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# What Every Dog Should Know About Quantum Physics

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A talk on the essential elements of quantum mechanics, given to a group of Albany area home-schooled students and parents. The second slide is a video of a dramatic reading of Chapter 3 of _How to Teach Physics to Your Dog_ (Scribner, 2009, available wherever books are sold); the video can be found on YouTube.

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### What Every Dog Should Know About Quantum Physics

1. 1. What Every Dog Should Know About Quantum Physics  xp  2 I like cheese Chad Orzel http://scienceblogs.com/principles/
2. 2. Schrödinger’s Dog
3. 3. Quantum Physics ~20 Nobel Prizes For quantum pioneers
4. 4. Quantum Problems
5. 5. What’s the Deal with Quantum Physics? Four essential elements: I) Wavefunctions Everything in the universe is described by a wavefunction II) Allowed States Quantum objects are only found in specific states III) Probability You can only predict the probability of a given state IV) Measurement An object’s state is indeterminate until you measure it
6. 6. Wavefunctions I) Wavefunctions Everything in the universe is described by a wavefunction Mathematical function, describes properties of object Put in position and time  Get out what’s going on Has both particle and wave properties Detect at specific position  like particle Function extends over space  like wave
7. 7. Allowed States II) Allowed States Quantum objects are only found in specific states “State”  collection of properties position, velocity, energy, momentum, etc. Only certain special states are allowed  NEVER find object with other properties Property that gives quantum physics its name “quantum” = “how much” in Latin
8. 8. Atomic Spectra
9. 9. Bohr Model Niels Bohr, 1913 Explains light emitted by atoms Strange idea, but effective Gets hydrogen almost perfectly Other elements don’t work as well, but better than any other method
10. 10. Bohr Orbits and Waves Wave behavior explains Bohr states Allowed orbits are a whole number of wavelengths in circumference Electron wavefunction ends in the same place it starts Need wave nature to get allowed states (Complete theory doesn’t have orbits, but this gets the basic idea)
11. 11. Probability III) Probability You can only predict the probability of a given state Wavefunction gives probability of each of the allowed states Can’t say definitely where a quantum object will be located  Outcome of a single experiment is completely random
12. 12. Probability is a Problem “The theory delivers a lot, but hardly brings us closer to the secret of the Old One. I for one am convinced that He does not throw dice.” -- Albert Einstein, letter to Max Born,1926
13. 13. “Physicists are silly…” Can never know exactly where thrown object will land, only probability
14. 14. Measurement IV) Measurement An object’s state is indeterminate until you measure it Wavefunction tells you probability Until you measure it, the object is in ALL possible states, AT THE SAME TIME
15. 15. Schrödinger’s Cat (from http://commons.wikimedia.org/wiki/File:Schrodinger_cat_everret.png )
16. 16. Schrödinger’s Cat Cat is both alive and dead AT THE SAME TIME Invented by Erwin Schrödinger to show philosophical problem with quantum physics Situation seems completely ridiculous  BUT IT’S TRUE
17. 17. Tennis Experiment
18. 18. Tennis Experiment  Find probability distribution with two stripes, one each slit
19. 19. Electron Experiment Send electrons at two slits in a barrier: Image and video from Hitachi: http://www.hitachi.com/rd/research/em/doubleslit.html
20. 20. What’s Going On? Phenomenon called “Interference” Waves from two different sources add to give bright and dark spots Peak + Peak = Bigger Peak Peak + Valley = Nothing = =
21. 21. Double Slit Pattern depends on distance from slits Get alternating pattern of “bright” and “dark” stripes
22. 22. Double Slit with Electrons Electrons behave like waves Probability shows the effects of interference BUT: electrons detected as particles One at a time, at single spots on screen  Each electron must pass through BOTH slits at SAME TIME
23. 23. Double Slit with Electrons “[A] phenomenon which is impossible, absolutely impossible, to explain in any classical way, and which has in it the heart of quantum mechanics. In reality, it contains the only mystery.” -- Richard Feynman
24. 24. More Interference Double-slit only scratches the surface of quantum weirdness Interference of molecules (C60, at right) “Quantum Eraser” Quantum Zeno Effect Entanglement and Teleportation “Spooky action at a distance” etc, etc,… Huge variety of weird stuff involving quantum physics
25. 25. What Every Dog Should Know About Quantum Physics Four essential elements, shown in double-slit experiment: I) Wavefunctions Electrons (particles) show interference (waves) II) Allowed States Each slit defines a state III) Probability Where each electron lands is random IV) Measurement Each electron goes through BOTH slits at once
26. 26. Quantum Books (History)
27. 27. Quantum Books (Theory)
28. 28. Quantum Books (Textbooks)
29. 29. The End