Physics: History and Context

• Physics: the scientific study of matter, its constituents, motion, behavior through space/time, energy, and force.
• Physics is a fundamental science and an old academic discipline.

Historical Context

• Physics, chemistry, biology, and some math branches were once part of natural philosophy.
• The Scientific Revolution of the 17th century led to their separation.
• Physics is interdisciplinary, with flexible boundaries, impacting fields like biophysics and quantum chemistry.
• Advances in physics drive development in other sciences, mathematics, philosophy, and result in new technologies.
• Electromagnetism, solid-state physics, and nuclear physics advancements have led to modern tech like television, computers and nuclear weapons.
• Thermodynamics advancements spurred industrialization, while mechanics inspired calculus.

Early Astronomy

• Early civilizations (Sumerians, Egyptians, Indus Valley) had predictive knowledge about the Sun, Moon, and stars before 3000 BCE.
• Stars/planets were often worshipped as gods.
• Early observations, though unscientific, helped later astronomy.
• Stars traverse great circles across the sky, planets don't.
• Western astronomy's origins trace back to Mesopotamia, with all Western exact sciences originating from late Babylonian astronomy.
• Egyptians had monuments showing constellation knowledge.
• Greek astronomers named constellations visible from the Northern Hemisphere.

Natural Philosophy in Greece

• Natural philosophy began in Greece (650 BCE – 480 BCE).
• Pre-Socratic philosophers (like Thales) rejected non-natural explanations.
• Philosophers proclaimed every event has a natural cause.
• Ideas were based verified by reason and observation.
• Atomism, proposed by Leucippus and Democritus, was proven correct ~2000 years later.
• During the classical period in Greece (6th-4th centuries BCE) and in Hellenistic times, natural philosophy developed along many lines of inquiry.

Aristotle's Physics

• Aristotle (384–322 BCE) wrote a treatise on "Physics" in the 4th century BC.
• His physics was influential for ~2 millennia.
• He mixed limited observation with logical deduction but lacked experimental verification; his approach is superseded today.
• He explained motion and gravity with the theory of four elements (air, fire, water, earth).
• Aristotle believed each element had a natural place determined by density.
• Fire at the top, then air, water, and earth.
• Small amounts of one element in another's place would revert naturally.
• Fire on the ground would rise up in an attempt to go back to it's natural place of fire in the sky.
• Heavier objects fall faster, speed is proportional to weight, depends inversely on the density of the medium.
• Violent motion speed depends on the force applied.
• Motion cause led to the "prime mover" concept.

Medieval Contributions

• The Western Roman Empire's fall led to intellectual decline in Europe.
• The Eastern Roman (Byzantine) Empire continued advancing learning.
• John Philoponus challenged Aristotelian science in the 6th century.
• Isidore of Miletus made a compilation of Archimedes' works in the 6th century.

Islamic Scholarship

• Islamic scholarship advanced Aristotelian physics, emphasizing observation and a priori reasoning.
• This scholarship developed early forms of the scientific method.
• Notable innovations were in optics and vision from scientists like Ibn Sahl, Al-Kindi, Ibn al-Haytham, Al-Farisi, and Avicenna.
• Ibn al-Haytham's "Book of Optics" challenged Greek ideas about vision.
• Ibn al-Haytham did camera obscura experiments, showed light moves in a straight line, and encouraged experiment reproduction, thus originating the scientific method.

The Emergence of Physics as a Separate Science

• Early modern Europeans used experimental and quantitative methods to discover the laws of physics.
• The geocentric model was replaced by the heliocentric Copernican model.
• Kepler determined planetary motion laws between 1609 and 1619.
• Galileo pioneered telescopes and observational astronomy.
• Isaac Newton discovered laws of motion and universal gravitation.
• Newton and Leibniz independently developed calculus and applied it to physics.
• Thermodynamics, chemistry, and electromagnetics laws emerged during the Industrial Revolution.
• By the late 19th century, thermodynamics, mechanics, electromagnetics theories matched many observations.
• These theories formed the basis for classical physics.

Late 19th Century Anomalies

• Classical electromagnetism required luminiferous aether for wave propagation, but it was undetectable.
• Blackbody light intensity didn't match predictions.
• Electron emission from illuminated metals differed from predictions.
• These failures led to 20th-century physics revolutions.

