Introduction to Physics

• Physics is the scientific study of matter, its motion and behavior through space and time, and the related entities of energy and force.
• Physics is a fundamental scientific discipline and one of the oldest academic disciplines.
• A scientist who specializes in physics is called a physicist.
• Physics, chemistry, biology, and some mathematics branches were part of natural philosophy before the Scientific Revolution in the 17th century.
• Physics intersects with interdisciplinary research areas like biophysics and quantum chemistry.
• New physics ideas often explain fundamental mechanisms studied by other sciences like mathematics and philosophy.
• Advances in electromagnetism, solid-state physics, and nuclear physics led to the development of television, computers, appliances, and nuclear weapons.
• Thermodynamics advances led to industrialization and mechanics inspired calculus development.
• Early civilizations like the Sumerians, ancient Egyptians, and the Indus Valley Civilization had predictive knowledge of the Sun, Moon, and stars before 3000 BCE.
• Early observations laid the foundation for later astronomy.
• Western astronomy's origins can be found in Mesopotamia, with all Western exact sciences efforts descended from late Babylonian astronomy, as stated by Asger Aaboe.
• Egyptian astronomers' monuments showed knowledge of constellations and celestial bodies' motions.
• Greek poet Homer wrote of celestial objects in his "Iliad" and "Odyssey".
• Greek astronomers later provided names, still used today, for most constellations visible from the Northern Hemisphere.
• Natural philosophy originated in Greece during the Archaic period (650 BCE – 480 BCE) when pre-Socratic philosophers, like Thales, rejected non-naturalistic explanations for natural phenomena.
• Pre-Socratic philosophers proclaimed that every event had a natural cause, proposing ideas verified by reason and observation.
• Atomism was found correct about 2000 years after Leucippus and Democritus proposed it.
• During the classical period in Greece (6th-4th centuries BCE), natural philosophy developed along many lines of inquiry
• Aristotle (384–322 BCE) wrote a substantial treatise on "Physics" in the 4th century BC.
• Aristotelian physics was influential for about two millennia and mixed limited observation with logical deductive arguments, without experimental verification.
• Aristotle's Physics formed a framework against which later thinkers further developed the field, though his approach is entirely superseded today.
• Aristotle explained motion and gravity with the theory of four elements: air, fire, water, and earth.
• Aristotle believed each element had a natural place based on density: fire at the top, then air, water, and earth.
• Aristotle stated that a small amount of one element entering another's natural place would cause it to revert to its own.
• Aristotle's laws of motion stated that heavier objects fall faster, with speed proportional to weight and inversely proportional to the density of the medium.
• Aristotle stated that the speed of an object in violent motion (motion caused by a force from another object) depends on the amount of force applied.
• The problem of motion and its causes led to the philosophical notion of a "prime mover".
• The Western Roman Empire's fall in the fifth century led to a decline in intellectual pursuits in western Europe.
• The Eastern Roman Empire (Byzantine Empire) resisted attacks and continued to advance fields of learning, including physics.
• In the sixth century, John Philoponus challenged the dominant Aristotelian approach to science while focusing on Christian theology.
• In the sixth century, Isidore of Miletus created an important compilation of Archimedes' works copied in the Archimedes Palimpsest.
• Islamic scholarship inherited Aristotelian physics from the Greeks and developed it further during the Islamic Golden Age, emphasizing observation and a priori reasoning.
• Early forms of the scientific method were developed in Islamic scholarship.
• Notable innovations under Islamic scholarship occurred in optics and vision from scientists like Ibn Sahl, Al-Kindi, Ibn al-Haytham, Al-Farisi, and Avicenna.
• Ibn al-Haytham's "The Book of Optics" presented an alternative to the ancient Greek idea about vision.
• Ibn al-Haytham discussed his experiments with the camera obscura, showing that light moved in a straight line.
• Ibn al-Haytham encouraged readers to reproduce his experiments, making him one of the originators of the scientific method.
• Physics became a separate science when early modern Europeans used experimental and quantitative methods to discover the laws of physics.
• Major developments include replacing the geocentric model of the Solar System with the heliocentric Copernican model.
