Frequently Asked Questions in Cosmology Tutorial : Part 1 | Part 2 | Part 3 | Part 4 | Age | Distances | Bibliography | Relativity What is the currently most accepted model for the Universe? The current best fit model is a flat ΛCDM Big Bang model where the expansion of the Universe is accelerating, and the age of the Universe is 13.7 billion years. Back to top. What is the evidence for the Big Bang? The evidence for the Big Bang comes from many pieces of observational data that are consistent with the Big Bang. The darkness of the night sky - Olbers' paradox. Why do we think that the expansion of the Universe is accelerating? The evidence for an accelerating expansion comes from observations of the brightness of distant supernovae. What is quintessence? Quintessence, or the fifth essence, is a fifth element beyond the standard earth, air, fire and water of ancient chemistry. If the Universe is only 14 billion years old, why isn't the most distant object we can see 7 billion light years away? What is the redshift?
Ionization Process by which atoms or molecules acquire charge by gaining or losing electrons Ionization (or ionisation) is the process by which an atom or a molecule acquires a negative or positive charge by gaining or losing electrons, often in conjunction with other chemical changes. The resulting electrically charged atom or molecule is called an ion. Ionization can result from the loss of an electron after collisions with subatomic particles, collisions with other atoms, molecules and ions, or through the interaction with electromagnetic radiation. Uses[edit] Everyday examples of gas ionization are such as within a fluorescent lamp or other electrical discharge lamps. Production of ions[edit] Negatively charged ions are produced when a free electron collides with an atom and is subsequently trapped inside the electric potential barrier, releasing any excess energy. Adiabatic ionization[edit] Ionization energy of atoms[edit] Semi-classical description of ionization[edit] Tunnel ionization[edit] where
List of particles List of particles in matter including fermions and bosons This is a list of known and hypothesized particles. Standard Model elementary particles[edit] Fermions[edit] Fermions are one of the two fundamental classes of particles, the other being bosons. Fermion particles are described by Fermi–Dirac statistics and have quantum numbers described by the Pauli exclusion principle. Fermions have half-integer spin; for all known elementary fermions this is 1⁄2. Quarks[edit] Leptons[edit] ^ A precise value of the electron mass is 0.51099895000(15) MeV/c2.[6]^ A precise value of the muon mass is 105.6583755(23) MeV/c2.[7] Bosons[edit] Bosons are one of the two fundamental particles having integral spinclasses of particles, the other being fermions. According to the Standard Model, the elementary bosons are: The Higgs boson is postulated by the electroweak theory primarily to explain the origin of particle masses. Hypothetical particles[edit] Graviton[edit] Other hypothetical bosons and fermions[edit]
Ununoctium The radioactive ununoctium atom is very unstable, due to its high mass, and since 2005, only three or possibly four atoms of the isotope 294Uuo have been detected.[12] While this allowed for very little experimental characterization of its properties and possible compounds, theoretical calculations have resulted in many predictions, including some unexpected ones. For example, although ununoctium is a member of Group 18, it may possibly not be a noble gas, unlike all the other Group 18 elements.[1] It was formerly thought to be a gas but is now predicted to be a solid under normal conditions due to relativistic effects.[1] History[edit] Unsuccessful synthesis attempts[edit] In late 1998, Polish physicist Robert Smolańczuk published calculations on the fusion of atomic nuclei towards the synthesis of superheavy atoms, including ununoctium.[13] His calculations suggested that it might be possible to make ununoctium by fusing lead with krypton under carefully controlled conditions.[13]
Plasma (physics) State of matter Early history Except near the electrodes, where there are sheaths containing very few electrons, the ionized gas contains ions and electrons in about equal numbers so that the resultant space charge is very small. We shall use the name plasma to describe this region containing balanced charges of ions and electrons. Definitions The fourth state of matter Plasma is distinct from the other states of matter. Ideal plasma Non-neutral plasma Dusty plasma Properties and parameters Density and ionization degree For plasma to exist, ionization is necessary. , that is, the number of charge-contributing electrons per unit volume. is defined as fraction of neutral particles that are ionized: where is the ion density and the neutral density (in number of particles per unit volume). . , where is the average ion charge (in units of the elementary charge). Temperature Plasma potential Since plasmas are very good electrical conductors, electric potentials play an important role. Magnetization Fluid model
