Gas laws 1662 Robert Boyle studied the relationship between volume and pressure of a gas of fixed amount at constant temperature. He observed that volume of a given mass of a gas is inversely proportional to its pressure at a constant temperature. Boyle's law, published in 1662, states that, at constant temperature, the product of the pressure and volume of a given mass of an ideal gas in a closed system is always constant. It can be verified experimentally using a pressure gauge and a variable volume container. It can also be derived from the kinetic theory of gases: if a container,
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