• Kepler (1609-1619) determined the laws governing the motion of planetary bodies.
• Galileo pioneered work 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 and Newton applied it to solve physical problems.
• The discovery of laws in thermodynamics, chemistry, and electromagnetics resulted from research efforts during the Industrial Revolution as energy needs increased.
• By the end of the 19th century, theories of thermodynamics, mechanics, and electromagnetics matched a wide variety of observations and became the basis for classical physics.
• Classical electromagnetism presumed a medium, a luminiferous aether to support the propagation of waves, but this medium could not be detected.
• The intensity of light from hot glowing blackbody objects and the character of electron emission of illuminated metals differed from predictions.
• Modern physics began in the early 20th century with Max Planck's work in quantum theory and Albert Einstein's theory of relativity.
• These theories came about due to inaccuracies in classical mechanics in certain situations.
• Classical mechanics predicted the speed of light depends on the observer's motion, conflicting with Maxwell's equations.
• Einstein's theory of special relativity corrected this discrepancy, replacing classical mechanics for fast-moving bodies and allowing for a constant speed of light.
• Planck proposed that the excitation of material oscillators is possible only in discrete steps proportional to their frequency.
• Planck's theory, along with the photoelectric effect and a complete theory predicting discrete energy levels of electron orbitals, led to quantum mechanics, improving 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 work in related fields.
• Following the discovery of a particle consistent with the Higgs boson at CERN in 2012, all fundamental particles predicted by the standard model appear to exist; however, physics beyond the Standard Model, with theories such as supersymmetry, is an active area of research.
• Areas of mathematics in general are important to this field, such as the study of probabilities and groups.
• Physics deals with a wide variety of systems, using certain theories tested experimentally to be adequate approximations of nature.
• Central theories include classical mechanics, quantum mechanics, thermodynamics and statistical mechanics, electromagnetism, and special relativity.
• Physics was revolutionized by the discoveries of quantum mechanics and relativity in the early 20th century, leading to "modern physics" and "classical physics" divisions.
• Most applications of physics are essentially classical.
• Classical physics accurately describes systems with length scales greater than the atomic scale and motions much slower than the speed of light
• Outside of this domain, observations do not match predictions provided by classical mechanics.
• Classical physics includes traditional branches recognized and well-developed before the 20th century: classical mechanics, thermodynamics, and electromagnetism.
• Classical mechanics is concerned with bodies acted on by forces and bodies in motion.
• Classical mechanics can be divided into statics, kinematics, and dynamics
• Mechanics may also be divided into solid mechanics and fluid mechanics (continuum mechanics), including hydrostatics, hydrodynamics, and pneumatics.
• Acoustics is the study of how sound is produced, controlled, transmitted, and received; acoustics includes ultrasonics, bioacoustics, and electroacoustics.
• Optics, the study of light, is concerned with visible, infrared, and ultraviolet radiation, exhibiting phenomena like reflection, refraction, interference, diffraction, dispersion, and polarization.
• Heat is a form of energy, the internal energy possessed by the particles of which a substance is composed; thermodynamics deals with the relationships between heat and other forms of energy.
• Electricity and magnetism have been studied as a single branch since the connection 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.
• Electrostatics deals with electric charges at rest, electrodynamics with moving charges, and magnetostatics with magnetic poles at rest.
• Modern physics includes effects related to quantum mechanics and relativity and transformed the conceptual basis of physics.
• Classical physics is generally concerned with matter and energy on the normal scale of observation.
• Much of modern physics is concerned with 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.
• The physics of elementary particles is on an even smaller scale and is also known as high-energy physics because of the high energies needed to produce particles in accelerators.
• On this scale, ordinary notions of space, time, matter, and energy are no longer valid.
• Classical mechanics approximates nature as continuous.
• Quantum theory is concerned with the discrete nature of phenomena at the atomic and subatomic level and with the complementary aspects of particles and waves.
• The theory of relativity describes phenomena in a frame of reference that is in motion with respect to an observer.
• The special theory of relativity is concerned with motion in the absence of gravitational fields, and the general theory of relativity with motion and its connection with gravitation.
• Physicists use the scientific method to test the validity of a physical theory by comparing the implications of a theory with the conclusions drawn from related experiments and observations.
