Quantum Theory Cannot Hurt You_ A Guide to the Universe - Marcus Chown [74]
ALPHA CENTAURI The nearest star system to the Sun. It consists of three stars and is 4.3 light-years distant.
ALPHA DECAY The spitting out of a high-speed alpha particle by a large, unstable nucleus in an attempt to turn itself into a lighter, stable nucleus.
ALPHA PARTICLE A bound state of two protons and two neutrons—essentially a helium nucleus—that rockets out of an unstable nucleus during radioactive alpha decay.
ANTHROPIC PRINCIPLE The idea that the Universe is the way it is because, if it was not, we would not be here to notice it. In other words, the fact of our existence is an important scientific observation.
ANTIMATTER Term for a large accumulation of antiparticles. Anti-protons, antineutrons, and positrons can in fact come together to make anti-atoms. And there is nothing in principle to rule out the possibility of antistars, antiplanets, or antilife. One of the greatest mysteries of physics is why we appear to live in a Universe made solely of matter when the laws of physics seem to predict a pretty much 50/ 50 mix of matter and antimatter.
ANTIPARTICLE Every subatomic particle has an associated antiparticle with opposite properties, such as electrical charge. For instance, the negatively charged electron is twinned with a positively charged antiparticle known as the positron. When a particle and its antiparticle meet, they self-destruct, or “annihilate,” in a flash of high-energy light, or gamma rays.
ATOM The building block of all normal matter. An atom consists of a nucleus orbited by a cloud of electrons. The positive charge of the nucleus is exactly balanced by the negative charge of the electrons. An atom is about one 10-millionth of a millimetre across.
ATOMIC ENERGY See Nuclear Energy.
ATOMIC NUCLEUS The tight cluster of protons and neutrons (a single proton in the case of hydrogen) at the centre of an atom. The nucleus contains more than 99.9 per cent of the mass of an atom.
BIG BANG The titanic explosion in which the Universe is thought to have been born 13.7 billion years ago. “Explosion” is actually a misnomer since the Big Bang happened everywhere at once and there was no preexisting void into which the Universe erupted. Space, time, and energy all came into being in the Big Bang.
BIG BANG THEORY The idea that the Universe began in a superdense, superhot state 13.7 billion years ago and has been expanding and cooling ever since.
BIG CRUNCH If there is enough matter in the Universe, its gravity will one day halt and reverse the Universe’s expansion so that it shrinks down to a Big Crunch. This is a sort of mirror image of the Big Bang.
BLACK BODY A body that absorbs all the heat that falls on it. The heat is shared among the atoms in such a way that the heat radiation it gives out takes no account of what the body is made of but depends solely on its temperature and has a characteristic and easily recognisable form. The stars are approximate black bodies.
BLACK HOLE The grossly warped space-time left behind when a massive body’s gravity causes it to shrink down to a point. Nothing, not even light, can escape—hence a black hole’s blackness. The Universe appears to contain at least two distinct types of black hole—stellar-sized black holes that form when very massive stars can no longer generate internal heat to counterbalance the gravity trying to crush them and “supermassive” black holes. Most galaxies appear to have a supermassive black hole in their heart. They range from millions of times the mass of the Sun in our Milky Way to billions of solar masses in the powerful quasars.
BOSE-EINSTEIN CONDENSATION Phenomenon in which all the microscopic particles