Antimatter In modern physics, antimatter is defined as a material composed of the antiparticle (or "partners") to the corresponding particles of ordinary matter. In theory, a particle and its anti-particle (e.g., proton and antiproton) have the same mass as one another, but opposite electric charge and other differences in quantum numbers. For example, a proton has positive charge while an antiproton has negative charge. A collision between any particle and its anti-particle partner is known to lead to their mutual annihilation, giving rise to various proportions of intense photons (gamma rays), neutrinos, and sometimes less-massive particle–antiparticle pairs. Annihilation usually results in a release of energy that becomes available for heat or work. The amount of the released energy is usually proportional to the total mass of the collided matter and antimatter, in accordance with the mass–energy equivalence equation, E = mc2.[1] Formal definition[edit] History of the concept[edit] Notation[edit]
Electromagnetic radiation The electromagnetic waves that compose electromagnetic radiation can be imagined as a self-propagating transverse oscillating wave of electric and magnetic fields. This diagram shows a plane linearly polarized EMR wave propagating from left to right. The electric field is in a vertical plane and the magnetic field in a horizontal plane. The two types of fields in EMR waves are always in phase with each other with a fixed ratio of electric to magnetic field intensity. Electromagnetic radiation (EM radiation or EMR) is a form of radiant energy, propagating through space via electromagnetic waves and/or particles called photons. In classical physics, EMR is considered to be produced when charged particles are accelerated by forces acting on them. EMR carries energy—sometimes called radiant energy—through space continuously away from the source (this is not true of the near-field part of the EM field). Physics[edit] Theory[edit] Maxwell’s equations for EM fields far from sources[edit]
Ion Particle, atom or molecule with a net electrical charge An ion ()[1] is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by convention. A cation is a positively charged ion with fewer electrons than protons[2] while an anion is a negatively charged ion with more electrons than protons.[3] Opposite electric charges are pulled towards one another by electrostatic force, so cations and anions attract each other and readily form ionic compounds. History of discovery The word ion was coined from Greek neuter present participle of ienai (Greek: ἰέναι), meaning "to go". Characteristics Ions in their gas-like state are highly reactive and will rapidly interact with ions of opposite charge to give neutral molecules or ionic salts. Anions and cations Anion (−) and cation (+) indicate the net electric charge on an ion. Chemistry
Lepton A lepton is an elementary, spin-1⁄2 particle that does not undergo strong interactions, but is subject to the Pauli exclusion principle.[1] The best known of all leptons is the electron, which governs nearly all of chemistry as it is found in atoms and is directly tied to all chemical properties. Two main classes of leptons exist: charged leptons (also known as the electron-like leptons), and neutral leptons (better known as neutrinos). Charged leptons can combine with other particles to form various composite particles such as atoms and positronium, while neutrinos rarely interact with anything, and are consequently rarely observed. The first charged lepton, the electron, was theorized in the mid-19th century by several scientists[3][4][5] and was discovered in 1897 by J. J. Thomson.[6] The next lepton to be observed was the muon, discovered by Carl D. Leptons are an important part of the Standard Model. Etymology[edit] Following a suggestion of Prof. History[edit] Properties[edit]
Radiation Illustration of the relative abilities of three different types of ionizing radiation to penetrate solid matter. Typical alpha particles (α) are stopped by a sheet of paper, while beta particles (β) are stopped by an aluminium plate. Gamma radiation (γ) is damped when it penetrates lead. Note caveats in the text about this simplified diagram. In electromagnetic radiation (such as microwaves from an antenna, shown here) the term "radiation" applies only to the parts of the electromagnetic field that radiate into infinite space and decrease in intensity by an inverse-square law of power so that the total radiation energy that crosses through an imaginary spherical surface is the same, no matter how far away from the antenna the spherical surface is drawn. Gamma rays, x-rays and the higher energy range of ultraviolet light constitute the ionizing part of the electromagnetic spectrum. Ionizing radiation[edit] Ultraviolet radiation[edit] Main article: Ultraviolet X-ray[edit] Beta radiation[edit]