Quantum Theory Cannot Hurt You (18 page)

EXOTIC MATTER Hypothetical matter with repulsive gravity.

EXPANDING UNIVERSE The fleeing of the galaxies from each other in the aftermath of the Big Bang.

FERMION A microscopic particle with half-integer spin—that is,
¹
/
₂
unit,
³
/
₂
units,
⁵
/
₂
units, and so on. By virtue of their spin, such particles shun each other. Their unsociability is the reason that atoms exist and the ground beneath our feet is solid.

FRAME DRAGGING The dragging around of space-time by a massive rotating body. The effect is very small—though potentially measurable—in the vicinity of Earth but enormous near a fast-rotating black hole. Such a black hole sits at the eye of a tornado of whirling space-time.

FUNDAMENTAL FORCE One of the four basic forces that are believed to underlie all phenomena. The four forces are the gravitational force, electromagnetic force, strong force, and weak force. The strong suspicion among physicists is that these forces are actually facets of a single superforce. In fact, experiments have already shown the electromagnetic and weak forces to be different sides of the same coin.

FUNDAMENTAL PARTICLE One of the basic building blocks of all matter. Currently, physicists believe there are six different quarks and six different leptons, making a total of 12 truly fundamental particles. The hope is that the quarks will turn out to be merely different faces of the leptons.

FUSION See Nuclear Fusion.

GALAXY One of the basic building blocks of the Universe. Galaxies are great islands of stars. Our own island, the Milky Way, is spiral in shape and contains about 200,000 million stars.

GAS Collection of atoms that fly about through space like a swarm of tiny bees.

GENERAL THEORY OF RELATIVITY Einstein’s theory of gravity that shows gravity to be nothing more than the warpage of spacetime. The theory incorporates several ideas that were not incorporated in Newton’s theory of gravity. One was that nothing, not even gravity, can travel faster than light. Another was that all forms of energy have mass and so are sources of gravity. Among other things, the theory predicted black holes, the expanding Universe, and that gravity would bend the path of light.

GEODESIC The shortest path between two points in warped, or curved, space.

GRAVITATIONAL FORCE The weakest of the four fundamental forces of nature. Gravity is approximately described by Newton’s universal law of gravity but more accurately described by Einstein’s theory of gravity—the general theory of relativity. General relativity breaks down at the singularity at the heart of a black hole and the singularity at the birth of the Universe. Physicists are currently looking for a better description of gravity. The theory, already dubbed quantum gravity, will explain gravity in terms of the exchange of particles called gravitons.

GRAVITATIONAL LIGHT BENDING The bending of the trajectory of light that passes by a massive body. Because the space in the
vicinity of such a body is warped like a valley, the light has no choice but to travel along a curved path.

GRAVITATIONAL RED SHIFT The loss of energy as light climbs out of the valley in space-time around a massive celestial body. Since the “colour” of light is related to its energy, with red light having less energy than blue light, astronomers talk of light being shifted to the red end of the spectrum or “red-shifted.”

GRAVITATIONAL WAVE A ripple spreading out through spacetime. Gravitational waves are generated by violent motions of mass, such as the merger of black holes. Because they are weak, they have not yet been detected directly.

GRAVITY See Gravitational Force.

HALF-LIFE The time it takes half the nuclei in a radioactive sample to disintegrate. After one half-life, half the atoms will be left; after two half-lives, a quarter; after three, an eighth, and so on. Half-lives can vary from the merest split-second to many billions of years.

HEISENBERG UNCERTAINTY PRINCIPLE A principle of quantum theory that there are pairs of quantities such as a particle’s location and speed that cannot simultaneously be known with absolute precision. The uncertainty principle puts a limit on how well the product of such a pair of quantities can be known. In practice, this means that if the speed of a particle is known precisely, it is impossible to have any idea where the particle is. Conversely, if the location is known with certainty, the particle’s speed is unknown. By limiting what we can know, the Heisenberg uncertainty principle imposes “fuzziness” on nature. If we look too closely, everything blurs like a newspaper picture dissolving into meaningless dots.

