5th Solvay Conference, Brussels, 23-29 October 1927

5th Solvay Conference, Brussels, 23-29 October 1927 Back row: A Piccard, E Henriot, P Ehrenfest, D Durfee, Ed Herzen, Th De Donder, E Schroedinger

E Verschaffelt, W Pauli, Waldo, W Heisenberg, R H Fowler, L Brillouin.Middle Row: P Debye, M Knudsen, W L Bragg, H A Kramers, P A M Dirac, A H Compton,

L de Broglie, M Born, N Bohr.Front Row: I Langmuir, M Planck, Mme Curie, H A Lorentz, A Einstein, P Langevin, Ch E Guye,

C T R Wilson, O W Richardson.

Postulates of Quantum Mechanics

Every physically-realizable system is described by a state function ψ that contains all accessible physical information about the system in that state

The probability of finding a system within the volume dv at time t is equal to |ψ|2dv

Every observable is represented by an operator which is used to obtain information about the observable from the state function

The time evolution of a state function is determined by Schrödinger’s Equation

“Weirdness” of QM Things are quantized

– The radius of the Earth’s orbit can’t be changed by an arbitrarily small amount

Waves don’t have to be in one place– Interferometry

More generally – superposition– Schrödinger’s cat

Thought QuestionI put a cat into an ideal box (one which no

information can flow in or out of) with a bottle of poison. A device in the box will open the bottle and kill the cat when a radioactive atom decays. After the cat has been in the box for a time t, is the cat dead or alive?

A – Yes B – No

Why do I care? Need it to understand

– Small things (like transistors in computer chips and red blood cells, for example)

– “Degenerate” things (like laser beams and neutron stars)

You can do some interesting things with QM– Quantum computation– Quantum encryption / key distribution

Notation Atomic number-Z, # of protons in the nucleus

Determines which element it is Neutron number-N, # of neutrons in nucleus Mass number- A=Z+N

AZX

Isotopes—Nuclei of the same element (same Z) with different A (and N) values.

How many Protons does 263

106Sg have?

A. 263B. 106C. 157D. 42E. I can’t tell because I do not know where Sg

is on the periodic table.

How many Neutrons does 263

106Sg have?

A. 263B. 106C. 157D. 42E. I can’t tell because I do not know where Sg

is on the periodic table.

How many electrons does 263

106Sg have?

A. 263B. 106C. 157D. 42E. I can’t tell because I do not know where Sg

is on the periodic table.

Nuclear Strong Forcea short range attractive force

between nuclear particles Holds the atom together Very short range—almost touching If the distance between two protons

is >10-15 m then the coulomb repulsive force is too strong and the nuclei breaks apart.

THE TEN VIRGINSThey WERE prepared for the coming of the bridegroom. What they weren't prepared for was . . .

Radioactive Half Life

Discussion Question: You start with 1000 dice. Every time you get a six you take it out. How many rolls is a half-life?A. 2B. 4C. 6D. 8E. 10

If I start with 10000 pennies and every time I toss all the coins I remove the tails, how many tosses does it take to

get down to less than a dollar left?A. 3B. 5C. 7D. 9E. 11

For radioactive decay where No

is the number of nuclei you start with and N is the number of nuclei after a time t

toeNN

How do I solve for λ?