Physical Terms

Don't Know these terms? Read On...

ANTIPARTICLE: For every type of particle, there exists an antiparticle with opposite properties, such as the sign of its electric charge (for example, the electron has a negative charge; the anti-electron, or the positron, has a positive electric charge).
Note: The antiparticles of photons and gravitons are the same as particles.

BIG BANG THEORY: The theory that says that the universe began in a state of enormous density and pressure and exploded outward and expanded until it was as we see it today.

BLACK HOLE: A region of space-time, shaped like a sphere (or a slightly bulged out sphere, in the case of rotating black hole) which cannot be seen by distant observers because gravity there is so strong that no light (or anything else) can escape from it. Black holes may form from the collapse of massive stars. This was the classical definition of black hole. Hawking showed that the black hole does not radiate energy and may not be entirely black.

PRIMORDIAL BLACK HOLE: Tiny black hole created not by the collapse of a star but the pressing together of matter in the early universe. Some of the most interesting ones are about the size of the nucleus of the atom, with the mass of about a billion tons.

BOSONS: Particle with spin expressed in whole numbers. The messenger particles of the forces (gluons, W+, W-, Z°, photons and gravitons) are bosons.

BOUNDARY CONDITIONS: What the universe was like at the instant of beginning, before any time had passed. Also what it is like at any other edge of the universe – the end of the universe, for example, or the centre of a black hole.

COSMOLOGICAL CONSTANT: Albert Einstein introduced a “cosmological constant”, to counteract gravity, into his theory of relativity. Without it, the theory predicted the universe ought to be either expanding or collapsing, neither of which Einstein believed to be true. He later called it “the greatest blunder of my life”. We now use the term to mean energy density of vacuum.

EINSTEIN’S GENERAL THEORY OF RELATIVITY: The theory of gravity in which gravity is explained as a curvature in four-dimensional space-time caused by the presence of mass or energy. It provides a set of equations that determines how much curvature is generated by any distribution of mass or energy. It is a theory we use to describe gravity at the level of very large.

EINSTEIN’S SPECIAL THEORY OF RELATIVITY: Einstein’s new view of space and time. This theory is based on the idea that the laws of science should be same for all freely moving observers, no matter what their speed. The speed of light remains same, no matter what the velocity of the observer measuring it is.

ELECTROMAGNETIC FORCE: One of the four fundamental forces of nature. It causes the electron to orbit the nucleus of atoms. It shows up as light and all other electromagnetic radiation, such as radio waves, microwaves, X-rays and gamma rays. The messenger particle (boson) of the electromagnetic force is photon.

ELECTROMAGNETIC INTERACTION: The interaction in which an electron emits a photon and another electron absorbs it.

ELECTROWEAK THEORY: A theory developed in the 1960s by Abdus Salam at Imperial College, London, and Steven Weinberg and Sheldon Glashow at Harvard, which unified the electromagnetic force and the weak force.

EVENT HORIZON: The boundary of a black hole; the radius where the escape velocity becomes greater than the speed of light. It is marked by hovering photons, which (moving at the speed of light) cannot escape and also cannot be drawn into the black hole. Light emitted inside it is drawn back into the black hole. To calculate the radius at which the event horizon forms, multiply the solar mass of the black hole (the same as that for the star that collapsed to form it, unless that star lost mass earlier in the collapse) by 2 for miles or 3 for kilometres. Thus a 10-solar mass black hole has its event horizon at a radius of 20 miles or 30 kilometres.

FERMION: Particles of ordinary matter (electrons, neutrons, protons) belong to class of particles called fermions. A more technical definition of a fermion is a particle with half integer spin which obeys the Pauli Exclusion Principle.

GLUON: The messenger particle which carries the strong force from one quark to another and causes the quarks to hold together in protons and neutrons in the nucleus of the atom. Gluons also interact with one another.

GRAVITON: The messenger particle which carries the gravitational force among all the particles in the universe, including gravitons themselves. None has ever been directly observed.

PHOTON: The messenger particle of the electromagnetic force. Photons have zero mass and move at the speed of light.

POSITRON: Antiparticle of the electron. It has positive electric charge.

PULSAR: A neutron star that rotates very rapidly and sends our regular pulse of radio waves, sometimes several hundred to thousand times a second.

QUANTUM MECHANICS OR QUANTUM THEORY: The theory developed in the 1920s that we use to describe the very small, generally things the size of atom and smaller. According to the theory, light, X-rays and any other wave can only be emitted and absorbed in certain “packages” called quanta. For instance, light occurs in quanta known as photons, and it can’t be divided up into smaller packages than one photon. You can’t have half a photon or three quarter photons. In quantum theory, energy is said to be “quantized”. The theory includes the uncertainty principle.

QUANTUM WORMHOLE: A wormhole of an unimaginable small size.

QUARKS: The fundamental particles, which, banded together in groups of three, make up photons and neutrons. Quarks also band in groups of two (one quark and one anti-quark) to form particles called mesons.

SPACETIME: The combination of the three dimensions of space and one dimension of time.

SUPERNOVA: an enormous explosion of a star in which all but the inner core is blown off into space. The material blown off in the supernova forms the raw material for new stars and planets.