irreverent quantum mechanics giancarlo borgonovi may 2004
TRANSCRIPT
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IRREVERENT QUANTUM MECHANICS
Giancarlo Borgonovi
May 2004
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For the purpose of this presentation the term Quantum Mechanics is equivalent to Quantum Theory Personal opinion: Quantum Mechanics is the most significant intellectual achievement of the 20th
Century. Reasons in support of this statement: QM is totally counter intuitive QM was created/invented to explain phenomena only indirectly accessible to our senses QM was created/invented to explain phenomena in the eV energy range (atomic spectra) QM has maintained its validity up to the GeV energy range (11 orders of magnitude)
QM
People
Concepts
History Applications
Results
Criticism
InterpretationImplications
MOTIVATION
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What is irreverent quantum mechanics?
A discipline for OFs to keep involved with QM:
• Develop allegories/metaphors about QM • Design/build models/representations of QM effects• Investigate QM trivia• Explore connection between science and art• Write fiction around QM subjects/characters• Develop humor about QM subjects/characters• Quantum mechanical cooking?• Give presentations to other OFs.
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GENERAL PRINCIPLES
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Classical and quantum mechanics comparison
QuantumClassical
SystemState vector
Represented by real numbersPossible statesDefinite state
Deterministic transition from one state to another
SystemState vector
Represented by complex numbersPossible states
Superposition of statesProbabilistic transition from one state to another
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The formal elements of quantum mechanics
A
B
AB
AB
Abstract state vector
Abstract state vector in dual space
Probability amplitude for going from state A to state B
Matrix element of operator
Operator
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The great law of quantum mechanics
From The Feynman Lectures on Physics, Vol. 3
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That is a statement, not a question
I have not understood howyou passed from A to B
Are thereany questions?
The unforgiving logic of P. A. M. Dirac
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Observables in Quantum Mechanics
• Represented by real operators• Describe possible states (eigenvectors) which are associated with possible outcomes of measurements (eigenvalues)• Before the measurement: calculate probabilities of different outcomes• After the measurement: only one outcome
Example
Expectation values for different cases
EdCandidatesEd
MaryCodeZipMary
JohnIncomeJohn
_
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?
Hilbert space and human life
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Human life according to Classical Mechanics
Hamilton’s Equations
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Human life according to Quantum Mechanics
Schroedinger Equation
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Schroedinger
Heisenberg
Dirac Feynman
The different forms of quantum mechanics
333231
232221
131211
aaa
aaa
aaa
Wave FunctionMatrix Mechanics
Symbolic Method Path Integral
A
B
BA
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1900 - Max Planck, studying the black body radiation, discovers the “brick”.
Planck’s constant h = 6.55 x 10-27 erg sec can be considered as the building block of quantum mechanics.
h
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h
2π=
A new, downsized model of the ‘brick’ is introduced
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2
1
2
1
1925 - The ‘brick’ is split in half (Uhlenbeck and Goudsmit introduce the spin).
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Particles position and momentum and Heisenberg uncertainty principle
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BOSONS and FERMIONS
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A wrong representation of the hands of God building matter
A more realistic representation of the hands of God building matter
Identical particles are not distinguishable
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Quantum Mechanics divides the Universe into two Categories
• Every particle in the universe is either a boson or a fermion, that is to say everything in the universe is made up of bosons and fermions.
• What distinguishes a boson from a fermion?
• What are the effects of this categorization?
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What distinguishes a boson from a fermion
1) Bosons have spin integer, fermions have spin semi-integer
2) The possible states for a system of bosons (at least two) are symmetric3) The possible states for a system of fermions (at least two) are antisymmetric
4) Two bosons interfere with the same phase5) Two fermions interfere with the opposite phase.
1fAmplitude 2fAmplitude
2
2ff y ProbabilitCaseBoson 1
2
2ff y ProbabilitCaseFermion 1
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+
+
Boson
+
-
Fermion
+
-
Pauli or ExclusionPrinciple
Shapes represent quantum states, colors represent particles
(Symmetric under exchange)
(Antisymmetric under exchange)
(Null for fermions under exchange)
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Effects due to boson like features
• Bosons are very gregarious and tend to congregate together. If bosons exist in a state, there is a tendency for another boson to enter that state.
• The laser is an example of this tendency of the bosons to come together
• Superfluidity of Helium-4 (not Helium-3 which emulates a fermion) at low temperature is a macroscopic example of the result of the tendency of bosons to get into the same
state of motion.
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Effects due to fermion like features
Fermions tend to avoid each other. If a fermion exists in a state, another fermion will not want to enter that state.
