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