cosmic background radiation or 3 degree radiation, is electromagnetic radiation left over from the original formation of the universe in the Big Bang around 15 billion years ago. It corresponds to an overall backgroundtemperature of 3K (-2700C/-4540F), or 30C above absolute zero. In 1992 the Cosmic Background Explorer satellite, COBE, detected slight 'ripples' in the strength of the backgroundradiation that are believed to mark the first stage in the formation of galaxies.
Cosmic background radiation was first detected 1965 by the American physicists Arno Penzias and Robert Wilson, who in 1978 shared the Nobel Prize for Physics for their discovery. Research Cosmic Background Radiation
Gas is an elastic aeriform fluid, a term originally synonymous with air, but afterwards restricted to such bodies as were supposed to be incapable of being reduced to a liquid or solid state. Under this supposition gas was a term applied to all permanently elastic fluids or airs differing from common air. After the liquefaction of gases by Faraday, the old distinction between gas and vapour, that the latter could be reduced to a liquid or solid condition by reduction of temperature and increase of pressure, while a gas could not be so altered, was no longer tenable, so that the term resumed nearly its original signification, and designates any substance in an elastic aeriform state.
Gases are distinguished from liquids by the name of elastic fluids; while liquids are termed non-elastic, because they have, comparatively, no elasticity. But the most promient distinction is the following: Liquids may be compressed to a slight extent, but when the pressure is released they return to their original condition, and in so far they are elastic; but gases when left unconfined expand in every direction. In respect of this expansiveness, all gaseous bodies obey more or less strictly two laws, commonly called the 'gaseous laws'.
The first, known as Boyle's Law, given first by Robert Boyle in 1662, and then by Mariotte in 1676, is that 'The volimie of a given mass of gas varies inversely with the pressure to which the gas is subjected'.
The second of the gaseous laws is that of Charles or Gay-Lussac. Dalton published it in 1801; but Gay-Lussac, who stated it in 1802, gives the credit of having discovered it, fifteen years previously, to Citizen Charles. The law may be stated as follows: 'The volume of a gas maintained under constant pressure increases for equal increments of temperature by a constant fraction of its original volume; and this fraction is the same whatever is the nature of the gas. A mass of gas, whose volume is 273 at 0 degrees C., becomes 274 at 1 degree, and 373 at 100 degrees, the pressure remaining constant'. This law may also be stated in the form - the volume of a given mass of any gas is directly proportional to the absolute temperature of the gas, provided the pressure remain constant. The absolute temperature is obtained by adding 273 degrees to the temperature in degrees centigrade, since the absolute zero is -273 degrees C.
In virtue of these laws a gas may now be defined to be a substance possessing the condition of perfect fluidelasticity, and presenting under a constant pressure a uniform state of expansion for equal increments of temperature - a property distinguishing it from vapour. There is, however, no known gas that obeys these two laws perfectly: thus, of the six gases oxygen, hydrogen, nitrogen, carbon monoxide, nitric oxide, and methane, all except hydrogen are more compressible than they should be theoretically, while hydrogen deviates slightly in the opposite direction, being less compressible than Boyle's law would indicate. The other gases exhibit even greater deviations from Boyle's law, and the amount of the deviation rapidly increases as the gas is brought nearer and nearer to liquefaction.
Charles' law, according to which equal rises in temperature should produce equal increments in volume, does not hold absolutely for all gases, and the deviations become greater as the point of liquefaction is approached. Characteristic of gases is the fact that they all possess a critical point or critical temperature, at which all distinction between the liquid and gaseous phases disappear wlien a suitable pressure (the critical pressure) is used. This was first observed by Andrews for carbon dioxide, the critical temperature of which is 31.3 degrees C, and its critical pressure 72.9 atmospheres. The liquefaction of gases is effected by the aid of low temperature and high pressure.
In thermodynamics, the Nernst heat theorem is the principle that reactions in crystalline solids involve changes in entropy that tend to zero as the temperature approaches absolute zero. Research Nernst Heat Theorem
Thermodynamics is the study of the laws that govern the conversion of energy from one form to another, the direction in which heat will flow, and the availability of energy to do work. It is based on the concept that in an isolated system anywhere in the universe there is a measurable quantity of energy called the internal energy (U) of the system. This is the total kinetic and potential energy of the atoms and molecules of the system of all kinds that can be transferred directly as heat; it therefore excludes chemical and nuclear energy. The value of U can only be changed if the system ceases to be isolated. In these circumstances U can change by the transfer of mass to or from the system, the transfer of heat (Q) to or from the system, or by the work (W) being done on or by the system. For an adiabatic (Q = 0) system of constant mass, DU = W. By convention, W is taken to be positive if work is done on the system and negative if work is done by the system. For nonadiabatic systems of constant mass, DU = Q + W. This
statement, which is equivalent to the law of conservation of energy, is known as the first law of
thermodynamics. All natural processes conform to this law, but not all processes conforming to it can occur in nature. Most natural processes are irreversible, i.e. they will only proceed in one direction. The direction that a natural process can take is the subject of the second law of
thermodynamics, which can be stated in a variety of ways. R Clausius stated the law in two ways: 'heat cannot be transferred from one body to a second body at a higher temperature without producing some other effect' and 'the entropy of a closed system increases with time'. These statements introduce the thermodynamic concepts of temperature (T) and entropy (S), both of which are parameters determining the direction in which an irreversible process can go. The temperature of a body or system determines whether heat will flow into it or out of it; its entropy is a measure of the unavailability of its energy to do work. Thus T and S determine the relationship between Q and W in the statement of the first law. This is usually presented by stating the second law in the form DU = TDS - W. The second law is concerned with changes in entropy (DS). The third law of thermodynamics provides an absolute scale of values for entropy by stating that for changes involving only perfect crystalline solids at absolute zero, the change of the total entropy is zero.
This law enables absolute values to be stated for entropies. One other law is used in
thermodynamics. Because it is fundamental to, and assumed by, the other laws of thermodynamics it is usually known as the zeroth law of thermodynamics. This states that if two bodies are each in thermal equilibrium with a third body, then all three bodies are in thermal equilibrium with each other. Research Thermodynamics
The Probert Encyclopaedia was designed, edited and programed by
Matt and Leela Probert
Abbreviations
Research William Kelvin
