Quantum_ Einstein, Bohr and the Great Debate About the Nature of Reality - Manjit Kumar [197]
Superposition
A quantum state composed of two or more other states. Such a state has certain probabilities for exhibiting the properties of the states out of which it is composed. See Schrödinger's cat.
Thermodynamics
Commonly described as the physics of the transformation of heat into and from other forms of energy.
Thermodynamics, the first law
The internal energy of an isolated system is a constant. Or equivalently, energy cannot be created or destroyed – the principle of the conservation of energy.
Thermodynamics, the second law
Heat does not flow spontaneously from cold to hot objects. Or equivalently, since there are different formulations of the law, the entropy of a closed system cannot decrease.
Thought experiment
An idealised, imaginary experiment conceived as a means to test the consistency or limits of a physical theory or concept.
Ultraviolet catastrophe
Classical physics distributes an infinite amount of energy among the high frequencies of blackbody radiation. This so-called ultraviolet catastrophe predicted by classical theory does not occur in nature.
Ultraviolet light
Electromagnetic radiation with wavelengths shorter than those of visible violet light.
Uncertainty principle
The principle discovered by Werner Heisenberg in 1927 that it is not possible to measure simultaneously certain pairs of observables – such as position and momentum, energy and time – with a degree of accuracy that exceeds a limit expressed in terms of Planck's constant h.
Velocity
The speed of an object in a given direction.
Wave function ()
A mathematical function associated with the wave properties of a system or particle. The wave function represents everything that can be known about the state of a physical system or particle in quantum mechanics. For example, using the wave function of the hydrogen atom it is possible to calculate the probability of finding its electron at a certain point around the nucleus. See probability interpretation and Schrödinger's equation.
Wave mechanics
A version of quantum mechanics developed in 1926 by Erwin Schrödinger.
Wave packet
A superposition of many different waves that cancel each other out everywhere except within a small confined region of space, allowing the representation of a particle.
Wave-particle duality
Electrons and photons, matter and radiation, may behave either like waves or like particles depending upon the experiment performed.
Wavelength ()
The distance between two successive peaks or troughs of a wave. The wavelength of electromagnetic radiation determines which part of the electromagnetic spectrum it belongs to.
Wien's displacement law
Wilhelm Wien discovered in 1893 that as the temperature of a blackbody increases, the wavelength at which it emits the greatest intensity of radiation shifts to ever-shorter wavelengths.
Wien's distribution law
A formula discovered by Wilhelm Wien in 1896 that described the distribution of blackbody radiation in accordance with the experimental data then available.
X-rays
The radiation discovered by Wilhelm Röntgen in 1895 for which he was awarded the first Nobel Prize for physics in 1901. X-rays were later identified as electromagnetic waves of extremely short wavelength, emitted when very fast-moving electrons strike a target.
Zeeman effect
The splitting of spectral lines when atoms are placed in a magnetic field.
NOTES
PROLOGUE: THE MEETING OF MINDS
1 Pais (1982), p. 443.
2 Mehra (1975), quoted p. xvii.
3 Mehra (1975), quoted p. xvii.
4 Excluding the three professors (de Donder, Henriot and Piccard) from the Free University of Brussels invited as guests, Herzen representing the Solvay family, and Verschaffelt there in his capacity as the scientific secretary, then seventeen out of the 24 participants had already or would in due course receive a Nobel Prize. They were: Lorentz, 1902; Curie, 1903 (physics) and 1911 (chemistry); W.L. Bragg, 1915; Planck, 1918; Einstein, 1921; Bohr,