Music, Math, and Motion with Dr. Arun Chandra & Dr. E.J. Zita The Evergreen St. College Fall week 5 Tuesday 28 Oct. 2008

Overview Looking ahead and resources Your Research Projects Copenhagen and Quantum Mechanics Arun

Looking ahead Look at Moodle:

Moodle details for this week

Library research resource wiki

Your team research projects Due this Saturday at noon More guidelines on Moodle Time to work on them in Friday workshop

Copenhagen + program themes Scientific method Brecht: compromise for the greater good? (p.76) Harding: reflexivity & strong objectivity (p.72-73, 86-87);  “Jewish physics”  morality of working on certain science applications Message & communication Variations – different perspectives - uncertainties

Brief overview of Quantum mechanics Classical: light as wave Quantum: light as particle (photoelectric effect) Classical: electron as particle Quantum: electron as wave (H atom) Uncertainty Complementarity

Classical: light as wave

Quantum: light as particle (photoelectric effect + Compton effect) hc/ = K max + 

Classical: electron as particle J.J. Thomson discovered electrons as particles in 1897, and shortly thereafter proposed estimating the electron mass using E = mc 2, a decade before Einstein.

Quantum: electron as wave Louis deBroglie predicted electron waves in 1923, and was initially ridiculed for the idea deBroglie was awarded the Nobel Prize in 1929.

What if we fire single electrons through double slits, one by one? Predict how electrons will land on the screen…

Electrons interfere as waves!

Uncertainty: Beyond theory-laden facts: Observations can change measurement outcomes. Old paradigm: Who decides position is a good thing to measure?

Complementarity We may observe a phenomenon as wave or particle, depending on our choice of observation method and the situation. Fundamental entities such as electrons and photons are not fundamentally only waves or only particles, but both. Our inability to tell if an electron is a particle or a wave is not a flaw or limit in our understanding – it is a fact of nature. Particles and waves make sense to humans; Nature makes electrons something more complex.

Davisson and Germer discovered electron waves in 1927, by accident So did G.P. Thomson, later that year (son of J.J. Thomson). Davisson, Germer, and G.P. Thomson shared the Nobel Prize in 1937.

Hydrogen atom: pre-Bohr Plum-pudding-model … tested by Rutherford Surprise – the atom has a nucleus!

Bohr’s Hydrogen atom: Bohr implicitly assumed something like resonant electron orbital wavelengths in his successful model of the Hydrogen atom in 1913 (quantized angular momentum)

Bohr’s Hydrogen atom

Quantum mechanical uncertainty What is the chance that an electron with energy E 2 will be found in orbit r 1 ?

How can QM be “true”, given all this uncertainty? Statistical predictions are highly uncertain for a few particles, and very accurate & precise for systems of many particles: modern electronics (e.g. semiconductors) diagnostics (scanning tunnelling microscope, SEM, atomic force microscope) lasers quantum computing (coming soon?)

Particles & Waves 2.Photon1. classical light waves Newton’s corpuscles, Einstein’s PEYoung’s diffraction 1.Classical electrons2. deBroglie’s theory Davisson & Germer’s experiment Bohr’s H atom Frayn’s model: Bohr ≈ nucleusHeisenberg ≈ electron Musical models: Gabor’s ♫ particlesFourier’s ♫ waves

Frayn’s atom

How to make decisions, in the face of uncertainty? “The idea that the value of pursuing the truth rests on the possibility of certainty is a myth.” (Lynch, True to Life: Why truth matters, p.27)

Liese Meitner and fission Lise Meitner was part of the team that discovered nuclear fission, an achievement for which her colleague Otto Hahn was awarded the Nobel Prize. Meitner is often mentioned as one of the most glaring examples of scientific achievement overlooked by the Nobel committee.[2][3][4] A 1997 Physics Today study concluded that Meitner's omission was "a rare instance in which personal negative opinions apparently led to the exclusion of a deserving scientist" from the Nobel.[5]nuclear fissionOtto HahnNobel Prize[2][3][4][5]

Gamow-Bethe-Weizsacker and the liquid drop model of the nucleus The liquid-drop model in nuclear physics was originally proposed by George Gamow and developed by Hans Bethe and Carl von Weizsäcker in the 1930s. It treats the nucleus as an incompressible fluid of protons and neutrons bound together by the strong nuclear force. It treats the nucleus as an incompressible fluid of protons and neutrons bound together by the strong nuclear force. veDecayModes/

Resources for images and info ment/tourquan/tourquan.htm esign/final/jjthom.htm cience/physics/atom_particle/electron.html Many other images from Giancoli’s Physics text, or public domain online.