Glossary of terms
Absolute Zero: Defined as 0K or -273 o Celsius.
Acceleration: The change in velocity of an object, v - u.
Antiparticle: The opposite of a particle, sometimes referred to as 'anti - matter'. If a particle meets an antiparticle they annihilate eachother.
Asymptotic freedom: As high energies are applied to particles, quarks and gluons behave like free particles due to the weakening of the strong force. Normally quarks and gluons would not be found in isolation, and the condition is only temporary while the energy is being applied.
Atom: Particle made up of protons, neutrons and orbiting electrons. The protons and neutrons make up the atom's nucleons.
Big Bang: Presumed singularity of infinite density that resulted in the formation and expansion of the observed universe.
Big Crunch: Possible singularity at which the universe may arrive at its demise, after contraction.
Black Hole: Collapsed star or other object that creates a singularity from which light or anything else cannot escape, as the escape velocity required exceeds the speed of light, c.
Doppler Effect: The relationship between frequency and speed, e.g. A siren will sound at a low pitch (frequency) at a distance, which rises to a high pitch as it comes nearer, then descends back to a low pitch as the source moves away again. Light and radio waves also behave in this way.
Electric Charge: Property of particles such that they attract or repel eachother - opposite charges attract, likes repel - assigned positive or negative values.
Electromagnetic Force: The force that arises between particles with electric charge, either attractive (+ve and -ve), or repulsive between like charges.
Electron: Negatively charged particle orbiting the nucleus of an atom.
Electroweak unification energy: Energy level c. 100 GeV above which distinction between electromagnetic force and weak nuclear force disappears.
Energy to mass equivalence: E = mc2 This law disallows speeds exceeding the speed of light. Because of the equivalence of energy and mass, the energy of motion a body has will add to its mass. If its energy of motion exceeds c, its gravity of mass will form a singularity, as no repulsive force would be strong enough to stop its collapse.
Entropy: Chaos increases as the time elapsed or the size of an isolated system increases.
Event: A point in space time specified by its time and place which are given as coordinates.
Event Horizon: Boundary of space - time from which escape is impossible, as required escape velocity exceeds c, which is disallowed. This is the region around a black hole.
Exclusion Principle: All matter particles obey Pauli's exclusion principle. Similar particles cannot exist in the same state - same position and velocity, within the limits of the uncertainty principle. This is why matter doesn't collapse under imposed forces. If matter particles are in nearly the same position, then their velocities must differ. The force carrying particles of integer spin do not obey the exclusion principle. Exchanged force carrying particles are termed 'virtual' particles because they cannot be observed directly, as yet.
Field: A field exists throughout space and time, unlike a particle, which only exists at 1 point at a time.
Fission, nuclear: The splitting of a nucleus by neutrons resulting in the formation of 2 or more new nuclei, a release of consumed mass as heat energy and radiation. The reaction of a neutron and a nucleus of U235 is:
General Relativity: The speed of light is constant regardless of the position or motion of the observer. Gravity is a force that is caused by the curvature of space, which in turn is caused by the distribution of masses and energies within it. Gravity will act on a light ray and deflect it inward. Time is not absolute and is dependant on position (Twins paradox). While this theory did away with absolute time, so too Newton's Laws of Motion abolished absolute position. Thus, the laws of science hold regardless of an observer's motion.
Geodesic: The shortest distance between 2 points, e.g. through curved space, or conversely the longest path between points.
GeV: Giga electron volt. Energy gained by electron from field of 1V = 1eV x 109. 1 eV = 1.602 x 10 -13 J. So a 100 W light bulb would give out c. 6.25 x 1012 eV / s. Energies from electron transitions producing spectral lines are only a few eVs, and 13.6 eV will knock the electron from a hydrogen atom. Energy from radioactive particles are typically c. a few to several million eVs.
Gravity: The formula for gravitational force is
F = G x M1M2 / r2.
For the earth g = 9.8 m/s. The earth's mass is given by m = gR2 / G
where R = 6.37 x 106m, G = 6.67 x 10 -11m3s -2kg -1
= 5.96 x 1024kg
h = 6.7 x 10 -34J/s
(Height of wave)2 = Intensity
Heisenberg's Uncertainty Priciple: Uncertainty in position of particle x Uncertainty in motion (velocity) x Mass = > Planck's Constant.
Imaginary Numbers: Form of root -1, denoted i, which when squared gives a negative number, e.g. 2 root i2 = -4. Complex numbers of form x + root -1y where y is multiplied by the imaginary number i can be multiplied, added or subtracted in the normal way by substituting (i)2 for i.
