Transcript Structure of Physics

Overview of the Structure of Physics
Where do Statistical &Thermal Physics fit in?
Niels Bohr
1922 Nobel Prize in
Physics for
“His services in the
investigation of the
structure of atoms and
of the radiation
emanating from them.”
Interesting Trivia (to me)!
Neils Bohr is the Only Nobel Prize winner
to have also been an Olympic Medalist!
In the 1908 Olympics,
he & his brother Harald*
were on the Danish
soccer team, which won
a sliver medal!
*Harald Bohr later became
a world famous
mathematician!
The Structure of Physics
Classical Physics is The Foundation
of pure & applied (macroscopic) physics & engineering!
Newton’s Laws + Electromagnetism
+ Statistical Mechanics + Thermodynamics.
These give a good description of most of the
macroscopic world.
Classical Mechanics
(Newton, Lagrange, Hamilton,..)
The Physics of the 17th & 18th Centuries.
Still useful in the 21st Century!!
Physics Structure
Classical Electromagnetism & Optics
(Newton, Coulomb, Gauss, Faraday, Maxwell,..)
The Physics of the 18th & 19th centuries.
Still useful in the 21st Century!
High Speeds (v ≤ ~ c)  Special Relativity
(Einstein, ..) 20th Century Physics!
Small Size (atomic & smaller):
Quantum Mechanics
(Bohr, Schrödinger, Heisenberg….)
20th century physics!
“Mechanics”
• HOW objects move (behave) under given forces.
• (Usually) Does not deal with the sources of forces.
Answers the question:
Given the forces, how do objects move?
• Forces in the universe are classified into 4 types:
The 4 Fundamental
Forces Of Nature!
Some version of Mechanics
applies to all four!
The 4 Fundamental Forces of Nature
The sources of the forces, in order of decreasing strength
The Strong Nuclear Force:
Binds nuclei together. Explained by “Standard Model” &
Quantum Chromodynamics. Still being researched.
The Electromagnetic Force:
E&M phenomena. Chemical forces. Most everyday
forces. Maxwell, Coulomb, Ampere, Faraday, ...
The Weak Nuclear Force:
Nuclear decay. Fermi, Bethe, others. Electroweak Theory.
The Gravitational Force:
Newton (classical mechanics), Einstein (general
relativity), Hawking….
The 4 Fundamental Forces of Nature
The sources of the forces, in order of decreasing strength
The Four Fundamental Forces
The “Electro-Weak” Force
Since ~ the late 1960’s, in some sense, the
4 fundamental forces
have been reduced to three!
That is, the Electromagnetic Force & the
Weak Nuclear Force
were combined into one theory. This was first
done by S. Weinberg & A. Salaam. For this
work, they received the
1972 Nobel Prize in Physics!
The Standard Model of Particle Physics
The
“Periodic Table for Elementary Particles”!
Quantum Chromodynamics (QCD)
& the Electroweak Theory
Protons & Neutrons consist of 3 Quarks each.
The Standard Model
The Standard
Model
The Standard Model
SUMMARY: THE STRUCTURE OF PHYSICS
Low Speed
High Speed
v << c
v<~c
Large size
Classical Mechanics
Special Relativity
>> atomic size (Newton, Hamilton,
(Einstein)
Lagrange)
Small size Quantum Mechanics
< ~ atomic size
(Schrodinger,
Heisenberg)
Atomic Physics
Molecular
Physics
Solid State
Physics
Nuclear & Particle Physics
Relativistic Quantum
Mechanics
(Dirac)
Quantum Field Theory
(Feynman, Schwinger)
Quantum Electrodynamics
(Photons, Weak Nuclear Force)
Quantum Chromodynamics
(Gluons, Quarks, Leptons
Strong Nuclear Force)
The Rest of Physics!
• What we’ve mentioned so far is  all of physics except:
Statistical Mechanics: (This course ≡ “Stat Mech” )
“Stat Mech” is the mechanics of systems of
huge numbers (>> ~ 1023) of particles.
Statistical Mechanics
1. Uses Probability & Statistics to calculate macroscopic
properties from microscopic force laws.
2. Applies to BOTH the Classical & the Quantum worlds!
3. Is the major link between microscopic & macroscopic physics!
4. Contains Thermodynamics as a sub-theory!