Introduction to Physics

• Physics is the scientific study of matter, its constituents, motion, behavior through space and time, energy, and force.
• It is a fundamental scientific discipline.
• A physicist specializes in the field.
• Physics is one of the oldest academic disciplines.
• Physics, chemistry, biology, and some mathematics were part of natural philosophy for millennia.
• During the 17th-century Scientific Revolution, these sciences became separate endeavors.
• Physics intersects with biophysics and quantum chemistry.
• New physics ideas explain fundamental mechanisms in other sciences.
• Advances in physics enable new technologies.
• Electromagnetism, solid-state physics, and nuclear physics advancements led to television, computers, appliances, and nuclear weapons.
• Thermodynamics advances led to industrialization.
• Mechanics advances inspired calculus development.
• Astronomy is among the oldest natural sciences.
• Civilizations before 3000 BCE had predictive knowledge of the Sun, Moon, and stars' motions.
• The stars and planets were often worshipped as gods.
• Early observations laid the foundation for later astronomy.
• Stars traverse great circles across the sky.
• Planet positions could not be explained.
• Western astronomy originated in Mesopotamia.
• All Western exact sciences are descended from late Babylonian astronomy.
• Egyptian astronomers showed knowledge of constellations and celestial motions.
• Homer wrote of celestial objects in the Iliad and Odyssey.
• Greek astronomers named most constellations visible from the Northern Hemisphere.
• Natural philosophy originated in Greece (650 BCE – 480 BCE).
• Pre-Socratic philosophers like Thales rejected non-naturalistic explanations.
• Every event has a natural cause.
• They proposed ideas verified by reason and observation.
• Atomism was correct 2000 years after Leucippus and Democritus proposed it.
• Natural philosophy developed along many lines of inquiry during the classical period in Greece (6th, 5th, 4th centuries BCE) and in Hellenistic times.
• Aristotle (384–322 BCE) wrote on many subjects, including a treatise on "Physics".
• Aristotelian physics was influential for about two millennia.
• His approach mixed limited observation with logical deductive arguments.
• He did not rely on experimental verification.
• Aristotle's work formed a framework for later thinkers.
• He explained motion and gravity with the theory of four elements.
• The four classical elements (air, fire, water, earth) each had a natural place.
• Elements revert to their specific place in the atmosphere due to differing densities.
• Fire would be at the top, air underneath fire, then water, then earth.
• A small amount of one element in another's natural place will automatically move.
• Fire on the ground goes up into the air.
• Heavier objects will fall faster.
• Speed is proportional to weight.
• The speed of a falling object depends inversely on the density of what it falls through.
• Violent motion (force applied by a second object) speed is as fast as the force applied.
• Motion and its causes led to the philosophical notion of a "prime mover".
• The Western Roman Empire fell in the fifth century.
• This resulted in a decline in intellectual pursuits in western Europe.
• The Eastern Roman Empire (Byzantine Empire) resisted attacks and advanced learning.
• In the sixth century, John Philoponus challenged Aristotelian science.
• His work focused on Christian theology.
• In the sixth century, Isidore of Miletus created an important compilation of Archimedes' works in the Archimedes Palimpsest.
• Islamic scholarship inherited Aristotelian physics from the Greeks and developed it further.
• Emphasis was placed on observation and a priori reasoning.
• Early forms of the scientific method were developed.
• Notable innovations were in optics and vision.
• Scientists like Ibn Sahl, Al-Kindi, Ibn al-Haytham, Al-Farisi, and Avicenna contributed.
• Ibn al-Haytham wrote The Book of Optics (Kitāb al-Manāẓir).
• He presented an alternative to the ancient Greek idea about vision.
• He discussed experiments with camera obscura.
• Light moved in a straight line.
• He encouraged readers to reproduce his experiments.
• He was one of the originators of the scientific method.