HELIUM Second lightest element in nature and the only one to have been discovered on the Sun before it was discovered on Earth. Helium is the second most common element in the Universe after hydrogen, accounting for about 10 per cent of all atoms.

HORIZON The Universe has a horizon much like the horizon that surrounds a ship at sea. The reason for the Universe’s horizon is that light has a finite speed and the Universe has been in existence for only a finite time. This means that we only see objects whose light has had time to reach us since the Big Bang. The observable universe is therefore like a bubble centred on Earth, with the horizon being the surface of the bubble. Every day the Universe gets older (by one day), so every day the horizon expands outwards and new things become visible, just like ships coming over the horizon at sea.

HORIZON PROBLEM The problem that far-flung parts of the Universe that could never have been in contact with each other, even in the Big Bang, have almost identical properties such as density and temperature. Technically, they were always beyond each other’s horizon. The theory of inflation provides a way for such regions to have been in contact in the Big Bang and so can potentially solve the horizon problem.

HYDROGEN The lightest element in nature. A hydrogen atom consists of a single proton orbited by a single electron. Close to 90 per cent of all atoms in the Universe are hydrogen atoms.

HYDROGEN BURNING The fusion of hydrogen into helium accompanied by the liberation of large quantities of nuclear binding energy. This is the power source of the Sun and most stars.

HYDROSTATIC EQUILIBRIUM The state in which the gravitational force trying to crush a star is perfectly balanced by the force of its hot gas pushing outwards.

INERTIA The tendency for a massive body, once set in motion, to keep on moving, at constant speed in a straight line in unwarped space and along a geodesic in warped space. Nobody knows the origin of inertia.

INERTIAL FORCE A force we invent to explain a motion that is actually due to nothing more than inertia. A good example is centrifugal force. There is no such force flinging us outwards in a car rounding a sharp corner. We are simply continuing to move in a straight line because of our inertia, and the interior of the car, because it is moving along a curved path, intercepts us.

INFLATION, THEORY OF Idea that in the first split-second of its creation the Universe underwent a fantastically fast expansion. In a sense, inflation preceded the conventional Big Bang explosion. If the Big Bang is likened to the explosion of a grenade, inflation was like the explosion of an H-bomb. Inflation can solve some problems with the Big Bang theory such as the horizon problem.

INFRARED Type of invisible light that is given out by warm bodies.

INTERFERENCE The ability of two waves passing through each other to mingle, reinforcing where their peaks coincide and cancelling where the peaks of one coincide with the troughs of another.

INTERFERENCE PATTERN Pattern of light and dark stripes that appears on a screen illuminated by light from two sources. The pattern is due to the light from the two sources reinforcing at some places on the screen and cancelling at other places.

INTERSTELLAR MEDIUM The tenuous gas and dust floating between the stars. In the vicinity of the Sun this gas comprises about one hydrogen atom in every 3 cubic centimetres, making it a vacuum far better than anything achievable on Earth.

INTERSTELLAR SPACE The space between the stars.

ION An atom or molecule that has been stripped of one or more of its orbiting electrons and so has a net positive electrical charge.

ISOTOPE One possible form of an element. Isotopes are distinguishable by their differing masses. For instance, chlorine comes in two stable isotopes, with a mass of 35 and 37. The mass difference is due to a differing number of neutrons in their nuclei. For instance, chlorine-35 contains 18 neutrons and chlorine-37 contains 20 neutrons. (Both contain the same number of protons—17—since this determines the identity of an element.)

JOULE The standard scientific unit of energy. The energy of motion of a flying cricket ball is about 10 joules; the chemical energy provided by a single slice of bread is about 100,000 joules; and the electrical energy of a lightning discharge is about 10 billion joules.

LAMBDA POINT Temperature below which liquid helium begins to turn into a superfluid.

LASER Light source in which the gregarious nature of photons—bosons—comes to the fore. Specifically, the more photons there are passing through a material the greater the probability that other atoms will emit others with the same properties. The result is an avalanche of photons all travelling in lockstep.

LIGHT, CONSTANCY OF The peculiarity that in our Universe the speed of light in empty space is always the same, irrespective of the speed of the source of light or of anyone observing the light. This is one of two cornerstones of Einstein’s special theory of relativity, the other being the principle of relativity.