Imaginary Time: Measured in imaginary numbers. It is thought that if time could be run backward from the present (ignoring the entropy law of thermodynamics) that an object would return to previous states. Imaginary time disallows space-time singularities or boundaries. Imaginary time is synonymous with spatial direction where one may go forward or backward. Real time in contrast does not obey the symmetry T, because of entropy.
Infinite Density: The point at which the gravitational attraction of matter exceeds c, e.g. collapsed stars forming black holes.
Lifecycle - stars: Hydrogen and other gases collapse inward due to gravity. The pressure and temperature rise as atomic kinetic energy increases. When it gets hot enough, the hydrogen atoms no longer rebound, but coalesce into helium. Eventually, pressure balances gravity, and the star is stable. However, it must consume its mass in order to maintain equilibrium. When its fuel runs out it starts to contract again, possibly overcoming the limit to repulsion provided by the exclusion principle, as the difference in velocities of the matter particles cannot exceed the speed of light. Density and gravity would not be balanced by repulsion. The greater the mass, the more energy needed maintain equilibrium and the shorter its lifespan. Eventually, if massive enough, it would collapse to infinite density. Light would no longer be able to escape the gravity. A black hole would be formed, with the event horizon coinciding with the paths of light rays just failing to escape.
Light cone: A surface boundary marking out all possible directions for light rays passing through an event.
Light Year / second: The distance it takes for light to travel (through a vacuum or air) in 1 year / second.
Massive Vector Boson: A particle carrying weak nuclear force that can act only on matter particles of spin 1/2. These spin 1 particles are W-, Zo and W+, each of mass c. 100 GeV.
Microwave background radiation: The radiation from the early universe, so red - shifted it appears as microwaves rather than light waves.
Naked singularity: A space - time singularity without a black hole.
Neutrino: Massless or near massless particle that is only affected by weak nuclear force or gravity.
Neutron: 0 charge particle in nucleus.
Neutron Star: A cold star supporting its mass through the exclusion principle of repulsion acting between its neutrons and protons.
No Boundary Condition: The idea of the universe as being finite, but having no boundary in imaginary time - like a sphere or ovoid.
Particle accelerator: A machine that uses electromagnets to accelerate moving charged particles.
Period - Doubling: The route to chaotic behaviour in a system sensitive to initial conditions. In order to predict the state of the system over time, all variables at its initial state must be known to an infinite degree of accuracy, which is impossible. An example of chaos troubling to physicists and others is fluid dynamics. Brownian motion is an example of chaotic motion of particles. It is almost impossible to predict the random motion of fluids or model this. Chaos is found in all systems from the simplest to the most complex involving many factors. Chaos is generally characterised by non - linear behaviour, put simply, disorder and randomness.
Phase - waves: The position in a wave cycle at a given moment i.e. - a crest, trough or some point between.
Phase - general: State - solid, liquid, gas
Photon: A quanta of light
Planck's Constant: E = hv, where v is frequency, and h is Planck's constant at 6.55 x 10 -27 erg seconds. hv is a 4 - dimensional mapping of the energy of a particle. An energy level of 1018GeV cannot be exceeded as the particle would form a black hole.
Positron: The antiparticle of an electron
Proton: Positively charged particle in a nucleus
Pulsar: Neutron star that emits regular pulses of radio waves.
Quanta / quantum: Discrete packet/s of wave energy. Energy needed for emission of a quanta is proportional to frequency (rather than amplitude). The higher the frequency, the higher the energy.
Quarks: Charged particles affected by strong nuclear force. The 6 types are up, down, top, bottom, strange and charmed. A proton has 2 up and 1 down quark, a neutron has 2 down and 1 up. Particles made up of the other types tend to have mass and decay to protons and neutrons.
Quasars: Galaxy whose central region has collapsed to form huge black hole, whose mass would be possibly c. 100 million times the sun's mass.
Red Shift: As a distant body emitting energy waves moves further away, its energy will show up as red - shifted on the electromagnetic spectrum. If the body were moving closer, its energy would tend more toward a blue - shift. This is because the wavelength increases, going from violet to red.
Singularity: Region of infinite density
Special Relativity: As nothing can exceed the speed of light which is constant at any event and in any direction, the set of all possible paths of light emitted into space - time by an event form a light cone identical and pointing in the same direction as all the light cones. The path of an object must be a straight line within a light cone for every event on it. Special relativity ignores gravitational effects, whereas general relativity takes these into account.