• Experiments are performed and observations are made to determine the validity or invalidity of a theory.
• Theorists develop mathematical models agreeing with experiments and predicting 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 upon each other.
• Progress in physics comes about when experimental results defy explanation by existing theories.
• New theories generate experimentally testable predictions, inspiring new experiments and equipment.
• Physicists at the interplay of theory and experiment are called phenomenologists, studying complex phenomena observed in experiment and working to 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 like parallel universes, a multiverse, and higher dimensions in hopes of solving problems and 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.
• Experimental physicists 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, from elementary particles to the largest superclusters of galaxies, and is sometimes called the "fundamental science".
• Physics aims to describe various phenomena in nature in terms of simpler phenomena, connecting observable things to root causes.
• The ancient Chinese observed magnetism and the ancient Greeks knew of electricity, later studied in the 17th century.
• Further work in the 19th century revealed that electricity and magnetism were two aspects of one force—electromagnetism.
• Physics hopes to find a "theory of everything" to explain why nature is as it is.
• Research in condensed matter physics includes high-temperature superconductivity and fabricating spintronics and quantum computers.
• Particle physics shows experimental evidence for physics beyond the Standard Model, such as neutrinos having non-zero mass.
• Research aims to prove or disprove supersymmetry and uncover the mysteries of dark matter and dark energy, which extend the Standard Model of particle physics.
• Everyday phenomena involving complexity, chaos, or turbulence are still poorly understood, gaining attention since the 1970s due to modern mathematical methods and computers.
• Complex physics has become part of increasingly interdisciplinary research, as exemplified by turbulence in aerodynamics and pattern formation in biological systems.
• Complex problems include the formation of sandpiles, nodes in trickling water, the shape of water droplets, mechanisms of surface tension catastrophes, and self-sorting in shaken heterogeneous collections
• Branches of physics include classical mechanics; thermodynamics and statistical mechanics; electromagnetism and photonics; relativity; quantum mechanics, atomic physics, and 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 table.
• Since the 20th century, the individual fields of physics have become increasingly specialised, and today most physicists work in a single field for their entire careers.
• "Universalists" such as Einstein (1879–1955) and Lev Landau (1908–1968), who worked in multiple fields of physics, 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" because many elementary particles do not occur naturally but are created only during high-energy collisions of other particles.
• Currently, the interactions of elementary particles and fields are described by the Standard Model, accounting 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, respectively).
• The Standard Model also predicts a particle known as the Higgs boson.
• The European laboratory for particle physics, CERN, announced the detection of a particle consistent with the Higgs boson in July 2012, an integral part of the Higgs mechanism.
• Nuclear physics is the field of physics that studies the constituents and interactions of atomic nuclei.
• Commonly known 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—matter interactions on the scale of single atoms and molecules.
• The three areas are grouped together because of their interrelationships, the similarity of methods used, and the commonality of their relevant energy scales.
• All three areas include both classical, semi-classical and quantum treatments; they can treat their subject from a microscopic view (in contrast to a macroscopic 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), but 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 is distinct from optics in that it tends to focus not on the control of classical light fields by macroscopic objects but on the fundamental properties of optical fields and their interactions with matter in the microscopic realm.
• Condensed matter physics deals with the macroscopic physical properties of matter.
• Condensed matter physics is concerned with the "condensed" phases that appear whenever the number of particles in a system is extremely large and the interactions between them are strong.
• The most familiar examples of condensed phases are solids and liquids, which arise from the bonding by way of the electromagnetic force between atoms.
• More exotic condensed phases include the superfluid and the Bose–Einstein condensate found in certain atomic systems at very low temperature, the superconducting phase exhibited by conduction electrons in certain materials, and the ferromagnetic and antiferromagnetic phases of spins on atomic lattices.
• Condensed matter physics is the largest field of contemporary physics.
• Historically, condensed matter physics grew out of solid-state physics, which is now considered one of its main subfields.
• The term condensed matter physics was coined by Philip Anderson when he renamed his research group—previously solid-state theory—in 1967.