Physics as a Separate Science

• Physics became a separate science when early modern Europeans used experimental and quantitative methods to discover what are now considered to be the laws of physics.
• Major developments included replacing the geocentric model with the heliocentric Copernican model.
• Laws governing planetary motion were determined by Johannes Kepler between 1609 and 1619.
• Galileo's pioneering work was done on telescopes and observational astronomy in the 16th and 17th centuries.
• Isaac Newton discovered and unified the laws of motion and universal gravitation.
• Newton and Gottfried Wilhelm Leibniz developed calculus.
• Newton applied calculus to physical problems.
• The discovery of laws in thermodynamics, chemistry, and electromagnetics resulted from research during the Industrial Revolution.
• By the end of the 19th century, thermodynamics, mechanics, and electromagnetics theories matched observations.
• These theories became the basis for classical physics.
• Some experimental results remained inexplicable.
• Classical electromagnetism presumed a luminiferous aether to support wave propagation.
• This medium could not be detected.
• The intensity of light from hot glowing blackbody objects did not match predictions.
• Electron emission of illuminated metals differed from predictions.
• These failures upset the physics world in the first two decades of the 20th century.

Modern Physics

• Modern physics began in the early 20th century with Max Planck's quantum theory and Albert Einstein's theory of relativity.
• These theories arose due to inaccuracies in classical mechanics.
• Classical mechanics predicted the speed of light depends on the observer's motion.
• This could not be resolved with the constant speed predicted by Maxwell's equations.
• Einstein's special relativity corrected this discrepancy.
• It replaced classical mechanics for fast-moving bodies and allowed for a constant speed of light.
• Black-body radiation provided another problem for classical physics.
• Planck proposed that the excitation of material oscillators is possible only in discrete steps proportional to their frequency.
• This, along with the photoelectric effect and a complete theory predicting discrete energy levels of electron orbitals, led to quantum mechanics.
• Quantum mechanics improved on classical physics at very small scales.
• Quantum mechanics was pioneered by Werner Heisenberg, Erwin Schrödinger, and Paul Dirac.
• The Standard Model of particle physics was derived from this early work and related fields.
• A particle consistent with the Higgs boson was discovered at CERN in 2012.
• All fundamental particles predicted by the standard model appear to exist.
• Physics beyond the Standard Model, with theories like supersymmetry, is an active area of research.
• Areas of mathematics are important to this field.
• Physics deals with various systems.
• Certain theories are used by all physicists.
• Each theory was experimentally tested and found to be an adequate approximation of nature.
• Central theories are important tools for research into more specialized topics.
• Any physicist is expected to be literate in classical mechanics, quantum mechanics, thermodynamics and statistical mechanics, electromagnetism, and special relativity.
• Discoveries of quantum mechanics and relativity revolutionized physics in the early 20th century.
• These new concepts became the foundation of "modern physics".
• Other topics became "classical physics".
• Most applications of physics are classical.
• Classical physics laws accurately describe systems whose length scales are greater than the atomic scale and whose motions are much slower than the speed of light.
• Observations do not match predictions provided by classical mechanics outside of this domain.
• Classical physics includes traditional branches and topics recognized and well-developed before the 20th century.
• These include classical mechanics, thermodynamics, and electromagnetism.
• Classical mechanics concerns bodies acted on by forces and bodies in motion.
• It may be divided into statics, kinematics, and dynamics.
• Mechanics may also be divided into solid mechanics and fluid mechanics (continuum mechanics).
• Fluid mechanics includes hydrostatics, hydrodynamics, and pneumatics.
• Acoustics studies how sound is produced, controlled, transmitted, and received.
• Modern branches of acoustics include ultrasonics, bioacoustics, and electroacoustics.
• Optics studies light.
• It concerns visible light, infrared, and ultraviolet radiation.
• These exhibit phenomena of visible light except visibility like reflection, refraction, interference, diffraction, dispersion, and polarization.
• Heat is a form of energy.
• It is the internal energy possessed by particles of a substance.
• Thermodynamics deals with relationships between heat and other forms of energy.
• Electricity and magnetism have been studied as a single branch of physics since the 19th century.
• An electric current gives rise to a magnetic field.
• A changing magnetic field induces an electric current.
• Electrostatics deals with electric charges at rest, electrodynamics with moving charges, and magnetostatics with magnetic poles at rest.
• The discovery of relativity and quantum mechanics transformed physics.
• The practical value of most physical theories developed up to that time was unchanged.
• Physics topics have come to be divided into "classical physics" and "modern physics".
• Modern physics includes effects related to quantum mechanics and relativity.
• Classical physics generally concerns matter and energy on the normal scale of observation.
• Modern physics concerns the behavior of matter and energy under extreme conditions or on a very large or very small scale.
• Atomic and nuclear physics study matter on the smallest scale at which chemical elements can be identified.
• Elementary particle physics is on an even smaller scale.
• It concerns the most basic units of matter.
• This branch is also known as high-energy physics due to the high energies necessary to produce particles in accelerators.
• Ordinary notions of space, time, matter, and energy are no longer valid on this scale.
• The two chief theories of modern physics present a different picture of space, time, and matter from classical physics.
• Classical mechanics approximates nature as continuous.
• Quantum theory concerns the discrete nature of phenomena at the atomic and subatomic level.
• It also concerns the complementary aspects of particles and waves.
• Relativity theory concerns phenomena in a frame of reference in motion with respect to an observer.
• Special relativity concerns motion in the absence of gravitational fields.
• General relativity concerns motion and its connection with gravitation.
• Quantum theory and relativity theory have applications in modern physics.
• Fundamental concepts in modern physics are extremely important.

