Regardless of this theoretical argument, experience clearly shows that K ′ decreases with pressure, or in other words that the second derivative of the incompressibility modulus K ″ is strictly negative. A second order theory based on the same principle (see next section) can account for this observation, but this approach is still unsatisfactory. Indeed, it leads to a negative bulk modulus in the limit where the pressure tends to infinity. In fact, this is an inevitable contradiction whatever polynomial expansion is chosen because there will always be a dominant term that diverges to infinity.