| 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 predicted. 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 electromagnetic wave. 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 (460-370 B.C.). 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. |