History of the Physical Sciences 1650-1950 Color Key: Red corresponds to the development of chemistry, early atomic theory, the problem of heat, thermodynamics, and kinetics); Blue corresponds to the development of electromagnetic theory; Green corresponds to the development of quantum theory
Considered the first modern chemist, Boyle criticized the 3-Principal system of the Alchemists and the four-element system of the Aristotelians in his work the Skeptical Chymist. In his other works, including The Excellency and Grounds of the Corpuscular or Mechanical Philosophy, Boyle argued for a corpuscular view of matter and proposed “change results from the motion, bulk, shape, and texture of the minute parts of matter.” Boyle also raised important questions about pressure and volume (Boyle’s Law), rust and oxidation, and the relationship between fire and air.
In his work "Concerning the First Principle of Metal and Stones," Becher proposed that all matter is made up of three parts, one being called “combustible.” When matter burned, the combustible was released. This led to Stahl’s phlogiston theory and was one of the earliest attempts to deal with the problem of heat.
Hooke demonstrated the power of the microscope in his works "A New Theater of Nature" and "Micrographia." Hooke coined the term “cell,” and most importantly turned the focus of the scientific world towards things too small for the human eye to see. Hooke also conducted experiments that caused him to see a relationship between combustion and air, though he did not pursue these fully.
Building on the work of Kepler and Galileo, Isaac Newton ushered in the new paradigm of physical science, henceforth to be known as Newtonian Mechanics. He published the Principia Mathematica in 1687, one of the most important texts in the history of the physical sciences. Newton’s chief theories included the laws of motion (which describe the rules of force, inertia, velocity as a vector, momentum, and the possibility of action at a distance), the development of differential and integral calculus, and the law of universal gravitation. Newton’s most important accomplishment was banishing the Aristotelian cosmology and replacing it with a mechanics that governed both the Earth and the Heavens.
In "Preliminaries," Stahl argued that the “combustible” property of matter described by Becher should be termed a “phlogiston.” Like Becher, Stahl believed that the presence of this phlogiston was necessary for a substance to burn. The phlogiston theory was a further attempt to explain heat and combustion, though it had several problems, notably that observation revealed some substances would actually increase in weight when burned.
Believed that air was a mixture, and argued in his "On Dephlogisticated Air" that when a substance underwent combustion or oxidation it released a phlogiston. Basically, Priestley believed that what is floating all around us is air + phlogiston, and that in the absence of phlogiston you have something called “pure air.” Lavoisier would later pronounce this Oxygen.
In his "Memoirs on Heat" (with Laplace), Lavoisier used a calorimeter to demonstrate that combustion and respiration were the same process, furthering the mechanization of all physical processes. In the work "Elements of Chemistry" Lavoisier proposed the caloric theory of heat and announced the discovery of “oxygen” as the correct term for “pure air.” The caloric was essentially a view of heat as a subtle fluid and a motion that moves in and out of things. Lavoisier ended the phlogiston theory of heat and air held by Priestley.
Along with Humphrey Davy, Thompson demonstrated through experiment in 1798 and 1799 that mechanical work could be converted into heat through friction. This dealt a serious blow to the caloric theory and led to a revival of Boyle’s dynamical theory of heat, though it would take Joule’s demonstration in 1847 to convince Thompson of the dynamical theory.
Dalton, in his "A New System of Chemical Philosophy," helped to lead the way into modern atomic theory. Dalton proposed that every element was made up of atoms unique to that element. He also published a basic system of relative atomic weights.
Young published "On the Theory of Light and Colors," a groundbreaking work that sought to explain a phenomenon of light observed in the famous double slit experiment. Young concluded that light must be of a wavelike nature (as opposed to Newton’s particulate light) when he noticed that light occasionally interferes with itself. This led Young to believe in the existence of an aether which, though ultimately proved incorrect by quantum mechanics, was the best explanation at the time for how light could be a wave (waves need a medium to travel through).
Following Oersted’s discovery of electromagnetism, Ampere furthered the work by demonstrating that parallel wires either attract or repel each other depending on the direction of the electric current running through them, making clear the difference between static and dynamic electricity.
In his work "Determining Relative Masses of Elementary Molecules," Avogadro developed what is known as Avogadro’s Law. This holds that at constant temperature and pressure, the masses of the same volume of different gases is related to the relationship between the molecular weights of those gases. Clausius later confirmed Avogadro’s theory.
Oersted wrote in "The Electromagnetic Effect" of his discovery that running an electric current near a compass would cause the needle to move. Oersted was thus responsible for the theory that electric currents create magnetic fields, fundamentally linking the two previously separate fields under electromagnetic theory.
Most famous for Gay-Lussac’s Law, which helped to determine the relationship between pressure, volume and temperature of a gas. Gay-Lussac was an early contributor to the dynamic, or kinetic theory of heat through his work on gases.
Faraday expanded upon the work done by Oersted and Ampere. By moving a magnet up and down a coiled wire (attached to a battery and a device that detected a flow of current by moving) Faraday demonstrated that it’s the motion that’s important. Faraday conceptualized lines of force extending outwards from the magnet that caused pressure in the wire and thus forced an electrical current through it. Faraday came to believe that electricity and magnetism were causing each other and that it was happening at the speed of light, though this was harshly criticized at the time.
Carnot’s 1824 publication of "Reflections on the Motive Power of Fire" provided what is now known as the 2nd Law of Thermodynamics, the fact that heat flows from hotter to cooler regions, i.e. a temperature difference is required for work to be done. This was also the first statement of entropy, though Carnot used the term caloric to describe it. Carnot ultimately came to support the emerging kinetic theory of heat.
Demonstrated that heat could be converted into mechanical work and vice versa. Joule is considered the discoverer of the conservation of energy principle, and went a long way in supporting the dynamical theory of heat.
