Modern Physics: Quantum Mechanics

• Modern physics includes the developments in physics from the early 20th century to the present.
• Quantum mechanics and relativity are primary focuses of modern physics.
• Classical physics had limitations which led to the emergence of modern physics.
• A deeper understanding of the universe at fundamental levels is provided by modern physics.

Quantum Mechanics

• Quantum mechanics looks at matter and energy behavior at atomic and subatomic levels.
• In classical physics, energy, momentum, and angular momentum can take on continuous values, in contrast to quantum mechanics.
• Quantum mechanics restricts energy, momentum, angular momentum etc to discrete values, called quantization.
• Wave-particle duality, superposition, and quantum entanglement are key concepts.
• Wave-particle duality states every particle or quantum entity can be described as both a particle and a wave.
• Superposition is a quantum system's ability to be in multiple states at once.
• Quantum entanglement links two or more quantum particles, where one particle's state affects the others instantly, regardless of distance.
• The Heisenberg uncertainty principle says there's a limit to the precision with which certain pairs of particle properties, like position and momentum, can be known at the same time.
• Technologies including lasers, transistors, and medical imaging have come from quantum mechanics.
• The Schrödinger equation describes how the quantum state of a physical system changes over time; it's a fundamental equation.

Relativity

• Relativity consists of special and general relativity, two interrelated theories by Albert Einstein.
• Special relativity, published in 1905, concerns space and time for observers in relative motion at a constant velocity.
• Key postulates of special relativity: Physics laws are the same for all observers in uniform motion; the speed of light in a vacuum is the same for all observers, regardless of the light source's motion.
• Time dilation, length contraction, and mass increase are consequences of special relativity.
• Time dilation refers to the slowing of time for an observer in relative motion.
• Length contraction refers to the shortening of an object in motion's direction as its speed nears light speed.
• Mass increase refers to the increase in an object's mass as its speed nears light speed.
• Mass-energy equivalence is expressed as E=mc², with E for energy, m for mass, and c for light speed.
• General relativity, published in 1915, describes gravity as the curvature of spacetime caused by mass and energy, rather than as a force.
• Key concepts include the principle of equivalence, spacetime curvature, and gravitational waves.
• The principle of equivalence says the effects of gravity are indistinguishable from the effects of acceleration.
• Spacetime curvature refers to the distortion of space and time caused by mass and energy.
• Gravitational waves are ripples in spacetime from accelerating masses.
• General relativity predicts the bending of light around massive objects, black holes, and the expansion of the universe.
• Tests of general relativity include observing the precession of Mercury's orbit and detecting gravitational waves by LIGO and Virgo.
• Understanding cosmology, astrophysics, and gravity's behavior in extreme conditions relies on general relativity.

Atomic Physics

• Atomic physics focuses on the structure and behavior of atoms.
• The study of electrons, atomic nuclei, and their interactions falls under atomic physics.
• Atomic spectra, electron configurations, and quantum numbers are central concepts.
• Atomic spectra refers to the patterns of electromagnetic radiation emitted or absorbed by atoms.
• Electron configurations describe how electrons arrange in an atom's energy levels and orbitals.
• Quantum numbers describe an electron's properties in an atom, like energy, angular momentum, and spin.
• The periodic table organizes elements by atomic number and electron configurations.
• Chemistry, materials science, and technologies such as atomic clocks and lasers rely on atomic physics.

Nuclear Physics

• Nuclear physics is the study of atomic nuclei's structure, properties, and interactions.
• Investigating nuclear forces, radioactivity, nuclear reactions, and nuclear structure models are part of nuclear physics.
• Nuclear forces hold protons and neutrons (nucleons) together in the nucleus.
• Radioactivity is the spontaneous emission of particles or energy from unstable nuclei.
• Nuclear reactions involve changes in the composition or energy of atomic nuclei, like fission and fusion.
• Nuclear structure models describe how protons and neutrons arrange within the nucleus.
• Isotopes, nuclear binding energy, and nuclear decay modes are key concepts.
• Isotopes are atoms with the same number of protons but different numbers of neutrons.
• Nuclear binding energy is the energy needed to separate a nucleus into its protons and neutrons.
• Alpha decay, beta decay, and gamma decay are examples of nuclear decay modes.
• Nuclear physics is crucial for understanding nuclear energy, nuclear medicine, and the origin of elements.

Particle Physics

• Particle physics, or high-energy physics, studies the fundamental particles and forces that make up the universe.
• The properties and interactions of elementary particles, like quarks, leptons, and bosons, are investigated.
• The Standard Model describes the known fundamental particles and forces, including the strong, weak, and electromagnetic forces.
• Quarks make up protons and neutrons.
• Leptons, like electrons and neutrinos, don't experience the strong force.
• Bosons mediate the fundamental forces.
• The Higgs boson is associated with the Higgs field, which gives mass to other particles.
• Particle accelerators like the Large Hadron Collider (LHC) create high-energy collisions to produce new particles and test the Standard Model's predictions.
• Particle interactions, conservation laws, and symmetry principles are key concepts.
• Particle interactions involve exchanging force-carrying particles between interacting particles.
• Conservation laws state that energy, momentum, and electric charge are conserved in particle interactions.
• Symmetry principles, like charge-parity-time (CPT) symmetry, explain particles' behavior and interactions.
• Particle physics seeks to answer fundamental questions about the origin, evolution, and composition of the universe.

Cosmology

• Cosmology studies the origin, evolution, and large-scale structure of the universe.
• Physics, astronomy, and mathematics are combined to understand the universe's past, present, and future.
• The Big Bang theory describes the universe expanding from an extremely hot, dense state about 13.8 billion years ago.
• The cosmic microwave background radiation (CMB), the abundance of light elements, and the observed expansion of the universe support the Big Bang theory.
• The CMB is the afterglow of the Big Bang, a faint radiation that permeates the universe.
• The abundance of light elements like hydrogen and helium aligns with predictions from Big Bang nucleosynthesis.
• The redshift of distant galaxies evidences the universe's expansion.
• Dark matter and dark energy are significant, unobservable parts of the universe.
• Dark matter accounts for about 27% of the universe's total mass-energy content.
• Dark energy is causing the expansion of the universe to accelerate.
• Cosmological models like the Lambda-CDM model use dark matter, dark energy, and other components to describe the universe's structure and evolution.
• Inflation is a period of early, rapid expansion which smoothed out the universe and seeded the formation of large-scale structures.
• Understanding the formation of galaxies, galaxy clusters, and other large-scale structures, as well as the universe's fate, is the goal of cosmology.