Introduction to Physics

• Physics is the scientific study of matter, its motion, behavior through space and time, and the related entities of energy and force.
• It is a fundamental scientific discipline and one of the oldest academic disciplines.
• A physicist specializes in the field.
• Physics, chemistry, biology, and certain branches of mathematics were part of natural philosophy for much of the past two millennia.
• During the Scientific Revolution in the 17th century, these natural sciences branched into separate research endeavors.
• Physics intersects with interdisciplinary areas like biophysics and quantum chemistry, with no rigidly defined boundaries.
• New ideas in physics often explain fundamental mechanisms studied by other sciences and suggest new research avenues in mathematics and philosophy
• Advances in physics often enable new technologies.

Historical Advances

• Advances in the understanding of electromagnetism, solid-state physics, and nuclear physics led to the development of technologies such as television, computers, domestic appliances, and nuclear weapons.
• Advances in thermodynamics led to industrialization.
• Advances in mechanics inspired the development of calculus.

Astronomy

• Astronomy is one of the oldest natural sciences.
• Early civilizations like the Sumerians, ancient Egyptians, and the Indus Valley Civilization had predictive knowledge of the motions of the Sun, Moon, and stars before 3000 BCE.
• The stars and planets were believed to represent gods and were often worshipped.
• Early observations laid the foundation for later astronomy, despite often unscientific explanations.
• Stars were found to traverse great circles across the sky, which could not explain planet positions.
• The origins of Western astronomy are traced to Mesopotamia, with Western efforts in exact sciences descended from late Babylonian astronomy.
• Egyptian astronomers had knowledge of constellations and celestial body motions.
• Greek astronomers later provided names for most constellations visible from the Northern Hemisphere, as written about by Homer.

Natural Philosophy

• Natural philosophy originated in Greece during the Archaic period (650 BCE – 480 BCE).
• Pre-Socratic philosophers like Thales rejected non-naturalistic explanations for natural phenomena, asserting that every event had a natural cause.
• Ideas were verified by reason and observation.
• Atomism, proposed by Leucippus and Democritus, was confirmed approximately 2000 years later.
• During the classical period in Greece (6th, 5th and 4th centuries BCE) and in Hellenistic times, natural philosophy developed along many lines of inquiry.
• Aristotle wrote a treatise on "Physics" in the 4th century BC, influential for about two millennia.
• Aristotelian physics mixed limited observation with logical deductive arguments, without experimental verification.
• Aristotle explained motion and gravity with the theory of four elements, each with its natural place based on density: earth, water, air, and fire.
• Heavier objects fall faster, with speed proportional to weight and inversely related to the density of the medium.
• Violent motion depends on the force applied to an object.
• The problem of motion led to the concept of a "prime mover" as the ultimate source of all motion.

Developments

• The Western Roman Empire's fall led to a decline in European intellectual pursuits.
• The Eastern Roman Empire (Byzantine Empire) continued to advance learning, including physics.
• John Philoponus challenged Aristotelian science in the sixth century.
• Isidore of Miletus created a compilation of Archimedes' works in the sixth century.
• Islamic scholarship inherited and developed Aristotelian physics, emphasizing observation and a priori reasoning and developing early forms of the scientific method
• Innovations occurred in optics and vision through the works of Ibn Sahl, Al-Kindi, Ibn al-Haytham, Al-Farisi and Avicenna.
• Ibn al-Haytham's Book of Optics presented an alternative to ancient Greek ideas about vision, discussed experiments with the camera obscura, and showed that light moved in a straight line.

Physics as a Separate Science

• Physics became a separate science when early modern Europeans used experimental and quantitative methods to discover the laws of physics.
• Major developments include the heliocentric Copernican model replacing the geocentric model, Kepler's laws of planetary motion (1609-1619), Galileo's work on telescopes and observational astronomy, and Isaac Newton's laws of motion and universal gravitation.
• Newton and Leibniz developed calculus and applied it to physical problems.
• Discoveries in thermodynamics, chemistry, and electromagnetics resulted from research during the Industrial Revolution.
• By the end of the 19th century, theories of thermodynamics, mechanics, and electromagnetics matched a wide variety of observations, becoming the basis for classical physics.
• Some experimental results such as electromagnetism, blackbody radiation, and electron emission remained unexplained, which would 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 addressed inaccuracies in classical mechanics.
• Einstein's theory of special relativity replaced classical mechanics for fast-moving bodies and allowed for a constant speed of light.
• Planck proposed that the excitation of material oscillators is possible only in discrete steps proportional to their frequency, to correct Black-body radiation
• Quantum mechanics was pioneered by Werner Heisenberg, Erwin Schrödinger and Paul Dirac, improving on classical physics at very small scales.
• The Standard Model of particle physics was derived, and all fundamental particles predicted by the model appear to exist, following the discovery of a particle with properties consistent with the Higgs boson at CERN in 2012.
• However, physics beyond the Standard Model, with theories such as supersymmetry, is an active area of research.
• Areas of mathematics in general are important, such as the study of probabilities and groups.