• Pauli’s Exclusion Principle
• What if electrons were bosons
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Electrons as fermions (real)
Electrons as bosons (imagined)
Matter under different assumptions
From The Feynman Lectures on Physics, Vol. 3
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Classical and Quantum Statistics
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Bosons
Fermions
Fermi sphere
The different nature of bosons and fermions
My army of bosons will move
and attack as one man
Unknown Barbarian King
Everyone in my army of fermions will occupy his place and defend the empire
Unknown Roman Emperor
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New States of Matter
Bose_EinsteinCondensate
Degenerate FermiGas
What they are Macroscopic Quantum SystemsPredicted 1930s 1930sRealized 1995 2001Nobel prize 2001 (Cornell, Wieman,
Ketterle)-
Atoms used Rubidium 87 Lithium 6Made possible by Optical bowls (laser containment)How is observed Velocity Distribution after expansionWhy it is important Permits extrapolations to unobservable states
of matter
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THE PERIODIC TABLE
(Ability and Weirdness)
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Quantum Mechanics and Weirdness - Thoughts about the periodic table
I 1 2II 3 10III 11 18IV 19 36V 37 54VI 55 56 71 86VII 87 92
57 R a r e E a r t h s 70
Energy(n)
Angular momentum()
Including m(2 +1)
Including s (spin)(×2)
TotalStates
1 0 1 2 22 0,1 1,3 2,6 83 0,1,2 1,3,5 2,6,10 184 0,1,2,3 1,3,5,7 2,6,10,14 325 0,1,2,3,4 1,3,5,7,9 2,6,10,14,18 506 0,1,2,3,4,5 1,3,5,7,9,11 2,6,10,14,18,22 727 0,1,2,3,4,5,6 1,3,5,7,9,11,13 2,6,10,14,18,22,26 98
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K 2L 2 6M 2 6 10N 2 6 10 14O 2 6 10 14 18P 2 6 10 14 18 22Q 2 6 10 14 18 22 26
s p d f
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K 1L 2 3M 4 5 6N 7 8 9 10O 11 12 13 14 15P 16 17 18 19 20 21Q 22 23 24 25 26 27 28
s p d f
K 1L 2 3M 4 5 7N 6 8 10 13O 9 11 14P 12 15 17Q 16
s p d f
FORMATION OF THE PERIODIC TABLE
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Low Angular Momentum
High Angular Momentum
Spherical symmetry, angular momentum, and weirdness
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Sociological implications of the periodic table
• Consider the order of the states as some kind of social order, or rank, or job position. In a rigid, hierarchical society, positions would be occupied according to certain parameters (e.g. diplomas, family connections, religious or ethnical factors, etc.). In a more intelligent society, people of higher ability pass in front of others and acquire a higher social status. This process has some similarity to the buildup of the periodic table. Thus nature rewards ability.
• The external shells, which are responsible for the chemical behavior of the elements, consist of s and p electrons only. The “weirder” d and f electrons are left behind, and are used to fill incomplete shells, so in a sense they hide behind less weird electrons at a higher level. Thus, nature tends to hide weirdness.,
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SECOND QUANTIZATIONand
QUANTUM FIELDS
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Second Quantization
36
25
24
13
12
11
36
25
24
13
12
11
123)(123 r
Occupation number representation
This operator creates or destroys particles
Fixed number of particles
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One- particle space
(Hilbert space}
N- particle space
Many particle space
(Fock space)
Symmetric or
antisymmetric states
Collection of
n-particle states
Principle of symmetrization
QUANTUM MECHANICAL SPACES
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VIRTUAL PARTICLES
• Virtual particles are like words, they can result in attraction or repulsion
• Virtual particles have a very short lifetime
• An exchange of momentum can be interpreted as the action of a force over a time interval
Photons Electromagnetic field
Phonons Cooper pairs, superconductivity
Mesons Nucleons
Gluons Quarks
Hideki Yukawa
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Quantum Fields
A classical field is easy to visualize and understand A quantum field is an operator which is a function of position To understand a quantum field one needs to understand the local creation and annihilation operators Everything (energy, number of particles, total momentum, etc.) can be expressed in terms of the creation and annihilation operators A quantum field is expressed in terms of creation and annihilation operators A quantum field is a nice way to express the duality particle wave that pervades QM What are the eigenvalues and eigenvectors of a quantum field?
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Quantum Cooking - Potatoes a la Brillouin
Leon Brillouin, 1927
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THANK YOUAND MAY YOU HAVE
A HAPPY TRANSITION TO ASTATE OF HIGHER
ANGULARMOMENTUM