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Wednesday, October 17

Wednesday, October 17. Ford Chs: 6&7. Agenda. Announce: Read Chs. 8 & 9 Project Ideas due by Halloween Another project idea: Modern Physics in Modern Medicine Ch. 6 Ch. 7. Probability Pre-Quantum.

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Wednesday, October 17

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  1. Wednesday, October 17 Ford Chs: 6&7

  2. Agenda • Announce: • Read Chs. 8 & 9 • Project Ideas due by Halloween • Another project idea: Modern Physics in Modern Medicine • Ch. 6 • Ch. 7

  3. Probability Pre-Quantum • Physicists accepted probability even before quantum mechanics, but where? And how was it “different” from that in QM?

  4. Probability In QM • Can be computed precisely • All that one can compute…fundamentally limited in ability to predict (nondeterministic universe) • Mathematics describes a probability wave • Examples: • Jumps of electron to different states • Radioactive decays

  5. Radioactivity • Geiger counter makes activity at the level of the nucleus apparent! • Characterized by half-life • Wide range of half-lives • All unstable particles follow same exponential curve

  6. Nuclear Waste (spent fuel) • Lots of nasty radioactive material left over from nuclear reactors • Half-lives of years to hundreds of years • Can’t fix chemically • Essentially never safe • Need nuclear furnace (e.g. Sun, nuclear reactor)

  7. Quantum Tunneling • Object can pass through barriers which classically they could not

  8. Quantum Tunneling

  9. Uncertainty Principle • Fundamental limit to how well we can “know” certain pairs of quantities • The better you know one, the less well you know the other • E.g. position/momentum or energy/time • Already saw when trying to compress electrons…so knew where they were meant we knew little about momentum • Will see later on in the book (w/ waves)

  10. Is quantum probability real or just reflect our ignorance?

  11. Fermion/Boson • Fermions—half-odd-integer spin (e.g. electron, proton, neutron) • Bosons—integer spin (e.g. photon) • Very different behavior

  12. Quantum States • Particles can be in specific states • Such states have specific, quantized values for certain physical quantities (even if their motions are “fuzzy”) • Each state has certain quantum numbers (n,l,m)

  13. Pauli’s Exclusion Principle • No two fermions exist in the same state • No two fermions share the same quantum numbers • Predicted a fourth quantum number for the electron, spin • Responsible for chemistry, why?

  14. Bose-Einstein Condensate • Einstein predicted that bosons, at low enough temperature, would share the same state • Race in early 1990s to create one • Won by Wieman and Cornell in 1995 (shared in the 2001 Nobel Prize) • Practical applications? • Superfluidity • Atom lasers • superconductivity

  15. Keys to QM so far… • Interactions governed by? • Interactions & Jumps determined by? • Knowledge of these processes limited by?

  16. Keys to QM so far… • Interactions governed by? • Fundamental particles • Absorbing and emitting force carriers • Following certain conservation laws • Interactions & Jumps determined by? • probabilities • Knowledge of these processes limited by? • Uncertainty principle

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