Modern Physics Emergence

• Modern physics began in the early 20th century.
• Max Planck worked on quantum theory.
• Albert Einstein worked on the theory of relativity.
• Classical mechanics had inaccuracies, leading to these theories.
• Classical mechanics predicted light speed depends on the observer's motion.
• Einstein's special relativity corrected this by replacing mechanics for fast-moving bodies and allowing for constant light speed.
• Planck proposed material oscillator excitation in discrete steps proportional to frequency, solving black-body radiation.
• The photoelectric effect and discrete energy levels led to quantum mechanics.
• Quantum mechanics was pioneered by Werner Heisenberg, Erwin Schrödinger, and Paul Dirac.
• The Standard Model of particle physics was derived from this.

Continued Physics Advances

• The Higgs boson discovery at CERN in 2012 confirmed all Standard Model particles.
• Research beyond the Standard Model, like supersymmetry, is ongoing.
• Mathematics is important, with areas like probabilities and groups.

Core Physical Theories

• Physics deals with diverse systems, using common theories.
• Each theory is experimentally-tested and considered an adequate approximation of nature.
• These theories form an important toolset for research into more specialized topics: Classical mechanics, Quantum mechanics, Thermodynamics and statistical mechanics, Electromagnetism, and Special relativity.
• These theories are important tools for research into more specialized topics.

Classical vs Modern Physics

• Early 20th-century quantum mechanics and relativity discoveries revolutionized physics.
• The change was so fundamental that the new concepts became the foundation of modern physics while earlier topics became known as classical physics.
• Most physics applications are classical.
• Classical physics laws describe systems with length scales greater than atomic and motions slower than light.
• Observations outside this range don't match classical mechanics predictions.
• Classical physics includes traditional branches recognized before the 20th century: classical mechanics, thermodynamics, and electromagnetism.

Classical Physics Branches

• Classical mechanics deals with bodies acted on by forces, divided into:
  • Statics: forces on non-accelerating bodies.
  • Kinematics: motion without cause.
  • Dynamics: motion and forces.
• Mechanics is divided into solid and fluid mechanics (continuum mechanics).
  • Fluid mechanics further includes:
    • Hydrostatics
    • Hydrodynamics
    • Pneumatics
• Acoustics = sound study.
  • Modern acoustics branches:
    • Ultrasonics
    • Bioacoustics
    • Electroacoustics
• Optics concentrates on light.
  • Also studies infrared and ultraviolet radiation.
  • includes light phenomena such as:
    • Reflection
    • Refraction
    • Interference
    • Diffraction
    • Dispersion
    • Polarization
• Heat = is a form of energy.
  • Thermodynamics is the study of heat and other forms of energy.
• Electricity and magnetism.
  • Electricity and magnetism have been studied as a single branch of physics since the connection between them was discovered in the early 19th century.
  • An electric current gives rise to a magnetic field, and a changing magnetic field induces an electric current.
  • Subdivisions
    • Electrostatics deals with electric charges at rest.
    • Electrodynamics deals with moving charges.
    • Magnetostatics deals with magnetic poles at rest.

Transition to Modern Physics

• Relativity and quantum mechanics in the early 20th century changed physics conceptually.
• Established theories retained practical value.
• Topics are divided into classical and modern physics, the latter including quantum mechanics and relativity effects.
• Classical physics studies matter and energy normally, while modern physics studies matter and energy under extreme conditions or scales.
• Atomic and nuclear physics study the smallest matter scales.
• Elementary particle physics studies the most basic matter units and is also known as high-energy physics due to the high energies needed to produce particles in accelerators.
• Ordinary notions of space, time, matter, and energy aren't valid at this scale.
• Modern physics presents a different view of space, time, and matter than classical physics.
• Classical mechanics approximates nature as continuous.
• Quantum theory focuses on the discrete nature of phenomena at atomic/subatomic levels, examining particle/wave aspects.
• Relativity theory deals with phenomena from moving frames of reference.
• Special relativity deals with motion without gravity.
• General relativity deals with motion and gravity.
• Quantum theory and relativity have applications in modern physics.

Scientific Method Use

• Physicists test theory validity using the scientific method.
• They compare theory implications with experiment/observation conclusions logically and repeatably.
• Experiments/observations determine theory validity.
• Theorists develop mathematical models aligning with experiments and predicting results.
• Experimentalists design/perform experiments to test predictions.
• Theory and experiment are developed separately but depend on each other.
• Progress occurs when experiment resists theory, or theories generate testable predictions.
• Phenomenologists study complex phenomena in experiment and relate them to theory.
• Electromagnetism was unified this way.

Theoretical Physics Frontiers

• Theoretical physics deals with hypothetical issues beyond the known universe.
• These include parallel universes, multiverses, and higher dimensions.
• Theorists solve problems, explore consequences, and make testable predictions.