Scientific Method

• Physicists use the scientific method to test the validity of a physical theory.
• A methodical approach compares the implications of a theory with conclusions from experiments and observations.
• This helps test the validity of a theory in a logical, unbiased, and repeatable way.
• Experiments are performed and observations are made to determine the validity of a theory.
• Theorists develop mathematical models that agree with existing experiments and predict future results.
• Experimentalists devise and perform experiments to test theoretical predictions and explore new phenomena.
• Theory and experiment are developed separately but strongly affect and depend on each other.
• Progress in physics often comes when experimental results defy explanation by existing theories.
• New theories generate experimentally testable predictions, inspiring new experiments.
• Physicists at the interplay of theory and experiment are called phenomenologists.
• They study complex phenomena observed in experiment and relate them to a fundamental theory.
• Theoretical physics has historically taken inspiration from philosophy.
• Electromagnetism was unified this way.
• Theoretical physics also deals with hypothetical issues.
• These include parallel universes, a multiverse, and higher dimensions.
• Theorists invoke these ideas to solve problems with existing theories.
• They explore the consequences of these ideas and work toward making testable predictions.
• Experimental physics expands and is expanded by engineering and technology.
• Experimental physicists in basic research design and perform experiments with equipment like particle accelerators and lasers.
• Those involved in applied research often work in industry, developing technologies like MRI and transistors.
• Feynman noted that experimentalists may seek areas not explored well by theorists.
• Physics covers a wide range of phenomena including elementary particles and superclusters of galaxies.
• It includes the most basic objects composing all other things.
• Physics is sometimes called the "fundamental science".
• Physics aims to describe natural phenomena in terms of simpler phenomena.
• Physics aims to connect observable things to root causes and connect these causes together.
• The ancient Chinese observed that certain rocks were attracted to one another by an invisible force.
• This was called magnetism, which was studied in the 17th century.
• Ancient Greeks knew that amber rubbed with fur would cause a similar attraction.
• This was called electricity and was first studied in the 17th century.
• Physics had come to understand two observations in terms of electricity and magnetism.
• Further work in the 19th century revealed that these two forces were aspects of electromagnetism.
• This process of "unifying" forces continues today.
• Electromagnetism and the weak nuclear force are now the electroweak interaction.
• Physics hopes to find an ultimate reason (theory of everything) for why nature is as it is.

Current Physics Research

• Research in physics is continually progressing.
• In condensed matter physics, an unsolved problem is high-temperature superconductivity.
• Many experiments aim to fabricate workable spintronics and quantum computers.
• In particle physics, experimental evidence for physics beyond the Standard Model has begun to appear.
• There are indications that neutrinos have non-zero mass.
• These results appear to have solved the solar neutrino problem.
• The physics of massive neutrinos remains an area of research.
• The Large Hadron Collider has found the Higgs boson.
• Future research aims to prove or disprove supersymmetry, which extends the Standard Model.
• Research on the nature of dark matter and dark energy is ongoing.
• Many everyday phenomena involving complexity, chaos, or turbulence are poorly understood.
• Complex problems that seem solvable by dynamics and mechanics remain unsolved.
• Examples include sandpile formation, nodes in trickling water, water droplet shape, and surface tension catastrophes.
• Complex phenomena have received growing attention since the 1970s due to modern methods and computers.
• Complex physics has become part of interdisciplinary research.
• Examples include turbulence in aerodynamics and pattern formation in biological systems.

