Quantum Theory Cannot Hurt You_ A Guide to the Universe - Marcus Chown [75]
BOSON A microscopic particle with integer spin—that is, 0 units, 1 unit, 2 units, and so on. By virtue of their spin, such particles are hugely gregarious, participating in collective behaviour that leads to lasers, superfluids, and superconductors.
BOYLE’S LAW The observation that the volume of a gas is inversely proportional to its pressure—that is, doubling the pressure halves the volume.
BROWNIAN MOTION The random, jittery motion of a large body under machine-gun bombardment from smaller bodies. The most famous instance is of pollen grains zigzagging through water as they are repeatedly hit by water molecules. The phenomenon, discovered by botanist Robert Brown in 1827 and triumphantly explained by Einstein in 1905, was powerful proof of the existence of atoms.
CAUSALITY The idea that a cause always precedes an effect. Causality is a much-cherished principle in physics. However, quantum events such as the decay of atoms appear to be effects with no prior cause.
CHANDRASEKHAR LIMIT The largest possible mass for a white dwarf. It depends on a star’s chemical composition, but for a white dwarf made of helium it is about 44 per cent more massive than the Sun. For a star bigger than this, the electron degeneracy pressure inside is insufficient to prevent gravity from crushing the star farther.
CHARGE-COUPLED DEVICE (CCD) Supersensitive electronic light detector that can register close to 100 per cent of the light that falls on it. Since photographic plates register a mere 1 per cent, CCDs allow a telescope to perform as well as a telescope with 100 times the light-collecting area.
CHEMICAL BOND The “glue” that sticks atoms together to make molecules.
CHRONOLOGY PROTECTION CONJECTURE The stricture that time travel is impossible. No one has yet managed to prove it—in fact, the laws of physics appear to permit time travel—but physicists such as Stephen Hawking remain convinced that some, as-yet-undiscovered law of nature forbids time machines.
CLASSICAL PHYSICS Nonquantum physics. In effect, all physics before 1900 when the German physicist Max Planck first proposed that energy might come in discrete chunks, or quanta. Einstein was the first to realise that this idea was totally incompatible with all physics that had gone before.
CLOSED TIME-LIKE CURVE (CTC) Region of space-time so dramatically warped that time loops back on itself in much the same way that space loops back on itself on an athletics track. A CTC, in common parlance, is a time machine. It is permitted to exist by the current laws of physics.
COMET Small icy body—usually mere kilometres across—that orbits a star. Most comets orbit the Sun beyond the outermost planets in an enormous cloud known as the Oort Cloud. Like asteroids, comets are builders’ rubble left over from the formation of the planets.
COMPTON EFFECT The recoil of an electron when exposed to high-energy light just as if the electron is a tiny billiard ball struck by another tiny billiard ball. The effect is a graphic demonstration that light is ultimately made of tiny bulletlike particles, or photons.
CONDUCTOR A material through which an electrical current can flow.
CONSERVATION LAW Law of physics that expresses the fact that a quantity can never change. For instance, the conservation of energy states that energy can never be created or destroyed, only converted from one form to another. For example, the chemical energy of petrol can be converted into the energy of motion of a car.
CONSERVATION OF ENERGY Principle that energy can never be created or destroyed, only converted from one form to another.
COOPER PAIR Two electrons with opposite spin that pair up in some metals at extremely low temperature. Cooper pairs, unlike individual electrons, are bosons. Consequently, they can crowd into the same state, moving together in lockstep through