what every dog should know about quantum physics
DESCRIPTION
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.TRANSCRIPT
What Every Dog Should Know
About Quantum Physics
I like cheese
Chad Orzel
http://scienceblogs.com/principles/
2x p
Schrödinger’s Dog
Quantum Physics
~20 Nobel Prizes
For quantum pioneers
Quantum Problems
What’s the Deal with Quantum Physics?
Four essential elements:
I) Wavefunctions
II) Allowed States
III) Probability
IV) Measurement
Everything in the universe is described by a wavefunction
Quantum objects are only found in specific states
You can only predict the probability of a given state
An object’s state is indeterminate until you measure it
WavefunctionsI) 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
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
Atomic Spectra
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
Bohr Orbits and WavesWave behavior explains Bohr states
Allowed orbits are a whole
number of wavelengths
in circumference
Electron wavefunction ends
in the same place it starts
(Complete theory doesn’t have orbits, but this gets the basic idea)
Need wave nature to get allowed states
Probability
III) Probability
You can only predict the
probability of a given state
Can’t say definitely where a
quantum object will be located
Wavefunction gives probability
of each of the allowed states
Outcome of a single experiment is completely random
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
“Physicists are silly…”
Can never know exactly where thrown
object will land, only probability
MeasurementIV) 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
Schrödinger’s Cat
(from http://commons.wikimedia.org/wiki/File:Schrodinger_cat_everret.png )
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
Tennis Experiment
Tennis Experiment
Find probability distribution with two stripes, one each slit
Electron Experiment
Image and video from Hitachi:
http://www.hitachi.com/rd/research/em/doubleslit.html
Send electrons at two slits in a barrier:
What’s Going On?
Phenomenon called “Interference”
Waves from two different sources
add to give bright and dark spots
Peak + Peak =
= =
Peak + Valley =Bigger Peak Nothing
Double Slit
Pattern depends on distance from slits
Get alternating pattern of “bright” and “dark” stripes
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
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
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
What Every Dog Should Know
About Quantum Physics
Four essential elements, shown in double-slit experiment:
I) Wavefunctions
II) Allowed States
III) Probability
IV) Measurement
Electrons (particles) show interference (waves)
Each slit defines a state
Where each electron lands is random
Each electron goes through BOTH slits at once
Quantum Books (History)
Quantum Books (Theory)
Quantum Books (Textbooks)
The End