Boyle's law of the gas, and "k" is a constant. The equation states that the product of pressure and volume is a constant for a given mass of confined gas and this holds as long as the temperature is constant. For comparing the same substance under two different sets of conditions, the law can be usefully expressed as The equation shows that, as volume increases, the pressure of the gas decreases in proportion. Similarly, as volume decreases, the pressure of the gas increases. The law was named after chemist and physicist Robert Boyle, who published the original law in 1662. This relationship
Thermodynamics of the universe the Friedmann-Lemaître-Robertson-Walker metric: by dividing the equation above with formula_10 and identifying formula_11 (the energy density), we get one of the FLRW equations of motions. In the comoving coordinates, formula_12 is equal to the mass density formula_13. For radiation, formula_14 whereas for matter formula_15 thus formula_12 is proportional to formula_17 For matter formula_18 thus formula_12 is proportional to formula_20 This can be understood as follows: For matter, the energy density is equal (in our approximation) to the rest mass density. This is inversely proportional to the volume, and is therefore proportional to formula_20. For radiation, the energy density depends on