Theories

• Physics deals with a wide variety of systems, using theories tested experimentally and found to be adequate approximations of nature.
• Central theories: classical mechanics, quantum mechanics, thermodynamics and statistical mechanics, electromagnetism, and special relativity.
• In the early 20th century, the discoveries of quantum mechanics and relativity revolutionized physics, leading to "modern physics" and "classical physics".
• Classical physics accurately describes systems with length scales greater than the atomic scale and motions much slower than the speed of light.
• Classical physics includes classical mechanics, thermodynamics, and electromagnetism.

Classical Mechanics

• Classical mechanics is concerned with bodies acted on by forces and bodies in motion and may be divided into statics, kinematics, and dynamics.
• Mechanics may also be divided into solid mechanics and fluid mechanics (continuum mechanics).
• Acoustics studies sound production, control, transmission, and reception, including ultrasonics, bioacoustics, and electroacoustics.
• Optics studies light, including infrared and ultraviolet radiation, and phenomena such as reflection, refraction, interference, diffraction, dispersion, and polarization.
• Thermodynamics deals with the relationships between heat and other forms of energy.
• Electricity and magnetism have been studied as a single branch since the 19th century.
• Electrostatics deals with electric charges at rest, electrodynamics with moving charges, and magnetostatics with magnetic poles at rest.

Conceptual Basis

• The discovery of relativity and of quantum mechanics transformed the conceptual basis of physics without reducing the practical value of most physical theories developed up to that time.

Modern vs Classical Physics

• Classical physics is generally concerned with matter and energy on the normal scale of observation, while 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.
• Elementary particle physics studies matter on an even smaller scale and is also known as high-energy physics.
• Ordinary notions of space, time, matter, and energy are no longer valid on the particle scale.
• Classical mechanics approximates nature as continuous, while quantum theory deals with the discrete nature of many phenomena at the atomic and subatomic level and with the complementary aspects of particles and waves.
• The theory of relativity deals with phenomena in a frame of reference that is in motion with respect to an observer.
• Special relativity deals with motion in the absence of gravitational fields.
• General relativity deals with motion and its connection with gravitation.
• Quantum theory and the theory of relativity find applications in many areas of modern physics.

Scientific Method

• Physicists use the scientific method to test the validity of a physical theory.
• Experiments are performed and observations are made to determine the validity of a theory.
• Theorists develop mathematical models that agree with existing experiments and successfully predict future experimental results.
• Experimentalists devise and perform experiments to test theoretical predictions and explore new phenomena.
• Progress in physics often occurs when experimental results defy existing theories or when new theories generate experimentally testable predictions.
• Physicists who work at the interplay of theory and experiment are called phenomenologists. Theoretical physics has historically taken inspiration from philosophy.
• Beyond the known universe, theoretical physics also deals with hypothetical issues.
• Experimental physics expands, and is expanded by, engineering and technology.
• Experimental physicists in basic research design and perform experiments with equipment such as particle accelerators and lasers.

Scope

• Physics covers from elementary particles (quarks, neutrinos, and electrons) to superclusters of galaxies.
• Physics aims to describe phenomena in nature in terms of simpler phenomena.
• Physics connects observable things to root causes and then connects these causes together.
• Magnetism and electricity were two observed phenomena that became understood in terms of electromagnetism.
• Physics hopes to find an ultimate reason (theory of everything) for why nature is as it is.

Research

• Research in physics is continually progressing on many fronts.
• In condensed matter physics, an unsolved theoretical problem is high-temperature superconductivity.
• Experiments aim to fabricate spintronics and quantum computers.
• In particle physics, evidence for physics beyond the Standard Model is appearing, such as indications that neutrinos have non-zero mass.
• The Large Hadron Collider has found the Higgs boson, and future research aims to prove or disprove supersymmetry.
• Research on the nature of dark matter and dark energy is ongoing.
• Complex phenomena involving complexity, chaos, or turbulence are still poorly understood.
• 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.
• Complex phenomena have received growing attention since the 1970s due to modern mathematical methods and computers.

