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# What Every Dog Should Know About Quantum Physics

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A talk given to the IB class from Schenectady high School, 5/24/10.

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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. Quantum Physics ~20 Nobel Prizes For quantum pioneers
3. 3. Why Should Dogs Care About Quantum Physics? Three reasons: 1) Computers Semiconductor chips 2) Telecommunications Lasers, fiber optics 3) Sunlight Quantum physics allows the Sun to shine
4. 4. 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
5. 5. 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
6. 6. Electrical Conductors Electrical properties of materials depend on electron motion:
7. 7. Electron Waves Electrons behave like waves
8. 8. Semiconductor Chips Control electron properties by modifying material Key to making silicon computer chips  Computers are Quantum!
9. 9. 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
10. 10. Atomic Spectra
11. 11. Bohr Model Niels Bohr, 1913 Explains light emitted by atoms Strange idea, but effective Gets hydrogen almost perfectly (not as successful with other elements)  Not the full story, but gets started in right direction
12. 12. Lasers Lasers work using allowed states Start with excited atoms Emit light, drop down in energy Light causes other atoms to emit  Amplification Build up between mirrors
13. 13. Laser Communications First Laser: May 16, 1960 “A solution looking for a problem…” Gordon Gould, Union „41 One problem it solves: T. Maiman Fiber optic communications Telephone, Internet sent using laser light  Telephones are Quantum!
14. 14. 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  Some chance of things happening even when they shouldn‟t
15. 15. Sunlight Temperature of Sun: 10,000,000 degrees Shines by nuclear fusion: Stick 4 protons together, make helium
16. 16. Sunlight Temperature of Sun: 10,000,000 degrees Shines by nuclear fusion: Stick 4 protons together, make helium Problem: Protons repel each other (unless they‟re really, really close) Temperature needed to get fusion directly: 15,000,000,000 degrees 1,500 times the Sun‟s temperature!
17. 17. Sunlight Temperature of Sun: 10,000,000 degrees Shines by nuclear fusion: Stick 4 protons together, make helium Problem: need 15,000,000,000 degrees Solution: Quantum Tunneling Small probability of particles passing through impassable barriers Allows enough fusion to power Sun  Sunlight is Quantum!
18. 18. 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
19. 19. “Physicists are silly…” Can never know exactly where thrown object will land, only probability
20. 20. 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
21. 21. Schrödinger‟s Cat (from http://commons.wikimedia.org/wiki/File:Schrodinger_cat_everret.png )
22. 22. 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
23. 23. Tennis Experiment
24. 24. Tennis Experiment  Find probability distribution with two stripes, one each slit
25. 25. Electron Experiment Send electrons at two slits in a barrier: Image and video from Hitachi: http://www.hitachi.com/rd/research/em/doubleslit.html
26. 26. 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 = =
27. 27. Double Slit Pattern depends on distance from slits Get alternating pattern of “bright” and “dark” stripes
28. 28. 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
29. 29. 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
30. 30. 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
31. 31. 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
32. 32. Schrödinger‟s Dog
33. 33. The End