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5th Solvay Conference, Brussels, 23-29 October 1927

5th Solvay Conference, Brussels, 23-29 October 1927 Back row: A Piccard, E Henriot, P Ehrenfest, D Durfee, Ed Herzen, Th De Donder, E Schroedinger

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5th Solvay Conference, Brussels, 23-29 October 1927

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  1. 5th Solvay Conference, Brussels, 23-29 October 1927 Back row: A Piccard, E Henriot, P Ehrenfest, D Durfee, Ed Herzen, Th De Donder, E Schroedinger E Verschaffelt, W Pauli, Waldo, W Heisenberg, R H Fowler, L Brillouin.Middle Row: P Debye, M Knudsen, W L Bragg, H A Kramers, P A M Dirac, A H Compton, L de Broglie, M Born, N Bohr.Front Row: I Langmuir, M Planck, Mme Curie, H A Lorentz, A Einstein, P Langevin, Ch E Guye, C T R Wilson, O W Richardson.

  2. Postulates of Quantum Mechanics • Every physically-realizable system is described by a state function ψ that contains all accessible physical information about the system in that state • The probability of finding a system within the volume dv at time t is equal to |ψ|2dv • Every observable is represented by an operator which is used to obtain information about the observable from the state function • The time evolution of a state function is determined by Schrödinger’s Equation

  3. “Weirdness” of QM • Things are quantized • The radius of the Earth’s orbit can’t be changed by an arbitrarily small amount • Waves don’t have to be in one place • Interferometry • More generally – superposition • Schrödinger’s cat

  4. Thought Question I put a cat into an ideal box (one which no information can flow in or out of) with a bottle of poison. A device in the box will open the bottle and kill the cat when a radioactive atom decays. After the cat has been in the box for a time t, is the cat dead or alive? A – Yes B – No

  5. Why do I care? • Need it to understand • Small things (like transistors in computer chips and red blood cells, for example) • “Degenerate” things (like laser beams and neutron stars) • You can do some interesting things with QM • Quantum computation • Quantum encryption / key distribution

  6. Notation • Atomic number-Z, # of protons in the nucleus Determines which element it is • Neutron number-N, # of neutrons in nucleus • Mass number- A=Z+N AZX Isotopes—Nuclei of the same element (same Z) with different A (and N) values.

  7. How many Protons does 263106Sg have? • 263 • 106 • 157 • 42 • I can’t tell because I do not know where Sg is on the periodic table.

  8. How many Neutrons does263106Sg have? • 263 • 106 • 157 • 42 • I can’t tell because I do not know where Sg is on the periodic table.

  9. How many electrons does263106Sg have? • 263 • 106 • 157 • 42 • I can’t tell because I do not know where Sg is on the periodic table.

  10. Nuclear Strong Force • a short range attractive force between nuclear particles • Holds the atom together • Very short range—almost touching • If the distance between two protons is >10-15 m then the coulomb repulsive force is too strong and the nuclei breaks apart.

  11. THE TEN VIRGINS They WERE prepared for the coming of the bridegroom. What they weren't prepared for was . . .

  12. Radioactive Half Life

  13. Discussion Question: You start with 1000 dice. Every time you get a six you take it out. How many rolls is a half-life? • 2 • 4 • 6 • 8 • 10

  14. If I start with 10000 pennies and every time I toss all the coins I remove the tails, how many tosses does it take to get down to less than a dollar left? • 3 • 5 • 7 • 9 • 11

  15. For radioactive decay where Nois the number of nuclei you start with and N is the number of nuclei after a time t How do I solve for λ?

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