Branches of Physics

• Branches of physics: 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.
• Since the 20th century, individual fields of physics have become increasingly specialised.
• Physicists today typically work in a single field for their entire careers.

Particle Physics

• 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.
• Currently, the 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.
• The Standard Model also predicts the Higgs boson, detected at CERN in July 2012.

Nuclear Physics

• Nuclear physics studies the constituents and interactions of atomic nuclei.
• Applications include nuclear power generation, nuclear weapons technology, nuclear medicine, magnetic resonance imaging, ion implantation in materials engineering, and radiocarbon dating in geology and archaeology.

Atomic, Molecular, and Optical Physics (AMO)

• Atomic, molecular, and optical physics (AMO) studies matter, light, and matter-light 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.
• Atomic physics studies the electron shells of atoms, focusing on quantum control, cooling and trapping of atoms and ions, low-temperature collision dynamics, and the effects of electron correlation on structure and dynamics.
• 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 the "condensed" phases that appear whenever the number of particles in a system is extremely large and the interactions between them are strong.
• Examples include solids and liquids, superfluids and Bose–Einstein condensates, superconducting phases, and ferromagnetic and antiferromagnetic phases.
• Condensed matter physics is the largest field of contemporary physics.
• Historically, condensed matter physics grew out of solid-state physics.
• Condensed matter physics has a large overlap with chemistry, materials science, nanotechnology and engineering.

Astrophysics and Astronomy

• Astrophysics and astronomy apply 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 mechanics, electromagnetism, statistical mechanics, thermodynamics, quantum mechanics, relativity, nuclear and particle physics, and atomic and molecular physics.
• The discovery that radio signals were emitted by celestial bodies initiated radio astronomy.
• Space exploration has expanded the frontiers of astronomy, making space-based observations necessary for certain types of energy detection, as the Earth's perturbations and interference do not allow for accurate data retrieval.

Physical Cosmology

• 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.
• Discoveries such as Hubble's discovery that the universe is expanding prompted explanations like the steady state universe and the Big Bang.
• The Big Bang was confirmed by Big Bang nucleosynthesis and the discovery of the cosmic microwave background in 1964. cosmology, dark energy, and dark matter.
• Cosmologists have established the ΛCDM model of the universe, which includes cosmic inflation, dark energy, and dark matter.

Physicist

• A physicist specializes in the field of physics.
• Physicists are interested in the root causes of phenomena and frame their understanding in mathematical terms.
• Physicists research across a wide range of fields, from sub-atomic and particle physics to cosmological length scales.
• Field includes experimental physicists, who specialize in observation and experiment analysis, and theoretical physicists, who specialize in mathematical modeling.
• Physics 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.
• Study of the philosophical issues surrounding physics, the philosophy of physics, includes issues such as the nature of space and time, determinism, and metaphysical outlooks such as empiricism, naturalism, and realism.

Mathematics in Physics

• Mathematics provides a compact and exact language used to describe the order in nature.
• Physics uses mathematics to organise and formulate experimental results.
• From those results, precise or estimated solutions are obtained from which new predictions can be made and experimentally confirmed or negated.
• The 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 statements are synthetic, while mathematical statements are analytic.
• Mathematics statements have to be only logically true, while predictions of physics statements must match observed and experimental data.

Applied Physics

• Physics is a branch of fundamental science, also called basic science.
• Physics is called "the fundamental science" because all branches of natural science including chemistry, astronomy, geology, and biology are constrained by laws of physics.
• Applied physics is research and development that is intended for a particular use.
• An applied physics curriculum usually contains a few classes in an applied discipline, like geology or electrical engineering.
• It usually differs from engineering in that an applied physicist may not be designing something in particular, but rather is using physics or conducting physics research with the aim of developing new technologies or solving a problem.
• Applied physicists use physics in scientific research.
• For instance, people working on accelerator physics might seek to build better particle detectors for research in theoretical physics.
• Physics is used heavily in engineering, forensics and video game design
• Physics can be used to study things that would ordinarily be mired in uncertainty
• There is also considerable interdisciplinarity, so many other important fields are influenced by physics (e. g., the fields of econophysics and sociophysics).