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 Question
I 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

A
ZX
Isotopes—Nuclei of the same element (same Z) with
different A (and N) values.
How many Protons does
263
106Sg have?
A.
B.
C.
D.
E.
263
106
157
42
I can’t tell because I do not know where Sg is
on the periodic table.
How many Neutrons does
263 Sg have?
106
A.
B.
C.
D.
E.
263
106
157
42
I can’t tell because I do not know where Sg is
on the periodic table.
How many electrons does
263
Sg
have?
106
A.
B.
C.
D.
E.
263
106
157
42
I can’t tell because I do not know where Sg is
on the periodic table.
Nuclear Strong Force
a
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 VIRGINS
They 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.
B.
C.
D.
E.
2
4
6
8
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.
B.
C.
D.
E.
3
5
7
9
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
N  Noe
 t
How do I solve for λ?