Download Welcome to Physics 112N

How I learned to stop worrying
and love physics
The Course So Far…
• Introduction to the debates
• General Epistemology
• Epistemology of Science
• Epistemology of Religion
From here on ……
• The big debates
• Physics
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– Quantum Mechanics, Thermodynamics &
Relativity
– Astronomy & Cosmology
Evolution, Creationism and Intelligent Design
Mind and Cognition
Morality, Ethics and Sociobiology
Process thought
Physics – The Beginnings
• Assyrians, Babylonians, Egyptians
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– Astronomy (Agrarian Societies)
– Astrology
Mayans, Aztecs
Greeks – Systematized Scientific Thought
Democritus vs. Aristotle (Two World Views)
Astronomy, Mechanics, Optics…….
Ptolemy vs. Aristarchus
9
14
16
28
30
Q/M
Physics
Q/M
Philosophical
Issues
Implications
Discussion
Quiz
Relativity
Thermodynamics
Implications
Discussion
4
6
9
11
13
18
20
Astronomy/
Cosmology
Religious
Cosmologies
Implications
Discussion
Quiz
Evolution
The Science
Creationism
Intelligent
Design
Implications
Discussion
Summary
Discussion
Quiz
Essay Due
Greek Physics
• Aristotle – Four Elements (earth, Water, Air,
fire)
• Democritus – Atomistic View
• Ptolemy – Geo-centric Universe
• Aristarchus of Samos – Heliocentric Universe
Ideas that prevailed in
antiquity….
• Infinitely divisible matter, geocentric
universe, ‘natural state’ of objects
• Aristotle and Ptolemy
• Dominated thought through the middle
ages
• Completely incorrect astronomy and
mechanics
• Alternate views present
• Why did they not prevail?
The Middle Ages
• Rise of the Islamic empire
• Translations from Greek
• Developments in Astronomy, Optics,
Mechanics
• Did the ‘scientific method’ develop?
The Scientific Revolution
• Astronomy
– Copernicus
• Heliocentric Universe
• Explains rotation of stars etc. in terms of earth’s
movement around the sun
– Galileo
• Observations using telescope
• Laws of motion
– Kepler’s Laws
• Tycho Brahe carefully collected data
• Formulated mathematical laws
The Scientific Revolution
• Huygens
– Wave theory of light
– Astronomical observations
• Boyle
- Boyle’s Law
- Steps towards Atomic Theory
• Pascal
– Fluid flows
– Pascal’s Law
The Scientific Revolution
• Newton
– Laws of Motion
– Law of Gravitation
– Kepler’s Laws follow from these general
principles
– Corpuscular Theory of Light
– Development of Calculus to aid in
understanding physics
Philosophical Underpinnings
• Realism
– Theories describe the world as it is in itself
• Determinism
– Present state predicts future state
• Reductionism
– Whole is the sum of its parts
Demise of Classical Physics
• Ultraviolet Catastrophe
– Quantization of energy
• Nature of Light (Newton or Huygens)
– Photoelectric Effect
• Nature of Electrons
– Double Slit Experiment
The Ultraviolet Catastrophe
Classical physics can describe the shape of the
blackbody spectrum only at long wavelengths.
At short wavelengths there is complete
disagreement.
This disagreement
between observations
and the classical theory
is known as the
ultraviolet catastrophe.
Planck’s Solution
In 1900, Max Planck was able to explain the
observed blackbody spectrum by assuming that
it originated from oscillators on the surface of
the object and that the energies associated with
the oscillators were discrete or quantized:
En = nhf
n = 0, 1, 2, 3…
n is an integer called the quantum number
h is Planck’s constant: 6.62  10-34 J·s
f is the frequency
The PhotoElectric Effect
When light is incident on
a surface (usually a
metal), electrons can be
ejected. This is known
as the photoelectric
effect.
Around the turn of the century, observations of the
photoelectric effect were in disagreement with the
predictions of classical wave theory.
Photoelectric Effect
Observations of the Photoelectric Effect
• No electrons are emitted if the frequency of the
incident photons is below some cutoff value,
independent of intensity.
• The maximum kinetic energy of the emitted
electrons does not depend on the light
intensity.
• The maximum kinetic energy of the emitted
electrons does depend on the photon
frequency.
• Electrons are emitted almost instantaneously
from the surface.
The Photoelectric Effect Explained
The photoelectric effect can be understood as follows:
• Electrons are emitted by absorbing a single photon.
• A certain amount of energy is required to remove the
electron from the material.
• The maximum observed kinetic energy is the
difference between the photon energy and this
energy.
Double Slit Experiment
• Electrons through a single slit act as
particle
• If we now have two slits close by a
diffraction pattern is observed i.e wave
like behavior
• If we try and detect which slit the
electron goes through the diffraction
pattern disappears
Double Slit Experiment
The Strange Quantum World
• Wave Particle Duality
• How to describe systems?
• Wave Function describes the state of a
system in a probabilistic sense
• Systems exist a superposition of states
• Observation collapses to a particular state
Schrodinger’s Cat
Philosophical Underpinnings
• Classical Realism
– Physical theories describe nature as it is in itself
• Instrumentalism
– Theories a human constructs for correlating
observations and making predictions
• Critical Realism
– Physical theories are a partial representation of
limited aspects of the world as it interacts with us
EPR Paradox
• Two particles separate with zero initial
momentum
• Measure component of momentum of one
• Automatically component of momentum of
second is determined !!!!
– Action at a distance?
– Hidden Variables?
– Holistic World?
Two Views
• Complementarity (Critical Realism?)
– Must consider interaction between subject
and object in an experiment
– Conceptual limitation of understanding
• Realism
– Theories are description of nature in itself
– Hidden Variables to explain away apparent
indeterminacy?
Points to Ponder
• Does Complementarity imply
instrumentalism?
• Complementarity a good paradigm for
science and religion?
• Indeterminacy
– temporary ignorance?
– measurement or conceptual issue?
– inherent to nature?
• Parts and Wholes – A new paradigm for
understanding the world?