LIGHT, SPEED OF The cosmic speed limit—300,000 kilometres per second.

LIGHT BENDING See Gravitational Light Bending.

LIGHT-YEAR Convenient unit for expressing distances in the Universe. It is simply the distance that light travels in one year in a vacuum, which turns out to be 9.46 trillion kilometres.

LORENTZ CONTRACTION The contraction of a body moving relative to an “observer.” The observer sees the body shrink in the direction of its motion. The effect is noticeable only when the body is moving close to the speed of light with respect to the observer.

LUMINOSITY The total amount of light pumped into space each second by a celestial body such as a star.

MAGNETIC FIELD The field of force that surrounds a magnet.

MANY WORLDS The idea that quantum theory describes everything, not simply the microscopic world of atoms and their constituents. Since quantum theory permits an atom to be in two places at once, this must mean that a table can be in two places at once. According to the Many Worlds idea, however, the mind of the person observing the table splits into two—one that perceives the table to be in one place and another that perceives it to be in another. The two minds exist in separate realities, or universes.

MASS A measure of the amount of matter in a body. Mass is the most concentrated form of energy. A single gram contains the same amount of energy as 100,000 tonnes of dynamite.

MAXWELL’S EQUATIONS OF ELECTROMAGNETISM The handful of elegant equations, written down by James Clerk Maxwell in
1868, that neatly summarise all electrical and magnetic phenomena. The equations reveal that light is an electromagnetic wave.

MILKY WAY Our galaxy.

MOLECULE Collection of atoms glued together by electromagnetic forces. One atom, carbon, can link with itself and other atoms to make a huge number of molecules. For this reason, chemists divide molecules into “organic”—those based on carbon—and “inorganic”—the rest.

MOMENTUM The momentum of a body is a measure of how much effort is required to stop it. For instance, an oil tanker, even though it may be going at only a few kilometres an hour, is far harder to stop than a Formula 1 racing car going 200 kilometres per hour. The oil tanker is said to have more momentum.

MOMENTUM, CONSERVATION OF Principle that momentum can never be created or destroyed.

MULTIVERSE Hypothetical enlargement of the cosmos in which our Universe turns out to be one among an enormous number of separate and distinct universes. Most universes are dead and uninteresting. Only in a tiny subset do the laws of physics promote the emergence of stars, planets, and life.

MUON Short-lived subatomic particle that behaves like a heavy version of the electron.

NEUTRINO Neutral subatomic particle with a very small mass that travels very close to the speed of light. Neutrinos, of which there are three kinds, hardly ever interact with matter. However, when created in huge numbers, they can blow a star apart in a supernova.

NEUTRON One of the two main building blocks of the atomic nucleus at the centre of atoms. Neutrons have essentially the same mass as protons but carry no electrical charge. They are unstable outside of a nucleus and disintegrate in about 10 minutes.

NEUTRON STAR A star that has shrunk under its own gravity to such an extent that most of its material has been compressed into neutrons. Typically, such a star is only 20 to 30 kilometres across. A sugar cube of neutron star stuff would weigh as much as the entire human race.

NEWTON’S UNIVERSAL LAW OF GRAVITY The idea that all bodies pull on each other across space with a force that depends on the product of their individual masses and the inverse square of their distance apart. In other words, if the distance between the bodies is doubled, the force becomes four times weaker; if it is tripled, nine times weaker; and so on. Newton’s theory of gravity is perfectly good for everyday applications but turns out to be an approximation. Einstein provided an improvement in the general theory of relativity.

NONLOCALITY The spooky ability of objects subject to quantum theory to continue to “know” about each other’s state even when separated by a large distance.

NUCLEAR ENERGY The excess energy released when one atomic nucleus changes into another atomic nucleus.

NUCLEAR FUSION The welding together of two light nuclei to make a heavier nucleus, a process that results in the liberation of nuclear binding energy. The most important fusion process for human beings is the gluing together of hydrogen nuclei to make helium in the core of the Sun since its by-product is sunlight.