2010 PHYSICS 002C Lecture 22

2010 PHYSICS 002C Lecture 22 - PHYSICS 002C Lecture 22...

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PHYSICS 002C Lecture 22 May 19, 2010 Serway and Jewett Chapter 28 – Quantum Mechanics Chap 28.1-4 Blackbody radiation, the photo & Compton effects proved beyond doubt that light comes in little packets of energy hf E and yet somehow is able to exhibit wave-like interference effects. Chap 28.5-7 – The Double slit experiment and Wave-Particle duality In this lecture you will learn that quantum effects are universal – every degree of freedom, every coordinate associated with any physical system, is both wave-like and particle-like – light, electrons, buckyballs, all! The double slit experiment or its equivalent has been done with photons (1803), electrons (1927), positrons (1980), and buckyballs (1999), proving de Broglie’s (1922) hypothesis correct - p h / . The experiment has been done with very weak beams of photons and electrons, proving that whatever constitutes the wave that is interfering is associated with single particles that are detected all at once at a point. Finally, the experiment has been done with a delayed choice, such that a single photon cannot know before it is launched into a beam splitter that produces two interfering beams whether it will eventually have to interfere with itself or choose one or the other of two possible paths. This seems to prove that, as the electric field has a reality independent of the charge that produced it and is not merely a device for calculating distant forces, that the probability amplitude distribution, or wavefunction, has an existence that is independent of what measurement will be performed on it. Thomas Young's sketch of two- slit diffraction of light. Narrow slits at A and B act as sources, and waves interfering constructively are shown at C, D, E, and F. Royal Soc. 1803. The 2007 delayed choice experiment of Vincent Jacques et al. brought to life the gedanken experiment envisioned by John A. Wheeler (1984). The delayed choice experiment is the Michelson-Morley experiment of quantum physics. Chap 28.5 Louis de Broglie and the wave nature of “particles” . De Broglie’s (1923) Hypothesis: Because photons have particle as well as wave natures, perhaps all forms of matter have wave as well as particle properties . The inspiration for this amazing hypothesis was likely the Rydberg series for the energy levels of the hydrogen atom , where the fact that n = 1,2,3, … suggests standing waves have something to do with the states of electrons in “orbit” around a nucleus.
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