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PC251 – Introductory Modern Physics

Electron diffraction
Electron diffraction


Adjunct Associate Professor Stephanie DiCenzo email
Associate Professor Patricia Purdue email

As the 19th Century drew to a close, Newton’s account of mechanics and Maxwell’s exquisite description of electromagnetism seemed to cover all the laws of physics. All that remained was to detect the elusive ether that was understood to carry electromagnetic waves and perhaps to give an explanation of the radiation from a hot object (a “black body”). In 1905 Einstein provided the simplifying but shattering explanation that there is no ether and that light travels at the same speed relative to every observer. This premise destroys the intuitively appealing notion that time flows at the same rate for everyone, everywhere – now even the sequence of events can change depending on an observer’s frame of reference. In that same year of 1905, Einstein made a leap that had even greater consequences when, building upon Planck’s explanation of blackbody radiation, he proposed that light (and all electromagnetic radiation) occurred only in packets of energy called quanta. In other words, something thought to be a wave is actually a particle (or collection of particles). De Broglie proposed the converse of this idea: things thought to be particles (electrons, nuclei, baseballs…) behave like a wave. From this "wave-particle duality", physicists inevitably developed quantum mechanics, the rules that must be applied to small-scale phenomena. The consequences of these rules include Heisenberg’s Uncertainty Principle and the even more disturbing property of indeterminacy. By 1925 a physicist trained only 30 years earlier could easily be bewildered by the new orthodoxy emerging in physics.

Prerequisite: PC 242 or equivalent