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.

1. What Every Dog Should Know
About Quantum Physics

xp 
2 I like
cheese
Chad Orzel
http://scienceblogs.com/principles/

2. Schrödinger’s Dog

3. Quantum Physics
~20 Nobel Prizes
For quantum pioneers

4. Quantum Problems

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. 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. 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. Atomic Spectra

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. 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. 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. 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. “Physicists are silly…”
Can never know exactly where thrown
object will land, only probability

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. Schrödinger’s Cat
(from http://commons.wikimedia.org/wiki/File:Schrodinger_cat_everret.png )

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. Tennis Experiment

18. Tennis Experiment
 Find probability distribution with two stripes, one each slit

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. 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. Double Slit
Pattern depends on distance from slits
Get alternating pattern of “bright” and “dark” stripes

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. 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. 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. 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. Quantum Books (History)

27. Quantum Books (Theory)

28. Quantum Books (Textbooks)

29. The End