Branches of Physics

• Branches of physics include classical mechanics, thermodynamics and statistical mechanics, electromagnetism and photonics, relativity, quantum mechanics, atomic physics, molecular physics, optics and acoustics, condensed matter physics, high-energy particle physics and nuclear physics, cosmology, and interdisciplinary fields.
• The major fields of physics, along with their subfields and the theories and concepts they employ, are shown in the following table.
• Since the 20th century, the individual fields of physics have become increasingly specialised.
• Most physicists work in a single field for their entire careers.
• "Universalists" like Einstein and Lev Landau, who worked in multiple fields, are now very rare.
• Particle physics is the study of the elementary constituents of matter and energy and the interactions between them.
• Particle physicists design and develop high-energy accelerators, detectors, and computer programs.
• The field is also called "high-energy physics".
• Many elementary particles do not occur naturally but are created during high-energy collisions.
• Interactions of elementary particles and fields are described by the Standard Model.
• The model accounts for the 12 known particles of matter (quarks and leptons) that interact via the strong, weak, and electromagnetic fundamental forces.
• Dynamics are described in terms of matter particles exchanging gauge bosons (gluons, W and Z bosons, and photons).
• The Standard Model also predicts a particle known as the Higgs boson.
• CERN announced the detection of a particle consistent with the Higgs boson in July 2012.
• Nuclear physics studies the constituents and interactions of atomic nuclei.
• Applications of nuclear physics are nuclear power generation and nuclear weapons technology.
• Research has applications in nuclear medicine and magnetic resonance imaging, ion implantation in materials engineering, and radiocarbon dating in geology and archaeology.
• Atomic, molecular, and optical physics (AMO) is the study of matter, matter, and light and matter interactions on the scale of single atoms and molecules.
• The three areas are grouped together due to their interrelationships, the similarity of methods used, and the commonality of their relevant energy scales.
• All three areas include classical, semi-classical, and quantum treatments.
• They can treat their subject from a microscopic view.
• Atomic physics studies the electron shells of atoms.
• Current research focuses on activities in quantum control, cooling and trapping of atoms and ions, low-temperature collision dynamics, and the effects of electron correlation on structure and dynamics.
• Atomic physics is influenced by the nucleus (see hyperfine splitting).
• Intra-nuclear phenomena such as fission and fusion are considered part of nuclear physics.
• Molecular physics focuses on multi-atomic structures and their internal and external interactions with matter and light.
• Optical physics focuses on the fundamental properties of optical fields and their interactions with matter in the microscopic realm.

Condensed Matter Physics

• Condensed matter physics deals with the macroscopic physical properties of matter.
• It is concerned with "condensed" phases that appear whenever the number of particles in a system is extremely large and the interactions between them are strong.
• Condensed phases are solids and liquids, which arise from the bonding via the electromagnetic force between atoms.
• Exotic condensed phases include the superfluid and the Bose–Einstein condensate found in certain atomic systems at very low temperature.
• They also include the superconducting phase exhibited by conduction electrons in certain materials.
• Other example are the ferromagnetic and antiferromagnetic phases of spins on atomic lattices.
• Condensed matter physics is the largest field of contemporary physics.
• Condensed matter physics grew out of solid-state physics.
• Solid-state physics is now considered one of its main subfields.
• Philip Anderson coined the term condensed matter physics when he renamed his research group in 1967.
• The Division of Solid State Physics of the American Physical Society was renamed as the Division of Condensed Matter Physics in 1978.
• Condensed matter physics overlaps with chemistry, materials science, nanotechnology, and engineering.
• Astrophysics and astronomy apply physics theories and methods to study stellar structure, stellar evolution, the origin of the Solar System, and cosmology.
• Astrophysicists apply mechanics, electromagnetism, statistical mechanics, thermodynamics, quantum mechanics, relativity, nuclear and particle physics, and atomic and molecular physics.
• Karl Jansky's discovery in 1931 that radio signals were emitted by celestial bodies initiated radio astronomy.
• The frontiers of astronomy have been expanded by space exploration.
• Infrared, ultraviolet, gamma-ray, and X-ray astronomy require space-based observations due to atmospheric perturbations.
• Physical cosmology studies the formation and evolution of the universe on its largest scales.
• Albert Einstein's theory of relativity plays a central role in modern cosmological theories.
• Hubble's discovery that the universe is expanding in the early 20th century led to the steady state universe and the Big Bang theories.
• The Big Bang was confirmed by Big Bang nucleosynthesis and the discovery of the cosmic microwave background in 1964.
• The Big Bang model rests on general relativity and the cosmological principle.
• Cosmologists have established the ΛCDM model of the evolution of the universe.
• This includes cosmic inflation, dark energy, and dark matter.

