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 temperature formula_22 as well, and is therefore proportional to formula_23. As the universe expands it cools down, so formula_22 depends on formula_9 as well. In fact, since the energy of a relativistic particle is inversely proportional to its wavelength, which is proportional to formula_9, the energy density of the radiation must be proportional to formula_17. From this discussion it is also obvious that the temperature of radiation is inversely proportional to the scale factor formula_9. Plugging this information to the Friedmann-Lemaître-Robertson-Walker equations of motion and neglecting both the cosmological constant formula_29 and the curvature parameter formula_30, which is justified