• Solid State Physics of the American Physical Society was renamed as the Division of Condensed Matter Physics in 1978
• Condensed matter physics has a large overlap with chemistry, materials science, nanotechnology and engineering.
• Astrophysics and astronomy are the application of the theories and methods of physics to the study of stellar structure, stellar evolution, the origin of the Solar System, and related problems of cosmology.
• Astrophysicists apply many disciplines of physics, including mechanics, electromagnetism, statistical mechanics, thermodynamics, quantum mechanics, relativity, nuclear and particle physics, and atomic and molecular physics.
• Radio signals emitted by celestial bodies were discovered by Karl Jansky in 1931 which initiated the science of radio astronomy.
• Perturbations and interference from the Earth's atmosphere make space-based observations necessary for infrared, ultraviolet, gamma-ray, and X-ray astronomy.
• 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 all modern cosmological theories.
• Hubble's discovery that the universe is expanding prompted rival explanations known as the steady state universe and the Big Bang.
• The Big Bang was confirmed by the success of Big Bang nucleosynthesis and the discovery of the cosmic microwave background in 1964.
• The Big Bang model rests on two theoretical pillars: Albert Einstein's general relativity and the cosmological principle.
• Cosmologists have recently established the ΛCDM model of the evolution of the universe, which includes cosmic inflation, dark energy, and dark matter.
• A physicist specializes in physics, encompassing matter and energy interactions at all scales.
• Physicists seek root causes of phenomena and frame understanding in mathematical terms.
• Physicists work across research fields spanning sub-atomic, biological, and cosmological scales.
• The field includes experimental physicists (observation and experiment) and theoretical physicists mathematical modeling).
• Physics, like the rest of science, relies on the philosophy of science and its "scientific method" to advance knowledge of the physical world.
• The scientific method employs a priori and a posteriori reasoning as well as the use of Bayesian inference to measure the validity of a given theory.
• The philosophy of physics studies issues like space, time, determinism, and metaphysical outlooks.
• Physicists have written about philosophical implications, like Laplace on determinism and Schrödinger on quantum mechanics.
• The mathematical physicist Roger Penrose is a Platonist, while Hawking called himself a "reductionist".
• Mathematics provides a language to describe the order in nature, as noted by Pythagoras, Plato, Galileo, and Newton.
• Some theorists, like Hilary Putnam and Penelope Maddy, hold that logical truths depend on the empirical world.
• Physics uses mathematics to organize and formulate experimental results, obtaining solutions or results to make predictions.
• Results from physics experiments are numerical data with units of measure and error estimates.
• 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, while 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 applies mathematics in physics, with mathematical methods and a physical subject, where every statement has a physical meaning.
• Physics is a branch of fundamental science (basic science), constrained by laws of physics.
• Chemistry studies properties, structures, and reactions of matter (molecular and atomic scale), with structures formed by electrical forces and reactions bound by physics laws.
• Fundamental physics explains phenomena in all spheres without a particular practical application as a goal.
• Applied physics is physics research and development intended for a particular use; an applied physics curriculum contains classes in an applied discipline, like geology or electrical engineering.
• Applied physics differs from engineering, as it may not design something in particular.
• Applied physicists use physics or conduct physics research with the aim of developing new technologies or solving a problem, similar to applied mathematics.
• Applied physicists use physics in scientific research, such as building better particle detectors for research in theoretical physics.
• Physics is used heavily in engineering, such as statics in building bridges and acoustics in sound control.
• Understanding physics makes for realistic flight simulators, video games, and forensic investigations..
• The laws of physics are universal and do not change with time, so physics can be used to study things that would ordinarily be mired in uncertainty.
• For example, in the study of the origin of the Earth, a physicist can reasonably model Earth's mass, temperature, and rate of rotation, as a function of time allowing the extrapolation forward or backward in time and so predict future or prior events.
• Physics allows for simulations in engineering that speed up the development of a new technology..
• There is considerable interdisciplinarity, so many other important fields are influenced by physics (e. g., the fields of econophysics and sociophysics).

Physics is the study of matter, energy, and their interactions. Physicists explore the fundamental principles governing the universe. This field has driven advancements in technology and other sciences, contributing to our understanding of the world.