Experimental Physics

• Experimental physics expands and is expanded by engineering and technology.
• Basic research experimental physicists design and perform experiments using particle accelerators and lasers.
• Applied research experimental physicists develop technologies like MRI and transistors in industry.
• Experimentalists may seek areas unexplored by theorists.

Areas of Physics

• Physics covers phenomena from elementary particles to galaxy superclusters.
• It includes basic objects composing everything.
• Thus, physics is the "fundamental science".
• Physics relates nature's phenomena to simpler phenomena
• For example, the study of these phenonmena contributed to physics understanding:
  • Magnetism
  • Electricity
  • Electromagnetism
  • Electroweak interaction

Current Research

• Research is progressing on many fronts.
• A key unsolved condensed matter problem is high-temperature superconductivity.
• Many experiments aim to fabricate spintronics and quantum computers.
• Particle physics shows experimental signs beyond the Standard Model.
• Indications that neutrinos have non-zero mass have solved the solar neutrino problem; massive neutrino physics is under investigation.
• The LHC has found the Higgs boson, but aims to confirm or deny supersymmetry.
• Dark matter and dark energy nature is under research.
• Many complex phenomena are still not well understood.

Complex Problem Examples

• Complex problems that seem like they could be solved by a clever application of dynamics and mechanics remain unsolved.
• The formation of sandpiles.
• Nodes in trickling water.
• The shape of water droplets.
• Mechanisms of surface tension catastrophes
• Self-sorting in shaken heterogeneous collections.
• Complex phenomena grew in attention since the 1970s due to mathematical methods/computers.
• Complex physics has grown into interdisciplinary research, such as turbulence in aerodynamics and pattern formation in biological systems.

Horace Lamb Quote

• Horace Lamb hoped for quantum electrodynamics and turbulent fluid motion enlightenment in heaven.

Branches of Physics Overview

• Branches:
  • Classical Mechanics
  • Thermodynamics
  • Statistical Mechanics
  • Electromagnetism
  • Photonics
  • Relativity
  • Quantum Mechanics
  • Atomic Physics
  • Molecular Physics
  • Optics and Acoustics
  • Condensed Matter Physics
  • High-Energy Particle Physics
  • Nuclear Physics
  • Cosmology
  • Interdisciplinary Fields
• Individual fields have become specialized since the 20th century.
• "Universalists" like Einstein and Landau are now rare.

Particle Physics

• Studies elementary matter/energy constituents and interactions.
• Designs/develops high-energy accelerators, detectors, and computer programs.
• Also called "high-energy physics" because many particles are created during high-energy collisions.
• The Standard Model describes elementary particle/field interactions.
• The model accounts for 12 known matter particles (quarks and leptons) that interact via strong, weak, and electromagnetic forces.
• Dynamics are described in terms of matter particles exchanging gauge bosons (gluons, W and Z bosons, and photons).
• The Standard Model predicts the Higgs boson.
• CERN announced detecting a particle consistent with the Higgs boson in July 2012, an integral part of the Higgs mechanism.

Nuclear Physics

• Studies atomic nuclei constituents and interactions.
• Applications include power generation, weapons, medicine, MRI, ion implantation, and radiocarbon dating.

Atomic, Molecular, and Optical Physics (AMO)

• Studies matter-matter and light-matter interactions on the atomic and molecular scale.
• The three areas are grouped together because of their interrelationships, the similarity of methods used, and the commonality of their relevant energy scales.
• Includes classical, semi-classical and quantum treatments.
• Can treat their subject from a microscopic view.
• Atomic physics studies electron shells, focusing on quantum control, atom/ion cooling and trapping, low-temperature collision dynamics, and electron correlation effects.
• Atomic physics is influced by the nucleus.
• Molecular physics centers on multi-atomic structures.
• Optical physics studies optical fields and their interactions with matter in the microscopic realm, differing from optics.

Condensed Matter Physics

• Deals with the macroscopic physical properties of matter.
• Concentrates on "condensed" phases with many particles and strong interactions.
• Condensed phases include solids, liquids, superfluids, Bose-Einstein condensates, superconducting phases, and ferromagnetic/antiferromagnetic phases.
• Condensed matter physics is the largest field.
• Grew out of solid-state physics and now considered one of its main subfields.
• Term coined by Philip Anderson in 1967 when renaming his research group.
• Overlaps with chemistry, materials science, nanotechnology, and engineering.

