and
further elaborated upon by others including Pierre and Marie Curie. The three split
the Nobel Prize for physics in 1903. The understanding of atomic instability initiated
the field of atomic and nuclear physics.
In 1897, Thompson discovered the elementary particle that carries currents within
electrical circuits, the electron. In 1904, he proposed the first model of the atom (the
smallest form of energy that can still be described as an element). Many models
came after this one further revising its properties. Although John Dalton was the first
to predict the existence of atoms in modern terms, the first prediction to state that
matter was composed of individual atoms was set forth by the Greek, Democritus
Einstein formulated the theory of special relativity in 1905. This theory saw time as a
forth physical dimension and unified space with time to create what is now called
spacetime. Relativity, which has been substantiated over the years by experiment
after experiment, contradicts some of the propositions of classical, Newtonian
mechanics. The theory contends that neither time, nor space is absolute (meaning
that the properties of space and time are not homogeneous throughout the
universe). Einstein showed us that things like mass and speed can warp spacetime,
creating different observed realities for different observers. In 1915, Einstein
introduced his theory of general relativity, modifying Newton’s law of gravitation.
One important thing to note is that in most physical systems, like the ones that we
encounter here on earth, relativity only very slightly modifies classical mechanics, thus
its role is quite trivial in most calculations. Relativistic implications should not be
ignored in the calculations that relate to systems involving very large amounts of
mass and energy. For instance astronomers and physicists will obtain slightly
incorrect predicted velocities for large planetary bodies if they use strictly classical
calculation. In a system such as this one, it is necessary to implement relativity in
order to obtain predicted values that will coincide with the observed values.
In 1911, Rutherford used what he called scattering experiments to deduce the
existence of the compact atomic nucleus. He shot beams of alpha radiation through
extremely thin sheets of gold foil. Very few of the alpha particles bounced back, and
this told him that the majority of the atom, is empty space. He calculated that only
about 1/100,000 of the diameter of an atom actually consisted of matter. He was
also able to determine that the nucleus was composed of positively charged particles
dubbed protons. Chadwick discovered the existence of the electrically neutral
nuclear constituent, the neutron, in about 1911.
The year 1900 brought giant advancements in small scale physics, also known as
quantum physics. In 1900 Max Plank’s work on blackbody radiation lead him to
conclude that light is composed of discrete, non-continuous packets of radiation.
This was highly anomalous at the time and it inspired many great minds to further
investigate the elementary properties of matter and energy. In the 1920s
Heisenberg, Schrodinger and Dirac formulated quantum mechanics, successfully
describing quantum observations
in physical and mathematical terms. Quantum mechanics generally describes how
subatomic particles act and interact in a probabilistic fashion and the theory
describes the calculations of these probabilities. Physics does not have a method of
uniting quantum physics to classical physics. In other words the inherently
unpredictable, stochastic behavior of subatomic particles translates into the regular,
predictable behavior of the bigger objects which they constitute. We have not,
however, come to understand how this takes place and general and quantum physics
have remained theoretically disparate for many decades.
Quantum mechanics has provided the conceptual tools for condensed matter physics
which is the study of the physical behavior of solids and liquids. Phenomena such as
crystal structures, absolute zero temperature, semiconductivity and superconductivity
have all stemmed from the efforts made by condensed matter physicists such as
Bloch, Drude and Sommerfeld.
Led by Fermi, nuclear physicists in America, motivated by the second World War,
successfully achieved the first man-made nuclear chain reaction in 1942. The
explosion of the nuclear bombs at Alamogordo and later at Hiroshima and Nagasaki
(in 1945) proved that E does equal MC², validating Einstein’s matter-energy
equivalency theory empirically.
Quantum field theory was formulated in an effort to unify special relativity with
quantum mechanics. By the end of the 1940s work by Feynman, Schwinger,
Tomonaga and Dyson helped to build upon this theory, further explicating the
quantum theory and initiating quantum electrodynamics. Quantum field theory has
created the groundwork for modern particle physics. In 1954 Yang and Mills
developed the framework for the standard model, which was subsequently
completed in the 1970s, that successfully describes the nature of almost all of the
elementary particles currently discovered.