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 –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 –Astronomy (Agrarian Societies) –Astrology Mayans, Aztecs Greeks – Systematized Scientific Thought Democritus vs. Aristotle (Two World Views) Astronomy, Mechanics, Optics……. Ptolemy vs. Aristarchus

Q/M Physics Q/M Philosophical Issues Implications Discussion Quiz Relativity Thermodynamics Implications Discussion 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: E n = nhf n = 0, 1, 2, 3… n is an integer called the quantum number h is Planck’s constant: 6.62  J·s f is the frequency

The PhotoElectric Effect Around the turn of the century, observations of the photoelectric effect were in disagreement with the predictions of classical wave theory. When light is incident on a surface (usually a metal), electrons can be ejected. This is known as the photoelectric effect.

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?