Astrophysics and Astronomy

• Applies physics theories/methods to study stellar structure, evolution, Solar System origin, and cosmology.
• Applies mechanics, electromagnetism, statistical mechanics, thermodynamics, quantum mechanics, relativity, nuclear and particle physics, and atomic and molecular physics.
• Karl Jansky's 1931 discovery of radio signals from celestial bodies launched radio astronomy.
• Space exploration has expanded astronomy.
• Space-based observations are needed for infrared, ultraviolet, gamma-ray, and X-ray astronomy due to Earth's atmospheric interference.

Physical Cosmology

• Studies universe formation and evolution on the largest scales.
• Einstein's relativity plays a central role.
• Hubble's discovery of an expanding universe prompted the steady state universe and the Big Bang rival explanations.
• The Big Bang was confirmed by Big Bang nucleosynthesis and the cosmic microwave background discovery in 1964.
• The Big Bang model hinges on general relativity and the cosmological principle.
• Cosmologists have created the ΛCDM model including cosmic inflation, dark energy, and dark matter.

Physicist Defined

• Physicist: a scientist specializing in physics, encompassing matter/energy interactions across all scales.
• Physicists are interested in the root causes of phenomena, and usually frame their understanding in mathematical terms..
• Work spans sub-atomic, particle physics, biological physics, and cosmological scales.
• Includes experimental physicists (observing phenomena, developing experiments) and theoretical physicists (modeling systems).
• Physics relies on the philosophy of science (scientific method) to advance knowledge.
• The scientific method employs a priori and a posteriori reasoning and Bayesian inference to measure theory validity.
• Philosophy of physics involves space/time, determinism, empiricism, naturalism, and realism.
• Physicists have written on work implications, such as causal determinism (Laplace) and quantum mechanics (Schrödinger).
• Roger Penrose (mathematical physicist): Platonist.
• Stephen Hawking: reductionist.

Mathematics in Physics

• Mathematics provides a compact language to describe the world.
• Mathematics based concepts were advocated by:
  • Pythagoras
  • Plato
  • Galileo
  • Newton
• Logical truths and math reasoning depend on the empirical world.
• Logic laws express universal regularities found in the world's structural features.
• Physics uses mathematics to organize/formulate experimental results.
• This results in precise/estimated solutions, quantitative results, and new predictions can be confirmed or negated.
• Physics experiment results: numerical data, units of measure, and error estimates.
• Computation use has made computational physics active.

Physics in Education

• Ontology is a prerequisite for physics, but not for mathematics. It means physics is concerned with descriptions of the real world, wheras mathematics is concerned with abstract patterns.
• Physics statements are synthetic, while mathematical statements are analytic.
• Mathematics contains hypotheses, while physics contains theories.
• Mathematics statements have to be only logically true, while predictions of physics statements must match observed and experimental data.
• Mathematical physics: mathematics applied in physics.
• Mathematical statements used for solving have a hard-to-find physical meaning.

Fundamental vs Applied Physics

• Physics: a fundamental (basic) science.
• Physics is "the fundamental science" because other natural sciences are constrained by physics laws.
• Chemistry studies matter properties/structures/reactions, distinguishing it from physics.
• Fundamental physics seeks to explain phenomena without specific practical applications.
• Applied physics: physics research and development for particular uses.
• Applied physics curriculums include applied disciplines like geology or electrical engineering.
  • Physics is used in application toward:
    • developing new technologies
    • solving a problem
• Similar to applied mathematics.
• Applied physicists use physics in research.

Interdisciplinary Applications of Physics

• With the standard consensus that the laws of physics are universal and do not change with time, physics can be used to study things that would ordinarily be mired in uncertainty.
• People working on accelerator physics might seek to build better particle detectors for research in theoretical physics.
• Statics (mechanics) is used to build bridges and structures. acoustics is used to get better sound control in concert halls.
• Optics is used to create better devices.
• Physics understanding makes flight simulators, video games, movies more realistic and is critical in forensic investigations.
• Physics can study things mired in uncertainty and allows simulations.
• There is also considerable interdisciplinarity.

Concepts changing with time

• Concepts denoted can change with time.
• For example, the atom of nineteenth-century physics was denigrated by some, including Ernst Mach 's critique of Ludwig Boltzmann 's formulation of statistical mechanics
• By the end of World War II, the atom was no longer deemed hypothetical.
• Universalism is encouraged in the culture of physics.
• For example, the World Wide Web , which was innovated at CERN by Tim Berners-Lee , was created in service to the computer infrastructure of CERN, and was/is intended for use by physicists worldwide.