Quantum_ Einstein, Bohr and the Great Debate About the Nature of Reality - Manjit Kumar [193]
Determinism
In classical mechanics, if the positions and momenta of all the particles in the universe at some instant of time were known, and if all the forces between those particles were also known, then the subsequent state of the universe could in principle be determined. In quantum mechanics it is impossible to specify simultaneously the position and momentum of any particle at any instant. The theory therefore leads to an indeterministic view of the universe, one in which its future cannot be determined in principle. Nor can a particle's.
Diffraction
The spreading out of waves when they pass a sharp edge or through an aperture, such as water waves entering a harbour through a gap in the wall.
Dynamical variables
Quantities used to characterise the state of a particle such as position, momentum, potential energy, and kinetic energy.
Electromagnetic radiation
Electromagnetic waves differ in the amount of energy they transfer, called electromagnetic radiation. Lower-frequency waves like radio waves emit less electromagnetic radiation than higher-frequency waves such as gamma rays. Electromagnetic waves and electromagnetic radiation are often used interchangeably. See electromagnetic waves and radiation.
Electromagnetic spectrum
The entire range of electromagnetic waves: radio waves, infrared radiation, visible light, ultraviolet radiation, X-rays, and gamma rays.
Electromagnetic waves
Generated by oscillating electric charges, they differ in wavelength and frequency, but all electromagnetic waves have the same speed in empty space, approximately 300,000 kilometres per second. This is the speed of light, and it was the experimental confirmation that light was an electromagnetic wave.
Electromagnetism
Electricity and magnetism were regarded as two distinct phenomena described by their own sets of equations until the latter half of the nineteenth century. Following the experimental work of men like Michael Faraday, James Clerk Maxwell succeeded in developing a theory that unified electricity and magnetism into electromagnetism and described its behaviour in a set of four equations.
Electron
An elementary particle with a negative electric charge that, unlike the proton and the neutron, is not composed of more fundamental component.
Electron volt (eV)
A unit of energy used in atomic, nuclear and particle physics that is about ten-billionth-billionths of a joule (1.6×10-19 joules).
Energy
A physical quantity that can exist in different forms, such as kinetic energy, potential energy, chemical energy, thermal energy, and radiant energy.
Energy levels
The discrete set of allowed internal energy states of an atom corresponding to the different quantum energy states of the atom itself.
Entanglement
A quantum phenomenon in which two or more particles remain inexorably linked no matter how far apart they are.
Entropy
In the nineteenth century, Rudolf Clausius defined entropy as the amount of heat in or out of a body, or a system, divided by the temperature at which the transfer takes place. Entropy is the measure of the disorder of a system; the higher the entropy, the greater the disorder. No physical process that would lead to a decrease in the entropy of an isolated system can occur in nature.
Ether
A hypothetical, invisible medium that was believed to fill all of space and through which light and all other electromagnetic waves were thought to travel.
Exclusion principle
No two electrons can occupy the same quantum state, i.e. have the same set of four quantum numbers.
Fine structure
The splitting of an energy level or spectral line into several distinct components.
Frequency (v)
The number of complete cycles executed by a vibrating or an oscillating system in one second. The frequency of a wave is the number of complete wavelengths that pass a fixed point in one second. The unit of measurement is the hertz (Hz) and is equal to one cycle or wavelength per second.