In his work "The Nature of the Motion Which We Call Heat," Clausius objected to several principles of the caloric theory, specifically that the caloric was a substance itself that is conserved. Clausius was at the head of the shift towards a kinetic theory in his demonstration that temperature is related to velocity. The equation P=(mnu2)/3V and its derivation PV=cT showed that increased temperature of a gas is due to the increased velocity of its particles.
In his paper "A Course of Chemical Philosophy," Cannizzaro confirmed Avogadro’s distinction between molecular and atomic weights. Because Avogadro was correct, Cannizzaro demonstrated that you could use equal volumes of a gas to determine its respective atomic weight.
Meyer was one of the chief contributors to the periodic classification of the elements. He proposed in "Chemical Elements as a Function of Atomic Weight" that when arranged in order of their atomic weights the elements would demonstrate similar properties as a function of their weights.
In his 1865 paper "A Dynamical Theory of the Electromagnetic Field," Maxwell proved mathematically that Faraday was correct about the relationship between electromagnetism and light. Maxwell’s equations proved that electricity and magnetism travel in waves through space at the speed of light, though he remained confined to the existence of the aether. Maxwell also developed Faraday’s “lines of force” into the conception of an electromagnetic field.
Famous for his publication of the periodic table, Mendeleev brought a measure of predictability to the study of elements. In his Relation between Properties and Atomic Weights, Mendeleev (like Meyer) stated that when arranged in order of their atomic weights, the elements show a “periodicity” of properties. Mendeleev also proposed that these properties were due to the valences of the elements.
Boltzmann is important for his work with probabilities and statistical mechanics. Boltzmann’s equation contributed significantly to kinetic theory in that it described the dynamics of a gas as a function of probabilities. Boltzmann’s equations and way of thinking about probabilities would later become important in the discussion of quantum mechanics.
Planck, in his work on blackbody radiation, discovered the equation E=hv where E is a discrete amount of energy (now called quanta). This allowed him to state that a beam of light contains a huge number of these “e” particles and yet also behaves as a wave. This work made him one of the founders of quantum mechanics.
Rutherford famously proposed the experiment in which a beam of charged particles was shot at a thin gold foil. The results of the experiment revealed to Rutherford that the structure of the atom must be “planetary in nature.” This structure was his chief contribution to nuclear physics, yet it also raised questions as to how electrons could emit electromagnetic energy without collapsing. In this way it also stirred research into quantum mechanics.
Einstein’s 1905 work on relativity called into question the practical correctness of Newtonian mechanics on an incredibly small scale. Einstein proposed the theory of special relativity to reconcile mechanics and electromagnetism, and showed through the Lorentz Transformation that the fourth coordinate, time, could not be held constant. One of Einstein’s major contributions was that the speed of light is the only true constant in the universe; everything else is relative. With the derivation of the equation E=mc2 he demonstrated the total conservation of energy by its ability to converted into mass and vice versa. Einstein supported a dual particulate and wavelike nature of light that was highly significant in quantum mechanics. Finally, he expanded his theory to one of general relativity to include the idea that space-time is curved by gravity. Through his elevator thought experiment Einstein demonstrated that gravity could even bend light.
Born provided the popularly accepted interpretation of the Schrodinger equation that the wave function represents the probability P(x,y,z,t) of finding a particle at a position (x,y,z) at a time t. Born’s achievement was in this statistical interpretation of quantum mechanics.
Bohr’s chief contribution to quantum theory lay in his model of the atom, in which electrons circled the nucleus in one of several allowed orbits. Bohr claimed that we need to stop applying a classical system to the problem of energy loss in electron orbits. In his work on spectral lines, Bohr concluded that there are different orbital levels, and that when the electron jumps between levels it either absorbs or releases energy and thus emits a different color of light. Each substance emits its own color, and Bohr was able to get good results calculating atomic emission spectra from his model.
In 1927 Schrodinger wrote the wave function that could be used to describe where the electron is located. Einstein argued that the electron isn’t actually a wave, but that Schrodinger’s equation really gives us a probability of where the electron is in its orbit. Schrodinger’s equation is the fundamental dynamical equation of quantum mechanics, but as Einstein noted cannot give a definite value for position or momenta of the electrons. Schrodinger later proposed the famous “Schrodinger’s Cat” thought experiment to question the completeness of quantum mechanics due to the collapse of the wave function under any actual observation, for example observing the double slit experiment.
The Michelson-Morley experiment was performed to test for the existence of the aether that had long been maintained by proponents of a wave theory of light and electromagnetism. The null result of the experiment seriously called into question how light could operate as a wave without a medium. The answer to this would be found in the development of quantum physics.
De Broglie’s major contribution to quantum mechanics was that the proposition of wave-particle duality should be extended to all particles, not just light and photons as proposed by Einstein. De Broglie suggested that particles follow a “trajectory determined by its associated wave.”
Famous for postulating the Heisenberg Uncertainty Principle of quantum mechanics. Basically, Heisenberg asserted that we cannot know the position AND the speed of a particle on this small of a scale at the same time. The reason for this is that by the mere fact of observing (the only way to do so is to use some form of light or other sensor) we disturb the system and therefore collapse the wave function. The uncertainty principle places a massive importance on the part of the observer and raised many concerns as to the completeness of quantum mechanics.
Dirac’s contribution to the discussion of quantum mechanics has to do principally with an assessment of the limitations of classical physics as applied to systems on the atomic level. Dirac notes that there is a fundamental distinction between large and small on this scale. Dirac, among others, questioned the completeness of quantum mechanics with regard to the dual slit experiment. Essentially, when unobserved electrons act just like light but as soon as one “turns on the light,” the electrons act like large particles. This is the collapse of the wave function.