Quantum Theory Cannot Hurt You_ A Guide to the Universe - Marcus Chown [82]
QUANTUM THEORY The theory of objects isolated from their surroundings. Because it is very hard to isolate a big object, the theory is essentially a theory of the microscopic world of atoms and their constituents.
QUANTUM TUNNELLING The apparently miraculous ability of microscopic particles to escape their prisons. For instance, an alpha particle can tunnel through the barrier penning it in the nucleus, the equivalent of a high jumper jumping a 4-metre-high wall. Tunnelling is yet another consequence of the wavelike character of microscopic particles.
QUANTUM UNPREDICTABILITY The unpredictability of microscopic particles. Their behaviour is unpredictable even in principle. Contrast this with the unpredictability of a coin toss. It is unpredictable only in practice. In principle, if we knew the shape of the coin, the force exerted on it, the air currents around it, and so on, we could predict the outcome.
QUANTUM VACUUM The quantum picture of empty space. Far from ultra-shorth ultra-short-lived microscopic particles that are permitted by the Heisenberg uncertainty principle to blink into existence and blink out again.
QUASAR A galaxy that derives most of its energy from matter heated to millions of degrees as it swirls into a central giant black hole. Quasars can generate as much light as a hundred normal galaxies from a volume smaller than the solar system, making them the most power-ful objects in the Universe
QUBIT A quantum bit, or binary digit. Whereas a normal bit can only represent a “0” or a “1,” a qubit can exist in a superposition of the two states, representing a “0” and a “1” simultaneously. Because strings of qubits can represent a large number of numbers simultaneously, they can be used to do a large number of calculations simultaneously.
RADIOACTIVE DECAY The disintegration of unstable heavy atomic nuclei into lighter, stabler atomic nuclei. The process is accompanied by the emission of either alpha particles, beta particles, or gamma rays.
RADIOACTIVITY Property of atoms that undergo radioactive decay.
RADIUM Highly unstable, or radioactive, element discovered by Marie Curie in 1898.
RELATIVITY, GENERAL THEORY OF Einstein’s generalisation of his special theory of relativity. General relativity relates what one person sees when looking at another person accelerating relative to them. Because acceleration and gravity are indistinguishable—the principle of equivalence—general relativity is also a theory of gravity.
RELATIVITY, PRINCIPLE OF The observation that all the laws of physics are the same for observers moving at constant speed with respect to each other.
RELATIVITY, SPECIAL THEORY OF Einstein’s theory that relates what one person sees when looking at another person moving at constant speed relative to them. It reveals, among other things, that the moving person appears to shrink in the direction of their motion while their time slows down, effects that become ever more marked as they approach the speed of light.
SCANNING TUNNELLING MICROSCOPE (STM) A device that drags an ultrafine needle across the surface of a material and converts the up-and-down motion of the needle into an image of the atomic landscape of the surface.
SCHRÖDINGER EQUATION Equation that governs the way in which the probability wave, or wave function, describing, say a subatomic particle, changes with time.
SIMULTANEITY The idea that events that appear to happen at the same time for one person should appear to happen at the same time for everyone in the Universe. Special relativity shows that this idea is mistaken.
SINGULARITY Location where the fabric of space-time ruptures and so cannot be understood by Einstein’s theory of gravity, the general theory