Speed of Light, c: 1m per 0.000000003335640952 seconds or 3 x 108 m/s. Its frequencies range from c. 4 - 7 hundred million million waves p/s. Its wavelengths vary between 40 - 80 millionths cm.
Spin Particles: Both matter and energy can be described in terms of particles. Particles have an inherant property - spin. Particles of spin 1/2 make up matter, e.g. electrons have spin 1/2, which can be either +1/2h or -1/2h depending on conditions. Particles of 0, 1 and 2 give rise to forces between matter particles. See also exclusion principle. Force carrying particles are classified as gravitational (gravitons), electromagnetic (electrons, photons and quarks, etc), weak nuclear (massive vector bosons), and the strong nuclear (gluons) that 'glue' the protons, neutrons and quarks in the nucleus. The strong force always glues particles into combinations that have no colour. A string of quarks and gluons in R,G,B combination forms a proton or neutron. A quark and antiquark combination forms a meson. A string of glouns without anything else is a glueball. Mesons and glueballs are unstable. Lone quarks or gluons are disallowed because of the confinement property.
Spontaneous Symmetry Breaking: The appearance of a particle in different states, giving an illusion of separate particles due to a decrease in energy.
Star: Gaseous body such as the sun, composed mainly of hydrogen, with some other gases.
String Theory: Instead of particles or waves, everything is made up of infinitely thin vibrating strings. They may be close looped or open. A string occupies a line in space at any moment in time. Its history in space - time is represented as its world - sheet, (unlike a particle existing at a point at a given time, whose history would be represented by its world - line). Any point on the world sheet is a coordinate giving the time and the position of the point on the string. Strings can join together forming a composite. String theories along with other theories tend to undergo modification over time.
Sum over history: A particle travels between 2 points by every possible path. Each path is represented by 2 numbers representing the amplitude and phase of a wave. The probability of the particle making the journey from 1 point to the other is found by adding up the waves for all the paths. Some waves will cancel while others reinforce eachother.
Thermodynamics Laws:
Zeroth Law: If A and B are in thermal equilibrium, and B and C are in thermal equilibrium, then A and C are in thermal equilibrium.
1. Energy is neither created nor destroyed, only changed from one form to another. DE = q - w, where DE = change in internal energy of the system, q = applied / removed heat, w = work output from system. (Applies to its mass equiv. also) For a heat engine, Q h = W + Q c.
2. Entropy in a system increases with time. If 2 systems are joined, then combined entropy will be greater than the sum of the original entropies. DS = q / T, where q = heat applied, T = absolute Kelvin temperature, DS = change in state function. Heat cannot flow spontaneously from a cooler body to a warmer body.
3. The higher the temperature, the greater the entropy of the system. As T ---> 0 K, then entropy, s ---> 0.
Entropy = K x log e W
where W is the quantum degeneracy of the system, K is a constant.
Twins Paradox: The idea that time depends on one's position and speed. e.g. 2 twins separate; one goes into space for some years travelling at near light speed, while the other stays on earth. Afterward, they meet up again and the one that stayed on earth would have aged more.
Unification of Physics: The theory that will explain all observed phenomena. At the present, the main problem is to unify relativity (study of the macrocosm) with quantum mechanics (study of the microcosm) in a way that fits observed data.
Variable: Any value that can change. For a rolling ball, the variables may include its 2 spatial coordinates on a plane at a given moment, the 2 variables denoting its direction of axis of spin and 2 for their corresponding speeds, 2 variables for its velocity, making 8 variables in all for a given moment. These may then be plotted on graphs. What we end up with is 8 dimensions, rather than just the usual 3, but each representing numerically a physical quantity.
Virtual Particle: A particle which cannot be observed at present. Their effects on other particles can be observed, as they create quantum fluctuations. A virtual particle may become either a particle or anti-particle if given the right conditions, e.g. a black hole.
Wave / Particle Duality: All particles are waves. The higher the particle's energy, the shorter the wavelength of its wave, (quantum mechanics). Planck's equation E = hv expresses the relationship between the particle's energy, E, the frequency of its wavelength, v, and the coefficient h = 10 -27 erg seconds (units of action).
White Dwarf: Settled state of a star whose mass is less than the Chandresekhar limit. It is supported by the exclusion principle of repulsion acting between the electrons.
World Sheet: String Theory, the history of a string. Sum over history of the string's path through space - time.