Classical Physics at the End of the 19 th Century Sir Isaac Newton (1702) by Godfrey Kneller Toward the close of the nineteenth century it appeared as if the penultimate chapter in physics had been written. There were indications that the final chapter would be little more than the working out of details of fundamental theories and their applications to problems in physics, chemistry, engineering, and hopefully, in all fields of human endeavor. In fact, a well-known physicist was led to make the remark that all that remained to be done in physics was the calculation of the next decimal point. The twentieth century opened on a scientific world in which all physics appeared to be encompassed within the mechanics of Newton and the electromagnetic theory of Maxwell. The labors of many mathematicians and physicists had extended newtonian mechanics to an elegance that appeared to lack little, if anything, in perfection. By the use of Newton’s laws and certain of their generalizations, one could carry out very precise calculations concerning the motions of astronomical bodies and the behavior of machines. Indeed, by purely theoretical calculations, Leverrier and Adams in 1846 used the known perturbations of the motion of Uranus to predict the existence of the then unknown planet Neptune. Elementary Quantum Chemistry Frank L. Pilar

Wave Behavior of Light - Young’s Double Slit Expt. Slit >> Slit ~ Diffraction of Waves Interference

Thomas Young (1773 – 1829)

Augustin Jean Fresnel (1788 – 1827) An interesting triumph of the wave theory was an experiment suggested to Fresnel by Poison, who sought to discredit the wave theory. Poison noted that if an opaque disk is illuminated by light from a source on its axis, the Fresnel wave theory predicts that light waves bending around the edge of the disk should meet and interfere constructively on the axis, producing a bright spot in the center of the shadow of the disk. Poisson considered this to be a ridiculous contradiction of fact, but Fresnel’s immediate demonstration that such a spot does in fact exist convinced many doubters that the wave theory of light is valid. Physics Paul A. Tipler

Electromagnetic Theory Michael Faraday (1791 – 1867)James Clerk Maxwell (1831 – 1879)

Heinrich Hertz (1857 – 1894)

The Ultraviolet Catastrophe

Lord Rayleigh (1842 – 1919)James Jeans (1877 – 1946)

After a few weeks of the most strenuous labor of my life, the darkness lifted and a new, unimagined prospect began to dawn. Max Planck (1858 – 1947)

The Photoelectric Effect

Albert Einstein (1879 – 1955) Einstein’s equation was a bold prediction, for at that time there was no evidence that Planck’s constant had any applicability outside of blackbody radiation and there were no experimental data on the [kinetic energy] as a function of frequency. Physics by Paul A. Tipler Robert Millikan ( )

Wave – Particle Duality The Double Slit Expt. Again

Atomic Structure - Gold Foil Experiment One day Geiger came to and said, “Don’t you think that young Marsden, whom I am training in radioactive methods, ought to begin a small research?” Now I had thought that too, so I said, “Why not let him see if any alpha particles can be scattered through a large angle?” I may tell you in confidence that I did not believe that there would be, since we knew the alpha particle was a very fast massive particle, with a great deal of energy, and you could show that if the scattering was due to the accumulated effect of a number of small scatterings the chance of an alpha particle being scattered backward was very small. Ernest Rutherford (1871 – 1937) Then I remember two or three days later Geiger coming to me in great excitement and saying, “We have been able to get some of the alpha particles coming backwards…” It was quite the most incredible event that has ever happened to me in my life. It was almost as incredible as if you fired a 15-inch shell at a piece of tissue paper and it cam back and hit you.

Postulates Certain orbits are stationary. Photon emission occurs upon orbital trans. Angular momentum is quantized. Neils Bohr (1885 – 1962)

L. H. GermerC. J. Davisson …studying electron scattering from a nickel target at Bell Laboratories. After heating the target to remove an oxide coating that had accumulated during an accidental break in the vacuum system, they found that the scattered-electron intensity as a function of the scattering angle showed maxima and minima. Their target had crystallized, and by accident they had observed electron diffraction. Physics by Paul A. Tipler Louis de Broglie (1892 – 1987) Matter Waves

Constructive InterferenceDestructive Interference ( Standing Wave)

William Hamilton (1805 – 1865) H = T + V Hamiltonian Mechanics

The Wave Equation Erwin Schrodinger (1887 – 1961) The wave function contains all possible information about a system, so instead of speaking of “the state described by the wave function ,” we simply say “the state .” Quantum Chemistry by Ira N. Levine

Max Born (1882 – 1970) Quantum mechanics does not say that an electron is distributed over a large region of space as a wave is distributed. Rather, it is the probability patterns (wave functions) used to describe the electron’s motion that behave like waves and satisfy a wave equation. Quantum Chemistry by Ira N. Levine