Physicists

• A physicist specializes in the field of physics.
• Physics encompasses the interactions of matter and energy at all length and time scales in the physical universe.
• Physicists are interested in the root causes of phenomena.
• They frame their understanding in mathematical terms.
• They work across a wide range of research fields from sub-atomic and particle physics to cosmological length scales.
• The field includes experimental physicists and theoretical physicists.
• Experimental physicists specialize in the observation of natural phenomena and the development and analysis of experiments.
• Theoretical physicists specialize in mathematical modeling of physical systems to rationalize, explain, and predict natural phenomena.
• Physics relies on the philosophy of science and its "scientific method" to advance knowledge.
• The scientific method employs a priori and a posteriori reasoning.
• It also uses Bayesian inference to measure the validity of a given theory.
• The study of philosophical issues surrounding physics involves the nature of space and time, determinism, empiricism, naturalism, and realism.
• Many physicists have written about the philosophical implications of their work.
• Laplace championed causal determinism.
• Erwin Schrödinger wrote on quantum mechanics.
• The mathematical physicist Roger Penrose has been called a Platonist by Stephen Hawking.
• Hawking referred to himself as an "unashamed reductionist".
• Mathematics provides a compact and exact language used to describe the order in nature.
• Pythagoras, Plato, Galileo, and Newton noted and advocated for math.
• Some theorists hold that logical truths and mathematical reasoning depend on the empirical world.
• The laws of logic express universal regularities found in the structural features of the world.
• Physics uses mathematics to organize and formulate experimental results.
• Precise or estimated solutions are obtained.
• Quantitative results which new predictions can be made and experimentally confirmed or negated.
• Results from physics experiments are numerical data with their units of measure and estimates of the errors in the measurements.
• Technologies based on mathematics, like computation, have made computational physics an active area of research.
• Ontology is a prerequisite for physics, but not for mathematics.
• Physics is concerned with descriptions of the real world.
• Mathematics is concerned with abstract patterns, even beyond the real world.
• Physics statements are synthetic.
• Mathematical statements are analytic.
• Mathematics contains hypotheses.
• Physics contains theories.
• Mathematics statements have to only be logically true.
• Predictions of physics statements must match observed and experimental data.
• Mathematical physics applies mathematics in physics.
• Its methods are mathematical, but its subject is physical.
• Mathematical models of physical situations or systems and mathematical descriptions of physical laws that will be applied to that system are used.
• Every mathematical statement has a physical meaning.
• The final mathematical solution has an easier-to-find meaning.
• Physics is a branch of fundamental science.
• All branches of natural science are constrained by laws of physics.
• Chemistry is often called the central science.
• Chemistry studies properties, structures, and reactions of matter.
• Structures are formed because particles exert electrical forces on each other.
• Properties include physical characteristics of given substances.
• Reactions are bound by laws of physics like conservation of energy, mass, and charge.
• Fundamental physics seeks to better explain phenomena without a specific practical application.
• Applied physics is research and development intended for a particular use.
• Applied physics contains classes in an applied discipline like geology or electrical engineering.
• Applied physics may not be designing something in particular.
• It uses physics or conducts research with the aim of developing new technologies or solving a problem.
• Its approach is similar to applied mathematics.
• Applied physicists use physics in scientific research.
• People working on accelerator physics might seek to build better particle detectors.
• Physics is used heavily in engineering.
• Statics is used in the building of bridges and other static structures.
• The understanding and use of acoustics results in sound control and better concert halls.
• The use of optics creates better optical devices.
• An understanding of physics makes for more realistic flight simulators, video games, and movies.
• Physics is often critical in forensic investigations.
• 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.
• In the study of the origin of the Earth, a physicist can model Earth's mass, temperature, and rate of rotation as a function of time.
• This allows extrapolation forward or backward in time and so predict future or prior events.
• It also allows for simulations in engineering that speed up the development of a new technology.
• There is also considerable interdisciplinarity.
• Many other important fields are influenced by physics.